Lateral patellar dislocation

Lateral patellar dislocation refers to lateral displacement followed by dislocation of the patella due to disruptive changes to the medial patellar retinaculum.

Patellar dislocation accounts for ~3% of all knee injuries and is commonly seen in those individuals who participate in sports activities.

Patella dislocation most commonly results from a twisting motion, with the knee in flexion and the femur rotating internally on a fixed foot (valgus-flexion-external rotation) 1.

  • lateral displacement of patella noted on skyline projection
  • joint effusion
  • sliver sign

The following features are noted:

  • medial retinacular abnormalities (ranging from strain to complete disruption) with adjacent periligamentous edema and hemorrhage
  • lateral displacement of patella
  • medial patellar contusion +/- corresponding lateral femoral condyle contusion
  • joint effusion

The presence of an abnormal medial retinaculum should suggest the diagnosis of transient lateral patellar dislocation 1.

The images should be scrutinized for the presence of chondral or osteochondral injury, especially if displaced as an intra-articular body, as this may affect surgical management.

The trochlear groove and patella may have abnormal morphology that predisposes to patellar dislocation.

  • acute ACL tear: no medial patella contusion in this injury
  • direct trauma to lateral knee: normally no patellar contusion 4
Knee pathology

The knee is a complex synovial joint that can be affected by a range of pathologies:

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Article information

rID: 27273
Synonyms or Alternate Spellings:
  • Transient lateral patellar dislocation

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Cases and figures

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  • Case 8: relocated
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  • Case 9: torn medial patellar retinaculum
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  • Case 11
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