Measurement of bone density around the Oxford medial compartment knee replacement using iDXA. A precision study.

The goal of this study was to evaluate whether the Lunar iDXA densitometer can accurately measure the bone mineral density (BMD) around the tibial component of the Oxford unicompartment knee replacement (UKR). Both knees in 20 patients were measured 3 times in the supine position with repositioning between each scan. We chose 7 regions of interest to evaluate the bone density around the implant. Small but significant differences between the implant and nonimplanted knee were noticed with the nonimplanted knee having slightly higher BMD and bone mineral content (BMC) in areas 1-3 (p≤0.001) and area 6 (p=0.002). There was higher BMD in area 4 (p=0.028). The precision for BMD in the 7 areas of interest in the implanted knee varied between 0.55% and 4.04% and BMC between 1.8% and 5.3%. There was no significant difference in the precision between the nonimplanted and implanted knees. Prospective serial measurements around the Oxford UKR using iDXA will be able to assess specific areas of stress shielding and potential implant stability, which is likely to help predict the survival of the implant.