Measurement of early bone loss around an uncemented femoral stem

BACKGROUND AND PURPOSE Dual-energy X-ray absorptiometry (DXA) is a precise method to study changes in bone mineral density (BMD), including the pattern of bone remodeling around an implant. Results from implant studies are usually presented as changes in BMD as a function of time. The baseline and reference value for such calculations is the first measurement after the operation. The baseline measurement has been performed at different time points in different studies. If there is rapid bone loss immediately after an operation, this will influence the reference value and hence the results. To evaluate DXA as a method, we studied the very early changes by doing 3 DXA measurements within the first 2 weeks after surgery. PATIENTS AND METHODS We included 23 hips in 23 patients who were operated with an uncemented total hip prosthesis (THP). Each Gruen region was measured with DXA at 1, 5, and 14 days, and 3 and 12 months after the operation. 16 of the patients completed all 5 follow-ups. RESULTS There was no detectable change in BMD in the first 14 days after the operation. In all zones, the lowest BMD was measured after 3 months. INTERPRETATION We conclude that DXA measurements done within 14 days after the operation can be used as reference measurements for later follow-up studies.