Sports Medicine

Patellar Instability

Our Pediatric Sports Medicine team put together these videos to provide information for you.

Paul Benfanti, MD

Hi, I'm Dr. Paul Benfanti from Johns Hopkins All Children's Hospital and Children's Orthopedics and Scoliosis Surgery Associates. Today we are going to talk about patellar instability, a common condition that occurs in children and adolescents.

Our bodies are amazing machines and as long as everything lines up properly we don't have any problems. Unfortunately, sometimes things don't line up quite right and problems can occur. This is the case with patellar instability.

The patella or kneecap is a relatively small round bone that has a big job. It connects the powerful quadriceps muscles of the thigh to the tibia or leg bone. The patella glides though a groove at the end of the femur or thighbone. As you bend and straighten the knee the patella glides up and down the groove. Normally the patella fits nicely in the groove and everything goes well. However, if the patella doesn't fit well, or slides out of the groove, patellar instability occurs which can cause pain with the knee cap coming partially or completely out of the groove.

There are many reasons this can happen. The patella can be misshapen and not fit in the groove well. The groove can be shallow or tilted and the patella can slide out. The shape of the leg can be off causing an abnormal pull of the muscles that forces the patella out of the groove. The muscles themselves can be weak on one side of the knee and not the other which pulls the patella out. The tissues or ligaments can be lax (that is you can be loose jointed) and can't hold the patella in. Or, you can simply get bumped on the side of the patella and knock it out of the groove. To make matters worse, the reason can be a combination of these things.

The symptoms of patellar instability vary with its severity. They can be relatively mild such as stiffness after sitting for a long time or pain with climbing stairs or pain around the patella with activities. Or it can be severe, such as having the patella buckle or catch or the patella come completely out.

The diagnosis may or may not be obvious. If the patella came completely out it's a no brainer, but if not it may be difficult to tell exactly why you are having knee pain. A careful examination of your knee and leg will be performed. X-rays and an MRI may be needed as well.

Treatment depends on the severity of the dislocation. If it's completely out, it may have to be put back in if it doesn't pop back by itself. Sometimes cartilage and bone are knocked off the patella or femur when it dislocates and arthroscopic surgery may be needed to remove or fix the pieces. If the patella hasn't dislocated treatment is usually with exercises, physical therapy and a brace. If the patella instability persists surgery may be needed to correct the underlying problem.