lipohaemarthrosis ultrasound

This 14 year-old female patient fell and sustained a patellar dislocation-relocation injury. There was ongoing pain and swelling. An ultrasound was requested to look for ligamentous injury. No ligamentous injury was identified, however there was a large lipohaemarthosis in the suprapatellar bursa (F = fat; FL = fluid). Note the straight fluid-fluid level. Click on the image for the corresponding plain film (initially and erroneously interpreted as normal by junior Emergency Department staff). There is a large joint effusion with fluid-fluid level indicating a lipohaemarthrosis. There is irregularity of the lateral femoral condyle suggesting an osteochondral fracture.

A lipohaemarthrosis always indicates an intraarticular fracture, most often fractures of the tibial plateau. Thirty-five percent of intraarticular fractures will be associated with a lipohaemarthrosis visible on plain film, whereas 65% will have a simple haemarthrosis. The appearances of lipohaemarthrosis on ultrasound, CT and MRI are described in the literature. Note that a fluid-fluid level may appear on MRI in a simple haemarthrosis – make sure the upper layer drops signal on fat-sat sequences before calling it a lipohaemarthrosis.

Reference: Lee JH et al. Lipohemarthrosis of the Knee: A Review of Recent Experiences. Radiology 1989; 173:189-191

Credit: Dr Laughlin Dawes