Topics in Clinical Chiropractic 1995: 2 (2): 1-10
Charles A. Lantz, DC. PhD.
Director of Research
Life Chiropractic College West, 2005 Via Barrett, San Lorenzo, California 94580-1368
The concept of intervertebral subluxation has been one of the fundamental components of chiropractic theory since the founding of the profession. A history of the evolution of subluxation concepts is provided from DD Palmer's original anatomic and vitalistic model through BJ Palmer's model of blocked mental impulses and concluding with contemporary comprehensive theories of vertebral subluxation complex involving kinesiopathology, neuropathology, myologic and connective tissue involvement and vascular and inflammatory processes from their anatomic, physiologic, and biochemical perspectives. A recommendation for the future is made, encouraging a dynamic, comprehensive approach to the ongoing development and refinement by the chiropractic community of subluxation concepts.
Key words: chiropractic, joint dysfunction, subluxation, vertebral subluxation complex
An Account of chiropractic concepts of subluxation from the beginning, even before DD Palmer founded the practice of chiropractic, to the present involves a review of a wealth of historical, scientific, and clinical information. This particular review traces the evolution of the subluxation concept within the context of the chiropractic profession. There is a growing body of evidence, from both within and outside the discipline, that supports many of chiropractic's basic concepts. Evidence regarding the contribution of spinal joint derangement to a number of significant health problems becomes more compelling as more is learned. The role of manual procedures, especially as performed by chiropractors, becomes more prominent each year. A new environment without the overt ostracism of political medicine and a burgeoning research enterprise within chiropractic academia and practice are helping to poise the profession for greater contributions to the health care of society, as chiropractic enters its next century.
It is important to discuss a few parallel concepts in medical theory that have had a strong molding influence on the development of subluxation theory. The very term subluxation is a medical term meaning "less than a true dislocation (luxation)." For chiropractors. the term took on a life of its own. One feature of subluxation that emerged early in its development was the almost unspoken idea that the subluxation was often "medically" subclinical. Typically, medical physicians overlooked the subtle clinical manifestations of subluxations. Medicine's official perspective was that there was no legitimate evidence of what chiropractors called "subluxation", and it simply did not exist.  It therefore became a matter of policy to discredit the very existence of chiropractic, from fundamental concepts to clinical practice.
This perspective extended into the 1970s; there was nothing legitimate about chiropractic, and it therefore deserved little or no serious scientific scrutiny. Research into chiropractic conducted by the medical community was so obviously biased that it had little credibility, although it did have tremendous political appeal.
 What little research chiropractors themselves engaged in was often proprietary and rarely disseminated and scrutinized. Thus, chiropractors built their practices in the shadow of medical dominance that depicted them as charlatans, quacks, and unscientific cultists.  The lack of scientific credence was wielded by organized medicine against the chiropractic profession in an attempt to "contain and elminate" chiropractic.  It was in a sociopolitical climate of medically controlled academic research that the concept of subluxation, the theoretical underpinning of the practice of chiropractic, evolved.
SUBLUXATION: LA CAUSE CELEBRE
In the early formulations of the theory of subluxation and extending into contemporary times, the idea of subluxation has been linked with the idea of adjustment, the uniquely chiropractic procedure directed at reducing subluxation. Because the chiropractic subluxation concept emphasized a relationship between mechanical joint dysfunction and the establishment of nerve interference, [5-7] chiropractic adjustment has often been equated to removal of "nerve interference." [2, 5] The subluxation is the "raison d' etre" of the adjustment; it is that which chiropractors do what they do to. In this sense, the subluxation is analogous to the medical concept of disease; it is no less simplistic, no less intricate and complicated - in fact, it is the focus of chiropractic therapeutic efforts.
