Hill-Sachs lesion engagement, which is used for clinical decision-making in shoulder instability, is typically based on a static assessment, but would ideally be dynamically evaluated. The aim of this study was to evaluate differences between subject-specific and generalized glenohumeral motion. For five arm movements (forward elevation, scapula abduction, coronal abduction, external rotation at 90° abduction and external rotation at rest) of 20 participants, the average rotation and translation of the scapula and humerus throughout the forward movement were calculated. Metrics (length, distance, angle, and area) of the glenoid projection on the humerus were compared between the subject-specific and generalized (average of all subjects) motion. The impact of virtually generated glenoid bone loss (GBL) on the glenoid projection area was also investigated. Humeral rotation confidence intervals were narrow for abduction movements. The generalized and subject-specific glenoid projection metrics were similar. The average difference in the length of the glenoid movement over the humeral surface between the subject-specific and generalized motion ranged between 1-3 mm and the glenoid projection area differed between 1% and 7% for the five motions. The average distance between the subject-specific and generalized motion at the start or end position was less than 1 mm apart. GBL resulted in a subtly reduced glenoid projection area.

Statement of Clinical Significance:​ The similarity between the subject-specific and generalized glenohumeral motion for the five movements included in this study suggests that applying a generalized motion to patient-specific three-dimensional bone models may be an interesting direction for evaluating bipolar bone loss.

Level of Evidence:​ Level II (Control subjects;​ Development of diagnostic criteria)