Finding hip forces in healthy and hip replacement subjects using musculo-skeletal modeling

Aseptic loosening is seen as the most important cause if late failure after total hip replacement surgery and it is believed that hip joint forces on the hip prosthesis from movements such as stair climbing, and even walking, over a long time can lead to the loosening of the prosthesis. Motion analysis was carried out using 6 inferred cameras and 15 markers placed on the subject using the Helen Hayes Marker Set. The data was recorded and processed using EVaRT 5.0 (Santa Rosa, CA, USA). The marker positions were then used as the motion input for models created in LifeMod (San Clemente, CA, USA), a musculo-skeletal modeling software. Results were found for forces at the hip joint and at the ground where the foot hits the floor. Moments were found in the sagittal, coronal and transverse planes. Although there were slight differences in the forces for all 4 subjects there was very little difference between the moments for all the subjects. Only 4 subjects have been tested so more subjects, both healthy and hip replacement subjects, are needed to get a better understanding of the differences in hip forces.