Irreducible dislocation of the knee.

Irreducible knee dislocation is a rare injury. This case report describes a knee dislocation in a 39-year-old male U.S. Army noncommissioned officer who was injured while playing in a softball game. Arthroscopy showed the medial collateral ligament and capsule to be locked in the intercondylar notch, covering the medial femoral condyle. Arthrotomy and open reduction were required. Staged posterior cruciate ligament reconstruction using patellar tendon autograft was later performed. Review of the magnetic resonance imaging scan showed the irreducible lesion. The diagnostic clinical and radiographic features of this unusual injury are described.