Revision for instability following reverse total shoulder arthroplasty: outcomes and risk factors for failure.

Abstract

Revision of unstable reverse shoulder arthroplasty (RSA) is significantly challenging with recurrence rates ranging 20-40%. The purpose of this study was to identify factors associated with recurrent instability. The factors studied included 1) indication for the revision RSA (failed primary RSA vs failed revision RSA), 2) previous attempts at stabilization, 3) mechanisms of instability, 4) clinical history of instability, and 5) surgical technique. Outcomes were reported in patients with 2-year follow-up. All patients undergoing RSA for instability were identified at our institution. A total of 43 surgeries in 36 patients were included. Arthroplasty indication prior to instability (14 failed primary RSA vs 22 failed revision RSA), instances of prior attempts at stabilization (14 patients treated outside), mechanism of instability classification, clinical history of instability (17 recurrent, 26 chronic), and surgical technique were collected. Stability at final follow-up (min.12 months), and clinical outcomes at 2-year follow-up were assessed. Overall, 32/36 patients (89%) required 38 revisions to achieve stability at final follow-up (average 53±47 months; range: 12-210 months). When comparing stability to indication, 13/14 (93%) patients in the failed primary group were stable (average 65±59 months; range 12-210 months compared to 19/22 (86%) in the failed revision group (45±36 months; range: 12-148 months, p=0.365). Average number of procedures per patient was 3 in the failed primary group (range: 2-10) compared to 4.5 in the failed revision group (range: 3-7; p = 0.008). Stability was achieved in 12/14 (86%) patients with history of failed stabilization procedures. The mechanism leading to persistent instability was loss of compression. Stability was achieved in 14/16 patients treated for recurrent instability compared to 18/20 treated for chronic/locked dislocation (p = 0.813). Continued instability occurred in 33% of patients managed glenoid-sided only, 33% humeral-sided only, and 10% of bipolar revision tactics performed. At 2-year follow-up, 18/21 patients evaluated were found to be stable with improvements in ASES, FF, ABD, ER, and SST (p=0.016, <0.01, 0.01, <0.01, and 0.247 respectively). Patients who had multiple revisions after failed previous arthroplasty will require more surgical attempts to achieve stability compared to patients who had a revision after a failed primary RSA. Loss of compression was the most common mechanism for persistent instability. Recurrent instability was more reliably stabilized than chronic/locked dislocations. Continued instability was noted in 1/3 of patients with humeral-sided only or glenoid-sided only revisions and in 10% of patients undergoing bipolar revisions. Successfully stabilized patients had improved clinical outcomes.