The Effects of Cervical Spine Position and Spinal Manipulation on Shoulder Rotation Strength

Abstract

Shoulder rotation strength is included as part of an orthopedic examination for clinicians treating patients presenting with shoulder pathology. However, for populations prone to shoulder injury, such as overhead athletes and trades workers, shoulder function is required in non-neutral cervical spine positions, which differs from how it is assessed in clinic. Further, spinal manipulation is used in clinic to address shoulder issues arising from cervical radiculopathy and thoracic outlet syndrome. A case can be made for the functional positions of overhead athletes and trades workers mimicking mechanisms of injury for cervical radiculopathy and thoracic outlet syndrome. Therefore, the purpose of this dissertation was to examine the effects of a rotated cervical spine on shoulder rotation strength, to examine the effects of thoracic and cervicothoracic spinal manipulation on shoulder external rotation strength, and to see if spinal manipulation moderates the potential deleterious effect of an altered cervical spine position on shoulder rotation strength. Fifty-two healthy, active volunteers participated. Isokinetic external and internal rotation strength was assessed using an isokinetic dynamometer. Multilevel model analyses revealed a negative effect of a rotated cervical spine on shoulder rotation strength. There was no evidence found to support the use of spinal manipulation for improving shoulder rotation strength or for moderating the effect of a rotated cervical spine on shoulder rotation strength. The results of this study indicate the functional position for populations such as overhead athletes and trades workers may contribute to shoulder weakness. This may serve as a basis to help explain the higher injury rates in these populations.