Lateral patellar dislocation
Updates to Article Attributes
Lateral patellar dislocation refers to lateral displacement followed by dislocation of patella due to disruptive changes to the medial patellar retinaculum.
Epidemiology
Patellar dislocation accounts for ~3% of all knee injuries and is commonly seen in those individuals who participate in sport activities.
Pathology
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.
Radiographic features
Plain radiograph
- lateral displacement of patella noted on skyline projection
- joint effusion
- sliver sign
MRI
The following features are noted:
- medial retinacular abnormalities (ranging from strain to complete disruption) with adjacent periligamentous edema and haemorrhage
- 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 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.
Differential diagnosis
- acute ACL tear: no medial patella contusion in this injury
- direct trauma to lateral knee: normally no patellar contusion 4
-<li>medial retinacular abnormalities (ranging from strain to complete disruption ) with adjacent periligamentous edema and haemorrhage</li>- +<li>medial retinacular abnormalities (ranging from strain to complete disruption) with adjacent periligamentous edema and haemorrhage</li>
-</ul><p>The presence of an abnormal medial retinaculum should suggest the diagnosis of transient lateral patellar dislocation <sup>1</sup>.</p><h4>Differential diagnosis</h4><ul>- +</ul><p>The presence of an abnormal medial retinaculum should suggest the diagnosis of transient lateral patellar dislocation <sup>1</sup>.</p><p>The images should be scrutinized for presence of chondral or <a title="Osteochondral injury staging" href="/articles/osteochondral-injury-staging">osteochondral injury</a>, especially if displaced as an intra-articular body, as this may affect surgical management.</p><p>The trochlear groove and patella may have abnormal morphology that predisposes to patellar dislocation.</p><h4>Differential diagnosis</h4><ul>
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