Scapular dyskinesis: patterns, functional disability and associated factors in people with shoulder disorders

Abstract Background Patterns of scapular dyskinesis have unique scapular kinematics and associated muscular activation. The characteristics of unique dyskinesis patterns may be associated with functional disability. Objectives To investigate whether the shoulder function level and primary dysfunction items were different in unique dyskinesis pattern. The factors associated with shoulder dysfunction in different dyskinesis patterns were identified. Design Cross-sectional study. Methods Fifty-one participants with unilateral shoulder pain were classified as having a single dyskinesis pattern (inferior angle prominence, pattern I; medial border prominence, pattern II) or a mixed dyskinesis pattern (patterns I + II). Clinical measurements with the Flexilevel Scale of Shoulder Function (FLEX-SF), shoulder range of motion and pectoralis minor index were recorded. These clinical measurements, 3-D scapular kinematics (electromagnetic-based motion analysis), and associated muscular activation (electromyography on the upper/middle/lower trapezius and serratus anterior muscles) during arm elevation were analyzed for associations with functional disability. Results We found FLEX-SF scores and primary dysfunction items were similar among the patterns of dyskinesis. In inferior angle prominence, increased shoulder function was associated with decreased upper trapezius activity (R 2  = 0.155, p = 0.035), which accounted for approximately 16% of the variance of FLEX-SF scores. In medial border prominence, increased shoulder function was associated with increased lower trapezius activity (R 2  = 0.131, p = 0.017), which accounted for approximately 13% of the variance of FLEX-SF scores. Conclusion Upper and lower trapezius activities are important to consider in the evaluation of patients with pattern I and II, respectively. No other factors were related to shoulder dysfunction due to insufficient challenge of arm elevation tasks.