Alteration in shoulder kinematics and associated muscle activity in people with idiopathic scoliosis.

STUDY DESIGN A cross-sectional control-matched study in adolescents with idiopathic scoliosis (IS). OBJECTIVE To evaluate whether subjects with IS had shoulder dysfunction and associated impairment in shoulder kinematics and muscular activation. SUMMARY OF BACKGROUND DATA Evidence indicates that shoulder kinematics are related to shoulder pain and dysfunction. Despite the degree of morbidity associated with altered shoulder kinematics likely to occur in subjects with IS, no report has been published to address this hypothesis. METHODS In this investigation, shoulder kinematics (scapular tipping, scapular upward rotation, and scapulohumeral rhythm) and associated muscular activities [upper trapezius (UT), lower trapezius (LT), serrantus anterior (SA), and middle deltoid (MD)] were evaluated with a 3-dimensional electromagnetic tracking device and electromyography during arm elevations in 13 female subjects with IS and 13 age-gender-dominant hand-matched controls. Additionally, self-reported Flexilevel Scale of Shoulder Function (FLEX-SF) was evaluated between the 2 groups. RESULTS Subjects with IS demonstrated lower FLEX-SF scores than the controls (P = 0.01). For the convex side, more anterior tilt of the scapula in resting position was identified (P = 0.006). For the concave side, more scapular upward rotation in resting position was identified (P = 0.01). For the EMG amplitude, higher LT contraction activity on the convex side and lower LT and SA contraction activity on the concave side were established (P = 0.007 and less than 0.01, respectively). A moderate positive association was found between scapular posterior tipping during movement and FLEX-SF functional score (R = 0.51). A moderate negative association was found between LT muscular activity and FLEX-SF functional score (R = -0.54). CONCLUSION Given the progressive nature of IS and kinematic linkage among the thoracic spine, scapula, and arm, inadequate posterior tipping movement and high LT muscular activity on the convex side of IS are important to consider in rehabilitation programs for subjects with IS.