Locked lateral patellar dislocation with impaction fracture of patella.

Irreducible lateral patellar dislocation is rare. It has previously been described with rotation around a vertical axis. We describe a case of irreducible lateral patellar dislocation in a 66-year-old lady with an impaction fracture of medial facet of patella locked on the lateral femoral condyle. Closed reduction was unsuccessful and the patient was treated by total knee replacement. Such a case has not been described previously in the literature.