Chondromalacia is a diagnosis referring to damage, and subsequent pain, to the cartilage under your kneecap.  It can be caused by several factors, and produces discomfort with such activities as walking up and down stairs, kneeling, squatting, or getting up from a seated position. It can occasionally produce swelling in the knee and a sensation of giving way or "catching" ("locking").

The usual precipitating cause of pain in the patient with chondromalacia is either trauma (an injury such as a fall on the knee or a car accident) or a developmental abnormality (Malalignment) of the knee, which may predispose a patient to knee cap pain.  Some patients suffer from a kneecap that repeatedly dislocates (usually towards the outside of the knee), which not only causes pain, but buckling of the leg and damage to the undersurface of the kneecap.

There is a "normal" relationship between the thigh muscle, the patella, and the point of attachment of the patellar tendon.  This is described by the Quadriceps Angle (Q-angle). In those people in which the Q-angle is larger than normal, there is a greater tendency for the kneecap to track abnormally in the groove on the front of the femur with knee bending, leading to increased pressure in certain parts of the kneecap-femur joint.