The human legs provide strong resistance to motion during a car crash. Laboratory simulators of large deceleration accidents typically utilize anthropomorphic dummies in place of human volunteers. In order to better understand the biomechanics of car crash injury and to develop more realistic dummies, improved knowledge of knee kinematics must be obtained. Most mathematical and physical analogs of human knees consider the motion to be modeled by a hinge or pin type joint. In recent years, many complex models have been suggested to better approximate the knee in walking. The present research suggests that the simplicity of a pinned joint be retained, but that the pin location be chosen to best simulate the in-plane motion of the human knee. High speed flash x-rays of the knee region were photographed during a highly simplified mock car crash. The relative positions of a rotating femur about a fixed tibia were observed over a 25° range or rotation. Using an optimization method, an effective pivot location was found that most closely matched the complex motion of the actual knee. The results of this preliminary study show this optimum pin position to be nearly 2.5 cm from the pin location that would have been obtained by constraining the location to lie along the tibia centerline (a geometric center). Also, the appropriate pin position was located more anterior than for tests with non-weight bearing and cadaver subjects.
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