The doctor is in control of the treatment movements at all times. The posterior disc space increases in height. Flexion decreases disc protrusion and reduces stenosis. Discs protrude and degenerate into the concavity of a curve, into the side of extension. Flexion stretches the ligamentum flavum to reduce stenosis.
Flexion increases metabolite transport into the disc.
Flexion opens the apophyseal joints and reduces posterior disc stress. The nucleus pulposus does not move on flexion. Intradiscal pressure drops under distraction to below 100 mm Hg. On extension the nucleus or anulus is seen to protrude posterior into the vertebral canal. Intervertebral foraminal openings enlarge giving patency to the nerve.