On the first look the most striking abnormality is a calcification adjacent to the medial femoral condyle, corresponding to the location of the MCL. This is however a chronic condition, corresponding to a Stieda-Pellegrini lesion due to prior avulsion injury of the MCL.
The suprapatellar recess is widened, and of reduced transparency, suggestive of articular effusion - considering the acute setting most likely due to haemarthrosis.
A more closer scrutiny reveals a tiny avulsed bone flake next to the the distal aspect of the patella (see magnified key image), corresponding to an avulsion fracture of the patella.
For further evaluation for operative management a noncontrast CT was requested.