In chiropractic, vertebral subluxation is a set of signs and symptoms of the spinal column.[specify] Those chiropractors who assert this concept (specifically, "straight chiropractors") also add a visceral component to the definition. Chiropractors maintain that a vertebral subluxation complex is a dysfunctional biomechanical spinal segment which is fixated. Chiropractors additionally assert that the dysfunction actively alters neurological function, which in turn, is believed to lead to neuromusculoskeletal and visceral disorders. The WHO acknowledges this difference between the medical and chiropractic definitions of a subluxation. Medical doctors only refer to "significant structural displacements" as subluxations, whereas chiropractors suggest that a dysfunctional segment, whether displaced significantly or not, should be referred to as a subluxation. This difference has been noted in the proceedings of the chiropractic profession's Mercy Center Consensus Conference: "The chiropractic profession refers to this concept as a 'subluxation'. This use of the word subluxation should not be confused with the term's precise anatomic usage, which considers only the anatomical relationships."
The chiropractic vertebral subluxation complex has been a source of controversy since its inception in 1895 due to its metaphysical origins and claims of far reaching effects on health and disease. Although some chiropractic associations and colleges support the concept of subluxation, many in the chiropractic profession reject it and shun the use of this term as a diagnosis In the United States and in Canada the term nonallopathic lesion is commonly used in place of subluxation as a diagnosis, and is considered a more accurate descriptor of lesions that chiropractors treat most commonly.
In 1909 B.J. Palmer wrote that:
- "Chiropractors have found in every disease that is supposed to be contagious, a cause in the spine. In the spinal column we will find a subluxation that corresponds to every type of disease. If we had one hundred cases of small-pox, I can prove to you where, in one, you will find a subluxation and you will find the same conditions in the other ninety-nine. I adjust one and return his functions to normal... . There is no contagious disease... . There is no infection... . There is a cause internal to man that makes of his body in a certain spot, more or less a breeding ground [for microbes]. It is a place where they can multiply, propagate, and then because they become so many they are classed as a cause." -- B.J. Palmer, The Philosophy of Chiropractic, V. Davenport, IA: Palmer School of Chiropractic; 1909
Definitions and current official status
The WHO definition of the chiropractic vertebral subluxation is:
- "A lesion or dysfunction in a joint or motion segment in which alignment, movement integrity and/or physiological function are altered, although contact between joint surfaces remains intact. It is essentially a functional entity, which may influence biomechanical and neural integrity."
The purported displacement is not necessarily visible on X-rays. This is in contrast to the medical definition of spinal subluxation which, according to the WHO, is a "significant structural displacement", and therefore visible on X-rays.
In 1996 an official consensus definition of subluxation was formed. Cooperstein and Gleberzon have described the situation: "... although many in the chiropractic profession reject the concept of "subluxation" and shun the use of this term as a diagnosis, the presidents of at least a dozen chiropractic colleges of the Association of Chiropractic Colleges (ACC) developed a consensus definition of "subluxation" in 1996. It reads:
- "Chiropractic is concerned with the preservation and restoration of health, and focuses particular attention on the subluxation. A subluxation is a complex of functional and/or structural and/or pathological articular changes that compromise neural integrity and may influence organ system function and general health. A subluxation is evaluated, diagnosed, and managed through the use of chiropractic procedures based on the best available rational and empirical evidence."
In 2001 the World Federation of Chiropractic, representing the national chiropractic associations in 77 countries, adopted this consensus statement which reaffirms belief in the vertebral subluxation.
The ACC paradigm has been criticized by chiropractic authors:
- "All in all, the ambiguities that permeate the ACC's statements on subluxation render it inadequate as a guide to clinical research... Whether the ACC's subluxation claims have succeeded as a political statement is beyond our concern here. These assertions were published as a priori truths (what many chiropractors have traditionally referred to as "principle"), and are exemplary of scientifically unjustified assertions made in many corners of the profession. It matters not whether unsubstantiated assertions are offered for clinical, political, scientific, educational, marketing or other purposes; when offered without acknowledgment of their tentative character, they amount to dogmatism. We contend that attempts to foster unity (among the schools or in the wider profession) at the expense of scientific integrity is ultimately self-defeating. To be sure, the profession's lack of cultural authority is based in part upon our characteristic disunity. However, attempts to generate unity by adoption of a common dogma can only bring scorn and continued alienation from the wider health care community and the public we all serve."
