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

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 (R2  = 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 (R2  = 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.