Changes in cortical microarchitecture are independent of areal bone mineral density in patients with fragility fractures

Dual-energy X-ray absorptiometry (DXA) and high-resolution peripheral quantitative computed tomography (HR-pQCT) are commonly used to assess the areal bone mineral density (aBMD) and peripheral microstructure, respectively. While DXA is the standard to diagnose osteoporosis, HR-pQCT provides information about the cortical and trabecular architecture. Many fragility fractures occur in patients who do not meet the osteoporosis criterion (i.e., T-score ≤ −2.5). We hypothesize that patients with T-score above −2.5 and fragility fracture may have abnormal bone microarchitecture. Therefore, in this retrospective clinical study, HR-pQCT data obtained from patients with fragility fractures and T-scores ≥ −2.5 (n = 71) were compared to corresponding data from patients with fragility fractures and T-scores ≤ −3.5 (n = 56). Types of secondary osteoporosis were excluded from the study. To verify the dependency of alterations in bone microarchitecture and T-score, the association between HR-pQCT values and aBMD as reflected by the T-score at both proximal femora, was assessed. At the distal tibia, cortical thickness was lower (p < 0.001), cortical porosity was similar (p = 0.61), trabecular number was higher (p < 0.001), and bone volume fraction (BV/TV) was higher (p < 0.001) in patients with T-scores ≥ −2.5 than in patients with T-scores ≤ −3.5. Trabecular number and BV/TV correlated with T-score (r = 0.68, p < 0.001; r = 0.61, p < 0.001), whereas the cortical values did not. Our results thus demonstrate the importance of bone structure, as assessed by HR-pQCT, in addition to the standard DXA T-score in the diagnosis of osteoporosis.