Childen's Hospital Boston 300 Longwood Avenue
Boston, MA 02115
(617) 355-6000
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My Child Has:
Dislocated Patella
Programs that treat this condition
General Orthopedic Program  
What is a dislocated patella?
A dislocated patella occurs when the kneecap (patella) pops out from its normal position. This can occur as the result of force or, is more often related to a developmental condition that leads to an improper alignment of the kneecap with the thighbone (femur). This is sometimes called "unstable kneecap."
What causes a dislocated patella?
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 (femoral groove or sulcus) at one end to accommodate the moving kneecap.

In a normal knee, the kneecap fits nicely in the groove. But if the groove is uneven or too shallow, the kneecap could slide off, resulting in a partial or complete dislocation. Other problems that could predispose your child to knee dislocation are laxity of the ligaments surrounding the knee or a sharp blow to the kneecap, as in a fall, could also pop the kneecap out of place, but this occurs in only a minority of cases.

A family history of knee instability that leads to dislocation occurs in one-fourth of patients with this problem.

Whom does a dislocated patella most often affect?
Most dislocations first occur in active teenagers and young adults from the ages of 14-20 years old. Often, contact sports like football are commonly involved, although a significant number of dislocations occur from simple falls or a wide variety of activities such as gymnastics, dancing, or cheerleading. More girls experience knee dislocations than boys do.
What are the symptoms of a dislocated patella?
The following are the most common symptoms of a dislocated knee. However, each child may experience symptoms differently. Symptoms may 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.
The symptoms of a dislocated knee may resemble other conditions or medical problems. Always consult your child's physician for a diagnosis.
How is a dislocated patella diagnosed?
An evaluation should be performed by a pediatric orthopedic surgeon. During the examination, the physician will obtain a complete medical history of your child and ask about how the injury occurred.

During the examination, the physician may ask your child to walk around or to straighten and bend your knee. He or she may carefully feel the area around the kneecap and take 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. The following imaging procedures may be used to see how the include:

  • x-ray - a diagnostic test that uses invisible electromagnetic energy beams to produce images of internal tissues, bones, and organs onto film.

  • magnetic resonance imaging (MRI) - a diagnostic procedure that uses a combination of large magnets, radiofrequencies, and a computer to produce detailed images of organs and structures within the body.
Treatment
Specific treatment for a 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 reduce spontaneously; meaning the kneecap goes back to its proper place on its own. However, for those dislocations that do not go back into place, your child's physician will need to gently push the kneecap back into its grove. Your child will receive sedation to help him/her remain comfortable before the procedure. Sedation will also 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 off track (subluxated), the doctor may recommend nonoperative treatments, such as exercises and braces. Exercises will help strengthen the muscles in your thighs so that the kneecap stays aligned.

A stabilizing brace may also be prescribed. This brace immobilizes the dislocated area to promote alignment and healing and protects the area from motion or use.

With the proper treatment, your child should be able to return to normal activities within one to three months.

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.

Additional recommendations may include:

  • activity restrictions (while the dislocation heals)
  • crutches/wheelchair (to enable your child to move around during healing)
  • physical therapy (to stretch and strengthen the injured muscles, ligaments, and tendons. Cycling may be recommended as part of the physical therapy.
Long-term outlook after a dislocated patella:
With the proper treatment, the long-term outlook for a dislocated knee is very favorable. It is important that your child adhere to the activity restrictions and/or stretching and strengthening rehabilitation programs to prevent re-injury.
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