Effects of femoral offset distance on femur and muscle forces

To investigate effects of femoral offset on hip reaction force, hip abductor muscle force and stresses on femur, a musculoskeletal model of lower extremity was build with a modified optimization algorithm. Kinetic and kinematic data were applied to determine the muscle and hip joint reaction forces in the presence of hip prosthesis with varying from -10 milimeter to +10 milimeter offsets during a gait cycle. Obtained muscle and joint reaction forces transfered to finite element model to analyze stresses on femur. Also, the effect of prosthesis with varying femoral offsets on joint reaction forces and compensation ability were evaluated in case of abductor muscle weakness after total hip arthroplasy. Increasing or decreasing the femoral offset by 5 mm was statistically insignificant while increasing by 10 mm showed a significant difference. All variations of the offset within 10 milimeter affected hip abductor muscle forces significantly. No siginificant differences were observed in stress values on femur. Finally, it was observed that as the level of abductor muscle weakness increased, the effect of femoral offset on joint reaction forces increased.