Abstract
Cortical bone contributes the majority of overall bone mass and bears the bulk of axial loads in the peripheral skeleton. Bone metabolic disorders often are manifested by cortical microstructural changes via osteonal remodeling and endocortical trabecularization. The goal of this study was to characterize intracortical porosity in a cross-sectional patient cohort using novel quantitative computational methods applied to high-resolution peripheral quantitative computed tomography (HR-pQCT) images of the distal radius and tibia. The distal radius and tibia of 151 subjects (57 male, 94 female; 47 ± 16 years of age, range 20 to 78 years) were imaged using HR-pQCT. Intracortical porosity (Ct.Po) was calculated as the pore volume normalized by the sum of the pore and cortical bone volume. Micro–finite element analysis (µFE) was used to simulate 1% uniaxial compression for two scenarios per data set: (1) the original structure and (2) the structure with intracortical porosity artificially occluded. Differential biomechanical indices for stiffness (ΔK), modulus (ΔE), failure load (ΔF), and cortical load fraction (ΔCt.LF) were calculated as the difference between original and occluded values. Regression analysis revealed that cortical porosity, as depicted by HR-pQCT, exhibited moderate but significant age-related dependence for both male and female cohorts (radius ρ = 0.7; tibia ρ = 0.5; p < .001). In contrast, standard cortical metrics (Ct.Th, Ct.Ar, and Ct.vBMD) were more weakly correlated or not significantly correlated with age in this population. Furthermore, differential µFE analysis revealed that the biomechanical deficit (ΔK) associated with cortical porosity was significantly higher for postmenopausal women than for premenopausal women (p < .001). Finally, porosity-related measures provided the only significant decade-wise discrimination in the radius for females in their fifties versus females in their sixties (p < .01). Several important conclusions can be drawn from these results. Age-related differences in cortical porosity, as detected by HR-pQCT, are more pronounced than differences in standard cortical metrics. The biomechanical significance of these structural differences increases with age for men and women and provides discriminatory information for menopause-related bone quality effects. © 2010 American Society for Bone and Mineral Research.
Highlights
Osteoporosis is characterized by loss of bone mass and compromised bone structure resulting in reduced bone strength and an increased risk of fracture
Micro-computed tomography has become an important tool for investigating a wide range of aspects related to the biology of bone and other calcified tissues.[5,6,7] Until recently, true 3D in vivo assessment of bone microstructure has been limited to small-animal microtomographic systems.[8,9] Highresolution peripheral quantitative computed tomography (HRpQCT) is a promising noninvasive method for in vivo 3D
Clinical high-resolution peripheral quantitative computed tomography (HR-pQCT) studies have focused primarily on trabecular microstructure.[15,16,17] there is considerable evidence that the cortical bone bears the bulk of axial loads in the distal radius and tibia[18] and that the distribution of load is an important factor in bone strength and fracture prediction.[19,20] Consistent with these observations, both gross geometric and microstructural properties of cortical bone are known to contribute to overall bone strength.[21]. These properties are modified through distinct physiologic processes and represent unique targets for pharmacologic intervention
Summary
Osteoporosis is characterized by loss of bone mass and compromised bone structure resulting in reduced bone strength and an increased risk of fracture. The standard clinical method for assessing bone mass, areal bone mineral density (aBMD) determined by dual-energy X-ray absorptiometry (DXA), does not entirely explain fracture risk. This X-ray projection technique does not account for 3D geometry and obfuscates independent effects in cortical and cancellous bone compartments.[1,2,3,4] the development of quantitative endpoints based on 3D imaging techniques is an important goal toward an improved mechanistic understanding of bone mechanics, fracture risk, disease progression, and therapeutic efficacy. In combination with measures of crosssectional geometry and trabecular microstructure, treatment selection could be tailored to specific bone deficit patterns (eg, cortical porosity, cortical thinning, trabecular thinning, etc.)
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