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Patterns of Shoulder Imbalance in Adolescent Idiopathic Scoliosis: A Retrospective Observational Study

Study Design: Retrospective cohort study. Objective: To study the relationship between the proximal spine and shoulder levels in adolescent idiopathic scoliosis (AIS). Summary of Background Data: It has been frequently observed that the shoulder levels do not correspond to the spinal curve direction in AIS. Materials and Methods: Eighty-five operated cases of AIS were analyzed retrospectively of which 69 were Lenke type I and II curves. Preoperative anteroposterior standing x-rays of the spine and clinical photographs were studied. T1 tilt and intercoracoid line (ICL) tilt and their mutual relationship were documented. The curve type (Lenke), magnitude, and direction of the proximal and main thoracic (PT and MT) curves were also noted. Results: The shoulder level as depicted by the ICL showed 3 patterns—horizontal, left side elevated, or right side elevated. The T1-ICL relationship was either concordant or discordant. In the concordant case the T1 was tilted to the same side as the ICL; and vice versa in the discordant. The shoulder level was dependent on the MT curve if the ICL tilted to the same side as the MT curve and it was dependent on the PT curve if it tilted to the same side as the PT curve. This relationship appeared unrelated to curve type. Conclusions: Preoperative shoulder levels in AIS may be concordant with the T1 or discordant—each can have left or right shoulder elevation or balanced shoulders. Further, the shoulder might be MT dependent or PT dependent. Theoretically therefore, surgical balancing of the shoulder and upper instrumented vertebra placement should not depend only on the magnitude and stiffness of the PT curve.