Systematic review of prevalence, risk factors, and management of instability following reverse shoulder arthroplasty

BACKGROUND: Since its approval for use, reverse shoulder arthroplasty (RSA) has become the primary treatment for cuff tear arthropathy, with indications expanding more recently to include revision fracture, osteoarthritis with significant glenoid bone loss, tumor, and chronic instability. Instability is a well-described postoperative complication, occurring in 1to 31% of relatively small cohorts and case series. Given the relative infrequency of instability, there remains a need for a comprehensive review of instability with a focus on risk factors and management. Our goal of this systematic review is to describe the prevalence, risk factors, and management strategies for instability following RSA. METHODS: A systematic review of the PubMed, EMBASE, MEDLINE, Scopus, and Cochrane Library databases was performed according to PRISMA guidelines. Inclusion criteria included primary RSA cohorts ≥ 100 patients, revision RSA cohorts of any size, and minimum 1-year follow-up. The primary outcome of interest was postoperative instability. MINORS criteria were used to assess study bias. Descriptive statistical analysis was performed with data reported as ranges. RESULTS: Seventeen studies that included 7885 cases of RSA were reviewed. The mean follow-up ranged from 12 to 84 months. Mean age ranged from 64 to 77 years old, and males represented 19 to 39% of cohorts. There were 204 (2.5%) dislocations in 7885 cases, accounting for a rate of instability from 0.4 to 49% across all studies. By intervention, instability rates ranged from 1 to 5% (primary RSA cases), 1 to 49% (revision RSA cases only), and 0.4 to 10% (mixed cohorts). Subscapularis insufficiency and proximal humerus fractures, and fracture sequelae (malunion and nonunion) were identified as risk factors for instability. Closed reduction and casting and revision RSA were reported as successful treatment strategies with acceptable rates of stable prostheses (28-100% and 55-100%, respectively, across studies). Hemiarthroplasty or resection arthroplasty due to recurrent instability was not uncommon after 2 or more episodes of instability. CONCLUSION: Instability following RSA occurs infrequently (1-5%) following primary RSA and more commonly following revision RSA (1-49%). RSA for acute proximal humerus fracture and fracture sequelae carries a higher risk of instability. Subscapularis repair appears to be a protective factor. While instability may be successfully treated with closed management or revision RSA, recurrent instability may ultimately require hemiarthroplasty or resection arthroplasty.