The anthropometric total hip femoral prosthesis. Preliminary clinical and roentgenographic findings of exact-fit cementless application

Abstract

Total hip arthroplasty in the young patient remains a considerable challenge. Cemented arthroplasty has an unacceptably high failure rate. Porous ingrowth designs are one alternative, but bone ingrowth is unpredictable, thigh pain is a frequent clinical finding, stress shielding is often observed, revision is more complicated, and microporous components are mechanically weaker. A new anthropometric femoral component has been designed with a goal of long-term stability through osseointegration. The prosthesis is optimized for canal fill in the distal metaphysis and proximal diaphysis. The components are manufactured in 16 sizes, with cutting broaches precisely machined to the same dimensions to provide an exact fit to the femur. The high-strength TiAl6V4 alloy stem is combined with heads of either CoCr alloy or alumina (Al2O3) for reduced polyethylene wear. The 135 degrees neck-shaft angle and modular design allow for restoration of the abductor lever arm. Because the prosthesis is not porous coated, it is also suitable for use with cement. In cemented application, the prosthesis shape provides an optimal cement mantle. Seventy-one total hip arthroplasties have been performed using the Anthropometric Total Hip (ATH) prosthesis: 31 with exact-fit cementless fixation and 40 with cement. Of those using cementless fixation, 21 have been followed for more than one year (mean, 20 months; range, 12-48 months). The early clinical findings are as good as, or superior to, other cementless designs used at the authors' institution. Stress remodeling of the proximal femur occurs early and stabilizes by one year. The observed changes appear to improve the stability of the prosthesis. Clinical and roentgenographic findings suggest the osseointegration of the ATH femoral component.