Tibial plateau fracture with lipohaemarthrosis.
In addition to the cortical irregularity in the medial tibial plateau (the fracture), there is a large joint effusion, best seen on the lateral view. The joint effusion contains a straight line, representing a fluid-fat level, with the lighter fat from the bone marrow ("lipo") floating above the heavier blood ("haem"). The straight line also reveals that the patient's leg is actually lying on a table and the film was rotated to present the knee in an upright position (the blood is layering dependently).