Lateralización y distalización objetiva en prótesis reversa de lateralización glenoidea

Abstract

Introduction: reverse shoulder arthroplasty (RSA) with a lateralized center of rotation has proven to reduce notching rates, restore shoulder contour and improve external rotation. Lateralization can be achieved from the glenoid component or from the humeral stem. Boutsadis et al. described two angular measurements on postoperative radiographs to objectively determine lateralization and distalization in RSA: the lateralization shoulder angle (LSA) and the distalization shoulder angle (DSA). These measurements are reproducible, and they correlate with functional outcomes and range of motion. The DJO prosthesis (DJO Surgical, Austin, TX, USA) features a lateralized center of rotation glenosphere, with a neck-shaft angle of 135°. This implant has yielded satisfactory clinical outcomes in the medium, and long term follow-up studies. To date, objective measurement of lateralization rates and their association postoperative range of motion using LSA and DSA has not been described in this type of implant.

Materials and methods: a retrospective review was performed of reverse shoulder arthroplasties performed in a single institution by a single fellowship trained shoulder surgeon (senior author) between January 2014 and April 2021. Patients were included if they underwent a RSA for rotator cuff arthropathy or primary glenohumeral osteoarthritis with a glenoid-side lateralized implant and a 135° neck-shaft angle. In all patients, a postoperative X-ray was obtained in order to evaluate the radiographic measurements of LSA and DSA. Radiographs were independently reviewed by three authors and the agreement between the examiners was assessed.

Results: a total of thirty-nine patients met the inclusion criteria. Their average age was 77.5 years, the sex distribution was 74.3% female patients. Final median active external rotation was 26° and final median active forward flexion was 125°. The radiographic analysis performed by the three reviewers resulted in a lateralization angle with a cut-off point of 93° (73° – 118°) and a distalization angle with a cut-off point of 40° (15° – 65°). The correlation coefficient between the three evaluators for the lateralization angle was 0.59and for the distalization angle was 0.79.

Discussion: the main finding of this research is that an RSA implant with glenoid-side lateralization provides an objective lateralization with LSA of 93° and a distalization with DSA of 40°. These results met the ideal range for optimal restoration of motion. Postoperative radiographic lateralization and distalization measurements for this type of implant are reproducible between different observers.