Patellar (kneecap) instability

Patellar instability

In this condition the patella doesn't rest in the groove at the lower end of the thighbone (femur) where it should


The patella is a very important part of your knee joint forming part of the extensor mechanism. This is the chain of structures at the front of your leg that provide the ability for the knee to straighten. Patellar instability refers to a knee cap that moves out of position.

Need to know

  • Symptoms of patellar (kneecap) instability icon plus

    Symptoms may include: 

    • Intense pain across the front and side of your knee and a sensation of something ‘giving way’ or ‘popping out’ 
    • A visible deformity of the knee owing to the patella moving out of position. This is usually to the lateral side of the knee
    • There may be a rapid onset of swelling within the first couple of hours after injury
    • You may have recurrent episodes of dislocation in which the patella moves out of position more easily and can go back into its original position with certain knee movements, usually on straightening the knee
  • Diagnosis icon plus

    Your consultant will perform a physical assessment of your knee to diagnose patellar instability. Further investigation generally involves MRI or CT scanning to evaluate the medial patello-femoral ligament and obtain a detailed understanding of the anatomy and degree of articular cartilage damage sustained.
  • Potential treatment options icon plus

    Treatment depends on the severity of your condition and the impact it has on your day-to-day life. It may include:

    • Physiotherapy rehabilitation
    • Activity modification
    • The use of knee supports
    • Surgery

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This content is intended for general information only and does not replace the need for personal advice from a qualified health professional.
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