Broken Bones: Anthropological Analysis of Blunt Force Trauma

BROKEN BONES

BROKEN BONES Anthropological Analysis of Blunt Force Trauma

Edited by

ALISON GALLOWAY, PH.D., D.A.B.F.A. (With 16 Other Contributors)

CHARLES C THOMAS • PUBLISHER, LTD. Springfield • Illinois • U.S.A.

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With THOMAS BOOKS careful attention is given to all details of manufocturing and design. It is the Publisher's desire to present books that are satisfoctory as to their physical qualities and artistic possibilities and appropriate for their particular use. THOMAS BOOKS will be true to those laws of quality that assure a good name and good will.

Printed in the United States ofAmerica TH-R-3 Library of Congress Cataloging-in-Publication Data Broken bones: anthropological analysis on blunt force trauma / edited by Alison Galloway; with 16 other contributors p. cm. Includes bibliographical references and index. ISBN 0-398-06992-1 l. Forensic anthropology. 2. Blunt trauma. 3. Fractures. I. Galloway, Alison, 1953GN69.8.B76 1999 614'.l--dc21 99-34122 CIP

To Walter H. Birkby whose gUidance has helped so many of his students, whose professional standards provided our goals, and who knew when we should be allowed to work on our own.

CONTRIBUTORS M.H. CZUZAK, PH.D. Department ofAnatomy University ofArizona Health Science Center 1501 N. Campbell Tucson, AZ 85724

SANDRA K. ELKINS, M.D. Director ofAutopsy Services and Forensic Pathology Regional Forensic Center 1924 Alcoa Highway Box 71 Knox County Medical Examiner's Office Knoxville, TN 37920

DIANE L. FRANCE, PH.D. Human Identification Laboratory Department ofAnthropology Colorado State University Fort Collins, CO 80523

LAURA FULGINITI, PH.D. Maricopa County Medical Examiner's Office 120 S. 6th Avenue Phoenix, AZ 85003

ALISON GALLOWAY, PH.D. Department ofAnthropology Social Science One University of California Santa Cruz, CA 95064

WILLIAM D. HAGLUND, PH.D. Director of the International Forensic Program for Physicians for Human Rights 20410 25th Ave., NW Shoreline, WA 98177

NICHOLAS P. HERRMANN Department ofAnthropology University of Tennessee Knoxville, TN 37996 Vll

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JOHN W. HUDSON, DDS Professor and Program Director Diplomate-American Board of Oral and Maxillofacial Surgery Department of Oral and Maxillofacial Surgery University of Tennessee Medical Center Suite 335 7930 Alcoa Highway Knoxville, TN 37920

MURRAY MARKS, PH.D. Forensic Anthropology Center Department ofAnthropology University of Tennessee Knoxville, TN 37996

RUSSELL NELSON, M.S. University ofMichigan Museum ofAnthropology 4035 Museums Boulevard Ann Arbor, ME 48709-7079

LAUREN A. ROCKHOLD, M.A. Department ofAnthropology University of Tennessee Knoxville, TN 37996 Monterey County Coroner's Division 7474 Natividad Road Salinas, CA

TAL SIMMONS, PH.D. Department ofAnthropology Western Michigan University Kalamazoo, MI 49008

STEVEN A. SYMES, PH.D. UT Medical Group, Inc. 858 Madison Avenue Memphis, TN 38763

K.M. TAYLOR, MA King County Medical Examiner's Office 325 9th Avenue Seattle, WA 98704

BARBARA THORNBURG University ofMichigan Museum ofAnthropology 4035 Museums Boulevard Ann Arbor, MI 48709-7079

Contributors CURTIS WIENKER, PH.D. Department ofAnthropology University of South Florida Tampa, FL 33620-8700

JOAN E. WOOD, M.D. Medical Examiner - District VI, Florida 70850 Ulmerton Road Largo, FL 34648

IX

PREFACE Forensic anthropology builds upon the skills developed within physical anthropology which focus on human osteology. The aim is to allow the bones to "speak," to allow the deceased to tell a story about who they were, how they lived and how they died. Our ability to "listen" depends largely upon our willingness to understand the principles by which the body is formed, how and why humans may vary phenotypically, and how the body responds to the environment in which it lives and dies. Traditionally, physical anthropologists have engaged in analysis of archaeological skeletal series. The primary information gained includes the age, sex and ancestry that is used to construct life tables and position the collection within the past populations. Analysis of trauma has been used to discuss the difficulty of life, the types of injuries which affected different social classes of people, sex differences in injury and the ability of people to survive and accommodate to injury. While the results of analysis can be contested, differences of opinion are expected and tolerated. Forensic anthropology faces a different situation. In most cases, we deal not with a skeletal series, which can be sorted with an understanding of populational variation, but with isolated individuals. In some respects, this parallels the situation of the paleoanthropologist with the exception that forensic anthropologists have the ability to generate information from the gTeater contemporary population. Unfortunately, information on the smaller population from which the specific individual was drawn is often obscured and may be the reason for the request for anthropological analysis. Forensic practitioners must develop information a step further in some areas but, simultaneously, pull back from the interpretations of trauma possible in archaeological material. Each individual injury must be more extensively examined, recorded and fit within a set of plausible causes. On the other hand, the interpretations cannot extend beyond the forensic anthropologist's area of expertise-the human skeleton. Interpretations can include the application of forces and indications that the defects are or are not consistent with specific causes. They may not include the discussion of the scenario in which these injuries may have been inflicted unless this can specifically be read from the bone. They also should not cross into the arena of the forensic pathologist and address the clinical implications of such injuries. This delicate balance is not easily mastered. Unlike archaeological analysis, the costs of an overextended or incorrect interpretation in forensic analyXl

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sis are high. At the extreme, it may cost a defendant his or her life or freedom or may produce subsequent victims if the evidence is found insufficient to convict a guilty party. Fortunately, in most cases the testimony of the anthropologist is not critical to the determination of "ultimate cause" (guilt or innocence). Ignorance of the limitations of forensic analysis can, however, leave the anthropologist open for extremely aggressive cross-examination. Aside from demolishing the ego and reputation of this individual, impeachment of the anthropologist casts a poor light on the subdiscipline and on other, more seasoned practitioners. Forensic analysis places the individual under extreme scrutiny-everything relies on what can be read from the bones recovered. Each bone must be thoroughly examined and, often, each has a "story" to tell. The victim in many forensic cases lived a life that took its toll on their body. Rarely, then, can the anthropologist find this chance to devote so much time to a well-preserved skeleton with the hope of checking his or her conclusions in the relatively near future. Forensic cases present a rare opportunity to examine bone in often pristine condition. While preservation is compromised due to differential predation, trauma or recovery, in many cases the bone in forensic cases is extremely well preserved with remarkable surface detail. This is particularly so when the skeletal remains are still housed in soft tissue. This allows interpretation of details often obscured by time, burial and other taphonomic factors. While forensic anthropologists are working within the medicolegal community and must respect its requirements, we are still anthropologists. In addition to the questions raised with regards to the individual cases, we must retain a broader perspective. Forensic anthropology provides an excellent opportunity to examine the factors and influences that affect the human body. Human skeletal structure has evolved in such a way as to withstand the normally encountered stresses with a relatively large safety margin. At the same time, the bones must retain the ability to distort during stress. This seeming contradiction enables the body to monitor the stresses it encounters and allows the bone to respond to increases or decreases in dynamic loading. Decreases in loading typically result in gradual loss of bone mass while increased loading is accompanied by activation of bone formation processes. At the same time, bones fulfill many other functions within the body. Since both the anatomical and physiological requirements of bone change throughout life, the morphology, microstructure and associated organic components may also change. While forensic anthropologists exploit this trend in order to estimate age, these variables also affect how the bones resist forces and ultimately fail.

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The morphology of the skeletal elements must be seen as having evolved to cope with a range of motions and loading that has been the norm during our evolutionary past. In most cases, this evolutionary pathway has not included changes in response to violence or accident. Unfortunately, the modern world also imposes an additional set of hazards that may often greatly exceed even the extremes of loading experienced in our evolutionary past as well as the resistance of bones to loading. To our benefit, we have also improved our ability to medically repair this damage, increasing survivability and decreasing morbidity. Frequently, we, as forensic anthropologists, deal with an individual, or a small group of individuals, lacking the luxury of a populational perspective. How much can we say? What can we substantiate? How can we begin to address the broader questions that can be raised in the individual cases with which we work. An examination of the bone shape, an understanding of bone tissue and strength and analysis of the biomechanics of fracture production combine to allow interpretation of skeletal trauma. With such a foundation, the forensic anthropologist can begin to address broader questions of secular change in bone strength, the influence of normal life events on bone morphology, the range of phenotypic expression, genetic factors in bone strength and the influence of habitual loading. Much of our thinking in human osteology has been geared toward the determination of patterns. What features are "characteristic" of females or males? What clusters of anatomical traits are indicative of certain ancestries? How can we assess age from the pattern of skeletal and dental changes? While these interests have stimulated much valuable research, it has also led us away from the assessment of the individual. Many of the "sex determination features" are, in fact, simply differences in robusticity. The principles that predict how trauma may affect "females" could, therefore, be as easily applied to gracile males. While there will always be a need for updating and refining our understanding of the patterns within populations, forensic anthropologists are in the position to reaffirm the focus on the individual. We need to study how the complex of skeletal characteristics that identify each person work together. What features within the life-style, physiology, disease profile or activity patterns will affect the expression of the skeletal traits that would be predicted due to sex or age or ancestry? This volume is designed to serve as an overview of the principles behind interpretation of skeletal blunt force trauma. It is intended for those of us confronting human skeletal material, whether from archaeological or forensic contexts which requires analysis of traumatic defects. While relying on clinical reports in large part, it is designed for those dealing with dry bone. Survivability of injuries and morbidity is rarely mentioned and treatment

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ignored. Rather, the emphasis is first on documentation and second on interpretation. At a second level, this volume aims to emphasize the importance of the individual in interpretation of skeletal trauma. The inclusion of case studies returns to this focus. Small peculiarities of the circumstances of injury, including the position of the body, the configuration of the impacting object and the speed of impact; the anatomical structure of the individual at that point in his or her life; and the perspective of the anthropologist must all mesh to produce a viable interpretation of the trauma production. In forensic anthropology, as in anthropology in general, when all else is done, we must still deal with the individual.

Alison Galloway

ACKNOWLEDGMENTS In the creation of any work, there are many people to whom thanks is owed-and this work is no exception. This book began as a suggestion by J. Stanley Rhine and George Gill that a volume of case reports be compiled on trauma analysis by forensic anthropologists. Over the next several years this project was substantially modified, but, to them, lowe thanks for lighting the spark. The members of the Mountain, Desert and Coastal Forensic Anthropologists (MD&C) kept the spark alive. Completing this work required time away from my other responsibilities at the University of California. The bulk of the writing and all the illustrations were completed while on sabbatical leave for which I am very grateful. Their computer support and other facilities were essential in preparing this manuscript. There have been many contributors and collaborators who participated in the book. Their endurance in the lengthy production of this work is most commendable. In addition, I have had considerable editorial assistance fromJ.Josh Snodgrass, who took time away from his other projects to meticulously read this work and from Lauren Rockhold, who also read through the volume and made many suggestions. On a personal level, I would like to thank Dr. Walter Birkby at whose doorstep responsibility for my training lies. I would also like to thank Dr. M.E. Morbeck most heartily for continual encouragement in my work, even when it was not aligned with her interests. The members of the MD&C and the Physical Anthropology section of the American Academy of the Forensic Sciences whose research and enthusiasm have driven this field must also be acknowledged. This is truly a community of scholars, each of whose work builds upon that of the others. Finally I need to thank my family for their support. My parents have always stressed academics and service to others. I cannot blame them for my involvement in forensic anthropology, but they have been very supportive of my interests (after I finally told them what I do). My daughter has always been very helpful and gTeatly amused by her mother's work-unfortunately to the point of demonstrating what it takes to produce a supracondylar fracture of the humerus! I hope her interests will continue and I thank her for her presence which connects me to an exciting new world.

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CONTENTS Page Priface .......................................................xi Chapter I. Trauma Analysis 1. The Role of the Forensic Anthropologist in Trauma Analysis ....... 5 Principles of Skeletal Trauma Analysis ....................... 6 The Process of Skeletal Trauma Analysis .................... 18 Post-Analytical Procedures and Expert Witness Responsibilites ......................................... 26 Summary .............................................. 31

Alison Galloway, Steven A. Symes, William D. Haglund and Diane L. France II. Principles for Interpretation of Blunt Force Trauma 2. The Biomechanics of Fracture Production ..................... 35 Biomechanics of Fracture Production ....................... 35 Classification of Forces .................................. .46 Classification of Fractures ............................... .48 Interpretation of Direct Versus Indirect Trauma ............... 57 Systems of Classification ................................. 60 Summary .............................................. 62

Alison Galloway 3. Fracture Patterns and Skeletal Morphology: Introduction and the Skull .................................. 63 Cranial Vault ........................................... 64 Facial Bones ........................................... 72 Mandible .............................................. 77 Throat Structures ....................................... 79

Alison Galloway XVI

Contents Chapter

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Page

4. Fracture Patterns and Skeletal Morphology: The Axial Skeleton ........................................ 81 Vertebrae .............................................. 81 Ribs ................................................. 106 Sternum .............................................. 110 Alison Galloway 5. Fracture Patterns and Skeletal Morphology: The Upper Extremity ..................................... 113 Clavicle .............................................. 114 Scapula ............................................... 117 Humerus ............................................. 120 Radius ............................................... 134 Ulna ................................................. 141 Carpals .............................................. 146 Metacarpals ........................................... 152 Phalanges of the Hand .................................. 156 Alison Galloway 6. Fracture Patterns and Skeletal Morphology: The Lower Extremity ..................................... 160 Innominates .......................................... 160 Femur ................................................ 172 Patella ............................................... 186 Tibia ................................................. 187 Fibula ............................................... 202 Talus ................................................ 207 Calcaneus ............................................ 211 Other Tarsals .......................................... 216 Metatarsals ........................................... 220 Phalanges of the Foot ................................... 222

Alison Galloway 7. The Circumstances of Blunt Force Trauma .................... 224 Homicidal Injuries ..................................... 225 Motor Vehicle Accidents ................................ 236 Falls ................................................. 249 Alison Galloway

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III. Case and Experimental Studies

Page Introduction to Case Studies ................................... 256 Craniofacial Fractures: Collaboration Spells Success ................ 258 Murray Marks, John W Hudson and Sandra K. Elkins A Case Study of a Vehicular Hit-and-Run Fatality: Direction of Force ............................................ 287

Lauren A. Rockhold and Nicholas P. Herrmann A Traumatic Confession ....................................... 291

Alison Galloway Violent Encounters: Multiple Trauma of Differing Ages ............. 297

William Haglund Home Alone: Distinguishing Blunt Force Trauma from Possible Taphonomic Processes ........................................ 301

Tal Simmons Some Examples of Survived Blunt Force Head Trauma from a Nineteenth Century Medical School Comparitive Collection ......... 304

Russell Nelson and Barbara Thornburg An Atypical Skull: Trauma and Asymmetry Mimic Pathology ........ 315

Curtis W Wienker andJoan E. Wood Scatter Versus Impact During Aircraft Crashes: Implications for Forsensic Anthropolgists ....................................... 322

Laura Fulginiti, M. H. Czuzak and K. M. Taylor Bibliography . .................................................331 Index . ......................................................365

BROKEN BONES

Section I TRAUMA ANALYSIS

Chapter 1 THE ROLE OF FORENSIC ANTHROPOLOGY IN TRAUMA ANALYSIS ALISON GALLOWAY, STEVEN A. SYMES, WILLIAM D. HAGLUND AND DIANE L. FRANCE

A

s forensic anthropologists are increasingly being asked to render an opinion on the circumstances of death and the decay process, analysis of traumatic defects of the skeletal material is also falling within their purview. The forensic anthropologist does not determine the cause of death which is a medical opinion, just as he or she does not determine manner of death (Galloway et al. 1990a). The expertise of the anthropologist may contribute to the interpretation of the evidence and determination of the manner of death by the medical examiner or coroner through the documentation of the injuries present on bone, analysis of the interval at which these were formed (antemortem, perimortem or postmortem) and the mechanisms involved in their formation. In this volume, analysis of trauma concerns injuries inflicted to bone as the result of blunt force forces applied with sufficient velocity to cause some degTee of fracturing or breakage. Skeletal trauma can be divided into three primary forms based upon the type of force used: (1) blunt force trauma, (2) sharp force trauma and (3) gunshot and projectile injuries. Blunt force trauma is defined as relatively low-velocity impacts over a relatively large surface area. In homicidal cases, this includes blows delivered with sticks, clubs, pipes, boards, rocks, fists, etc. These objects cause bone breakage due to direct impact and, indirectly, through the bending, pulling and twisting of skeletal elements. In addition, the definition of blunt force trauma can be expanded to include the fracturing resulting from vehicular accidents and falls and compaction of the body such as occurs with manual strangulation. Massive trauma, involving fragmentation of the body, may occur in highspeed, heavy-impact situations such as aircraft accidents, train wrecks and explosions. These result in a less organized pattern of injury but one in which there are unique requirements in the analysis of bones in terms of establishing not only identity but location and position of the victim at the

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time of impact and the dynamics of the forces causing the trauma. Sharp force trauma, in contrast, involves forces directed along a very narrow surface with the discontinuities produced by physical interruption of the skeletal tissue by a foreign object (knife, saw, axe, etc.). Sharp force often combines with blunt force producing fractures of bone beyond the sections immediately cut. Injuries from gunshots and other projectiles involve substantially higher velocities distributed over small areas. Tissue destruction with these types of wounds is not limited to penetrating trauma of primary and secondary missiles. This trauma must be examined in conjunction with cavitation deformation within the soft tissues that can induce indirect fragmentation of bone. Multiple types of trauma can co-occur. In these cases not only must the question of sequence within each trauma category be addressed but also when the switch was made between the forms of the attack. Awareness of the limitations of the interpretability of skeletal trauma is critical in all analyses. In this volume we aim to provide the theoretical framework through which to address trauma analysis and, through case studies, to show how these techniques can be applied. We begin this chapter with a discussion of the role of the forensic anthropologist in trauma analysis. When the trauma occurred, how it was induced and how much force was involved are particularly crucial questions to consider.

PRINCIPLES OF SKELETAL TRAUMA ANALYSIS

Three points are of critical importance in examination of skeletons for indicators of trauma. The first is distinguishing traumatic defects from either natural variation in skeletal morphology or existing pathological conditions and determining the mode of manufacture of the trauma (i.e., blunt force, sharp force, gunshot, explosion, implosion). Secondly, forensic anthropologists need to determine the number of incidents and the sequence in which they were delivered, when possible. The third responsibility is establishing the injury interval-is it antemortem, perimortem or postmortem?

Distinguishing Trauma from Pathological Conditions and Normal Variation Bone is formed and managed by osteoblasts, cells that produce collagen, amass calcium ions and regulate the onset of resorption. The actual degradation of bone is undertaken by osteoclasts, cells derived from the macrophage lineage, that attack bone as if it is a foreign substance. The combined and coordinated activities of these two cell types are responsible not

The Role of the Forensic Anthropologist in Trauma Analysis

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only for the modeling of new bone but the process of bone remodeling that occurs throughout our lives. This process is a coupled response. Osteoblasts release an enzyme to clear away the collagen coating which covers bone. This action exposes the bone to recognition by the osteoclasts that begin the resorption process, removing pre-existing organic and inorganic material. Once a section of bone is removed, new formation under the control of the osteoblasts begin to fill the void of the resorptive cavity. This coupled sequence is an ongoing process throughout our lives in response to the hormonal triggers and the body's need for calcium. It is also triggered in response to microdamage within the bone. This allows for renewing the bone tissue and accommodates changes in bone architecture. Because bone is a rigid material, it cannot be expanded from within. Newly formed bone must be placed in an area not already filled by a hard tissue. Growth, therefore, is appositional. Pathological changes in bone are severely restricted by limited ways in which bone tissue can be altered (Ortner and Putschar 1981; Aufderheide and Rodriguez-Martin 1998). Basically, bone tissue can be resorbed or formed. The formed bone may be located within the very limited resorption cavities that restrict its size or deposited on the endosteal (internal) or periosteal (external) surface. This new bone may be of poor quality, inadequately mineralized or insufficient to replace the amount lost. Defective bone composition is, then, a product of the formation process. Resorption consists of the loss of both organic and inorganic components. Pathological conditions consist of variations on these themes of (1) formative lesions, (2) resorptive or lytic lesions or (3) a combination of both formative and lytic changes within a closely specific set of possible locales (Ortner and Putschar 1981). Formative changes can be induced by pathological conditions or increased loading of bones through weight-bearing exercise. Periostitis refers to abnormal bone formation on the external surface of the bone (Ortner and Putschar 1981). Although technically this term refers to inflammation of the soft tissue lining the bone, in the dry bone, it is seen as deposition of new bone. Formative changes vary with the speed at which they are produced. Initially bone is laid down as woven bone that is gradually replaced by bone in which the collagen fibers are more regularly aligned with the long axis of the bone. When the new bone is laid exuberantly, often associated with malignancies, it may appear as spicules, plates or nodules of bones. The deposition of new bone induced by an increase in exercise is usually quite gTadual. Thin layers of woven bone form on the periosteal surface and are replaced by denser, more organized bone with time. This is usually only seen in bones that are robust (heavier and possibly slightly wider) in comparison to the bones of other individuals of similar age, sex, ancestry, stature

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and health conditions. It may also be associated with pronounced muscle insertion sites on the bones. Lytic changes are seen as (1) a generalized process that affects all bones but is particularly severe in trabecular bone or (2) localized loss resulting in erosion areas within bone. The former, known as osteoporosis, is recognized by thinning of the cortical walls and loss of trabeculae often with thickening of remaining struts as the body strives to maintain structural integTity. Such weakened bone is susceptible to fracturing with minimal trauma, particularly in the more trabecular regions of the long bones such as the proximal femur and humerus or the distal radius. The latter, localized osteolysis, may be seen as isolated defects or a series of defects. These erosions may be extensive, forming caries in the bone. In many cases, the bone lysis occurs secondary to gTowth of adjacent tissue. Benign or malignant growths exert pressure on the bone tissue prompting localized resorption. When this tissue is experiencing rapid growth, the lysis of the bone tissue is not accompanied by subsequent bone formation. When the growth is slow, new bone will have sufficient time to form behind those areas which are being resorbed. Consequently there is gradual drift of bone, with an apparent cortical surface retreating in the face of the gTowing mass to form a smooth pit or groove. Separation of traumatic from pathological conditions or normal variation is relatively easy, prior to the commencement of the healing process. In fresh traumatic injuries, the margins of the lesion are sharp. Trabecular or diploic bone is readily seen in the interior and there is no indication of remodeling at the site. The Haversian systems within the bone should be interrupted and there are often fractures or tears in the bone that run along the main axis of the bone as forces separate the components of the bone tissue. Obviously pathological bone formation will present little area for confusion with such recent trauma but rapidly progressing lytic lesions may. In most cases, these can be distinguished under low-power magnification by examining for (1) undercutting, which commonly occurs in bone lysis, (2) crushing of bone, as seen in trauma or (3) presence of newly laid woven bone, as may occur in a defect. Macroscopically, lytic lesions tend to be irregular or rounded in shape and may occur on surfaces not easily accessible without significant damage to other bony elements. Developmental defects must also be kept in mind when assessing the possibility of traumatic defects. Foramina, such as those located in the sternum, can easily be mistaken radiographically for gunshot injuries. The absence of exposed trabecular bone and the smooth cortical margins clearly show that these are not of recent origin. Knowledge of normal skeletal development and the interaction of bone, blood vessels and nerves will often indicate the possibility of anomalies masquerading as traumatic injuries.

