Unstable Kneecap

When things are “in the groove,” they’re going smoothly. That certainly is the case with your knee. As long as your kneecap (patella) stays “in the groove,” you can walk, run, sit, stand and move easily. When the kneecap slips out of the groove, problems and pain often result.

The kneecap connects all the muscles in the thigh to the shinbone (tibia). As you bend or straighten your leg, the kneecap is pulled up or down. The thighbone (femur) has a V-shaped notch (femoral groove or sulcus) at one end to accommodate the moving kneecap. In a normal knee, the kneecap fits nicely in the groove. But if the groove is uneven or too shallow, the kneecap could slide off, resulting in a partial or complete dislocation. A sharp blow to the kneecap, as in a fall, could also pop the kneecap out of place.


  • Knee buckles and can no longer support your weight.
  • Kneecap slips off to the side.
  • Pain in the front of the knee increases with activity.
  • Stiffness.
  • Creaking or cracking sounds during movement.
  • Swelling.


During the examination, your doctor may ask you to walk around or to straighten and bend your knee. He or she may carefully feel the area around the kneecap and take measurements to determine if the bones are out of alignment or if the thigh muscles are weak. X-rays may be recommended to see how the kneecap fits in its groove. Your doctor will also want to eliminate other possible reasons for the pain, such as a tear in the cartilage or ligaments of the knee.


If the kneecap has popped totally out of its groove (dislocated), the first step is to return it to its proper place. This process is called reduction. Sometimes this happens spontaneously; other times, your doctor will have to apply gentle force to push the kneecap back in place. A dislocation often damages the underside of the kneecap and the end of the thighbone, which can lead to additional pain and arthritis. Arthroscopic surgery can correct this condition.

If the kneecap is only partially off track (subluxated), your doctor may recommend nonoperative treatments, such as exercises and braces. Exercises will help strengthen the muscles in your thighs so that the kneecap stays aligned.

Cycling is often recommended as part of the physical therapy. A stabilizing brace may also be prescribed. The goal is for you to return to your normal activities within one to three months.

A chronic condition, in which the knee continues to be unstable, can often be corrected by surgery. For example, surgery can be used to realign and tighten tendons to keep the kneecap on track, or to release tissues that pull the kneecap off track.