How to Measure Glenoid Track and Hill-Sachs Interval and Distance to Dislocation

Anterior shoulder instability often presents with bony lesions on the glenoid, humeral head, or both. The glenoid track (GT) method was validated to provide surgeons with a method to assess the risk of instability caused by this bone loss. Computed tomography scan is the gold standard of assessment, but subjects patients to a higher dose of radiation. Magnetic resonance imaging can be utilized with the GT to reliably evaluate patients with anterior shoulder instability and bipolar bone loss to determine the existence of an off-track Hill-Sachs lesion (HSL) preoperatively. The study revealed 84.2% accuracy, and statistical analysis established. This as a significant predictor. The purpose of this video is to illustrate how to calculate the GT, Hill-Sachs interval (HSI), and distance to dislocation (DTD) using MRI.

Yamamoto et al were the first to present the GT, demonstrating that when assessing HSLs, the most crucial part of evaluation is their location on the humeral head.

The GT can be defined as the area of contact of the humeral head on the glenoid during shoulder abduction and external rotation. If there is a glenoid bone defect, the GT width is reduced, and the new GT width is calculated. The following equation is used: GT = (0.83 * D) - d, where "D" is the diameter of the intact glenoid, and "d" is the diameter of the glenoid defect. The HSI is the width from the medial edge of the HSL to the insertion of the rotator cuff. The DTD is calculated by subtracting the GT from the HSI. An HSL is "off-track" if the medial margin of the lesion is more medial than the GT, resulting in no bone support. If an HSL is "off-track," there is a higher risk of recurrence after arthroscopic Bankart repair. Therefore, for "off-track" lesions, adding remplissage is recommended or performing a bone block procedure.

Utilizing the GT technique is crucial when creating a treatment plan for patients with anterior shoulder instability as glenoid bone loss and "off-track" HSL have been shown to be predictors of recurrent instability, even in patients who have undergone prior surgical stabilization procedures.

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