Dislocation of the Kneecap

The patella (kneecap) is a bone that covers the knee joint and protects it. Its main job is to help the quadriceps (front thigh muscle) complete the action of straightening your leg. Though the patella is movable, it stays in place because it sits on a groove at the end of your femur (thighbone). If the patella moves out of this groove, an injury called patella instability occurs.

Patella instability is also called kneecap dislocation. There are two types:

  • Traumatic patellar dislocation.This is when the kneecap moves completely out of the groove. Traumatic patellar dislocation can occur if you suddenly change direction while playing a sport or being active.
  • Chronic patellar instability. Also called patellar subluxation, this is when the kneecap partially slides out of the groove. Injury to the ligaments or muscles surrounding the knee can cause chronic patellar instability.

Symptoms, Diagnosis and Outlook

With patella instability, the kneecap usually moves toward the outside of your leg. Other signs and symptoms include a deformed-looking knee, difficulty straightening your leg (or you can’t straighten it), knee pain and knee swelling.

Untreated patella instability causes damage to the knee joint and increases your risk for osteoarthritis, making it important to see your doctor for a diagnosis even if the pain isn’t severe. He or she will perform a physical exam and order an X-ray to look at the location of the kneecap.

With the right treatment and rehabilitation, the function of your knee can be restored. Mild cases of patella instability can heal with a few weeks of rest and physical therapy. Repeat cases and severe cases that cause damage to the cartilage or ligament often require surgery.

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