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 the knee joint. This disc-shaped bone in front of the knee is important, along with the quadriceps muscle on the front of the thigh, for extending and straightening the leg when you walk or stand, Ostermeier says.
Whenever you bend or stretch your leg, the kneecap moves back and forth inside a groove on top of the thighbone. Cartilage helps the bones glide smoothly against each other. When cartilage wears away, the resulting friction can be painful – and even audible.