Relationship between the prosthesis scapular neck angle and clinical outcomes in reverse shoulder arthroplasty.

Abstract

Optimal glenosphere positioning in reverse shoulder arthroplasty (RSA) remains highly debated. We aimed to characterize the association between the prosthesis scapular neck angle (PSNA) and postoperative range of motion (ROM) and clinical outcome scores. A retrospective review of 284 RSAs using a single design with minimum 2-year follow-up was performed. Glenosphere tilt was measured postoperatively using PSNA. ROM and functional outcome scores were assessed preoperatively and at latest follow-up. The PSNA was dichotomized to inferior or superior groups (>90° vs ≤ 90°, respectively) and stratified into quartiles; ROM and outcome score measures were compared between groups controlling for inferior glenosphere overhang. No range of PSNA was consistently associated with superior ROM, clinical outcome scores, or rates of complications including scapular notching. However, greater preoperative to postoperative improvement in active FE was found for superiorly (PSNA ≤ 90°) versus inferiorly tilted glenospheres (37° ± 33° vs 53° ± 35°, P = 0.005) and the greater improvement in active FE (57° ± 35°, P = 0.004) was further isolated to the first quartile (mean 85.1° ± 3.5°). A lack of variation in clinical outcomes based on PSNA suggests negligible short-term (median follow-up 3.1 years) clinical significance when glenosphere tilt falls within the distribution of this cohort (mean 92.6° ± 6.2°).