Forensically Significant Skeletal Anatomy

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Nancy E. Tatarek, PhD and Dorothy E. Dean, md

1. Introduction

Forensically significant cases are those in which remains are recovered that have come from humans who died violently or unexpectedly, or for which the cause of death or manner of death is potentially a legal or otherwise significant issue (this may exclude very old or prehistoric remains). This text discusses the subset of forensically significant remains that are partially or completely decomposed, fragmented, or unidentified. This chapter is not meant to reiterate what other experts have described. Rather, we present the authors' philosophy regarding the evaluation of cases in which the lower extremities, or parts thereof, represent the majority of the forensically significant and useful remains recovered. Results expected from the analysis of such remains form a biological profile that is potentially capable of providing positive identification (which is discussed further in later chapters) leading to and perhaps facilitating the determination of the cause and manner of death, a task that usually requires the integration of data from multiple sources and which is outside the scope of this book.

Fragmentary or partial remains, such as a single lower extremity, clearly pose a somewhat more daunting task than a more complete set of remains. Human anatomy is easily recognizable when complete, fleshed remains are involved. Skeletonized remains are less familiar and can be confused with nonhuman skeletal elements or even wood or rocks. The lower extremity is composed of the thigh, the knee, the leg, the ankle, and the foot. Basic familiarity with the overall skeletal anatomy of the femur, tibia, fibula, patella, and foot bones can aid investigators in determining exactly which segments are present (and of course, those that are missing) in medicolegal investigations involving lower extremity remains. This chapter is a summary of some of the more forensically

From: Forensic Science and Medicine Forensic Medicine of the Lower Extremity: Human Identification and Trauma Analysis of the Thigh, Leg, and Foot Edited by: J. Rich, D. E. Dean, and R. H. Powers © The Humana Press Inc., Totowa, NJ

Hip Osteophytes Dog
Fig. 1. Anterior view of femoral proximal end. The "ball-and-socket" of the ball and socket hip joint.

important skeletal landmarks and is intended to aid in the identification of the bone to which they belong. Readers interested in a more detailed account should consult one of the several excellent human osteology books available.

2. Forensically Significant Skeletal Anatomy

The thigh contains the largest bone in the human body: the femur. The proximal end of the femur consists of a rounded head made of spongy bone that forms the ball of the ball-and-socket hip joint (Fig. 1). This head is distinctive in shape and size; the femur is the only bone in the human body with this skeletal configuration. The distal epiphysis forms part of the knee and is made up of two large condyles. Anteriorly the femur is devoid of significant landmarks. Posteriorly, the linea aspera is the point of muscle attachment for the short head of the biceps femoris, and next to it is a nutrient foramen. In heavily muscled individuals, the linea aspera can be quite large, forming a large bony ridge that runs the length of the femur. Juvenile and adult femoral morphology is largely similar, with the exception that unfused juvenile femora consist of multiple segments and adult femora (barring trauma or abnormal development) consist of a single segment.

The patella (knee cap) is the largest sesamoid (bone nodule) in the human body. It lies anteriorly to the lower extremity of the distal end of the femur and slightly superior to the proximal tibia. The patella has two articular surfaces posterior—a larger lateral and slightly smaller medial surface. Multiple nutrient foramina on the anterior surface may be mistaken by the inexperienced as rocks with pits caused by erosion. If the entire patella is covered with mud, it may be mistaken at the forensic scene for a clump of mud or a rock. Variation in the patella is common; triangular, elliptical, circular, and oblique shapes have been documented (1). A comprehensive discussion of markers of stress and injury in the knee joint is provided in Chapter 3.

The lower leg contains two bones, the tibia and the fibula. The tibia is the larger and is commonly known as the "shin bone." (Fig. 2). The tibial shaft is somewhat triangular compared with the relatively more rounded femoral shaft. The proximal posterior

Nutrient Foramina
Fig. 2. Lateral view of tibial proximal end.

shaft is marked by the popliteal line, which forms a boundary for insertion of the popli-teus muscle. A nutrient foramen also appears at the same location lateral to the popliteal line and nearly always slopes distally, exiting the bone proximally (1) (Fig. 3). The proximal epiphyseal end is formed by two large, flat condyles and the tibial tuberosity on the proximal anterior side. The distal epiphyseal end is characterized by the medial malleolus, a projection of bone that is felt on the medial aspect of the ankle.

The fibula is the smaller of the two leg bones and its distal end forms the outside part of the ankle. In contrast to the relatively wider tibia, the fibula is irregular and narrow in shape. The proximal epiphysis consists of a slightly rounded formation with a styloid process (posterior projection of bone), and its the distal end consists of a lateral malleolus, which forms the outside part of the ankle. The fibular shaft is largely unremarkable, offering no distinguishing features because it bears no weight. Unlike the femur, it is not expected to be significantly larger in well-muscled individuals.

