Short term results of cemented total hip arthroplasty are very good. However, long term results remain less successful. Noncemented prostheses indicate biological fixation may provide the solution to long term clinical difficulties. Prediction of clinical performance of noncemented prostheses rests in part in predicting bone ingrowth. Prediction of bone ingrowth from in vitro tests requires two criteria be met:​ First, apply three-dimensional load patterns that adequately match the load patterns observed in vivo. and second determine three-dimensional micromotion over the entire surface of the porous-coated region of the prosthesis. In an attempt to better understand in vivo processes and predict bone ingrowth, testing procedures were developed for both the femur and the acetabulum to simulate hip loading for level walking and stair climbing, and to determine the relative motion between the prosthesis and bone over the entire prosthesis during these activities. The procedures were then employed to study various fixation techniques for both femoral and acetabular components. Present data suggest that to achieve sufficient fixation conducive to bone ingrowth in the porous-coated region for the femoral prosthesis studied, a tight proximal fit must be achieved. The quality of distal fit exhibited minimal effect on the stability of the femoral prosthesis. The acetabular data indicate that two central screws are the best configuration for cup stability.