In the simplistic, causality-driven Newtonian-Cartesian, turn-of-the-century mindset in which the concept was developed, subluxation was seen as the "cause of all disease" or the "one cause" for which there was but "one cure."  This concept gave rise to an extensive proliferation of chiropractic techniques and procedures for adjusting for the removal of subluxation. Attacking the concept of subluxation, one of chiropractic's central foundations, became an instrumental part of the strategy to discredit chiropractic. With continuing assault from organized medicine, chiropractors became more entrenched in their defense of the concept, for if there is no subluxation, there is no need for an adjustment; no adjustment, no need for chiropractors. Medical critics attacked the concept from an extremely narrow perspective, while chiropractic defenders interpreted the concept much more broadly.  Since the idea of subluxation was first adapted by DD Palmer as a central conceptual focus of chiropractic, it has undergone continual refinement and development.
THE ORIGINS OF CHIROPRACTIC SUBLUXATIONS
The term subluxation was not coined by chiropractic's founder. Rather, it was a medical term adapted by DD Palmer to most closely describe the phenomenon that he experienced in his newly "discovered" clinical practice. Palmer stated, "I am not the first person to replace subluxated vertebrae, for this art has been practiced for thousands of years."  The term was quite popular at the turn of the century and was utilized by both chiropractors and osteopaths to describe their primary "lesion": It appears to have been borrowed from Palmer by Still.  Osteopathy would later abandon subluxation-based terminology and utilize terms such as osteopathic spinal joint lesion, spinal lesion, bony lesion, etc. [9-12] It should also be pointed out that subluxation was a medical term of little consequence when chiropractic was developed. There was no radiologic definition of subluxation at that time, as X-rays had only just been discovered.
Much of the controversy regarding the "chiropractic lesion" may stem from the fact that the term already had a precise meaning in medical terminology. Arguments on both extremes ranged from claims that minor "subluxations" of vertebrae are not detectable or clinically significant, to claims that subluxations are measurable to absurd levels of precision and are the ultimate cause of all ills afflicting humanity (with the possible exception of "cataractous conditions").  Many of the arguments regarding subluxations were polemic, relying heavily on subtle differences in definition and nuances of language; often they were frank "ad hominem" attacks that appealed more to emotions than to reason.  Until recently, no amount of logic, reason, or evidence would sway the medical community-and through it, the public-regarding the validity or credibility of chiropractic clinical practice; it was pure and simple quackery, and until the mid-1970s, it was official medical policy to remove "the cult's shield of legitimacy" to combat and eliminate "their brand of cultistic therapeutic nonsense. " 
DD Palmer proposed that the "subluxation of a vertebrae is a slight deviation from its normal relation to adjacent vertebrae,"  and this is said to cause "an alteration and narrowing of intervertebral foramina." With regard to adjustive procedures, "The Chiropractor places vertebrae in line by hand, thereby removing impingements and returning the nerves to their normal tonicity. Normal tension produces normal functions, harmony and health, "  Palmer stated. " I do claim to be the first to replace displaced vertebrae by using the spinous and transverse processes as levers wherewith to rack subluxated vertebrae into normal position,"  Although this assertion sounds plausible, it is questionable whether it is true. [15, 16
Palmer was the first to formulate the conceptual framework and systematize the process of utilizing the spinous and transverse processes to "adjust" subluxated vertebrae. Palmer also contributed to the development of a plausible hypothesis regarding the nature of subluxation, and a mechanistic model of clinical practice for correcting the basic problem (lesion, dysfunction).
Two distinctly chiropractic conceptions regarding subluxations are:
- They are correctable by adjustive (manipulative) proceedures, and
- Subluxated vertebrae somehow interfere with proper neurologic functioning.
Terrett  traces the term subluxation prior to 1895 and attributes the first recorded use to 10annes Herricus Hieronymus in 1764. In 1820, Edward Harrison described a subluxation as "a small irregularly in the height and disposition of some particular vertebra. . . ."  Later, in 1828, the concept developed of compression of nerves "as they issue from the spinal marrow," resulting in "spinal irritation" as the "immediate cause" of pain, nervous complaints, and poor health. Throughout the mid- to late 19th century, medical authors referred explicitly to subluxation in a context similar to that later adopted by DD Palmer:
"A vertebra is said to be displaced or luxated when the joint surfaces are entirely separated. Sub-luxation is a partial or incomplete separation: one in which the articulating surfaces remain in partial contact. This latter condition is so often referred to and known by chiropractors as sub-luxation. The relationship existing between bones and nerves are so nicely adjusted that anyone of the 200 bones, more especially those of the vertebral column, cannot be displaced ever so little without impinging upon adjacent nerves. Pressure on nerves excites, agitates, creates an excess of molecular vibration, whose effects, when local, are known as inflammation, when general, as fever. A subluxation does not restrain or liberate vital energy. Vital energy is expressed in functional activity. A subluxation may impinge against nerves, the transmitting channel may increase or decrease the momentum of impulses, not energy."
