The glenoid-intramedullary humeral angle: a measurement of compensatory scapular abduction in advanced rotator cuff arthropathy and its potential effects on implant choice

BACKGROUND: This study establishes measurements to evaluate pathologic compensation in rotator cuff tear arthropathy and resultant considerations for reverse shoulder arthroplasty. METHODS: Radiographs of patients with intact rotator cuffs were measured establishing interobserver and intraobserver reliability. Reverse shoulder arthroplasty cases performed by a single surgeon were then retrospectively reviewed. One year of follow-up radiographs were required for inclusion. Preoperative radiographs were analyzed for relative humeral head elevation ratio and humeral abduction relative to the glenoid face, termed the glenoid-intramedullary humeral angle. Statistical analyses assessed associations for radiographic measurements with presence and severity of scapular notching based on the Nerot-Sirveaux classification system. RESULTS: A total of 221 patients met inclusion criteria. At the 1-year follow-up, 61 (27.6%) shoulders had radiographic notching. There was a moderately strong (r = -0.56) negative correlation between glenoid-intramedullary humeral angle and humeral head elevation ratio. Patients with humeral head elevation ratio ≥ 20% were significantly (P = .024) and 9.2 times more likely to have notching of any grade. Patients with glenoid-intramedullary humeral angle ≤ 5 degrees were significant (P < .0001) and 6.7 times more likely to have notching of any grade and significantly (P = .00018) and 145 times more likely to have high-grade (3 and 4) notching. CONCLUSIONS: Preoperative humeral head elevation and compensatory scapular rotation with relative adduction of the humerus have significant associations with high-grade notching. These radiographic findings have potential to help surgeons in preoperative decision-making regarding implant choice and patient education.