Exploring age-related differences in asymptomatic male shoulder kinematics using four-dimensional computed tomography.

Background: Understanding age-related differences in shoulder glenohumeral and scapulothoracic motion has implications for the understanding, treatment, and management of shoulder injuries and diseases. Previous studies have investigated age-related differences, although statically and in single-plane motion. The shoulder, however, is a complex joint capable of a wide range of motion (ROM) and involves coordinated and synchronous movements from both the glenohumeral and scapulothoracic joints. Therefore, the objectives of this study were to measure age-related differences in kinematics of the glenohumeral and scapulothoracic joints during motion, as well as differences in the neutral positioning of the scapula and humerus. Methods: Thirty-one male participants comprised 2 cohorts based on age (<45 and ≥ 45 years). Participants performed 2 motions, forward elevation (FE) and internal rotation (IR) to the back, with 4-dimensional computed tomography scanning to dynamically track the bones. The kinematics of the humerus and scapula were calculated with 6 degrees of freedom. The neutral position of the scapula and humerus was also calculated based on a static computed tomography scan. Results: During the FE motion, IR of the humerus was significantly greater (13°, Conclusion: Overall, this study found age-related differences in kinematics and neutral positioning of the scapula and humerus, which may help improve understanding of age-related differences in subluxation, diseases, injuries, and ROM.