In Which Arm Position Is a Hill-Sachs Lesion Created?

Background: It has been believed that a Hill-Sachs lesion (HSL) is created with the arm in abduction and external rotation at the time of dislocation. However, no studies have clarified the arm position in which an HSL is created. Purpose: To determine the arm position in which an HSL is created. Study Design: Descriptive laboratory study. Methods: The computed tomography images of 100 shoulders of 100 patients (72 males and 28 females; mean age, 30 years old) with recurrent anterior dislocation of the shoulder were investigated using an image analyzing software. Three-dimensional surface bone models of the scapula and humerus were created separately. The humerus was moved so that the HSL perfectly fit the anterior rim of the glenoid. This arm position was recorded 3-dimensionally. Results: Considering the scapulohumeral rhythm, the average arm position in which the HSL and the anterior glenoid rim best fit was 74 degrees of abduction, 27 degrees of external rotation, and 3 degrees of horizontal flexion relative to the trunk. Conclusion: The arm position when an HSL and the anterior glenoid rim best fit is 74 degrees of abduction, 27 degrees of external rotation, and 3 degrees of horizontal flexion, which seems to be the arm position when the HSL has been created. This result suggests 2 possibilities: dislocation occurred in this midrange position or HSL was not created at the time of dislocation but later in the mid-range of motion. However, as we have no information on the arm position at the time of dislocation, we cannot conclude which of these possibilities is true in our study.