Identifying the potential factors that are associated with OA has been one of the major efforts in elucidating OA.18–21 Knee joint destruction in various animals models of RA may be caused by either an excessive amount of active TGFβ or elevated COX-2 expression in subchondral bone.4,22 It appears that different factors may be associated with a single OA pathogenesis and vice versa. Here, PTGS2 is linked to rheumatoid arthritis.