Predictors of scapular notching in patients managed with the Delta III reverse total shoulder replacement.

BACKGROUND The reverse Delta III shoulder prosthesis can relieve pain and restore function in patients with cuff tear arthropathy. The most frequently reported radiographic complication is inferior scapular notching. The purpose of the present study was to evaluate the clinical relevance of notching and to determine the anatomic and radiographic parameters that predispose to its occurrence. METHODS Seventy-seven consecutive shoulders in seventy-six patients with an irreparable rotator cuff deficiency were managed with a reverse Delta III shoulder arthroplasty and were followed clinically and radiographically for a minimum of twenty-four months. The effects of cranial-caudal glenoid component positioning and the prosthesis-scapular neck angle on the development of inferior scapular notching and clinical outcome were assessed. RESULTS All shoulders that had development of notching did so in the first fourteen months. Of the seventy-seven shoulders that were studied, thirty-four (44%) had inferior scapular notching, twenty-three (30%) had posterior notching, and six (8%) had anterior notching. Osteophytes along the inferior part of the scapula occurred in twenty-one (27%) of the seventy-seven shoulders. The angle between the glenosphere and the scapular neck (r = 0.667) as well as the craniocaudal position of the glenosphere (r = 0.654) were highly correlated with inferior notching (p < 0.001). A notching index was calculated with use of the height of implantation of the glenosphere and the postoperative prosthesis-scapular neck angle. This allowed prediction of the occurrence of notching with a sensitivity of 91% and specificity of 88%. The height of implantation of the glenosphere had approximately an eight times greater influence on inferior notching than the prosthesis-scapular neck angle did. Inferior scapular notching was associated with a significantly poorer clinical outcome. CONCLUSIONS Inferior scapular notching after reverse total shoulder arthroplasty adversely affects the intermediate-term clinical outcome. It can be prevented by optimal positioning of the glenoid component.