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Once the injuries have been determined to result from trauma, the mode through which they are or were inflicted must be determined. This volume provides an overview of the characteristics found in blunt force trauma. It must be remembered that multiple causes can often be identified in one individual and all must be documented. As the interval between the traumatic event and the demise of the individual extends, however, the interpretation of the mode of injury may become increasingly difficult.

Determining Number and Sequence of Skeletal Injuries In all cases of trauma investigation, both a written and a schematic record should be made. Written records should note the location and condition of each defect and can be used to sort out multiple defects on each bone. Diagrams of the injuries drawn onto a representation of a skeleton or skull as appropriate (Figures 1-1 and 1-2) prove extremely useful (1) in visualizing the sequence and number of incidents that produced the trauma, (2) as an explanatory tool for medicolegal or legal personnel and (3) as a quick and accurate reference for pretrial conferences and testimony in court. All records should be supplemented by photographs that include overall shots and close-ups detailing the specific defect. Scales and case numbers should be visible in each photograph. A log of photographs is often helpful in determining views and elements. Notations of the dimensions of defects should be documented. The use of color is helpful in distinguishing fractures and other injuries, preservational anomalies and other defects. Computer-scanned images are an excellent means of producing clear and effective gTaphics. In some cases, a rendition from the actual skull may be appropriate, particularly if the skull or defect is unusual. Digital recording of the skull and other skeletal elements is also possible and provides not only a visual image of the remains but dimensions which can be measured at a later date. Determining the number of injuries requires repositioning bones in anatomical position since a single insult can result in defects to multiple bones. It is important to remember that the decedent may have moved to fend off blows, adopted defensive positions or actively fought off the attacker. As a result, injuries to multiple parts of the body can occur from a single event. For example, a person may raise their hands in front of them so that a bullet passes through the hands before entering the torso or head. Living bone has greater flexibility than the dry skeleton and will bend in response to blows to a greater extent than can be replicated in dry bone. Indirect blows may dislocate bones or disturb the normal anatomical arrangement due to stretching of muscles or ligaments. Such dislocation may be completely missed if examination of remains is forestalled until all the

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Figure 1-1. Skeletal Chart. Schematic representation of the human skeleton in anatomical position provides an excellent means to plot the inventory of elements and the injuries. both anterior and posterior views are seen and inventory and injuries should match in both views

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Figure 1-2. Skull Chart. Six views of the skull allow full plotting of injuries. Extra care must be taken to continue fracture lines from one view to another. None of the images should be left so as to not represent the actual skull unless this fact is specifically stated.

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bones are thoroughly cleaned. It must be shown that no postmortem activity, such as carnivores, body recovery or drying and shrinkage of ligaments and tendons, could have induced the mal alignment of the skeletal elements. Sequencing of injuries depends upon an understanding of the biomechanics of skeletal tissue. Fractures will be propagated through bone until the energy is dissipated by leaving the bone, encountering a pre-existing fracture or open suture or when the strength of the bone is greater than the force. Sequences can be determined only if the fractures or defects intersect each other. In some cases, logical sequences can be determined despite a lack of overlapping injuries. For example, fatal injuries probably preceded those consistent with dismemberment. In such cases the pattern of defects should be described, but final determination of the sequence should rest with the medical examiner or coroner, as this person has access to additional information that may radically alter the assessment.

Distinguishing Ante-, Peri- and Postmortem Injuries One of the essential portions of analysis of skeletal trauma is determining when the injury occurred in relation to the time of death. This is divided into three categories: (1) antemortem or before death, (2) perimortem or at the time of death and (3) postmortem or after death. While the death of the individual is the determining event in separating these periods, in skeletal tissue the divisions are based instead on qualities of the bone tissue. "Antemortem" for the anthropologist requires that some evidence of healing be seen and therefore injuries that occur well before death, but in which healing is not seen, will be counted as perimortem. Similarly, postmortem skeletal injuries are determined by changes in the mechanical properties of bone due to decomposition. If decomposition is slowed, injuries may again be seen as perimortem. The "perimortem" interval, as reflected in the skeletal material, therefore, is actually quite long and includes portions of the true antemortem and postmortem intervals. It will vary depending upon the conditions of injury and the environmental factors that affect bone desiccation. For example, bone dehydration will proceed rapidly in the desert regions with complete exposure to bone following mummification of remaining surrounding soft tissue. In northern regions, cold and freezing temperatures can maintain a body in virtually fresh condition for months after death. Breaks in the bones of a dead body may appear "perimortem" longer in northern climes.

The Role of the Forensic Anthropologist in Trauma Analysis

Antemortem

~rsus

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Perimortem Injuries

Antemortem injuries are indicated by evidence of healing (Figure 1-3). The healing process begins immediately after the injury as blood flows from the disrupted blood vessels within the soft tissue, fractured bone and the marrow to form a hematoma. The blood supply to the cortical bone is limited with fewer collateral branches than in the marrow or periosteum leaving it more susceptible to necrosis (Rogers 1992). Granulation tissue forms around the fracture site in which osteoclasts begin to resorb the dead bone. After about a week, there is a shift in cell population as osteoblasts and chondroblasts move into the fracture area. These cells work to form a callus that begins to mineralize a week after the callus initiation but takes four weeks to over four months to complete. This callus consists of woven bone that depends upon the quality of the blood supply to the injured area and, hence, oxygen availability. Gradually over one to four years in adults, the callus will be remodeled into a fully healed fracture. In younger individuals, active modeling of bone can occur, eventually obliterating much of the evidence of the previous fracture. The process of healing is highly variable, with some individuals or fractures healing at accelerated rates while others are significantly delayed or never heal completely (Rogers 1992). The location of injury also mitigates the healing rate since there usually is greater availability of blood supply in the metaphyseal region than in the diaphysis. When both blood and oxygen are poor, or when movement remains at the site, there is a greater proportion of cartilage formed than mineralized callus. This can eventually result in the development of a pseudoarthrosis or "false joint." In some cases, complete disruption of the blood supply can severely limit the possiblities for recovery. The severity of the injury is a compounding factor (Rogers 1992). Where bone is missing or seriously displaced, production of new bone will slow overall healing. When the fracture involves extensive soft tissue damage, the risk of infection is high and resources normally available to fracture healing will be diverted to containment and elimination of infected tissue, slowing the bony changes. Surgical intervention plays a role in the healing process (Rogers 1992). External fixation that immobilizes the bone will accelerate callus formation. In contrast, internal fixation or the use of plates and surgical screws to realign the segments may eliminate or minimize the production of a callus since, in effect, the device fills the function of the callus. How does this process translate into a pattern which can be recognized by the forensic anthropologist? How can we distinguish antemortem from perimortem injuries? The forensic anthropologist must assess injuries in light of

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Figure 1-3. Antemortem Healing. Initial healing is seen as new bone formation associated with the establishment of the cartilagenous callus (see also Figure D-2).

Figure 1-3 (continued). Woven bone replaces the soft callus to provide union between the two portions of bone (left) which is gradually remodeled to approximate the original state of the bone (right).

The Role of the Forensic Anthropologist in Trauma Analysis

15

their severity, location, the decedent's age and potential for associated infection and, together with the forensic pathologist, discuss survivability. The first signs of healing are often difficult to detect. Murphy and associates (1990) reviewed Civil War amputation material for which both injury date and cause, as well as surgery dates, were available. Rather than the expected erosion of the fracture margin, the first indicator visible macroscopically was a narrow band of periosteal resorption about 1/4-112 inch from the fracture site. This feature most likely correlates with the area of inflammation where the periosteal membrane has been torn from the underlying bone. Following this development, there is gradual erosion of the bone adjacent to the fracture site. A second unexpected finding was that these indicators did not appear until about thirteen days after injury. While this may be attributable to a heavy infection rate, it should be taken as a cautionary note regarding the length of time during which bone will macroscopically appear as a perimortem injury. Radiographically the repair is seen as a blurring of the fracture margins as a result of resorption of the dead bone (Rogers 1992). This is also not apparent until ten to fourteen days following fracture. There is also widening of the gap between the fractured ends when there is callus formation. This is followed by the slow disappearance of the fracture line as there is fibrocartilage mineralization and bone formation (Rogers 1992). Histologically, the evidence of healing appears sooner that it will either radiographically or macroscopically. The initial manifestations of new bone formation can be seen in about 5-7 days as spicules of woven bone within the callus (Ashhurst 1992). If the material is completely skeletonized, however, it is likely that these will be lost. Degeneration of the fractured ends also begins within this period, due largely to to the release of lytic agents by macrophages rather than the activity of osteoclasts. Unfortunately, histological analysis means destruction of evidence in preparation of the section. It is often the only means of resolving a particularly critical case and must only be conducted with full authorization from the medical examiner. Examination of the evidence by another expert will be precluded once the section is cut and this may limit admissibility of that evidence in court. Alternatively, it may force the opposing counsel to target the forensic anthropologist who conducted the original analysis for impeachment. In most cases once healing has begun, the forensic value moves into an identification arena. In some cases, however, evidence of healed fracture is indicative of a pattern of abuse, as in battered child syndrome, elder abuse or an event in which the victim was held for a long period of time prior to death. In these cases, assessment of the extent of callus formation and discrimination of woven bone or lamellar bone remodeling becomes important.

16

Broken Bones

When the individual may have survived the injury for a period of time prior to death, reconstruction of the events leading to the death of the individual must include information on the circumstances of this intervening period. The size of the callus cannot be used to gauge the age of injury since it refers less to the stage of development than to the location and severity of the injury. Callus formation tends to be more pronounced on larger bones, diaphyseally rather than metaphyseally and with greater dislocation.

Perimortem Ji;>rsus Postmortem Injuries The second distinction to be made is often the more common case-the distinction between perimortem and postmortem fracturing. Again, the terms are somewhat deceptive in that the skeletal distinction has less to do with the time of death than it does with the integrity of the bone tissue. In fresh living or recently decreased bone, the moisture content is relatively high and the collagen component flexible. This permits deformation of bone to occur with greater resistance to failure (Lyman 1994). As decomposition occurs, however, the moisture is lost from bone and the collagen degrades, making the bone less flexible. The bone responds to loading more in line with a purely inorganic material and fails at smaller forces of dynamic loading, although it may be stronger in static loading (David 1985). Breaks in bone that occur during the initial drying process, therefore, are less clean with more jagged edges (Maples 1986) (Figure 1-4). Fragments are smaller as the bone is more likely to shatter and adherent spurs of bone, relatively common in fresh bone, are infrequent. Fractures produced from the transmission of energy through the bone, such as concentric circular fractures and radiating fractures, are rare in dry bone. We tend to assume that bone dries eventually, but this is not necessarily the case. For example, in mass graves, body fluids and moisture may be trapped for years in the core of the grave within a mass of bodies. When buried remains are below water tables or in areas inundated much of the time with water, moisture may also be retained. In such cases, the bones may become excessively wet and mineral may leach from them leaving the remains soggy and malleable. In some instances there may never be a time in some instances when the bones dry out and our conventional ideas of postmortem, dry fracture characteristics are visible. Postmortem damage may exhibit more crumbling and compressing defects rather than fracturing. Perimortem fractures can often be distinguished by staining of the fracture surface by decomposition and the release of bodily fluids. Examination of remains prior to cleaning is, therefore, essential. Maggots and other larvae may have invaded trabecular regions of bone broken during the perimortem period or early in the postmortem period and may indicate a longer duration of fracture.

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17

Figure 1-4. Fractures in Green and Dry Bone. Fractures in green or fresh bone (top) are clean while those in dry bone (bottom) tend to have jagged, tom edges

18

Broken Bones

Many postmortem fractures are produced by carnivores and rodents that produce characteristic patterns of damage. Briefly, carnivore damage is typically seen as crushing of bone with puncture marks left by the canine teeth (Haglund 1997a). Rodents produce parallel striation to the bone (Haglund 1997b). These striations may not be present on some bones, such as the phalanges, where the cortex is thin and the bone breaks rather than withstanding the pressure of the scraping of the rodent incisors. Postmortem fracturing can also be produced by thermal changes, particularly fire (Rhine 1998). Fire will often produce fractures of the long bones as the muscles contract with the heat. The skull will often exfoliate or rupture due to the pressure built up by the gasses and steam generated from the body tissues. Because fire consumes the organic component of bone, the remnants are more brittle and are easily broken during the postmortem period, especially during the fire containment and discovery. In many cases the mode of discovery of the remains is important as this often results in postmortem injury. Backhoes used to "explore" for buried remains can have disastrous results in fragmentation of skeletal material. Similarly, plowing can produce massive damage at the same time as it exposes the body. In such cases, the distinction of peri- or postmortem damage will require extensive detailed examination of the remains (Ubelaker and Adams 1995).

THE PROCESS OF SKELETAL TRAUMA ANALYSIS

The complete analysis of skeletal material for traumatic defects follows a series of three stages that cover not only the handling of the remains but also maintains the context under which the remains exist and their usability in court proceedings. These stages begin with the preanalytic procedures of recovery, autopsy, initial documentation and skeletal processing. The analysis of the remains for skeletal defects and, when necessary, the development of experimental studies to test interpretive model follows. Finally, the postanalysis phase includes the production of a final written report, preparation for court and the actual testimony. Running parallel to these stages is a line of documentation known as the "chain of custody." This set of papers allows the material to be tracked through each stage from the point of recovery to that of final disposition. At all stages in which the anthropologist is responsible for the integTity of skeletal evidence, information about the measures taken to secure the remains must be reconstructable. Signatures must accompany each transfer of evidence into or out of the care of the anthropologist.

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19

Recovery and Processing of the Remains The analysis of skeletal trauma is an area in which the forensic anthropologist can greatly contribute to the reconstruction of circumstances through which an individual met his or her death. It is also an area which is emotionally charged. As one begins to comprehend the magnitude of the violence or the deliberation with which it has been imparted or the vulnerability of the victim, it may be hard to resist the tendency to align oneself with one adversarial party against the other. The "golden rule" of the expert witness is that they are not personally involved in the case. The interpretation of the results is based solely on the material analyzed and must not be adjusted according to the desires of the party requesting the anthropological analysis. The expert is being compensated for the time they devote to the analysis; their opinion is not being bought. While most likely to be important in cases involving criminal charges, analysis of trauma is increasingly addressed in civil suits. In both criminal and civil cases, sequencing of events and discrimination of antemortem, perimortem and postmortem injuries is important. Reconstruction of the events in relation to other victims or with contact with possibly defective materials are often addressed in civil suits. It is important that the forensic anthropologist become involved in the analysis as early as possible (Maples 1986). While inclusion in the scene recovery is the most preferable, attendance at the autopsy is also extremely beneficial. At this time, total body trauma can be appraised while specific insults (e.g., hemorrhage surrounding fracture sites) can be scrutinized. The sequence in which soft tissue is removed can be documented. The anthropologist can also gain important information from examination of soft tissue, although descriptions on any soft tissue defects should be kept in general terms. Blunt force trauma may result in unusual patterns of decomposition that are evident on the body at initial inspection. In most instances, insects invade the body through the normal openings on the face (i.e., eyes, nose, mouth and ears) or in the ano-genital region. Massive trauma may, however, provide an additional avenue of entrance. When blunt force results in extensive soft tissue damage, insect activity can be intense. The frequent involvement of the head in blunt force injuries also means that injuries to the face or cranial vault may be distorted by the mere association with this body segment with the natural portals to the soft tissue. During autopsy, any marks on the bone left by the pathologist or technicians can be noted and documented during the later analysis. The association of soft tissue damage with underlying skeletal defects may be useful in linking the reports of the forensic pathologist and the anthropologist. The

20

Broken Bones

perspective gained from such observation is also extremely important for the continuing education of the anthropologist and other investigators. Bodies can also be radiogTaphed for documentation of metal or other radio opaque materials. This is critical in recording the presence or absence of bullets or other projectiles, which may be passed to the anthropologist's custody along with skeletal material. Recovery of bone fragments in cases of blunt force trauma can itself be a somewhat traumatic experience. In many instances, this entails sifting through masses of soft tissue, in various stages of decomposition. Small splinters of bone are easily lost within maggot masses and can be rapidly transported away from the initial location. Despite the unpleasantness of the task, it is essential that as many fragments as possible be recovered. While decomposed human tissue is generally more odious than dangerous, basic safety procedures should be taken when handling human remains (Galloway and SnodgTass 1998). As many of the remains handled by anthropologists are unidentified, the health status may never be known. Most infectious agents are relatively unstable and dissolve during autolysis and putrefaction. Some, including hepatitis B, are remarkably resistant to destruction. Double latex gloves both inhibit the transfer of odor as well as provide added protection. Protective clothing such as scrub suits, aprons or lab coats prevent staining and provide a barrier for the analyst. All personnel should have current vaccines including the hepatitis series and tetanus shots or boosters. All injuries to team members while handling the body should be thoroughly cleaned, tended and logged. Once in the hands of the anthropologist, the condition of the remains should be noted and documented through photogTaphs, each including the case number and a scale. When bags have been collected with regard to particular locations at the crime scene, then each bag should be inventoried and photographed separately. In particular, the condition of any obvious skeletal defects should be noted such as inclusion of decomposition materials or decayed body fluids within the defects. This may be critical in the determination of perimortem versus postmortem injury. Such evidence may be lost or obscured by further cleaning. Missing portions should be documented. Later recovery of these portions may allow determination of initial areas of injury or decomposition, which can be essential to the reconstruction of the series of events leading to the recovery of the victim's remains. Carelessness in recovery of portions may jeopardize these interpretations. Once documentation has taken place, bones should be separated as much as possible prior to cleaning. Records should be kept for any cutting that must be done to afford separation. While maceration in water or use of natural decomposition techniques, such as dermestid beetle colonies, may be preferable for removing soft tissue, the length of time may be incompatible

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21

with the needs of the agency requesting the anthropologist's services. If DNA analysis is needed to establish identity, untreated portions of bone and/ or teeth should be retained in the freezer. In most cases, skeletal material can be cleaned in a simmering detergent solution. In these cases, care must be taken to preserve the integrity of the bone during cleaning. Overcooking and overheating must be avoided. It is essential that exposure to bleach be limited and that a very low temperature be used during cleaning in a degreaser. With attention being paid to these points, it is difficult to damage skeletal material during cleaning. Nylon bristle brushes, hemostats, tongue depressors and spatulas should be used in cleaning rather than metal instruments such as knives and scalpels, which can further damage bone (Maples 1986). If these are insufficient, documentation of where metal tools are used and witnesses and/or videotapes of the process are helpful. As in all cases, care in cleaning bones must include avoidance of extreme temperatures or rapid temperature changes for the bones. Heated bone should be rinsed in hot water, while refrigerated bone should never be placed directly into a boiling solution. A heated mild ammonia bath can diminish the surface gTease making the bones easier to handle.

Analysis of the Remains and Experimental Studies Prior to defleshing and cleaning of the skeletal material, fractures should be identified radiographically on the intact remains. Usually the fracture is seen as an abnormal line of radiolucency, frequently with displacement of the fragments (Rogers 1992). Additional indicators include discontinuities in the cortex or abrupt increases in density due to overlap of skeletal fragments or compaction of trabeculae. If the remains still consist of substantial amounts of flesh, then two views should be taken to establish the extent of the displacement prior to removal of the overlying soft tissue and examination of the break by the pathologist. After cleaning is completed, the bones should be inventoried and examined for gross evidence of trauma. Recording of observations should be detailed and maintained with the folder in which other items of the work product are placed. Standard forms for skeletal inventory, measurements and non-metric assessments have been produced by a number of institutions. However, the analysis of skeletal trauma appears to largely elude our ability to provide a routine approach (Reichs et al. 1995). Nevertheless, a thorough examination of all elements is required rather than a focus only on those elements that have the most obvious defects. A systematic approach is essential to ensure complete coverage. Gross observation should be followed by examination under a dissecting microscope. Each element should be examined separately and any defects

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Broken Bones

noted. Once these defects are identified by specific element, then the anatomical relationship between elements should be reconstructed. Each defect should then be documented photographically as to location within the bone and with appropriate magnification to reveal those features that enable interpretation. Scales, such as the A.B.F.O. "L"-format scale and case numbers should be included, and appropriate lighting is important. Radiographic documentation is strongly recommended. Interpretation of skeletal injuries due to blunt force is often best achieved through reconstruction of the injured areas. In many cases, this entails careful use of consolidants and adhesives, preferably those that are strong enough to endure handling but easily soluble and archivally sound. Applicator rods, Plexiglass strips or other clearly identifiable items can be used to replace portions of the bone that were not recovered or were fragmented beyond repair. All reconstructed areas should be carefully noted on the documentation. Prior photographs of the fractured areas may be important, especially in reconstructing the postmortem events. In one case, examination of many of the fractures was precluded by reconstruction, making it difficult to distinguish postmortem fire damage from blunt force trauma (AG, personal communication). A constant area for concern is the presence of non-union between epiphyseal areas and the rest of the bone, which may be incorrectly identified as fractures. Certain bones, such as the hyoid, are prone to non-union throughout life. An equally troubling problem is that of determining epiphyseal separations in the skeletal elements of subadults. These may be accompanied by shearing fractures and avulsion fractures on the adjacent bony areas, but, given the low density of this bone, recovery of non-exposure-damaged bone is unlikely.

