Chapter 10 Theoretic Models of Subluxation
Vertebral malposition, joint fixation, meniscoid entrapment, somatic dysfunctional adhesion, nuclear fragmentation, facet tropism, motion segment buckling, somatic reflexes
After reading this chapter you should be able to answer the following questions:
| Question 1 | How does the early model of chiropractic subluxation differ from the model of osteopathic lesion? |
| Question 2 | How can one tell if a chiropractic theory is of high quality? |
| Question 3 | What are the strengths and weaknesses of using subluxation models as a scientific theory, a professional identity, a clinical finding, and a diagnosis? |
| Question 4 | What is motion segment buckling and how might it be best classified (e.g., as a biomechanical, neurologic, or trophic model)? |
| Question 5 | How might chiropractors use the placebo effect to benefit their patients? |
This discussion offers an overview of models of chiropractic subluxation along with an approach for classification (Box 10-1). The “chiropractic vertebral subluxation” remains a controversial concept. Its nature remains elusive, and its diagnostic and political values have been vigorously debated.1–3 Numerous reviews, discussions, definitions, and justifications abound,4–7 but the ability to discuss, support, critically evaluate, and differentiate between what is known, what is only supported, and what is purely conjecture regarding the subluxation remains an emotional issue within the profession. A lack of agreement on standardization in definitions and classifications has permeated discussions on adjusting and subluxation.8,9 This lack of agreement has stimulated a study for the development of chiropractic nomenclature through consensus. In addition to chiropractors, other health care providers manipulate the spine, including some osteopaths, physical therapists, and physical medicine practitioners. Each professional group has developed and perpetuated a philosophically trademarked “brand name” for the spinal lesion it manipulates. Historically, each has offered its own explanations of the lesion and any physiologic implications. These are summarized in Box 10-2.
BOX 10-1 Criteria for Plausible and Acceptable Theory
• Systematic set of interrelated concepts, definitions, and propositions that formulates explanation of relationships
• Components are orderly and based on data
• Derived from empirical observations and facts (as opposed to speculations)
• Contributes to classification of concepts and constructs
• Empirical generalizations may inform conceptual frameworks
• Informs research hypotheses about predicted relationships that are scientifically testable
BOX 10-2 Historical Development of Manipulable Spinal Lesion Concepts
Osteopathic concepts
• Early conception of osteopathic lesion (1899): Altered relationship of zygapophyseal joints affecting flow of vital body fluids (blood, lymph, nerve).
• Modern conception of somatic dysfunction (1973): Impaired or altered function of related somatic components (musculoskeletal, arthrodial, and myofascial) and related vascular, lymphatic, and neural elements.
Medical manipulable spinal lesion concepts
• Early conceptions (1930s): Facet fixation due to mechanical derangement of the posterior joints may cause pain; intervertebral disc dysfunction may cause pain and/or radiculopathy.
• Modern conception (1978): Joint dysfunction contributes to complex neurologic reflexes that affect the neuromusculoskeletal system.
From Mootz RD. Chiropractic models: current understanding of vertebral subluxation and manipulable spinal lesions. In: Sweere J, editor. Chiropractic family practice. Gaithersburg, MD: Aspen Publishers; 1992.
The Palmers originally described and defined the chiropractic subluxation by a number of clinically observable characteristics.10,11 They proposed that subluxation was a structural disrelation that resulted in altered or impeded neurologic function.12,13 The American Chiropractic Association has established that a subluxation represents an abnormal physical relationship between adjacent anatomic structures whose contiguous tissues elicit neurologic responses.7 Although the sophistication of hypothetical mechanisms has increased,5,14,15 chiropractors have continually emphasized the proposed neurologic component of the subluxation. This emphasis on the neurologic components of the subluxation has led to development16 and refinement of the vertebral subluxation complex.17 (See Chapter 9.)
Osteopathy describes a different lesion altogether. A.T. Still18 coined the term osteopathic lesion to describe an altered relationship of the zygapophyseal joints affecting the flow of “vital body fluids,” especially blood and lymph. In recent years the osteopathic profession has agreed on a name change to somatic dysfunction. This has been defined as “impaired or altered function of related components of the somatic system: musculoskeletal, arthrodial and myofascial structures, and related vascular, lymphatic, and neural elements.”19,20 Throughout its history, the osteopathic world has speculated on the ischemic and trophic qualities of spinal disrelation as well as neurologic aberration.
Manual medicine also has recognized manipulable spinal lesions. However, medicine’s terminology has been based on strict anatomic diagnoses. Mennell21 was convinced that a mechanical posterior joint derangement was responsible for loss of joint play. Cyriax22 emphasized the contribution of “intervertebral disc dysfunction.” Other manual medicine practitioners and physical therapists have theorized an important role for loss of soft tissue elasticity.23 Although medical manipulators’ opinions differ as to what the manipulable lesion is, they have tended to be skeptical of any significant neurologic component other than pain being associated with it. With recent English-language works of East European neurologists such as Lewit24 and Janda,25,26 medical thought is beginning to appreciate more complex neurologic ramifications of spinal joint dysfunction. Organized medicine as a whole has only recently begun to acknowledge benefits from spinal manipulation.
