A dislocated knee cap is when the triangle-shaped bone covering the knee (patella) moves or slides out of place. The problem usually occurs toward the outside of the leg. See dislocation.

Dislocated knee caps most often occur in women. It is usually a result of sudden direction changes while running. This puts the knee under stress.

Dislocation may also occur as a direct result of injury. When it is dislocated, the knee cap may slip sideways and around to the outside of the knee.

The first few times this occurs, you will feel pain and be unable to walk. However, if dislocations continue to occur and are untreated, you may feel less pain and have less immediate disability. This is not a reason to avoid treatment. Knee cap dislocation damages your knee joint.

• Knee cap (patella) is displaced to the outside of the knee
• Knee swelling
• Knee pain and tenderness
• "Sloppy" knee cap; that is, able to move the knee cap excessively from right to left (hypermobile patella)

Splint (stabilize) the knee with the leg fully extended (straight), and see medical attention.

Your health care provider will examine the knee, which could provide confirmation of the dislocated knee cap. The knee cap will move incorrectly when touched.

A knee x-ray and, sometimes, MRIs should be done to make sure that the dislocation did not cause a bone to break or cartilage to be damaged. If tests show that you have no such damage, your knee will be placed into an immobilizer or cast to prevent you from moving it for several weeks (usually about 3 weeks). After this time, physical therapy is done to help build back your muscle strength and improve the knee's range of motion.

If the knee remains unstable, surgery may be necessary to stabilize the knee cap. This may be done using arthroscopic or open surgery.

Call your health care provider if you injure your knee and symptoms of dislocation occur.

Call your health care provider if you are being treated for a dislocated knee and you notice increased instability in your knee, if pain or swelling return after they initially subsided, or if your injury does not appear to be resolving with time.

Also call if you re-injure your knee.

Use proper technique when exercising or playing sports. Maintain strength and flexibility of the knee. Some cases of knee dislocation may not be preventable, especially if anatomic factors predispose you to dislocation.