Tapered design for the cementless total hip arthroplasty femoral component.

The long-term behavior of total hip arthroplasty ultimately is determined by adaptive bone remodeling. Stress adaptation creating various degrees of metaphyseal bone atrophy has occurred with prostheses designed for tight distal fit and fill. This phenomenon has been explained as bone adaptation resolving the conflict between femoral component stiffness and bone flexibility. However, clinical observations indicate that a different premise may be operational when prostheses with tapered geometries are used. The results of four published reports (748 arthroplasties) using cementless femoral components of a tapered design were reviewed. The review found a low incidence of aseptic loosening (0.5%) and significant thigh pain (0.5%), and a radiographic incidence of proximal bone atrophy of 6%. In no case was the metaphyseal bone atrophy described as severe or extensive. These findings challenge the premise that reactive bone adaptation is related to the issues of femoral component stiffness exclusively and propose that femoral component geometry may have an influence on bone adaptation.