Patellar Dislocation

What is the patella?
It is the kneecap. It rests on the groove at the end of the femur (thigh bone).

What causes patellar dislocation?
The causes of dislocations can be either a twisting injury to a normal knee or an abnormality in the structure of the knee. The twisting injury can occur during sports or doing normal household activities. Abnormalities in the knee include a shallow or uneven groove in the end of the femur where the patella rests, or loose ligaments. Loose ligaments occur more often in girls than in boys and these patients are usually aware of being more flexible than other people.

What are the symptoms of a patellar dislocation?
Patellar dislocations are usually a sudden and painful event. When the patella dislocates you may hear a “pop” and feel the kneecap shift or slide out of place. Pain and swelling will usually follow. The knee will look misshapen or deformed if the kneecap does not automatically relocate. If the kneecap does not automatically relocate, it will have to be put back into place; this is often done in an emergency room, but can be done on the scene. When the patella automatically relocates it is very difficult for the doctor to later determine if a patella dislocation occurred or if the patient has a different injury such as an ACL tear.

What problems can a patellar dislocation cause?
Sometimes a small piece of bone with cartilage breaks off the back of the patella or the end of the femur bone when the patella dislocates. If this piece is pretty big, surgical removal of it is necessary. A ligament called the medial patellofemoral ligament (the MPFL) almost always tears when a person sustains a Patellar dislocation. The MPFL is an important patella tracking stabilizer and once it is torn, the patella can have recurrent dislocations.

What is the treatment for a patellar dislocation?
Most likely your son or daughter will initially be placed in a knee immobilizer. X-rays and an MRI will be required. Both x-rays and an MRI can show if there is a large piece of bone and cartilage needing removal. The MRI is important for seeing any other damage and for determining if the injury is truly a Patellar dislocation or something else such as an ACL tear. Except for the occasion when a large piece of bone needs to be removed, first time Patellar dislocations are treated without surgery. A knee immobilizer is worn for 2 to 3 weeks; then home exercises and physical therapy are done until the knee feels normal. Patients who sustain a Patellar dislocation usually need 6 to 12 weeks before returning to sports. Patients who sustain repeated Patellar dislocation are best treated with an operation. Dr. Bradley usually performs an MPFL reconstruction. After MPFL reconstruction, patients wear a knee immobilizer for 2 to 3 weeks. They then have home exercises and therapy and are usually able to return to full activities including sports 3 months after the surgery.

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