Bone density, geometry, microstructure, and stiffness: Relationships between peripheral and central skeletal sites assessed by DXA, HR-pQCT, and cQCT in premenopausal women

High-resolution peripheral quantitative computed tomography (HR-pQCT) is a new in vivo imaging technique for assessing 3D microstructure of cortical and trabecular bone at the distal radius and tibia. No studies have investigated the extent to which measurements of the peripheral skeleton by HR-pQCT reflect those of the spine and hip, where the most serious fractures occur. To address this research question, we performed dual-energy X-ray absorptiometry (DXA), central QCT (cQCT), HR-pQCT, and image-based finite-element analyses on 69 premenopausal women to evaluate relationships among cortical and trabecular bone density, geometry, microstructure, and stiffness of the lumbar spine, proximal femur, distal radius, and distal tibia. Significant correlations were found between the stiffness of the two peripheral sites (r=0.86), two central sites (r=0.49), and, between the peripheral and central skeletal sites (r=0.56-0.70). These associations were explained in part by significant correlations in areal bone mineral density (aBMD), volumetric bone mineral density (vBMD), and cross-sectional area (CSA) between the multiple skeletal sites. For the prediction of proximal femoral stiffness, vBMD (r=0.75) and stiffness (r=0.69) of the distal tibia by HR-pQCT were comparable with direct measurements of the proximal femur: aBMD of the hip by DXA (r=0.70) and vBMD of the hip by cQCT (r=0.64). For the prediction of vertebral stiffness, trabecular vBMD (r=0.58) and stiffness (r=0.70) of distal radius by HR-pQCT were comparable with direct measurements of lumbar spine: aBMD by DXA (r=0.78) and vBMD by cQCT (r=0.67). Our results suggest that bone density and microstructural and mechanical properties measured by HR-pQCT of the distal radius and tibia reflect the mechanical competence of the central skeleton.