Radiographic Analysis of the Hill-Sachs Lesion in Anteroinferior Shoulder Instability After First-Time Dislocations

Purpose: To identify the relation between the Hill-Sachs (H-S) angle and arm position at the time of the initial dislocation, and to see if this correlates with the glenoid track. Methods: A total of 102 patients (89 male patients, 87.2%), with a mean age of 32 years (range, 17 to 38 years), were divided into 2 groups, abduction (ABD) and adduction (ADD), dependent on the position of the arm at the time of the instability event. All patients were evaluated with bilateral computed tomography scans (3-dimensional) to define the H-S position on the glenoid track and to measure the H-S angle. One-way analysis of variance was used to compare the H-S angle between the 2 groups. Results: Dislocation occurred in ABD in 45 patients (44.1%) and in ADD in 57 (55.9%). The H-S angle was 32.4 degrees +/- 4.7 degrees in the ABD group versus 16.1 degrees +/- 2.9 degrees in the ADD group. All patients' injuries were "on-track" glenoid injuries in both groups. Conclusions: This study identified a difference in the H-S angle relative to arm position at the time of initial dislocation. Patients whose injury occurred in the ABD position showed a higher H-S angle, leading to an increased risk of engagement, because the long axis of the H-S lesion is parallel to the glenoid in a position of function. Thus arm position at the time of the initial instability event may be a risk factor for engagement and higher risk of recurrence.