In May 2010 the General Chiropractic Council, the statutory regulatory body for chiropractors in the United Kingdom, issued guidance for chiropractors stating that the chiropractic vertebral subluxation complex "is an historical concept" and "is not supported by any clinical research evidence that would allow claims to be made that it is the cause of disease or health concerns."
Traditionally there have been 5 components that form the chiropractic subluxation. The vertebral subluxation complex is differentiated by the fifth component, general systemic disturbances secondary to the spinal misalignment (vertebral subluxation).
- Spinal Kinesiopathology
Historically, the detection of spinal misalignments (subluxations) by the chiropractic profession has relied on X-ray findings and physical examination. At least 2 of the following 4 physical signs and/or symptoms must be documented to qualify for reimbursement:
- Pain and tenderness
- Range of motion abnormality
- Tissue/tone changes
It has been proposed that a vertebral subluxation can negatively affect general health by altering the neurological communication between the brain, spinal cord and peripheral nervous system. Although individuals may not always be symptomatic, straight chiropractors believe that the presence of vertebral subluxation is in itself justification for correction via spinal adjustment.
Chiropractic treatment of vertebral subluxation focuses on delivering a chiropractic adjustment which is a high velocity low amplitude (HVLA) thrust to the dysfunctional spinal segments to help correct the chiropractic subluxation complex. Spinal adjustment is the primary procedure used by chiropractors in the adjustment. Adjustment/manipulation has been shown to help with low back pain, neck pain and tension type headaches, but further studies are inconclusive on the use of spinal manipulation outside the treatment of neuromusculoskeletal disorders.
Rationale and disagreements
In 1910, D.D. Palmer, the founder of chiropractic, wrote:
- "Physiologists divide nerve-fibers, which form the nerves, into two classes, afferent and efferent. Impressions are made on the peripheral afferent fiber-endings; these create sensations which are transmitted to the center of the nervous system. Efferent nerve-fibers carry impulses out from the center to their endings. Most of these go to muscles and are therefore called motor impulses; some are secretory and enter glands; a portion are inhibitory their function being to restrain secretion. Thus, nerves carry impulses outward and sensations inward. The activity of these nerves, or rather their fibers, may become excited or allayed by impingement, the result being a modification of functionating — too much or not enough action — which is dis-ease."
Chiropractors use and have used various terms to express this concept: subluxation, vertebral subluxation (VS), vertebral subluxation complex (VSC), "killer subluxations", and the "silent killer".
Some chiropractors have described the disagreements within the profession about the concept, and have written skeptically about BOOP as an antiquated idea. In 1992 one wrote:
- "The main problem we often run into is the bone out of place (BOOP) concept. It seems we somehow step on toes when we describe the spine as a functioning entity instead of a stack of bones that can be shifted back and forth into the ideal configuration. The BOOP concept will eventually fade, and we are grateful for its contribution to chiropractic. For many decades, it offered a model to work from. This model has been updated by the rest of the healing profession, but chiropractors have been hesitant to let this antiquated model go. Some within our profession hold onto this model with a religious fervor. The chiropractic profession has moved into a new age. The BOOP concept has been updated and science is ever upon us in the 90s. Let's start asking questions again and drive the chiropractic profession kicking and screaming into the 21st century."
One wrote in 1994 about the "brutal civil war":
- "According to various gossip columnists in chiropractic, our profession appears to be currently enmeshed in a brutal civil war between BOOP (bone-out-of-place) practitioners and low back pain practitioners. It should be known that the BOOPers incorrectly call themselves subluxation-based practitioners. My experience has demonstrated that the BOOPers do not know enough about subluxation to call themselves subluxation-based chiropractors. We would all do well to not be subluxation-based in the BOOP sense. It should also be know that this so-called war is really an over-dramatized skirmish between vocal BOOPers and a theoretical group of anti-chiropractic DCs. I have yet to meet any of these anti-chiropractic DCs. Unfortunately, the BOOPers seem to think that those who do not embrace the totality of BOOP philosophy are merely non-BOOPers who are still very pro-chiropractic and appreciate the philosophy of chiropractic from a contemporary and nondogmatic perspective."
