Irreducible traumatic posterior dislocations of the hip

Posterior dislocation is the most common form of traumatic dislocation of the hip. It is usually the result of severe force applied to the flexed knee of a sitting occupant of a car involved in a high-speed accident. Closed reduction is usually successful; however, failed or irreducible dislocations occur in 3–16% of patients and may be complete or incomplete. We discuss three patients in whom closed reduction was unsuccessful, each with a different cause: buttonhole tear of the posterior capsule, interposition of the piriformis muscle, and dislodgement of an osteocartilaginous fragment into the hip joint.