Osteology and Skeletal Radiology

Within approximately two years of death, and sometimes considerably sooner, all that remains of a body is a skeleton. Identification of skeletal remains can sometimes be an important task in the investigation of a suspicious death. A forensic pathologist or anthropologist will use osteology, the study of bones, to find out as much as possible about the identity of a skeleton or collection of bones. Sometimes they rely on skeletal radiology, the study of bones through x rays or fluorescence (light-emission) to help make the identification.

When confronted by skeletal remains, the investigator works from general concepts to the more specific when trying to identify them. First, they will ensure that the items are in fact bones. It is not uncommon for the public, who often discover such remains, to mistake stones or bits of wood for bones. A physician will recognize the shape and texture of bone. It can, however, be a little more difficult to determine whether the bones are human. When it comes to intact skulls, it is relatively easy to distinguish humans from other animals. With smaller bones, especially those from children, identifying them as human is more challenging. Bear paws, for instance, can be remarkably similar to human hands and feet once stripped of their flesh. Sheep and deer ribs can be hard to distinguish from those of humans.

The investigator is fortunate if he or she gets a whole skeleton to work with. Over time, natural forces and predators tend to scatter bones, so it is more likely that a collection of bones, a single bone, or even just a fragment will be all there is to examine. If necessary, the investigator will have to extract DNA from the bone marrow for analysis to confirm the identification.

Bones discovered in the ground may be anything from around two to hundreds of years old. Establishing their probable age is clearly important as very old bones will not be relevant to a current forensic investigation, although they may well be of great interest in a historical or archaeological context. There are various methods for aging bones. The level of nitrogen in bones decreases over time, although this depends upon temperature and moisture. High levels of nitrogen can distinguish between bones that are a few years old and those that are decades old. Fresh bones glow when exposed to ultraviolet light. This fluorescence decreases from the outside of the bone to the inside over time. A bone that is hundreds of years old may not show any fluorescence.

Nuclear weapon use in World War II and weapons testing in the 1950s and 1960s led to the accumulation of certain radioactive materials in bones of that era. Finding substantial levels of carbon-14, strontium-90, cesium-137 or tritium, a radioactive isotope of hydrogen, suggests the bones date back from around 1950.

Having established the relevance of the bones, the investigator then sets out to discover some general characteristics which will narrow down the search for the identity of the deceased. Information on sex, age, height and race can all be deduced from careful study of skeletal remains. Of course, much depends on how many bones are available for study; far less can be deduced from single bones than from a whole skeleton.

Gender-specific changes in the skeleton do not start to appear until puberty, so distinguishing the sex of a child can be difficult. In general, males have bigger and thicker bones than females. But much depends on nutrition and level of physical activity. A woman who ate well and carried out manual labor will have bigger, stronger bones than a malnourished and inactive male. The long bones, that is, the bones of the arms and legs, are often indicative of sex. The diameter of the heads of the humerus (upper arm bone) the radius, (lower arm bone) on the thumb side, and the femur (thigh bone), are usually bigger in males. The pelvis of a male and female are quite different. A female pelvis is wider and has a wider outlet to allow for childbirth. A pathologist will look at the sciatic notch, which is the point where the sciatic and other nerves pass from the pelvic cavity to the leg. Typically, this is wider in females than in males. The back side of the pubic bone may be pitted or scarred in a woman who has borne a child. The skull may also be indicative of gender, for male skulls are larger and thicker, particularly in the jaw area.

Determining the age at death from skeletal remains is easier for children and adolescents than for adults. The way the skeleton grows and develops from birth to adulthood is well defined. For instance, the skull can be quite useful in determining the age of an infant. The bones of the skull knit together gradually in early childhood along lines called suture lines. The pattern of closure of these lines does, however, vary widely between individual infants so age estimation from this observation is not highly accurate. The symphysis, a thin band of cartilage attaching the pelvis to the spine, has a zigzag shape at birth, which straightens as someone ages up to the age of 50. Bone density decreases with age, as calcium is lost. Radiological examination of skeletal remains can determine bone density and this may help indicate the person's age; however, malnutrition and osteoporosis can also decrease bone density independent of age.

The long bones continue to grow till someone has reached the age of about 25. Therefore, their length may be indicative of age. The areas where the ribs join the breastbone also change with age. They start off smooth and rounded, but become more pitted and sharp over time. In general, the age at death of a skeleton can be determined to around five to ten years, inaccuracy increasing with age.

The height of a person can be estimated from a full skeleton. It will not, however, be the same as the head to heel length of the skeleton itself, because of factors like muscle relaxation and shrinkage of the discs between the spinal bones. If only long bones are available, the investigator can use standard tables that associate the length of these bones with height. The thickness of the bones can also indicate whether the person was of slight or muscular build. Right-handed people tend to have thicker bones on the right side of the body and vice-versa.

Using skeletal remains to determine a person's race is a difficult task, as no single trait is racially distinct. It may, however, be possible to assign a skeleton to one of three racial groups: Caucasoid, Negroid, or Mongoloid. Caucasians tend to have high, rounded, or square skulls with a straight face and a narrow nose. Negroid skulls are lower and narrower with wider, flatter noses. Monogoloids have broad, round skulls with an arched profile. Eye sockets can be distinctive as well; Caucasians' are triangular, Negroids' more squared, and those of Mongoloids tend to be rounded. If someone is of mixed racial origin, they will have a blend of these features making determination of race extremely difficult.

Once the investigator has narrowed down the search for the identity of the skeleton as above, they will look for individualizing characteristics. Should there be ante-mortem x-ray images of the deceased, they can be very useful in establishing identity. A skull x-ray can be distinctive for each person has a unique shape to the frontal sinus area which is evident on comparing the x-ray images with the skull. Ribs, the humerus, and the femur can also be usefully compared between x-rays taken in life and skeletal remains.

Clothing or jewelry found with skeletal remains can be a useful aid to identification, as can injuries found on the body. Of course, many injuries do not affect the skeleton at all. If someone is strangled, it will not be apparent by examining his or her skeleton. However, blunt and sharp force injuries do sometimes impact on bone and these marks may be informative. Similarly, bullet entry and exit wounds may sometimes be apparent. It is important for the investigator to distinguish when the wounds may have been made. During life, wounds heal and create scar tissue, which is apparent on examination of the bone. Wounds without scar tissue may have been inflicted close to the time of death and may, indeed, have been the cause of it. Bones may be damaged after death, but a post-mortem injury looks very different from an ante-mortem injury. Dead bones are brittle and they crumble and break cleanly. The fracture would usually occur parallel or perpendicular to the long axis of the bone. Living bone fractures in a twisted or splintering manner.

X-ray examination of skeletal remains may also indicate disease such as bone cancer or osteoporosis that may be correlated with medical records. Some people have medical appliances like hip replacements or cardiac pacemakers. It is possible that they will even bear a reference number that will reveal the identity of the deceased. DNA analysis provides the ultimate identification. It is possible to extract DNA from the bone marrow or the bone itself. There is increasing interest in looking at mitochondrial DNA, genetic material that occurs in the mitochondria of the cell rather than its nucleus. Mitochondrial DNA is passed down the maternal line and is very resistant to destruction, so is likely to be present in even very old skeletal remains. Mitochondrial DNA from the bones can be compared to that of a living family member to try to establish identity.

see also Anthropology; Sinus print; Skeletal analysis.