Quantifying success after first revision reverse total shoulder arthroplasty: the minimal and substantial clinically important percentage of maximal possible improvement

Background: When patients require reoperation after primary shoulder arthroplasty, revision reverse total shoulder arthroplasty (rTSA) is most commonly performed. However, defining clinically important improvement in these patients is challenging because benchmarks have not been previously defined. Furthermore, although the minimal clinically important difference and substantial clinical benefit are commonly used to assess clinically relevant success, these metrics are limited by ceiling effects that may cause inaccurate estimates of patient success. Our purpose was to define the minimal and substantial clinically important percentage of maximal possible improvement (MCI-%MPI and SCI-%MPI) for commonly used pain and functional outcome scores after revision rTSA and to quantify the proportion of patients achieving clinically relevant success. Methods: This retrospective cohort study used a prospectively collected single-institution database of patients who underwent first revision rTSA between August 2015 and December 2019. Patients with a diagnosis of periprosthetic fracture or infection were excluded. Outcome scores included the American Shoulder and Elbow Surgeons (ASES), raw and normalized Constant, Shoulder Pain and Disability Index (SPADI), Simple Shoulder Test (SST), and University of California, Los Angeles (UCLA) scores. We used an anchor-based method to calculate the MCI-%MPI and SCI-%MPI. In addition, we calculated the MCI-%MPI using a distributionbased method for historical comparison. The proportions of patients achieving each threshold were assessed. The influence of sex, type of primary shoulder arthroplasty, and reason for revision rTSA were also assessed by calculating cohort-specific thresholds. Results: Ninety-three revision rTSAs with minimum 2-year follow-up were evaluated. The mean age of the patients was 67 years; 56% were female, and the average follow-up was 54 months. Revision rTSA was performed most commonly for failed anatomic TSA (n = 47), followed by hemiarthroplasty (n = 21), rTSA (n = 15), and humeral head resurfacing (n = 10). The indication for revision rTSA was most commonly glenoid loosening (n = 24), followed by rotator cuff failure (n = 23) and subluxation and unexplained pain