At the same time that DD Palmer was developing the concept of the chiropractic subluxation, AT Still was developing a parallel profession of osteopathy with its own concept of subluxation. In osteopathy, subluxation was seen to be the result of pressure applied by muscles to the blood vessels coursing through or around them, thereby shutting off the vital nutritional life force of the involved tissue.  Defending one or the other of these concepts of subluxation became a matter of principle and an indication of one's allegiance to one's chosen profession. Clearly in the age of health care "turf wars," each side clung tenaciously to its narrow perspective of subluxation, and never the twain should meet. With the assimilation of osteopathy into medicine, the concepts of subluxation and osteopathic lesion were in great part abandoned for more acceptable and conventional approaches.
THE DEVELOPER OF CHIROPRACTIC
The concept of subluxation developed by DD Palmer's son, BJ Palmer, was distinct from that of his father. According to BJ Palmer, a subluxation represented a displaced bone that impinged on a nerve, thus interfering with the transmission of vital nerve energy (or, more specifically, the transmission of "mental impulses").  BJ Palmer came to the conclusion that the only significant subluxation was that of the atlas relative to the occiput or axis:
I reaffirm that no amount of "adjusting" upon any, many or all vertebrae below occiput, atlas, or axis, could or would directly ADJUST THE SPECIFIC three-direction torqued subluxation causing any, many or all sickness in a body. Any vertebra below atlas or axis MAY BE misaligned but CANNOT BE subluxated.
A clear delineation was made between a simple "misalignment" and a "true" subluxation, although no formal evidence was presented to justify such a distinction, BJ Palmer thus conceived that "vital energy" originating in the brain was transmitted from above, down, inside out (ADIO). Thus an impingement near the origin of the transmission (ie, the brainstem at the level ofthe atlas ring) would affect the whole system. The concept was appealing in its simplicity. For a significant portion of BJ Palmer's life, he believed that a subluxation could occur only at the Atlas because of its unique position in relation to whole-body function. Perhaps it was such musing that led his father to call him "the pseudodeveloper of Chiropractic- the man who makes such changes in anatomy as seems best to suit his philosophy."  DD Palmer was not a supporter of the "foot on the hose" concept of subluxation. 
Perhaps the most widely quoted early definition of subluxation was that provided by RW Stephenson's 1948 Chiropractic Text Book: "A subluxation is the condition of a vertebra that has lost its proper juxtaposition with the one above or the one below, or both; to the extent less than a luxation; which impinges nerves and interferes with thc transmission of mental impulses."  Stephenson cautions that all components of the definition must exist to qualify the problem as being "chiropractic."
SEEING IS BELIEVING
To more precisely determine the location and direction of subluxated vertebrae, radiographs were utilized to evaluate osseous misalignment. At the time that DD Palmer "discovered" chiropractic, there was no radiologic definition of subluxation, since the first clinical radiographs had not yet been taken. However, the term was readily found in the medical literature  and detined in medical lexicons.  Radiographs continue to be a clinical tool used by many chiropractors for documenting the existence and location of subluxation pathologies. [20, 21] Although current applications are intensively debated, [22, 23] radiation technologies and other imaging techologies continue to contribute to the development of subluxation theory. [24, 25]
It is perhaps serendipitous that chiropractic was "discovered" in the same year as X-radiation. Certainly the coincidence was not lost on either the founder or the developer of chiropractic, as one of the first clinical X-ray units was installed at the Palmer Clinic in Davenport, Iowa, near the turn of the century. Radiographs allowed the chiropractor to "see" and show others the misalignment. The incorporation of radiographs into diagnostic procedures in chiropractic led to the development of systems of X-ray markings [21, 26] for "precise localization" of the subluxation and calculation of the extent of misalignment. For the structuralists, such marking systems became the goal of diagnosis and the confirming evidence of the existence of subluxations. With such analytic precision, the chiropractor defended his or her practice on objective grounds. Exacting X-ray protocol and marking systems became the hallmark of many techniques, including Gonstead and Upper Cervical practices. X-ray marking became codified with the adoption of Medicare requirements that subluxations be demonstrated radiographically. Essential support for the concept of radiographic subluxation was provided by a medical physician named Hadley, [27-30] who, between 1935 and 1955, described in detail radiologic accounts of osseous vertebral subluxation [29-31] and discussed subsequent nerve impingement and alterations in neurologic function. [27, 29] Such evidence provided considerable ammunition for chiropractic practitioners and theoreticians.
