On-track and off-track shoulder lesions

Last revised by Michał Marek on 15 Sep 2023

Bipolar shoulder lesions of anterior glenohumeral dislocations (i.e. combined bony Bankart lesions and Hill-Sachs defects) put patients at increased risk of Hill-Sachs engagement or recurrent instability. Determining if the Hill-Sachs defects are on-track or off-track can help guide management, although arthroscopy remains gold-standard for diagnosis. 

The glenoid track refers to the area of contact between the humeral head and glenoid and is defined as ~83% of glenoid width 2,3. A Hill-Sachs defect that is smaller than the track ("on-track") will maintain contact and is at lower risk of engagement and instability. Conversely, a Hill-Sachs defect that is larger than the glenoid track ("off-track") will be at increased risk of engagement and instability (i.e. is an "engaging Hill-Sachs defect") 3

Thus, there are two factors that contribute to determining if a bipolar bone lesion is on-track or off-track:

Off-track lesions can result from either a large bony Bankart lesion or Hill-Sachs defect, or from a combination of a moderate-sized Hill-Sachs defect and moderate-sized bony Bankart lesion. 

Determining on-track or off-track lesions was initially described on CT but can also be calculated on MRI 2. Two measurements are required 2,3:

  • glenoid track: calculated on a sagittal oblique plane of the glenoid using the best-fit circle method

    • a best-fit circle is placed on the glenoid, matching the posterior and inferior borders

    • a horizontal line is drawn through the center of the best-fit circle reaching both anterior and posterior aspects (D)

    • a second horizontal line is drawn along the same plane from the anterior aspect of the circle to the anterior glenoid (d), i.e. measuring the width of anterior glenoid bone loss

    • glenoid track = (0.83 x D) - d

  • Hill-Sachs interval = Hill-Sachs defect + bone bridge between the rotator cuff attachment and lateral margin of the Hill-Sachs defect

    • measured in the axial plane

A bipolar lesion is said to be engaging if the Hill-Sachs interval is larger than the glenoid track:

  • non-engaging, on-track Hills-Sachs defect = Hill-Sachs interval < glenoid track

  • engaging, off-track Hills-Sachs defect = Hill-Sachs interval > glenoid track

Off-track bipolar lesions may be treated surgically with reconstitution of the anteroinferior glenoid bone stock (commonly via a Latarjet procedure) +/- remplissage depending on the size of the Hill-Sachs defect 3.

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