Ten years later (in 2004) he openly disparaged the idea still propounded by "modern-day advocates of this concept":
- "... it is essentially impossible to have nerve interference. To summarize, nerve interference is described, by modern-day advocates of this concept, as a reduction of neural or mental impulses, which occurs in response to a bone-out-of-place (BOOP) subluxation... Clearly, the BOOP subluxation model fails miserably when considered in the light of basic neuroscience facts... BOOP subluxationists become angry and defensive when the BOOP model of subluxation is criticized... The reactionary nature of certain BOOP subluxationists is to accuse those who don't buy into the BOOP model of being anti-chiropractic - an astonishing leap of ignorance, to say the least. Furthermore, anyone who does not buy into the model is trying to "medicalize chiropractic" - another example of low-IQ thinking. And if tears do not well up in your eyes when you hear the phrase, "The power that made the body, heals the body," you are accused of having no passion for chiropractic - still another example of depressed, frontal-lobe activity. Even worse, if you don't buy into every bizarre, New Age, tree-hugging notion that comes down the pike and is circularly attached to subluxation, you will be accused of being an atheist - an excellent example of the need for psychiatrists and the drugs they prescribe."
|Spinal nerve roots|
The formation of the spinal nerve from the dorsal and ventral roots
A spinal nerve with its anterior and posterior roots.
V. Strang, D.C., describes several hypotheses on how a misaligned vertebra may cause interference to the nervous system in his book, Essential Principles of Chiropractic:
- Nerve compression hypothesis: suggests that when the vertebrae are out of alignment, the nerve roots and/or spinal cord can become pinched or irritated. While the most commonly referenced hypothesis, and easiest for a patient to understand, it may be the least likely to occur.
- Proprioceptive insult hypothesis: focuses on articular alterations causing hyperactivity of the sensory nerve fibers.
- Somatosympathetic reflex hypothesis: all the visceral organ functions can be reflexly affected by cutaneous or muscular stimulation.
- Somatosomatic reflex hypothesis: afferent impulses from one part of the body can result in reflex activity in other parts of the body.
- Viscerosomatic reflex hypothesis: visceral afferent fibers cause reflex somatic problems.
- Somatopsychic hypothesis: the effects of a subluxation on the ascending paths of the reticular activating system.
- Neurodystrophic hypothesis: focuses on lowered tissue resistance that results from abnormal innervation.
- Dentate ligament-cord distortion hypothesis: upper cervical misalignments can cause the dentate ligaments to put a stress on the spinal cord.
- Psychogenic hypothesis: emotions, such as stress, causing contraction in skeletal muscles.
The vertebral subluxation has been described as a syndrome with signs and symptoms which include: altered alignment; aberrant motion; palpable soft tissue changes; localized/referred pain; muscle contraction or imbalance; altered physiological function; reversible with adjustment/manipulation; focal tenderness.
Investigation to confirm the existence of vertebral subluxations has been ongoing since it was first postulated in 1895. The early practitioners used palpation and the anatomy of the nervous system as a guide (meric system). In their efforts to be more specific, they seized the newly discovered X-ray technology and introduced the neurocalometer (a heat sensing device). It was during those early years that the medical establishment first criticized the chiropractic profession, saying that the conditions that those early chiropractors were treating were only psychophysiologic disorders. To prove that chiropractic patients had real conditions, BJ Palmer opened a research clinic as a part of the Palmer College of Chiropractic. When a patient entered the clinic, they were first examined by medical doctors and a diagnosis was formulated. They were then sent to the chiropractic part of the clinic, treated, and sent back to the medical doctors for evaluation. Since then, chiropractors have sought a greater understanding of the mechanisms and effects of the vertebral subluxation. Today we see motion x-rays, surface EMG, and digital thermography though none of these methods have been proven to be reliable or valid in the detection of vertebral subluxations.
As research projects are able to employ new techniques and technologies to evaluate nervous system function and effects, further support for chiropractic principles has surfaced. Chiropractors have long suggested that spinal joint fixation that results from subluxation will result in degenerative effects that compromise the spinal joints. A 2004 research team at the National University of Health Sciences evaluated changes of the lumbar vertebral column following fixation (immobility) by surgically fusing spinal joints in experimental rats. The fixated joints showed significant degeneration compared to the mobile joints, confirming that surgical fixation results in time-dependent degenerative changes of the zygapophysial joints.
