Chondromalacia Patellae (also known as CMP, Patello-femoral Pain Syndrome, or Runner's Knee) is a degenerative condition of the cartilage surface of the back of the knee cap, or patella. It produces discomfort or dull pain around or behind the patella. It is common in young adults, especially soccer players, cyclists, rowers, tennis players and runners. Rugby players are also prone to this injury, especially those playing in positions where the knees are under great stress, such as Prop. The condition may result from acute injury to the patella or from chronic friction between the patella and the groove in the femur through which it passes during motion of the knee. CMP specifically refers to a knee that has been structurally damaged, while the more generic term Patello-femoral Syndrome refers to the earlier stages of the condition, where symptoms might still be fully reversible.