Evaluation of Global Track in Patients With Anterior Shoulder Instability and Glenohumeral Bone Loss.

BACKGROUND: Identifying critical bipolar bone loss in anterior shoulder instability remains a challenging clinical problem. The global track concept has been recently described as a unified framework for predicting engagement of Hill-Sachs lesions (HSLs). Despite strong theoretical justification, the global track concept has not yet been clinically validated against established instability metrics.

PURPOSE: To evaluate global track parameters against traditional imaging-based metrics of instability to attempt to contextualize measurements and determine critical threshold values.

METHODS: A total of 40 patients with anterior shoulder instability who underwent 3-dimensional computed tomography-based measurement of glenoid and humeral bone loss were retrospectively identified. Global track metrics were measured, including the humeral angle (angular distance from the global apex of the humeral articular surface to the medial edge of the HSL), glenoid angle (angular distance from the glenoid articular surface to the edge of the glenoid defect), and global track angle (sum of the humeral and glenoid angles). Traditional metrics also measured included glenoid bone loss, glenoid track width (GT), Hill-Sachs interval (HSI), distance to dislocation, and occupancy ratio (HSI/GT). A patient-specific critical humeral angle was derived from the glenoid track width and humeral radius. The critical glenoid angle was set at the glenoid angle, which correlated to 13.5% glenoid bone loss. Receiver operating characteristic analysis evaluated global track angle as a predictor of off-track lesions and glenoid angle as a predictor of 13.5% glenoid bone loss.

RESULTS: In total, 40 patients met the inclusion criteria. The mean humeral angle was 51.8°± 12.5°, the mean glenoid angle was 21.7°± 6.2°, and the mean global track angle was 73.5°± 13.7°. The mean critical humeral angle was 42.2°± 6.1°, the critical glenoid angle was 23.2° (95% CI, 21.6°-24.8°), and the mean critical global track angle was 65.5°± 6.1°. The glenoid angle demonstrated a moderate inverse correlation with glenoid bone loss (R2 = 0.43; P < .001), with each 10% increase in glenoid bone loss corresponding to a 4.5° decrease in glenoid angle. For traditional off-track status, the global track angle demonstrated an area under the curve (AUC) of 0.649 (95% CI, 0.458-0.840). For glenoid bone loss of ≥13.5%, the glenoid angle demonstrated an AUC of 0.757 (95% CI, 0.591-0.922).

CONCLUSION: The global track may provide a continuous, bone-based surrogate of engagement risk that appears to align with traditional occupancy ratio thresholds. The critical glenoid angle threshold of approximately 23° may correspond to 13.5% glenoid bone loss. In this imaging-based cohort, a global track cutoff of <66° was associated with off-track lesions; however, further validation with larger cohorts and clinical outcome correlation is required before it can be considered a robust objective marker of bipolar defect severity.

STUDY DESIGN: Case series; Level of evidence, 4.