Changes in bone mineral density of the proximal femur after total knee arthroplasty.

This study investigates the relationship between total knee arthroplasty (TKA) and bone mineral density (BMD) in the same and opposite hips. The study prospectively evaluated 24 consecutive patients undergoing TKA (31 knees, 47 hips). The mean follow-up was 48 months. The mean age at latest follow-up was 69 years, and all patients had the preoperative diagnosis of osteoarthritis. BMD of the hip was measured by dual-energy x-ray absorptiometry. Despite a predicted age-related loss of 4% during 2 years, 45% of the hips on the operative side and 59% of the hips on the nonoperative side had BMD higher than preoperative levels. Of hips, 81% on the operative side and 82% on the nonoperative side had BMD that was within the expected 4% age-related loss. Assuming that higher hip BMD may be protective against later hip fractures, the results infer that, by increasing hip BMD, TKA may be protective against later hip fractures. The increase with TKA in patient mobility and the increased hip loading may be a mechanism whereby the hip BMD increases.