DUAL-ENERGY X-RAY ABSORPTIOMETRY OF IMPLANTED FEMORA AFTER CEMENTED AND PRESS-FIT TOTAL HIP-ARTHROPLASTY IN A CANINE MODEL

The effect of a press-fit and cemented titanium alloy endoprosthesis on the measurement of bone mineral density (BMD) of the proximal femur in a canine model with dual energy x-ray absorptiometry (DXA) was determined. Seven regions of interest, corresponding to zones 1-7 according to Gruen et al., were measured. Eight unpaired femora were scanned with DXA before implantation (five separate scans per femur), after press-fitting with a titanium alloy femoral component (five separate scans per femur); and after cementing with the same component (five separate scans per femur). When the titanium alloy endoprosthesis was press-fit, the BMD of five of seven regions of the proximal femur increased significantly (range, 2.7-23.1%; mean, 11.2%), although the mean precision error of this measurement was not altered (before implantation, 1.1%; after press-fit 1.8%). Cementing of the implant caused a variable effect on BMD, resulting in a decrease in distal regions where cortical bone was relatively thin compared with the cement mantle (regions 3, 4, and 5) and in an increase in the other regions. Cementing of the implant significantly increased the mean precision error of measurement to 7.2% (range, 1.1-12.6%).