This knee x-ray shows a comminuted intra-articular tibial plateau fracture and a fat-fluid level in the suprapatellar pouch consistent with a lipohaemarthrosis.

Lipohaemarthrosis results from an intra-articular fracture when fat and blood from the bone marrow is extruded into the joint space. It is most commonly seen in the knee but has also been described in the shoulder, elbow and hip. On x-ray the fat-fluid level is seen with a horizontal beam. The fat-fluid level may also be detected with ultrasound, CT or MRI. A lipohaemarthrosis is significant because it indicates the presence of an intra-articular fracture – if a fracture is not seen on x-ray, further imaging is required.

Reference: Costa DN et al. Sonographic and CT Findings in Lipohemarthrosis. American Journal of Roentgenology 2007;188:W389

Credit: Dr Donna D'Souza