Magnetic resonance imaging provides computed tomography-equivalent measurements of glenoid retroversion, concavity, and bony shoulder stability ratio after anterior shoulder dislocation.

BACKGROUND: Assessment of bony parameters-such as glenoid version, glenoid concavity, and the bony shoulder stability ratio (BSSR)-has gained increasing attention after anterior shoulder dislocation, as they may contribute to persistent instability. Although computed tomography (CT) remains the gold standard for bony assessment, magnetic resonance imaging (MRI) is the primary imaging modality in many patients. Yet evidence comparing CT and MRI for these specific parameters remains limited. This study aimed to evaluate the agreement between MRI and CT in measuring glenoid version, glenoid concavity, and BSSR following anterior shoulder dislocation. We hypothesized that MRI provides measurements to those obtained with CT, demonstrating good agreement without clinically meaningful differences following anterior shoulder dislocation.

METHODS: A retrospective case-series study was conducted at a Level I trauma center, screening patients who sustained anterior shoulder dislocation between 2011 and 2020. Glenoid version, glenoid depth, humeral head radius, and BSSR were measured using standardized multiplanar reconstructions by 2 independent raters. Interrater reliability was calculated using the intraclass correlation coefficient (ICC). Agreement between modalities was assessed using Student's t-tests, Pearson correlation coefficients, concordance correlation coefficients, and Bland-Altman analysis.

RESULTS: Sixty-one patients (mean age, 45 ± 19 years; 75% male) met inclusion criteria. Inter-rater reliability was excellent for glenoid version (ICC, 0.92) and good for glenoid depth (ICC, 0.87) and humeral head radius (ICC, 0.82). No significant differences were observed between CT and MRI for glenoid version (3.7° ± 4.0° vs. 3.4° ± 3.7°; P = .10), glenoid depth (1.4 ± 0.7 mm vs. 1.3 ± 0.7 mm; P = .49), humeral head radius (23.1 ± 2.0 mm vs. 22.5 ± 4.9 mm; P = .33), or BSSR (34.8% ± 10.1% vs. 33.5% ± 11.2%; P = .34). Bland-Altman plots demonstrated good agreement, with MRI showing only minimal underestimation across parameters.

CONCLUSION: MRI provides reliable measurements of glenoid version, glenoid concavity, and BSSR that closely align with CT following anterior shoulder dislocation. These findings support MRI as a viable modality for assessing key bony stability parameters, potentially reducing the need for supplemental CT in many clinical scenarios. Prospective studies are warranted to validate these results and explore their implications for surgical decision-making and recurrence risk stratification.