Neck shaft angle in reverse shoulder arthroplasty: 135 vs. 145 degrees at minimum 2-year follow-up

Background: The most common complication with reverse shoulder arthroplasty Grammont based design with a 155 degrees neck shaft angle (NSA) is scapular notching. Scapular notching has been associated with reduced clinical outcomes. Reducing the humeral NSA from 155 degrees has been shown to reduce the incidence of scapular notching however it is unknown whether there is a difference in scapular notch-ing between a 145 degrees and 135 degrees NSA. The purpose of this study was to evaluate the effect of decreasing the NSA on scapular notching rate and postoperative range of motion comparing 145 degrees and 135 degrees NSA stems at minimum 2 yr of follow-up.Methods: Consecutive patients undergoing primary reverse shoulder arthroplasty with a NSA of either 145 degrees or 135 degrees between January 2014 and February 2019 were retrospectively reviewed. Patients were included if they were over the age of 18, had minimum clinical follow-up of 24 mo with true postoperative anteroposterior radiographic view.Results: One hundred and three patients were included for the final analysis: 73 with a 145 degrees NSA and 30 with a 135 degrees NSA stem. The mean age and mean follow-up were respectively 70.9 yr (range, 52.0-89.0) and 32.1 mo. The overall incidence of scapular notching was 46.6 %. There was a statistically significant difference in scapular notching between the 145 degrees (53.4%) and 135 degrees (30%) NSA groups (P = .028). There was no difference in terms of postoperative Constant-Murley Score (mean, 66.1 vs. 68.2; P = .395), Subjective Shoul-der Value (mean, 76.5 vs. 83.1%, P = .167), forward flexion (mean, 140 degrees vs. 142 degrees, P = .704), abduction (mean, 123.2 degrees vs. 121.5 degrees, P = .771), external rotation with the arm at the side (mean, 34.1 degrees vs. 37.3 degrees, P = .341) and internal rotation (mean, 5.3 vs. 5.4 pts P = .336) between the 2 groups.Conclusion: This is the first study to compare the effect of a 145 degrees vs. 135 degrees NSA on scapular notching rates. The key finding of this study is that scapular notching rate was significantly reduced from 53% to 30% in 135 degrees NSA compared to 145 degrees NSA, after at least 24 mo of follow-up. Our data also show that glenoid lateralization and inferiorization has an influence on scapular notching. We are unable to state that the reduced scapular notching rate was due to a reduction in NSA alone. Despite a lower rate of scapular notching, the 135 degrees NSA group has not shown any significant better clinical and functional outcomes.