Mechanism of Action of Spinal Manipulation

Spinal manipulation therapy results in:
  • Facet joint (zygapophyseal or Z-joint) separation which is accompanied by a release of pressure within the joint and usually an audible cavitation or "popping noise".
  • Stretching of the paraspinal musculature that results in muscle relaxation (for which the mechanism has yet to be uncovered).
  • Decreased intradiscal pressure (particularly affecting the annulus and endplates, which when under pressure may activate nociceptive receptors that propagate pain).
  • Rise in beta endorphin (short-term analgesic effect after manipulation).
  • Inhibition of afferent presynaptic pain (spino-thalamic tract) via mechanoreceptor activation, therefore providing short-term cutaneous pain relief.

1) "Review: Mechanism of Action of Spinal Manipulation Therapy." J Maigne, P Vautravers. Joint Bone Spine. 2003;70:336-341.
Based on pre and post MR Imaging of the lumbar spine, patients who underwent side-posture manipulation of the lumbar spine exhibited gapping of the Z-joints that was not present prior to the manipulative procedure. Side-posture position in and of itself also produced gapping of the Z-joints, but less than those who received manipulation.

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2) "The Effects of Side-Posture Positioning and Spinal Adjusting on the Lumbar Z Joints: A Randomized Controlled Trial with Sixty-Four Subjects." G Cramer, D Gregerson, JT Knudsen, B Hubbard, L Ustas, J Cantu. Spine. 2002;27(22):2459-2466.