Assessment of glenoid inclination on routine clinical radiographs and computed tomography examinations of the shoulder

Background: Accurate assessment of glenoid inclination is of interest for a variety of conditions and procedures. The purpose of this study was to develop an accurate and reproducible measurement for glenoid inclination on standardized anterior-posterior (AP) radiographs and on computed tomography (CT) images. Materials and methods: Three consistently identifiable angles were defined: Angle alpha by line AB connecting the superior and inferior glenoid tubercle (glenoid fossa) and the line identifying the scapular spine; angle beta by line AB and the floor of the supraspinatus fossa; angle gamma by line AB and the lateral margin of the scapula. Experimental study: these 3 angles were measured in function of the scapular position to test their resistance to rotation. Conventional AP radiographs and CT scans were acquired in extension/flexion and internal/external rotation in a range up to +/- 40 degrees. Clinical study: the inter-rater reliability of all angles was assessed on AP radiographs and CT scans of 60 patients (30 with proximal humeral fractures, 30 with osteoarthritis) by 2 independent observers. Results: The experimental study showed that angle alpha and beta have a resistance to rotation of up to +/- 20 degrees. The deviation from neutral position was not more than +/- 10 degrees. The results for the inter-rater reliability analyzed by Bland-Altman plots for the angle beta fracture group were (mean +/- standard deviation) -0.1 +/- 4.2 for radiographs and -0.3 +/- 3.3 for CT scans; and for the osteoarthritis group were -1.2 +/- 3.8 for radiographs and -3.0 +/- 3.6 for CT scans. Conclusion: Angle beta is the most reproducible measurement for glenoid inclination on conventional AP radiographs, providing a resistance to positional variability of the scapula and a good inter-rater reliability. Level of evidence: Basic Science Study, Anatomic Study, Imaging Study. (C) 2012 Journal of Shoulder and Elbow Surgery Board of Trustees.