In people where the groove is too shallow, their patella may actually slip out of the groove, causing a patellar dislocation. This is not only painful when it occurs, but can damage the articular cartilage underneath the patella. If this occurs repeatedly, degeneration of the patello-femoral joint occurs fairly rapidly. Chondromalacia patellae exists when there is damage to the articular cartilage underneath the patella. This does not necessarily mean that the knee will be painful.
Some people never have problems.
Others experience vague pain in the knee which is difficult to localize. Pain may be felt along the inside edge of the patella, though this is not always the case. Typically, people who have patello-femoral problems experience pain when walking down stairs or down hills. Keeping the knee bent for long periods , as in sitting in the car or sitting in the movie theater, may cause pain. The knee may feel as if it gives out on occasion.