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 o n the measurement of bone mineral density (BMD) of the proximal femur in a canine model with dual energy x-ray absorptiometry (DXA) was dete rmined. Seven regions of interest, corresponding to zones 1-7 accordin g to Gruen et al., were measured. Eight unpaired femora were scanned w ith DXA before implantation (five separate scans per femur), after pre ss-fitting with a titanium alloy femoral component (five separate scan s per femur); and after cementing with the same component (five separa te 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 preci sion 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 cortic al 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 measuremen t to 7.2% (range, 1.1-12.6%).