KidsMD Health Topics

Dislocated Patella

  • Overview

    A dislocated patella 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."

    How Boston Children's Hospital approaches dislocated patellas

    If your child is physically active and participates in contact sports and other activities, he or she may be more prone to having a dislocated patella. While our team of doctors is committed to helping stabilize and re-strengthen your child's knee, they're also interested in helping active young people prevent these injuries in the first place. Past efforts included a sports clinic to teach young athletes about how to take proper care of their knees.

    Boston Children's Hospital
    300 Longwood Avenue
    Fegan 2
    Boston MA 02115


    Boston Children's at Waltham
    9 Hope Avenue
    Waltham MA 02453

    Boston Children's at Lexington
    482 Bedford Street
    Lexington MA 02420

    Boston Children's North
    10 Centennial Drive
    Peabody MA 01960

    Boston Children's Physicians South
    Stetson Medical Center
    541 Main Street
    Weymouth MA 02190

    Children's Hospital Physicians at Good Samaritan Medical Center
    830 Oak Street
    Brockton MA 02301


    Boston Children's Hospital  
    319 Longwood Avenue
    Boston MA 02115


  • In-Depth

    Who is at risk for a dislocated patella?

    • Active teenagers and young adults from the ages of 14-20 years old
    • Participants of contact sports, such as football
    • Those suffering simple falls from a wide variety of activities such as gymnastics, dancing, or cheerleading
    • More girls experience knee dislocations than boys do
    • A family history of knee instability that leads to dislocation occurs in one fourth of patients with this problem.

    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.

    • If the groove is uneven or too shallow, the kneecap could slide off, resulting in a partial or complete dislocation.
    • Laxity of the ligaments surrounding the knee
    • 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.

    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 doctor for a diagnosis.

  • Tests

    How does a doctor know my child has a dislocated patella?

    An evaluation should be performed 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.

    During the examination, the physician may ask your child to walk around or to straighten and bend the 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 the knee:

    • 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.
  • 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 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 grove. Your child will receive sedation to help him/her 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.
    • 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 the 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/or stretching and strengthening rehabilitation programs to prevent re-injury.

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