FIT OF THE UNCEMENTED FEMORAL COMPONENT AND THE USE OF CEMENT INFLUENCE THE STRAIN TRANSFER TO THE FEMORAL CORTEX

To determine whether the strain patterns produced in the femoral corte x after uncemented femoral arthroplasty are influenced by the fit of t he component and whether these patterns are different from those of ce mented components, cortical surface strains of cadaveric femurs subjec ted to loads simulating single-limb stance were measured before and af ter the insertion of uncemented, collared, straight-stemmed femoral co mponents. The effects of press fit, loose fit, and precise fit of the components were evaluated and were contrasted to the strain patterns o ccurring after insertion of cemented femoral components. Strains varie d markedly, depending on the fit of the stem of the uncemented femoral component within the isthmus. Nearly normal patterns of femoral strai n were produced when the femoral stem was fit precisely at the isthmus , and the proximal femoral strains were similar to those of the intact state. In contrast, press fit and loose fit at the isthmus altered th e strain patterns. The proximal medial axial strains were significantl y reduced with press fit, to a mean of 39% of normal (p < 0.05), and i ncreased with loose fit, to a mean of 141% of normal (p < 0.05). The p rostheses fixed with cement showed a mean reduction in proximal medial axial strains to 33% of normal, which was comparable with press fit u ncemented components even though the collar was well seated. Thus, our findings indicated that, in the immediate postoperative period, femor al strain patterns can be influenced by the fit of an uncemented compo nent within the isthmus and by the use of cement.