Why does patellar dislocation cause visible deformity after injury?

The kneecap normally sits in a shallow groove at the end of the thighbone. During a dislocation, it moves to one side, often after a twist, fall, or impact. This can create an indentation where the kneecap should be and a noticeable bulge along the outer side of the knee. Swelling and muscle spasm may make the outline harder to judge. The appearance alone cannot show whether there is a fracture or cartilage injury, so the knee should be examined.

Keep the leg still and supported in the position that feels most comfortable. Do not push, pull, or massage a visibly displaced kneecap, and do not try to straighten the knee by force. Seek urgent medical assessment. While waiting, protect the knee from weight and use a wrapped cold pack if it does not increase discomfort. A clinician can assess the joint and arrange imaging when needed.

Treat a knee that looks deformed after injury as an urgent problem, particularly if the kneecap has not returned to position. Go promptly if the foot is cold, pale, numb, or weak, or if pain and swelling are severe. Inability to bear weight or move the knee also warrants urgent evaluation because other structural injuries can occur with the displacement.

Ask whether the kneecap has fully realigned, whether an X-ray or other scan is needed, and which tissues may have been strained. Discuss temporary support, weight-bearing limits, and the rehabilitation plan that can restore strength and confidence.