Superior dislocation of the patella: a pathognomonic finding and review of literature

Abstract

A 59-year-old woman with a painful right knee that became locked in extension after a trivial trauma was seen at the emergency room. This was caused by unloaded hyperextension in bed. She was diagnosed with a superior dislocation of the patella. A closed reduction was performed, but a recurrent episode was seen within a week. An arthroscopy was performed, in which the causative osteophytes were removed. In the 12-month follow-up after treatment, no recurrence was seen. A superior dislocation of the patella is caused by patellofemoral osteophytes that interlock. This can cause a degenerative knee to become locked in extension. Beside interlocking osteophytes of the patella and the distal femur, the superior part of the patella is tilted away from the femur. This is caused by the pull of the patella tendon and the simultaneous relaxation of the quadriceps tendon. This is a pathognomonic finding on radiographs that, to the best of our knowledge, has been identified but not been appreciated as such in previous reports. As illustrated in this report, a superior dislocation of the patella can easily be recognized on physical examination and radiographic imaging alone when familiar with the specific abnormalities. This will reduce unnecessary diagnostic imaging studies and delay in treatment. This case report illustrates a recurrent case of superior dislocation of the patella. We summarize and evaluate previous reports, discuss trauma mechanisms, physical examination, classification, and treatment including recurrent cases. After reading this case report the reader will be able to diagnose a superior dislocation of the patella with near certainty on physical examination and radiographic imaging of the knee alone.