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Subluxation is a term that continues to generate controversy into the 21st Century. This paper describes the controversy surrounding terminology arrived at through consensus in the latter part of the 20th century in addition to ongoing issues surrounding the use of the term subluxation.

Introduction

A word is not a crystal, transparent and unchanged; it is the skin of a living thought and may vary greatly in color and content according to the circumstances and time in which it is used.

– Oliver Wendell Holmes, Jr.

Historically subluxation has been central to the philosophy, science, and practice of chiropractic as the primary articular lesion treated by chiropractors. A number of issues have surrounded the use of the term subluxation including: terminology, the nature of the lesion (aberrant motion versus misalignment), and clinical, economic and political issues. The complexity of these issues precludes discrete discussion, classifying them as such, however, gives focus to much of the controversy.

Aberrant Motion versus Misalignment

The controversial nature of the chiropractic subluxation began as early as 1906 with the Palmers emphasizing vertebral displacement (misalignment) [1] at the same time that Smith Langworthy and Paxson emphasized aberrant motion as the primary characteristic of subluxation [2] They stated that:

“A simple subluxed vertebra differs from a normal vertebra only in its field of motion and the center of its field of motion.” [2]

The aberrant motion concept subsequently became more popular in Europe, However in North America, Budden [3] was using the term “fixation” when referring to a subluxation at Western States Chiropractic College by 1930.

His definition described the vertebral fixation as:

“The fixation of a joint in a position of motion, usually at the extreme of motion.” [3]

In the 1940/s Leikans and the Gillet brothers in Belgium, [4] independently of Carver [5] and Vladef [6] in the United States, were describing motion palpation as a method of detecting spinal fixations. Homewood [7] in his text The Neurodyanmics of the Vertebral Suluxation while emphasizing the restricted motion component of subluxation preferred the term subluxation to fixation. In the late 70’s and early 80’s Grice [8] at Canadian Memorial Chiropractic College in Canada and Faye [9] through post graduate seminars in United States enlarged upon Gillet’s work by teaching motion palpation.

Consensus Terminology

An effort was made to develop chiropractic nomenclature through consensus in the early 1990’s. [10] This project sponsored by the Consortium for Chiropractic Research was published in 1994. The ten terms agreed to include the definition of subluxation that included both the characteristics of misalignment and restricted motion as follows.

“Subluxation: a motion segment in which alignment, movement integrity, and/or physiological function are altered although contact between the joint surfaces remains intact.” [10]

This definition includes the term motion segment because it was found that this was the term used most commonly used in the clinical literature related to the spine. The term spinal motion segment was defined as:

Two adjacent vertebrae and the connecting tissues binding them to each other. [10]

The spinal motion segment is a three joint complex that forms the functional unit of the spine. [11] This concept is central to understanding spinal motion and how restriction of motion at one joint affects the other two joints of that segment. [11] Motion segment is the literal translation of the German Bewegungssegment popularized by Junghanns following his introduction of this concept in 1971. [12] It is unfortunate that it was translated into English as “motor unit” [12, 13] and confusion arose because of the prior use of this term by physiologists to designate a motor nerve and the muscle fibers that it innervates. Motor unit was the term presented at the conference on the research status of spinal manipulative therapy in 1975 [14] and it is still used to designate the spinal motion segment by those schools influenced by the National College of Chiropractic now National University of Health Sciences (NUHS). [15] A 2008 NUHS task force on the use of the term “subluxation” states that “the entity that is called a manipulable lesion” is to be referred to as a functional articular lesion defined as: an abnormally functioning motor unit involving the spine, pelvis or extremities. [16]

Before we leave the semantic confusion in the chiropractic profession surrounding the term subluxation it should be noted that the chiropractic profession has the propensity to use whatever term they can devise to refer to subluxations. Rome [17] documented 296 synonyms for subluxation in 1996. Do we hear 500 in 2009? Unfortunately, when it comes to the word subluxation, too many chiropractors act quite like Humpty Dumpty in Lewis Carroll’s Through the Looking Glass …’When I use a word,’ Humpty Dumpty said, in rather a scornful tone, ‘it means just what I choose it to mean – neither, more nor less. …” [18]

Early Medical Use of the Term Subluxation

The origin of the word subluxation comes from the root words combining the Greek sub and lux, meaning “less than a dislocation.” In 1746, Hieronymus described a subluxation, identifying the following characteristics: [19]

…subluxation of joints is recognized by lessened motion of the joints, by slight change in position of the articulating bones and pain….

