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Kneecap Instability (Dislocated Knee): Overview

What is kneecap instability, commonly called a dislocated knee?

Your knee cap (patella) is designed to move in the groove that is at bottom of the thigh bone (femur). If the kneecap moves and tracks in the groove of the femur, the joint functions smoothly and you can walk, run, sit and stand without problems. When the kneecap comes out of the groove, problems and knee pain can result.

The tendons above and below the kneecap connect the muscles in the front of the thigh to the shinbone (tibia). By flexing and extending the leg, the kneecap is pulled up or down in the groove of the femur (femoral groove). This V-shaped notch or femoral groove accommodates the moving kneecap.

Normally, the kneecap fits nicely in the femoral groove. If the groove is uneven or too shallow, the kneecap could slide out of the groove. This can result in a partial or complete dislocation. Trauma to the knee could also dislocate the kneecap. This is known as knee dislocation or instability.

Who gets kneecap instability?

Kneecap dislocation and instability can occur in older children, adolescents and adults. Instability is very common in teens who play high school sports. After an initial kneecap dislocation, the chances of dislocating again are very high.

Physical therapy and bracing can decrease the risk of future dislocations. Occasionally, surgery is needed to help prevent the kneecap from partially or completely dislocating.

Helpful knee resources:

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