Stability of custom glenoid implants in a vault reconstruction system and kinematic comparison to healthy shoulders using biplane video radiography

Background: The incidence of reverse total shoulder arthroplasties (rTSAs) has drastically increased in recent years, but standardized implants have limitations and may not always be used in patients with extensive glenoid bone loss. The Vault Reconstruction System (VRS; Zimmer Biomet, Warsaw, IN) is a patient-specific custom glenoid implant (CuGI) derived from pre-operative computed tomography scans in rTSA for patients with severe glenoid bone loss. However, the in vivo orientation and stability during active range of motion (ROM) have yet to be evaluated. The purpose of this study was to evaluate the in vivo kinematics and implant positioning of patients who underwent rTSA with VRS-CuGI. Methods: Patients with the CuGI underwent biplane video radiography while performing unrestrained scapular plane abduction. Using analogous anatomical coordinate systems, the stability of the glenoid implant on the scapula and the kinematics of patients with CuGI were compared to those of patients with healthy shoulders. Results: Implant orientation closely matched the pre-operative plan overall, with the largest deviation observed in retroversion (mean 5.9°). Implant–scapula motion remained minimal across all evaluated components; a small difference was observed in superior–inferior translation (maximum mean difference 1.4 mm), which was within measurement precision. Discussion: Implant–scapula motion was minimal across the motion arc, with differences remaining within measurement precision. During active ROM, patients with a VRS-CuGI showed similar elevation and plane of elevation mechanics to healthy controls but differed in axial rotation. Greater variability was present across all planes of motion in patients with CuGI, indicating that individuals who undergo this procedure likely employ unique compensatory strategies to achieve functional ROM. Conclusion: The VRS-CuGI was shown to have increased retroversion (5.9°) in comparison to pre-operative planning but maintains stable fixation to the scapula during dynamic arm elevation in patients with severe glenoid bone loss. Despite kinematic differences from healthy shoulders, participants experienced minimal functional impairment and pain, suggesting that the altered motion patterns may reflect adaptive mechanisms that support successful clinical outcomes in complex shoulder reconstructions.