Imaging Case of the Week 338 Answer

The horizontal beam lateral view demonstrates a lipohaemarthrosis (fat-fluid interface). There is no obvious fracture on the frontal view.

The patient subsequently had an MRI scan of knee which revealed an intra articular undisplaced lateral tibial plateau fracture.

The presence of lipohaemarthosis on a knee x-ray indicates presence of an intra articular fracture around the knee. Although sometimes these fracture may not be obvious on a plain film, these patients should be treated as having one and should have orthopaedic follow up.