Fig. 3

Proposed phenotypes of endochondral bone formation in rheumatic diseases (a) Mechanical or inflammatory signals may initiate mesenchymal recruitment chondrocyte hypertrophy and osteoblast mediated bone formation in a stepwise process mimicking endochondral bone formation. b Similarly, excessive mechanical stress may lead to activation of chondrocytes at the periarticular bone, leading to increased hypertrophy, osteoblast recruitment from the vasculature and endochondral bone formation. c Mechanical stress, inflammation and genetic predisposition, may cause alteration in cytokine expression, including BMP and Wnt signaling leading to mesenchymal recruitment and proliferation followed by endochondral bone formation leading to ankylosis of the spine