What is lipohemarthrosis associated with a tibial plateau fracture?

What is Lipohemarthrosis with Tibial Plateau Fracture?

Lipohemarthrosis is a pathognomonic radiographic sign of intra-articular fracture, appearing as a fat-fluid level in the knee joint that indicates bone marrow fat has leaked into the joint space following a tibial plateau fracture. 1

Pathophysiology and Clinical Significance

Lipohemarthrosis occurs when an intra-articular fracture disrupts the bone marrow cavity, releasing fat globules into the joint space where they mix with blood from the fracture. The fat, being less dense than blood, rises to create a characteristic layered appearance on imaging 1. This finding is highly specific for intra-articular fracture and serves as a critical indirect sign when fractures may not be immediately obvious on standard radiographs 2.

Key Clinical Points:

• Lipohemarthrosis is frequently seen with tibial plateau fractures and indicates the fracture extends into the joint surface 1
• The finding has high diagnostic value: ultrasound detection of lipohemarthrosis shows sensitivity and specificity of 94% for acute intra-articular fractures 1
• In one MRI study of acute tibial plateau fractures, 41% demonstrated characteristic features of lipohemarthrosis, while 59% showed simple joint effusions 3

Radiographic Detection

The optimal method to visualize lipohemarthrosis is a cross-table lateral radiograph with a horizontal beam, obtained with the knee at 25-30 degrees of flexion 1. This technique allows the fat to separate and layer above the blood, creating the diagnostic fat-fluid level in the suprapatellar bursa.

Imaging Considerations:

• Standard lateral views may miss lipohemarthrosis if not obtained with horizontal beam technique
• The appearance can vary based on suprapatellar anatomy—a well-developed suprapatellar plica can create a "double fat-fluid level" 4
• Ultrasound can also detect lipohemarthrosis and may be useful when radiographs are equivocal 1, 5

Associated Injuries

When lipohemarthrosis is present with tibial plateau fracture, there is a very high likelihood of associated soft tissue injuries. MRI studies show that 97% of patients with acute tibial plateau fractures have evidence of internal derangement 3:

• Tibial collateral ligament injuries: 55%
• Lateral meniscus tears: 45%
• Anterior cruciate ligament injuries: 41%
• Fibular collateral ligament injuries: 34%
• Posterior cruciate ligament injuries: 28%
• Medial meniscus tears: 21%

Clinical Management Algorithm

When lipohemarthrosis is identified on radiographs with tibial plateau fracture:

1. CT imaging is frequently performed next for fracture classification and characterization of severity 1

   • CT shows 100% sensitivity for tibial plateau fractures (vs. 83% for radiographs) 1
   • Helps predict ligamentous and meniscal injuries based on degree of articular depression 1

2. MRI should be obtained to evaluate for soft tissue injuries given the high rate of associated ligamentous and meniscal damage 1

   • MRI is superior for detecting bone marrow contusions, occult fractures, and all soft tissue injuries 1
   • The degree of articular surface depression on CT can help determine when MRI is indicated 1

Common Pitfall:

Do not assume an isolated bony injury when lipohemarthrosis is present—the finding mandates evaluation for associated soft tissue injuries that will significantly impact surgical planning and long-term outcomes 3, 6.