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What is a dislocated knee?

A dislocated knee occurs when the kneecap (patella) pops out from its normal position. This can occur as the result of force or — more often — is related to a developmental condition that leads to an improper alignment of the kneecap with the thighbone (femur). This is sometimes called "unstable kneecap."

Who is at risk for a dislocated knee?

Kneecap dislocations typically occur in active teenagers and young adults from the ages of 14 to 20 years old. They are most common in teenage athletes who participate in contact sports, such as football, and those suffering simple falls from a wide variety of activities, such as gymnastics, dancing, or cheerleading. A family history of knee instability that leads to dislocation is present in one-fourth of patients with dislocated patellas.

How we care for dislocated knees

If your child is physically active and participates in contact sports and other activities, they may be more prone to having a dislocated patella. While our team of doctors at the Boston Children’s Hospital Lower Extremity Program is committed to helping stabilize and restrengthen your child's knee, they're also interested in helping active young people prevent these injuries in the first place.

Dislocated Knee | Symptoms & Causes

What are the symptoms of a dislocated knee?

Each child may experience symptoms differently. The most common symptoms include:

  • pain in the front of the knee that increases with activity
  • swelling and/or stiffness
  • kneecap slips off to the side
  • difficulty using or moving the leg in a normal manner
  • deformity of the dislocated area
  • warmth, bruising, or redness in the injured area
  • creaking or cracking sounds during movement

Because the symptoms of a dislocated knee may resemble other conditions or medical problems, always consult your child's doctor for a diagnosis.

What causes a dislocated knee?

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 has a v-shaped notch at one end to accommodate the moving kneecap.

In a normal knee, the kneecap fits nicely in the groove. However, if the groove is uneven or too shallow, the ligaments are loose or there is a sharp blow to the kneecap, the kneecap could slide off, resulting in a partial or complete dislocation.

Dislocated Knee | Diagnosis & Treatments

How is a dislocated knee diagnosed?

A dislocated knee should be evaluated by a pediatric orthopedic surgeon. During the examination, the physician will obtain a complete medical history of your child. If the dislocated patella resulted from an injury, the physician may ask about how the injury occurred. The physician also may ask your child to walk around or to straighten and bend the knee, in addition to checking the area around the kneecap and taking 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. X-ray or magnetic resonance imaging procedures may be used to view the knee.

How is a dislocated knee treated?

Specific treatment for a knee dislocation will be determined by your child's physician based on:

  • your child's age, overall health, and medical history
  • the extent of the injury
  • the type of injury
  • your child's tolerance for specific medications, procedures, or therapies
  • expectations for the course of the condition
  • your opinion or preference

A dislocated patella may go back to its proper place on its own, but if it doesn't, your child's physician will need to gently push the kneecap back into its groove. Your child will receive sedation to remain comfortable and help the muscles around the dislocated joint relax, so the joint can be put back into place more easily.

A dislocation can damage 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 dislocated, the doctor may recommend non-operative treatments.

Exercises will help strengthen the muscles in your thighs, so that the kneecap stays aligned. And, a knee brace will immobilize the dislocated area to promote alignment and healing.

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.

With proper treatment, your child should be able to return to normal activities within one to three months. It is important that your child adhere to the activity restrictions and stretching and strengthening rehabilitation programs to prevent re-injury.

Dislocated Knee | Programs & Services