Teenager with knee pain after twisting their knee while playing football

Radiograph of patellar dislocation
AP (above left) and lateral (above right) radiographs of the knee show the patella to be dislocated laterally and posteriorly and there is a small knee effusion. AP (below left) and lateral (below right) radiographs of the knee obtained post reduction show the patella now to be in its correct position.

The diagnosis was patellar dislocation.