• A 35 years old man
  • Involved in motor vehicle accident
  • complains of painful swelling of left knee
Left knee radiograph in AP and lateral views

Radiographic findings:

  • There is comminuted fracture involving the tibial plateau (white arrows)
  • Extension of fracture lines to articular surface
  • Fracture also seen involving the proximal fibula (yellow arrows)
  • There is fluid level seen at suprapatellar pouch (red arrow)

Diagnosis: Lipohemarthrosis from fracture of tibial plateau


  • Lipohemarthrosis 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. Hemorrhagic fluid is usually homogeneous. If free fat is present, the fluid is not of similar density, and will tend to separate into layers.
  • This is also known as FBI sign (fat blood interface).
  • The fat-fluid level may also be detected with ultrasound, CT or MRI.
  • A lipohemarthrosis is significant because it is an indication of severe injury with tearing of the synovial membrane and presence of an intra-articular fracture – if a fracture is not seen on x-ray, further imaging is required.
Author: radhianahassan