Cervical segmental motion induced by shoulder abduction assessed by magnetic resonance imaging.

STUDY DESIGN: A comparative measurement study of in vivo cervical rotation, induced by shoulder abduction, measured using magnetic resonance imaging.

OBJECTIVE: The purpose of this study was to clarify the kinematics between cervical rotation and shoulder abduction.

SUMMARY OF BACKGROUND DATA: Although it is believed that abduction of the shoulder induces rotational movement of the cervical spine, there have been no in vivo studies to measure the influence of shoulder movement on the cervical spine at a segmental level.

METHODS: Twenty-two participants [12 men, age 24.2 years (range, 20-32 years)] without history of significant cervical spine disorders were studied. Kinematic magnetic resonance imaging of the cervical spine was performed with a 0.2-T horizontally open unit. Cervical rotation was assessed with the shoulder in 0, 30, 60, 90, and 120 degrees abduction. In each position, 2 conditions were applied. Firstly no muscle contraction with the arm relaxed and supported and secondly isometric contraction of the shoulder abductors. Isometric contraction was standardized by a 2-kg adduction force applied at the wrist, perpendicular to the arm.

RESULTS: No statistically significant differences were found in cervical segmental rotation between each shoulder position under passive conditions (P > 0.05). When the right shoulder was abducted, with isometric contraction, at each shoulder position up to 90 degrees abduction, each cervical vertebra tended to rotate to the left and the largest vertebral movement was seen at C6, being 5.20 degrees (SD = 3.66) at 0 degrees abduction. The pattern of movement changed at 120 degrees abduction, with C1 and C2 rotating to the right.

CONCLUSION: Shoulder abduction up to 90 degrees induced left rotation throughout the cervical spine only in the presence of muscle contraction, with the largest movement occurring at C6. A contrasting pattern of upper and lower cervical rotation occurred when the arm was positioned in 120 degrees abduction.