This elderly patient had fallen and was struggling to bear weight. What acute sign can you see on this Xray? And what does it mean?
There is a lipohaemarthrosis, which occurs when fat floats on the aqueous fluid in the joint (blood and/or normal synovial fluid). Just to the right of the patella is very distinct perfectly straight line - at right angles to the arrow which points up - telling you that it is truly horizontal; the surface of a liquid layer.
The fat can only have come from Marrow, which under normal circumstances is contained within the bony cortex. So it means there is almost certainly a fracture there somewhere . The ones we tend to miss are tibial plateau fractures (as indeed this was).
You can get a similar appearance from a simple haemarthrosis (as the cells in the fluid settle to the bottom giving a denser layer) but it's generally better to assume there's a break until proven otherwise.
They're surprisingly common, and are mostly missed because we don't look for them.
The Derrifoam Blog
Welcome to the Derrifoam blog - interesting pictures, numbers, pitfalls and learning points from the last few weeks. Qualityish CPD made quick and easy.....