I have been diagnosed with chondromalacia of the knee. What is this?

I have been diagnosed with chondromalacia of the knee. What is this?

Chondromalacia, sometimes referred to as “patellofemoral pain syndrome,” is a common problem in young adults. When the kneecap (patella) moves up and down, it usually follows a track that runs along the bones underneath. If the patella is not in the center, it starts to move off the track. This can cause wear and tear of the cartilage behind the knee. The back of the patella becomes rough and catches on the bone. This produces a crunching sound called crepitus. When this happens, pain, aching, and muscle weakness can develop.