Case 33 - 20 year old male with left knee injury while playing soccer; patient felt a "pop"
20 year old male with a left knee injury while playing soccer; the patient felt a "pop."
- The patient has a moderate joint effusion. Additionally, we can see a fluid-fluid level, however, the signal characteristics of the layering fluid are different from the cases of hemarthrosis we've seen previously. This layering material is bright on T1 and PD images, but suppresses on all of the fat saturated sequences, indicating fat! But what is fat doing inside the joint? We call this a lipohemarthrosis and it indicates an interarticular fracture.
- We also have a new pattern of kissing contusions, with marrow edema in the medial patella and lateral femoral condyle. One can imagine that for the two affected bones to touch, the patella would need to move laterally; indeed, this pattern is pathognomonic for a transient patellar dislocation. There's mild associated impaction fractures of the femoral condyle and patella, which account for the lipohemarthrosis.
- We do not see any associated injury to the menisci or cartilage, although there is a partial tear of the medial patellar retinaculum.
This pattern of kissing contusions is characteristic of transient patellar dislocation, which typically occur laterally. It's important to inspect for an associated chondral injury, as well as the integrity of the medial patellofemoral ligament. A high-grade tear of the medial patellofemoral ligament and patellar retinaculum can predispose to additional episodes of patellar dislocation.
Accession: CL0045
Study description: MR JOINT LOWER KNEE-LT