Huang T.S.1, Ou H.L.1,2, Huang C.Y.1, Lin J.J.1,3
1School and Graduate Institute of Physical Therapy, College of Medicine, National Taiwan University, Taipei, Taiwan, 2Department of Physical Medicine and Rehabilitation, Taipei Medical University Hospital, Taipei, Taiwan, 3Division of Physical Therapy, Department of Physical Medicine and Rehabilitation, National Taiwan University Hospital, Taipei, Taiwan
Background: Scapular dyskinesis is defined as alteration of scapular position and movement. In current literature, it is still not clear whether the scapular kinematics and muscle activation were specific to pattern of scapular dyskinesis.
Purpose: This study used principal component analysis (PCA) to detect the main movement features in 2 patterns of dyskinesis including inferior angle (pattern I) and medial border (pattern II) prominence of scapula during lowering phase of arm elevation.
Methods: One hundred thirty-four participants with shoulder pain and scapular dyskinesis were recruited and classified as pattern I and II. Movement outcomes were recorded as 3-dimendional scapular kinematics by electromagnetic motion-capture system and upper/middle/lower trapezius and serratus anterior muscles activations by surface electromyography during arm elevation in scapular plane. Clinical outcomes included pectoralis minor length index and posterior shoulder tightness. PCA was performed to detect movement characteristics specific to dyskinesis pattern I and pattern II. The PC accounting at least 10% of the total variance was retained in the final model.
Results: The three PCs were retained for both dyskinesis pattern I and pattern II. For pattern I, all kinematics variables including scapular upward rotation/posterior tipping/internal rotation and middle/lower trapezius muscle activation were shown in three PCs. Additionally, all kinematics variables and upper/middle/lower trapezius muscle activations were selected in three PCs for pattern II. The total variance explained by these selected PCs for pattern I and pattern II were 41% and 43%, respectively. The dominant movement characteristics with significant loading coefficients (PC1) in pattern I relied on upward rotation and posterior tipping of scapula and muscle activation of middle and lower trapezius. On the other hand, patients with pattern II exhibited significant loading coefficient (PC1) for upper and middle trapezius muscles activation.
Conclusion(s): The dominant movement characteristics were specific to pattern of scapular dyskinesis during lowering phase of arm elevation. On the other hand, low total variance explained by PCs may be due to other possible factors related to movement characteristics in dyskinesis participants.
Implications: Evaluation and treatment of patients with inferior angle and medial border prominence should focus on different components with dominant activation of lower trapezius and upper trapezius muscles, respectively. Low total variance explained by PCs indicates that other factors may be characterized and specific to each pattern of dyskinesis.
Funding acknowledgements: Ministry of Science and Technology, 101-2314-B-002-019-MY3, Taiwan
Topic: Musculoskeletal: upper limb
Ethics approval: Human Subject Research Ethics Committee, National Taiwan University Hospital
All authors, affiliations and abstracts have been published as submitted.