Chiropractic also asserts that spinal health and function are directly related to general health and well-being. David Seaman, DC, MS reviewed the work of several researchers concerning autonomic nervous system relationship to the somatic tissues of the spine. He noted that Feinstein et al. were the first to clearly describe some symptoms associated with noxious irritation of spinal tissues. They injected hypertonic saline into interspinous tissues and paraspinal muscles of normal volunteers for the purpose of characterizing local and referred pain patterns that might develop. His observations included:
- "The pain elicited from muscles was accompanied by a characteristic group of phenomena which indicated involvement of other than segmental somatic mechanisms … The manifestations were pallor, sweating bradycardia, fall in blood pressure, subjective faintness, and nausea, but vomiting was not observed. Syncope occurred in two early procedures in the series of paravertebral injections and was subsequently avoided by quickly depressing the subject's head or by having him lie down at the first sign of faintness. These features were not proportional to the severity of or to the extent of radiation; on the contrary, they seemed to dominate the experience of subjects who complained of little pain, but who were overwhelmed by this distressing complex of symptoms."
Feinstein referred to these symptoms as autonomic concomitants. It is likely that these autonomic concomitants were caused by nociceptive stimulation of autonomic centers in the brainstem, particularly the medulla. Feinstein indicated that "this is an example of the ability of deep noxious stimulation to activate generalized autonomic responses independently of the relay of pain to conscious levels." In other words, pain may not be the symptomatic outcome of nociceptive stimulation of spinal structures. Such a conclusion has profound implications for the chiropractic profession. Clearly, patients do not need to be in pain to be candidates for spinal adjustments.
The efficacy and validity of spinal manipulation to address visceral disorders systems remains a source of controversy within the chiropractic profession. Although research is ongoing on this topic, conclusions that support the usefulness of spinal manipulation for organic disorders remains to be seen. Additionally, to complicate matters, chiropractic professors and researchers, Nansel and Szlazak, found that:
- "the proper differential diagnosis of somatic (musculoskeletal) vs. visceral (organ) dysfunction represents a challenge for both the medical and chiropractic physician. The afferent convergence mechanisms, which can create signs and symptoms that are virtually indistinguishable with respect to their somatic vs. visceral etiologies, suggest it is not unreasonable that this somatic visceral-disease mimicry could very well account for the "cures" of presumed organ disease that have been observed over the years in response to various somatic therapies (e.g., spinal manipulation, acupuncture, Rolfing, Qi Gong, etc.) and may represent a common phenomenon that has led to "holistic" health care claims on the part of such clinical disciplines."
Considering this phenomenon, Seaman suggests that the chiropractic concept of joint complex (somatic) dysfunction should be incorporated into the differential diagnosis of pain and visceral symptoms because these dysfunctions often generate symptoms similar to those produced by true visceral disease and notes that this mimicry leads to unnecessary surgical procedures and medications.
Other chiropractic researchers have also questioned some of the claimed effects of vertebral subluxation:
- "The literature supports the existence of somatovisceral and viscerosomatic reflexes, but there is little or no evidence to support the notion that the spinal derangements (often referred to as subluxations by chiropractors) can cause prolonged aberrant discharge of these reflexes. Equally unsupported in the literature is the notion that the prolonged activation of these reflexes will manifest into pathological state of tissues, and most relevantly, that the application of spinal manipulative therapy can alter the prolonged reflex discharge or be associated with a reversal of the pathological degeneration of the affected reflexes or tissues. The evidence that has been amassed is largely anecdotal or case report based and it has attracted much intra disciplinary debate because of its frequent association with certain approaches to management (largely described as being traditional or "philosophical" in nature)."
Still other chiropractic researchers state quite directly:
- "… early chiropractic philosophy … considered disease the result of spinal nerve dysfunction caused by misplaced (subluxated) vertebrae. Although rejected by medical science, this concept is still  accepted by a minority of chiropractors… Indeed, many progressive chiropractors have rejected the historical concept of the chiropractic subluxation in favor of ones that more accurately describe the nature of the complex joint disfunctions they treat."
Researchers at the RMIT University-Japan, Tokyo studied reflex effects of vertebral subluxation with regards to the autonomic nervous system. They found that "recent neuroscience research supports a neurophysiologic rationale for the concept that aberrant stimulation of spinal or paraspinal structures may lead to segmentally organized reflex responses of the autonomic nervous system, which in turn may alter visceral function."
