This chapter concerns the principles of joint prostheses. Load transmission is a common misconception for those not involved in study of the musculoskeletal system that the majority of force carried by bone is related to bearing weight. Analysis of two-legged and one-legged stance is a static analysis because the body is assumed to be unmoving. The situation becomes more difficult to analyze when accelerations are included in the analysis-a dynamic analysis. To set the body or a part of the body in motion, there must be an acceleration and a force to cause acceleration. The joint implant must be in very close contact with bone to bear the required loads. Thus, a basic requirement for the implant is that the material be compatible with living tissues. In the functioning joint replacement, wear debris is unavoidably produced from articulation of the prosthetic femoral component with the acetabular component.