In chiropractic, a vertebral subluxation means pressure on nerves, abnormal functions creating a lesion in some portion of the body, either in its action, or makeup (defined by D.D. Palmer and B.J. Palmer, founders of chiropractic), not necessarily visible on X-rays. Straight chiropractors continue to follow Palmer's tradition, claiming that vertebral subluxation has considerable health effects and also adding a visceral component to the definition. [Source: Wikipedia ]