Interpretation of Instrument, Sequence and Force Once the bone has been reconstructed, the configuration of the injury will allow for some interpretation. Unusual outlines at the point of impact may indicate a specific type of instrument. While this can often be linked to specific tools found at the crime scene or from the property of a suspect, care must be taken to make any assessment of the overall shape and size of the defect before comparing the injury to the tool. The anthropologist should not look for injuries due to a crowbar but rather should look for injuries that have dimensions and spacing later found consistent with that of a crowbar or similar shaped instrument. Reconstruction will also allow some interpretation of the sequence in which the injuries were received. Initial injuries will often produce linear fractures that extend long distances through the bone. Subsequent injuries

The Role of the Forensic Anthropologist in Trauma Analysis

23

may also produce linear fractures, but these will not cross the pre-existing fractures as the energy is dissipated through the gap present in the bone. The anthropologist can determine which injury preceded, plotting the linear fractures associated with each impact point and determining where the progress of one group of fractures is terminated by that of another group of fractures. Understanding of this sequence may require very meticulous documentation of all resulting fractures and the creation of overlying charts prior to the full interpretation. In many cases, however, blunt force trauma is not easily sequenced as the blows may occur on isolated elements. Also, the anthropologist must be open to the possibility that sequence information may simply not be available from the skeleton. A rough estimation of the force required to produce injury can be made based on the thickness of the bone and the extent of damage. Calculation of the force involved can be gTOssly estimated given the information available in the published literature (Gurdjian 1975; McElhaney et al. 1976). The required force, however, will vary by the rate at which it is applied and the quality of the bone. A discussion of the interaction of loading and bone integrity and strength is provided in Chapter 2.

Experimental Studies Application of published information on the force involved to a specific individual case is often extremely difficult and may require the use of experimental studies. Samples must be matched for the material and structural properties of the bone to be compared such as the gTain orientation, the location within the skeleton, the density and the external and internal morphology. The type and rate of loading must also be replicated. Such studies are also extremely difficult to develop due to the availability of a suitable sample of study material and the ability to reproduce a sample that closely matches the characteristics of the decedent (age, ancestry, sex, robusticity). Bone is known to vary in its resistance to forces depending upon internal components and postmortem alterations. Fracturing response varies depending on whether the bone retains its internal moisture or has dried and whether it is live or embalmed (Reilly and Burstein 1974). Matching of the nature of the bone must be as exact as possible in order to construct a model from which to calculate the forces needed to produce specific injuries. Obviously use of live human material is entirely unethical, despite any secret desires on the part of the researcher. Matching of cadaver material must acknowledge potential differences in bone quality due to drying and/or embalming. In addition to the resistance provided by bone itself, other tissues may increase the dispersal of force from blunt trauma. For example, on the head

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Broken Bones

there is 114-112 inch of soft tissue overlying the vault (McElhaney et al. 1976) that acts as a cushion and diffuses the force applied. The tissues that form the scalp provide tensile strength of varying degTees. This resistance is less than found in the skin over much of the rest of the body since there is less underlying soft tissue to cushion the blow and allow deformation (Gurdjian 1975). The difference in resistance to fracture conferred by the scalp and by moisture in the bone is amazing. A dry skull can fracture at about one-tenth the force load applied to an intact head (Gurdjian et al. 1949). It is estimated that the scalp absorbs 6%-13% of the available impacter energy on the intact head (McElhaney et al. 1976) but may be as high as 35% (Gurdjian 1975). Experimental studies must sometimes be performed to address issues raised in a specific case, including questions such as "How much force would it take to produce this type of injury?"; "How many individual blows are involved in the trauma affecting multiple bones?" or, "Which position of the body would best explain the pattern of injury?" In these cases, the forensic anthropologist is responsible for developing experiments that not only address the specific questions involved but also are admissible or likely to be admitted in court. Until recently, the admissibility of evidence fell under the Frye rule, which stated that the key factor was general acceptance among the scientific community of the techniques used. This caused problems in designing new experiments since, although the technology and procedures may have been commonly used within the physical anthropological community, the specific results may be less securely established. In other cases, the court has admitted testimony simply because the techniques were commonly used, even if the application in the particular case was debatable. The decision in Daubert v. Merrell Dow Pharmaceutical, Inc. in 1993 had the potential of radically changing the introduction of new tests and expert witness testimony into court, but may still not rectify the problem of disputed scientific claims (Allen 1994; Black et al. 1994). In brief, the Supreme Court ruled that the Frye decision was an inappropriate precedent and that reference should instead be made to the Federal Rule of Evidence 702. This rule specifies that scientific, technical or other specialized knowledge that may assist the judge or jury to understand the evidence may be presented by a witness who is qualified as an expert by knowledge, skill, expertise, training or education. The judge is established as the determiner of whether testimony will or will not be admitted. Unfortunately, specific guidelines as to how this decision is reached are not provided. Instead, four general questions are formulated about the technique: (1) Is it testable and been tested? (2) Has it been published in peer-reviewed journals? (3) Is it accompanied by error rates and the use of standards? and (4) Is it generally accepted?

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In many respects anthropology holds an unusual position within the forensic sciences, as its use in criminal proceedings is only now becoming widely utilized despite a history of involvement in criminal investigations in the United States since the 1950s. In many instances, there is little understanding of the general principles of forensic anthropology, the qualifications of its practitioners and the validity of its techniques. Under the new guidelines it is possible that techniques that are acceptable in archaeological practice, such as aging techniques based primarily on seriation, may be entered into the record if the opposing counsel is unwilling, unaware of the possibility, or unable to mount a critical assessment. The definition of who qualifies as a "forensic anthropologist" is unclear despite the formation of national and regional organizations and a progTam of board certification. The community of scholars from whom there must be general acceptance is still unspecified as to level of education, experience or even orientation within the very broad field of anthropology. Despite these uncertainties or, perhaps, because of them, it is likely that the Daubert decision will have little effect on forensic anthropology. Experimental studies in forensic anthropology usually take two forms. One examines the relationship between skeletal and soft tissue morphology or between biological parameters, such as age and sex and changes in skeletal tissue. This type of study often occurs outside the needs of a specific case and only rarely involves investigation of trauma to the bones. A second form of experimental study is one that reconstructs the events and causative agents of trauma rather than focuses on the biological profile of the victim. These include experiments on the effects of different types of weapons on bone, such as comparing the marks left by hacksaws versus chainsaws or the calculation of the force required to produce the observed fracture patterns in blunt force cases. In both forms, careful documentation of the experiment and of the anthropologist's calculation of the variation within human anatomy must be made. For example, bracketing of data by using comparative material of both heavier and lighter build as well as of comparable size is extremely useful (GillKing, personal communication). This requires appropriately large sample sizes. Unfortunately, these are extremely difficult to obtain outside of access to cadaver material specifically donated for scientific use. Even in these cases, alteration of the strength of material may have been induced by decomposition, dissection, embalming, etc. Non-human animal models are frequently used in order to overcome the problems of sample size. For instance, Ubelaker (personal communication) used chicken bones as a proxy for the metacarpals in recreating injuries due to a slamming car door. Here, however, the difficulty of extrapolation from one species to another arises. This is often an area through which the oppos-

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Broken Bones

ing attorney can question the validity of the results, and while the work may be scientifically sound, a jury may have difficulty accepting the results which cross species lines. In all events, animals of approximately the same body size as the victim or potential victims should be used. Taxonomic affinity may also be important as there are microstructural differences which can radically change fracture patterns. Approval by the institutional animal care and use committees must be obtained for any such experiments. Experiments which inflict unnecessary pain on animals must be avoided, if only because they are likely to be perceived negatively by the jury. Photography and graphics of the results of the experiments are useful in presenting the outcome to the jury. These should be kept as simple as possible and should avoid excessive "gore," which could be seen as prejudicial. While an endless stream of charts is not recommended, large amounts of data should not be packed into one chart. Usually three or four points is the upper limit for information that can be presented with maximum visual impact. Ultimately, the results should be presented at professional meetings and submitted for publication in journals directed toward the forensic science community. Information about the reception of these experiments in court is also extremely important to other practitioners, in that precedents may be established that can ease the admission of similar work elsewhere. In addition, presentation style may be critical in admissibility and how we approach these tests should be more closely examined (Gill-King, personal communication).

POST-ANALYTICAL PROCEDURES AND EXPERT WITNESS RESPONSIBILITIES

The Written Report The report by the anthropologist is a legal document and therefore must clearly outline the analysis, conclusions and limitations of the analysis. This document is usually provided to the agency who engaged the services of the anthropologist, in most cases the coroner or medical examiner, and from there, to the investigating agency and the prosecutor's office. In the event that the case goes to court, this report will be provided to the opposing attorneys. Care must be taken in discussion of trauma to distinguish between observations and interpretation. Observations of skeletal defects should note each instance of a traumatic defect on the bone. This catalog should not make reference to the relationship between defects or to the reconstruction of the events that produced

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27

them. This serves to lay the foundation upon which the further interpretations are based. This listing should be specific to allow easy recognition of the defects by others examining the document or the remains. Interpretations include the professional opinion on the type of force used, the direction and force of delivery, and the number and sequence of incidents that gave rise to the overall trauma. Links between individual injuries should be discussed so that the minimum number of blows, shots or cuts can be calculated. It is within this context that the experience of the forensic anthropologist, the results of experimentation and discussion of limitations must be laid out. These interpretations must not address either cause or manner of death, which is the purview of the medical examiner! coroner. Instead, they must be limited to the skeletal material. Relationships between the overlying or underlying soft tissue should be kept to general terms, as noted above. Pathological descriptions or interpretations of soft tissue should be avoided. The anthropological report should specify what documentation such as photographs and/or radiographs have been prepared and where they are retained. Some of these may be later used in court testimony or in preparation of the attorneys for examination. Photographs of unadjudicated cases, when the case is identifiable, should not be used for teaching or public presentations. In some jurisdictions, the medical examiner!coroner will support retention of those skeletal elements that exhibit traumatic defects. This may be particularly useful in subsequent re-evaluation and may reduce possible conflicts over admissibility of anthropological testimony. It may also prevent the problem of future exhumation. It is unfortunate that there is a "mindset" that tends to assume that all material will be automatically reburied. In part, this is due to the lack of adequate storage in many jurisdictions where centralized morgue facilities are lacking. It can be overcome if the anthropologist provides secured storage within his or her laboratory. All efforts should be made to prevent the cremation of unidentified remains or remains that show evidence of homicidal trauma. While buried remains can be exhumed for later study, all possibility of retrieving additional and possibly critical information is lost with cremation. The availability of newer three-dimensional imaging techniques promise better ways of presenting evidence of blunt force trauma to the court. These systems allow for the duplication, with varying levels of detail, of the skeletal element in question. This will not replace the necessity of retaining skeletal material for future re-analysis by consulting anthropologists.

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Broken Bones Preparing for Court

As in all court cases, the key to good expert witness testimony often lies in the care devoted to pretrial preparation. This is particularly true for presentation of analysis of trauma, which may lie at the heart of the dispute regarding guilt or innocence. Pretrial conferences should review every aspect of direct testimony, the possible areas of approach for cross-examination by the opposing attorney, and how to counter any misconceptions generated during re-direct questioning. In discussing the qualifications of the anthropologist as an expert witness, specific work on skeletal trauma, such as the number of previous cases in which trauma was analyzed, research on traumatic injuries or experimental projects, should be highlighted. Pretrial discussions are the ideal time to review these with the attorney. The anthropologist must make the attorney aware of links between the testimony regarding the skeletal material and that on the cause and manner of death. Since the anthropologist's work inevitably raises questions about how the victim died that the anthropologist will not be able to answer, the attorney must be ready to address these points in his or her examination of the medical examiner! coroner. It is the responsibility of the anthropologist to prepare the attorney for this situation. Preparation of photogTaphs, diagTams or models prior to trial are important, as these may be the clearest way to show the jury how the events are best explained by the anthropologist's interpretations. In most cases, references to soft tissue should be avoided. These visual presentations may be ruled inadmissible due to their possible inflammatory nature. Preparation should, therefore, include alternate means of conveying the necessary information. The issue of consultation fees should be raised with the attorney if these have not already been established. In addition to actual testimony time, consultation, including telephone calls, should be logged and charged. Expenses such as travel, hotel and communication charges should be included in the cost of hiring an expert witness in addition to the hourly or daily rates. Often expert witnesses charge the hiring agency for all the time required from when they leave their place of business to attend a trial until they return. Attorneys need to understand this and arrange their budget and schedule accordingly.

Court Testimony Courtroom testimony on the analysis of skeletal trauma must provide a clear discussion of the injuries, sequence (if determinable) and the type of

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29

instruments believed to be responsible (if appropriate). In essence, the anthropologist must guide the jury through the evidence and provide an impartial assessment of what can and cannot be determined. This must be done in such a way as to not prejudice the jury but without detracting from the information being provided. In actuality, this balance can be difficult to attain. The prosecution or defense attorney is interested in providing a case in support of their perspective in this highly adversarial situation. Attorneys also have very different ways in which they approach court testimony from expert witnesses. Some prefer to allow the expert to speak at length by responding to very broad questions, while others prefer to "walk through" the material with short answers to very specific questions. In the latter case, it is essential that the important areas be covered well in pretrial conferences. It is best to coordinate when and how the illustrations and other supporting items will be introduced. The anthropologist should be well-prepared for the testimony, reviewing not only the specifics of the case in terms of injuries but also when and how they were contacted, what was discussed prior to testimony, and when new lines of evidence were introduced, such as a confession or the report from another expert. While notes are allowed in the courtroom, they may be held as evidence and it is often difficult and time-consuming to fumble through files trying to find notes on a specific conversation. Illustrations, when used in conjunction with the testimony, should be clear and large enough to be easily seen in the courtroom. Often it is good to show an overall image of the skeleton with the bone indicated alongside the photograph you wish to discuss. The use of color to highlight portions of the charts is often helpful as long as gaudy colors or color combinations are avoided. Photographs should allow members of the jury to quickly determine the orientation. Video depictions of the results, such as matching an alleged weapon to the trauma or diagramming the sequence of shots through animation of the radiating fracture patterns, may be useful. Courtrooms come equipped with varying levels of media for presentation. In most cases large easels are used to mount panels that are visible to the judge, jury and attorneys. Slides, overheads and overhead cameras may also be available, but this fact should be established prior to testimony. While a specific order of illustrations may be used in the initial testimony, it is often necessary to work back and forth between a number of illustrations later in the testimony. Retained skeletal material may be brought to the court. Often, if a pressing question or dispute arises, the anthropologist can offer to demonstrate to the jury how interpretations were made using the actual bone. The outcome in such cases is either (1) the opposing counsel will relinquish their objections

30

Broken Bones

to the interpretation for fear that the jury will be exposed to the remains or (2) the skeletal material is used and the point can often be made relatively quickly and clearly. If the actual bone is not to be presented, it is often helpful to have plastic models of specific areas such as the skull or pelvis, where the complex threedimensional shape is difficult to illustrate. These models are available from anatomical supply companies, as well as establishments that cater to the needs of attorneys. Portions that are moveable or easily separated may be very helpful in demonstrating the movements that would occur to produce specific defects. Cross-examination, re-direct and re-cross can consume as much time as the initial testimony. Cross-examination is designed to either show flaws in the anthropologist's work or find ways in which this work supports an alternative interpretation. Occasionally, the questions from attorney or the defendant (if he or she is acting on their own defense) may seem at odds with standard interpretation or the basic theoretical framework of the discipline. Rarely do these attorneys have as much experience with forensic anthropologists as the person who retained your services, and this may be the first time they have had to question anyone from the discipline. Questions are aimed not only at the work specifically but also at the role of the anthropologist. Often questions attempt to test the limits of what you are saying by asking for you to determine cause of death or degree of disability induced by various injuries. If the anthropologist strays into the area of the forensic pathologist, he or she has left themselves open for working beyond their training. Questions are almost always made about the fees charged for analysis and testimony and should be answered openly. While the bulk of the trial cases handled by forensic anthropologists are derived from the prosecution's perspective, defense attorneys are increasingly utilizing the services of forensic anthropologists as expert witnesses to support the case for the defendant. This poses a difficult situation but one which should be met as a professional challenge in that one anthropologist may be testifying in opposition to the prosecution, medical experts or even another forensic anthropologist. This may be personally difficult since, within the limited community of physical/biological anthropologists engaged in forensic science, people have established strong collegial ties. In addition, there is the problem of accounting for alterations to the bones produced during previous analyses without automatically adopting any opinions set forth by earlier work. In these cases, it is best to complete one's own thorough examination of the material prior to comparing findings to the earlier work. The warning for anyone working on trials is to arrive prepared to spend longer than anticipated. Changes of clothing, overnight kits and some reading material are important to pack for any trial that requires more than a

The Role of the Forensic Anthropologist in Trauma Analysis

31

short drive. One-day trips often turn into three days spent sitting in a courthouse corridor awaiting your turn. It is for this reason that "portal-to-portal" fees or "waiting time" fees are charged. Few attorneys remember to inform the experts they have consulted about the eventual outcome. It is wise to check some time later as to the verdict, to see if your services may be needed for subsequent court proceedings, and whether you are now free to discuss the case more openly.

SUMMARY

The analysis of skeletal trauma provides an important turning point for anthropological analysis of skeletal material within the forensic context. The dramatic increase in studies and case reports within professional journals documents this shifting focus. Increasingly, the techniques upon which the anthropologist's involvement in a forensic case was necessitated, those for the identification of age, sex, ancestry, stature and peculiarities, are accepted and, in some case, surpassed by other techniques. The anthropological analysis of skeletal trauma is, however, increasingly important as challenges to interpretations become more prevalent. Skeletal trauma analysis provides a vast new area with almost unlimited potential for anthropologists to assist the medical examiner, law enforcement personnel and the legal community. Strengthening the links between soft tissue defects and those of the better preserved skeletal tissue may be the keystone for a strong prosecution case. Likewise, discrepancies between the soft tissue interpretations and those derived from later analysis of the more easily maintained and preserved skeletal material may draw attention to issues that otherwise would have been overlooked. Skeletal trauma is highly variable and each case presents a unique set of challenges in the interpretation and reconstruction of the events that produced them. The aim of this volume is to present some guidelines that may help facilitate this process and provide documented support for this growing area of research and application within forensic anthropology. The care given to the documentation of the defects and the depth of work in reconstruction of the events that produced them quickly becomes evident in the quality of the written report and subsequent court testimony. It is upon this foundation that we can advance our influence within this exciting area of forensic analysis.

Section II PRINCIPLES FOR INTERPRETATION OF BLUNT FORCE TRAUMA

Chapter 2

THE BIOMECHANICS OF FRACTURE PRODUCTION ALISON GALLOWAY

B

lunt force trauma consists of damage inflicted through a number of different forces in which the area of impact is relatively large. While there is no specific size at which one can separate sharp from blunt force, the latter is usually thought to include injuries due to fists, sticks, clubs, boards, etc., as well as those induced by motor vehicle accidents, falls and manual compaction of the body. In general, these are characterized not only by a larger area of contact but also at a much lower velocity than is seen in more penetrating injuries such as gunshots. Skeletally, blunt force trauma is seen as a wide range of fracture patterns. These depend, in part, upon the biomechanical properties of bone tissue and the nature of the applied loading forces. The morphology, structural integTity, mineralization and density of the skeletal elements adds another level of factors which help shape the fracture pathway. The shape, mass and velocity of the instrument through which forces are applied also affect the fracturing. This discussion of the factors involved in production of blunt force trauma to the skeleton is divided into (1) the biomechanical factors of bone tissue in response to loading, (2) the nature of the loading forces, (3) a classification of the fractures based on morphology, (4) the fractures associated with direct and indirect trauma and (5) how these fractures appear on individual elements and allow interpretation of direct and indirect trauma. This chapter covers the first four points while the final point is discussed in Chapters 3 through 6.

BIOMECHANICS OF FRACTURE PRODUCTION Loading is the application of a force to an object. Loading forces are applied to bone from a number of different sources. In sedentary use, such

35

36

Broken Bones

as standing or sitting, the weight of the body itself forms a load on the bones. This weight will vary by body size and composition and changes throughout the lifetime. The force is determined by the weight superior to each bone and calculated based on the area of contact for transmission of the load. Thus, when seated, the ischial callosities can support a substantial portion of the body's weight, consisting of the torso, head, neck and upper limbs. In addition, muscle contraction can increase the force applied to bone. When the contraction is constant, or the person is at rest, the force is said to be static, meaning that the loading does not change. In routine movement, however, the forces are dynamic-meaning that the force must be calculated as not only the mass but also the acceleration or deceleration with which it is applied. This dramatically increases the load-bearing of bones. For example, a woman walking on high heels can be loading the heel at about 700 psi (pounds per square inch), even though she weighs no more than 125 lbs. Beyond these loads, there are the forces brought to bear when the body strikes, or is struck by, an object or surface. These loads are usually not in alignment with the normal weight-bearing of the body and so generate deformations in the body as the tissues absorb the energy transmitted. If the loads are low and applied repeatedly, the body will gTadually compensate for the new function (Meade 1989). When these forces are relatively high, they can overwhelm the ability of the tissues to absorb energy without damage. Among the types of injury found are those that affect the skeleton. The focus of this work is on those events that result in acute damage rather than longterm adjustments.

