Scapular Mechanisms of Movement-Related Shoulder Dysfunction

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PROJECT SUMMARY Clinicians rely on examination of movement to inform treatment planning for shoulder dysfunction. However, the links between scapular movement abnormalities, muscle activation, and rotator cuff deformation remain unclear, limiting the development of precise, individualized treatment of each patient. The long-term goal of this research is to understand movement-related development and treatment of shoulder dysfunction. The overall objectives for this project are to identify muscle activation and rotator cuff compression or glenoid obstruction, as proxies for deformation, in two specific scapular movement groups. The hypotheses are that individuals who demonstrate an excessive scapular anterior tilt movement pattern will have relatively reduced serratus anterior muscle activity and relatively increased rotator cuff compression from the coracoacromial (CA) arch. Individuals who demonstrate a scapular lateralization movement pattern will have relatively reduced lower trapezius muscle activity and relatively increased rotator cuff obstruction from the glenoid. The hypotheses will be tested through two specific aims. 1: Determine the extent to which scapulothoracic muscle activation differs during arm elevation between two specific scapular movement groups. The approach for this aim will be to classify participants into the two movement patterns based on overhead reaching kinematics derived from biplane video radiography and optical motion capture. Simultaneously collected electromyography will record muscle activity of key scapulothoracic muscles which will be compared between groups. 2: Determine the extent to which two specific scapular movement patterns during arm elevation result in subacromial compression or glenoid obstruction of the rotator cuff. The approach for this aim will be to recreate each participant’s arm motion using models of their humerus, scapula, and supraspinatus (rotator cuff) tendon and their specific arm raising kinematics. In instances when the tendon and the CA arch or glenoid make contact, the volume of intersection of the models will be quantified as a proxy for tendon deformation. This proposed research will contribute to science through the elucidation of patterns of muscle activation and rotator cuff tendon deformation in individuals with two specific scapular movement patterns. These contributions are expected to be significant because they will provide a framework for clinical treatment planning with regard to specific movement patterns and muscle activity patterns that should be targeted for individualized treatment. This proposed study is part of a fellowship training plan including medical imaging and advanced statistical analysis coursework, guided lab training, and mentored training in research skills needed to become an independent biomechanical researcher. Research activities and training will take place at the University of Minnesota. The University’s expansive research infrastructure, the multi-disciplinary Program in Rehabilitation Science, and the Minnesota Rehabilitation Biomechanics Laboratory create an ideal environment for completing this research and training.