Skeletal Analysis

The human skeletal system is primarily composed of a supportive structure found inside the body called the endoskeleton. The endoskeleton is made up of either bone or cartilage. Bone is hard, calcified tissue of the skeleton found in vertebrates and consists of collagen, calcium phosphate, calcium carbonate, and is innervated by blood vessels. Analysis of an endoskeleton from the remains of an individual can provide information about the identity of the person that died, as well as information regarding physical characteristics about that person. This is particularly useful to forensics scientists, who are responsible for handling human remains during criminal investigations and determining the identity of a victim, the manner of death, and if a crime was committed.

Ascertaining the cause of death can be problematic because the integrity of the remains is often significantly compromised (decomposed) and the cause of death can be due to a myriad of reasons (fires, homicides, explosions, wild animals, poisoning, drowning, among other causes). Forensic anthropologists are often consulted in these difficult cases. They are experts who combine their knowledge and training in human evolution, human variability, human development, human genetics, and human osteology (the study of bones) to be used for criminal investigations or following natural disasters. Examinations of skeletal remains are often performed by forensic anthropologists.

There are three primary subspecialties recognized in forensic anthropology used for skeletal analysis: forensic osteology, forensic archaeology, and forensic taphonomy. Forensic osteology involves the study of

human bones and includes understanding how bones form, disease states relating to bone, and distinguishing disease from trauma-induced alterations to the skeletal system. Forensic archaeology is the study of human remains at their site, and involves how to excavate human remains found in a potential crime scene. Finally, forensic taphonomy helps forensic scientists determine the skeletal alterations that transpired at the time of death and afterwards. These alterations can be analyzed by identifying diffuse or focal traumatic injury to the skeletal system, the rate, extent, and type of decomposition that occurs, and any environmental modifications that might be important.

Forensic osteologists usually become involved in the criminal investigation at the beginning of the search (as part of a team) for hidden or buried remains with the assistance of specially trained cadaver search and rescue dogs and law enforcement experts. Once the remains are located, osteologists and archaeologists excavate the remains and help to determine evidence relevant to the investigation. Bone collection must follow careful visual analysis of the crime scene to help understand the position of the body or, if buried, what types of tools were used on the body or for burying it.

Once the remains are removed from the site, they are cleaned and analyzed in a laboratory. Forensic osteologists can then apply radiographic techniques to compare skeletal remains to archived x rays, which could help identify the individual. These radiographic techniques are especially helpful if there is suspicion of foul play. If necessary, the skeleton is sectioned or cut and put onto a slide to be analyzed by a bone histologist, who may be able to make assumptions regarding the extent and type of damage inflicted on the bone.

Other techniques such as scanning electron microscopy can provide information regarding the extent of decomposition, which helps determine approximate time of death or the nature of the environmental affects on the bones. Scanning electron microscopes magnify images using electrons to create three-dimensional images. Bone samples can also be sent to other forensics experts for biochemical or trace element analysis, as well as for DNA analysis. Once laboratory tests are complete, the bones are usually casted (molded) and curated (preserved) using commercially available skeletal preservatives.

The race, age (at death), height, size, sex, and type of physique of a person can often be ascertained by examining their skeletal remains. Bone can also be analyzed for traits such as dental hygiene and habits such as smoking and frequent exercise. It is not possible, however, to determine the weight of an individual based on bone structure. Similar bone structures do not indicate similar fat cell size and distribution.

A laboratory that specializes in skeletal biology and forensic archaeology uses equipment such as x-ray machines, microscopes, bone casting supplies, peripheral x-ray bone densitometers (to determine bone density), ultrasonometer, cutting saws, calipers, mandibulometers (specialized calipers for the jaw), and other anthropology equipment. Collections of bones from autopsy specimens with known conditions such as arthritis, infections, fractures, cancer, and osteoporosis are also preserved in these laboratories, and aid in distinguishing trauma-induced bone changes from disease-induced bone changes. This distinction could provide critical information to a criminal investigation.

A forensic scientist must be able to analyze the skeletal system given different situations. For example, if a child suffers multiple fractures and dies due to related complications, the parents might be under suspicion for child abuse and homicide. Either the medical examiner or the forensic pathologist should identify the rare cases of multiple fractures in deceased children that involve a genetic-based cause of disease, such as osteogenesis imperfecta, where affected individuals are extremely susceptible to multiple fractures with little mechanical force.

Technological advances have paved the way for forensics sciences to gain a plethora of information from scantly detectable evidence in a crime scene. Even in cases where skeletal remains are scattered, contemporary techniques that use three-dimensional digital imagery can help remodel and restore the skeletal remains. Anthropometric (body proportion) measurements from a large enough sample size from a given population can be used for computer modeling programs to estimate body measurements. Three-dimensional facial reconstruction techniques can provide a visual representation of the victim. It is possible, based on the size and shape of an individual’s skull, to estimate race and use computerized programs to help reconstruct what the individual looks like. These computerized models have begun to replace recreating the remains of a person using casts. However, in general, facial reconstructions cannot be used in a court of law as positive identification, as they can be subjective, unreliable, and difficult to reproduce.

In examining skeletal remains resulting from natural disasters, knowledge of how the natural surrounding environment participates in the decomposition of the skeletal system is important. For example, certain insects and microorganisms become involved in the decaying remains of an individual in a time-dependent fashion. When the body begins to decay, there are enzymes found in the digestive system that can liquefy the tissues, a process called putrefaction. Maggots are efficient at using rotting flesh for their energy requirements. By examining their life cycles, insect activity can sometimes reveal the time of death.

Additionally, trace amounts of DNA from bone remains can be recovered and analyzed by a molecular geneticist. DNA survival is greatest in dense bone, such as teeth, than in any other type of tissue. In fact, it has been possible to extract small amounts of DNA recovered from bones that are thousands of years old and perform DNA analysis by amplifying the DNA sequences with a technique known as poly-merase chain reaction, or PCR. Bones from murder victims have been successfully identified almost a decade after the person died using comparative DNA typing and DNA markers. DNA markers from the bone sample are compared to DNA markers from samples from the possible parents of the victim. If enough DNA markers are analyzed and these markers match the parents, it is possible to conclude with a high level of certainty the identity of the victim. The degradation rate of DNA extracted from rib bones has also been used to determine the time interval since death of a victim.

In general, although it requires highly trained and specialized experts, skeletal analysis for forensic purposes can be useful and informative, especially in cases where bone is the only recovered evidence.

See also Crime scene investigation; Forensic science; Skeletal system.

Bryan Cobb