Periprosthetic bone loss and regional bone turnover in uncemented total hip arthroplasty: a prospective study using high resolution single photon emission tomography and dual-energy X-ray absorptiometry.

Single photon emission computed tomography (SPECT) at 6 and 12 months and dual-energy X-ray absorptiometry (DXA) at 0, 6, and 12 months were performed prospectively in 15 patients who had undergone uncemented total hip arthroplasty (THA) without any complications. Periprosthetic bone mineral density (BMD) decreased significantly in all regions of interests (ROIs) during 1 year of follow-up. The greatest annual decrease was found in the lesser trochanter region (22.1%). From 6-12 months, SPECT activity in the operated side decreased significantly (10-24%) in all ROIs, with the exception of the medial cortex ROI. In contrast, increases (8-36%) were found in the contralateral side. At 12 months, the operated versus control difference was still 10% in the lesser trochanter ROI, but as much as about 70% in the greater trochanter and tip ROIs. The decrease in BMD was significantly related to an increase in SPECT activity in the lesser trochanter region (r = -0.589, p < 0.05). In conclusion, increased periprosthetic SPECT activity seems to be associated with increased bone loss. We suggest that increased SPECT activity and subsequent bone loss reflect altered stress distribution and bone remodeling in the femur after prosthesis implantation.