Radiologic assessment of reverse shoulder arthroplasty.

The reverse shoulder prosthesis was approved for clinical use in the United States in March 2004. This new prosthesis reverses the normal ball-and-socket relationship of the shoulder joint. As a result of replacement of the glenoid component with a ball and of the humeral head with a socket, the center of rotation is moved distally and medially, allowing more control of shoulder motion by the deltoid muscle. This improved geometric configuration allows shoulder reconstruction in patients who have irreparable rotator cuff damage with secondary arthropathy, pain, and "pseudoparalysis" (ie, inability to lift the arm above the horizontal). Patients experience a significant improvement in range of motion and markedly decreased pain after undergoing reverse shoulder arthroplasty; however, the procedure is associated with a relatively high rate of complications, including dislocation, infection, loosening, malpositioning of the glenoid component or fixation screws, disassembly of the humeral component, periprosthetic fracture, and inferior glenoid impingement leading to scapular erosion. Therefore, it is important that the radiologist be familiar with the normal and abnormal imaging appearances of this new prosthesis.