Use of peripheral quantitative computed tomography for densitometry of the femoral neck and spine in cynomolgus monkeys (Macaca fascicularis)

Quantitative computed tomography (QCT) allows for the separate densitometric examination of cortical and cancellous bone in vivo. With the new peripheral QCT (pQCT) instrument (the Norland/Stratec XCT-3000A), we evaluated the clinically relevant axial sites of spine and femoral neck in nonhuman primates in vivo. The reproducibility was good (coefficient of variation [CV] <3% at both sites for cortical, trabecular, and total bone mineral density [BMD]; CV 3%–7% for bone mineral content [BMC] and cross-sectional bone area). One hundred sixty intact female cynomolgus monkeys (M. fascicularis) were scanned at the femoral neck. There was less variability among monkeys in cortical BMD (mean 802 mg/mL, CV 6%) as opposed to trabecular BMD (mean 334 mg/mL, CV 28%) or transition zone BMD (mean 457 mg/mL, CV 12%). Scans were performed on lumbar vertebrae (L-4, L-5, and L-6) from five monkeys in vivo and ex vivo. Removal of soft tissue increased measured BMD. Decreasing voxel size from 0.4 mm to 0.2 mm increased measured BMD by diminishing the partial volume effect. Factor analysis demonstrated the expected relationships between pQCT parameters and physical measurement of bone mass and volume ex vivo. Preliminary results in eight ovariectomized and eight reproductively intact monkeys revealed a lower transition zone BMD at the femoral neck, and lower total BMD of the vertebral body in estrogen-deficient animals.