Design of total hip prosthesis: the femoral stem.

This report is a summary of the research carried out in an effort to improve the reliability of total hip replacement procedures. The current state of knowledge of hip mechanics was examined and found adequate in its description of the normal hip, but totally lacking in any but qualitative terms in its description of the diseased hip, or the load transfer between prosthesis and bone in reconstructed hips. The mechanics of the hip joint and femur indicate that the positioning of the femoral head is crucial in achieving a correct balance between muscle force and joint load. Consequently, it is recommended that a great deal more attention be devoted to the positioning of the prosthesis at hip surgery. Experimental and theoretical studies were directed to one aspect of total hip replacement - the design of the femoral stem. Results indicate that all current designs should be adequate if set in acrylic, and provided subsequent bone resorption is small. Further results indicated satisfactory load transfer from a long thick prosthesis stem, fitted without acrylic cement.