Last Updated on Jun 26, 2019

What is Patellar Instability?

Patellar instability is a common knee injury occurring in pediatric and adolescent population. This clinical problem affects about 5-25 people per 100,000.

This condition is also known as patellar or kneecap dislocation or unstable kneecap.

The patella is also known as kneecap. It is connected to the femur (thighbone) and tibia (shinbone) by ligaments and tendons. The patella fits into a groove or space in the knee joint, at the end of the femur. As the knee is bent, the patella slides up and down.

Patellar instability occurs when the patella moves outside of this space and results in patellofemoral pain in front of the knee. It is most often a result of knee injury.

What are the Types of Patellar Instability?

There are two types of patellar instability:

  • Traumatic Patellar Dislocation: In this type, the patella gets pushed out of the groove. The most likely cause is an injury to the knee
  • Chronic Patellar Instability: The patella or kneecap slides slightly out of the groove. It is also known as patellar subluxation (partial dislocation) and can occur due to overuse of the knee joint

What are the Causes of Patellar Instability?

Some of the causes of patellar instability include the following:

  • Hypermobility
  • Weakness or muscle imbalance
  • Obesity
  • Poor muscle flexibility and strength
  • Uneven groove or space in femur (thighbone)
  • Defect in alignment of bone or kneecap
  • Dislocation or injury
  • Soft tissue abnormality such as torn patellofemoral ligament
  • Previous injury


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  2. Knee Instability: The Problem and How to Prevent It - Debilitating Diseases - (
  3. Sanchis-Alfonso V. How to Deal with Chronic Patellar Instability: What Does the Literature Tell Us? Sports Health. 2016; 8(1): 86-90. - (
  4. Tanner SM, Garth WP Jr, Soileau R, Lemons JE. A Modified Test for Patellar Instability: The Biomechanical Basis. Clin J Sport Med. 2003; 13(6): 327-38. - (
  5. Patellar Instability and Patellofemoral Pain - Gillette Children’s Specialty Healthcare - (
  6. Patellar Instability (Kneecap Dislocation) - Rady Children’s Hospital San Diego - (
  7. Colvin AC, West RV. Patellar Instability. J Bone Joint Surg Am. 2008; 90: 2751-62. - (
  8. Patellar Instability - Mayo Clinic - (
  9. Patellar Dislocation and Instability in Children (Unstable Kneecap) – OrthoInfo - (

Latest Publications and Research on Patellar Instability

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