Performance characteristics of total hip femoral components as a function of prosthesis modulus.

A study of total hip femoral components was performed to demonstrate the effects of changes in prosthesis modulus upon strain levels and subsidence data measured in vitro. Femoral components of identical geometry but fabricated from dissimilar alloys were implanted sequentially in the same femoral specimens so that their relative performance could be compared. It was found that the components fabricated from titanium alloy produced higher levels of calcar strain than the cobalt-chromium components when collar/calcar contact was preserved. However, when collar/calcar contact was removed, cobalt-chromium stems showed a greater propensity for subsidence into the medullary cavity. The increased rate of subsidence of the stiffer stems produced concomitantly greater circumferential strain levels in the proximal cortical shell. It is concluded that the increased tensile hoop strain caused by subsidence of the cobalt-chromium stems will be particularly deleterious to the integrity of the cement mantle.