Patellar (kneecap) dislocation is caused by an unnatural twist, or a blunt impact to the knee. If surrounding ligaments are weak, or if there is an anatomical predisposition, the chances for patellar dislocation increases. Following a patellar dislocation, the most important aspect is to relocate the kneecap back to its proper position, which means relocating the patella into the trochlear groove (groove for the kneecap in the front end of the thigh bone). This often happens spontaneously, or by straightening the leg, but sometimes requires an emergency room. The ligaments that hold the kneecap in place may tear, and pieces of the cartilage lining of the kneecap or trochlear groove may break loose. Without proper therapy, and in some cases surgery, recurrent dislocation, or subluxations (partial dislocation), of the patella can occur. Loose bodies can also cause catching, locking, buckling, or additional cartilage damage.

Symptoms and Diagnosis

Symptoms of a patellar dislocation include rapid, acute swelling and extreme pain. This extreme pain will exist until a relocation of the kneecap occurs; then, the pain will diminish. Other symptoms include the inability to move the knee, bruising, and deformity of the knee, because the kneecap is out of position.

If the kneecap dislocates and pops back into position (relocates) quickly, a more careful history and physical examination is required. Your physician will perform a thorough history and physical exam, but will also assess this injury using an X-ray and an MRI to confirm the diagnosis and to evaluate the medial patellofemoral ligament, loose bodies, cartilage, and other ligaments in the knee.


Initial treatment for a patellar dislocation, once the dislocation has been reduced, is to immobilize the knee for a short period of time. For a first time dislocation, without loose bodies, non-surgical treatment with rehabilitation is recommended. Bracing the joint will allow the swelling to decrease and may help to stabilize the patella. Physical therapy is prescribed, and a full recovery can be expected within an 8-12 week period.

In many cases, once a patellar dislocation occurs, laxity of the ligaments (stretching) or complete tearing of the medial patellofemoral ligament will lead to recurrent dislocations or subluxations, or in some cases, loose bodies may occur. For recurrent dislocation, or for patients with loose bodies, surgery is recommended. Arthroscopic surgery is used to remove loose bodies and treat cartilage or other damage. Small incisions are used to repair or reconstruct the medial patellofemoral ligament (MPFL).


Your physician will prescribe a progressive rehabilitation program that will initially consist of immobilization of the joint, followed by range of motion, strengthening, and physical therapy to regain function of the knee joint. A return to full activities can be expected as early as 8-12 weeks after surgery, depending on a patient’s goals. Athletes participating in contact sport may require additional time to ensure full healing.