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Kneecap dislocation occurs 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 also: Dislocation

A dislocated kneecap most often occurs 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 kneecap may slip sideways and around to the outside of the knee.

• Kneecap (patella) moves to the outside of the knee
• Knee pain and tenderness
• Knee swelling
• "Sloppy" kneecap -- you can move the kneecap excessively from right to left (hypermobile patella)

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. Kneecap dislocation damages your knee joint.

Stabilize (splint) the knee with the leg fully straight (extended), and get medical attention.

Your health care provider will examine the knee, which could confirm that the kneecap is dislocated.

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 can help build back your muscle strength and improve the knee's range of motion.

If the knee remains unstable, you may need surgery to stabilize the kneecap. This may be done using arthroscopic or open surgery.

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

Call your health care provider if you are being treated for a dislocated knee and you notice:

• Increased instability in your knee
• Pain or swelling return after they went away
• Your injury does not appear to be getting better with time

Also call if you re-injure your knee.

Use proper techniques when exercising or playing sports. Keep your knee strong and flexible.

Some cases of knee dislocation may not be preventable, especially if anatomic factors make you more likely to dislocate your knee.

Dislocation - kneecap; Patellar dislocation or instability

Updated by: Andrew L. Chen, MD, MS, Orthopedic Surgery and Sports Medicine, The Alpine Clinic, Littleton, NH. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.