An elderly warfarinised patient presents after minor shoulder trauma with a painful and swollen left shoulder.
The shoulder joint is distended with fluid. There is layering with the fine echogenic particulate matter settling within the joint, typical of haemarthrosis - as this was proven to be.
Infection could look similar although layering is less common, and particulate matter often not as fine. There is considerable overlap however.
In this case the diagnosis was a clinical one.
Blood that is not flowing often relatively rapidly separates (like in an ESR tube). The cellular material is fine, echogenic and dependent and the serum is anechoic and layers above.
This case was a clinical diagnosis, and as the indication for warfarin was marginal it was reversed and the joint aspirated to the patient's relief.