Patellar (Knee) Instability/Dislocation


Also called patellar subluxation, patellar instability occurs when the kneecap does not slide centrally within its natural groove in the femur (thigh bone). It may even move completely out of its normal location – this is called patellar dislocation.

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Causes & Risk Factors

The patella is another term for kneecap. It is held in place by ligaments and tendons. When there is a severe force against the kneecap, the patella can slide to the side of the knee joint.

The following are at risk for these kinds of injuries:

  • Active teenagers and young adults ages 14-20
  • Participants in contact sports like rugby, football or lacrosse
  • Athletes who experience simple falls during activities such as gymnastics, dancing or cheerleading

Girls experience knee dislocations more often than boys. A family history of knee instability and dislocation is another risk factor.

Symptoms & Types

There are 2 types of patellar injuries: subluxation or dislocation, depending on how far the patella moves away from its normal position.

Symptoms of patellar subluxation or dislocation include:

  • Knee pain or swelling
  • Inability to bend the knee due to pain or locking of the joint
  • Redness or warmth over the knee
  • Pus or fluid from any abrasion on the knee
  • Inability to bear weight on the injured leg due to pain
  • Feeling like the knee is wobbly and might give out

Diagnosis & Tests

Your child’s doctor will examine the knee for:

  • Fluid in the knee
  • Limited range of motion
  • Difficulty in bearing weight

Patients with significant pain or recurrent dislocation may require surgery. In these cases, your child’s doctor will look into the knee with an arthroscope (a tiny camera on a skinny tube inserted into the knee through a small hole). This procedure allows the surgeon to assess the damage to the knee.

Treatment & Care

Sometimes the patella moves back in place by itself. Otherwise, a doctor will have to move it manually. It can take about 4-6 weeks for the tissues to heal. Therefore, the knee must be protected during this time to prevent another injury.

In some cases, your child’s doctor will recommend surgery. This may be arthroscopic (using tiny cameras) or open surgery so the kneecap can be realigned.  The 3 most common types of surgery are:

  1. Releasing tissue (lateral release): This is done with either open surgery or arthroscopy. The tissues that pull on the kneecap are cut to allow it to move into the proper place. Releasing a plica band (a thick fibrotic band that can be found in several areas of the knee) may also reduce pain.
  2. Shifting the attachment of the patellar tendon (patellar realignment): This procedure improves tracking and is done using open surgery. Part of the tendon and the underlying bone are moved to a new location.
  3. Reconstruction of medial patellofemoral ligament (MPFL): When the kneecap dislocates, the normal ligaments holding the kneecap in place are torn.  This procedure restores the ligament function. 

Living & Managing

Once patellar subluxation or dislocation has occurred, there is an increased risk that it may happen again. This is due to weakened tissues around the kneecap. When playing sports that have a high risk of knee injury (soccer, skateboarding, football, skiing, snowboarding, skating, etc.), athletes should wear a protective knee brace and/or a padded shield. These devices add support to your child’s knee and reduce risk of further injury.