Navigation in reverse shoulder arthroplasty: how the lateralization of glenosphere can affect the clinical outcome

INTRODUCTION: One of the main causes of RSA failure is attributable to the malpositioning of the glenoid component. Initial experiences with computer-assisted surgery have shown promising results in increasing the accuracy and repeatability of placement of the glenoid component and screws. The aim of this study was to evaluate the functional clinical results, in terms of joint mobility and pain, by correlating them with intraoperative data regarding the positioning of the glenoid component. The hypothesis was that the lateralization more than 25 mm of the glenosphere can led to better stability of the prosthesis but should pay in term of a reduced range of movement and increased pain. MATERIALS AND METHODS: 50 patients were enrolled between October 2018 and May 2022; they underwent RSA implantation assisted by GPS navigation system. Active ROM, ASES score and VAS pain scale were recorded before surgery. Preoperative data about glenoid inclination and version were collected by pre-op X-Rays an CT. Intraoperative data—inclination, version, medialization and lateralization of the glenoid component—were recorded using computer-assisted surgery. 46 patients had been further clinically and radiographically re-evaluated at 3-months, 6-months, 1-year, and 2-years follow-up. RESULTS: We found a statistically significant correlation between anteposition and glenosphere lateralization value (DM − 6.057 mm; p = 0.043). Furthermore a statistically significant correlation has been shown between abduction movement and the lateralization value (DM − 7.723 mm; p = 0.015). No other statistically significant associations were found when comparing the values of glenoid inclination and version with the range of motion achieved by the patients after reverse shoulder arthroplasty. CONCLUSION: We observed that the patients with the best anteposition and abduction results had a glenosphere lateralization between 18 and 22 mm. When increasing the lateralization above 22 mm or reducing it below 18 mm, on the other hand, both movements considered decreased their range. LEVEL OF EVIDENCE: Level IV; Case Series; Treatment Study.