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 periprosth etic bone mineral density and bone mineral content, dual-energy x-ray absorptiometry scans were obtained on 45 randomly selected patients wh o had had a unilateral total hip arthroplasty within the previous 3 ye ars. The coefficients of variation of the bone mineral density in the proximal Gruen zones were 5.0 and 5.3%, corresponding to errors of 0.0 7 and 0.11 g/cm(2). The coefficients of variation of the bone mineral density for the distal zones averaged 2.8%, with an error of 0.08 g/cm (2). 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 bo ne mineral density, the coefficients of variation were 5.0% for the pr oximal zones and 4.8% for the distal zones. The bone mineral content w as 6.0% for the contralateral regions. These results imply that differ ences in bone mineral density greater than 0.16 g/cm(2) (2 standard er rors) can be reliably measured. Dual-energy x-ray absorptiometry there fore provides a highly reproducible technique for quantitatively monit oring the changes in bone density that occur after total hip arthropla sty.