Effects of Stem Loosening on Periprosthetic Bone Remodeling After Cementless Hip Replacement

Abstract

We studied the influence of stem stability on periprosthetic bone remodeling around a cementless femoral component in bone densitometric examinations and determined if the specified bone remodeling patterns according to stem stability can be explained by mechanical environment. Using dual-energy X-ray absorptiometry (DEXA), we examined bone mineral density (BMD) distribution of the proximal femur in 48 hips with a press-fitted collared stem and 45 hips without a stem. Those hips operated on included 34 and 14 hips with stable and loose stems, respectively, as shown on plain radiographs. For mechanical assessment, we analyzed three-dimensional finite element (FE) models of the proximal femur with a stable stem, with an unstable stem, and without a stem. The DEXA evaluations revealed significant differences of BMD distribution with regard to stem stability. A remarkable increase in BMD in the proximal medial region was a salient feature of femora with loose stems. The biomechanical analysis with the FE model for the unstable stem showed an elevation of equivalent stresses in the proximal medial cortical bone. The stress distribution of the stable and unstable FE models was correlated well with BMD distribution of the stable and loosening groups, respectively. The present study suggests that stability of the stem influences bone remodeling enough to be evident in the evaluation of BMD distribution, and that the analyses of periprosthetic BMD distribution offer the possibility for estimating the stability of the stem per se, based on biomechanical environment.