New research shows the immediate effect of a chiropractic adjustment on the facet (or  Zygapophysial joint) on MRI. Watch this video which explains all.

http://www.chironexus.net/2013/07/chiropractic-adjustments-produce-immediate-results-visible-on-mri-video/

Reference

Cramer GD, et al. Magnetic resonance imaging zygaphosphyseal joint space changes (gapping) in low back pain patients following spinal manipulation and side-posture positioning: a randomized controlled mechanisms trial with blinding. Journal of Manipulative and Physiological Therapeutics 2013; pii: S0161-4754(13)00055-9. doi: 10.1016/j.jmpt.2013.04.003.