Femoral strain profiles under simulated 3-D muscle and joint loads for heel strike, midstance, and toe off.

A universal static hip joint simulation apparatus was designed to simulate both 3-D joint and 3-D muscle forces for each of the three load-bearing phases of normal gait. The adjustability provided by the apparatus allowed for the consideration of femoral orientation, hip joint contact force, and primary active muscle loads for each simulated activity. Use of this apparatus enables the biomechanical response of the femur to be more fully and accurately determined under a full range of everyday activities. Results demonstrate that the proximal femur experiences significantly higher levels of strain during the activities of toe off and heel strike than during midstance. This evaluation underscores the importance of considering each phase of gait when investigating the biomechanical response of the femur, which should be especially relevant in the design and evaluation of femoral components for hip joint arthroplasty. Future studies are planned for femoral strain evaluation following simulated hip joint replacement. By providing a more complete strain profile evaluation of the femur as a function of implant design, the use of this apparatus should contribute to the development of new femoral component designs for improved patient care.