Initial stability of stainless steel and titanium alloy total hip arthroplasty femoral components

Loosening of the femoral component in total hip arthroplasty remains the primary cause of long-term failure. STH titanium alloy stems have demonstrated 38% greater risk of developing radiolucent lines than Charnley stainless steel stems. To assess whether this could be attributed to the modulus of elasticity, Charnley and STH femoral stems were implanted in cadaveric femur pairs. LVDT's measured gaps on the proximal lateral and anterior sides, and axial migration of the stem under physiological walking and stair climbing cycles. Displacements were approximately the same during all cycles. No systematic difference was found between the STH and Charnley femoral stems. The data in this study does not support mechanical effects as the primary cause of loosening, suggesting that the complex biological reactions may play a greater role.