Fig. 3

Iwano classification for PF osteoarthritis. A Stage I: mild osteoarthritis with joint space at least 3 mm; B) Stage II: moderate osteoarthritis with joint space < 3 mm but no bony contact; C) Stage III: severe osteoarthritis with bony contact less than one quarter of the joint surface; D) Stage IV: very severe osteoarthritis with joint surfaces entirely touching each other, often accompanied by a large lateral patellar osteophyte, and bone loss of the lateral patellar facet