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Kneecap Dislocation

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Updated December 15, 2011

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A dislocation of the kneecap occurs when the patella comes completely out of its groove on the end of the thigh bone (femur), and comes to rest on the outside of the knee joint. Kneecap dislocations usually occur as a significant injury the first time the injury occurs, but the kneecap may dislocate much more easily thereafter.

Signs of a Kneecap Dislocation

A kneecap dislocation causes significant pain and deformity of the knee joint. The kneecap always dislocates to the outside of the joint. Pain and swelling are common symptoms of a kneecap dislocation. Over time, bruising may also develop around and below the knee joint.

A kneecap dislocation should not be confused with a knee dislocation. A knee dislocation occurs when the thigh bone (femur) and shin bone (tibia) lose contact. A kneecap dislocation occurs with the kneecap dislodges from its groove on the thigh bone. Sometimes people use the words knee dislocation to describe a kneecap dislocation; this is incorrect.

Recurrent Kneecap Dislocations

When the kneecap comes out of joint the first time, ligaments that were holding the kneecap in position are torn. The most important torn structure is called the medial patellofemoral ligament, or MPFL. This ligament secures the patella to the inside (medial) of the knee. When a kneecap dislocation occurs, the MPFL must be torn.

Once the MPFL is torn, it often does not heal with proper tension, and the kneecap can subsequently dislocate more easily. That is why recurrent dislocation of the kneecap occurs in a high percentage of patients who have this injury.

Treatment of a Kneecap Dislocation

Most kneecap dislocations are initially with prompt reduction (repositioning) of the kneecap. Most patients will go to emergency room, and while repositioning the kneecap is relatively straightforward, pain and muscle spasm can prevent this from being easily accomplished. Therefore, anesthesia (either local or general) may be administered to help reposition the bone. Most kneecap dislocations can be repositioned by simply straightening the knee once control of the pain and spasm allows.

After repositioning the kneecap, treatment usually begins with R.I.C.E. treatment to control pain and help with swelling. Crutches and a knee brace are usually offered to help control pain. While preventing weight on the leg may help with pain, it is not necessary to keep all weight off of the leg. Once the acute swelling has subsided, treatment may progress.

The next phase of treatment usually consists of physical therapy and bracing the kneecap. As discussed earlier, kneecap dislocations can become a recurrent problem. By strengthening the muscles around the joint, and with the use of specialized knee braces, the hope is to help prevent recurrent injury.

In patients who have recurrent (repeat) dislocations, there are surgical options. The usual treatment is to loosen the lateral (outside) ligaments that pull the kneecap, called a lateral release procedure. Some surgeons also recommend either tightening the muscle or reconstructing the ligaments that pull from the inside of the kneecap. In some rare circumstances, a realignment of the extremity, involving cutting and repositioning bone, may be recommended.

Is surgery an option after a first-time dislocation?
Recent interest has developed in preventing these recurrent dislocations. Each time the kneecap dislocates, the cartilage can be injured, and the ligaments can become more stretched out. Concerns about increasing the liklihood of arthritis development from repeated trauma has made some doctors more aggressive in trying to prevent repeat dislocations. Some surgeons are trying to restore the normal anatomy by repairing the MPFL after a first-time dislocation. This surgery is controversial, because not all patients who dislocate their kneecap will have another dislocation. In addition, early surgery has not been shown through scientific study to be helpful in preventing arthritis.

Sources:

Hing CB, et al. "Surgical versus non-surgical interventions for treating patellar dislocation" Cochrane Database Syst Rev. 2011 Nov 9;11:CD008106.

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