One aspect of chiropractic subluxation that distinguishes it from classic medical subluxation is the existence of so-called "nerve interference." Although the elder Palmer's definition of subluxation stressed the "bone out of place," emphasis was also given to pressure on, or irritation of nerves, leading to increased nerve tension.  The original formulation of the concept of subluxation was based on the principle of "tone," a vibrational state of biologic tissue believed to be somehow related to vitality or life. According to DD Palmer, who practiced as a magnetic healer, the nervous system as well as other vital tissues existed in a state of vibration. Nerves were considered to be under a certain amount of "tension," similar to the strings of a piano or guitar. Metaphorically speaking, when the strings are tuned properly, the instrument plays harmoniously; when they are out of tune, there is dissonance or disharmony (dis-ease). Vitality, or health, represented a tone that was harmonious with a vital principle that Palmer referred to as "Innate Intelligence." This tone was transmitted to all tissues via the nervous system, and any interference with this transmission led to a disharmony and, subsequently, disease.
Janse  stated that "The Chiropractic adjustment helps to remove nerve impingement at the intervertebral foramen", even though he acknowledged that there was no tangible evidence of this phenomenon; he defended his position by stating that the assertion finds its "support in logic and anatomical reasoning." The concept of nerve interference remains central to many approaches to chiropractic practice and is primary in some of the more traditional and conservative perspectives.
In 1971, Haldeman and Drum  reviewed the relationship between compression lesions and the concept of subluxation and suggested that there was sufficient evidence to verify the existence and importance of the compression subluxation. Many of the theories supporting the effectiveness of chiropractic revolve around the "neurological connection." Anatomically and physiologicaI1y, such a relationship can be readily characterized. Chiropractors adjust vertebrae, presumably restoring normal position or functional capacity. It is a simple extension of logic to postulate that the segmental nerves, coursing within the intervertebral canal (IVC) traversing between adjacent vertebrae could be compressed by a subluxated vertebra.
Thus, it was insufficient to have vertebrae merely displaced. To identify a subluxation, there must be some sort of neurologic involvement. Because the nervous system is nearly ubiquitous throughout the body, and is the mediator of all bodily functions, it is easy to see how early chiropractors made the association between the concept of subluxation and the idea of general distress or disease development through either "nerve interference" or nerve irritation. Uncovering or new evidence characterizing a direct relation hetween the nervous system and immunologic responses [34-37] has been interpreted in some circles as supportive of these basic chiropractic concepts.
THE DISC-WEDGE HYPOTHESIS
In 1934 Mixter and Barr  promulgated the concept of a herniated disc as a "cause" of low back pain; this concept became the pathophysiologic basis of orthopedic surgical intervention for low back pain. Many of the same undercurrents of information infuencing Mixter and Barr likely infuenced Clarence Gonstead to develop the disc-wedge hypothesis of vertebral subluxation. The intervertebral disc (IVD) consists of a gelatinous nucleus pulposus surrounded by tough sheets of annular fibers. According to Gonstead, the nucleus pulposus served as a pivot for the tilting of vertebrae, a sort of hydraulic ball bearing. It was the shifting of the nucleus that caused the vertebrae to become wedged and therefore subluxated: "subluxation is a disorder of the disc." 