The human foot is made up of 14 phalanges, 5 metatarsals, and 7 tarsals (calcaneus, talus, cuboid, navicular, and the first, second, and third cuneiforms). Additionally, two sesamoids sit inferiorly on the distal first metatarsal. The calcaneus forms the heel and the talus articulates with the distal tibia, forming the medial aspect of the ankle. The human foot is unique amongst mammalian extremities, because it is constructed for upright walking. The four toes are in line with the first (big) toe (the hallux), unlike the toes of other apes (humans are considered apes), in which the hallux is offset from the remaining toes. To a large extent, the human foot has lost its grasping ability, which is characteristic of the other apes. In humans, the tarsals usually form an arch—an ideal structure for weight-bearing in a bipedal animal. The relatively large number of skeletal elements and articular surfaces results in a number of unique skeletal features, including trabecular patterns and osteophytes, which may be useful within forensic contexts, e.g., for comparing radiographs (2,3). Similar to the patella, the tarsals also exhibit foramina for blood vessels that may be confused with surface erosion by the untrained eye. Additionally, the foot may often be well preserved when it remains in footwear, frequently surviving intact for forensic analysis.

Nutrient Foramen
Fig. 3. Arrow denotes tibial nutrient foramen.

3. Embryology

The development of the human is complex, yet orderly. There are critical periods of human development during which certain major elements are formed. For the lower extremity, the critical period begins during the third week after fertilization with the formation of the cardiovascular system, including vessels for limbs. During the third and fourth weeks, limb buds appear. By the end of the eighth week, all the major organ systems have begun to develop. It is between the third and eighth weeks of gestation that in utero exposure to toxins (teratogens) may cause abnormal development of the limbs persisting into extrauterine (postnatal) life (4). Examples of such toxins are numerous and include thalidomide and cocaine. However harmful teratogens are, their

Forensic Radiography
Fig. 4. Anterior views of six adult femora, illustrating variation in size.

effects may become useful when evaluating forensically significant case material. For example, fetal malformations caused by maternal substance abuse may provide anatomic features unique to that individual that can be used to assist identification efforts. Alcohol consumption by the mother can cause fetal alcohol syndrome, and cocaine use may cause vascular malformations. Both of these teratogens may result in potentially unique anatomic features that can be used for premortem and postmortem comparisons.

Normal bone growth involves the development of blood vessels that penetrate the cortices via nutrient canals. Both the location and angle of entry of vascular elements into the bony cortex are highly variable from person to person and even from one side of the bone to the other in the same individual. This variation may be of significant forensic utility. For example, the nutrient artery for the femur arises from the deep femoral artery and enters the femur posteriorly along the linea aspera, but the location of entry of the vessel is somewhat variable. If two femora are recovered whose general physical characteristics indicate that they are from the same individual, the disparate positions of the nutrient canals should not dissuade the examiner from the concluding that they are from the same person.

Because muscles attach to bone, the absence of one or more muscles can cause limb deformities. Any muscle of the body may fail to develop. If the opposing muscle is present, the limb contracts at the joint. Such deformities can be corrected with braces or surgical repair. Although functionally insignificant, slight variations in muscle development or attachment can be used forensically. Additionally, population differences in skeletal development can cause a slight variation in limb appearance, especially with regard to limb length (Figs. 4, 5). The ratio between the lengths of the tibia

Forensic Radiography
Fig. 5. Anterior views of five adult tibiae, illustrating variation in size.

and femur varies and may provide clues to ethnicity (1). (Postnatal aberrations will be discussed in a later chapter.)

4. Procedural Approaches

When confronted with decomposed or partial human remains, attention to anatomical detail, careful consideration of the available human remains, and scrutiny of the surrounding scene or environment are important for identification and trauma analysis purposes. Because of the complexity of procedures involved in examining human remains within various contexts, the authors advocate a multidisciplinary team approach to the recovery and analysis of suspected human remains. Thus, when remains are discovered, securing the scene and maintaining it in an undisturbed fashion until all appropriate personnel (e.g., medical examiner/coroner's agent, law enforcement, forensic anthropologist, odontolo-gist, and radiologist) are present is important. Although it may seem obvious, the authors cannot emphasize enough that human remains can look remarkably like sticks, rocks, or chunks of mud or dirt. The following figure presents a summary list of questions that may be of use in the analysis of suspected human remains (Fig. 6).

