The influence of clinical factors on periprosthetic bone remodeling

The femurs of 11 patients with well-functioning unilateral hip replacements were retrieved at autopsy and analyzed for periprosthetic bone remodeling by dual energy xray absorptiometry. Each case involved a femur with a porouscoated endoprosthesis; the endoprosthesis remained implanted for an average of 5.9 years. In the contralateral femur, a matching prosthesis was implanted in vitro, to serve as a control for comparisons. There was an average 22.6% decrease in bone mineral content in the in vivo implanted femur (range, 5.4%-47.4%). Females experienced an average bone loss of 31.2%, which was significantly higher than the 12.3% average loss in males. Longitudinal analysis revealed an average decrease in bone mineral content of 42.1% proximally, 23% in the midsection, and 5.5% distally. Percent decreases in total bone mineral content were correlated with the following clinical variables: weight, age, implant diameter, duration of implantation, and contralateral femoral bone mineral content. Only the bone mineral content of the contralateral femur had a strong predictive value. Bone loss was greater in femurs with low bone mineral content than in those with high bone mineral content. Weight, age, implant diameter, and duration of implantation were not correlated with bone loss.