Well well!
Its all makes sense.
I think we were on the money with this one.
The ultrasound was never going to make the final diagnosis, but the presence of a small haemarthrosis triggered the investigation of an intra-articular derangement and bingo, the MRI has found exactly that.
I do like these sort of cases where ultrasound plays a pivotal role in pressing for further cross sectional imaging and the other modalities justify our concern.
Great work.
Steve.