[A painful knee that cannot bend].

A 59-year-old woman was seen at the ER with a painful right knee locked in extension. This was caused by unloaded hyperextension in bed. Interlocking patellofemoral osteophytes and a superior patella dislocation tilted away from the femur were seen on the X-ray, which are both pathognomonic signs of a superior dislocation of the patella.