What abnormalities are present?
There is a large knee effusion and a flake of bone projected adjacent to the tibial spine.
With knee effusion, what is it important to exclude? Is it present here?
The important diagnosis to exclude here is a lipohaemarthrosis. While there is a fat-fluid interface on the lateral radiograph, the appearances are of a large effusion juxtaposed against the fat adjacent to the quad-tendon.
What does the flake of bone adjacent to the tibial spine suggest?
It is highly suggestive of significant ligamentous injury and a likely ACL tear.
There is a large knee effusion and a bone fragment in the joint. No fracture demonstrated. The effusion and bone fragment are highly suggesting of an ACL injury.