What is your diagnosis?

This point of care ultrasound demonstrates findings consistent with lipohemarthrosis. Notice the layering within the joint effusion which is indicative of blood as well as fat containing fluid. Echogenic clot and blood components will sink to the dependent portion of the joint, while the fat-containing component will remain superficial to these portions and appear as distinct layering on ultrasound [2,3].

What underlying pathology are you most concerned for?

The presence of lipohemarthrosis within joint fluid is highly concerning for occult intra-articular fracture in the setting of negative radiographs. Fat containing fluid is not a normal finding in the knee joint and should raise suspicion for either tibial plateau fracture or femoral condyle fracture [2,3].

What is your disposition?

Most often these patients will require admission for operative intervention depending on the fracture found.  

• Pearl: Ideally advanced cross-sectional imaging, most likely CT in the emergency department, would better delineate a fracture pattern.  Both tibial and femoral articular fractures often require admission [4,5].

Do you consult orthopedics in the Emergency Department?

After identifying underlying intra-articular fracture, urgent but non-emergent orthopedic consultation is indicated. 

• Pearl: Tibial plateau fractures most often require operative intervention to ensure stability of the articular surface, particularly when there is significant depression or displacement.  These can be classified using the Schatzker scheme [4].  Similarly with femoral condyle fractures, surgical intervention is often indicated.  Contraindications include frail patients or those with significant disqualifying co-morbid conditions [5].  The patient in this case is relatively healthy without contraindications.