Purpose: To inform physicians treating sport injuries of a rare and unique form of patella dislocation, the horizontal intra-articular dislocation of the patella.
Case summary: A young male sustained a direct blow to the upper pole of the patella and came into the emergency room with a knee locked at 75 degrees of flexion. He had an irreducible dislocation of the patella in which the patella was displaced inferiorly, rotated 90 degrees, and locked into the intercondylar notch of the femur.
Discussion: This injury occurs most often in young men and usually requires open reduction. Literature review indicates patients presenting a knee near full extension have a better chance for successful closed reduction, possibly because of a lesser degree of patella entrapment in the intercondylar notch.
Relevance: Most physicians are unaware of this rare type of patella dislocation. It can, however, be recognized by its typical mechanism of injury and clinical features. Unlike the common lateral patella dislocation, on-site reduction is not possible. This injury requires closed and often open reduction under general anesthesia.