This study measured the effects of a chiropractic adjustment on the low back (facet) joints. It proved that there was an effective gapping and stretching of these joints which was shown to help improve mobility and reduce the adhesions that are common place in the low back.
MRI scans were used to show how the gapping was most effective in the group using chiropractic techniques which also was the group which had the greatest reduction in pain.
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