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The more medial the Hill-Sachs lesion extends, the more likely it is to be "off-track"
51%
455/889
"On-track" lesions are more likely to engage
20%
180/889
Risk of engagement is higher with unipolar than bipolar lesions
3%
29/889
Glenoid track can only be determined using CT
17%
148/889
If the Hill-Sachs interval calculated is less than the glenoid track, it will engage
8%
70/889
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As a Hill-Sachs lesion extends more medial from the rotator cuff insertion, the humeral head is more likely to engage on the anterior bony glenoid defect. Traumatic anterior shoulder dislocations can be associated with anterior glenoid bone loss as well as a Hill-Sachs lesion which involves bony impaction of the posterosuperior humeral head. In cases where the bone loss is bipolar, the Hill-Sachs lesion can engage on the anterior glenoid rim with external rotation/abduction of the shoulder. This concept has recently become popularized as the glenoid track (GT) model. The GT is equal to 0.83D-d (where D=diameter of the inferior glenoid and d = width of the anterior glenoid bone loss). The Hill-Sachs interval (HSI) is also important to understand and is calculated by measuring the distance between the rotator cuff insertion to the medial aspect of the Hill-Sachs lesion. If the HSI is greater than the width of the GT, the Hill-Sachs defect is deemed "off-track," and more likely to engage with the shoulder externally rotated and abducted. If the HSI is less than the GT, it is "on-track," and unlikely to for the humeral head to engage in the glenoid defect. The understanding of this concept is important to help dictate treatment and decrease recurrence. Arner et al. reviewed the management of anterior shoulder instability including operative indications, techniques, and outcomes. They note that CT is helpful in addition to MRI and radiographs to evaluate glenoid bone loss. They review the glenoid track concept in detail, noting that off-track lesions can be an indicator of higher failure risk. Di Giacomo et al. dive into further detail regarding bipolar bone loss and the engaging vs. non-engaging Hill-Sachs lesion. They discuss specific methods for quantifying the glenoid track and its interplay with the Hill-Sachs lesion size. After taking these measurements (HSI/GT), they talk about whether the cases are "on-track," (HSIGT).Trivedi et al. also reviewed bipolar bone loss in the setting of shoulder instability with a focus on the GT concept. They note the degree of engagement is dependent on how far medially the Hill-Sachs lesion extends (>HSI). A greater HSI, in combination with an increase in glenoid bone loss, decreasing the GT, increases the risk for engagement and is deemed, "off-track"Illustration A is a diagram that demonstrates the concepts of glenoid track and Hill-Sachs Interval and how the lesion may engage.Incorrect Answers:Answer 2: "Off-track" lesions are more likely to engage.Answer 3: The presence of a bipolar lesion (glenoid and Hill-Sachs lesions), pertains higher risk to be "off-track," and engaging than a unipolar lesion. Answer 4: Classically, CT has been the gold standard for evaluating glenoid bone loss, however, newer studies have shown MRI may also be utilized. Answer 5: The Hill-Sachs interval is the distance between the medial aspect of the rotator cuff insertion and the most medial aspect of the Hill-Sachs lesion. If this number is greater than the glenoid track (GT), then the lesion is likely to engage, or be "off-track."
3.4
(7)
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