Measurement of periprosthetic bone density in hip arthroplasty using dual-energy x-ray absorptiometry. Reproducibility of measurements.

To define the precision (reproducibility) of measurement of periprosthetic bone mineral density and bone mineral content, dual-energy x-ray absorptiometry scans were obtained on 45 randomly selected patients who had had a unilateral total hip arthroplasty within the previous 3 years. The coefficients of variation of the bone mineral density in the proximal Gruen zones were 5.0 and 5.3%, corresponding to errors of 0.07 and 0.11 g/cm2. The coefficients of variation of the bone mineral density for the distal zones averaged 2.8%, with an error of 0.08 g/cm2. The coefficients of variation of the bone mineral content were 4.8 and 2.9% for the proximal and distal zones. The contralateral femur was also scanned in 32 of the patients. For the contralateral femur bone mineral density, the coefficients of variation were 5.0% for the proximal zones and 4.8% for the distal zones. The bone mineral content was 6.0% for the contralateral regions. These results imply that differences in bone mineral density greater than 0.16 g/cm2 (2 standard errors) can be reliably measured. Dual-energy x-ray absorptiometry therefore provides a highly reproducible technique for quantitatively monitoring the changes in bone density that occur after total hip arthroplasty.