Glenoid Lateralization in Reverse Shoulder Arthroplasty: Metal versus Bone Offset in Different Implant Designs

Background Higher bone or metal glenoid offset in reverse shoulder arthroplasty reduces scapular notching, improves range of motion, and reduces postoperative instability. This retrospective multicenter study compared two implant designs to evaluate the short-term clinical and radiologic results of bone increased offset (BIO-RSA) and metal increased offset (MIO-RSA) in reverse shoulder. We hypothesized no difference between groups. Methods This study analyzed n=62 BIO-RSA and n=90 MIO-RSA cases with a mean follow-up of FUBIO-RSA=29.7±6.0 months (range 24-49 months) and FUMIO-RSA=24.0±1.1 months (range 22-28 months). A 145 onlay humeral stem was utilized in BIO-RSA cases while a 135 semi-inlay humeral stem was implanted in all MIO-RSA cases. Preoperative and postoperative radiologic imaging was reviewed to identify signs of scapular notching. Additionally, lateralization was evaluated according to Erickson et al. The Constant score, Subjective Shoulder Value, and range of motion were evaluated during the baseline and follow-up consultations and the findings of both groups were subsequently compared. Results Scapular notching was observed in 7.0% (n=8) of MIO-RSA cases and 8.1% (n=5) of BIO-RSA cases (p=0.801). MIO-group had a higher lateralization angle (p=0.020) and the BIO-group a higher distalization angle (p=0.005). At baseline, mean Constant score in the MIO-RSA group was higher than in the BIO-RSA group (p<0.001) and it significantly increased to 67.8±12.1P (MIO-RSA) and 69.5±12.3P (BIO-RSA) to a similar level (p=0.399). Range of motion improved in both groups with no significant difference between both groups at follow-up. Conclusion BIO- and MIO- RSA in two distinct implant designs provide comparable short-term outcomes with a similar increase in shoulder function with notable variations in the lateralization and distalization angles between both implants. Scapular notching was rarely seen and unaffected by the method of glenoid lateralization. Follow-up investigations of both techniques are necessary to complement and track changes in the long-term outcome.