Fig. 3

Schematic illustration of the hypothesised growth of subarticular osteophytes into articular cartilage. a Healthy joint surface with articular cartilage, calcified cartilage and subchondral bone. b High density mineralised protrusions (HDMP) emerged from cracks in the calcified cartilage and subchondral bone. c Endochondral ossification of the high density mineralised protrusions resulting in subarticular osteophytes and superficial fibrillation of the articular cartilage. d The subchondral bone penetrates the articular cartilage. e Complete loss of the articular cartilage, and subchondral bone sclerosis