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Background
The major types of shoulder replacement include anatomic total shoulder arthroplasty (TSA), reverse TSA, and hemiarthroplasty. The incidence of shoulder arthroplasty, especially reverse TSA, is increasing worldwide due to an aging population and improving evidence of beneficial outcomes. As a result, the incidence of associated complications is increasing. Mechanical differences between anatomic TSA and reverse TSA lead to specific associated complications. The specific complications associated with reverse TSA include acromial stress fracture and scapular notching. The primary complication seen with anatomic TSA is glenoid component loosening. It is important for radiologists to be familiar with these particular complications in addition to shared nonspecific complications seen with all shoulder arthroplasties. Findings are often subtle, but are necessary to detect as they may alter management.

Educational Goals / Teaching Points
The initial goal is to review the different types of shoulder arthroplasty, including the components that comprise them and their mechanical differences on surrounding muscular and osseous structures. Photographs of the hardware components will be provided followed by a discussion of normal positioning and radiographic appearance. Next, specific complications of reverse TSA are examined, including scapular notching and acromial stress fractures. Exclusive complications of anatomic TSA will follow, including glenoid component loosening. Subsequently, general complications affecting all shoulder arthroplasties are depicted, including shoulder dislocation, periprosthetic fracture, component failure, small particle disease, heterotopic ossification, and stress shielding. The final teaching point is to understand treatment options for the various complications.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Anatomic TSA preserves the use of the rotator cuff and functions similarly to the original shoulder. Reverse TSA results in depression and medialization of the glenohumeral rotation center. It also eliminates use of the rotator cuff, leaving the deltoid primarily responsible for abduction and elevation of the arm. This causes increased stress on the scapular spine, where the deltoid originates, and leaves the infraglenoid scapula vulnerable to impaction. Multimodality imaging with an emphasis on radiography and CT will be used to illuminate both the specific and general complications of each type of shoulder arthroplasty.

Conclusion
Shoulder arthroplasty complications are increasingly being reported due to increased incidence of shoulder replacement surgery. Findings may be radiographically subtle, but are important to recognize as they may alter management. Familiarity with the underlying mechanics and various types of complications is crucial for the radiologist to improve patient care. This exhibit will provide a review of the shoulder arthroplasty types and a multimodality approach to diagnosis of the major complications.