Association Between Glenohumeral Bony Morphology and Anterior Shoulder Instability: An Advanced Three-Dimensional Analysis.

BACKGROUND: Glenohumeral bony morphology plays an important role in anterior shoulder instability (ASI), but the specific acquired and constitutional anatomical features associated with ASI remain incompletely understood. This study aimed to quantitatively evaluate and compare glenohumeral bony morphological characteristics between patients with ASI and controls using three-dimensional (3D) computed tomography (CT) imaging analysis.

METHODS: A total of 210 participants were included, comprising 105 patients with unilateral ASI and at least one recurrence and 105 controls. Bilateral shoulder CT scans were obtained for the ASI group, whereas unilateral CT scans were obtained for the control group. The following parameters were measured on 3D models: glenoid index (GI), glenoid version angle, glenoid inclination angle, glenoid depth, humeral head containment angle, and the humeral head-to-glenoid diameter ratio. Within-patient comparisons were performed between affected and contralateral unaffected shoulders, and the contralateral unaffected shoulders were further compared with control shoulders. Sex-based subgroup analyses were also performed.

RESULTS: The affected shoulders had a greater GI than the contralateral unaffected shoulders, with a mean paired difference of 0.19 (95% CI, 0.16-0.23; Holm-adjusted P < 0.001). The humeral head containment angle was nominally smaller on the affected side, but the difference did not remain significant after correction for multiple comparisons (raw P = 0.013; Holm-adjusted P = 0.067). Compared with control shoulders, the contralateral unaffected shoulders demonstrated a greater GI (1.39 ± 0.11 vs. 1.32 ± 0.10; mean difference, 0.07; 95% CI, 0.04-0.09; Holm-adjusted P < 0.001) and reduced glenoid depth (2.9 ± 0.8 mm vs. 3.6 ± 0.9 mm; Holm-adjusted P < 0.001). No significant differences were observed in the remaining morphological parameters after Holm correction. In the exploratory sex-stratified analyses, greater GI and reduced glenoid depth remained significant among male participants, whereas no parameter differed significantly among female participants after correction for multiple comparisons.

CONCLUSION: ASI was associated with distinct glenohumeral bony morphological characteristics on 3D analysis. A greater glenoid index and reduced glenoid depth were the most consistent features, including in the contralateral unaffected shoulders of patients with ASI, suggesting a possible anatomical association.

LEVEL OF EVIDENCE: Level III, Cross-Sectional Design, Prognosis Study.