This does not differ significantly from the consensus definition agreed on by the nominal and Delphi panels of the Consortium for Chiropractic Research. [10] (See above)

In 1821 Harrison [20] included physiologic dysfunction, which he described as follows:

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…

In 1824 [21] he considered alignment and motion when describing subluxations as:

…the articular motions are imperfectly performed, because the surfaces of the bones do not fully correspond.

Both Palmers focused on the neurologic effects produced by a subluxation in addition to vertebral misalignment. Within a decade of its inception, the chiropractic profession was arguing over the definition of subluxation and the primary focus of chiropractic treatment. Was it misalignment, altered motion, or joint dysfunction? Why not any one, two, and/or all three as the early medical definitions indicated?

Subluxation as a Manipulable Lesion

Following the 1975 conference on the research status of spinal manipulative therapy, [14] and the 1979 New Zealand report of the Royal Commission of Inquiry into Chiropractic, [22] interest in the nature of the lesion responding to manipulation increased both within and outside the chiropractic profession. While some preferred that the term subluxation be abandoned, [23] the use of the term subluxation when labeling the manipulable lesion appears in the medical literature in the late nineteen seventies and eighties.

In 1977 Turek, [24] an orthopedic surgeon, wrote that “sacroiliac subluxation” implies that:

…ligamentous stretching has been sufficient to permit the ilium to slip on the sacrum.

He described the mechanism as:

an irregular prominence of one articular surface becoming wedged upon a prominence of the opposed articular surface, with the ligaments taut, reflex muscle spasm intense and pain severe and continuous until reduction is effected.

He noted that the pain of sacroiliac subluxation is often:

relieved dramatically and suddenly by manipulation.

In 1980 [25] Keim and Kirkaldy-Willis used the term subluxation when describing the lesion that produces low back pain that responds to chiropractic manipulation. They concluded that:

The facet syndrome, which can cause severe back pain, consists of a subluxation or partial dislocation of a lumbar vertebral facet joint. This is the condition most likely to be relieved when a chiropractor manipulates the spine.

This concept and the term subluxation as a lesion responding to manipulation appears in texts on managing low back pain well into the 1980’s. [26, 27]

The Non Manipulable Subluxation

Not all subluxations respond to manipulation and one of the reasons given for abandoning the use of the term subluxation when referring to a manipulable lesion is that to the orthopedic surgeon subluxations are usually considered to require surgical repair. It is understandable that given this use of the term, the introduction of a forceful adjustment or manipulation would seem contraindicated as a treatment for the orthopedic subluxation. The non manipulable subluxation therefore is one in which manual thrust procedures are not indicated. Subluxations most often seen on radiographs by orthopedic specialists are often nonmanipulable or pathologic subluxations that are not reversible except through surgery. The treatment of these subluxations is seen as being the orthopedist’s turf. [28] It is important that when describing subluxations, that the concept should be broad enough to include the surgical or pathological subluxation that is a non manipulable lesion. (Table 1)

In the 1990s recognition of subluxation as the lesion successfully treated by chiropractors, largely disappeared from both medical and chiropractic literature. This is especially noticeable in the peer reviewed scientific Journals. [29] Of necessity, those seeking grants from eternal agencies must use the terminology preferred by the reviewers and subluxation as used by the chiropractic profession was used less and less by those seeking external funding.

In 2003 Wenban [29] surveyed the leading chiropractic scientific journals from 1990 to 1999. He found that only 6.3% of the original research published during this period included the term subluxation in titles, abstracts or clinical trials. Among the possible explanations for this he suggested that the chiropractic research community may have conducted subluxation-related research but abandoned the term, and except for a handful of chiropractic researchers, who seemed to publish predominantly in the Chiropractic Research Journal, most largely abandoned research of the entity that many practitioners call subluxation. A show of hands at a 2003 research agenda conference (RAC) following a presentation on the usefulness of the term subluxation demonstrated a preference by the research community to abandon the term; just one researcher eloquently making the case for the continued use of the term subluxation. [30]

There has been a preference to abandon the term subluxation amongst the radiology community and also the use of radiographs as the sole criteria to detect subluxations. The American College of Chiropractic Radiologists has opposed the routine use of radiographs solely for the detection of subluxation, and most chiropractic radiologists believe that an x-ray examination is performed primarily for pathological evaluation. [31]

Modified from: Peterson CK, Gatterman MI. The nonmanipulable subluxation. In Gatterman MI. Ed. Principles of Chiropractic: Subluxation 2nd Ed St Louis. Mosby 2005 169-90.

