Lateral patellar dislocation
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Lateral dislocation of patella
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Lateral patellar dislocation refers to lateral displacement followed by dislocation of the 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 sports 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 oedema and haemorrhage
- lateral displacement of patella
- medial patellar contusion +/- corresponding lateral femoral condyle contusion
- joint effusion
The presence of an abnormal medial patellar 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.
Differential diagnosis
- acute ACL tear: no medial patella contusion in this injury
- direct trauma to lateral knee: normally no patellar contusion 4
-<p><strong>Lateral patellar dislocation </strong>refers to lateral displacement followed by dislocation of the <a href="/articles/patella">patella</a> due to disruptive changes to the <a title="Medial patellar retinaculum" href="/articles/medial-patellar-retinaculum">medial patellar retinaculum</a>.</p><h4>Epidemiology</h4><p>Patellar dislocation accounts for ~3% of all knee injuries and is commonly seen in those individuals who participate in sports activities.</p><h4>Pathology</h4><p>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) <sup>1</sup>.</p><h4>Radiographic features</h4><h5>Plain radiograph</h5><ul>-<li>lateral displacement of patella noted on <a title="Skyline view" href="/articles/knee-skyline-laurin-view">skyline</a> projection</li>-<li><a title="Joint effusion" href="/articles/joint-effusion">joint effusion</a></li>- +<p><strong>Lateral patellar dislocation </strong>refers to lateral displacement followed by dislocation of the <a href="/articles/patella">patella</a> due to disruptive changes to the <a href="/articles/medial-patellar-retinaculum">medial patellar retinaculum</a>.</p><h4>Epidemiology</h4><p>Patellar dislocation accounts for ~3% of all knee injuries and is commonly seen in those individuals who participate in sports activities.</p><h4>Pathology</h4><p>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) <sup>1</sup>.</p><h4>Radiographic features</h4><h5>Plain radiograph</h5><ul>
- +<li>lateral displacement of patella noted on <a href="/articles/knee-skyline-laurin-view">skyline</a> projection</li>
- +<li><a href="/articles/joint-effusion">joint effusion</a></li>
-</ul><p>The presence of an abnormal <a title="Medial patellar retinaculum" href="/articles/medial-patellar-retinaculum">medial patellar retinaculum</a> should suggest the diagnosis of transient lateral patellar dislocation <sup>1</sup>.</p><p>The images should be scrutinized for the presence of chondral or <a 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>- +</ul><p>The presence of an abnormal <a href="/articles/medial-patellar-retinaculum">medial patellar retinaculum</a> should suggest the diagnosis of transient lateral patellar dislocation <sup>1</sup>.</p><p>The images should be scrutinized for the presence of chondral or <a 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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