Comparative high-resolution pQCT analysis of femoral neck indicates different bone mass distribution in osteoporosis and osteoarthritis

Osteoarthritis is linked to a reduced risk of femoral fracture despite osteoporosis. Different bone distribution in the femoral neck in osteoarthritis and fracture was revealed using a peripheral quantitative computed tomography (pQCT) comparative analysis. Our findings sustain the presence of an adaptive mechanism of bone structure providing fracture protection in osteoarthritis. Although osteoarthritis is associated with reduced femoral fracture risk, it does not protect from bone loss. We investigated whether adaptive mechanisms are present at the arthritic joint, leading to reduced fracture risk, despite the presence of low bone mass density. We performed pQCT comparative analyses of human femoral neck specimens derived from 32 postmenopausal women who received hip prostheses for osteoarthritis (n = 19) or femoral fracture (n = 13) by applying an in-house automated software to extract bone structure descriptors, characterize trabecular and cortical bone distribution, and evaluate their mutual relationships. The cortical bone volume and trabecular thickness were significantly (p < 0.05) higher in the osteoarthritis group than in the fracture group. Trabecular bone volume was also significantly (p < 0.05) higher in the osteoarthritis group than the fracture group at the inferior and anterior quadrants. Significance was maintained after adjusting for age, cortical bone volume, and cortical porosity thickness. Multiple linear regression analysis showed that thickness, volume, and apparent density of the trabecular region significantly (p < 0.05) correlated with the same cortical descriptors in osteoarthritis, but no significant relationship was found in the fracture group. Age differentially affected the mutual relationships in the two groups, showing a significant correlation with trabecular thickness in both groups and with apparent trabecular density only in femoral fracture group. Starting from these differences in the structural descriptors, our study sustains the presence of a compensatory mechanism in osteoarthritis to preserve the mechanical competence of bone structure, despite the loss of trabecular bone, underlying lower fracture risk.