On-track and off-track shoulder lesions

Last revised by Michał Marek on 15 Sep 2023

Citation, DOI, disclosures and article data

Citation:

Knipe H, Marek M, Gilcrease-Garcia B, et al. On-track and off-track shoulder lesions. Reference article, Radiopaedia.org (Accessed on 16 Apr 2024) https://doi.org/10.53347/rID-72203

DOI:

https://doi.org/10.53347/rID-72203

Permalink:

https://radiopaedia.org/articles/72203

rID:

72203

Article created:

14 Nov 2019, Henry Knipe ◉ ◈

Disclosures:

At the time the article was created Henry Knipe had no recorded disclosures.

View Henry Knipe's current disclosures

Last revised:

15 Sep 2023, Michał Marek

Disclosures:

At the time the article was last revised Michał Marek had no financial relationships to ineligible companies to disclose.

View Michał Marek's current disclosures

Revisions:

16 times, by 7 contributors - see full revision history and disclosures

Systems:

Musculoskeletal

Sections:

Approach

Tags:

engaging hill-sachs lesion, engaging hill-sachs defect, cases

Synonyms:

On-track lesion
Off-track lesion

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:

anteroinferior glenoid bone loss
Hill-Sachs interval

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.

Radiographic features

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

Treatment and prognosis

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.