Comparative Analysis of 3D MRI and CT in Assessing Static Bone Loss and Dynamic Bipolar Interaction in Glenohumeral Instability.

Background: Accurate assessment of glenoid bone loss and morphological variations is crucial for determining optimal surgical care pathways for shoulder instability. While 2-dimensional (2D) and 3-dimensional (3D) computed tomography (CT) has been the gold standard for evaluating static bone quality, 3D magnetic resonance imaging (MRI) has recently been proven reliable for these static assessments but remains unvalidated for dynamic, advanced morphological variables.

Purpose/hypothesis: The purpose of this study was to compare the utility of 3D MRI and 3D CT in measuring advanced, dynamic morphological variables in glenohumeral instability. It was hypothesized that 3D MRI would be comparable with 3D CT for assessing both static bone loss and dynamic morphological parameters.

Study Design: Cohort study (diagnosis); Level of evidence, 2.

Methods: A total of 21 patients who had glenohumeral instability were included (mean age, 31.2 ± 14.9 years; 42.9% female; mean body mass index, 27.2 ± 5.8 kg/m). All participants underwent preoperative 2D MRI and 2D CT scans with 3D MRI and 3D CT reformats. Patients were stratified based on a 10% subcritical bone loss threshold to evaluate measurement sensitivity between 3D MRI and 3D CT. Static imaging variables such as glenoid version, inclination, and bone loss (both glenoid and humeral) were measured. Dynamic variables-which are fixed values but are interactive/dependent on static measurements for calculation, including Hill-Sachs occupancy, glenoid track zones, and distance to dislocation were subsequently quantified. Paired tests and χ tests were employed to compare imaging modalities.

Results: All patients demonstrated a Hill-Sachs lesion, with 15 having evidence of glenoid bone loss. There were no significant differences between 3D MRI and 3D CT in measuring glenoid or humeral bone loss, distance to dislocation, occupancy ratios, or glenoid track zones. Dynamic variables were consistent across imaging modalities, even after stratification by the 10% subcritical bone loss threshold. Both modalities accurately identified on/off track lesions and peripheral-track zones. Inter- and intrarater reliability was good to excellent for all CT and MRI measurements.

Conclusion: Overall, 3D MRI is a validated and reliable alternative to 3D CT for preoperative evaluation of static glenohumeral bone loss and dynamic morphological variables in shoulder instability, allowing clinicians to choose the modality that best fits their practice.