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Patellar dislocation

Last updated: March 21, 2019

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The patella is the largest sesamoid bone in the human body. It is located within the quadriceps femoris tendon and acts as a fulcrum to increase the force exerted on the tibia. In the case of patellar dislocation, the patella slips out of the trochlear groove, often laterally. Patellar dislocation usually occurs spontaneously following torsion of a semiflexed knee and is typically the result of underlying biomechanical abnormalities such as hyperlaxity of the medial patellofemoral ligament, high-riding patella, genu valgum, and/or patellofemoral dysplasia. Less frequently, trauma and congenital defects cause dislocation of the patella. The diagnosis is usually apparent after physical examination. X-ray, MRI, and arthroscopy are used to identify additional injuries. Patellar dislocations can usually be reduced by careful manipulation. In some cases, arthroscopy is also used therapeutically to perform surgeries that stabilize the patella.

Epidemiological data refers to the US, unless otherwise specified.

Lipohemarthrosis in the presence of normal knee x-rays indicates an osteochondral lesion!

  • Conservative therapy: indicated if no osteochondral fragment is present
    1. Patellar reduction by gently extending the knee while applying a caudally and medially directed force on the lateral edge of the patella
    2. Reduction should be followed by immobilization of the knee in extension for three weeks.
    3. Physiotherapy to strengthen the quadriceps femoris muscle: to prevent recurrent disclocation
  • Surgical therapy: generally indicated for complicated cases with associated fractures

We list the most important complications. The selection is not exhaustive.