Dislocation of the Kneecap

The patella (kneecap) is a bone that covers the knee joint and protects it. Its main job is to help the quadriceps (front thigh muscle) complete the action of straightening your leg. Though the patella is movable, it stays in place because it sits on a groove at the end of your femur (thighbone). If the patella moves out of this groove, an injury called patella instability occurs.

Patella instability is also called kneecap dislocation. There are two types:

  • Traumatic patellar dislocation.This is when the kneecap moves completely out of the groove. Traumatic patellar dislocation can occur if you suddenly change direction while playing a sport or being active.
  • Chronic patellar instability. Also called patellar subluxation, this is when the kneecap partially slides out of the groove. Injury to the ligaments or muscles surrounding the knee can cause chronic patellar instability.

Symptoms, Diagnosis and Outlook

With patella instability, the kneecap usually moves toward the outside of your leg. Other signs and symptoms include a deformed-looking knee, difficulty straightening your leg (or you can’t straighten it), knee pain and knee swelling.

Untreated patella instability causes damage to the knee joint and increases your risk for osteoarthritis, making it important to see your doctor for a diagnosis even if the pain isn’t severe. He or she will perform a physical exam and order an X-ray to look at the location of the kneecap.

With the right treatment and rehabilitation, the function of your knee can be restored. Mild cases of patella instability can heal with a few weeks of rest and physical therapy. Repeat cases and severe cases that cause damage to the cartilage or ligament often require surgery.

Experts in Care

Meet our doctors, view their profiles and select the one that’s right for you.

Find a doctor near you

Why Choose Penn State Health for Care

Top-Ranked by U.S. News & World Report

Penn State Health includes the Milton S. Hershey Medical Center, ranked as one of the best orthopedic providers in the country by U.S. News & World Report. This honor was earned because our doctors consistently deliver exceptional patient care and outcomes through their commitment to advanced treatments, translational research and provider training.

Coordinated, Specialized Care Through a Dedicated Institute

Our orthopaedic specialists work together through our dedicated Penn State Bone and Joint Institute. There, they focus on providing you with multidisciplinary, tailored care and state-of-the-art treatments and technologies. This produces the highest-quality patient outcomes. All physicians at the institute are fellowship-trained and subspecialize in additional niche areas of orthopaedics, including arthritis care and joint arthroplasty (joint replacement surgery).

Designated as a Blue Distinction® Center

Penn State Bone and Joint Institute is a Blue Distinction Center for Knee and Hip Replacement. This superior designation from BlueCross BlueShield is only given to health care facilities and providers that stand out for their expertise in delivering specialty knee and hip replacement care. Our surgeons specialize in a range of pain-relieving procedures, including partial knee replacement, total joint arthroplasty, joint preservation surgery and complex revision surgery. They perform more than 1,000 joint replacement procedures every year.

Confidence in Treatment Through Education

We developed a special joint replacement education website just for patients undergoing joint arthroplasty. The website takes you step by step through the joint replacement process. From things to consider before choosing surgery to recovery after surgery, you’ll find the information you need to help you feel confident in your decision to undergo joint replacement.

Advancing Orthopaedic Medicine Through Research

The doctors and researchers in our Center for Orthopaedic Research and Translational Science at the Milton S. Hershey Medical Center are committed to advancing our field through scientific discovery and education. As the only academic medical center in central Pennsylvania, Hershey Medical Center is a national leader in research, in partnership with Penn State College of Medicine, and on the leading edge of new treatment options, including clinical trials.

Support Groups

Support groups provide an opportunity to share your feelings and connect with other patients and caregivers who are experiencing similar struggles.

Learn more about support groups offered

Convenient Locations

Find the care your family needs, close to home, at one of our many locations throughout central Pennsylvania.

Find a location near you