UMEM Educational Pearls

Title: Fall down stairs with knee pain

Category: Orthopedics

Posted: 7/12/2025 by Brian Corwell, MD (Updated: 9/19/2025)
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What do you see?

There is no clear fracture line

Much like ice floats on water, fat also floats on water/blood because it is less dense.

An intra-articular fracture may allow for blood and fat to exit the bone marrow and settle in the joint space.

This is called a lipohemarthrosis.

Best seen with a cross-table horizontal lateral view x-ray.

Go back to the image and examine the supra patellar pouch.

Most commonly seen in the knee in presence of a tibial plateau fracture.

Seen in approximately 1/3rd of tibial plateau fractures

If you see this without a clear fracture, consider CT of knee which can help detect the hidden fracture.

Remember the DDx of knee hemarthrosis with negative plain films:

Meniscal tear, ligament tear (usually ACL), patellar dislocation and osteochondral fracture.

Except for meniscal tearing (>6h) these other pathologies cause rapid onset swelling (<2h).