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. Click here to see a video demonstration.
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.