Bone Mass Distribution of the Distal Tibia in Normal, Osteopenic, and Osteoporotic Conditions: An Ex Vivo Assessment Using HR-pQCT, DXA, and Computational Modelling.

Osteoporosis leads to bone loss and structural deterioration, which increase the risk of fractures. The aim of this study was to characterize the three-dimensional (3D) bone mass distributions of the distal tibia in normal, osteopenic, and osteoporotic conditions. High-resolution peripheral quantitative computed tomography (HR-pQCT) of the 33 % of the distal tibia and local dual-energy X-ray absorptiometry were applied to 53 intact, fresh-frozen tibiae. The HR-pQCTs were graded to assign local T-scores and merged into three equally sized average normal, osteopenic, and osteoporotic surface models. Volumetric bone mineral density (vBMD) was determined using categorized T-scores, volumetric visualization, and virtual bore probes at the dia-, meta-, and epiphyseal sites (T-DIA, T-META, and T-EPI). We observed a distinct 3D bone mass distribution that was gradually uninfluenced by T-score categories. T-DIA was characterized by the lowest bone mass located in the medullary cavity and a wide homogenous cortex containing the maximum vBMD. The T-META showed decreased cortical thickness and maximal vBMD. At the T-EPI, the relatively low vBMD of the mostly trabecular bone was similar to the maximal cortical vBMD in this sub-region. Four trabecular regions of low bone mass were identified in the recesses. The bone content gradually decreased at all sites, whereas the pattern of bone mass distribution remained essentially unchanged, with the exception of disproportionate losses at T-DIA, T-META, and T-EPI that consistently showed increased endocortical, intracortical, and trabecular bone loss. Extra information can be obtained from the specific pattern of bone mass distribution, potential disproportionate bone losses, and method used.