Herbst described this hypothesis as a shifting of the nucleus that "caused" the bodies to become wedged:
"With the containing envelope of the nucleus no longer intact, the nucleus migrates toward the periphery. This tilts the vertebral body, raising it in the direction that the nucleus shifts and dropping it in the opposite direction. It could be said that the nucleus moves toward the open side of the wedge. A subluxation will almost always show a wedged disc on either the A-P or lateral projection, and usually on both. The disrelationship of the facets is the result of, and secondary to, the misalignment at the fibrocartilaginous joint; that is, at the intervertebral disc."
Barge asserts that the facets, being freely movable diarthroidal articulations, are not in any way related to the "cause" of subluxation.  The wedging of the vertebrae leads to disc bulging on the side of the closed wedge, and it is the bulging disc that places pressure on the nerve roots in the IVF or neural canal.
One consequence of this wedging is presumed to be a loss of segmental mobility. The vertebra is considered fixed, and the area of reduced mobility between the fixed vertebra and subjacent vertebra has been termed biomechanically as a fixation.  For every fixation, there are apparent areas of compensatory hypermobility that manifest similar types of misalignment as the subluxated vertebrae. Consequently, it was an important distinction in the Gonstead system that subluxations themselves could not be seen on radiographs; there had to be independent evidence of nerve interference for an abnormality to qualify as a subluxation.
Radiographs were merely confirmatory of the existence of the subluxation and provided information regarding the direction in which the adjustive force would have to be applied. To uncquivocally identify thc location of the subluxation, "emphasis is placed on finding the nerve involved."  Considerable emphasis in Gonstead theory was placed on the role of edema and inflammation, but only from a mechanical perpective. Edematous swelling was seen to lead to nerve root compression. "A subluxation occurs when two osseous structures become misaligned to the degree where interarticular protrusion from intra-articular swelling produces compression of nerve fibers." 
Throughout their history, chiropractors have cited research in other fields to help support the concept of subluxations as the cause of all disease. Early in chiropractic's first century (1930-1950), an osteopath, Louisa Burns, published extensively on "spinal lesions" or general "bony lesions" and their effects on various processes and structures [9-12] and promoted a "sympathogenic" mechanism for such lesions to effect visceral changes. These same sentiments were espoused by Fred Illi,  whose works are held in high esteem by chiropractic philosophers,  as are the works of IM Korr. [42-43]
In 1921 a medical doctor, Henry Winsor,  published an article describing a correlation between visceral disease and spinal segmental (sympathetic) lesions. Even in medicine, as late as the early 1950s, Hadley was promoting similar "spinal lesion" mechanisms to explain visceral degenerative processes.
[27-31] After about 1955, the term subluxation largely disappeared from medical publications, and when it did appear, it was used only in a very narrowly defined radiological context. Although the focus and terminologies have changed today, scientists continue to search for evidence of "spinal lesions". In response to the volume of new biomechanic, neurologic, endocrinologic, and wellness research findings that are becoming available, chiropractic theorists are incorporating new concepts and terminologies into subluxation and adjustive (manipulative) procedures models. [45-48]
THE "MODERN" ERA
Currently, controversy over the term subluxation continues, [49-51] although its character has changed. Some of the controversy is fueled by the narrow medical definition of radiographic or anatomic subluxation as resulting from potential segmental instability, for which the application of "0manipulative forces" is actually contraindicated. [52-58] Still, support for the concept of subluxation appears from both within and outside the profession. [2, 33, 48, 49, 59, 60] The work ofDeBoer, [45, 61, 62] Verbon et al,  Nansel et al,  Sato and Swenson,  and thers have pointed out new paths for chiropractic research in exploring neurologic relationships inherent in somatovisceral pathways.
THE VERTEBRAL SUBLUXATION COMPLEX
In 1906 Smith et al  were apparently the first to characterize subluxations other than bones out of place, but as a dysfunctional state of motion of adjacent vertebrae. A reasonable concept of dysfunction is that of a tixation or restricted motion between adjacent vertebrae. Such a perspective, largely ignored for several decades, stimulated the development and refinement of motion palpation by a Belgian chiropractor. Henri Gillett.  This system was further refined by Faye  and developed into a prominent chiropractic technique system in North America. Motion became a preeminent focus of Faye' s model of subluxation and manipulation, eventually termed vertebral subluxation complex (VSC). This model originally consisted of five components involving kinesiopathology, neuropathology, myopathology, histopathology, and biochemical abnormalities.
