Abnormal microarchitecture and reduced stiffness at the radius and tibia in postmenopausal women with fractures

Abstract

Measurement of areal bone mineral density (aBMD) by dual-energy x-ray absorptiometry (DXA) has been shown to predict fracture risk. High-resolution peripheral quantitative computed tomography (HR-pQCT) yields additional information about volumetric BMD (vBMD), microarchitecture, and strength that may increase understanding of fracture susceptibility. Women with (n = 68) and without (n = 101) a history of postmenopausal fragility fracture had aBMD measured by DXA and trabecular and cortical vBMD and trabecular microarchitecture of the radius and tibia measured by HR-pQCT. Finite-element analysis (FEA) of HR-pQCT scans was performed to estimate bone stiffness. DXA T-scores were similar in women with and without fracture at the spine, hip, and one-third radius but lower in patients with fracture at the ultradistal radius (p < .01). At the radius fracture, patients had lower total density, cortical thickness, trabecular density, number, thickness, higher trabecular separation and network heterogeneity (p < .0001 to .04). At the tibia, total, cortical, and trabecular density and cortical and trabecular thickness were lower in fracture patients (p < .0001 to .03). The differences between groups were greater at the radius than at the tibia for inner trabecular density, number, trabecular separation, and network heterogeneity (p < .01 to .05). Stiffness was reduced in fracture patients, more markedly at the radius (41% to 44%) than at the tibia (15% to 20%). Women with fractures had reduced vBMD, microarchitectural deterioration, and decreased strength. These differences were more prominent at the radius than at the tibia. HR-pQCT and FEA measurements of peripheral sites are associated with fracture prevalence and may increase understanding of the role of microarchitectural deterioration in fracture susceptibility. © 2010 American Society for Bone and Mineral Research.

Fig. 1

Comparison of T-scores by DXA in postmenopausal women with and without fragility fractures. No significant differences at any site except for the ultradistal radius (*p < .01). Horizontal lines indicate the WHO thresholds for low bone mass (dashed line) and osteoporosis (dotted line).

Fig. 2

Comparison of the percent difference in HR-pQCT (A) and FEA (B) measurements between fracture and nonfracture subjects at the distal radius (filled bars) and tibia (open bars; *p < .05, **p < .01, ***p < .001 for comparisons between fracture and nonfracture subjects, and ⁺p < .05, ⁺⁺p < .01 for comparisons between radius and tibia). Ct.Th = cortical thickness; D.comp = cortical density; D.Trab = trabecular density; Tb.N* = trabecular number; Tb.Sp = trabecular separation; Tb.1/NSD = network inhomogeneity; E₁₁, E₂₂, E₃₃ = Young's moduli; G₁₂, G₂₃, G₃₁ = shear moduli.

Fig. 3

HR-pQCT scans from fracture subjects with (A) and without (B) measurable inner trabecular density and FEA at the distal radius (filled bars) and tibia (open bars). (C) Comparison of the percent difference in inner trabecular density (D_inn) and metatrabecular density (D_meta), detailed in the schematic on the right, between fracture and nonfracture subjects in the entire cohort and in a subcohort excluding those subjects without measurable inner trabecular density and FEA (*p <.05, **p < 0.01, ***p < .001 for comparisons between fracture and nonfracture subjects. ⁺p < .05 for comparison between radius and tibia).