Measurement of the Glenoid Track In Vivo as Investigated by 3-Dimensional Motion Analysis Using Open MRI

Background: A Hill-Sachs lesion is a common injury associated with anterior glenohumeral instability, and a Hill-Sachs lesion that engages with the anterior glenoid rim is 1 factor related to recurrent instability. In a cadaveric study in 2007, a new concept, the “glenoid track,” was proposed to evaluate the risk of engagement of Hill-Sachs lesions with the glenoid. Purpose: To investigate the glenoid track in vivo using a custom-developed noninvasive motion analysis system. Study Design: Descriptive laboratory study. Methods: Using a wide-gantry magnetic resonance imaging (MRI) scanner, the right shoulders of 30 healthy volunteers were examined. The MRI scans were taken of the right arm in 7 static supine positions from 0° to maximum abduction, keeping maximum external rotation and horizontal extension. Using the custom motion analysis system, 3-dimensional models of the scapula and humerus were created from the MRI data. Then, the movement of the humerus and scapula was calculated using voxel-based registration of each model, and the motion of the glenoid on the humeral head was analyzed. Results: The models demonstrated that glenoid contact shifted from the inferomedial to the superolateral portion of the humeral head. The mean widths of the glenoid track with the arm at 60°, 90°, 120°, and 150° of abduction were 20.7 ± 4.5 mm, 19.4 ± 3.9 mm, 18.9 ± 2.7 mm, and 18.7 ± 2.5 mm (89%, 83%, 82%, and 81% of the glenoid width), respectively. The width of the glenoid track at 60° of abduction was significantly greater than those at 90°, 120°, and 150° of abduction (P = .0472, .0148, and .0083, respectively). There were no significant differences among widths measured at 90°, 120°, and 150° of abduction. Conclusion: The existence and widths of the glenoid track were confirmed in vivo.