Occasionally, the patella can slide too far to one side and can dislocate.

INJURY
Patellar Dislocation and Instability in Children

ALSO KNOWN AS
Unstable Kneecap

ABOUT
A normal kneecap fits into a concave surface (trochlear groove) in the femur (thighbone) where it joins the muscles in the front of the thigh to the tibia. The kneecap moves up or down as you bend or straighten the leg. Occasionally, the patella can slide too far to one side and can dislocate. The patella can slip back in place by itself but will still need treatment.

COMMON INJURY
In children there are many ways that the patella can become unstable or dislocate. Many times because of an abnormality in the structure such as a shallow trochlear groove, looser ligaments in children that make the joint more flexible, children with cerebral palsy or down syndrome, and rarely children can be born with an unstable kneecap. In normal knee structures, direct force can cause the kneecap to be dislocated.

DIAGNOSIS
In general symptoms include, pain, swelling, knee instability, deformed knee appearance, child’s fear of running or changing direction, and hearing the popping sound when it dislocates. The doctor will do a physical exam to evaluate the knee and discuss the symptoms and activities. X-rays and/or MRI (magnetic resonance image) can aid in diagnosis.

NON SURGICAL TREATMENT
Even if the kneecap slides back into place you should take your child to the doctor as soon as you can. If the kneecap is out of place you should take your child immediately to the emergency room where they can put it back into place (reduction). Treatment methods consist of immobilization with a brace, crutches to keep weight off of the knee, and physical therapy. Continuous exercises that strengthen the quadriceps are suggested to prevent future dislocations.

SURGICAL TREATMENT
Depending on the cause of the unstable kneecap surgery may be done to reconstruct the ligaments holding the patella in place with arthroscopic surgery.

Patellar Dislocation and Instability in Children
(Left) The patella normally rests in a small groove at the end of the femur called the trochlear groove. (Right) As you bend and straighten your knee, the patella slides up and down within the groove.
Image courtesy of AAOS