▸ Group A: Definite osteophyte formation; full thickness cartilage loss.
▸ Group B: Subchondral marrow lesion or cyst not associated with meniscal or ligamentous attachments; meniscal subluxation, maceration, or degenerative (horizontal) tear; partial-thickness cartilage loss (without full thickness loss).
2. Patellofemoral OA requires the following features involving the patella or the anterior femur:
▸ Definite osteophyte formation.
▸ Partial- or full-thickness cartilage loss.