Domains of Chiropractic

In 2003 following the RAC conference it was noted that a single definition of subluxation fits all is not pragmatic. Nonetheless, it was considered that different expressions of the same concept must be consistent across cultural domains. [32] (Table 2) What is useful to the educator may not be entirely appropriate for the researcher; similarly what expresses the focus of the chiropractic clinician as we have seen may be inappropriate for the orthopedic surgeon. Politicians may prefer to use a different term altogether, one that has greater colloquial familiarity or lacks political or legal coloring. The premise that “different expressions of subluxation are needed with relevance to different cultural domains” was central to the consensus process used to develop chiropractic nomenclature published in 1994. [10]

Subluxation Complex

The subluxation complex as indicated under the different chiropractic domains is a tool utilized by educators to describe the various components of subluxation related to different disciplines. [32] It was defined through the consensus process as: a theoretical model of motion segment dysfunction (subluxation) that incorporates the complex interaction of pathological changes in nerve, muscle, ligamentous, vascular, and connective tissues. [10] Drawing on the disciplines of kinesiology, pathology, histology and biochemistry, Faye in 1967 developed a heuristic model that he termed the subluxation complex. He included the potential contribution of each discipline to subluxation theory [33] by building on the work of Gillet, Illi, Homewood, and Janse. Faye formulated a theory that the chiropractic spinal adjustment/manipulation) restores normal joint motion, which in turn normalizes physiologic function.

Lantz, in 1988, expanded on the Faye model under the concept of immobilization degeneration, [34] later incorporating this emphasis into the vertebral subluxation complex (VSC) [35] By 1995, he noted that critics of the term subluxation viewed the concept of the vertebral subluxation complex as just another veiled rationalization of a cultist group using unproven procedures. [36] There was justification for this view given that some practice building entrepreneurs in the 1990’s were presenting the VSC model scientific fact rather than the theoretical model that the developers put forth. This prompted the terminology consensus panel members to insist that the subluxation complex be defined as a theoretical model. [10]

Leach noted in 2003 that the consensus definition of the subluxation complex should include:

may influence organ system function and health. [37]

He thought that the consensus definition overlooked the Palmerian concept that subluxation may affect organ function and general health, a concept that had been discussed at the 1975 conference that examined the research status of spinal manipulation. [14] A further addition to the model was made by Ebrall in 2004 when he added the biopsychosocial component to the model. [38] The suffering accompanying the VSC was suggested earlier by Lantz, who discussed the effects that pain produces through nervous system irritation. [36]

Clearly, a comprehensive theory to test the subluxation complex hypothesis exists. The question arises: “If the term subluxation is not used by researchers testing the components of the subluxation complex theory then are the critics of subluxation theory justified in saying that there is no research to support subluxation theory?” It seems that the continued use of nomenclature unique to the chiropractic profession is a conundrum when most researchers are not studying the nature and effects of subluxation.

Basic Research

To many chiropractic basic researchers studying subluxation the articular lesion is the object of their study. Scholars both inside and outside the chiropractic community see animal models of the subluxation necessary to allow researchers to evaluate the effects predicted by chiropractic theory. [39]

Writing in 1975 Goldstein [14] noted that:

The lack of a relevant and reproducible animal model may be one important obstacle to clarification of these issues…Thus, subluxation remains a hypothesis yet to be evaluated experimentally.

In 1990 White and Panjabi, [40] wrote:

The concept of chiropractic subluxation remains a hypothesis yet to be evaluated experimentally. We believe that this has been one of the most frustrating aspects of certain views of the pathology that is purported to be altered with spinal manipulative therapy. When one is correcting a ‘subluxation’ that cannot be perceived by independent scientific observers, it is difficult to convince those observers that the treatment is effective.

The Basic Research Work Group Report from the National Workshop to Develop the Chiropractic Research Agenda [41] stated that:

Studies to address these kinds of questions (autonomic effects of adjustment) are hampered by the absence of a reliable animal model and “If the subluxation consists, at least in part, of fixation of the Z joints (zygapophyseal joints), then an animal model that mimics such fixation is clearly needed.