(see Table 1)
Although this work was abstracted from earlier work by Janse, [32, 68] it was Faye who popularized the idea and organized the model into component parts. The VSC model was widely promulgated by Flesia in the "Renaissance" practice management and promotional seminar program. [69-71] Dishman characterized the concept as "the chiropractic subluxation complex," [72-73] which provided additional rationale for Faye's model. Lantz [74-76] modified the original five components of the VSC model by postulating three more components: connective tissue pathology, vascular abnormalities, and the inflammatory response (see Table 1) . The concepts of a comprehensive model of VSC were integrated into Leach's widely accepted text, The Chiropractic Theories.
 An international scientific symposium was also organized to discuss and debate subluxation models; this resulted in the publication of another text based on the presentations from the conference. 
Table 1. Components of the Vertebral Subluxation Complex
Connective tissue pathology
(A) Faye LJ. "Motion Palpation 0f the Spine". Huntington Beach, Calif: Motion Palpation Institute; 1983
(B) Lantz CA. "The Vertebral Subluxation Complex". ICA Int Rev Chiro1989; September/October: 37 -58
The comprehensive contemporary model of VSC does not attempt to identify a single lesion or pathophysiologic entity to characterize as a subluxation. VSC incorporates multifactorial involvement from elements of each of the model's tissue-level components. Kinesiologic abnormalities are seen to be central in the concept of subluxation and are provided a position of prominence in the model; immobilization is seen as a primary but not exclusive element in specific subluxations.  Unique patterns of involvement are discernible in various types of subluxation; for instance, immobilization and inflammation are commonly seen as being involved in sacroiliac "lesions" or subluxations and may give rise to radicular problems. Nerve impingement by IVDs is yet another discernible class of subluxation potentially amenable to manual chiropractic methods.
Frank trauma with edema, as occurs after a blow from a blunt instrument or from sprains and strains, is also recognized as a class of subluxation, as are whiplash-type injuries. Degenerative disc disease and facet syndrome are additional medical diagnoses that represent classes of what chiropractors identify and treat as subluxations. The VSC provides a means of classifying and categorizing these various forms of subluxation and identifying the major components involved in their etiology, presentation, and resolution. The VSC provides a complete model encompassing multiple clinical and philosophic perspectives. Such a comprehensive approach to model building may help preclude jargon and obtuse vocabulary.
The VSC model appears to be developing its own momentum as the profession completes its first century. The profession's first formalized consensus effort to develop comprehensive practice parameters includes an explicit definition of VSC.  In his monograph. Chiropractic Theories,  Leach has integrated VSC concepts throughout the text of the third edition, in striking contrast to the second edition. The American Chiropractic Association (ACA) Council on Technique has incorporated the VSC model into its basic structure and protocol for the evaluation of chiropractic techniques. Sherman College of Straight Chiropractic in South Carolina conducts an annual conference on subluxation, and an international conference, cosponsored by Canadian Memorial Chiropractic College in Toronto and the Consortium for Chiropractic Research, was held to discuss issues relating to the VSC model.  A textbook by Plaugher and Lopes  incorporates VSC concepts as a conceptual framework for developing the content of the text.
Chiropractic colleges arc also incorporating the VSC model, or elements of it, into their curricula. Life Chiropractic College West, located in San Lorenzo, California, has a course entitled "Scientific Basis of the Subluxation Complex." Los Angeles College of Chiropractic has developed one of the better subluxation complex-based clinical protocols,  while National College of Chiropractic and Canadian Memorial Chiropractic College have incorporated the model in toto into the curricula. Several continuing education programs are devoted almost exclusively to the VSC model in its various formulations. Less formal integration of portions of the model is found at Logan College of Chiropractic in St. Louis, Life Chiropractic College in Marietta, Georgia, and both Cleveland Chiropractic colleges in Kansas City and Los Angeles.
