Three-dimensional measurement of cemented femoral stem stability: an in vitro cadaver study

Objective. To compare the in vitro stability of two cemented hip stem designs: Stem I was a collarless, double-tapered, highly polished implant; Stem II had a collar and matt finish. Background. Stability of the femoral component of a hip implant is important for its long-term clinical success. Excessive migration or cyclic motion can increase the risk of early implant failure. Methods. The stems were implanted in paired human cadaver femurs, and custom-designed micromotion sensors were used to measure three-dimensional motions of the stems at proximal, middle and distal locations during simulated in vivo loading cycles. Results. This study found that despite ‘rigid’ fixation, cemented stems exhibit detectable motions under a limited number of cycles of simulated physiologic loads. At four times the donor body weight, Stem I showed a subsidence of 90 μm, compared to 25 μm of Stem II (P<0.05). In contrast, the proximal end of Stem II exhibited greater cyclic motions in the medial–lateral direction (P<0.05). Conclusions. The different motion patterns could be due to the design differences, such as surface finish and geometry.