We present a case with a posterior fracture-dislocation in which interposition of the infraspinatus precluded closed reduction by means of standard manipulation. The fractured greater tuberosity included the lesser tuberosity, allowing the infraspinatus to dislocate anterior to the dislocated humeral head and interpose between the humeral head and the glenoid cavity. The infraspinatus constricted the humeral neck together with the teres minor. Traction in the zero-position was thus required for resolution of constriction and subsequent reduction. Computed tomography was useful to demonstrate interposition of the infraspinatus and to plan the treatment.