A 32 old male was hit by a car.

There was marked swelling of the knee, but no lacerations were present.

Neurovascular intact, no other injuries.

There is swelling of the soft tissues about the left knee. Notice that the x ray is marked "Horizontal Beam". This means that the knee was horizontal when x rayed. There is a radiolucent area just proximal to the patella. This is caused by fat floating on top of the effusion (blood) in the knee. A lipohaemarthrosis means that a fracture is preset and must be looked for. It may be obvious, or subtle, such as an occult crack in the condyle. In this case an undisplaced plateau fracture was the cause of the fat. A large effusion such as this needs aspiration.

The fluid was aspirated (it was a haemarthrosis, with fat droplets floating on it) and the knee placed in a Robert Jones bandage. The patient was hospitalised. A computer tomogramme showed an undisplaced plateau fracture. This was treated conservatively by means of a plaster cast, put on 5 days later, once the swelling had showed signs of subsiding.