Irreducible posterior dislocation of the shoulder: MR and CT findings.

Failure to reduce an acute posterior dislocation of the shoulder is rare and is usually due to the interposition of a structure into the joint. In this paper we report the MR and CT findings of a failed reduction due to interposition of a dislocated biceps tendon between the humeral head and anterior glenoid fossa. This was associated with an avulsed subscapularis tendon with its attachment to the lesser tuberosity and a nondisplaced fracture of the humeral neck, findings which were only evident on MR.