Bone as a Material Bone is a heterogeneous material, which complicates the prediction of its point of ultimate failure. At the material level, it consists of both inorganic and organic material. Calcium hydroxyapatite (Ca lO (P04)6(OH)2) forms the bulk of the mineral portion while the organic component consists of collagen along with the non-collagenous proteins. Bone also contains water, amorphous polysaccharides, cells and blood vessels. For the most part, tests of bone "material" consist of blocks of 4-20 mm2 that actually incorporate a number of microscopic structures moving this test above that of pure "material." Furthermore, tests of bone that has been embalmed or undergone drying will produce significantly different results from tests of wet bone (Reilly and Burstein 1974). The ability of any material to resist a force is directly proportional to both the cross-sectional area and the stiffness or springiness of that material. If two blocks of material are constant in stiffness but differ in area, they will differ in ability to withstand loading forces. Conversely, two materials with dif-

The Biomechanics ofFracture Production

37

fering stiffness but similar dimensions will also differ in resistance. Bone is not exempt from these principles; the material properties of bone, its overall morphology and the nature of the loading explain the patterns of fracture seen in the skeleton. The dynamics of fracture production are explained in terms of the stress resulting in the distortion of bone (Renner et al. 1978; Currey 1984; Cowin 1989a; Harkness et al. 1991; Hipp et al. 1992; Rogers 1992; Keaveny and Hayes 1993). Stress (0) is calculated as the applied force divided by the cross-sectional area. 0= Force /Area Stress is usually measured in MN/m 2 (meganewtons per square meter), MPa (megapascals), or pounds per square inch (psi) (McElhaney et al. 1976; Carter 1985; Cowin 1989a). One pascal (Pa) is equal to 116894 psi or one newton per square meter. Strain (f), in contrast, is the actual change or deformation in the shape. This feature is described as the ratio of the change in the dimension (length, width, height, area, angulation) to the original form (Currey 1970; McElhaney et al. 1976; Carter 1985; Cowin 1989a; Harkness et al. 1991). 10 = Deformation/Dimension The change in dimension may be negative or positive, depending upon the direction of the force. The strains in bone rarely exceed about 3% (Currey 1970). If a material is able to resist stresses equally in any direction, it is said to be anisotropic. If its resistance is aligned along one plane, the material is called transversely isotropic, but if there is no directional dependence the substance is isotropic. If this is the case, the properties by which its deformation is explained are limited. Bone should be treated as a transversely isotropic material (Reilly and Burstein 1974). Bone has also been considered to be orthotropic, meaning that it consists of layers surrounding a central core such as would occur in a tree trunk (Cowin 1989a, b). Bone is initially capable of absorbing and rebounding from tensile or compressive forces (Figure 2-1). In this phase the strain is proportional to the forces applied to the bone and the bone quickly returns to the original shape without loss of integrity. The bonds between the atoms of the material are strained but not broken or irreversibly deformed and is thus known as elastic deformation. The gTeater the resistance of the bone to the stress, the gTeater the "stiffness" or modulus of elasticity or Young's modulus is said to be (Reilly and Burstein 1974; Currey 1984, 1985; Harkness et al. 1991). The modulus is reflected in the steepness of the slope of the initial part of the curve. The steeper the slope, the gTeater the modulus, and the less deformation will be seen in response to loading.

38

Broken Bones

"'---

Yield Point

~ailure Point

Plastic deformation

Strain (mm/mm) Figure 2-l. Relationship of Strain and Stress Within Bone Tissue. The relationship between strain and stress changes as the stress increases. Initially elastic deformation allows for recovery of the original shape, but, as the yield point is passed, plastic deformation constitutes permanent change. Ultimately the bone will fail.

The modulus of bone is determined, in part, by the proportions of the organic and inorganic components of the bone. Increasing the mineral component also increases the stiffness of bone and allows it to better resist compression. Decreasing the proportion of mineral content in bone increases its bendability. The modulus varies by the type of bone tissue, being larger in cortical bone and less in trabecular bone (McElhaney 1970). It also varies by the water content of the bone and the internal architecture. Furthermore, it will vary by the direction in which the force is being applied. As deformation occurs in one direction, there is a complementary change in other directions. For example, compressing a length of material results in expansion of the width. The ratio of these corresponding changes is known as Poisson's ratio. Bone, like other materials, has such a property and this, too, is a factor in determining the stress experienced by the tissue (Reilly and Burstein 1974; McElhaney et al. 1976). Like the modulus, Poisson's ratio varies by bone type (McElhaney 1970). In general, the Poisson's ratios of bone are high, indicating that it tends to bulge when loaded in one direction (Keavney and Hayes 1993). Large changes in the modulus and strength of skeletal material are produced by minor changes in density of the bone mineral-the inorganic component of bone as can be measured by the ash content (Carter and Hayes 1976; Mazess 1987). Modest reductions in bone density correspond to much more serious reductions in the the modulus of elasticity and overall com-

The Biomechanics ofFracture Production

39

pressive strength, suggesting that bone architecture is the critical factor (Mosekilde et al. 1989). Even within normal healthy bone, reductions of 20% of tensile strength and 70% of compressive strength is comparable to that between fully calcified osteons and those only beginning calcification (Ascenzi and Bonucci 1967, 1968). As the stress increases, the linear relationship between the stress and strain is lost and small subsequent increases in the stress result in large increases in deformation or strain to the bone that cannot be fully recovered once the stress is released (Currey 1984; Hipp et al. 1992; Rogers 1992). The point at which this shift occurs is called the yield point and will differ by bone and by individual. This portion of the interrelationship between strain and stress is known as plastic deformation and is characterized by slippage between the layers of atoms and molecules. Normal loading of bone tissue peaks at about 2500-3500 microstrain, but routinely the loads range between 1000-1500 microstrain (Rubin and Lanyon 1982). The yield point is approximately 7000 microstrain, indicating that bone sustains a relatively large safety margin. At some point the stress becomes too great and there can be no further accommodation. This is the failure point and results in fracturing of the bone (Harkness et al. 1991; Rogers 1992). The difference in loading between the yield and fracture points in bone is often relatively small (Currey 1984). The fracture may actually begin well before failure as a series of microfractures that may be detectable at about 60%-70% of the ultimate load at failure (Sweeney et al. 1965). The resistance of any material to failure depends upon the proportions of the brittle and ductile components of the composite and this is true of the skeleton (Currey 1984). Brittle materials, such as bone mineral, are particularly resistant to compressive forces, while ductile organic ones are resistant to tensile forces. Brittle bones can withstand only a minimal amount of plastic deformation while ductile ones can exhibit considerable change. An important variable in the determination of the response is the rate at which the bone is loaded (Carter 1985; Harkness et al. 1991; Hipp et al. 1992; Keaveny and Hayes 1993) and the frequency with which such forces are encountered. Bone is a viscoelastic material; its deformation depends upon how fast the load is applied and for how long (Keavney and Hayes 1993). The speed of loading, the strain rate, increases as activities become more strenuous. Cortical bone has a higher modulus at higher strain rates, although in the normal range of usage this difference is negligible. As the modulus changes, the yield and ultimate strength of cortical bone increase so that the bone can withstand more strenuous activity better. At very high strain rates, the increased modulus means that the bone becomes brittle and the ultimate strain is decreased. Loading that is rapid is often associated with

40

Broken Bones

very rapid unloading so that fracture propagation is halted by the removal of the forces that would enhance crack spreading (Currey 1984). Forces that are applied rapidly may require higher loads to result in failure, but when failure occurs it tends to be more explosive. In contrast, when loads are prolonged, deformation will continue even though the stress level is well below the yield and ultimate strengths. Stress and fatigue fractures are extremely common and usually result from repeated subjection of bone to the same or similar force. Such loading is usually within the tolerable levels of resistance, but it is the repetitive nature of the loading which is catastrophic (Reilly and Burstein 1974; Harkness et al. 1991). This weakens the bone structure, and the heat generated by loading and unloading cycles probably also plays a role. Fracture will occur at a loading level that would be resisted if it had occurred as an isolated event. Stress and fatigue fractures will not be examined extensively in this volume, except as they may affect the interpretation of more obvious trauma. They generally are of little importance in the forensic setting except in personal identification.

Effect of Bone Morphology above the Level of Material While these principles guide the analysis of bone as a material, they are less useful in practical terms. The profile of resistance to loading differs considerably between an isolated cube of bone, especially one that has undergone some drying, and the living bone encased with the soft tissues of a living individual. Even the initial step from bone tissue to bone element presents difficulties. Both microstructural differences and varying cross-sectional geometry alter the determination of resistance within the bony element. The microstructure of the bone itself gTeatly influences its ability to withstand loading forces (Hipp et al. 1992). In the living organism, bone is found in two basic forms: cortical bone, which forms the diaphyses, and trabecular (cancellous) bone, which is found in the vertebral bodies, the metaphyses and the diploe. Cortical bone is dense, solidly packed and suitable to withstand considerable compressive loads. Cancellous bone, on the other hand, is composed of thin interconnected struts of bone that also support other tissues. Cortical bone is stronger and stiffer in its longitudinal axis than in the horizontal axis. It is less porous and has a gTeater density than trabecular bone due to the greater proportional content of mineralized tissue in the bulk volume. Cortical bone is defined as bone with less than 30% porosity and typically has about 10% porosity. In contrast, trabecular bone has high porosity, typically 50%-90%. Bone mineral density is also significantly gTeater in cortical bone, ranging from about 1.8-1.91 gm/cm 3 compared to 0.21-0.39 gm/cm3 for trabecular bone (McElhaney 1970).

The Biomechanics ofFracture Production

41

Cortical bone tissue is not homogenous in structure-being composed of lamellae, osteons and other forms and interspersed with lacunae, canaliculi, haversian canals, Volkmann's canals, etc. Because of this, stresses concentrate differentially within the tissue (Currey 1984). Collagen fibers, lamellae, osteons and haversian canals are aligned along the longitudinal axis of the bones, in part, explaining preference for longitudinal loading. Longitudinally oriented lamellae are best able to resist tensile stress while transversely oriented lamellae are better suited to support compressive loading (Ascenzi et at. 1983). The concentrations of the differently oriented lamellae vary in the cross-section and along the length of the bone, probably with respect to the normally occurring loads (Portigliatti Barbos et at. 1985). Boyde and Hobdell (1969) note that lamellar orientation can shift dramatically over a very short distance within bone. In bone in which haversian systems have replaced the lamellar structures, failure occurs preferentially along the cement lines that surround osteons (Evans and Bang 1966). Currey (1959) and Evans (1958) found a negative correlation between the number of haversian systems and the tensile strength of the bone. As a result, the tensile strength of haversian bone is only 30% that of lamellar bone. Dempster and Coleman (1960) suggested that interlamellar cement lines provided a weak link, while Aoji and colleagues (1959) found cracks between haversian systems and interstitial lamellae as well as in the interlamellar areas. The various vacuoles within bone tissue can increase the stresses within the remaining bone locally by as much as sevenfold (Currey 1984). Thus, a stress that would not affect a consistent segment of bone tissue may be allowed to spread because of the internal structure of actual bone. At the same time the fluids that fill these interconnected spaces in bone can absorb large amounts of energy, thereby increasing the resistance of bone to breakage (McElhaney et al. 1976). Accurate prediction of how much load any portion of bone can withstand from gross morphology is speculative, since, along their length, bones vary considerably in osteon number and size, lamellae orientation and morphology of porosity and there are significant differences by age within one individual and between individuals. In the living body, there is not a sharp dichotomy between cortical and trabecular bone. In some areas, such as the cranium and the end-plates of the vertebrae, the transition between trabecular and cortical bone is blurred. Trabecular strength depends on the mineral content of the bone and the density of the structure. In many respects it resembles many porous materials that will absorb energy upon impact. The modulus of elasticity for isolated trabecular bone tissue has been shown to be lower than that of similar amounts of cortical bone (Cowin 1989c). The modulus of trabecular bone is also highly variable, depending on anatomic site and age (Keavney and

42

Broken Bones

Hayes 1993). It is highly anisotropic in some locations, in that the mechanical properties depend upon the direction of loading. Where trabeculae are aligned there may be a tenfold difference in the modulus depending upon the orientation of the loading. Sensitivity to density is higher for the longitudinal modulus than for the transverse (Williams and Lewis 1982). In other sites such as the metaphyseal portions of long bones, trabecular strength may approach isotrophy, meaning that its mechanical properties are roughly equivalent in any given direction of loading. Because the modulus of trabecular bone is one-eighth that of cortical bone and the yield point is roughly one-third that of dense bone, forces applied to trabecular bone quickly will result in plastic deformation. The compaction of trabeculae, however, increase the modulus of elasticity as the bent and fractured trabeculae begin to fill the available marrow spaces (Carter 1985). This compaction also means that, unlike cortical bone, the Poisson's ratio of trabecular bone may be near zero indicating that there is little lateral expansion of the bone under axial compression. While there is failure under compression, at rapid strain rates trabecular bone ultimately is better able to resist compression albeit with plastic deformation. Under tension, trabecular bone is able to absorb less energy. The yield point is close to the level of failure and the ability of the bone to absorb additional energy is lost. Since whole bones consist of a complex of cortical and trabecular bone, neither tissue alone can predict the strength of the bone. The weight-bearing bones are the most dense, but even these bones vary in density throughout their length (Galloway et al. 1997). Side differences due to asymmetrical use, sex differences, populational differences and age-related differences are also factors in establishing density. Larger bones are more resistant to fracture simply because they can distribute internal forces over a larger volume of material (Carter 1985). The roughly tubular shape of the long bones allows for a more even distribution of the stress. Cross-sectional size and shape also affect the strength of the bone (Gonza 1982; Carter 1985; Hipp et al. 1992). Bone is distributed around the central axis asymmetrically. The shape of the cross-section, expressed as the moment of inertia, also helps predict the response of bone to loading. The area moment of inertia describes rigidity to bending. Tubular structures have larger moments of inertia and are stronger in the face of bending and torsion than a solid cylinder. The polar moment of inertia describes rigidity to torsion. While bones are not the strongest forms for resisting bending which is confined to a single direction, they have the advantage of having a higher polar moment of inertia, meaning they are better able to resist torsion or twisting. In circular bones, the moment of inertia (Jxx) can be calculated by the following formula: Ixx = 1t (R4 - r 4 )/4

The Biomechanics ofFracture Production

43

in which R is the outside radius of the bone and r is the radius of the medullary cavity. To maximize resistance, the bulk of the cross-sectional area of an object is placed as far as feasibly possible from the bending axis. In long bones, this means that an increase in diameter will increase bone strength even if the cross-sectional area is constant. Bone which is farther from the axis is more efficient at resisting bending than bone which lies along the axis. Because of this, areas of long bones which are narrowed tend to have a low moment of inertia and may, therefore, be more prone to fracture. In a similar manner, cranial vault shape will affect the ability of the skull to resist compression.

Loading Within the Living Organism While these above described relationships are relatively simple principles to apply to a material subject to loading in only one direction, they are less simple to accommodate in living bone. The reasons are threefold. First bone is subject to forces being applied in many directions. Bone is relatively ductile in the longitudinal direction but brittle in the transverse. The picture is complicated, however, as bone is usually loaded in multiple directions simultaneously as the forces generated by weight-bearing, muscle contraction and impact upon other materials are accommodated. In these cases, the ultimate strength is reduced. For instance, the maximum tensile or compressive stress that can be withstood, is lowered as shear stresses are superimposed (Cezyirlioglu et al. 1985). Second, meeting the need of all these loading patterns, as well as other functions invested in the skeleton, could require a bone which entailed some serious limitations in function. Particularly vulnerable sites such as the femoral neck would need to be quite different in morphology in order to be best suited to load-bearing alone. Bipedal locomotion could be jeopardized in such circumstances. The added weight of the "redesigned" bone would also drastically increase the energy expenditures of locomotion. Instead the evolution of the human skeleton is one of continual compromises resulting in a set of bony elements capable of meeting locomotor and postural needs as well as maintaining the other functions of these organs including muscle attachment and insertion, housing of hemopoietic tissue and a calcium and trace element reserve for the body. The cells within the bone tissue must be nourished and waste products removed and the medullary cavity must be supported. Blood vessels and nerves must pass along or through the bone. Any sudden transition in the shape of bone, however, to accommodate these soft tissue components will alter the distribution of stresses producing stress concentrations. Morphological features such as notches, abrupt changes in surface contours,

44

Broken Bones

sulci, foramina and nutrient foramen with the long bones are all likely sites of such concentrations (Currey 1984). Examination of overall bone morphology shows that these features rarely occur in places or take a course which will place the bone at greatest biomechanical risk. The third reason is that, if the body was impervious to changes which occur during elastic deformation, the first indication that loads in excess of tolerable levels were being reached would be the onset of plastic deformation and fracturing. Instead, large levels of elastic deformation permit the bone to measure the levels of forces being applied through proteoglycan deformation, piezoelectric changes or microfractures (Chamay and Tschantz 1972; Martin and Burr 1982; Carter 1983; Eriksson 1976). Living bone responds to normal loading by gradually altering the cross-sectional configuration to accommodate these forces but also retain enough flexibility to monitor changes in that force.

Age-Related Changes in Bone and Bone Tissue Bone varies through the lifetime and by organism. Woven bone is the initial form that appears in the fetus as well as in the callus of fracture repair. It can be formed quickly and consists of fine-fibered collagen with a random orientation, although there may be preference for alignment with the long axis of the bone. With time, woven bone is replaced by lamellar bone, which is laid more slowly than woven bone. In lamellar bone, collagen sheets about 5 mu thick surround the bone, although the fibrils in adjacent lamellae usually are not oriented the same direction. As humans get older, the lamellar bone is remodeled into haversian bone, which consists of bone formed by secondary osteons or haversian systems that replace previously existing bone. Each osteon has a total diameter of about 0.4 mm and is formed within a resorption cavity eaten into the previously existing bone. Osteons are aligned to the long axis of the bone. Bone strength is partly related to the proportions of primary and secondary osteons (Currey 1970, 1984). Secondary osteons weaken the overall bone structure, in part because haversian systems appear to be accompanied by decreases in density (Carter et al. 1976). The skeletons of young people are less brittle, more porous with larger haversian canals and a higher water content (Rogers 1992). As we age, osteon number increases while size decreases and allows for an overall increase in the cement lines along which fractures preferentially form (Evans 1975). The periosteum is thicker, more elastic and less firmly bound to the bone and, therefore, tends to remain intact, hinging fragments together (Rogers 1992). Small decreases in the modulus of elasticity are expected with age and average about 1.5% per decade after age 20 (Burstein et al. 1976). The max-

The Biomechanics ofFracture Production

45

imum strain that can be withstood falls more drastically-5%-7% per decade. Ultimate tensile strength of bone declines about 4% per decade under low strain rates (Melick and Miller 1966). Burstein and associates (1976) found decreases in strength under tension and compression in the femur although not in the tibia. Shear strength declined at about 4% per decade. In general, bone becomes less strong and stiff and more brittle as the individual ages, although this is not evenly distributed throughout the body. Maximum bone mineral density, a measure of the concentration of inorganic material within a given volume of bone, peaks between 30 and 35 years of age. This is followed by gradual age-related loss. Superimposed upon this loss among women is postmenopausal loss, which lasts 5-15 years after the climacteric. The loss is more severe although for a shorter period in trabecular bone, while more gTadual but prolonged in cortical bone. As this rate of loss tapers off, the age-related loss continues. In samples of very old populations, an apparent "leveling off" may be partly due to survivorship effects, rather than an actual slowdown in rates of bone loss. Bone mineral density is significantly correlated with fracture risk (Mazess 1987). Fracture thresholds have been established through clinical analysis of the density of the bones of those who have suffered characteristic osteoporotic fractures. These thresholds vary by bone and location within the bone, but show positive correlation within skeletal locations of the individual in most cases (Mazess 1987; Heaney 1989). Risk of fracture is particularly high in the proximal femur, vertebrae, distal radius, proximal tibia, pelvis and proximal humerus (Cummings et al. 1985, 1997; Riggs and Melton 1988, 1995; Melton and Cummings 1987; Melton 1993, 1995; Lips 1997) In many people, especially postmenopausal women, large amounts of bone tissue are lost, leading to the condition clinically termed osteoporosis (Mazess 1987; Melton and Cummings 1987). There is resorption along the medullary cavity with increasing porosity of adjacent cortical bone. This process is often associated with subperiosteal expansion, although this depends upon activity levels remaining relatively high. The net result is alteration of the modulus of elasticity. In trabecular bone, gradual elimination of cross-struts weakens the overall structural integrity despite increasing thickness of the remaining trabecular struts. The decreased bone mass increases susceptibility to fracture, often from minimal or no trauma. As healthy trabecular bone collapses, broken trabeculae fill the pores between the bony struts, increasing the stiffness. In osteoporotic individuals, there are fewer struts and the pores are greater in volume. This results in gTeater deformation before the stiffness due to in-filling of the spaces builds to the point where further collapse is halted. These changes are not confined to a simple loss of density. Osteoporotic fractures will be noted but not directly

46

Broken Bones

addressed in this volume, although it is likely they will occur with gTeater frequency in situations leading to forensic examination. Pathological changes in bone, such as those induced by diabetes, Paget's disease, Cushing's disease, rickets, osteogenesis imperfecta, scurvy, renal disease, neuromuscular disorders, rheumatoid arthritis, osteomyelitis, benign tumors and metastasizing cancers and the use of exogenous steroids, may increase the risk of fracture. While these may also occur in circumstances leading to forensic analysis, the presence of other bone pathologies (see Introduction, this volume; Ortner and Putschar 1981; Aufderheide and Rodriguez-Martin 1998) should alert the anthropologist to the possibility of weakened bone requiring substantially lower than normal forces to produce fracturing.

