Normal Vertebral Segment Motion

The identification of abnormal vertebral segment motion requires an understanding of normal vertebral segment motion. Normal motion at a lumbar vertebral segment with flexion and extension can be described as follows:

Flexion: The superior vertebral body rotates in relation to the inferior vertebral body around a transverse axis so that the anterior intervertebral space narrows while the posterior intervertebral space widens. The superior vertebral body also translates anteriorly on the inferior vertebral body of the segment. The inferior articulating processes of the superior vertebra glide superiorly on the superior articulating processes of the inferior vertebra of the segment. No side bending or rotation should occur if the movement stays within the sagittal plane.

Extension: The superior vertebral body rotates in relation to the inferior vertebral body around a transverse axis so that the anterior intervertebral space widens while the posterior intervertebral space narrows. The superior vertebral body also translates posteriorly on the inferior vertebral body of the segment. The inferior articulating processes of the superior vertebra glide inferiorly on the superior articulating processes of the inferior vertebra of the segment. No side bending or rotation should occur if the movement stays within the sagittal plane.

Symmetrical movement at the vertebral segment should occur if the movement is kept within the sagittal plane. With injury or adaptive changes, motion at a segment may become symmetrically reduced (hypomobility) or increased (hypermobility) or become asymmetrical. These changes in the quantity and/or quality of segmental motion help the clinician identify altered function at a vertebral segment. Of particular interest to muscle energy practitioners are the asymmetrical motion patterns that occur when symmetry is expected.
Flexion
Extension