ASSESSMENT OF THE SKELETAL STATUS BY PERIPHERAL QUANTITATIVE COMPUTED-TOMOGRAPHY OF THE FOREARM - SHORT-TERM PRECISION IN-VIVO AND COMPARISON TO DUAL X-RAY ABSORPTIOMETRY

In order to assess precision of peripheral quantitative computed tomog raphy (pQCT), duplicate bone mineral density (BMD) measurements at the radius were performed in 20 healthy premenopausal, 20 healthy postmen opausal, and 20 osteoporotic postmenopausal women using a Stratec XCT- 960 system. The short-term reproducibility in vivo for the total, trab ecular, and cortical regions of interest (ROI) was expressed as the ab solute precision error (standard deviation, SD) and as the relative pr ecision error (SD/mean x 100, or coefficient of variation, CV,in %). R eproducibility in vivo was good in all volunteers but was influenced b y the study group and the ROI. The precision error for trabecular BMD was 3 mg/cm(3), or about 1.6%. This is large relative to the aging dec rease of 0.22%/year, or to the difference (12 mg/cm(3) or 7%) between osteoporotic women and postmenopausal controls. In order to compare pQ CT to dual X-ray absorptiometry (DXA) at the forearm and at the lumbar spine (L1-L4), 40 premenopausal healthy controls, 40 postmenopausal h ealthy controls, and 35 postmenopausal osteoporotic women were assesse d. DXA measurements performed at the ultradistal, middistal, 1/3, and total ROI of the radius showed only moderate correlations between r = 0.38-0.75, r = 0.27-0.64, and r = 0.38-0.53 for the comparison versus pQCT total BMD, versus pQCT trabecular BMD, and versus pQCT cortical B MD, respectively. Correlations of DXA at the lumbar spine and pQCT wer e between r = 0.18 and 0.44. DXA at radius and spine was able to discr iminate between postmenopausal controls and osteoporotic women (p = 0. 001-0.004), but BMD measurements by pQCT did not show this ability (p = 0.15-0.52). However, two nonstandard pQCT parameters, namely the sur face area of the cortical bone and the cortical BMC were factors that discriminated well between these two groups (p = 0.002, p = 0.005, res pectively). These pQCT parameters also yielded the highest relative an nual changes in pre- and postmenopausal control subjects. The measurem ent of cortical bone in the distal radius proved to be a good predicto r of vertebral fracture status and was a good indicator of age-related skeletal change. Our data emphasize the importance of cortical measur ements when using pQCT of the radius to assess osteoporosis.