KidsMD Health Topics

Patellar instability

  • Overview

    The patella, or kneecap, is a small bone that fits into a groove on the end of the thighbone and sits over the knee, allowing it to function properly. When the groove is shallow or an accident happens, the kneecap can slide out of place; this is called patellar instability, or kneecap dislocation. 

    • In some young athletes, the kneecap repeatedly dislocates by itself, slipping back and forth into place over the course of a few days or weeks. This may cause no pain or mild pain.
    • But when the kneecap is pushed out of place because of an accident, it is usually more painful.
    • In both cases, it’s important to see a doctor, because without treatment there can be permanent damage and more pain. So, even though this is a fairly common injury, it’s important to be seen by a doctor, and often an orthopedist. 
    • Most of the time, kneecap dislocation can be treated with physical therapy and a brace, but in more serious cases, your child may need surgery to repair or tighten the surrounding ligaments.
    • Most children—including those who need surgery—are back to sports and other activities in three to four months.

    How Boston Children’s Hospital approaches kneecap dislocation (patellar instability)

    At Boston Children’s Hospital, our doctors specialize in orthopedic care. Our clinical experts lead the country in research and care, and have the pediatric orthopedic expertise to treat the unique needs of children and young adults' musculoskeletal systems.

    Each year, our orthopedic team conducts more than 92,000 patient visits and more than 6,000 surgeries. While assessing knee dislocation (patellar instability), our doctors will do everything possible to get the most precise diagnosis so your child can get back to his life. 

    Patellar instability: Reviewed by Dennis Kramer, MD

    Boston Children's Hospital
    300 Longwood Avenue
    Fegan 2
    Boston MA 02115
    617-355-6021

     



    Boston Children's Hospital at Lexington
    482 Bedford Street
    Lexington MA 02420
    617-355-6021


                  
    Boston Children's Hospital at Waltham
    9 Hope Avenue
    Waltham MA 02453
    617-355-6021


                  
    Children's Hospital Physicians at Good Samaritan Medical Center
    830 Oak Street
    Brockton MA 02301
    617-355-6021


                  
    Boston Children's Physicians South
    Stetson Medical Center
    541 Main Street
    Weymouth MA 02190
    617-355-6021


                  
    Boston Children's North
    10 Centennial Drive
    Peabody MA 01960
    617-355-6021

                  

  • In-Depth


    Causes 

    There are two general ways that kneecap dislocation occurs: 

    • The kneecap dislocates during an accident: If your child gets into an accident during sports or another physical activity, the kneecap may slide out of place quickly and painfully. It will usually go back into place on its own immediately after it slides out.

      After this, your child may feel a lot of pain and experience swelling in the front of his knee, whether he’s sitting or standing. If he tries to walk, he may feel the kneecap catch or slip, and have trouble supporting his weight.
       
    • The kneecap dislocates by itself: If your child’s kneecap slides in and out of place on its own, he should see a doctor within the first few weeks of experiencing symptoms, and should not play through pain.

      Whether his kneecap dislocates once in a while or very often, dislocation can damage the kneecap and the end of the thighbone. Sometimes the injury can become even more painful, and lead to arthritis later in life. 

     

    Signs and symptoms 

    If your child’s knee is bothering him because it buckles, slips off to the side or catches during movement, he may have kneecap dislocation. 

    Other symptoms include:

    • Pain in the front of his knee that gets worse with activity
    • Pain when he’s sitting down
    • Stiffness in the knee
    • Creaking sounds
    • Swelling
  • Tests

    • If your child can walk without causing the knee to dislocate, the doctor will ask him to walk around and to straighten and bend his knee.
    • Then, the doctor will feel around the kneecap area to make sure the bones and muscles feel normal.
    • X-rays may be needed to determine how well the kneecap can fit into the groove.
    • Occasionally, your doctor also may order an MRI to check for ligament tears in the knee.
  • Treatment for kneecap dislocation depends on how serious the injury is, and whether the kneecap will continue to stay in place over time.

    • The goal is to bring the kneecap to its proper place and keep it there.
    • Most of the time, the kneecap will go back into place on its own immediately after it dislocates.
    • Sometimes, the doctor might have to sedate the child so he can use more force to get the kneecap back into place.
    • After the kneecap is back in place, a supportive brace and physical therapy may be enough to fix the problem.
    • Other times, children need surgery to keep the kneecap in place. Both treatment options usually allow the child to return to sports and other activities in three to four months.

     There are two ways that children can be treated for kneecap dislocation: 

    Treatment without surgery

    • If your child's kneecap dislocates during an accident, he should go to the emergency room. Here, the doctor will do an X-ray to see if the kneecap is back in place. Most of the time it will be back in place. 
    • If it is still out of place, the doctor might be able to do place it back in its groove easily, with very little pain, but if it seems more complicated, then he may sedate your child and use more force to get it back in place.
    • After the kneecap is back in place, your child will wear a knee immobilizer, which is a tight but comfortable support placed around the knee to keep it straight.
    • For the next two weeks, he can walk around using the knee immobilizer and crutches, and should go back to the doctor for a check-up.
    • The doctor will look at the knee again, and might give him a more flexible brace that lets the knee bend more, and become stronger.
    • If the kneecap continues to slide out of place, your doctor may do an MRI to check for any tears in the ligament or loose pieces of bone that might have broken off during the dislocation. 
       

    Surgical treatment

    • If an MRI shows loose cartilage or bone, or tears in the ligaments, your child might need surgery to tighten the ligaments and make the area around the knee stronger.
    • After surgery, your child will probably wear a brace and walk with crutches for six weeks, and go to physical therapy for two to three months.
    • Once the pain and injury are gone, children usually can return to sports.


    Coping and support 

    At Boston Children's Hospital, we understand that a hospital visit can be difficult, and sometimes overwhelming. If your child is admitted to the hospital for an extended stay, or needs more extensive care, your family may want to take advantage of the Center for Families, which can help connect you with resources, should you need them: 

  • Research & Innovation

    While most surgeries for kneecap dislocation focus on repairing or tightening the ligaments, new research has allowed doctors to surgically transplant a healthy tendon from the patient’s hamstring to the knee for better stabilization.

    This method of treatment is already available at Boston Children’s.

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