Hill-Sachs Interval Less Than or Greater Than Glenoid Track ("Tire Too Narrow")

Instability as a bipolar concept—Some find it helpful to conceptualize on-track and off-track lesions in the setting of a tire and a pothole. Imagine the glenoid (and glenoid track) as a tire, and the Hill-Sachs interval as a pothole. In “on track” defects, HSI< GT, and the defect will not engage. It will be “off-track” and will “engage” on the glenoid if the HSI > GT. An off-track lesion is analogous to the tire falling into a pothole. This can occur in the setting of either marked glenoid bone loss (pictured) or a very large Hill-Sachs.