Periprosthetic femoral bone loss after total knee arthroplasty: 1-year follow-up study of 69 patients.

The clinical survival of joint arthroplasties is related to the quality of the surrounding bone environment. Bone mineral density (BMD) is an important measure of bone strength and quality. The aim of this prospective study was to measure the quantitative changes in BMD in the distal femur after cemented total knee arthroplasty (TKA) in osteoarthrotic knee joints. Sixty-nine patients with TKA were scanned postoperatively using dual-energy X-ray absorptiometry (DXA) within a week of surgery, and at 3-, 6-, and 12-month follow-ups. An average decrease in bone density of 17.1% (mean range of 12.1-22.8%) was measured adjacent to the prosthesis at the 12-month follow-up (repeated measures ANOVA P<0.0005). Bone loss was most rapid during the first 3 months after TKA. The clinical status and function parameters of the knee joint, evaluated by the American Knee Society (AKS) score, had improved significantly on the preoperative values at the three- and 12-month follow-ups (P<0.0005). However, improvement in the AKS score was not associated with periprosthetic BMD change (P=0.204), whereas age (P=0.067) and body mass index (P=0.019) correlated with BMD loss for the total metaphyseal region of interest (ROI), by repeated measures ANOVA. We suggest that the observed periprosthetic bone loss was mainly the result of prosthesis-related stress-shielding.