Fig. 3.

Merchant staged the severity of the disease based on the 45° skyline view. (A) Stage 1: mild with more than 3 mm of joint space. (B) Stage 2: moderate with less than 3 mm of joint space but no bony contact. (C) Stage 3: severe with bony surfaces in contact over less than one quarter of the joint surface. (D) Stage 4: very severe with bony contact throughout the entire joint surface.