Does your knee crunch like a coffee grinder whenever you move it? It could be a sign of patellofemoral osteoarthritis, the breakdown of cartilage on the underside of the patella (kneecap) and groove of the femur (thighbone). “Degenerative changes behind the kneecap are the cause,” says Dr Sven Ostermeier, an orthopaedist based in Freiburg, Germany, adding that the condition should be treated as early as possible or, ideally, prevented in the first place. The kneecap does more than merely protect...