Transient lateral patellar dislocation with osteochondral injury
Pain and swelling of the left knee following recent twist injury few days back.
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Bone marrow edema seen at the medial patellar articular facet and interfacetal ridge with focal osteochondral injury showing a large displaced fragment within the lateral synovial recess (stage IV). Lateral patellar subluxation is also noted.
Associated similar bone marrow edema exhibiting bright signals on STIR WIs is seen at the antero-lateral aspect of the lateral femoral condyle.
Medial patellar retinaculum shows relative thinning with partial fiber disruption and peri-ligamentous edema denoting partial-thickness tear.
Massive synovial effusion showing fluid/fluid level and internal dark signals on different pulse sequences, suggesting hemosiderotic and/or fibrotic deposits (hemarthrosis).
Vastus Lateralis muscle strain is also noted.
Lateral patellar dislocation is a relatively common injury in the pediatric age group, particularly in kids participating in sports.
Images should be scrutinized for the presence of osteochondral injury as this affects the management.