Glenosphere Posterior Eccentricity Effect on Range of Motion and Anterior Impingement in Reverse Shoulder Arthroplasty in a Virtual Model. A Study of La Tour Group.

Alberto Guizzi; Patrick J. Denard; Philippe Collin; Alaa Elsenbsy; Anthony Pernoud; Hugo Bothorel; Alexandre Lädermann

Abstract

Background: Reverse shoulder arthroplasty (RSA) improves outcomes in cuff-deficient shoulders, but internal rotation recovery and anterior impingement remain inconsistent. While inferior placement and eccentric glenospheres may enhance motion, the role of posterior eccentricity in impingement and multiplanar function is unclear.Purpose: This study evaluated the effect of glenoid lateralization and posterior eccentricity in RSA on impingement-free ROM, hypothesizing that posterior eccentricity would enhance Hand-Behind-Back motion and reduce anterior impingement.Methods: CT scans obtained in 13 patients (3 men and 10 women) with A1 primary osteoarthritis were analyzed using a three-dimensional (3D) computer model simulating implantation of a standardized RSA. A 135° inlay humeral component and the combination of four different glenoid-sided variables were analyzed: glenoid lateralization (0, 3, and 6 mm), 36 mm glenosphere eccentricity (concentric, posteroinferior (45°), and posterior (90°)). ROM, impingement, and the implant distance to the coracoid and conjoint tendon were recorded in each scenario.Results: Positioning the glenosphere 5 mm inferior to the glenoid rim resulted in significantly increased ROM: +51% in hand-to-contralateral motion, +26° in external rotation, and +52° in extension (p<0.001), compared to a flush glenosphere. Inferior glenospheres were further from the coracoid process by 2.6 mm but slightly closer to the conjoint tendon by 0.7 mm. Posteroinferior and posterior eccentricities enhanced extension (+18°) and external rotation (+5°), but decreased internal rotation (−5° to −11°) and hand-to-contralateral motion (−8% to −28%) (p<0.05). Posteroinferior and posterior eccentricities also increased the distance from the coracoid process by 1.3–1.6 mm and from the conjoint tendon by 1.1–1.3 mm (p<0.05).Conclusion: In a virtual RSA model with a 135° inlay humeral component, posteroinferior eccentricity with lateral offset optimized ROM, including HBB, and may reduce anterior impingement by increasing coracoid and conjoint tendon clearance.What this study adds: This study shows that in a virtual RSA model, posteroinferior/posterior glenosphere eccentricities with inferior positioning and lateral offset improved motion and clearance, potentially reducing anterior impingement and supporting implant optimization.Potential impacts on research, practice or policy: This study demonstrates that posterior or posteroinferior eccentricity with inferior positioning and lateral offset can enhance ROM and reduce anterior impingement, guiding implant strategies to optimize outcomes.Study design: Basic Science Study; Computer ModelingKeywords: Prosthesis; Implant configuration; Eccentric; PROMs; Reverse Shoulder Arthroplastyhttps://doi.org/10.70885/hmsj.2025.09.003

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