Simple posterior hip dislocations requiring open reduction is very few and reported approximately 3% of all posterior hip dislocations and we have little comments of the various causes preventing or blocking a concentric reduction following traumatic posterior hip dislocation. In a review of eleven cases of posterior dislocation requiring open reduction, we divided two groups, one is a failed closed reduction group, the other is a nonconcentric reduction group. A concentric reduction was prevented from an inverted limbus or an osteocartilagenous loose body from acetabulum or femoral head.