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

Abstract

BackgroundThis study establishes measurements to evaluate pathologic compensation in rotator cuff tear arthropathy and resultant considerations for reverse shoulder arthroplasty.MethodsRadiographs 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.ResultsA 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.ConclusionsPreoperative 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.