The biomechanical impact of glenosphere tilting, inferior translation, and humeral retroversion in reverse total shoulder arthroplasty: A 3D modelling study.

Abstract

Reverse Total Shoulder Arthroplasty (RTSA) is continuously evolving and gaining importance in shoulder pathologies. Although many studies have addressed implant-related factors, only a few have focused on variable implantation techniques and their effects on the range of motion (ROM) and impingement. This study aimed to develop computational 3D models capable of predicting ROM up to the point of impingement across various implant positions. 3D scapulohumeral models were created from preoperative CT images of patients using computer software (Amira^Ⓡ, VSG, USA). These models were virtually implanted with RTSA components. Glenosphere placement was modified to simulate varying angles (inferior tilt) and displacements (inferior translation), while humeral stem placement was adjusted at different degrees of retroversion. All possible combinations were evaluated for the range of motion until impingement. The maximum impingement free range of motion was observed in the group with only 3 mm inferior displacement without tilting (T3) and 0° of retroversion.Impingement was greatest at a humeral retroversion of 20° and least at the neutral position. The internal rotation and external rotation ranges were greater in the 3 mm inferior displacement groups (T3, T3-tilt). 20° of humeral retroversion showed reduced range for internal rotation and increased range for external rotation compared to neutral. Implantation of the glenosphere with 3 mm inferior translation without inferior tilt, combined with a humeral prosthesis positioned at 0° retroversion, showed the most favourable combination in terms of range of motion until impingement.