Basic Research Review

Henderson has reviewed [39] animal model studies of subluxation and manipulation from 1964 to 2004. He examined the evidence categorizing the studies as those looking at biomechanical change, nervous system change and the effects on organ or tissue function or symptom change. Table 3 summarizes the major chiropractic studies from 1964 to 2007. The external link model (ELM) developed by Henderson in the Palmer University Lab at Davenport [42] in collaboration with Cramer at NUHS has demonstrated the effects of induced hypomobility and demonstrates the effects of restricted motion on the zygapophyseal joints of the spine. This series of studies [42-44] also demonstrates the practicality that a line of research can attain when funding and cooperation from more that one chiropractic institution is obtained. Employing the ELM animal model these two labs have demonstrated the characteristics of induced hypomobility, the reversibility of induced hypomobility time dependent articular surface degeneration, adhesion development, and involution of synovial fold within the restricted joints. [45] Preliminary data also suggests that chronic vertebral hypomobility at L4 through L6 in the rat model affects synaptic density and morphology in the dorsal horn of the of the L2 spinal cord level. [46] This series of studies suggests that biomechanical lesions (in the form of induced hypomobility) can produce both functional and pathological changes in the spinal motion segments.

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Clinical Indicators for Manipulation of a Subluxation

The clinical indicators of subluxation are amongst the most controversial issues surrounding the subluxation as a manipulable lesion. [32] A mnemonic classification for indicating subluxation (joint dysfunction) was developed by Bergmann in 1992. [47] (Table 4)

• Pain/tenderness
  
• Asymmetry/misalignment
  
• Range of motion/ movement abnormality
  
• Tissue/tone changes
  
• Special Tests

This classification is used by the US Medicare Office [48] to reimburse chiropractors for the manual treatment of subluxation, replacing the original criteria that required evidence of subluxation on radiographs for reimbursement of the treatment subluxation. The original classification of criteria was agreed to at the Houston Conference published by the American Chiropractic Association in 1977 (Table 5). [49] This requirement became an impediment with the lack of evidence in the 1970’s and 1980’s that supported the original criteria. Part of the ongoing political controversy [16] surrounding the use of the word subluxation stems from the previous criteria that visual evidence of subluxation must be demonstrable on radiographs. This is a red herring given that subluxation was both defined and described prior to the advent of radiographic imaging.

The role of radiography in the evaluation of the chiropractic spinal subluxation has evolved considerably over the years. [50, 51] From 1918 until 1936, full spine techniques were developed. [50-52] In addition technique systems using spinographic analysis were developed by several chiropractors including Gonstead [53] and Logan. [54] A fundamental criticism of measuring misalignments on radiographs is the vagaries of anatomic asymmetry. [55] Taylor has suggested, however that with proper patient selection, careful attention to technical detail, and use of several technologic advancements, full spine radiography is a diagnostic an analytic procedure with an acceptable risk/benefit ratio. [51]

1. Flexion malposition
   
2. Extension malposition
   
3. Lateral flexion malposition-left or right
   
4. Rotational malposition left-or right
   
5. Anterolisthesis and/or spondylolisthesis
   
6. Retrolisthesis
   
7. Lateralisthesis-left or right
   
8. Altered interosseous spacing
   
9. Osseous foraminal encroachment

1. Hypomobility-fixation subluxation
   
2. Hypermobility-subluxation
   
3. Aberrant motion

1. Scoliosis and/or alteration of curves secondary to structural asymmetries
   
2. Scoliosis and/or alteration of curves secondary to muscular imbalance
   
3. Decompensation of adaptational curves
   
4. Abnormalities of motion

1. Costovertebral/costotransverse disreleationships
   
2. Sacroiliac subluxation-primary or secondary

Functional Radiography

Functional radiography that evaluates segmental spinal motion has proven more useful in the cervical region [56-60] than other areas of the spine. [51] Spinal motion segment movement has also been evaluated by videofluoroscopy and cineradiography. These have the advantage of monitoring movement throughout the entire range of movement and motion patterns as well as the end range of movement evident on plain films overlays. [61] Concern for the amount of radiation exposure prevents routine use of this form of imaging. The use of functional MRI shows promise for identifying persistent lesions, particularly in the cervical spine. [62]

Mathematical and Engineering Models of Subluxation

Documented by Ebrall, [38] the flames of the controversy over x-ray marking systems have been fuelled by the ongoing discourse between those who have applied mathematical and engineering models to the detection of subluxation. This approach to subluxation detection was promoted by Suh [63] during the 1970’s and 1980’s through the application of computer-aided biomechanics for the detection of spinal subluxation. Funded by the International Chiropractic Association during this period, Suh focused on an upper cervical model that was then followed by other mathematical and engineering models. Subsequently this approach to subluxation detection led to much controversy. [64-74]

Along with radiographic indicators of subluxation, palpation for pain, tenderness and asymmetries (misalignment) have been traditionally utilized. Table 6 summarizes a few of the studies that have evaluated these procedures. Palpation for pain and tenderness has demonstrated the greatest inter- as well as intra-examiner reliability, but lacks supporting evidence of validity. One would expect good agreement between examiners if the subjects are consistent in their response to palpation reporting on the site of pain and tenderness to palpation. Problematic is that pain and tenderness can come from lesions other than subluxation including various forms of pathology, fractures and infections. Palpation for temperature changes to monitor subluxations are outlined in Table 7.

