Fig. 2

Subchondral bone microstructural transformation during OA progression. Rod-like and plate-like trabeculae are distributed accurately at a proper ratio to disperse stress. Osteogenesis coupled with angiogenesis lead to an increased BMD and conspicuous microstructural changes at the subchondral level. A decrease in the rod/plate ratio and subchondral bone plate thickening result in excessive mechanical support, which is detrimental to chondrocyte metabolism. Vessel-induced digestion of the cartilage matrix from the bottom up also takes part in the progression of cartilage destruction. a Normal state; b early stage with BML and vascularization; c progressive stage with cartilage damage; d end stage with severe cartilage destruction and vessel erosion