Assessment of lumbar spine kinematics using dynamic MRI: a proposed mechanism of sagittal plane motion induced by manual posterior-to-anterior mobilization.

STUDY DESIGN Descriptive study. OBJECTIVE The purpose of this study was to describe the segmental motion of the lumbar spine during a posterior-to-anterior (PA) mobilization procedure using dynamic magnetic resonance imaging and to propose a mechanism of the lumbar spine's motion as a result of a PA force to a lumbar spinous process. BACKGROUND Studies reporting kinematic descriptions of PA mobilization are in agreement that motion takes place at all lumbar vertebrae. However, these studies differ in the reported direction of motion. METHODS AND MEASURES Twenty asymptomatic subjects (mean age +/- SD, 31.1 +/- 7.0 years) participated in this study. For each subject, a PA mobilization force was manually applied at each lumbar spinous process while sagittal plane magnetic resonance images were simultaneously obtained. Intervertebral motion was defined as the change in the intervertebral angle between the resting and end range vertebral positions imparted by the PA pressure. RESULTS PA force applied at 1 spinous process caused motion at the target vertebra and this motion was propagated caudally and cranially. Motion at the target segment was always into extension. CONCLUSIONS A PA force applied at a single lumbar spinous process caused motion of the entire lumbar region. The magnitude and direction of intervertebral motions varied with the segment at which the PA force was applied. We postulated that the intervertebral motion induced by a PA force on a spinous process could be in part explained by the morphology of the lumbar spine.