Professor Philip S. Bolton of the School of Biomedical Sciences at University of Newcastle, Australia writes in Journal of Manipulative and Physiological Therapeutics, "The traditional chiropractic vertebral subluxation hypothesis proposes that vertebral misalignment cause illness, disease, or both. This hypothesis remains controversial." His objective was, "To briefly review and update experimental evidence concerning reflex effects of vertebral subluxations, particularly concerning peripheral nervous system responses to vertebral subluxations. Data source: Information was obtained from chiropractic or, scientific peer-reviewed literature concerning human or animal studies of neural responses to vertebral subluxation, vertebral displacement or movement, or both." He concluded, "Animal models suggest that vertebral displacements and putative vertebral subluxations may modulate activity in group I to IV afferent nerves. However, it is not clear whether these afferent nerves are modulated during normal day-to-day activities of living and, if so, what segmental or whole-body reflex effects they may have."
Conclusions: Monitoring mixed-nerve root discharges in response to spinal manipulative thrusts in vivo in human subjects undergoing lumbar surgery is feasible. Neurophysiologic responses appeared sensitive to the contact point and applied force vector of the spinal manipulative thrust. Further study of the neurophysiologic mechanisms of spinal manipulation in humans and animals is needed to more precisely identify the mechanisms and neural pathways involved.
Researchers at the Department of Physiology, University College London studied the effects of compression upon conduction in myelinated axons. Using pneumatic pressure of varying degrees on the sciatic nerves of frog specimens, the study supported the idea of nerve conduction failure as a result of compression.
An area of debate among chiropractors is whether "vertebral subluxation" is a metaphysical concept (as posited in B. J. Palmer's philosophy of chiropractic) or a real phenomenon.
In an article on vertebral subluxation, the chiropractic authors wrote:
- "Subluxation syndrome is a legitimate, potentially testable, theoretical construct for which there is little experimental evidence. Acceptable as hypothesis, the widespread assertion of the clinical meaningfulness of this notion brings ridicule from the scientific and health care communities and confusion within the chiropractic profession. We believe that an evidence-orientation among chiropractors requires that we distinguish between subluxation dogma vs. subluxation as the potential focus of clinical research. We lament efforts to generate unity within the profession through consensus statements concerning subluxation dogma, and believe that cultural authority will continue to elude us so long as we assert dogma as though it were validated clinical theory."
Since its inception, the concept of vertebral subluxation has been a source of definitional debate. Tedd Koren, DC offers this explanation as a possible cause of the confusion:
The vertebral subluxation cannot be precisely defined because it is an abstraction, an intellectual construct used by chiropractors, chiropractic researchers, educators and others to explain the success of the chiropractic adjustment.
This is not a unique state of affairs, abstract entities populate many branches of science...
Subluxations, genes, gravity, the ego and life are all heuristic devices, "useful fictions" that are used to explain phenomenon that are far larger than our understanding. We use them as long as they work for us and discard or limit their application when they become unwieldy or unable to account for new observations...
Critics of chiropractic have incorrectly assumed that chiropractic is based on the theory or principle that vertebral subluxations cause "pinched" nerves that cause disease. They have it backwards. Chiropractic is based on the success of the spinal adjustment. The theory attempting to explain the success of the adjustment (nerve impingement, disease, subluxations) followed its clinical discovery.
Examples of such erroneous criticisms based on this straw man argument abound in the medical literature. Some examples: "The teachers, research workers and practitioners of medicine reject the so-called principle on which chiropractic is based and correctly and bluntly label it a fraud and hoax on the human race." "The basis of chiropractic is completely unscientific." The theory on which chiropractic is based [is false], namely that a "subluxation" of a spinal vertebra presses on a nerve interfering with the passage of energy down that nerve causing disease to organs supplied by that nerve, and that chiropractic "adjustments" can alleviate the pressure thereby treating or preventing such disease. There is no scientific evidence for the validity of this theory."
To be fair, statements by some chiropractors have tended to perpetuate this misunderstanding: "Pressure on nerves causes irritation and tension with deranged functions as a result."
When chiropractors declare that "pinched nerves" "nerve impingement" "spinal fixations" or others mechanisms of action explain how subluxations affect the person and how chiropractic works they are making the same mistake medical critics make - assuming chiropractic is based on theory. Mechanisms and theories are useful tools, but their limitations should always be kept in mind.
