The kneecap (patella) is in the V-shaped groove at the bottom of the thigh bone, the trochlear groove.. The knee joint is stabilised and supported by ligaments, which are thick bands of rubbery tissue connecting bones at the knee joint. The main ligament that stabilises the knee is the medial patella-femoral ligament (MPFL). If this is torn, it can mean the kneecap is more likely to dislocate in the future which is very painful and can also damage the surrounding tissues, leading to cartilage injuries.
Normally, the trochlear groove is smooth, allowing the patella to glide smoothly as the knee moves. Sometimes, however, the trochlea develops a bony spur or it may be malformed from birth – either flat or convex. Trochlear dysplasia is a condition in which the trochlear groove is abnormally shaped, causing the kneecap to dislocate by slipping out of the groove.