Fig. 2.

Human OA subchondral bone shows collagen disorganization and hypermineralization. a Control cadaveric (n = 5) and OA (lateral n = 5, medial n = 4) specimens stained with Picrosirius Red and imaged at low (4x, top, scale bars: 200 μm) or high (40x, bottom, scale bars: 100 μm) magnification using polarized light microscopy revealed differences in subchondral bone collagen organization. Collagen fibers are less organized in OA samples than control samples and in medial regions than lateral regions. b The distribution of collagen fiber orientation shows significant differences between all four groups. c, d Synchrotron Radiation X-ray micro-computed tomography (SRμT) of subchondral bone from the lateral and medial sides of cadaveric control and OA tibial plateaus showed a qualitative increase in mineralization, according to the colorimetric scale (800–3 200 mg HA‧cm⁻³), in 3D-reconstructed (d, top) and 2D high-magnification (d, bottom) images. The distribution of mineralization through the subchondral bone from each region (c) confirms the shift in the peak mineralization level in OA medial specimens (n = 5) compared with OA lateral (n = 4) specimens. OA curves were not statistically compared with medial or lateral control samples due to low sample size (n = 2). Lines represent the mean of all specimens in the group. *P < 0.05 by mixed model with random intercepts