Other chiropractors have declared its unproven status as an area that needs reform:
- "Some may suggest that chiropractors should promote themselves as the experts in "correcting vertebral subluxation." However, the scientific literature has failed to demonstrate the very existence of the subluxation. Until and unless sound research published in credible journals demonstrates the existence and reliable identification of vertebral subluxation, and vertebral subluxation is found to be an important public health problem, society at large will not care about its correction. Thus, "subluxation correction" alone is not a viable option for chiropractic's future."
A Beth Israel Deaconess Medical Center article describes the mainstream understanding of vertebral subluxation theory:
Since its origin, chiropractic theory has based itself on "subluxations," or vertebrae that have shifted position in the spine. These subluxations are said to impede nerve outflow and cause disease in various organs. A chiropractic treatment is supposed to "put back in" these "popped out" vertebrae. For this reason, it is called an "adjustment."
However, no real evidence has ever been presented showing that a given chiropractic treatment alters the position of any vertebrae. In addition, there is as yet no real evidence that impairment of nerve outflow is a major contributor to common illnesses, or that spinal manipulation changes nerve outflow in such a way as to affect organ function.
In 2009, four scholarly chiropractors concluded that epidemiologic evidence does not support chiropractic's most fundamental theory. Since its inception, the vast majority of chiropractors have postulated that "subluxations" (misalignments) are the cause or underlying cause of ill health and can be corrected with spinal "adjustments." After searching the scientific literature, the chiropractic authors concluded:
- "No supportive evidence is found for the chiropractic subluxation being associated with any disease process or of creating suboptimal health conditions requiring intervention. Regardless of popular appeal, this leaves the subluxation construct in the realm of unsupported speculation. This lack of supportive evidence suggests the subluxation construct has no valid clinical applicability."
- Robert Cooperstein, Brian J. Gleberzon. Technique systems in chiropractic. Elsevier Health Sciences, 2004, ISBN 0-443-07413-5, ISBN 978-0-443-07413-4, 387 pages.
- WHO guidelines on basic training and safety in chiropractic, p. 4, including footnote.
- Haldeman, Chapman-Smith, Petersen. Guidelines for chiropractic quality assurance and practice parameters p. 103.
- Donald M. Petersen Jr. WFC Lays Foundation for Worldwide Chiropractic Unity. Dynamic Chiropractic, July 2, 2001, Vol. 19, Issue 14.
- Robert D. Mootz, DC; Paul G. Shekelle, MD, PhD. Chiropractic in the United States: Training, Practice, and Research
- Campbell JB, Busse JW, Injeyan HS (2000). "Chiropractors and vaccination: a historical perspective". Pediatrics 105 (4): e43. doi:10.1542/peds.105.4.e43. PMID 10742364. "... considered disease the result of spinal nerve dysfunction caused by misplaced (subluxated) vertebrae. Although rejected by medical science, this concept is still accepted by a minority of chiropractors."
- Keating JC Jr, Charlton KH, Grod JP, Perle SM, Sikorski D, Winterstein JF (2005). "Subluxation: dogma or science?". Chiropr Osteopat 13 (1): 17. doi:10.1186/1746-1340-13-17. PMC 1208927. PMID 16092955.
- "Guidance on claims made for the chiropractic vertebral subluxation complex" (PDF). General Chiropractic Council. Retrieved 2010-11-04.
- Keating, Joseph, Jr. (March 2003). "Evaluating the quality of clinical practice guidelines". Journal of Manipulative and Physiological Therapeutics 26 (3): 209–11. doi:10.1016/S0161-4754(02)54104-X.
- "ACA CMS Clinical Documentation Guidelines" (PDF). American Chiropractic Association. Retrieved 2008-05-06.
- Palmer DD (1910) The Science, Art and Philosophy of Chiropractic Portland, Oregon: Portland Printing House Company p. 20.
- Joseph M. Flesia, Jr., D.C. The Vertebral Subluxation Complex: An Integrative Perspective. ICA International Review of Chiropractic 1992 (Mar): 25-27
- World Chiropractic Alliance. Position paper on caring for asymptomatic patients.
- Spinal Injury Foundation. "Bone Out of Place - Boop". Archived from the original on 17 March 2008.
