THE EVALUATION OF SCAPULAR KINEMATICS AND MUSCULAR CHARACTERISTICS OF THE SCAPULAR STABILIZERS IN OVERHEAD ATHLETES PRESENTING WITH SCAPULAR DYSKINESIS COMPARED TO HEALTHY CONTROLS

摘要

Proper scapular motion is essential to the performance of efficient and injury free overhead activities and altered scapular motion is known to be associated with shoulder pathology. Intervention strategies addressing scapular dyskinesis have yielded inconsistent results. The purpose of this study was to determine if differences were present in scapular kinematics, muscular strength and activation patterns between a healthy control and a dyskinesis group. Thirty-four overhead athletes subjects (Normal group: n=17, Obvious dyskinesis group: n=17) participated in this study. A surface infrared optical capture system was used to measure scapular kinematics during weighted humeral elevation and depression during flexion and abduction. Muscle activation patterns of the scapular stabilizers were assessed using surface and indwelling electromyography. Isometric strength of the pectoralis minor, rhomboid major, serratus anterior, upper, middle, and lower trapezius was assessed using hand-held dynamometry and normalized to body weight (%BW). Independent t-tests or Mann-Whitney U tests, for data that violated normality, were used to assess for mean differences in scapular upward/downward rotation (UR/DR), internal/external rotation (IR/ER), and anterior/posterior tilt (AT/PT) at 30°, 60°, 90° and 120° of humeral elevation/depression, %MVIC, on/off activation, and isometric strength (%BW) of each of the scapular stabilizers. A significance level was set a priori at alpha = 0.05. The dyskinesis group demonstrated significantly less scapular UR at 30° humeral elevation (p=0.012) and depression (p=0.004), increased %MVIC of the pectoralis minor 90-120° humeral elevation(p=0.038), decreased activation of the upper trapezius from 30°-60° of humeral elevation (p=0.045) and decreased activation of the rhomboid major from 120°-30° humeral depression(p=0.011-0.034). Delayed de-activation of the pectoralis minor (p=0.020) and serratus anterior (p=0.031) was also observed. No differences in isometric strength were found between groups. Overhead athletes with obvious scapular dyskinesis demonstrated decreased scapular UR, decreased activation of the upper trapezius and rhomboid major, and increased activation of the pectoralis minor. When clinicians clinically identify the presence of obvious scapular dyskinesis, rehabilitation strategies should aim to increase activation of the of the scapular upward and external rotators while addressing potential hyper-tonicity of the pectoralis minor in order to re-establish coordinated muscular control of dynamic scapular motion.