As part of a program to develop improved kneethigh- hip injury criteria, the dynamic force-deflection responses of twenty knee/femur complexes from eleven unembalmed cadavers were measured under knee loading directed along the length of the femur. An interface that was molded to the shape of each cadaver’s knee was used to distribute applied loads across the patella and femoral condyles. A fixed femoral head boundary condition was used to minimize inertial effects, allowing the skeletal stiffness of the knee/femur complex to be characterized. Average knee/femur stiffness is 0.37 kN/mm. This value primarily represents the stiffness of the femur because the molded-knee interface minimizes the contribution of knee compliance to the whole knee/femur stiffness.

Corridors developed from the cadaver knee/femur force-deflection responses were used to evaluate the response of the knee/femur complex of the Hybrid III and THOR. Prior to about 2 mm of deflection, the Hybrid III is 2.4 times stiffer than the upper bound of the cadaver response corridor and the THOR is 1.9 times stiffer. After 2 mm of deflection, the Hybrid III knee/femur complex response is approximately sixteen times stiffer than the upper bound of the cadaver corridor, while the THOR knee/femur response is approximately three times stiffer.