Fragmentary, burned, mummified, or partial lower extremities can resemble wood, rock, or other features of the surrounding scene, such as foam or asbestos (Figs. 7, 8).

Unfused Human Tibia
Fig. 6. Chart used to illustrate an algorithm in the analysis of fragmentary remains.

Juvenile remains—being smaller in size and having unfused epiphyses—are more likely to be confused with wood or mud than are whole adult remains. Adult tarsals, metatarsals, phalanges, and sesamoids are also likely to resemble wood, rocks, or mud due to their irregular shapes (Figs. 9, 10). Shafts of the infant femur, tibia, and fibula may be confused with small twigs or animal bones, while the epiphyseal ends may be confused with lumps of mud, dirt, or clay, particularly in outdoor settings (Fig. 11). Within an archaeological context, juvenile remains are sometimes not recovered due to preservation issues or, more commonly, lack of recognition by individuals who are

Job: Rich Operator: DTL

Chapter: 02 Date: 15/11/04

Size: 7 x 10 Revision: 1st Revises 24 Tatarek and Dean

Ostelogy Socket Bone
Fig. 7. Anterior views of fragmentary and whole femora.

Job: Rich Chapter: 02 Size: 7 x 10 Forensically Significant Skeletal Anatomy

Operator: DTL Date: 14/12/04 Revision: 2ndt Revises

Forensic Radiology Pictures
Fig. 8. Anterior views of fragmentary and whole tibiae.
Fig. 9. Photograph comparing a human first metatarsal (left) to a small twig.

inexperienced with children's skeletons. Within a forensic context, recognition of various juvenile segments and fragmentary adult segments is vital to facilitate recovery and subsequent analyses.

The next step in the analysis is to determine whether the remains are human. Numerous authors have documented similarities between both adult and juvenile human remains and those of various animals, particularly with respect to the lower extremity (5,6). Adult animals—such as dogs, sheep, goats, and rabbits—have smaller extremities than adult humans. The skeletal remains of adult cattle, horses, or other larger animals will exhibit limbs that are larger than those of adult humans. Differences in morphology and bone texture can yield clues as to species (Fig. 12). For example, human infant remains can be confused with avian skeletal remains; however; the lighter, hollow bones of birds help distinguish these materials from human skeletal remains. Comparative mammalian skeletal collections are also useful during this stage of the analysis. Extremely fragmented remains may not contain enough diagnostic features to assign a species designation.

If the remains are determined to be human, the next step is to consider their potential forensic significance. Human remains may be found within many contexts, not all of which necessitate forensic investigation or personal identification. Commonly, information gained from the context of the remains and the condition of the remains themselves

Forensic Science Bone Structure
Fig. 10. A photograph similar to that of Fig. 9; with a closer color match.

will aid in the determination. The accompanying presence of archaeologically significant materials such as arrowheads or pottery may indicate ancient remains. Tombstones, coffin hardware, buttons, and clothing may provide data with respect to the time frame. Extreme drying of remains, with little adherent soft tissue, often indicates remains of no forensic significance. In the United States, Native American Graves Protection and Repatriation Act (NAGPRA) laws dictate that law enforcement agencies, coroners, and medical examiners must identify the nearest Native American group and notify them of any finds before proceeding with removal (7). Experienced forensic or physical anthropologists will need to examine the remains in situ. In some situations, the determination of forensic significance can be made before any further investigative effort is undertaken.

The discovery of forensically significant remains should culminate in a recovery using standard archaeological procedures to maximize the preservation of information and maintain the chain of custody at the scene. A thorough search of the scene as well as detailed photography, mapping, packaging, and transporting of human remains are necessary to optimize the forensic recovery and subsequent evaluation. Scene context (indoor or outdoor, size of the scene, landscape, weather), available personnel, budget, resources, and legal issues all contribute to the nature of a recovery operation (7). Forensic anthropologists can often be located by contacting the nearest university with an anthropology department. These individuals, who have

Ostelogy Socket Bone
Fig. 11. Photograph illustrating similarities between non-human skeletal elements (left and right) and human infant or fetal skeletal elements (center).

advanced degrees and training in archaeology and human osteology, are typically best equipped to handle the recovery and analysis of fragmentary human remains. Following the team approach, the forensic anthropologist should be consulted early in the investigation and ideally would participate in recovery efforts.

