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

The most common complication with reverse shoulder arthroplasty Grammont based design with a 155° neck shaft angle (NSA) is scapular notching. Scapular notching has been associated with reduced clinical outcomes. Reducing the humeral NSA from 155° has been shown to reduce the incidence of scapular notching however it is unknown whether there is a difference in scapular notching between a 145° and 135° 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° and 135° NSA stems at minimum 2 yr of follow-up.

Consecutive patients undergoing primary reverse shoulder arthroplasty with a NSA of either 145° or 135° 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.

One hundred and three patients were included for the final analysis: 73 with a 145° NSA and 30 with a 135° 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° (53.4%) and 135° (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 Shoulder Value (mean, 76.5 vs. 83.1%, P = .167), forward flexion (mean, 140° vs. 142°, P = .704), abduction (mean, 123.2° vs. 121.5°, P = .771), external rotation with the arm at the side (mean, 34.1° vs. 37.3°, P = .341) and internal rotation (mean, 5.3 vs. 5.4 pts P = .336) between the 2 groups.

This is the first study to compare the effect of a 145° vs. 135° 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° NSA compared to 145° 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° NSA group has not shown any significant better clinical and functional outcomes.