CLASSIFICATION OF FORCES

Force is the time ratio of change in momentum and is determined by the mass multiplied by the acceleration (Adelson 1974; Harkness et al. 1991). The ability of a force to produce skeletal blunt force damage is dependent upon the amount of energy transferred from the impacting object and the size of the impacted area. In the present discussion, loading is the application of force to an object such as a bone or body segment. Fractures occur in response to forces that push the bone into plastic deformation and may exceed the ability of the bone to tolerate alteration in shape. The primary forces involved are those of (1) tension (stretching), (2) compression (compaction), (3) shearing (sliding), (4) rotation (twisting) and (5) angulation (bending) (Figure 2-2). Compression involves the squeezing of bone, which decreases the dimension of the tissue in line of the applied force. Structurally, the ability of a bone to resist compression is governed by (1) its stiffness as measured by the modulus of elasticity and (2) its geometry (area, moment of inertia) (Hipp et al. 1992). In most cases, compression occurs along the long axis of the bone as would be the case in normal locomotor or manipulative situations. While the body is well-suited for these loads, compression may exceed the preparedness of the body. Compression is a common force involved in falls but is also found when body segments make an impact with an object or surface that compacts the area struck. Microscopically, compression fractures expose the osteons at an oblique angle (Caler and Carter 1989). The ends of the lamellae can be folded over. As the compressive stress increases, osteon clarity declines so that the individual structures become more difficult to identify.

The Biomechanics ofFracture Production

47

t

1

+ +

Compression Tension

.I Rotation

Shear

Bending

Figure 2-2. Forces Acting Upon Bones. Forces on bone include compression, tension, rotation, and shear. Arrows indicate the direction of the application. In bending, force may be applied at a central point while the bone ends are stabilized or excessive compression may exaggerate the natural curvature of the bone. One side will experience compression while the other suffers tension (small arrows).

Tension is the "pulling apart" of bone, epitomized by the medieval rack. In these cases, the change in the dimension where strain is observed would be positive (Currey 1970). In pure tension, the body suffers damage to the joints and ligaments, rather than to the bones (Gonza 1982), although the tearing of ligaments may involve skeletal damage. This tearing apart is also visible at the microscopic level. Osteons are clearly visible in the transverse, irregular and rough surface, but fibers in the lamellae can be seen to be stretched out, often to a point (Caler and Carter 1989). When bone is bent, the tissue is subjected to a combination of both compressive and tensile forces; those portions on the concave side are compressed and those on the opposite side are under tension. Again, the important structural parameters are stiffness and moment of inertia. The distance of deformation must be considered along with the scale of the applied force. Bone has gTeater resistance to compression than to tension. The compressive strength of bone tissue is approximately proportional to the square of the apparent density (Hipp et at. 1992). The tensile strength, being less, yields first and, in bending, fractures begin on the side under tension. Trabecular bone responds somewhat differently and has similar initial strength under compression and tension. Shear forces act to tear tissue apart by sliding some portions of tissue across other. Shear modulus (G), the ability to withstand these forces, is the measure of resistance. It is the ratio of the shear induced to the resulting shear strain (Reilly and Burstein 1974). This elastic constant is dependent upon the modulus and the Poisson's ratio. Since the shear modulus is con-

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siderably less than the modulus of elasticity under compression, shearing action often occurs first, modifying the deformation wrought by compression. Shear strains are characterized by the change in angle undergone in response to loading (Currey 1984). When shearing is combined with twisting, the forces are classed as torsional or rotational. Torsional loading is a relatively common occurrence in human bones and is frequently involved in fractures (Carter 1985). Again, the distance of deformation is important in determining the level of damage. The distribution of bone around the long axis is still critical, but the orientation and distance from the bending axis become the measures of concern. The polar moment of inertia describes the distribution of material around the long axis as discussed above (Hipp et al. 1992). The more symmetrical a bone is, the more it is able to resist twisting. When bones are narrow and of irregular cross-section (i.e., has a low polar moment of inertia), they are more susceptible to rotational deformation (Conza 1982). Usually bone is under some form of compression during the same time that both shear and rotational forces are inflicted and this further modifies the expression of these forces. Bone varies in its response to stress depending upon the rate at which strain is produced. A dichotomy between dynamic and static loading is often presented. The yield and ultimate strength of bone tissue tends to increase as the rate at which the strain is applied increases. Within the normal range of loading, cortical bone becomes stronger with more strenuous activity (McElhaney 1966). At very high strain rates, however, the bone loses some of its ductile properties and becomes more brittle. Under static or constant loading, a different phenomenon occurs. Over an extended period of time, the bone under stress will continue to deform even though the level of loading is unchanged. This is known as creep behavior (Caler and Carter 1989). Eventually creep fracture occurs even at stress levels well below the yield and failure points. Even before fracture, there may be permanent deformation of the bone following static loading.

CLASSIFICATION OF FRACfURES Fractures are initially classified based on the degree of breakage and also on the pattern of breakage. These terms should be used in the forensic description of fractures, whenever possible, as they provide a universal set of terms. Specific fracture classifications differ by bone and are discussed in detail in the following chapters.

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49

IncoDlplete Fractures IncoDlplete fractures are characterized by retention of some continuity between the portions of the fractured bone (Figure 2-3). These are more common in children than adults (Rogers 1992) due to the higher organic nature of younger bones. Incomplete fractures are also indicative of a high moisture content and decrease in frequency in the postmortem period.

Bow Fradure or Plastic Deformation An incomplete fracture commonly found in juvenile material is the bow fracture (Rogers 1992). Here, the bone appears to have an exaggerated curvature which often encompasses the entire length of the bone. Biomechanically they can be explained as occurring between the yield point at the termination of elastic deformation and prior to the failure point. Bow fractures can occur during longitudinal compression (Chamay and Tschantz 1972). Histologically, they are seen as a series of oblique microfractures induced under both compression and tension Oones 1994). While such fractures can occur in any of the long, tubular bones, they are most common in the forearm.

Bone Bruise or Occult Intraosseous Fracture Although of little forensic importance, the possibility of bone bruises should be noted, especially in examination of radiographic and MRI images of the bones (Rogers 1992). A bone bruise is believed to be an area of extensive trabecular bone microfracturing that results from compression or impaction.

Torus or Buckling Fracture A torus fracture is a buckling of the bone cortex produced by compressive forces. It appears as a rounded expansion of the bone where the cortical bone has been outwardly displaced around the circumference of the bony element (Rogers 1992). In almost all cases, these appear in the ends of long bones, usually at the junction of the metaphysis and diaphysis Oones 1994). In some cases they may be combined with incomplete transverse fracture of one cortex while the opposite cortex has undergone compressive buckling. In these cases this type of fracture is often referred to as a "lead pipe" fracture (Rogers 1992).

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Toddler's Fracture

Depressed Fracture Figure 2-3. Classification of Incomplete Fractures. Incomplete fractures affect a range of different bones. This group includes a number of fractures which occur primarily in younger individuals such as the bow and toddler's fractures. Torus and greenstick fractures also are more common in youth. Verticle and depressed fractures may occur in older individuals.

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51

Greenstick The classic gTeenstick fracture results from bending or angulation forces placing one side of the bone in tension while the other is in compression (Rogers 1992). The result is an incomplete transverse fracture beginning on the tensile side which usually extends to about the midline of the bone. At that point, the fracture deviates at right angles, creating a vertical or longitudinal split in either or both the proximal or distal portions of the bone. The remaining unfractured portion of the bone remains bent or bowed.

Toddler's Fradure Rarely seen in forensic settings, this fracture occurs in infants and toddlers who suddenly demonstrate a severe limp, possibly without any clear history of specific injury or only relatively mild trauma (Rogers 1992, Tenenbein et al. 1990,john et al. 1997). Such fractures are usually non-displaced oblique or spiral fractures which may even not be visible radiographically until healing is well established. The distal tibia is most often affected, but the term has been applied to other lower limb injuries. These fractures of the lower limb seem to occur during the normal activity of young children but, in the medicolegal situation, must be distinguished from those seen with child abuse. These fractures only rarely result in epiphyseal separation and are usually solitary, unlike the multiple fractures more commonly associated with abuse.

Vertical Fradures Vertical fractures, while relatively rare, may occur in long bones and run along the long axis. These are generated by compressive forces or, in smaller bones, by direct blows (Rogers 1992). As the cortical bone approaches areas consisting of more trabecular bone, then the linear nature may deteriorate into a number of branches.

Depressed Depressed fractures occur primarily in the skull and result from direct blows that cause "caving-in." The scale of the injury depends, in part, upon the size of the impacted area and the velocity of the force (Gurdjian 1975). In many cases in the skull, where such fractures are more common, this injury will involve only the outer table with the inner table remaining intact. In other cases the outer table is broken and crushed with incomplete fractures occurring in the inner table.

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As the size of the impact area decreases and the velocity increases, the resulting fracture approaches that of a penetrating injury and inner damage may exceed that of the bone surface being impacted (McElhaney et al. 1976). When the impact is highly localized and is accompanied by considerable power, penetration is complete. Fracture is due, in part, to the rapid accumulation of compressive forces and subsequent collapse of any intervening trabecular or porous bone. The term "depressed fracture" is also used in describing fractures of the tibial plateau. In these the trabecular bone in the inner portion of the proximal tibia is unable to withstand loading forces and it and the outer cortical bone are pushed inward.

Complete Fractures A complete fracture is any that results in discontinuity between two or more fragments. Radiographically this can be distinguished by determining whether one or both cortices are involved in the fracture line (Rogers 1992). Clinically these are divided according to the extent of soft tissue involvement. Closed or simple fractures are characterized by no disruption of the overlying skin at the fracture site (Harkness et al. 1991; Rogers 1992). Clinically there is less likelihood of infection. In some cases, however, there will be additional injuries in the area not produced by the actual fracturing process. Open or compound fracture involve injuries to the skeletal element in which the overlying skin is also disrupted. This provides external organisms and contaminants with access to the injury site (Rogers 1992). The bones most often involved with open fractures are the tibia (46%), followed by the femur (12.5%) and then the radius and ulna (11 %) (Gustilo et al. 1969). In addition, complete fractures can be divided based upon the shape and location of the fracture line. It is according to this system that skeletonized material is usually described (Figure 2-4). The direction ofthe fracture is usually determined by the longest axis of the bone (Rogers 1992). The location of the fracture is then assigned by dividing the length of the bone into thirds and assignments are to the proximal, middle or distal portions.

Transverse Transverse fractures run at approximately right angles to the long axis of the long bone (Rogers 1992). They may be propagated in three-point load-

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53

t

Transverse Fracture

Oblique Fracture

Spiral Fracture

t

Comminuted Fracture

Butterfly Fracture

Segmental Fracture

Figure 2-4. Classification of Complete Fractures. Complete fractures are classified based on tbe morphology of the fracture. Arrows indicate tbe direction of tbe appled force. Compression is a common feature in oblique and butterfly fractures while torsion is involved in spiral fractures.

ing such as may occur when blunt force trauma bends a bone supported along the longitudinal axis by other structures. The object imparts a concentrated force producing severe angulation. Bones in these cases are not necessarily under compression from the normal weight-bearing functions in addition to the bending load. In these cases, the bone undergoes extreme tension along the convex side while the concave side is under compression (Gonza 1982; Hipp et al. 1992; Rogers 1992). Since bone is more resistant to compression than tension, the convex side is the first to yield producing a crack. As the outer layers of bone yield, the adjacent layers bear the brunt of the maximum stress and quickly

54

Broken Bones

fail. This process occurs at right angles to the long axis of the bone. This failure decreases the cross-sectional area, magnifying the forces acting on the remaining segments of bone. As the fracture crosses the bone it crosses the "neutral axis," the point where there should be a transition from the tensile to compressive loading. However, since the side of the bone bearing the tensile forces has failed, the neutral axis has correspondingly moved toward the compressive side. The initial break then quickly spreads across the bone.

Oblique Oblique fractures run diagonally across the diaphysis, usually at a 45 degree angle (Rogers 1992). They usually result from the combination of angulation and compressive forces of moderate force. When this happens there are several ways in which the fracture can be propagated (Gonza 1982). (1) If the compressive forces are large relative to the bending forces, the bone fails in compression producing a purely oblique fracture. (2) If the bending forces are relatively large then the failure may resemble a transverse fracture. (3) The more common situation is an oblique transverse fracture which is initiated as a transverse fracture, but, following the initial break, the tensile and compressive forces are magnified on the remaining bone. This results in shearing as compression forces the remaining bone downward. The result is a bone in which the initial fracture is perpendicular to the long axis while the latter portion is oblique. The magnitude of the tension and compression determine the proportion of transverse to oblique components in the fracture. The impact of the bending load can be determined by the position of the oblique fracture to which it should be adjacent. Oblique fractures can also be produced by a combination of angulation and rotation in the forearm and leg. In these areas, the paired bones act in a manner similar to spiral fractures resulting in oblique fractures in each bone, although at different levels.

Spiral Spiral fractures begin as small defects, then the cracks follow the peak of the tensile loading around the bone. In rotational forces, the tensile stresses are oriented at a 40-45-degree angle to the long axis of the shaft and are gTeatest at the surface and at zero along the axis (Gonza 1982; Rogers 1992). Compressive stresses are greatest at 180 degrees to the tensile stresses, and are also greatest on the bone surface and zero along the axis. The fracture begins at the point of maximal tension and follows the angle of rotation, approximately 45 degrees until the two ends are approximately above one another. At that time, a longitudinal crack appears and unites the ends.

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55

Spiral fractures circle the shaft and include a vertical step. Caused by rotational forces on the bone, these fractures tend to be the result of low-velocity forces. The direction of the spiral indicates the direction of the torsional forces (Conza 1982) and can be used to reconstruct the events that produced the fracture.

Comminuted A comminuted fracture is one in which more than two fragments are generated. These can be roughly classed as "slightly," "moderately" or "markedly" comminuted depending upon the severity of the fragmentation (Rogers 1992). Those in which both the number of fragments and the size are large are more severely fractured. These usually result from relatively high levels offorce (Conza 1982). In long bones, many comminuted fractures may be classified as consisting of the two segments of bone and a small "butterfly fragment," which is an elongated triangular fragment formed on the concave side of an angulation fracture (Conza 1982; Carter 1985; Hipp et al. 1992; Rogers 1992). These result from the combination of oblique transverse fractures produced when angulation occurs in the presence of compression. The protuberance left by the oblique fracture is leveraged against the remaining shaft of bone and a second oblique fracture results. The resulting triangular portion is sheared off the bone. Such fractures are most common in the lower extremity, which is often weight-bearing at the time of impact by an extraneous object. They are commonly seen in the legs of pedestrians hit by motor vehicles. Butterfly fragments are not common in pediatric victims who, being shorter, are usually pulled under the car and whose bones are more resilient. When they do occur, they are usually limited to the more heavily mineralized areas such as the midshaft of the femur, tibia or ulna Gones 1994). When multiple fractures leave diaphyseal portions separated from the proximal or the distal ends, the intervening segment is called a segmental fracture. This defect may result from multiple simultaneous fractures as would occur when a bone is hit at two points or by a large surface.

Epiphyseal Fradures Two categories of epiphyses exist in the long bones: (1) pressure epiphyses, which form the articular ends of bones and (2) traction epiphyses, the origin and insertion sites for major muscles or muscle groups (Salter and Harris 1963). Both are identified by the presence of a cartilagenous growth plate interspersed between the diaphysis and the epiphysis. Both are subject to injury.

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Broken Bones

The growth plates themselves are substantially weaker than either the surrounding bone or the ligaments and often rupture prior to loss of integrity in these adjacent structures (Wilber and Thompson 1994). Epiphyseal injuries may be limited to the cartilagenous growth plate but may also involve avulsion of adjacent bony structures or crushing of the epiphysis. The growth plate consists of four inter-digitating regions. The first two, attached to the epiphysis, are strong, consisting of the resting and proliferating cells. The next region, that of the hypertrophying cells, is much weaker. The final region includes substantial regions of calcification, which provide strength. Fractures therefore occur preferentially through the third region (Salter and Harris 1963) or the third and fourth zones of the physes. These are the regions where chondrocytes are undergoing massive hypertrophy and then gTadually becoming necrotic and replaced by the osseous incursions (Canale 1992). In children, fractures through the bone are more common than through the epiphysis, even though the latter is structurally weaker (Salter and Harris 1963). The underlying cause is that the plate is susceptible to only a limited range of forces, specifically avulsive and shearing forces, while the bone is vulnerable to the greater range of loading. Damage to the plate is most often seen at the distal radius, followed by the distal ulna and humerus, radial head, distal tibia and femur, proximal humerus and femur and phalanges. For a variety of reasons, the more distal portions of the bone are more prone to such injuries than the proximal ends (Canale 1992). Injuries are more common during the periods of rapid growth, particularly in the first year of life and during the adolescent gTOwth spurt. Clinically, these injuries are particularly disturbing as they are frequently associated with disruption of the gTowth plate (Canale 1992). Blood supply to the areas of the stem cells is essential for maintenance of the growth plate so destruction of the circulation is important in the genesis of these problems. Such injuries can terminate growth at this location completely or result in partial loss of gTOwth. The latter condition will, over time, result in angulation of the limb. The cleavage normally passes through the plate and into the metaphyseal bone, leaving a triangular fragment of the metaphysis attached to the epiphysis. Although these fractures are not easily recognizable in the forensic skeletal record, diaphyseal ends and the epiphyses should be closely examined for signs of avulsion. Since vascular compromise often accompanies these injuries, distortions of the epiphyses due to necrosis may be indicators of prior episodes of violence. These are usually classified by the SalterHarris system in which four of the five categories involve some osseous damage (Salter and Harris 1963) (Figure 2-5). Type I involves complete separation of the plate without associated fracture of bone and results from shear-

57

The Biomechanics ofFracture Production

ing or avulsive forces. This type afflicts very young children and is probably not recognizable in the skeletal record. Type II, most common form, involves a separation that extends through part of the epiphyseal plate and into the bony metaphysis. This form is usually found in children over 10 years of age and results from shearing or avulsive forces. Type III consists of an intra-articular fracture from the joint surface to the weak zone of the plate and is produced by shearing forces. Type IV is also an intra-articular fracture from the joint surface through the plate but extends beyond the growth plate into the metaphysis. The final type, Type V, involves crushing of the plate due to compression on the epiphysis.

Type II

Type III

Type IV

Type V

Figure 2-5. Salter-Harris Classification of Epiphysical Fractures. Of the five types of epiphysical fractures, four will show some form of skeletal damage. Type I involves separtation along the cartilageneous growth plate. Type II includes metaphysical portions, while Types III and IV fracture the articular surface. In Type V, fracture terminates the growth of a portion of the plate.

INTERPRETATION OF DIRECT VERSUS INDIRECT TRAUMA In addition to the simple classification system that describes the morphology of the fracture, a trauma typology compiles fracture morphology by associated biomechanical processes. These are initially divided into direct and indirect trauma.

Direct Trauma Direct trauma is induced when an object strikes the non-moving or slowly moving body or when the moving body strikes a stationary or slower moving object. This trauma is localized to the point of impact. Skeletally, direct

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trauma includes only those fractures by impact and not by deformation of the bone secondary to impact. Direct trauma produces a range of injuries from tapping injuries to extensive crush fractures. Tapping fractures result from a small force of slowing momentum on a relatively small area of the body. These are transverse fractures, although some may be more obliquely transmitted. When they occur in the forearm or lower leg, only one, and only the weakest or most exposed bone, is fractured. When they occur in the ulna, they are sometimes known as parrying fractures. These fractures are usually accompanied by relatively little soft tissue damage. Crush fractures occur when a large force is applied over a large area of the body. The degree of damage varies from transverse to severely comminuted fractures. In the forearm or lower leg, both bones are usually broken. These fractures are usually accompanied by extensive soft tissue damage and there is often penetration of the skin, which leads to the possibility of infection. On dry or exposed bone, direct trauma produces an impact or loading point (Lyman 1994). This defect appears as an area of incipient ring cracks or crushed bone, often with a crescent-shaped notch. There may also be a rebound point opposite the impact site from the force bouncing back from the anvil upon which the bone is positioned. In the forensic context this is less of a concern as, in most cases, the bone is still enclosed within soft tissue during the trauma.

Indirect Trauma Indirect trauma results in fracture beyond the site of immediate impact. These can be induced by tension, rotation and angulation, and often occur while the bone is under some form of compressive loading. Hyperflexion or hyperextension are also common forms of indirect injury brought on by deceleration or acceleration of the body.

Linear Fractures Linear fractures often occur in the skull and result from out-bending of large thin portions of bone as the result of a direct blow of high velocity. They are the result of indirect trauma but frequently extend to the fractures at the impact site. These are characterized by long fractures that usually seek the weakest region of the bone through which to propagate. The production of these is extremely rapid, often outpacing even fired projectiles into bone.

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59

Avulsion Fradures Avulsion fractures produce small fragments of bone that are detached from the bony prominences by the tension produced by the attached ligaments or tendons (Rogers 1992). Extremely tight bonds between the Sharpey's fibers (small spicules of bone at attachment sites) and the adherent soft tissue preclude rupture at the insertion point, and the nearest weak link is often the surrounding bone itself. These fractures are characterized by detached pieces of bone adjacent to ligament attachment sites and are more frequent in areas where the cortical bone is relatively thin. These fractures tend to be irregular in cleavage.

Traction/Tension Fractures Traction/tension fractures are an expansion of avulsion fractures and occur perpendicular to the direction of pull. Traction/tension fractures are most common in the patella, olecranon process and medial malleolus. Such pure tension fractures are relatively uncommon.

Angulation Fractures With angulation fractures, the bone is bent so that one side is under compression while the other is under tensile forces (see Figure 2-2). As discussed previously, the tensile side is most susceptible to fracture and results in a transverse fracture. As this fracture approaches the compression side, the bone fails in a shearing fracture to produce a triangular spur of bone, which may become separated from the bone.

