The association between reverse total shoulder arthroplasty neck-shaft angle on postoperative patient experienced shoulder disability: a retrospective cohort study

BACKGROUND: The neck-shaft angle (NSA) of the glenoid component used in reverse total shoulder arthroplasty (RTSA) was reduced to improve functional outcomes. This led to a decreased abduction but increased external rotation ability of patients who underwent RTSA. The impact of the decreased NSA on patient-reported shoulder disability is unknown but may have important implications for functional ability. Therefore, the aim of this study was to assess the difference in patient experienced shoulder disability between an NSA of 135° and 155° 12 months after RTSA. METHODS: In this retrospective cohort study, 109 patients undergoing RTSA were included. In 68 patients, a glenoid component with an NSA of 135° was used and 41 patients received a glenoid component with an NSA of 155°. The primary outcome was Disabilities of the Arm, Shoulder, and Hand (DASH) scores at 12 months and change scores between baseline and 12-month follow-up. Secondary outcomes were complications, Constant Murley Score, Numeric Rating Scale, active forward elevation and external rotation ability. Differences between groups were tested with t-tests or Mann-Whitney U-tests. RESULTS: A mean difference of 10.0 in 12 months postoperative DASH scores between NSA groups was observed in favor of the 135° NSA (P = .004), which did not exceed the Minimal Clinically Important Difference. DASH changes scores did not differ between NSA groups (P = .652). Mean postoperative Constant Murley Score at 12 months was 11.1 higher in the 135° NSA group (P = .013). No differences were observed in complications (P = .721) and postoperative pain (P = .710) between groups. Difference in postoperative external rotation and forward elevation at 12 months was 10° (P = .022) and 20° (P = .046), respectively, in favor of the 135° NSA group, exceeding Minimal Clinically Important Differences. CONCLUSIONS: No clinically important difference in patient-reported shoulder disability (DASH) was found between both groups, despite a larger range of motion in the 135° NSA group. This study is the first to show the impact of NSA on patient-reported shoulder disability using the DASH.