Inverted-bearing reverse shoulder arthroplasty: long-term survivorship, complications, clinical, and radiological outcomes.

Background: Inverted-bearing reverse shoulder arthroplasty (IB-RSA) is characterized by a polyethylene glenosphere and a metallic humeral liner to minimize polyethylene wear and debris secondary to impingement between the humerus and glenoid neck. IB-RSA long-term survivorship, complication and revision rates, as well as clinical and radiographic outcomes have not been reported yet.

Methods: This is a monocentric retrospective study on a consecutive series of 151 patients who underwent primary IB-RSA from January 2009 to September 2015 and were evaluated clinically and radiologically at the minimum 8-year follow-up. All complications and reoperations were recorded. Survivorship analysis with any revision surgery as endpoint was done using Kaplan-Meier survival curves.

Results: Seventy-eight patients (follow-up rate 51.7%) were reviewed at a mean follow-up of 10.1 ± 1.9 years. At 10 years, the revision-free survival was 98.7% (95% confidence interval: 94.8-99.7). Sixteen complications (10.6%) were observed: 2 axillary nerve injuries, 2 infections, 2 glenoid loosening (which stabilized within 1 year), 2 cases of otherwise unexplained painful stiffness, 4 acromial fractures, 1 post-traumatic scapular pillar fracture, and 3 post-traumatic humeral periprosthetic fractures. Two patients were revised due to infection. No cases of late glenoid loosening and humeral loosening were observed. The revision rate was 1.3%. All the clinical scores and range of motion significantly improved at the last follow-up compared with preoperative status: final Constant score was 66.1 ± 17.4, Subjective Shoulder Value 79.1 ± 20.9, and the American Shoulder and Elbow Surgeons 82.2 ± 17.7. Scapular notching was observed in 51.4% of patients: only 1 case of grade 3 notching was observed in an early glenoid subsidence case.

Conclusions: Primary IB-RSA appears to be a safe and effective procedure and does not present specific implant-associated complications at long-term follow-up. Radiographic analysis showed that inverting the biomaterials leads to a distinct kind of notching with mainly mechanical features.