Chondromalacia, or patellofemoral pain syndrome, occurs when the cartilage on the back of the kneecap (patella) becomes cracked and worn. The rough surface "catches" on the bones underneath, causing painful symptoms. The exact cause of this problem is unknown. Anything that pulls the patella off the center of the knee can be part of the problem.
The muscle in front of the thigh (quadriceps) is supposed to help hold the patella in the middle. Pain or injury can lead to a loss of control in this muscle. As a result, the patella gets off track. This is a major cause of chondromalacia of the patella.
Exercises to strengthen the quadriceps and other measures to help the patella track normally can help. Two-thirds of all patients with this problem have an overall positive result with this kind of program.