Home Knee Shoulder Hip Elbow References - Index


References - Index


What is lipohemarthrosis?

Simply put, lipohemarthrosis is the mixture of fat and blood in a joint cavity following trauma. The fat and blood enter the joint from the marrow space through an osteochondral defect at the articular surface of the joint. As fat is less dense than blood, it floats on the surface of the blood collection. With horizontal beam radiography, a fat-fluid level is detected due to differences in attenuation of these two substances. 

Lipohemarthrosis of the knee was first described in 1929. In 1942, radiography was used to identify the fat-blood interface on lateral radiographs of the knee. Lipohemarthrosis of the shoulder was first reported in 1962. Radiographic identification of hip and elbow lipohemarthroses were reported in the 1970's by multiple authors.

Since then, CT and MRI have been used to diagnose lipohemarthrosis, often to identify occult fractures not detected by radiography. CT relies on differences in x-ray beam attenuation by fat and blood, while MRI depicts differences in signal characteristics of tissue (relaxation times). 

Although lipohemarthrosis is not seen in all cases of intracapsular fracture, the presence of a fat-fluid level is nearly diagnostic of a fracture, even when that fracture is radiographically occult.

The purpose of this project is to describe the CT, MRI, and radiographic appearance of lipohemarthrosis of the elbow, hip, knee, and shoulder joints.


AUTHORS:    Sorenson SM, Wolfson K, 

                         Gentili A, Masih S, Seeger LL

                         UCLA School of Medicine




The FBI Sign: CT, MRI, and Radiographic Appearance of Lipohemarthrosis
Copyright 2000-2006 S.M. Sorenson, K. Wolfson, A. Gentili, S. Masih, L.L. Seeger. All rights reserved.