Rotational Fradures In rotational fractures, the bone is twisted so that there are both horizontal and vertical shear forces produced. These are initially seen as a series of small vertical cracks that widen and then are propagated as a spiral fracture (see Figure 2-4). Since the bone is often under compression simultaneously, the length of the spiral is often shortened.

Compression Fractures Compression fractures vary depending upon the direction of the force and the morphology of the bone. Compression fractures in long bones are identified as longitudinal or "teacup" fractures. Longitudinal fractures can

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Broken Bones

expand down the entire length of the diaphysis but end in a Y or T shaped fracture pattern at the metaphysis. This results from the shaft of the bone being driven into the cancellous and less resistant ends of the bone. Similarly, compression fractures of the vertebrae designate collapse the anterior portions of the vertebral body (Bucholz 1994), while burst fractures involve extensive fragmentation of the centrum as the intervertebral disk is driven downward (Rogers 1992).

SYSTEMS OF CLASSIFICATION

The classification of fracture patterns derives largely from the medical literature where determination of stability of the injury, probable extent of associated soft tissue damage and the prognosis for recovery are the primary motivations. Medical personnel must determine the fractures by external appearance, palpation and imaging techniques rather than by direct observation of the skeletal elements. Emphasis is placed not only on the degree of actual breakage but also upon dislocation or complete loss of contact between articulating surfaces and subluxation where there is partial or abnormal contact. In some cases, the degree of articulation is evident for the anthropologist in skeletal material, but this is often gTeatly distorted by taphonomic processes. In addition, the biomedical perspective focuses on the damage of joints rather than skeletal elements. The discussion in the following chapters aims to establish a common set of definitions that allows translation between the medical and anthropological sciences with a focus on the individual bones. Dislocations will be discussed when they are a frequent coincident injury to breakage. The focus will primarily be on fractures in adults or within the ossified regions of the bones in subadults since epiphyseal fractures may not be distinguishable in skeletal material. The validity of the classification systems must be addressed. Numerous, often contradicting, systems have been devised, in addition to the large number of fractures or fracture complexes that have been named for the person who first described them or is identified with their treatment. In an effort to bring some order to this chaos, uniform systems of classifying fractures have also been formulated. These include the Swiss Association for the Study of the Problems of Internal Fixation (AO/ASIF) for long bone fractures (Muller et al. 1991) and the OTA (Gustilo 1990). These are designed for application to the major long bones, and the correct assignment should be easily identified and interpretable. For example, the AO/ASIF system provides a code for each long bone which is then subdivided into segments. The "squares method" of defining the distal and proximal ends is adopted in which a por-

The Biomechanics ofFracture Production

61

tion equivalent to the maximum width of the bone is designated to the end segments. Each fracture is therefore localized within a segment by the first two numbers. Additional numbers are given for severity, fracture type and severity within type. Diaphyseal fractures are classified as (a) simple fractures, (b) wedge ("butterfly") fractures and (c) complex fractures. While these systems potentially allow comparison of results between various centers and could permit studies of the mechanism of injury, serious concerns over their utility have been raised. In a study of interobserver variation using the AO/ASIF system, only 32% of the responses were in complete agreement with the final consensus Uohnstone et al. 1993). Although all were able to agree on the bone, 7% were in error on the segment and 28% on the fracture type. Similar results were found within the humerus with a comparison of the AO/ASIF system and an older classificatory system for proximal fractures (Siebenrock and Gerber 1993). In this study even intraobserver reliability was poor. Even with extensive patient history, examination findings, photographs and radiographs, agreement on open injuries to the tibia only averaged 60% (Brumback and Jones 1994). For this reason, adoption of a straight medical classificatory system is not encouraged for the forensic anthropologist. Instead, all fractures should be charted, using multiple angles if this provides additional information. Photographs of the fracture should include at least one of the complete bone as well as detailed shots of the fracture. All photos should include a scale. Close-up photos should be oriented as to the correct view. The soft tissue trauma associated with skeletal fracture varies by location and severity of the injury, and any interpretation of the extent of such damage from the skeletal injuries should be left to the expertise of the forensic pathologist. Different bones respond differently to the various forces imposed upon them, resulting not only in different resistance to fracture but also to very different patterns of fracturing. The bones most resistant to tensile strengths were the radius, fibula, tibia, humerus and femur (Ko 1953). Compressive forces have the least effect on the femur, tibia, fibula, humerus, radius and then ulna (Yokoo 1952). Unique features of overall morphology, proportions of trabecular and cortical bone, articulation with other skeletal elements and attachment of ligaments and tendons also result in different fracture patterns in each bone. For this reason and the fact that forensic cases often consist of isolated elements or incomplete remains, in this volume each bone will be discussed separately.

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Broken Bones SUMMARY

The distinct morphology of fractures can provide significant information upon which to base an interpretation of the forces involved, the direction of the loading and the effect of bone strength. This requires a basic understanding of how the fracture level is reached in bone and where the primary strengths of bone as a tissue reside. Bones vary in strength with regard to the various forces in different areas. Each bone differs from other bones in the body of each individual. Each individual varies throughout his or her lifetime and differ from other members of the population. Despite these differences, patterns emerge in the ways in which bones fracture that enables the anthropologist to begin to understand the suite of injuries that produced the defects seen skeletally.

Chapter 3 FRACTURE PATTERNS AND SKELETAL MORPHOLOGY: INTRODUCTION AND THE SKULL ALISON GALLOWAY

T

he skull is a geometrically complex structure that exhibits a basic symmetry along the midsagittal plane. Functionally, it can be divided into the cranial vault, or neurocranium, that houses and protects the brain and the face, a much more delicate structure. There are fourteen bones with thirteen suture lines. The bony structures of the throat are included in this discussion. The cranial vault forms a relatively closed structure around the brain, which itself provides some additional resistance to impacts. The facial bones, in contrast, form a complex arrangement that houses not only fragile organs, muscles for the fine movements of facial expression and the dental arcade, but also large sinuses and areas for mucous membranes that provide little resistance to impact. In some areas of the face, forces derived from muscular contraction are minimal while in others, such as around the jaw, considerable strain is generated. Head injuries occur in a wide variety of situations. Motor vehicle accidents, motorcycle accidents and car-pedestrian accidents are the most common in the current era. Sports-related injuries are another source as are falls from heights. The head is particularly vulnerable in all of these situations. Interpersonal violence is of particular forensic interest. In many cases, the head and face are psychologically linked to the victim's identity in the mind of the perpetrator, making these areas the focal point of rage. Furthermore, identification of remains is commonly known to be made from dental records and radiogTaphs and may also be made from other structures in the skull. This may lead the perpetrator to attempt to disguise the identity of the victim by demolishing the face or the entire head. Blunt forces on the skull may be imparted by compression or by direct or indirect impact. These forces can be dynamic or relatively static. The cranial vault can undergo considerable compression in any direction without fracture, and may accommodate a decrease in diameter in one direction by

63

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Broken Bones

an increase in the perpendicular direction. The fragile facial bones are more susceptible to damage, and vault deformation may indirectly fracture the facial region. Because of the placement of the relatively weighty head at the top of a more fragile structure, the neck, the head is strongly influenced by acceleration and deceleration of the body. In situations such as motor vehicle accidents and falls, the force with which the head strikes an object can therefore be gTeater than that inflicted on the rest of the body. In static loading, forces are usually dissipated over a larger area but resistance is calculated to be about 20% of that withstood under dynamic conditions (Gurdjian 1975). Crushing injuries tend to be massive and devastating. Skulls vary in bone thickness and robusticity. Female skeletal material is, on the average, more gracile than that of males and, therefore, on average more prone to fractures. Large intra- and interpopulation variability precludes accurate assessment based solely on sex (Ross et al. 1998). Head shape also is important; elongated skulls are apparently somewhat better able to withstand compression along the long axis than a more rounded skull (Gurdjian 1975). Since head shape is determined partly by genetics and also some environmental factors, risk will vary depending on the population genetic profile and normal environmental conditions during the period of skull expansion. In this chapter, the skull is discussed in terms of the major segments rather than individually by bone. Discussion is divided into the cranial vault, the upper facial bones, the mandible, the hyoid and the thryoid and cricoid cartilages.

CRANIAL VAULT

The cranial vault consists of the frontal, parietals, temporals, occipital and sphenoid. There are outer and inner tables composed of dense cortical bone that sandwich a trabecular diploe. In most cases, the outer table is thicker than the inner. Gurdjian (1975) reports that the average adult skull has a thickness of .272 inches with .108 inches consisting of diploe. In some areas, this structural arrangement gives way to much thinner bone without diploe. This is especially common in the temporal and sphenoidal regions. The cranial vault appears to act isotrophically under loading, meaning that there is little linear organization within the bone tissue itself that will alter the modulus from one direction to another (McElhaney et al. 1976). The compressive strength of compact bone is 24,500 psi while that of the diploe is 3640 psi. Considerable variation has been noted between specimens (Melvin and Evans 1971).

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The degree of sutural closure influences fracture pattern. Infants have open sutures, and trauma to the vault tends to be localized by the inability of fractures to cross the membranes and patent sutures (Blount 1955, 1977). The bones of a child are much more elastic than in the adult, which allows for greater tolerance of deformation, at least in terms of bony damage. As the suture lines become joined, energy can be transmitted beyond the area of direct impact. Sutural closure and obliteration is a long and highly variable process. Sutures that completely disappear in one skull may still be open in another of similar age and the same sex and population. So, too, will fracture patterns vary. Observation of the sutures involved is essential, with the basic principle being that the less unified the bones on each side of the suture are to each other, the greater the chance that a fracture will be propagated along the suture rather than across it. The velocity and mass of the impact are critical in determining the type of injury. In direct impact, the cranial vault acts like a semi-elastic ball that can be bent inwards at the impact site, with out-bending occurring in all areas around this point (Gurdjian et al. 1953; Gurdjian 1975; Rogers 1992) (Figure 3-1). Fracturing will occur only if the tensile or bending strength of the cranial bones is exceeded. If this occurs, then a linear fracture will originate at an area of out-bending distant from the impact site and will radiate both toward the point of impact and in the opposite direction. The outer table may be involved more extensively than the inner table, although experimental studies show that, in some situations, the inner table will fracture without fracture of the outer table. Once a linear fracture has been sustained, relatively little energy applied subsequently will produce additional fractures and complete skull destruction. Another important factor is the shape of the object making the impact. A pointed impactor produces perforations of the bone. As the area of the impacting surface increases, the likelihood of penetration decreases. As the area of impaction increases still further, larger forces are required to produce fracture. Depressed fractures occur when the striking object is of moderate size, but when the impact site extends over much of the cranial vault surface, comminuted or linear fractures are more common. Another factor involved in determining the amount and form of fracturing is the amount of "padding" on the head. This usually consists of the scalp and the hair but may be augmented by a hat or other clothing. Additional protection may come from helmets or from other parts of the body used to ward off impact. Since head injuries are often involved in homicidal fatalities, careful preparation of the supporting documents by the forensic anthropologist during the analysis may become critical for supporting the conclusions in court. Features to note are the extent of damage, whether both the inner and outer

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Cunature

Figure 3-1. Deformation of the Cranial Vault with Impact. The cranial vault is depressed immediately beneath the point of impact, but out-bending in the adjacent areas place these regions under tension. Fracturing often begins at the point of out-bending rather than of impact.

table are involved, which bone(s) are affected and probable point of impact. If possible, fractures should be sequenced (see Chapter 1). Measurements of fracture lines, detailed charts, photogTaphs and radiographs complete the documentation.

Classification of Cranial Vault Fractures Cranial vault fractures are divided into five basic categories based on the morphology of the fracture. The most frequent type is a linear form, that accounts for about 70%-80% of all skull fractures (Gurdjian 1975; Rogers 1992). Diastatic fractures, where the fracture follows the suture and causes traumatic separation, account for about 5%. The remaining 15% of skull fractures are depressed, comminuted or stellate fractures. Linear or fissure fractures pass quickly through the cranial vault and tend to follow the path of least resistance (Figure 3-2). These breaks are any single fracture that passes through the outer and/or inner table. In most cases both tables and diploe are separated. Linear fractures may be displaced dramatically forming distinct pieces of bone or they may be essentially undisplaced. The latter is particularly true in the denser portions of the skull. Because there is inherent tension in the skull that is released by the fracture, warpage of the bone may occur and it may be very difficult to refit the fragments. Dense bone may divert the fracture line, and any pre-existing fracture or open suture can terminate a fracture since the energy can be dissipated through this intervening structure. Linear fractures are rarely straight,

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as the name may imply, and may diverge in some areas, especially when there is an incomplete fracture. Often, there is insufficient energy for the fracture to continue completely through a bone to a suture or other such structure and will terminate in the middle of the bone. Because of the serious complications that can arise from linear fractures, even when seemingly minor and undisplaced, all such injuries should be brought to the attention of the forensic pathologist for evaluation. Linear fractures of the skull are frequently associated with intracranial hematomas. Linear fractures tend to result from forces with a relatively large mass. They are often found in blunt force trauma as a result of direct impact with an object, such as a weapon used in assault or a portion of an automobile frame during an accident. Linear fractures may also appear due to forces transmitted from other areas of the body, particularly through the spinal column. Blows to one portion of the head may cause linear fractures in other areas. These tend to move downward from blows to the upper portions of the cranial vault more frequently than basilar fractures to extend upward into upper vault. In many cases there are multiple linear fractures that produce severe comminution, which have also been termed "composite" fractures (Gonzalez et al. 1954). For example, a blow to the right temporal may pass through the facial bones and extend posteriorly through the left frontal and parietal onto the occipital. Compression of the skull also will produce a massive complex of linear fractures as the cranial vault ruptures, such as occurs in many train-pedestrian accidents. In children, linear calverial fractures are less common because of the gTeater flexibility of the bone (Duncan 1993). Linear fractures are often found in victims of child abuse and careful attention needs to be paid to their identification in juvenile material. Knowledge of the normally appearing cleavages in cranial bones during the growth process is essential for distinguishing natural versus artificial separation. In young survivors of linear fractures, the fractures can enlarge in time and are known as growing skull fractures. They are most common in children under the age of three years (Naim-Ur-Rahman et al. 1994). Diastatic fractures usually are a variant of linear fracture that is diverted into a suture (Gurdjian 1975) (Figure 3-2). Shallow depressed fractures are sometimes called pond fractures (Knight 1991). These injuries usually result as a continuation of a linear fracture, although they may also result from compression or other mechanisms. They are more common in younger individuals whose sutures have not yet begun to unify. The most frequently affected sutures are the lambdoidal and coronal. While low-velocity impacts caused by forces with a large mass often result in linear fractures, higher-velocity forces with a small mass often result in depressed fractures (Figure 3-2). In the latter situation, there is in-bending at

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the impact site (Gurdjian et al. 1953) and this fracture form is characterized as one in which several fragments of bone usually angle inward. The tensile strength of the bone is exceeded at the impact site itself and fracture will occur at that point. The principle is "the higher the velocity and the smaller the mass of the object the more likely is a depressed fracture" (Rogers 1992: 303). Depressed fractures in the cranial vault may result in actual penetration of the skull (McElhaney et al. 1976) (Figure 3-2). Compressive forces may cause the diploe to collapse. This may be followed by failure of the outer and inner tables. Linear fractures may arise from these defects and radiate away from the point of impact. The fracture may be limited to the outer table, but if penetration is greater, the inner table may also be involved (Gurdjian 1975). Because of the relatively localized nature of these penetrating defects, however, an approximate outline of the impacting area can be seen (Gonzalez et al. 1954; Marks, this volume). In some cases, however, the area of damage is more extensive than the size of the impacting object, and the curvature of the skull may also limit the formation of an imprint of the object (Gurdjian 1975). The cranial vault of an infant or young child responds somewhat differently as the bones of the cranial vault are generally thinner and more flexible (Rogers 1992). Consequently, they are capable of absorbing a gTeater impact than the cranial vault of an adult without resulting in fracturing. This does not mean that they are less subject to brain damage, and the incidence of depressed fractures is 3.5 times greater in children than in adults (Zimmerman et al. 1981). Depressed fractures in young children, however, may never actually involve a fracture site but, rather, are limited to a depression in the vault (Gurdjian 1975; McElhaney et al. 1976; Rogers 1992; Duncan 1993). These are termed ping-pong, dishpan or derby hat fractures due to their resemblance to the depression that can be made by the fingers in a ping-pong ball. Depressed fractures can occur during birth and usually involve the parietal bones (Watsonjones 1941). Stellate fractures are "star-shaped" injuries and consist of multiple radiating linear fractures (Figure 3-2). These originate around the point of impact where the tensile forces become most pronounced. Heavy loads of relatively low velocity are a common cause, as they are most likely to produce the extensive in-bending that results in a stellate fracture (Gurdjian 1975). They tend to occur on the upper parietals although may be found somewhat lower. They are also associated in some cases with a depressed fracture at the point of impact. Comminuted fractures of the vault result from low-velocity/heavy-impact forces, that produce fragmentation of bone (Gurdjian 1975). These types of injury are often found in crushing incidents where the skull is compacted under great force although not necessarily with great speed. These fractures

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Figure 3-2. Cranial Vault Fractures. Fractures of the cranial vault follow a series of different patterns. A. Linear fractures can pass through a number of bones. B. Diastatic fractures are located within the sutures although may be extensions of linear fractures. C. Depressed fractures are localized at and around the areas of impact. D. Stellate fractures result from bending in the cranial vault and may be linked with depressed fractures as shown above.

tend to form on the convexities of the skull with the central area being extensively fragmented and circular fractures extending beyond the impact point. Such fractures are often so severe that recovery of all portions and reconstruction is nearly impossible.

Effects of Cranial Morphology on Fracturing While cranial fractures may occur in any portion of the vault, some areas are more susceptible than others. In an examination of 504 bodies, LeCount and Apfelbach (1920) revealed six regions where greater thicknesses of the cranial bones form arches that hindered the horizontal bending of bone

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(Figure 3-3). Between these arches, the bone can bend more easily in a vertical manner. The normal healthy adult skull is thicker and stronger in the midfrontal, midoccipital, parietosphenoidal and parietopetrous buttresses. In contrast, it is weaker in the temporal fossa where fractures can lead to epidural hematoma and laceration of the middle meningeal artery (Adelson 1974).

Figure 3-3. Le Count Buttresses. The system of buttresses or reinforcing arches proposed by Le Count is shown. These areas help limit and redirect linear fractures of the cranial vault. Within these struts are located some of the thickest regions of the the skull.

Since LeCount and Apfelbach's study, the work of Gurdjian and colleagues (Gurdjian and Lissner 1945; Gurdjian et al. 1953) examined fracture patterns in experimental conditions. Deformation from direct impact by a striking object was more pronounced in areas of weaker buttressing, particularly the frontal bone, areas around the foramen magnum and the parietotemporal area. Linear fractures can pass through the bony buttresses of the cranial vault, but usually this happens when the direction of travel is close to perpendicular to the long axis of the buttress. Fractures that encounter the buttresses at an oblique angle tend to be diverted toward structurally weaker areas. Blows that land on the top of the skull, between the parietal bones, tend to travel inferiorly through the side of the skull. Blows to the frontal region produce more vertically oriented fractures while blows to the sides and back of the skull lead to more horizontal defects. Linear fractures usually involve the cranial base (Gurdjian et al. 1953; Gurdjian 1975), especially

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with impacts on the frontal and occipital bones. This may involve a continuation of the initial linear fracture but also may be an indirect result of compression between the impact site and the spine. The cranial vault, which in many respects is a closed structure, must allow for the passage of blood vessels and nerves. The bulk of the foramina are located in the basilar region, but smaller foramina are found in most of the major bones. These foramina serve as focal points of fractures, as stress mounts rapidly in these areas where the integTity of the bone structure is already weakened. In particular, the foramen magnum as well as the foramina of the frontal bone are frequently involved in fractures. Basilar fractures, due to blows to the front of the head or indirectly through compression of the spine, may involve longitudinal or transverse fractures of the sphenoid (Rogers 1992). Basilar skull fractures are often accompanied by extensive brain stem contusions and tearing that results in a high mortality, much higher than expected given the fracture injury alone. Longitudinal fractures often extend into the frontal fossa while, posteriorly, they appear to jump the foramen magnum and continue into the occipital. They may also pass lateral to the foramen magnum. Transverse or hinge fractures divide the cranial vault anteroposteriorly, usually running anterior to the petrous portion and through the sella turcica. "Typical" basilar fractures extend anterior to the petrous portions, and pass through the base adjacent to the basilar synchondrosis. While this type of fracture has been linked to lateral blows to the head, it has proved to be an unreliable indicator of impact sites (Harvey and Jones 1980). Any blow at the level of the base of the skull can produce the classic pattern. Ring fractures of the cranial base are also found and are particularly common in falls from heights (Spitz and Fisher 1980). The skull base separates with the rim of the foramen magnum and detaches from the vault. The mechanism is usually impact transmitted through the spine when an individual lands on the feet or buttocks. Blunt force trauma in the form of blows to the head may result in fracturing of the temporal bone in the mastoid and petrous portion (Rogers 1992). Petrous fractures usually pass either transversely across the petrous or longitudinally along the petrous portion. The latter are the more common form and usually result as a continuation of a linear fracture in the temporal or parietal bones. Longitudinal fractures are also more common in the mastoid than are transverse ones, but the course of fracture in this area tends to be highly variable. Blunt force trauma requires considerable force to cause fractures in skeletal material. Linear fractures of the cranial vault usually require approximately 450 to 750 psi (Cox et al. 1987). Messerer (1880) examined the penetration loads required to induce fracturing and found that there was consid-

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erable variation between bones and individuals (Table 3-1). Estimation of the force required to produce fracturing is therefore difficult to address. Experimentation with agel sex matched material of similar structural appearance can prove useful (Gill-King, personal communication), but individual variation is still a major consideration. Table 3-1 LOADS AT FRACTURE UNDER EXPERIMENTAL CONDITIONS Cranial Vault Location

Falls from Height*

Penetration Load

Frontal bone

1100lbs

616-1816 IbsG

Parietal Bone

550lbs

396-1100 Ibs

G

Temporal Bone (Squamous Bone)

374-4181bsF

External Occipital Protruberance

1155-2145 Ibs F

FACIAL BONES The face consists of a number of relatively friable bones supported on braces of more rigid bone. These latter structures, often spared during fracturing, include the alveolar process of the maxilla, the malar eminence of the zygomatics and the nasofrontal process of the maxilla (Rogers 1992). The face can be visualized as a series of horizontal and vertical struts (Gentry et al. 1983) (Figure 3-4). Horizontal struts pass above and below the eye and at the roof of the mouth, while vertical struts pass midsagittally, along the side of the nose and diagonally from the lateral edge of the hard palate to the lateral edge of the orbit and then vertically along the orbit. Two additional struts can be visualized in the coronal plane; one formed by the anterior maxillary sinus and a second formed by the posterior wall of the sinus and associated bones. These struts provide resistance to fracture while the remaining bone tends to crumple with impact. The face is frequently involved in trauma as the result of motor vehicle accidents and other forms of blunt force trauma. More than 70% of injured persons in auto accidents have some form of facial injury (Rogers 1992). In general, the facial bones can withstand considerable force if the loading is distributed widely over the face thanks to the supporting struts. If the blow is concentrated, however, failure of these bones is common. *Nahum et al. 1968. GMesserer 1880 and Melvin et al. 1969. FMesserer 1880.

