Purpose: The purpose of this study was to evaluate the reproducibility of unilateral computed tomography (CT) measurement of glenoid surface area, based on the typically circular geometry of the inferior glenoid.
Methods: This study used 3-dimensional shoulder CT scans before reconstruction for anterior instability. The en face CT views of the normal and abnormal glenoids were randomized and evaluated by 3 independent observers (2 experienced shoulder surgeons and 1 medical student). ImageJ (National Institutes of Health, Bethesda, MD) was used to overlay a perfect circle that was fit to the glenoid. The anterior aspect of the circle was then adjusted to match the true anatomic contour of the anterior glenoid. This adjusted region was used to determine the percentage of the perfect circle occupied by the glenoid, which we defined as the anatomic glenoid index (AGI).
Results: For the 23 normal shoulders, the AGI reflected a nearly perfect fit of the circle, with very high consistency and reliability among the 3 observers. Overall, mean AGI for the normal shoulders was 100.5%, with an SD of 2.2%. For the 12 shoulders that underwent Bankart repair, the overall AGI was 92.1% ± 5.2%, and 9 of 12 patients had an AGI below the threshold of 96.1%. For the 11 shoulders that underwent Latarjet reconstruction, the overall AGI was 89.6% ± 4.7%.
Conclusions: This study confirms that the normal inferior glenoid surface is a nearly perfect circle with remarkably low variability. This observation allows for determination of a tight reference range that can be applied to clinical analysis of unilateral CT reconstructions of symptomatic shoulders. This pilot study evaluates a simple and reliable method for determination of the AGI, creating an anatomic preoperative description of bone loss.
Level of evidence: Level III, retrospective comparative study.
Copyright © 2011 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.