Children's Hospital Colorado

Kneecap Instability (Dislocated Knee)

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:

What are signs and symptoms of kneecap instability?


Signs that your child or young athlete may have a dislocated knee include:

  • Knee buckles or gives out
  • Kneecap slips to the outside of the knee
  • Knee catches or locks with movement
  • Pain in the front of the knee that is worse with activity
  • Pain after sitting for prolonged periods of time
  • Stiffness
  • Popping or cracking sounds with movement
  • Swelling around the knee

How will my child’s doctor diagnose kneecap instability?

During a physical exam, your child’s knee will be bent and straightened to determine the position of the kneecap. An expert at the Sports Medicine Program for Young Athletes will carefully feel the area around the kneecap 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 patella fits in the femoral groove. Your child’s doctor will also want to eliminate other possible reasons for the pain, such as a tear in the cartilage or injury to the ligaments of the knee.

How is kneecap instability (dislocated knee) treated?

Treatment for a fully dislocated knee

If the kneecap has been completely dislocated, the first step is to put the kneecap back in its proper place in the groove. This process is called a reduction. Reduction can happen spontaneously (on its own). If not spontaneous, your child’s doctor will have to apply gentle force to push the kneecap back in place.

A dislocation can damage the undersurface of the kneecap or the outside of the femur, which can lead to additional pain and popping symptoms. Surgery is commonly used to correct this condition.

Treatment for a partially dislocated knee

If the kneecap is only partially dislocated (called subluxation), your child’s doctor may recommend non-surgical treatments, such as physical therapy and knee-bracing. A physical therapist or your physician will recommend exercises that will help strengthen the muscles in the thigh to help prevent future occurrences.

Stationary cycling is often recommended as part of the physical therapy to keep in good cardiovascular shape. A stabilizing knee brace may also be used in the initial stages of treatment. The goal is for the patient to return to normal activities or sports within four to eight weeks.

Treatment after multiple dislocations

After multiple dislocations of the kneecap, the kneecap is considered to be unstable. This condition can often be corrected by surgery . Surgery can be used to realign and tighten tendons to keep the kneecap in the groove, or to release tissues that pull the kneecap out of the groove.

Learn more about our Sports Medicine Program for Young Athletes that treats kneecap instability.


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