TESTING THE MODEL
It is said that the true test of a theory is that it can generate testable hypotheses. A plethora of hypotheses can be generated by the VSC model, some related to fixation, some to hypermobility, some involving various neurologic components, and some exploring changes in connective tissue. Triano suggests that the addition of complex to the term subluxation is merely a ruse, but he correctly asserts that "the subluxation complex can only be quantified by characterizing each of the associated findings (components) independently."  It is this process of documenting the characteristics of each of the components and subcomponents, their precise role in the degenerative process, and their contribution to the presenting symptomatology that will allow specific hypotheses to be developed and tested.
Indeed, several studies are currently under way to explore various components of the VSC, and weekly many studies are reported that add to our current conceptual framework of spinal degeneration in general and subluxation degeneration in particular. To that end, it is perhaps important to reflect on Haldeman's definition of subluxation as being a "manipulatable lesion".  Rather than representing circular reasoning, this definition reflects the true nature of subluxation: that which is amenable to correction by manual procedures, specifically the spinal adjustment or manipulation. In this context, the development and use of the term subluxation to describe the chiropractic lesion is solidly rooted in empiricism. The subluxation is an explanation of a clearly demonstrable phenomenon: the physical improvement of human suffering and malaise through the application of manual forces without the use of drugs or surgery.
What lies ahead for chiropractic is the development of clinical and biologic research capabilities leading to more refined descriptions of what chiropractors do and how they do it. Subluxation model building will increasingly be driven by research findings and testable scientific queries will increasingly arise from clinical practice. There is a place for subluxation models to function as a focus for logical and scientific development in the pursuit of a greater understanding of human health. It is a basic function of humanity to develop theories and explanations of what goes on around and within us. No theory is perfect, be it Newtonian/Cartesian theory, relativity theory, or quantum theory.
It is the nature of theories and models to be dynamic, forever evolving as knowledge and understanding grow. As with all theoretical models, concepts of chiropractic clinical practice are also imperfect. The fact that chiropractic models continue to exhibit limitations and imperfections is not surprising. To suggest that chiropractic practice is without value in the absence of definitive "proof" is naive and perhaps even arrogant. Whenever people see things that they do not understand, theories will evolve to explain such things. Such is the case of the VSC. A tremendous amount of work remains to be done to refine the concepts that underpin the practice of chiropractic.
In the past, chiropractic has relied on research from other fields to substantiate its own theories. This is a result of the academic isolationism that grew out of organized medicine's policies to "contain and eliminate" the chiropractic profession, as well as chiropractic's long tradition of scientific neglect. Chiropractors, therefore, exerted no control over directions that medical research took (the specific questions asked, the design of research, etc). Currently, however, the foundations of chiropractic research are growing, and chiropractors are increasingly recognizing the need to contribute to the scientific knowledge base, examining basic mechanisms of subluxation pathology, manifestations of the "subluxation syndrome",  and the processes involved in correcting these lesions.
Chiropractic theory grew directly out of a working relationship between doctor and patient. One could say that the concept of subluxation was created to justify and explain the adjustive procedure utilized to correct it. The situation is similar for any clinical discipline, Science is a tool to be utilized and applied to the understanding of clinical experience. From a clinician's perspective, there is no greater need than to understand what he or she is doing and how to make it better.
If the concept of subluxation cannot be placed in a physical perspective (ie, anatomy, physiology, epidemiology, biochemistry), then the profession may experience limitation in its true growth. Chiropractic is increasingly in the spotlight of public awareness. With such "celebrity" status comes greater scrutiny and increasing demand for accountability from the public chiropractic serves. Although only a few questions have been answered, the tools and resources needed to obtain answers are more available to chiropractors than in earlier decades. The playing field has never been more favorable. However, with victory and recognition come responsibility.
The responsibility of the chiropractic profession is to provide answers for some very important questions. Chiropractic needs a solid foundation on which to build a sound clinical practice. The current direction of the development of the subluxation concept may help to define and anchor that foundation. Although it is both incomplete and imperfect, subluxation still offers a common conceptual model to describe the theory and practice of chiropractic. Attention and focus devoted to a comprehensive approach to VSC model building can serve as a common frame of reference for chiropractors everywhere well into the profession's second century .
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