Little attention has been paid to the various causes preventing or
blocking a concentric reduction following traumatic dislocation of the hip
without apparent fracture. In a review of fifty-four dislocations, nine
required open reduction after either a failed attempt at closed reduction
or a non-concentric reduction. The factors preventing closed reduction
included the femoral head buttonholed through the capsule and the
piriformis muscle displaced across the acetabulum. A concentric anatomical
reduction was prevented because of an inverted lumbus or an
osteocartilaginous loose body in the acetabulum. Guidelines for diagnosis
and treatment are discussed.