The term “subluxation” has a long history in the healing arts literature. According to Haldeman  it was used at the time of Hippocrates , while the earliest English definition is attributed to Randall Holme in 1688. Holme  defined subluxation as “a dislocation or putting out of joynt.” Watkins  and Terrett  refer to a 1746 definition of the term.
The matter is further complicated by the diverse array of alternative terms used to describe subluxations. Rome listed 296 variations and synonyms used by medical, chiropractic, and other professions. Rome concluded the abstract of his paper by stating, “It is suggested that, with so many attempts to establish a term for such a clinical and biological finding, an entity of some significance must exist.” 
The possible neurological consequences of subluxation were described by Harrison in 1821, as quoted by Terrett: “When any of the vertebrae become displaced or too prominent, the patient experiences inconvenience from a local derangement in the nerves of the part. He, in consequence, is tormented with a train of nervous symptoms, which are as obscure in their origin as they are stubborn in their nature…” 
Although medical authorities acknowledge that neurological complications may result from subluxation, classical chiropractic definitions mandate the presence of a neurological component. 
D.D. Palmer and B.J. Palmer defined subluxation as follows: “A (sub)luxation of a joint, to a Chiropractor, means pressure on nerves, abnormal functions creating a lesion in some portion of the body, either in its action, or makeup.” 
According to Stephenson’s 1927 text, the following must occur for the term “vertebral subluxation” to be properly applied:
1. Loss of juxtaposition of a vertebra with the one above, the one below, or both.
2. Occlusion of an opening.
3. Nerve impingement.
4. Interference with the transmission of mental impulses. 
As Lantz noted, “Common to all concepts of subluxation are some form of kinesiologic dysfunction and some form of neurologic involvement.” 
Future columns will address specific neurological models and their operationalization.
1. Haldeman S: “The pathophysiology of the spinal subluxation.” In: Goldstein M (ed): The Research Status of Spinal Manipulative Therapy. DHEW publication no. (NIH) 76-998. Bethesda, MD, 1975.
2. Adams F (trans): “The Genuine Works of Hippocrates. Volume 2.” Sydenham Society, London, 1849.
3. Holme R: Academy of Armory. Published by the author in 1688. Reprinted by The Scholar Press, Ltd., Menston, England, 1972.
4. Watkins RJ: “Subluxation terminology since 1746.” J Can Chiro Assoc (1968) 12(4):20.
5. Terrett AJC: “The search for the subluxation: an investigation of medical literature to 1985.” Chiro History (1987) 7:29.
6. Rome PL: “Usage of chiropractic terminology in the literature: 296 ways to say ‘subluxation:’ complex issues of the vertebral subluxation.” Chiropractic Technique (May 1996) 8(2):49.
7. Evans DK: “Anterior cervical subluxation.” J Bone Joint Surg (Br) (1976) 58(3):318.
8. Palmer DD, Palmer BJ: “The Science of Chiropractic.” The Palmer School of Chiropractic, Davenport, IA, 1906.
9. Stephenson RW: Chiropractic Text-book. Palmer School of Chiropractic. Davenport, IA, 1927.
10. Lantz CA: “The subluxation complex.” In: Gatterman MI (ed): “Foundations of Chiropractic Subluxation.” Mosby, St. Louis, MO, 1995.