Clinical and radiological comparison of three different reverse shoulder arthroplasty designs for patients with primary osteoarthritis

Aims: In reverse shoulder arthroplasty (RSA), different implant designs range from medializing implants to strongly lateralizing onlay designs with different neck-shaft-angles (NSA). Thus different degrees of lateralization are currently used. Aim of this study was to compare clinical and radiological outcomes of three different implant designs in a homogeneous patient cohort with primary osteoarthritis (OA). Methods: Patients with OA who underwent RSA between 03/2014 and 01/2020 were included and categorized into three groups based on RSA design: group MD (medialized-distalized design: eccentric glenosphere, 155° NSA), group L (lateralized design: +4mm centric glenosphere, 135° NSA), group LD (lateralized-distalized design: eccentric glenospheres, +3mm baseplate, curved onlay stem 145° NSA). Inclusion criteria were complete clinical and radiological 24 months follow-up (FU) including range of motion (ROM), Constant-Murley score (CS), Subjective Shoulder Value (SSV). In addition, scapular notching and adverse events were recorded. Results: Group MD including 26 patients (81% female; mean age: 77.9 years) reached 71 (range: 60-85) points in CS and 90% (range: 40-100) in SSV. In group L, 46 patients (98% female; mean age: 75.2 years) achieved a CS of 75 (59-85) points and SSV was 95% (60-100). In group LD, 25 patients (68% female; mean age: 76.3 years) presented a CS of 79 (30-100) points and SSV of 93% (50-100). Group L and group LD achieved significantly better abduction, internal and external rotation (p<0.001), forward flexion (p=0.023) and SSV (p=0.046). Scapular notching was present in 22% of MD patients (13% grade 1; 4% grade 2; 4% grade 4), 16% in group L (all grade 1) and 9% in group LD (all grade 2). No prosthesis related complication occurred in any group. Conclusion: In patients with primary OA, the lateralized and lateralized-distalized designs result in superior subjective satisfaction in SSV and improved ROM in all planes compared to the traditional distalized-medialized implant designs. In all three groups, no implant related complications were noted.