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Transient patellar dislocation

Case contributed by Ali Abougazia
Diagnosis almost certain

Presentation

Recent knee trauma. Progressive pain.

Patient Data

Age: 30 years
Gender: Male

Small depressed fracture of the anterior aspect of lateral femoral condyle is noted with surrounding altered marrow signal being of high T2 / PD / STIR and low T1 signals.Similar alteration of medial patellar surface marrow signal is noted with no definite fractures.
Mild thickening and intermediate signal of the ACL near its femoral attachment with no interruption of its fibers.
Intact PCL and collateral ligaments as well as both patellar retinaculae.Normal heights and signal intensity of both menisci with no evidence of meniscal tears.Normal appearance of the articular cartilage.Marked amount of joint effusion is noted with fluid-fluid level.
Normal girth and signal of the peri-articular musculature.

Case Discussion

Bone marrow edema / contusion of medial patellar surface and anterior aspect of lateral femoral condyle with small depressed fracture of the latter, diagnostic of transient patellar dislocation.

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