Contact between the glenoid and the humeral head in abduction, external rotation, and horizontal extension: A new concept of glenoid track

To date, no anatomic or biomechanical studies have been conducted to clarify what size of a Hill-Sachs lesion needs to be treated. Nine fresh-frozen cadaveric shoulders were tested in a custom device. With the arm in maximum external rotation, horizontal extension, and 0, 30, and 60 of abduction, the location of the entire rim of the glenoid was marked on the humeral head using a Kirschner wire. The distance from the contact area to the footprint of the rotator cuff with the arm in 60 of abduction was measured by a digital caliper. With an increase in arm elevation, the glenoid contact shifted from the inferomedial to the superolateral portion of the posterior aspect of the humeral head, creating a zone of contact (glenoid track). The medial margin of the glenoid track was located 18.4 +/- 2.5 mm medial from the footprint, which was equivalent to 84% +/- 14% of the glenoid width. A Hill-Sachs lesion has a risk of engagement and dislocation if it extends medially over the medial margin of the glenoid track.