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The most frequently used and studied procedures included in the parts examination for the detection of subluxation is palpation for segmental motion. (Table 8) More than 40 reliability studies have been conducted on movement palpation demonstrating mixed results. This is due in part to poor study design and the use of asymptomatic subjects. Overall intra-rater reliability is fair to good with inter-rater reliability poor to fair.(Table 8) Only a few studies have tested validity using facet joint blocks and congenitally blocked vertebra (Table 8). Used with other procedures motion palpation has been found to be useful in the detection of subluxations. The recommendation that when a number of studies are conducted together the reliability improves. (Table 10). This is consistent with the US Medicare requirements for the detection of subluxation that is no single procedure has demonstrated enough sensitivity or specificity to be relied upon solely as a clinical indicator for the detection of subluxation and that more than one procedure be relied upon for the application of the adjustment/manipulation. Tables 6-9 present only a small portion of the studies that have evaluated the clinical indicators for adjustment /manipulation of subluxations. It is important that future studies emphasize clinical verification of the validity of specific subluxation detection/analysis systems including comparison of the effectiveness of reduction or elimination of subluxations.

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Subluxation as a Risk Factor

In 2005 Hawk suggested that subluxation may be a risk factor. [75] Rather than suggest that subluxation is a risk factor for all disease as Palmer [76] noted, it is more practical to begin with the study of subluxation as a risk factor for musculoskeletal conditions most commonly treated by chiropractors (Table 10). Since there is evidence that subluxation syndromes are relieved by the adjustment/ manipulation rather than leaving these types of studies up to other disciplines it is important that this type of research be pursued by the chiropractic profession.

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Common Subluxation Syndromes

A subluxation syndrome has been defined as:

an aggregate of signs and symptoms that relate to pathophysiological or dysfunction of spinal and pelvic motion segments or to peripheral joints. [10]

It appears from studies that have linked subluxation to specific aggregates of signs and symptoms this would be a fruitful area for further chiropractic research. It also appears that subluxation of one region of the spine is a risk factor for signs and symptoms different from those of subluxation in another spinal area. Clinical observations suggest that different subluxation syndromes are associated with different spinal areas. [77] Greater pattern recognition of the aggregates of sign and symptoms that accompany the different subluxation syndromes can be enhanced by case series as well as RCTs.

The profession that will be recognized as “owning subluxation and its correction will not simply be the first or loudest proclaimer. Rather it will be the profession that is recognized for understanding the subluxation and converting that understanding into demonstrable clinical outcomes. [39]

Historical Perspective

The final issue is not whether subluxations exist given the consensus definition or whether there is evidence to support their detection according to the PARTS criteria, but whether chiropractors will continue to use nomenclature to describe the lesion that has characterized the profession for over a century. It has been important to the survival of chiropractic that chiropractic pioneers did not let other disciplines determine the direction of their profession. Central to this has been the term subluxation.

The word subluxation has been daubed in a kaleidoscope of colors and embodied with a multitude of meanings by chiropractors for over 100 years. [30]

To some it has become a holy word; [78] to others, an albatross to be discarded. [79]

The notion that by changing the word subluxation to another term we will somehow change the clinical, political, and philosophical connotations of the concept central to chiropractic practice is simply not rational. Changing the term used for the articular lesion treated by chiropractors (subluxation) does not eradicate the clinical, political, and philosophical issues that surround the construct; it obviously evades the issues. [30]

Conclusion

It is dangerous to reject something on the basis of lack of evidence, for lack of evidence is not evidence against. Even worse is to ignore the evidence and declare that there is none or to hide a political agenda behind a pseudoscientific argument. Rather than falling prey to this political ploy, Chiropractors must look at the evidence and support the concept basic to the chiropractic profession.

Currently, subluxation has been the most loved and hated, hotly debated, and consecrated term used by chiropractors. [30] Why then do we persist in using the term subluxation when it has become so “overburdened with clinical, political, and philosophical meaning and significance for chiropractors, that the concept that once helped to hold a young besieged profession together” [78] now divides and keeps it quarreling over basic semantics? The obvious answer was provided by Terrett: [80]