Comparative study of 145° onlay curved stem versus 155° inlay straight stem reverse shoulder arthroplasty: clinical and radiographic results with a minimum 2-year follow-up

Lateralized onlay reverse shoulder arthroplasty (RSA) are designed to ensure better clinical functional recovery and lower rate of complications compared to Grammont medialized inlay RSA. The purpose of the present study was to compare the clinical and radiographic outcomes between these two different designs. Eighty-five consecutive patients undergoing RSA were retrospectively analyzed. Nine patients were lost at FU; thirty-four received a curved onlay 145° NSA (Ascend Flex group) and forty-two received a long straight inlay stem with a 155° NSA (Delta Xtend group). Patients were reviewed at an average follow-up of 46.8±13.2 months (Ascend Flex group) and 36±10.8 months (Delta Xtend group). Clinical outcome measures included Active range of motion (ROM), strength, visual analog scale (VAS), Constant-Murley score (CMS), and the American Shoulder and Elbow Surgeons score (ASES). Radiographic evaluation at final follow-up was performed to assess scapular notching, stress shielding, acromial or scapular fractures, heterotopic ossification, and radiolucent lines or implant loosening. No differences emerged between the two groups in terms of VAS, ASES and CMS scores, pain, function, strength, mobility, active forward elevation, active internal rotation, active external rotation at 0° and 90° of abduction; abduction, forward elevation and external rotation strength (P = n.s). Statistically superior active abduction was observed in the Delta Xtend group (P = 0.0017). Scapular notching was observed in 12 shoulders (35.2%) in the Ascend Flex group (a grade 1) and in 10 shoulders (23.8%) in the Delta Xtend group (P= n.s.). No differences emerged between the two groups in terms of humeral or glenoid radiolucency (P= n.s.). Higher rate of humeral stress shielding rate was observed in the Ascend flex cohort (P= n.s.). No statistically significant difference emerged between the 145° onlay curved stem versus the 155° inlay straight stem according to most of the evaluated parameters. Statistically superior active abduction was observed in the 155° group although it did not affect patients satisfaction.