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CORR Insights®: Superior Baseplate Inclination Is Associated With Instability After Reverse Total Shoulder Arthroplasty

Reverse total shoulder arthroplasty (RTSA) has proven to be a reliable treatment option for many shoulder problems that previously did not have good solutions. The Food and Drug Administration approved RTSA for treating rotator cuff tear arthropathy, but the procedure also has utility when used off-label for any shoulder conditions where rotator dysfunction or bone loss of the glenoidmay be present. These conditions include rheumatoid arthritis, osteoarthritic shoulders with rotator cuff tears, malunited fractures, glenoid dysplasias, head-splitting proximal humerus fractures, dislocation arthropathy, and arthroplasty which develop rotator cuff pathology leading to pain, loss of motion, and implant loosening [4]. Although patients who undergo RTSA generally are satisfied with their pain relief, increased ROM, and improved function, complications are quite common, occurring in 19% to 68% of patients who undergo the procedure [1, 11]. The most common complications are notching (5% to 96%), dislocation of the prosthesis (2% to 31%), nerve injury (0% to 8%), baseplate loosening (0% to 11%) infection (1% to 10%), fracture (0% to 1%), and component disassociation (0% to 2%) [1, 11]. One of the most difficult complications to treat from this list is instability of the shoulder components, which can take the form of subluxations that spontaneously reduce or dislocations that require a general anesthetic for reduction. Reverse total shoulder arthroplasty dislocations result in pain and loss of function, but 62% can be successfully treated with immobilization alone [10]. For the others, revision is an option, but revision exposes the patient to the risks of infection, stiffness, and decreased function [5]. Recurrent dislocation of RTSA can be a difficult and devastating complication. Although RTSA has been largely successful for most patients, there are patients who still have shoulder pain for which an etiology cannot be ascertained despite extensive evaluations for infection, loosening, stress fractures, nerve injury, and component loosening. Patients may also describe minor but aggravating complications like popping and crepitus. In the current study, Tashjian and colleagues [9] report on patients who have undergone RTSA but continue to feel that the shoulder is unstable or loose. Patients describe the shoulder as clicking, sliding, or “as if the shoulder might come out of the socket” when picking up objects away from their bodies. This complaint is not uncommon; the authors of this study note that 13% of their patients had some sense of instability [9]. The risk factors for prosthetic instability in RTSA have been shown to be related to prosthetic design and revision surgery. The Grammont type of prosthesis may be at greater risk for instability than later designs that have a more-lateral center of rotation and a lower head-neck angle of 135° [3]. Revision surgery from an anatomic This CORR Insights is a commentary on the article “Superior Baseplate Inclination Is Associated With Instability After Reverse Total Shoulder Arthroplasty” by Tashjian and colleagues available at: DOI: 10.1097/ CORR.0000000000000340. The author certifies that neither he, nor any members of his immediate family, have any commercial associations (such as consultancies, stock ownership, equity interest, patent/ licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article. The opinions expressed are those of the writers, and do not reflect the opinion or policy of CORR or The Association of Bone and Joint Surgeons. This CORR Insights comment refers to the article available at DOI: 10.1097/CORR. 0000000000000340. Edward G. McFarland MD (✉), Johns Hopkins University, Department of Orthopaedic Surgery, 4940 Eastern Ave., #A672, Baltimore, MA 21224 USA, Email: emcfarl1@jhmi.edu