Osteoarthritis: what we have been missing in the patellofemoral joint.

Patellofemoral osteoarthritis is common clinically and often independent of tibiofemoral disease. Intriguingly, the patella demonstrates more severe degeneration earlier in the disease process compared with the juxtaposed femoral groove. Here, we consider three hypotheses influencing this disparity and thus discover crucial insights into the etiology of osteoarthritis.