Robert H. Cofield, MD, Award for Best Oral Presentation 2023: Up to 8 mm of glenoid-sided lateralization does not increase the risk of acromial or scapular spine stress fracture following reverse shoulder arthroplasty with a 135° inlay humeral component

Abstract

BackgroundGlenoid-sided lateralization in reverse shoulder arthroplasty (RSA) decreases bony impingement and improves rotational range of motion, but has been theorized to increase the risk of acromial or scapular spine fractures (ASF). The purpose of this study was to assess the if glenoid-sided lateralization even up to 8 mm increases risk for stress fracture following RSA with a 135° inlay humeral component. MethodsA retrospective review was performed from a multicenter prospectively collected database on patients who underwent primary RSA from 2015-2021. All RSAs were performed with a 135° inlay humeral component. Varying amounts of glenoid lateralization were used from 0 to 8 mm. Preoperative radiographs were reviewed for the presence of acromial thinning, acromiohumeral distance (AHD), and inclination. Postoperative implant position (distalization, lateralization, and inclination) as well as the presence of ASF were evaluated on minimum 1-year postoperative radiographs. Regression analyses was performed on component and clinical variables to assess for factors predictive of ASF. ResultsAcromial or scapular spine fractures were identified in 26 out of 470 shoulders (5.5%). Glenoid-sided lateralization was not associated with ASF risk (p = 0.890). Furthermore, the incidence of fracture did not vary based on glenoid-sided lateralization (0-2mm - 7.4%, 4mm - 5.6%, 6mm - 4.4%, 8mm - 6.0%; p > .05 for all comparisons). RSA on the dominant extremity was predictive of fracture (OR 2.21, 95% CI 1.20-5.75 p = 0.037), but there was no relationship between patient age, sex, preoperative acromial thinning, or diagnosis and risk of fracture. While there was no difference in mean postoperative AHD between groups (p = .443), the pre- to postoperative delta AHD was higher in the stress fracture group (2.0 ± 0.7 cm vs. 1.7 ± 0.7 cm; p = 0.015). For every centimeter increase in delta AHD, there was a 121% increased risk for fracture (OR 2.21, 95% CI 1.33-3.68; p = 0.012) Additionally, for 1 mm increase in inferior glenosphere overhang, there was a 19% increase in fracture risk (p = 0.025). ConclusionUp to 8 mm of glenoid-sided metallic lateralization does not appear to increase the risk of ASF when combined with a 135° inlay humeral implant. Humeral distalization increases the risk of ASF, particularly when there is a larger change between pre- and postoperative AHD or higher inferior glenosphere overhang. In cases of pronounced preoperative superior humeral migration, it may be a consideration to avoid excessive postoperative distalization, but minimizing bony impingement via glenoid-sided lateralization appears to be safe.