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Vertical struts

Anterior struts Figure 3-4. System of Facial "Struts." Gentry and associates visualize the face as consisting of a series of horizontal struts, verticle struts which lie in the sagittal plane, and the anterior struts form the outer surface of the face. Modified from Rogers, L., Radiology of Skeletal Trauma (2nd Ed.). New York: Churchill Livingstone, 1992.

Direct trauma to the face is usually focused on the central portion in the frontonasal region or laterally to the frontozygomatic region (Gruss 1982). Most facial fractures result from one segment of the face being sheared off from the rest of the skull. In addition, there may be depressed fractures from impacts with objects of small mass and higher force, as in the cranial vault (Rogers 1992). Fractures of the face are rarely fatal (Bone 1985) but are often associated with damage to other areas of the body such as the thorax or cranial vault. The maxilla is one of the most easily broken of all the facial bones. Fractures tend to be depressed and comminuted (Schneider 1985). Fractures in the upper third of the face usually involve the frontal sinuses and ethmoid labyrinth (Bone 1985). Midfacial fractures are often of the tripod or trimalar form, followed by fractures of the zygomatic arch and alveolar process of the maxilla (Rogers 1992). The majority of midface fractures, however, are complex and are difficult to classify accurately. Some facial fractures are so complex that they can only be termed small injuries, particularly when they affect the thin bones of the nasal region. One commonly used system of midfacial fracture classification was devised by Rene Le Fort (1901) in an analysis of maxillary fractures from human cadavers (Figure 3-5). He observed that there was a pattern for the pathways of facial fractures. He divided these into a set of three basic forms. A Le Fort I fracture separates the upper palate from the rest of the maxilla. These injuries usually are the result of a blow directly against the alveolar process of the maxilla on either side of the head. A Le Fort II causes a fracture through the maxilla, into the orbits and then through the interorbital

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area. Such fractures result from a blow directed more centrally. This may also be called a pyramidal fracture. A Le Fort III goes from behind the eyes, into the orbits and through the bridge of the nose. In reality, the majority of these facial fractures are variations on these types, with comminution and associated fractures in other bones (Rogers 1992). Both the second and third types are rarely encountered in the ideal form but are seen as combination of the two variations. When the two forms co-occur, the Le Fort III is usually on the side of injury, while the less severe Le Fort II is on the opposite side (Gruss 1982).

Figure 3-5. Le Fort Fractures of the Face. Le Fort devised a system of three different fracture patterns of the face. Type 1 passes through the maxilla and nasal aperture, Type 2 passes through maxilla, the lower portions of the orbit and across the upper part of the nasal bones, and Type 3 extends across the upper orbits and nasal region. Actual fractures rarely follow these exact patterns which represent guidelines rather than absolute standards and patterns that may be combined. Modified from Rogers, L., Radiology of Skeletal Trauma (2nd Ed.). New York: Churchill Livingstone, 1992.

Resistance to fracture by the maxilla is partly dependent upon the status of the dentition. Maxillae with poor or absent dentition tends to yield more readily, often resulting in a highly comminuted fracture (Gruss 1982). The tripod fracture is the separation of the zygomatic bone at three points (Figure 3-6). Fracture normally occurs at the zygomatic arch, at the zygomaticofrontal suture, and at the inferior orbital rim medial to the zygomaticomaxillary suture (Rogers 1992). This usually results from a blow over the malar eminence. Blows directed more posteriorly, over the zygomatic arch itself will result in isolated fractures of the zygomatic arch (Rogers 1992). This is usually a combination of three fractures as the arch is forced inward and causes breaks to occur at each end of the arch and at the point of impact.

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Figure 3-6. Tripod Fracture of the Zygomatic Bone. Frequent fracture pattern in the zygomatic is fracture of the zygomatic arch, fracture at the zygomaticofrontal joint and fracture medial to the zygomaticomaxillary suture to form a "3-1egged" structure known as a tripod fragment.

Punches, kicks and automobile accidents may all produce nasal fractures. Due to the fragile nature of the associated bones, these are often comminuted and impacted (WatsonJones 1941). They commonly fail at the junction of the nasal bone with the frontal (Gonzalez et at. 1954). Nasal fractures are often associated with fractures of the ethmoid and frontal sinuses, especially when these result from blows striking the head at about nasion (Rogers 1992). Fractures in this portion of the skull are usually produced by an impact that drives the nasal complex backward between the orbits (Gruss 1982). In these fractures, the thin medial orbital wall and nasal bones are rapidly fragmented. These have been classified by Gruss (1982) into five types, with the first representing the most limited and the fifth the most extensive. WatsonJones (1941) simply groups them into two groups based on the point of impact. Lateral impaction fractures occur when a blow to the side of the nose produces three vertical fracture lines that separate two fragments, with the one under the point of impact being driven under that of the contralateral side. Vertical impaction fractures result from blows at or close

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to the bridge of the nose. Central fragments are driven backwards often with four or more fracture lines and there is severe comminution. In both situations, the septum is severely deformed or crushed. For the anthropologist, documentation of the extent of damage by charting and photographs is more useful than determining a classification, although some assessment of the direction of force is helpful. This may be determined by the presence of a central fragment, although this may be difficult to distinguish given high degrees of comminution. Because of the vulnerability of these bones, they are frequently broken postmortem, and fracture lines should be closely examined to determine the probable time of fracture. The orbit consists of a funnel-shaped set of bones. Fractures may occur in the rim, roof, floor or on the medial or lateral walls and may be associated with marked displacement of bone (Gruss 1982). Direct blows to the rim of the eye may result in isolated fractures of the rim, especially on the superior or superior lateral margin (Rogers 1992). Fractures to the lateral rim are usually part of a larger fracture, such as a tripod fracture. When part of a larger fracture complex, most of the orbital fractures are linear except when associated with an orbital rim fracture. Fractures of the orbital roof and of the apex of the orbit are almost always part of a larger fracture complex. The floor or medial wall of the orbit can be broken as part of a LeFort or tripod fracture but also may be broken as an isolated injury known as a blow-out fracture. These injuries may be due to blows that impact directly on the orbit but do not result in fractures of the rim. In most cases, these involve the orbital floor. In this type of fracture, the orbit fractures downward due to (1) the hydraulic changes from compression of the orbit fluids or (2) through buckling of the floor after the blow hits the inferior margin. Blow-out injuries are usually due to blows from a fist or similar sized object to the eye. In contrast to the massive forces needed to cause fracturing in the cranial vault, the zygomatic arch will break under only 130 to 780 psi and the maxilla will crumble under on 140 to 445 psi. These are based on cadaver tests (McElhaney et al. 1976; Mackey 1984). Fractures of the paranasal sinuses, that consist of the frontal, ethmoidal, sphenoidal and maxillary sinuses, are relatively common in facial fractures due to the thinness of the bone in these areas. When large, the frontal sinus may only be broken through the anterior wall (Gruss 1982). If the sinus is small, then intracranial extension is more likely. Often the frontal sinus is involved due to continuation of linear fractures in other areas of the frontal.

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MANDIBLE

The arch shape of the mandible provides it strength, while the temporomandibular joints allows for some absorption of forces to the jaw. Fractures of the mandible often occur in multiples, usually with one fracture on the point of impact and another on the opposite side. Head injuries frequently accompany mandibular fractures with neck injuries also often being found. The most commonly cited place for mandibular fractures varies by the study (Figure 3-7). Rogers (1992) reported highest frequencies for the body followed by the angle, condyle and symphysis. In contrast, Fridrich and associates (1992) report higher frequencies for the angle, condyles with subcondylar regions, symphysis and associated areas, with the ramus, coronoid and alveolar fractures only rarely being noted. Another survey of mandibular fractures suggests that the angle is the most common site of injury, with symphyseal, condylar and body fractures also relatively frequent (Edwards et al. 1994). Fracture of the coronoid process and ascending ramus are not often encountered. Fractures in adults rarely occur exactly at the midline. The mandible is frequently injured in fistfights, as well as in motor vehicle accidents due to its prominent position of the chin (Fridrich et al. 1992; Rogers 1992). Motorcycle accidents also are a common cause of fractures along with falls, sports and work activities. The majority of those sustaining such fractures are male by a 4: 1 ratio (Fridrich et al. 1992; Edwards et al. 1994). Women seem more likely to break the mandible during a fall than are men, while traffic accidents appear to affect both sexes about equally (Edwards et al. 1992). Fridrich and associates (1992) noted some differences in the location of fracture based on the situation in which it occurred. Automobile accidents tended to result more often in condylar fractures or symphyseal fractures. Motorcycle accidents resulted in higher instances of symphyseal fractures and slightly fewer condylar fractures. Assaults, such as fistfights, tended to result in fractures at the mandibular angle and less frequently in condylar, symphyseal and alveolar fractures. Mandibular fractures are not common among children (Thoren et al. 1992; Cossio et al. 1994; Hubbard et al. 1995). Boys of all ages appear to be more susceptible to such fractures than girls. The greater resilience of the bones in children, as well as the smaller size of the jaw in proportion to the face, seem to account for their lower incidence of mandibular fracture. Often it is the relatively large frontal cranium that receives the impact rather than the chin, although this shifts when the children are in their early teens. In children, vehicular accidents including car passenger, car-pedestrian and bicycle accidents cause the majority of mandibular fractures followed by falls in some studies. Other studies point to falls and sports-related injuries. In

78

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Figure 3-7. Location of Mandibular Fractures. Mandibular fractures should be identified by location to the condyles, angle, symphysis, body, ascending ramus or coronoid process.

children, the most common site of fracture is the condyle, while the symphysis, angle and body are less often injured. In infants, the primary fracture site is the symphysis (Lustman and Milhem 1994). About one-fourth of victims suffered dental fractures or avulsions. With intact dentition, the mandible will break at about 350-620 lbs if struck centrally (McElhaney et al. 1976; Mackey 1984). When the mandible is struck on the side, the values for breakage drop to only 184-765 lbs. Eruption of the third molars is also a factor. In a study of 200 patients, it was calculated that those with both third molars unerupted were twice as likely to suffer angle fractures of the mandible as those with only one unerupted third molar (Safdar et al. 1995).

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If the dentures are included and the direction of impact has a sufficient superior-to-inferior component, the bulk of the force may be directed across the mandibular symphysis, resulting in failure of the mandibular body or symphysis (Schneider 1985). If the direction of the force, however, is approximately parallel to the denture contact line, the force will be transmitted through to the condyles that will fail to withstand the force of the blow. When the force is directed to small areas of the horizontal ramus, there usually will be a transverse fracture at this point.

THROAT STRUCTURES

The structures of the throat include the hyoid and the cartilagenous components which ossify or calcify with age. These are subject to damage due to direct blows or compression.

Hyoid The hyoid, which sits in the anterior neck within the curvature of the mandible, consists of a central body with two long protrusions or horns. This bone is usually protected from accidental violence by its position behind the mandible. Direct blows or compression of the lateral portions can, however, result in fracturing, especially of the gTeater horns. Because these structures are long and thin, they are extremely vulnerable though breakage may not indicate any life-threatening injuries. Frequently, hyoid fractures are linked to manual strangulation, although accidental fractures have been reported (Dickenson 1991). Accidental fractures are, however, usually associated with more massive damage such as mandibular fractures (DiMaio and DiMaio 1989). Even stress fractures have been reported as in a man who had induced vomiting (Gupta et al. 1995). Care must be taken to avoid interpreting an unfused epiphysis with one that is fractured. The hyoid forms from six centers of ossification forming the body, lesser and gTeater horns bilaterally. The greater horns do not fuse until late, rarely under the age of 20 years, and in a large portion of the population, as much as 25%-28% in one study, fail to ever fuse (O'Halloran and Lundy 1987). Many individuals, especially women, exhibit only unilateral fusion. For this reason, fractures of the hyoid are rare in children and infants where the unfused bone can fold rather than fracture. Hyoid fractures increase in incidence in the older segment of the population.

80

Broken Bones Thyroid and Cricoid Cartilages

Compression of the thyroid cartilages may occur when they are crushed against the vertebral column (WatsonJones 1941). This may occur with a direct blow or from hanging or strangulation. Since this region ossifies and calcifies with advancing age (Cerny 1983), fractures are more common in older individuals. Fracture lines tend to be vertical or at a sharp oblique angle and placed either at the midline or unilaterally across either plate (Gonzalez et al. 1954; Knight 1991). These fractures rarely are found extending horizontally. The superior horns may be broken. The ring-shaped cricoid cartilage is situated below the thyroid cartilage and may be broken in manual strangulation (Gonzalez et ai. 1954; Knight 1991). The fracture tends to be vertical or oblique and either across the anterior midline or the sides.

Chapter 4

FRACTURE PATTERNS AND SKELETAL MORPHOLOGY: THE AXIAL SKELETON ALISON GALLOWAY

T

he axial skeleton consists of the spinal column, rib cage and the sternum. The primary functions are enclosure of the torso, protection of the vital organs of the chest and abdomen, weight-bearing in the spine, maintenance of mobility in both the ribs and spine and support for the extremities. None of the axial bones have large proportions of cortical bone to prevent compressive injuries. Instead, the high mobility between skeletal elements allows for considerable absorption of energy. Impacts frequently affect multiple skeletal elements both directly and indirectly.

VERTEBRAE

Each vertebra consists of two components: the body (centrum) and the neural arch. Intervertebral disks are interspersed between the vertebral bodies and bind the vertebrae together. Anterior and posterior ligaments connect the centra longitudinally. The neural arches are linked by the articular facets, as well as a series of ligaments that line the dorsal side of the vertebral foramen, and join the spinous processes. The vertebrae are grouped by type. This reflects their function as well as critical differences in their morphology (Figure 4-1). The cervical vertebrae form the neck and consist of two units: the occipito-atlanto-axial complex (CI-2) and the lower cervical vertebrae (C3 and lower). These vertebrae are capable of high degrees of flexion and extension (White and Panjabi 1978). The lower cervical vertebrae are also associated with lateral bending and rotation. The CI-C2 joint is incapable of lateral bending but is capable of extreme rotation. The occipito-Cl joint is capable of some lateral bending but no axial rotation. The thoracic vertebrae are largely restricted in movement by the rib cage, although axial rotation in the upper segments is possi81

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Broken Bones

Figure 4-1. Diagram of the Spine Construction. Spinal curvature varies in relation to the line of gravity with the cervical spine showing lordosis, the thoracic spine being kyphotic and the lumbar spine returning to a lordotic curve. Since the line of gravity, extending superior to the center of gravity, indicates normal loading, the bones must resist compression and shear forces with regard to this line.

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ble. The lumbar vertebrae return to a flexion-extension capability but limit lateral bending and, even more severely, axial rotation. Each vertebra forms from three centers of ossification. One forms the centrum while the others form the lateral to posterior portions of each side of the neural arch. Fractures must be distinguished from non-union of these segments, or in rare cases, non-formation of one or more of the segments (Shapiro et al. 1973). In the latter instance, there is frequently compensatory curvature of the spine to accommodate the angulation produced by agenesis of one portion. Biomechanically, the spine can be modeled as a three-column structure (Stanitski 1982; Denis 1984) with an anterior and posterior portion pivoting around a fulcrum at the posterior centrum. The posterior portion is the arch and articular processes, the middle is the posterior third of the centrum and associated ligaments, while the anterior is the remainder of the centrum and the associated ligaments. When the fulcrum is damaged, the entire structure loses stability. In most cases, actual fractures to the spine are due to indirect trauma through excessive flexion, extension, compression, rotation, shearing action, or a combinations of these movements (Rogers 1992; Bucholz 1994). Though clinically less common, direct blows to the spine may also result in fractures. They are likely to be somewhat higher frequency in the forensic material due to the nature of the events that lead to victims requiring a medicolegal autopsy. Knowledge of the three-column concept and basic spinal anatomy helps in evaluation of vertebral fractures. For example, compressive forces on the vertebral column are commonly associated with fractures. As loads exceed about 500 lbs, end-plates fracture (Pennal et al. 1966) and the intervertebral disk, which is stronger than bone, is forced into the vertebral body (Evans 1982, Rogers 1992). This results in initially a concave fracture of the endplate and, if the forces continue, there is often an explosive fracture into the vertebral body. Age influences the response as the intervertebral disk is more fluid in younger individuals and can accommodate gTeater loads. In most cases compression is concentrated on the anterior column as the spine is flexed. Since the pressure on the anterior margin is 3-4 times greater than the rupture point of the posterior ligament, fracturing is concentrated anteriorly without associated posterior ligament tearing (White and Panjabi 1978; Evans 1982). This force produces a partial fracture of the vertebral body, most commonly in the form of a collapsed anterior portion. Simultaneously, there may also be fracture of the posterior portion of the vertebral centrum, which forms the middle column, to produce a complete vertebral collapse. Collapse fractures can be gTadual and result from fatigue failure of the centrum. Other forms of loading also produce characteristic fractures. When the spine is under extension, crush fractures tend to concentrate in the neural

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Broken Bones

arch. There may be little or no tension developed in the anterior ligament. Distraction, which is the opposite of compression, is where the spine is pulled simultaneously in two directions such as when the momentum of the head is distinct from that of the body (Rogers 1992). Distraction tends to result in fractures through the vertebral body and arch, although there may be ligamentous injury and displacement without significant skeletal damage. Shearing forces occur with other loading patterns but seldom alone, except under experimental conditions (Evans 1982). Such forces, which pull segments of the vertebrae out of alignment with the rest of the spine, may cause fractures of both the centrum and the neural arch. The spine, especially in the cervical and thoracolumbar regions, is vulnerable to rotation (Evans 1982). Rotational forces often do not result in major fracture of bone but rather dislocation with rupture of the ligaments and joint capsule. This is more common in children because of gTeater ligamentous laxity (EI-Khoury et al. 1984). In adults, posterior elements, such as the articular facets and laminae, may suffer damage during rotational movement. Fractures of the spinous processes may occur as the result of rotation of the trunk relative to the head and neck (Rogers 1992). Fractures of the articular pillars, articular facets and laminae may also occur. When combined with flexion, rotational forces often produce dislocation, but without this component, the facets are in opposition to each other and are broken (Stauffer et al. 1984). Spinal fractures tend to congregate in three main areas: C1-C2, C5-C7 and T12-L2. In these areas the ability of the spine to flex and extend appears the gTeatest with moderate ability for lateral bending (White and Panjabi 1978). About half of all vertebral body fractures occur at the thoracolumbar junction (Eismont et al. 1994). In addition to the risk of fracturing, the numerous elements of this unit are subject to dislocation, with or without skeletal damage. The incidence and distribution of spinal fractures varies considerably by age. In young children lower cervical fractures are less common (Hegenbarth and Ebel 1976; Hubbard 1976), while midthoracic fractures are more common. Horal and associates (1972) reported a concentration of injuries in the spine of children between T3 and T9 with a secondary increase in boys in T 1 to L2. Most of these injuries were the result of falls from heights and motor vehicle accidents. Children also are more likely to have adjacent vertebrae fracture (Hegenbarth and Ebel 1976; Henrys et al. 1977; EI-Khoury et al. 1984). Spinal fractures are extremely common in the elderly and often occur with minimal or no associated trauma (Cooper et al. 1993). Among women, one study showed an increase from 7.6% prevalence of one spinal fracture in women aged 50-54 years to 64.3% in those aged 90 and over. Age-related loss of bone mass may infringe upon bone integTity

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and increases the likelihood of fracture. In older individuals, lack of fluidity in the nucleus pulposus of the intervertebral disk is linked to marginal plateau fracture or general vertebral collapse when the compression is asymmetrical (Evans 1982). Age-related vertebral fractures are often associated with other fractures, especially of the hip and distal forearm. For the forensic anthropologist working with only skeletal elements and often in isolation from the rest of the spine, interpretation of the skeletal damage in the vertebrae can be difficult. Basic description of the fracture form, as discussed below, is the best starting place with the context of the spinal structure and its three "column" architecture kept in mind. Specific fractures can often be linked to specific predominant movements, but few spinal injuries are attributable to a single type of movement. More commonly, one form is the overriding type but has been modified by other factors, such as flexion-compression versus flexion-distraction. Location of all injuries should be carefully documented and recorded with illustrations and photographs. Reference to drawings that indicate the normal spinal curvature may be helpful, although significant deviations are obviously possible as the victim may have been hunched over or hyperextending at impact. Since many of the injuries of the spine have implications in terms of neural impairment, notation of middle and posterior column damage are important to report to the pathologist. For compression fractures, estimation of the extent of collapse may also be helpful. Evidence of direct impacts, particularly affecting the posterior elements, should also be remembered. While indirect forces account for most clinical injuries to the spine, this may not be so in the forensic population nor in the individual being examined.

