Summary

For the studied implant system, glenoid lateralization of 6 to 8 mm was associated with improved active internal rotation at one year compared to patients with less glenoid lateralization with no significant differences in active forward flexion, external rotation, or PROs.

Abstract

Background

Improvement in internal rotation (IR) is not reliably achieved after reverse total shoulder arthroplasty (RSA). There currently is a paucity of clinical literature specifically examining the influence of progressive glenoid lateralization on postoperative IR. The purpose of this study was to evaluate the relationship between postoperative IR and glenoid-sided lateralization following RSA in an implant using metallic lateralization

Methods

A multicenter retrospective study was conducted of RSAs with minimum 1-year clinical follow-up. All included patients had the same RSA prosthesis. Patients were stratified based on the amount of glenoid-sided implant lateralization into four groups: 0-2 mm (N = 57), 4 mm (N =238), 6 mm (N = 95) and 8 mm (N = 65). The primary study outcome was active internal rotation at a minimum of 1 year postoperatively, measured both by spinal level and in degrees with the shoulder abducted to 90 degrees. Secondary outcomes were: active forward flexion and external rotation, belly press strength and subjective patient-reported outcome measures (PROs). Comparisons were made with one-way ANOVA tests with p < 0.05. Linear regression analyses evaluating for the association of glenoid lateralization with active internal rotation were also performed to control for additional confounders, including demographics and other implant variables such as glenosphere diameter, humeral lateralization, humeral version and whether the subscapularis was repaired.

Results

455 patients were included in the study. The mean age was 69 years and 48% of patients were male. IR differences varied by the method of measurement (spinal level versus IR in degrees with arm abducted). Overall, patients with 8 mm of glenoid lateralization had significantly improved IR compared to all other lateralization groups. Patients with 6 mm of glenoid lateralization had significantly improved IR compared to the 0-2 mm and 4 mm groups. There were no significant differences in the secondary outcomes or PROs between lateralization groups. In the regression, glenoid lateralization was the only implant-related variable that was significantly associated with improved IR for both measurement methods. Glenosphere diameter and humeral version were both significantly associated with IR measured in degrees with the arm abducted, but not spinal level.

Conclusions

For the studied implant system, glenoid lateralization of 6 to 8 mm was associated with improved active internal rotation at one year compared to patients with less glenoid lateralization with no significant differences in active forward flexion, external rotation, or PROs.