Characterization of Bone Matrix Mineralization and Osteocyte Lacunar Density Unveils Microstructural Impairment at the Main Femoral Fracture-Initiating Site in Type 2 Diabetes Mellitus

This study aimed to perform microstructural characterization of the increased fragility of human bone in type 2 diabetes mellitus (T2DM) by exploring the matrix mineralization and osteocyte lacunar density at the superolateral femoral neck-the typical fracture-initiating site. Postmortem specimens of the full-length superolateral femoral neck from 16 elderly men with T2DM and age-matched non-DM controls were examined using backscattered-electron microscopy in terms of mineralization parameters and parameters of osteocyte lacunar density. The T2DM and control groups did not differ in age and body mass index (p > 0.05). In the endocortical region, T2DM was associated with a lower degree of mineralization (lower CaMean: p = 0.04), a higher proportion of extremely low-mineralized areas (higher CaLow: p = 0.027), and greater mineralization heterogeneity (higher CaWidth: p = 0.003) relative to controls. However, there were no significant intergroup differences in mineralization parameters in the periosteal region. In the endocortical region, T2DM showed lower unmineralized (p = 0.006) and total osteocyte lacunar number (Lc.N) per bone area (B.Ar) (p = 0.018) coupled with a higher percentage of mineralized lacunae (%Mn.Lc) relative to controls (p = 0.05). In the periosteal region, only Lc.N/B.Ar was lower in T2DM (p = 0.004). As for the trabecular compartment, T2DM was associated with lower trabecular CaMean (p = 0.048) and higher trabecular CaLow and CaWidth (p = 0.005, p = 0.007). Altered pattern of mineralization in the cortical (especially in the endocortical region) and trabecular compartments of the superolateral femoral neck and reduced cortical osteocyte lacunar density are structural hallmarks of bone fragility in T2DM.