Suspected and known human remains should be transported to a laboratory. All remains should be photographed immediately—in toto and each element separately— upon their arrival at the laboratory. Traditionally, 35-mm film cameras can provide a high level of resolution. However, high-quality digital cameras can also achieve high resolution. Inclusion of an American Board of Forensic Odontology standard grey scale in photographs is essential for accurate measurements and dimensions. Radiography is a routine procedure in forensic examinations and is useful for separating human from nonhuman and nonskeletal materials. Radiographs should be performed prior to the

Fig. 12. Photograph of broken bird bone to illustrate the thin walls of the medullary cavity.

removal of any clothing, soft tissue (if defleshing is desired), debris, or other adherent material. Highly decomposed remains frequently result in variable soft tissue density, which may obscure skeletal detail in the radiograph. Therefore, we recommend that the examiner who requires fine skeletal detail on radiograph remove the soft tissue and radiograph the remains again with various image orientations (e.g, anterior-posterior, lateral, medial, and oblique views). The authors have had success in macerating soft tissue using an enzymatic detergent followed by a wash in household ammonia, as described by Fenton et al. (8).

Radiographically, bone may demonstrate a discernable medullar cavity and trabecular latticework. Radiographs will also highlight potential features for individual identification (described in Chapter 6). It should be noted that prior to defleshing, tissue samples should be preserved in case of a need for pathological, DNA, or toxicological analysis. Thorough documentation of the soft tissue should be accomplished prior to tissue removal, and photographs should be taken and any individual characteristics noted.

Subsequent to radiography, an inventory of the remains should be made. This serves two purposes: first, a permanent inventory of the collected and any missing remains can be maintained and distributed to other agencies and is vital for comparison with any subsequent discoveries; second, information regarding the remains present also dictates the next steps of the analysis, i.e., determination of race, age, sex, and stature (which constitutes the biological profile). Investigators should make notes of any signs of pathology or disease processes, such as osteomyelitis or antemortem fractures, which can be compared with antemortem medical records for presumptive identification.

Documentation of any and all individualizing characteristics present on the soft tissue or skeletal elements can also aid in making a positive identification. Soft tissue characteristics may include tattoos, scars, birthmarks, or concentrations of melanin; characteristics intrinsic to the bone itself include the trabecular pattern (2). Fractures in various stages of healing can be compared with medical records, leading to a positive identification. Surgical alterations or implants such as rods, pins, or hip replacements can also be useful. Some implants are imprinted with serial numbers, which are recorded at the time of surgery and can be linked to an individual using available antemortem medical records.

Comparison with records of missing individuals is the final stage in the process. However, there is the possibility of finding no match between the remains and an individual, given the fragmentary nature of the skeletal materials. For example, a small segment of a human fibula may be forensically significant but otherwise unidentifiable. Some jurisdictions may choose not to treat the remains as forensically significant, because the removal of all or part of a skeletal element in the lower extremity is theoretically compatible with life (e.g., surgery). Fragmentary remains can be scattered across great geographical distances because of a traumatic event or animal scavenging; therefore, communicating with other agencies regarding the inventory of the remains is vital.

5. Summary

The process of recovering, analyzing, and positively identifying forensically significant skeletal remains is enhanced by adherence to the procedures outlined in this chapter and by focusing on an integrated multidisciplinary approach.

References

1. Scheuer L, Black S. Developmental juvenile osteology. New York, NY: Academic Press; 2000.

2. Rich J, Tatarek NE, Powers RH, Brogdon BG, Lewis BJ, Dean DE. Using pre- and post-surgical foot and ankle radiograph for identification. J Forensic Sci 2002;47:1319-1322.

3. Sudimack J, Lewis BJ, Rich J, Dean DE, Fardal PM. Identification of decomposed human remains from radiographic comparisons of an unusual foot deformity. J Forensic Sci 2002;47:218-220.

4. Moore KL, The Developing Human, Clinically Oriented Embryology. Philadelphia, PA: WB Saunders, 1988.

5. Bass WM. Human osteology: a laboratory and field manual of the human skeleton. 4th ed. Columbia, MO: Missouri Archaeological Society, 1995.

6. White TD. Human osteology. New York, NY: Academic Press, 2000.

7. Nafte M. Flesh and bone. An introduction to forensic anthropology. Durham, NC: Carolina Academic Press, 2000.

8. Fenton TW, Birkby WH, Cornelison, J. A fast and safe non-bleaching method for forensic skeletal preparation. J Forensic Sci 2003;48:274-276.

Further Reading

Byers D. Introduction to forensic anthropology. Boston: Allyn & Bacon, 2001.

Ortner DJ, Identification of pathological conditions in human skeletal remains, 2nd ed. New York, NY: Academic Press, 2003.

Reichs KJ. Forensic Ostelogy: advances in the identification of human remains. Reichs KJ, ed. Springfield: Charles C. Thomas, 1998.

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