Dislocated kneecap

A dislocated kneecap (luxating patella) is common and painful injury that involves the kneecap sliding out of its position at the front of the knee joint. Young and athletic people are more likely to suffer a dislocated kneecap. Usually, the kneecap slips sideways to the outside of knee and then returns unassisted to its original position (reduction). Nevertheless, a luxating patella must always be treated, because it can damage the surface of the cartilage and increase the risk of another dislocated kneecap in the future.

People usually suffer from dislocated kneecaps during sporting activities. It is assumed that they are caused by a congenital defect of the trochlear groove. The trochlear groove is normally responsible for stabilising the kneecap when the joint is moving. Patients with an unstable trochlear groove can suffer a luxating patella if they expose their knees to increased strain.  That is why a person’s first dislocated kneecap typically happens when they are quite young – especially during sporting activities that put a great deal of pressure on the kneecaps.

Dislocated kneecaps are very painful. The kneecap slips sideways out of its normal gliding path. This makes the knee immediately unstable. Often the cartilage behind the kneecap and the knee’s system of ligaments are also damaged.  That is why a dislocated kneecap must always be examined and treated by a doctor, even if the kneecap spontaneously returns to the correct position.

The diagnosis is based on the typical symptoms and appearance of the knee with the kneecap slid to one side. To check for cartilage and ligament damage, an x-ray or MRI examination is carried out and sometimes also knee joint imaging.

The first stage of any treatment is the immediate reduction (repositioning) of the kneecap, if it has not already spontaneously returned to the correct position. If the cartilage or ligaments have been damaged, surgery is usually unavoidable. During the operation, the surgeon will not only treat the injuries, but also reposition the ends of the tendons that attach to the kneecap. This makes it possible to change the direction in which the tendons are pulled, so that the kneecap sits more securely inside the trochlear groove.

An initial luxating patella that does not involve any other injuries can be treated conservatively. This includes special bandages, as well as targeted strengthening of the thigh muscles. Both approaches help to stabilise the kneecap. However, the risk of suffering another dislocated kneecap is relatively high. If it happens again, the kneecap will need to be surgically stabilised.