Knee (Patella) Instability

This information is useful for children and adults
Why Yale Medicine?
  • Corrective surgery for kneecap instability is complex, but our doctors' expertise treating difficult cases maximizes success and reduces the risk of complications.
  • Our doctors have expertise with traumatic injuries in which kneecap dislocation or instability difficult to diagnose.
  • We provide highly specialized care for all kinds of knee injuries, including ACL damage and injuries affecting multiple ligaments, among other problems.

It can occur because of a fall while playing sports or, sometimes, for no particular reason at all. The knee buckles and feels unstable. There may be an accompanying popping sound. If this happens to you, it's possible that your patella (or kneecap) has slipped out of place. Even if slips back and all seems well it's important to see a doctor. 

Treating kneecap  instability can be complex. Yale Medicine Orthopaedics & Rehabilitation surgeons work with the most difficult cases. They draw upon their experience to provide patients with the best outcomes possible, especially when surgery is involved. “That’s what we offer at Yale Medicine.” says knee specialist Michael Medvecky, MD, chief of Yale Medicine Sports Medicine and a professor at Yale School of Medicine.

According to Dr. Medvecky, when the leg bends, the kneecap should slide smoothly into an indentation (like a valley) in the femur (leg bone). There are several potential reasons why this doesn't always work as it should, and why the problem becomes recurrent. 

“Some people have mechanical factors that predispose them to having a loose kneecap,” Dr. Medvecky says, “while others have instability that is caused by a traumatic injury, such as in sports, that distorts the knee and makes it unstable.”

Patellar (or kneecap) instability most commonly occurs in people in their teens and 20s. Because of their wider hips, women are more likely to experience knee instability due to misalignment. In a person with a tendency toward misalignment, the problem can develop from overuse and/or the stress the knees experience when a person is overweight or obese. A kneecap that has popped out of place at least once is more likely to do so again than it is in a person who has never had a problem.