The Story Behind Bone Fractures
On the Scene E-Newsletter, Edition 124, October 6, 2010
Bones can tell a good story. They fracture in a very specific way depending upon the forces applied. Examining the injured bones within the context of an accident can be a very good way to deduce what may have happened. Scientists and engineers often use the science of fracture mechanics to verify the sequence of events that led to a particular injury or fatality.
Consider a pedestrian struck by a vehicle as a simplified example: The height of the leg fracture above ground can be compared to height of bumper above ground to determine whether a vehicle attempted to brake. A braking vehicle will be “nose-diving” thus the associated fracture will be lower than bumper height, usually just above ankle. Where as a non-braking vehicle will likely cause a fracture at bumper height.
The type of break in the bone is important as it can indicate the magnitude and direction of forces experienced at the time of an accident. For example, the feet of a skier are secured into ski boots attached to a ski, which can serve as a perfect lever to apply a rotational force to the leg. The X-ray of a skier’s leg that suffered an accident involving this type of rotational force would show a fracture line that twists around the bone. This is a spiral fracture that can only be caused by a violent torque effect on the leg. Alternatively, if the skier fell and slid horizontally into a tree, the X-ray would likely show a simple break traversing perpendicular to the leg.
Although joint injuries can add a level of complexity to an analysis, they can also be a rich source for clues. The ankle is one of the most frequently injured joints in the human body. The sophisticated arrangement of bones and ligaments in this joint provide an excellent canvass capable of capturing detailed information through injury. From an examination of medical records, a biomechanical expert can often tell which direction the foot was pointing, which direction the foot tilted, where the weight of the individual was centered and which direction and manner the individual fell. The science of fracture mechanics as applied to bones, can tell a credible story as to what action the person was attempting in the moments before injury.
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