Cervical Vertebrae The cervical vertebrae are particularly vulnerable to injury, as they are situated between the larger masses of the torso and head so that indirect trauma is more common in neck injuries than direct loading (Goldsmith 1984). Fractures can be induced by hyperflexion, hyperextension, rotation, lateral bending or by a combination of forces. Compression fractures due to transmission through the lower spinal column or from blows to the top of the head are also seen. Motor vehicle accidents and falls are the major causes of cervical fracture (Norton 1962). Diving headfirst into shallow water also contributes a significant number of such injuries. The degree of permissible flexion and extension varies through the neck (Evans 1982). In the lower cervical spine, there is greater movement during extension than flexion, which makes this region more vulnerable to injury during flexion. The upper neck is more prone to injury during extension or extension/flexion. This difference may explain the different distribution of

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Broken Bones

fractures. The most frequently injured neck vertebra is C2 followed by C5 and C6 (Ryan and Henderson 1992). Lower cervical vertebral fractures are more common in young individuals and appear to decline with age, although fractures of Cl and C2 gradually increase. Young children are more likely to suffer subluxation and dislocation without fracture, while bony injury is more common after about eleven years of age (McGrory et al. 1993). Fracture of the odontoid process of C2 is much more common in elderly individuals and is the injury most often found in isolation. Traumatic spondylolisthesis of C2 may be found without associated injuries. The uniqueness of the occipito-atlanto-axial complex makes this portion of the neck vulnerable to a specific pattern of injuries from indirect forces (Sherk and Nicholson 1970; Evans 1982). The atlas forms a ring of bone without a centrum and has two lateral masses that house the articular facets. The weakest point is where the arch joins the lateral masses (Landells and van Peteghem 1988). The axis has a large process, the odontoid or dens, that extends superiorly where it is held tightly against the atlas by the transverse ligament of the dens. The atlas-axis joint allows for extensive rotation but at the cost of stability (Shapiro et al. 1973). Flexion and extension are severely limited, about 10 0 . Direct injuries in the occipito-atlanto-axial complex are difficult to produce due to the depth of the overlying soft tissues at the top of the neck and base of the skull. Atlas fractures result primarily from motor vehicle accidents, followed by falls and motorcycle accidents (Hadley et al. 1988). Blows to the vertex of the head also may produce fractures to the atlas. Fractures to the axis are often produced in similar situations. During acceleration-deceleration situations, such as occur in many vehicular accidents, the neck usually undergoes violent movement. When there is a front-end collision, the head swings into hyperflexion then rebounds into hyperextension (Knight 1991). In rear-end collisions, the victim often suffers injuries of hyperextension. Typically these sequences can produce fractures in any of a number of locations including (1) arch of Cl or C2, (2) pedicles of C2 or (3) spondylolisthesis of the axis (Evans 1982). The most common fracture to the first cervical vertebra is a bilateral one through the neural arch (Sherk and Nicholson 1970; Shapiro et al. 1973; Hadley et al. 1988; Landells and Van Peteghem 1988) (Figure 4-2). This is caused by hyperextension of the head and neck that results in compression of the posterior portion of C 1 between the occipital and the neural arch of C2. Fractures occur at the weakest point where the foramina for the vertebral arteries pass through and then under the bone. About two-thirds of atlantal fractures follow this basic pattern. A similar situation, but with the fracture moved anteriorly, occurs when there are anterior arch fractures produced by hyperextension (Levine and

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Edwards 1989; Jarrett and Whitesides 1994) (Figure 4-2). In these cases the atlantoaxial joint is fixed leaving the anterior arch of C1 abutting the dens. A Jefferson fracture Oefferson 1920; WatsonJones 1941; Norton 1962; Shapiro et al. 1973; O'Brien et al. 1977; Evans 1982; Landells and Van Peteghem 1988;Jarrett and Whitesides 1994) is a comminuted fracture of C1 and involves both anterior and posterior portions of the ring (Figure 4-2). In these cases, usually the result of blows to the top of the head, compression of the bone causes the segments of C1 to burst outward, providing an alternate designation of burst fracture of C1 (Sherk and Nicholson 1970). The laterally sloping superior articular facets of C2 forms the wedge, driving apart the compacted Cl. The result is disruption of the atlas ring into an anterior, a posterior and two lateral portions. These are fairly common in traffic accidents.

Posterior Arch Fracture

Anterior Arch Fracture

Jefferson Fracture

Three-Part Jefferson Fracture

Lateral Mass Fracture

Transverse Process Fracture

Figure 4-2. Fractures of the Atlas. Fractures of the atlas include fractures of the posterior and anterior spine as well as Jefferson fractures (four or three part) which result from compression which burst the integrity of the atlantal ring. Asymmetrical placement of the head combined with verticle compression may produce fracture of the lateral mass while smaller fractures may include those of the transverse process.

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Broken Bones

A variant on the Jefferson fractures is a three-part fracture with a bilateral fracture of the neural arch and a midline anterior arch fracture (Hays and Bernhang 1992) (Figure 4-2). This type of fracture is extremely rare but has reportedly been linked to hyperextension during falls from a height. Fractures of the lateral masses of Clare also possible (Landells and Van Peteghem 1988) (Figure 4-2). These fractures extend through only one arch without passing "through" the center of the vertebra. This type of fracture is less common than either of the other two forms. Lateral mass fracture can be caused by blows to vertical compression or blows to the neck. It is probable that the head is out of a midline position, which drives the force through the lateral mass rather than bilaterally. Other fractures of Cl are less common but may occur (Figure 4-2). Transverse processes may be fractured (Levine and Edwards 1989; Jarrett and Whitesides 1994). Small avulsion fractures occur on the internal aspect of the lateral masses at the attachment site for the transverse ligament (Transfeldt and Aebi 1992). This defect will be produced by anterior movement ofthe Cl relative to the odontoid. This same movement is also responsible for odontoid fractures or simply a rupture of the transverse ligament. The inferior tubercle may also be avulsed, probably due to tension on the longus colli muscle during hyperextension of the neck (Levine and Edwards 1989; Jarrett and Whitesides 1994). Odontoid fractures are the most common fracture of C2 (Shapiro et al. 1973; Rogers 1992) (Figure 4-3), although fractures of the body may also occur. Odontoid fractures are relatively common among older adults and are usually oriented in the transverse direction and occur at the base of the dens. They are quite rare in children as the process does not fuse to the body of C2 until between ages three to seven years (Schippers et al. 1995). Odontoid injuries commonly result from sudden hyperflexion or hyperextension and are seen in motor vehicle accidents and falls from heights (Shapiro et al. 1973; Rogers 1992). Hyperflexion produces anterior displacement of the fragment with the atlas, while hyperextension is linked to posterior displacement of both dens and atlas. Odontoid fractures have been classified by Anderson and D'Alonzo (1974) into three categories: (1) avulsion fractures of the odontoid tip, (2) actual fractures of the process and (3) fractures of the C2 body. Avulsion fractures are due to tension on the attachment for the apical ligament. Fractures of the odontoid at the isthmus or waist are due to displacement of C 1 anteriorly or posteriorly. When flexion or extension are involved, the fractures are often angled down from a superior-posterior to an inferior-anterior location. Benzel and associates (1994) point out that the Anderson-D'Alonzo system includes more than just odontoid fractures and combines multiple mechanisms of injury.

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Odontoid Tip Fracture

89

Odontoid Fracture

Odontoid and C2 Body Fracture Figure 4-3. Fractures of the Odontoid. The classification system of Anderson and D' Alonzo (1974) divides the odontoid fractures into three groups including avulsion fractures of the odontoid tip, fractures at the odontoid waist and fractures of the odontoid and the C2 body.

Fractures of the C2 body may be oblique, horizontal or vertical (Figure 44). Vertical fractures may be oriented in the coronal or sagittal plane (Benzel et al. 1994). Coronally oriented fractures appear to be produced by extension with axial loading in which there is a shift of the fault line anteriorly from the pars interarticularis as would occur in spondylolisthesis. Hyperextension will mimic this pattern but adds a small fracture on the anterior inferior surface of the vertebral body caused by tension extending along the anterior surface. Fracture of the posterior elements and fractures involving the transverse foramen are also found in hyperextension. There may even be a two-point arch fracture of Cl. Coronal fractures may also be produced by flexion-compressive loading and flexion-distraction. Sagittally oriented body fractures are produced by axial loading usually applied to the vertex of the head and are often comminuted. The fracture line begins in the pedicle as the superior articular facets receive the load, which cannot be fully transmitted to the inferior vertebra. Horizontal fractures of the C2 body are usually flexion injuries and are often the result of a blow to the back of the head. "Hangman's fractures," traumatic spondylolistheses of C2, involve bilateral fractures of the neural arch of the axis. This is the aim of the executioner in judicial hangings (Woodjones 1913; Lachman 1972; Shapiro et al. 1973;

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Broken Bones

Spitz and Fisher 1980) (Figure 4-4). Such fractures are usually found at the weakest point in the neural arch, the pedicles. During hyperextension of the upper neck, the fracture line itself may be vertical, horizontal or oblique. The presence of the transverse foramen substantially weakens the bone at the pedicle (Evans 1982). Judicial hangings may also result in fracture of the pedicles or lamina of C3 or C4 (DiMaio and DiMaio 1989). Frequently, however, hangman's fractures and odontoid fractures will not occur in such circumstances and the damage may be primarily to soft tissue. In addition to hanging, hangman's fractures may also be found in victims of automobile accidents when head movement is terminated by contact with a dashboard or other object while the body is still in motion. This subjects the bone to vertical compression and extension (Shapiro et al. 1973). While the ligamentous injuries are different, the skeletal trauma is quite similar Uarrett and Whitesides 1994). These injuries may be associated with fractures at the C6/C7levei (Ryan and Henderson 1992). Extension fractures of C1 and C2 are often simultaneously inflicted by hyperextension of the neck, usually as the result of acceleration or violent movement of the head. In these cases there is fracture of the arches of both C1 and C2. Fractures may also occur at the anterior inferior margin of C2, in the form of a tear drop fragment (Shapiro et al. 1973) (Figure 4-4). These are usually produced by hyperextension of the neck, which squeezes the spinous and articular processes together and ruptures the anterior longitudinal ligament. In the lower cervical vertebrae, below the C 1-C2 region, a variety of fractures may form (Figure 4-5). These vertebrae differ in configuration from the C1-C2 fractures due to the rather unique configuration of the uppermost vertebrae. Most flexion and extension in the neck occurs in the lower cervical region, with the range peaking at the C5-C6 level (Bucholz 1994). Rotation and lateral bending are also relatively high in the neck and peak at the C4-C5 level. Compression in the mid to lower neck (C3-C7) may produce a burst fracture of the vertebral body with severe comminution. This may also occur in the thoracic and lumbar region. Most often these occur in C5-C6 (Evans 1982) and are the most common fracture in this region (Norton 1962). These fractures are often seen in football players as the result of impacts to the head (Bucholz 1994). Vertical or oblique fractures of the vertebral body have also been reported and are produced by vertical forces applied to the spine. Vertical fractures are due to massive, abrupt compressive forces and are usually in the sagittal plane. In diving accidents where the top of the head bears the brunt of impact, C5 is often the most affected of the cervical vertebrae (Stauffer et al. 1984). The anterior portion of the body may be displaced as a large teardrop fracture while the posterior portion is split sagittally. Complete and

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Sagittal Fracture

91

Coronal Fracture

"Hangman's" Fracture

Arch Fractnre Figure 4-4. Fractures of the Axis. Fractures of the C2 are quite varied. In addition to those of the odontoid and C2 body, the body can also be fractured in a number of planes. Hangman's fractures rupture the ring of the vertebra. Hyperextension of the neck can produce teardrop fractures due to tension on the anterior longitudinal ligament and fractures of the posterior arch.

incomplete split fractures are often associated with flexion (Transfeldt and Aebi 1992). Complete fractures in the coronal plane are sometimes called

pincer fractures.

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Broken Bones

Acute flexion of the neck may produce a teardrop type fracture-dislocation in the lower cervical spine that results in the production of a triangular or rectangular fragment (Schneider and Kahn 1956; Rogers 1992) (Figure 4-5). This is characterized by the crushing of the centrum by the superior vertebra so that the anterior portion of the superior centrum is often separated by a coronally placed fracture line. This failure is attributable to the lipped morphology of the cervical vertebrae, which allows sufficient leverage under the vertebrae, not possible in the lower vertebrae that have flattened end-plates. Anterior inferior margin fractures may also be linked to sagittal fractures in the posterior half of the vertebral body (Korres et al. 1994; Bucholz 1994). They are found in motor vehicle accidents, falls from heights and diving accidents. The centrum may be anteriorly compressed if hyperflexion of the neck is involved. The anterior cortex may buckle and the cancellous bone will collapse. This is similar to the pattern of hyperflexion injury seen in the lower vertebrae and known as an anterior wedge fracture. The anterior superior margin or even the entire anterior surface of the vertebra may become displaced (Norton 1962; Stauffer et al. 1984) (Figure 4-5). This may result from avulsion by the anterior longitudinal ligament or the annulus fibrosus or both. Shearing results from stresses induced during hyperflexion, hyperextension or chipping from the vertebral margin of the superior vertebra. Anterior superior margin fractures, while less frequent than compression fractures, are relatively common and account for about 10% of cervical fractures in one series (Norton 1962). When the neck is both flexed and rotated, or when there is severe rotation, there may be unilateral or bilateral fracturing of the facets (Evans 1982; Hadley et al. 1992; Bucholz 1994) (Figure 4-5). Bilateral fracturing suggests that there was anterior dislocation of the vertebra above while the cervical spine was under distraction. This may be associated with fracture of the anterior vertebral body. In some cases, the articular facets may also be involved in fracturing due to hyperextension. In some extreme situations there may be separation of the articular mass (Transfeldt and Aebi 1992). This injury is more common unilaterally and is attributed to rotation. Facet fractures are relatively rare and appear predominantly linked to motor vehicle accident and diving accidents (Hadley et al. 1992). The C6-C7 level is the area most often adversely affected by rotation but is also vulnerable to bilateral injury. If rotation is associated with extension, the spinous process tends to become the focus of the force and consequently fractures near its base (Figure 4-5). An injury similar in appearance, the clay-shoveler's fracture, can result from avulsion by the ligamentous and tendinous attachments (WatsonJones 1941; Norton 1962). In these cases the rhomboid muscles cause avul-

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Vertical Fracture in Sagittal Plane Burst Fracture

Pincer Fracture Tear-drop Fracture

Anterior Superior Margin Fracture Compression Fracture

Spinous v .."'P,".,,, Fracture

Lateral Mass Fracture

Lamiuar Fracture

Figure 4-5. Fractures of the Lower Cervical Vertebrae. Fractures of the lower cervical vertebrae include fractures of the body, spinous process and laminae.

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Broken Bones

sion of the spinous process during the upward thrust of the shoveling movement. Direct blows to the back of the neck can also induce spinous process fractures. Fractures of the vertebral laminae occur in about one-quarter of unifacet or bifacet dislocations (Lukhele 1994) (Figure 4-5). These injuries are the result of abrupt forces and are most often seen in motor vehicle accidents. These injuries may be produced by a number of mechanisms. The initial fracture may be due to flexion which produces an avulsion fracture by the interspinous process ligaments prior to dislocation. An alternate process is that the fracture is a rebound defect following flexion distraction forces that produced the dislocation. If combined with rotation, this would explain the unilateral injuries. Plezbert and Oestreich (1994) suggest that about half of the laminar fractures are due to hyperextension in which the posterior elements are forced together. In support for this theory, they note that teardrop fragments may be present due to avulsion of the anterior longitudinal ligament. Stuaffer and associates (1984) suggest these are due to hyperextension and associate chip fractures of the anterior superior vertebral body. Fractures of the cervical laminae most often usually occur in the lowest parts of the cervical spine (C5-C6 or C6-C7) (Beyer and Cabanela 1992). Plezbert and Oestreich (1994) cite a number of cases in which these fractures are associated with thoracic or lumbar fractures.

Thoracic and Lumbar Vertebrae In the lower spine, most fractures occur between the last thoracic and the second lumbar vertebrae Uefferson 1927-28; Nicoll 1949; Young 1973; Evans 1982). This is the area of transition between the thoracic and lumbar vertebrae that differ in their form, function and range of movement. The thoracic vertebrae have articular facets that are flat and approximately oriented in the coronal plane. While this allows for considerable movement, the degree of flexion and extension is reduced in comparison to the neck. The ribs act to stabilize the spinal column and are important in restricting flexion and extension. The amount of rotation in the thoracic region is high. The increasing size of the centra are adapted for weight-bearing. Lumbar vertebrae tend to have great stability and resistance to loading. They also have greater flexion-extension mobility compared to the other portions of the spine (Levine 1992). There is a progTessive increase from L1 to L5 in the flexion-extension capability. There is also a decrease in rotation with descent down the lumbar spine. The centra are massive, and the curved and interlocking orientation of the articular facets greatly restrict the range of movement. The posterior elements support about 30% of the weight in the

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lumbar region due to the lordotic position, which eases the stress on the vertebral body. The bulk of the spinous processes prevents hyperextension and the predominant movements are those of flexion. The mechanisms of injury in this region are due to axial compression, flexion, lateral compression, flexion-rotation, shear, flexion-distraction and extension (Eismont et al. 1994). While these are the normal movements of the spine, the spine can be forced beyond its normal range in accidents. The transition areas are particularly prone to injury as they also mark changes in the curvature of the spine as well as the ranges of movement. The kyphotic thoracic vertebrae make a transition into the lordotic lumbar spine. The last lumbar vertebra also marks a transition into the sacrum, which is associated with a severely sloped intervertebral disk. Hence, compressive loading may produce flexion injuries in the thoracic region but may produce extension injuries in the lumbar region (Stauffer et al. 1984). The breaking load of the thoracic and lumbar vertebrae varies by element and by age. Load-bearing is greatest in the lumbar vertebrae and declines slightly in the lower thoracic (Sonoda 1962). Midthoracic vertebrae have breaking loads about two-thirds that of the lumbar vertebrae while the upper thoracic, like the cervicals, are relatively weak with breaking loads of only about three-fifths that of the lumbar vertebrae. Flexion-compression injuries peak in the thoracolumbar region, especially at TI2-Ll (Kricun and Kricun 1992). Age-related loss of cancellous bone, which may be particularly extreme in women, is responsible for much of the incidence of vertebral fractures. As trabecular cross-struts are lost, the remaining trabeculae often thicken in an effort to withstand normal weight-bearing, but the thoracolumbar spine becomes ill-equipped to resist any additional loading. These fractures concentrate at the midthoracic region (T7 - T8) and the thoracolumbar junction (TI2-Ll). Fractures associated with only mild to moderate trauma skyrockets in the elderly of both sexes (Cooper et al. 1993). Fractures of the thoracic and lumbar vertebrae usually involve the indirect forces produced by extreme movement of the body or impact directed at other parts of the body such as the legs or buttocks then transmitted through the spine. For this reason, fractures in these bones can be grouped by the forces and motions involved in producing them. These include (1) flexion fractures with varying levels of compression, which are primarily wedge fractures, but also may form a burst fracture, (2) vertical compression, (3) lateral flexion, (4) flexion distraction injuries, which includes the Chance fractures, (5) torsion flexion, (6) translational or shear and (7) distractive extension injuries (Ferguson and Allen 1984). The most common injuries are those associated with some flexion that usually occurs when a person falls from a height into a sitting or hunched

96

Broken Bones

position, when a weight falls onto the hunched back of a person or when a person is struck from behind by a moving object (WatsonJones 1941). Auto accidents, in which the movement of the vehicle is arrested while that of the occupants is not, are the most common means of achieving acute flexion. These accidents may also be involved in the production of distraction injuries as the body is thrown forward while the vehicle decelerates. The angle of the body, the amount of weight-bearing on the legs at the time of impact and the force involved will all affect the degree of compression or distraction. Compression fractures, whether vertical or combined with flexion, are identified by the presence of a shortening of the anterior vertebral height, while lengthening indicates some degree of distraction (Ferguson and Allen 1984). The majority of the thoracic and lumbar fractures are simple wedgeshaped compression fractures (Denis 1984; Ferguson and Allen 1984; Kricun and Kricun 1992; Levine 1992; Rogers 1992; Eismont et al. 1994) (Figure 46). These result from compression with a degree of flexion. Wedge fractures are usually defined as those with less than 50% anterior compression. These fractures can involve (1) the fracture of both endplates, (2) only the superior surface, (3) only the inferior surface or (4) buckling of the anterior cortex (Denis 1982; Eismont et al. 1994). Under flexion and compression, the anterior body of the vertebra is severely compressed and the energy is dissipated by anterior wedging (Evans 1982). This preserves the posterior portions of the vertebrae which, therefore, usually remain intact. The fracture dissipates the energy relaxing the tensile forces on the posterior ligaments. Posterior avulsion fractures may, however, also be found (Eismont et al. 1994). Wedge fractures are less frequent in the lower spine because anterior compression is usually less in the lumbar vertebrae than in the thoracic or thoracolumbar junction (Kricun and Kricun 1992; Levine 1992). Wedge fractures often affect more than one vertebrae. Multiple fractures may reflect the osteoporotic condition and the wedges may have formed on different occasions. In younger adults or children, the traumatic nature of the accident may produce loading on multiple vertebrae which causes fracturing. These fractures may be found in cases of child abuse and may be accompanied by the presence of small bony fragments along the anterosuperior aspect that penetrate the end-plate (Kleinman and Marks 1992). Such injuries in the lower thoracic and upper lumbar region are probably the result of violent shaking of the child. As the level of forces applied to the centrum increase, so too does the destruction. About 10%-15% of vertebral body fractures are comminuted. These are produced by more localized acute flexion of the spine, such as occurs when a person falls and lands on the shoulders (WatsonJones 1941). These involve some degree of vertical compression, which distinguishes

The Axial Skeleton

Compression Fracture of Both End-plates

97

Compression Fracture of Superior End-plate

" ..",n'~"""