Shoulder Complex Mechanics in Adolescent Idiopathic Scoliosis and Their Relation to Patient-perceived Function

Background: Proper contribution of the scapulothoracic joint is necessary for adequate shoulder complex function. Associations between trunk shape and abnormal scapular kinematics and subsequent shoulder dysfunction have been established; however, the extent of shoulder dysfunction in adolescent idiopathic scoliosis (AIS) is still poorly understood. The purpose of this study was to perform a comprehensive analysis of scapular kinematics during multiplanar arm motion in patients with AIS and compare kinematics and patient-reported function with that of a typically developing cohort. Methods: Typically developing adolescents (n=33) and patients with AIS (n=26) with no history of spine or shoulder surgery were recruited for this study. A 3-dimensional optoelectronic motion capture system was used to analyze scapular kinematics in 4 positions: rest, full abduction, forward reach, and hand to spine. Subjects in each group also completed the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire as a measure of patient-reported function. Results: The convex shoulders of the patients with AIS exhibited deficits in scapular upward rotation and posterior tilt in all positions and reduced protraction range of motion during reaching. The AIS group also reported worse patient-perceived shoulder function than the typically developing group; however, this dysfunction was not related to specific scapular kinematic patterns. Conclusions: Patients with AIS show alterations in scapular kinematics that are associated with shoulder pathology. Despite displaying an unaffected ability to place the hand in space, the underlying joint mechanics place these adolescents at risk for future pathology. Accordingly, consideration of scapulothoracic and glenohumeral joint function is warranted in the treatment of AIS. Level of Evidence: Level III - cross-sectional comparison.