Case 8
History
Young male with “popping sound” after playing basketball.
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Diagnosis
Patellar dislocation.
Findings
Images demonstrate contusions of the medial facet of the patella (fig 1) and anterolateral femoral condyle (fig 2). There is a patellar chondral defect at the medial facet with minimal change at the medial retinaculum (fig 1). There is a nondisplaced linear fracture patellar fracture seen best on the most anterior coronal image (fig 3).
Discussion
MRI examination frequently suggests the clinically unexpected diagnosis of patellar dislocation. The patient presents to the clinician with acute knee pain. Patellar dislocation may be only momentary and, since the patella often reduces rapidly, the patient often may be unaware of the exact character of the event in up to 50 percent of cases.
Characteristically at MR, there is a contusion seen in the anterior lateral femoral condyle caused by impaction of the patella on the femur from patellar dislocation or reduction. A kissing contusion of the medial patellar facet is often, but not always, seen. There is frequently an associated injury of the medial retinaculum. An associated medial patellar facet significant chondral injury is an indication for arthroscopy. Without chondral injury or significant fracture, conservative treatment is usually offered.
Reference
Kaplan PA, Helms CA, Dussault R, Anderson MW, Major NM. Musculoskeletal MRI. W.B. Saunders Co; Philadelphia, PA. 2001; 282-283.
Submitted by: Steven Young, MD
Reviewed by: Paul Clifford, MD
