Measurement of periprosthetic bone mineral density by dual-energy x-ray absorptiometry is useful for estimating fixation between the bone and the prosthesis in an early stage.

Periprosthetic bone mineral density (BMD) was measured with dual-energy x-ray absorptiometry in 37 hips after cementless hip arthroplasty. Changes in BMD were evaluated longitudinally from 1 to 36 months. Stem fixation was evaluated at 5 years after surgery and was classified into a stable fixation group (30 hips) and an unstable fixation group (7 hips). On plain radiographs, distinct reactive lines around the proximal stem were detected at an average of 35 months after surgery in the unstable fixation group. In the unstable fixation group, the BMD decrease in the calcar region peaked 6 months after surgery, and BMD increased thereafter. In the stable fixation group, BMD continued to decrease until 36 months after surgery; a significant difference was observed between the 2 groups 24 months after surgery. Measurement of periprosthetic BMD is useful for estimating fixation between the bone and the prosthesis in an early stage.