A PROSPECTIVE-STUDY OF PROXIMAL FEMUR BONE MASS FOLLOWING CEMENTED AND UNCEMENTED HIP-ARTHROPLASTY

Cross-sectional studies have demonstrated significant decreases in bon e mass in femoral cortical bone adjacent to prostheses. Thirty-six pat ients who had undergone 31 cemented and 9 uncemented primary total hip arthroplasties (THA) were prospectively studied to define further the natural history of this femoral cortical bone loss. Dual-energy X-ray absorptiometry (DXA) was employed to quantify bone mineral density (B MD) changes in four subregions around the femoral prostheses. Femoral BMD loss (average 12.3%) was observed in the three proximal subregions 2 months postoperatively, This loss increased to 21.2% by 6 months po stoperatively, and by 2 years postoperatively it averaged 25.5% in the same three subregions, There were no significant BMD changes in the s ubregion distal to the prosthesis tip or in the contralateral hip. Sub groups were compared based on prosthesis size and cement use. Statisti cally significant differences in BMD Loss were observed between the la rge cemented cobalt chrome prosthesis group (n = 8) and the large unce mented titanium prosthesis group (n = 8). These differences were only present in the most proximal medial subregion where the large cemented groups had twice the bone loss in this area as compared-with the larg e uncemented group. The data indicate that bone loss occurs adjacent t o femoral prosthesis within 2 months of surgery and that DXA is a usef ul technique to quantify prospectively femoral cortical bone loss foll owing THA.