Comparison of Glenohumeral Bone Morphology Between Patients With Versus Without Anterior Shoulder Instability

Background: The stability of the glenohumeral joint is associated with anatomic characteristics including bony structures and soft tissues.Purpose: To compare the differences in specific bony glenohumeral geometries between shoulders with anterior shoulder instability (ASI), unaffected contralateral shoulders, and healthy control shoulders.Study Design: Cross-sectional study; Level of evidence, 3.Methods: Shoulder computed tomography (CT) scans of 36 patients with ASI and 36 matched healthy controls were retrieved and 3-dimensionally reconstructed. We measured the glenoid radius of curvature (GROC) in the anterior-posterior (AP) and superior-inferior directions, humeral head radius of curvature (HROC) in the AP direction, conformity index, glenoid height, glenoid width, glenoid index, stability angle, glenoid version, and glenoid depth. The differences between the groups were statistically calculated. CT scans of the unaffected contralateral shoulders from 21 of the ASI patients were also collected to identify the consistency of the bony structures in bilateral shoulders.Results: Patients with ASI had greater GROC in the AP direction (P < .001), HROC in the AP direction (P = .002), glenoid height (P = .005), and glenoid index (P < .001) and smaller conformity index (P < .001), glenoid width (P = .002), stability angle (P < .001), and glenoid depth (P < .001). In addition, the glenoid of the ASI patients was more anteverted compared with that of controls (P = .001). There was no statistical difference in half the measurements between the bilateral shoulder joints in patients with ASI.Conclusion: In this study, glenohumeral geometric differences were found between ASI patients and healthy control participants. Glenoid curvature and conformity index, based on bilateral comparisons of affected and contralateral shoulders, appear inherent and may predict ASI risk.