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Many things can leave marks on or in bones. Evidence of disease or injury (trauma) in a skeleton can help identify the deceased. It can also tell us about a person's general health in life, or the cause of death. Postmortem marks (left on bones after death) can explain events surrounding that person's death and burial.
Activity and Use
Bones change size and shape in response to forces placed on them. Repetitive, heavy use of certain muscles can affect the bones to which they are attached. The bone may thicken, modify in shape, or become roughened where the muscles connect. Similarly, inactivity can cause bone loss, or atrophy — as pictured here.
Some occupations and habits modify skeletons. The bones of body builders show well-developed ridges where muscles attach. The hips and knees of runners may develop joint deterioration. The right arm bones of someone who is right-handed may be larger than the left.
Disease
Illnesses that affect the skeleton tend to be chronic conditions. Diseased bone forms abnormally or loses tissue, leaving holes or lesions. Diseases in bone are identified through visual and X-ray examination. Techniques under development identify diseases in bone through molecular analysis.
Diet and Nutrition
Diet has a direct impact on the skeleton. A diet with sufficient nutrients, especially calcium, phosphorus, and vitamin D, is required to build strong bones and teeth. Nutrient deficiencies result in weak or abnormally formed bones. Bones and teeth of individuals lacking good nutrition can be identified visually and by X-ray.
Trauma
Bone may break due to accidental or intentional injury. If a break happens during life (antemortem), the bone can heal or repair itself. At death (perimortem) or after death (postmortem), no healing occurs. "Dry" or old bone breaks differently than "fresh" bone.
Most skeletal injuries are visible upon gross examination. X-rays may be needed to help interpret healed or perimortem trauma, including gunshot wounds.
Blunt Force
Sometimes the pattern of bone breakage (which bones are affected and how they are fractured) can identify the weapon or object that caused the damage, along with the circumstances of the injury. For example, an impact site on the skull can record the shape of the implement that inflicted the blow. Individuals in automobile accidents often fracture bones in the face, pelvis, and lower legs.
Gunshot Wounds
Bullets (projectiles) fracture "fresh" bone in characteristic ways, so that the direction of the projectile and its size can often be determined. Entrance wounds are characterized by a circular hole with fractures extending from the hole in a "sunburst" pattern. The outer edge of the entrance would will be sharp and the inner margin beveled due to the direction of the force. Exit wounds are typically larger than the entrance, with fractures extending from the exit area. For exit wounds, the inner edge is sharply defined and the outer margin is beveled.
Surgical Intervention
Surgical wires, rods, plates, screws, and orthopedic implants are lasting markers for identification. Many medical devices carry model or serial numbers that can be traced to specific medical procedures and patient records.
Postmortem Damage
Some bone modifications happen after death. Investigators have to distinguish perimortem trauma from postmortem changes, such as animal damage, burns, cremation, or coffin erosion.