Lipohemarthrosis of the Knee: Some Fine Points

• The most common types of fracture associated with lipohemarthrosis are tibial plateau and distal femoral fractures.
• However, the majority (> 60%) of patients with tibial plateau fractures actually do not exhibit lipohemarthnosis.
• The majority (65%) of intraarticular fractures are not accompanied by fat-fluid levels and demonstrate only hemarthrosis/joint effusion, possibly due to disturbance of the fat-fluid level by movement, insufficient time for a fat-fluid level to form, rupture of the joint capsule, or poor technique (e.g., improper centering)
• About 10-20 mL of fat and 80-100 mL of blood are thought to be required to form a visible level.
• Most patients with isolated patellar fractures do not exhibit fat-fluid levels.
• The presence of a fat-fluid level in the knee joint is almost always due to intraarticular fracture, although proximal fibular fractures may also be associated with fat-fluid levels if there is a communication between the tibiofibular joint and the knee joint.

References

Lee JH, Weissman BN, Nikpoor N, Aliabadi P, Sosman JL. Lipohemarthrosis of the knee: a review of recent experiences. Radiology. 1989 Oct;173(1):189-91.