- Robert A. Leach. The chiropractic theories. Lippincott Williams & Wilkins, 2003, ISBN 0-683-30747-9, ISBN 978-0-683-30747-4, 463 pages. Book search with numerous mentions of BOOP's history.
- Terry Elder, DC. Does Chiropractic Have All the Answers? Dynamic Chiropractic, March 27, 1992, Vol. 10, Issue 07.
- David Seaman, DC, MS, DABCN. Nociception and Subluxation. Dynamic Chiropractic, September 23, 1994, Vol. 12, Issue 20.
- David Seaman, DC, MS, DABCN. If Not Nerve Interference, Then What? Mechanical Low Back and Neck Pain? Not Good Choices. Dynamic Chiropractic, June 3, 2004, Vol. 22, Issue 12.
- Strang, V (1984) Essential Principles of Chiropractic Davenport : Palmer College of Chiropractic, OCLC: 12102972.
- M.I. Gatterman, M.A., D.C. One Step Further: The Vertebral Subluxation Syndrome. Dynamic Chiropractic, March 27, 1992, Volume 10, Issue 07.
- Cramer G, Fournier J, Henderson C, Wolcott C (2004). "Degenerative changes following spinal fixation in a small animal model". J Manipulative Physiol Ther 27 (3): 141–54. doi:10.1016/j.jmpt.2003.12.025. PMID 15129196.
- Seaman D, Winterstein J (1998). "Dysafferentation: a novel term for the neuropathophysiological effects of joint complex dysfunction. A look at likely mechanisms of symptom generation". J Manipulative Physiol Ther 21 (4): 267–80. PMID 9608382.Full text online.
- Nansel D, Szlazak M (1995). "Somatic dysfunction and the phenomenon of visceral disease simulation: a probable explanation for the apparent effectiveness of somatic therapy in patients presumed to be suffering from true visceral disease". J Manipulative Physiol Ther 18 (6): 379–97. PMID 7595111.
- Hardy K, Pollard H. "The organisation of the stress response, and its relevance to chiropractors: a commentary". Chiropractic & Osteopathy 2006 (14): 25. doi:10.1186/1746-1340-14-25.
- Budgell BS (February 2000). "Reflex effects of subluxation: the autonomic nervous system". J Manipulative Physiol Ther 23 (2): 104–6. doi:10.1016/S0161-4754(00)90076-9. PMID 10714536.
- Bolton P (2000). "Reflex effects of vertebral subluxations: the peripheral nervous system. An update". J Manipulative Physiol Ther 23 (2): 101–3. doi:10.1016/S0161-4754(00)90075-7. PMID 10714535.
- Colloca C, Keller T, Gunzburg R, Vandeputte K, Fuhr A (2000). "Neurophysiologic response to intraoperative lumbosacral spinal manipulation". J Manipulative Physiol Ther 23 (7): 447–57. doi:10.1067/mmt.2000.108822. PMID 11004648.
- Fern R, Harrison PJ (January 1991). "The effects of compression upon conduction in myelinated axons of the isolated frog sciatic nerve". J. Physiol. (Lond.) 432 (1): 111–22. PMC 1181320. PMID 1886055.
- Ernst E (2008). "Chiropractic: a critical evaluation". J Pain Symptom Manage 35 (5): 544–62. doi:10.1016/j.jpainsymman.2007.07.004. PMID 18280103.
- Tedd Koren, D.C. "Does the Vertebral Subluxation Exist?" Used here by permission.
- Murphy, et al. "Bringing Chiropractic Into the Mainstream in the 21st Century - Part II", Dynamic Chiropractic, September 1, 2005, Vol. 23, Issue 18.
- Robin Brett Parnes, MS, MPH, "Chiropractic Treatment: What You Should Know", Beth Israel Deaconess Medical Center.
- Mirtz TA et al. An epidemiological examination of the subluxation construct using Hill's criteria of causation." Chiropractic & Osteopathy 2009, 17:13, 2009.
- Vertebral Subluxation in Chiropractic Practice - Council on Chiropractic Practice
- Models of Vertebral Subluxation:A Review - Christopher Kent, DC
- Chiropractic's Elusive Subluxation - Stephen Barrett, M.D.
- Subluxation - The Silent Killer - Ronald Carter, DC, MA, Past President, Canadian Chiropractic Association