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 desig ns: 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 importan t 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 custo m-designed micromotion sensors were used to measure three-dimensional motio ns 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 exh ibit detectable motions under a limited number of cycles of simulated physi ologic loads. At four times the donor body might, Stem I showed a subsidenc e of 90 mu m, compared to 25 um of Stem II (P < 0.05). In contrast, the pro ximal 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 diffe rences, such as surface finish and geometry.