Conceptual Models and Controversy
Although the medical and osteopathic professions have a small number of proponents for manipulation and models of spinal lesion, in the chiropractic profession attention to subluxation is found in virtually every dimension of its existence, be it clinical, political, philosophical, or scientific. Although few chiropractors dispute that manipulative and adjustive interventions in the spine are targeted at some kind of physical dysfunction, chiropractors have varied substantially in the rationale, importance, and use of the syntax surrounding that dysfunction. Subluxation has been used at least four distinct ways by chiropractors (Box 10-3). All four uses of subluxation have merits and liabilities within different contexts.
• Subluxation as Chiropractic Theory: Subluxation is used as an explanatory mechanism for physical effects of chiropractic intervention.5
• Subluxation as Professional Identity: Subluxation forms the entire basis of and for chiropractic practice.27
• Subluxation as a Clinical Finding: Subluxation serves as target for localizing manipulative and adjustive intervention.28
• Subluxation as a Clinical Diagnosis: Subluxation represents a distinct clinical condition or syndrome.10
Use as Theory
As a theory, subluxation has merit in that the kinds of models and contentions proposed for subluxation are consistent with how models are developed within the greater scientific and health communities. Using subluxation in this way is understandable by nonchiropractors and experimental verification and refinement are enhanced as more information is learned. Subluxation theory remains poorly developed, however. Most models are primarily conceptual and explanatory. Although basic science research, particularly in biomechanics, has grown dramatically in recent years, experimental evolution of models remains in its infancy. Underdeveloped theory also has potential for “mis-use” or “misguided” use when promulgated as a justification to avoid accountability to conventional medical or health care constraints (e.g., appropriateness of care determinations, duration, and frequency of care issues). Chiropractic theory represents the primary context in which subluxation is used in this chapter.
Use as Professional Identity
When an identity becomes codified in laws and policies, updating them is difficult once conventions or knowledge changes. The x-ray requirement to document subluxation radiographically for Medicare coverage in the United States is a classic example. After studies reported problems with demonstrating subluxation on x-ray, new and better dynamic models of subluxation were developed, and alternative clinical methods for detection became standard. Chiropractors and their representatives spent countless dollars and hours trying to change laws and had to practice for decades under outdated conventions that they themselves had championed at one point. It is not surprising that all other health professions aim to “legislate as broadly as possible” and “practice as narrowly” as they choose. When this is superimposed on a lack of professional consensus about subluxation as well, it contributes to substantial confusion in the minds of policy makers and the public.29
Use as a Clinical Diagnosis
Subluxation is also used as a clinical diagnosis. Frequently modified to be a complex or syndrome, the idea here is to actually label a patient’s condition with this. Some feel a unique diagnostic term confers legitimacy to practice models, and just focusing on a single diagnostic term simplifies initial insurance reporting. However, diagnostic conditions that lack accepted case definitions (e.g., presentation, progression) are sources of controversy in policymaking, and coverage decisions can become problematic. For example, if a condition is to be covered by many payers, the health consequences need to be well established. A “diagnosis” of subluxation further lacks specificity to drive intervention or even a systematic approach to options for intervention. The single diagnosis of subluxation really implies that any chiropractic technique is appropriate for any subluxation. Techniques must be modified to the area of complaint and the uniqueness of the individual. In addition, clustering around a single diagnostic entity for actuarial purposes can be a problem. Diagnostic categorization of all chiropractic patients who have subluxation reveals dramatic practice variation and serves as policy justification for arbitrary cost containment policies. If subluxation can be fixed in three visits with some patients, why can it not be fixed that quickly in all patients? Consideration of the aggregate of signs and symptoms that commonly occur with subluxation of different regions of the spine along with concomitant pathology is necessary to describe and document the true status of the patient’s condition. (See Chapters 17 to 27.)
Clinical Rationale Provides Logical Method for Model Classification
Development of clinical theories and models are typically the result of attempts to rationally explain empirically observable clinical phenomena. Such is the case with manipulable subluxations. The historical models discussed earlier represent isolated attempts to do so. Research in this arena originally occurred primarily within the osteopathic profession.30,31 In recent years, advances in understanding of spinal cord neural behavior, pain generation, reflex effects, and biomechanics have generated a substantial amount of scientific literature that is shedding light on how chiropractors approach subluxation models.32–34 It is worthwhile to characterize some clinical issues in attempting to classify subluxation models. All practitioners tend to follow similar clinical processes in attempting to identify the site of a manipulable subluxation. Box 10-4 lists some common clinical characteristics looked for by manipulators. This approach provides the basis for organizing the various models of subluxation presented here.
