Bony increased-offset reverse total shoulder arthroplasty (BIO-RSA) associated with an eccentric glenosphere and an onlay 135° humeral component: clinical and radiological outcomes at a minimum 2-year follow-up

BACKGROUND: Various implant designs have been proposed to increase active range of motion (ROM) and avoid notching in patients treated by reverse total shoulder arthroplasty (RSA). The purpose of this study was to investigate the efficacy and safety of an onlay prosthesis design combining a 135° humeral neck-shaft angle with the glenoid component lateralized and inferiorized. METHODS: A retrospective descriptive study was conducted of the clinical and radiological outcomes at the final follow-up (≥24 months) of all RSAs performed by the same surgeon between September 2015 and December 2016 in the study center. At the last follow-up, patients were clinically assessed for ROM, Constant score, and subjective shoulder value and radiologically for scapular notching and glenoid radiolucent lines. Patients were followed up radiographically at 1 month and clinically at between 6 and 12 months (midterm) and again at between 24 and 48 months (final follow-up). Scapular notching was graded as per the Sirveaux classification at the last follow-up on anterior-posterior radiographs. RESULTS: Seventy-nine RSAs were included with a mean follow-up time of 31 months. The mean Constant score at the final follow-up was 42 points higher than before surgery (69 vs. 27, P < .001). There were also significant postoperative improvements in ROM (active anterior elevation, active external rotation, and active internal rotation). The final means for motions were 133° for active anterior elevation, 32° active external rotation, and level 7 for active internal rotation. The overall notching rate was 3% (2/67), and there were no cases of severe notching. Radiolucent lines were observed in 8 of 70 prostheses (11.5%) around the peg, and they were observed in 9 prostheses (13%) around the screws. Among the 79 RSAs included, there were 11 complications (13.9%) (two infections, two fractures, four cases of glenoid component loosening, and three cases of instability), 2 reoperations, and 4 prosthesis revisions. CONCLUSION: This study shows that an RSA design with a 135° humeral neck-shaft angle and an inferiorized and lateralized glenoid component is associated with significant improvements in active ROM, especially in rotation, and a low notching rate. However, rates of 3.8% for dislocation and 5% for glenoid loosening are certainly a concern at such a short follow-up of two years. Future studies with a larger population are needed to confirm these rates.