Morphological and biomechanical analyses of the subchondral mineralized zone in human sacral facet joints: Application to improved diagnosis of osteoarthritis

Abstract

The anatomy of the facet joint subchondral mineralized zone (SMZ) is the main parameter used in diagnosing osteoarthritis. Usually, a single CT scan slice is used to measure the thickness, but the measurement is highly location-dependent. Bone mineral density (BMD) and porosity could be more reliable than thickness for detecting SMZ sclerosis, and linking them to stiffness can provide insights into the mechanism of osteoarthritis progression. The goal of this study was two-fold: (1) to assess spatial heterogeneity in thickness, BMD, and porosity within the non-pathological human facet joint SMZ; (2) to correlate these measurements with the static modulus of elasticity (MOEsta). Four non-pathological facet joints were excised and imaged using micro-computed tomography (μCT) to measure SMZ thickness, BMD, and porosity. A total of eight parallelepiped SMZ samples were similarly analyzed and then mechanically tested. The mean SMZ BMD, porosity, and thickness (± Standard Deviation) of the whole facet joints were 611 ± 35 mgHA/cc, 9.8 ± 1.3%, and 1.39 ± 0.41 mm, respectively. The mean BMD, porosity, and MOEsta of the eight SMZ samples were 479 ± 23 mgHA/cc, 12 ± 0.01%, and 387 ± 138 MPa, respectively, with a positive rank correlation between BMD and porosity. BMD and porosity were more homogeneous within the facet joint than thickness and they could be more reliable parameters than thickness for detecting SMZ sclerosis. The values for the physiological SMZ and MOEsta of human facets joints obtained here were independent of BMD. SMZ BMD and porosity were related to each other. Clin. Anat. 28:538-544, 2015.