After a thorough history and physical examination, practitioners perform a mechanical evaluation. The manipulator may look for contributing mechanical causes (nature of injury, repetitive postural activities), static asymmetries (e.g., high shoulder, altered curves, externally rotated hip or foot), dynamic asymmetries (gait, other movements), as well as passive and active individual joint ranges of motion (static and motion palpation). Some practitioners try to image these altered mechanics radiographically.35
Most practitioners also look for changes in neurologic activity, often identified by patient symptomatology. Pain distribution patterns provide historic cues. Palpating for tenderness and muscle spasm or altered tone also may suggest neurologic activity. Some look for indirect indications of neurologic involvement by assessing vasoconstriction or dilation (thermography), and sudomotor activity (galvanic skin response). Standard neurologic indicators including hyperreflexia or hyporeflexia, sensory changes, and motor changes also may suggest spinal dysfunctions. Some consider altered tissue texture and edema as indications of aberrant local tissue metabolism or vascularization (e.g., rubor, tumor, dolor, calor).
When assessing the purposes of manipulation, it is clear that aberrant mechanics, neurologic activity, trophic function, or psychosocial problems are addressed. The argument then is made that a classification system for models of subluxation as a manipulable spinal lesion should be based on commonalities of generic clinical practice rather than “brand-name” theories. Specific explanations of the vertebral subluxation within each of these four general categories of biomechanical, neurologic, trophic, and psychosocial models are presented and summarized in Box 10-5. Rationale, explanations, and brief reviews of relevant literature of these clinically derived models are presented in the following discussion.
Models of Chiropractic Subluxation
Biomechanical Models
Vertebral Malposition
One of the oldest concepts of subluxation considers trauma to be a major cause of altered joint position. Palmer12 and Still36 both discussed this model, and Leach’s chapter5 on intervertebral subluxation reviews medical literature regarding radiographically demonstrable articular disrelationships. Trauma, disc degeneration, erosive arthritides, and congenital factors all have been shown to cause such radiographic changes. However, reduction of such mechanical alterations has not been demonstrated with manipulation. More subtle mechanical alterations are probably what chiropractors adjust; these are difficult to demonstrate radiographically.35 The clinical value of radiography for such assessments has been questioned.37,38 (See Chapters 6 and 8.)
The concept of a static misalignment, although promising initially, seems difficult to support. Chiropractic studies have thus far shown interobserver and intraobserver agreement of many technique-based x-ray markings to be relatively poor.38 Some radiographic mensuration methods indicating disc wedging and overall articular contours can be evaluated consistently and are sometimes used as indications for mechanical therapies. However, good quantitative outcome studies clearly identifying usefulness remain to be done. Although this mechanical approach may potentially indicate aberrant segmental position, it also may be representative of activity of surrounding musculature. Discussion of the latter lies within the domain of neurologic models, specifically somatosomatic reflexes. Mechanically, the “out-of-place bone” is not likely to be the sole explanation for chiropractic subluxation.
Fixation Caused by Adhesion
Adhesion in and around synovial joints may arise in two ways. It may result from trauma that results in extracellular accumulation of inflammatory exudate and blood.39 Platelets then release thrombin-converting fibrinogen into fibrin, which organizes into collagenous scar tissue, resulting in a variety of soft tissue and articular adhesions. A second type of adhesion results from the dehydration associated with immobilization. Extensibility of connective tissue is caused by infusion of water between layers of proteoglycan molecules. This provides lubrication, allowing for a more parallel configuration and greater stretch under longitudinal tension.40 Immobilization leads to dehydration with resultant approximation of the proteoglycans, which tend to stick together, creating movement restrictions.41,42 Another by-product of prolonged immobilization can be intraarticular fatty adhesion within synovial joints.43 The relevance to spinal lesion models is that both trauma and immobilization are frequently implicated causes in patients with subluxation. Manipulation increases movement in dehydrated tissues, promoting the imbibition of fluid, or the actual mechanical shearing or breakdown of newly deposited adhesions. This model explains many clinical phenomena and is supportable based on the literature.44
Fixation Caused by Meniscoid Entrapment
Bogduk and Engel45 and Giles and Taylor46,47 have reported on the presence of intraarticular synovial tabs, or meniscoids. These tabs may cause fixation when the fibrocartilaginous edge of a tab gets caught between the articular surfaces.48 The resultant deformation and restriction, especially at end range, is also thought to stress the joint capsule from which the meniscoid originates. This may result in irritation of the capsular nerve endings and may contribute to pain and spasm. Meniscoids appear to be present throughout the spinal facet joints.48,49 However, problems with this model have been identified:42 Meniscoids may not be present in fixed joints, and most meniscoids may actually be softer than the joint cartilage and therefore may be more likely to be deformed or cleaved by the joint.44 Disorders such as rheumatoid arthritis appear to have associated proliferation of synovial tabs,48 yet there does not seem to be any reporting of increased likelihood of fixation in these individuals. Although the potential is promising for some kind of role of synovial tabs, particularly as instigators of muscle spasm,45 or perhaps through extrapment where the meniscoid becomes trapped beyond the articular facets, they do not seem likely to be the primary cause of subluxation.
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