| Hypothesis Formulation for Scientific Investigation of Vertebral
Subluxation
Owens, Edward F.; Koch, David B.; Moore, Leroy
Abstract -- Chiropractic research in recent years has more often focused
on the effects of spinal manipulative therapy as a treatment for certain
musculoskeletal conditions, than on the detrimental effects of vertebral
subluxation on the body's ability, to maintain its own health. Many
practitioners and some institutions, however, maintain that vertebral
subluxation, not the treatment of musculoskeletal conditions, should be the
central focus of the chiropractic profession. Research into the phenomenon of
vertebral subluxation has suffered due to a lack of well-defined operational
definitions for elements of the phenomenon, and a framework for linking
philosophical constructs, clinical observations, and scientific methods. The
goal of this work is to develop a vertebral subluxation model that is grounded
in a philosophy of science as applied to chiropractic, beginning with the
abstract construct and branching out into diverse testable hypotheses in
stages. The present authors liken this development to the structure ora tree,
where the roots are the philosophy, the trunk the major principle and the
branches particular versions of more defined, but still abstract theories. As
development continues, specific quantifiable and testable hypotheses will be
proposed that can be used to verify or falsify the theories. This article
details the development of the hypothesis tree, and outlines some areas of
fruitful research that might arise from its application in a concerted effort
to investigate the aspects of the vertebral subluxation.
Key words: Vertebral Subluxation, Chiropractic, research strategy, research methodology
Introduction
Debate regarding practice objectives and methods is certainly nothing new
in the chiropractic profession. A popular topic is the profession's continued
focus on the correction of vertebral subluxation as a practice objective. The
debate centers around the existence and importance of a subclinical lesion
which chiropractors refer to as the vertebral subluxation. On the one hand, at
least half of the practitioner's see benefit in continued study of the
vertebral subluxation.(1) As recently as 1996, the Association of Chiropractic
Colleges reaffirmed that chiropractic should be defined in terms of the
vertebral subluxation.(2) On the other hand, researchers have pointed out that
even though vertebral subluxation theories have not been refuted, there is
little compelling published evidence that vertebral subluxation exists.(3)
There are no generally accepted operational measures of vertebral subluxation,
and hence no good way to study the phenomenon. Perhaps as a result,
chiropractic research in recent years has more often focused on the effects of
spinal manipulative therapy as a treatment for certain musculoskeletal
conditions, than on the detrimental effects of vertebral subluxation on the
body's ability to maintain its own health.
In this age of evidence-based health care, it is becoming increasingly
important to be able to verify theories using scientific methods in order to
justify their continued use. The present paper attempts to clarify and perhaps
unify subluxation theories, and develop a hypothesis-generating framework that
will be amenable to scientific investigation.
Much of the groundwork for this effort has already been done, presented
in the form of commentaries in the Journal of Manipulative and Physiological
Therapeutics, and as articles in the Journal of Chiropractic Humanities.
Coulter, Keating and Marks have discussed at length the philosophy of science
and its metaphysical nature.(4-10) Deductive and inductive methods work
together in science. Deduction can be used to postulate meta-physical
constructs, such as universal intelligence, which may be untestable. To
complete the picture, though, an inductive process must be used to derive and
test refined hypotheses that stem from the metaphysical construct. The authors
all agree that any science of subluxation must consist of specific falsifiable
hypotheses based on measurement and operational definitions. Keating has also
offered practical advice on how to construct hypotheses and develop research to
test their validity.
More recently, Nelson(11) and Leboeuf-Yde(3) have examined subluxation
hypotheses in terms of particular tenets and principles, and discussed ways of
evaluating them. Nelson critiqued the multicomponent descriptive models of
subluxation and found them lacking in usefulness as the basis for scientific
investigation. Nelson also laid down a number of guidelines for a subluxation
theory: it should attempt to explain existing phenomena and observations, it
should be consistent with current basic science, it should make predictions
that lead to future discovery, it should bear some resemblance to historical
antecedents, it should be clinically meaningful, it should present a distinct
point of view, and it should be testable.
Both Nelson and Leboeuf-Yde appear to view the ultimate goals of
vertebral subluxation research as the demonstration that vertebral subluxation
can cause certain diseases, and that the correction of subluxation can
alleviate them. This traditional model of vertebral subluxation would tend to
restrict the use of chiropractic to care for sick individuals. Many
chiropractors contend, though, that chiropractic care can be health enhancing
even for the essentially healths, and that vertebral subluxations should be
corrected whether they are linked to any disease process or not. This view of
chiropractic care as a health enhancement strategy creates special challenges
for research from both philosophical and methodological standpoints.
Boone and Dobson have proposed a modernized model that attempts to
reintegrate B.J. Palmer's concept of interference to mental impulses as an
essential element of vertebral subluxation.(12-14) In their view, the mental
impulse is a description of nerve function that is not restricted to the action
potential, but might include other modalities of interaction between the
nervous system and the tissue cells. In part three of their series of articles,
the authors evaluate research methods that might be used to assess vertebral
subluxation, challenging the appropriateness of the randomized controlled trial
(RCT) for complementary and alternative medicine research. RCTs focused on the
causes of and relief from disease may not be an appropriate research design to
detect the impact of chiropractic care on quality of life or general
health.(14)
Mealing points out the limitations of using a quantitative reductionist
paradigm, investigating the whole by studying its parts, in understanding
complex systems.(15) He goes on to describe several qualitative paradigms that
might be complimentary in developing the science of chiropractic, such as
positivism and emergence. The approaches of Boone and Dobson, and Mealing hold
out promise for a scientific investigation of the straight chiropractic concept
that the correction of vertebral subluxation may be of benefit to anyone,
regardless of their state of health.
The goal of this work is to develop a vertebral subluxation model that is
grounded in a philosophy of science as applied to chiropractic, beginning with
the abstract construct and branching out into diverse testable hypotheses in
stages. The present authors liken this development to the structure of a tree,
where the roots are the philosophy, the trunk the major principle and the
branches particular versions of more defined, but still abstract theories. The
fruit of the tree, if buds can be formed, will be the quantifiable and testable
hypotheses that can be used to verify or falsify the theories.
Discussion
Philosophical development
A goal of this work was to develop hypotheses consistent with
chiropractic tradition. Thus, this presentation started with a philosophic
construct described by B.J. Palmer, and reported in Stephenson's text as the
major premise.(16) The major premise has been slightly altered here to reflect
the more recent appreciation of Einstein's realization that matter and energy
are interconvertible.
Although many construe the major premise to be a reference to a governing
consciousness or god, that is not the intent here. Universal intelligence is
presumed to exist, based on the observation that organization exists in the
universe. The development of increasingly complex organisms seems to be a
violation of natural law. In a closed system driven by entropy, the second law
of thermodynamics demands that the system should eventually devolve into a
uniform level of disorganization. Living systems, however, are self-organizing,
energetically open systems that increase complexity and organization and that
emerge from the prior organization of the universe itself. Universal
intelligence is the construct that there exists a source of information that
drives the process of organization.
Gold expounded on this major premise in The Triune of Life.(17) The
triune is the philosophic model that nature can be divided into three
interdependent parts: the matter itself, the intelligence that creates
information determining how that matter is organized and the force that allows
the information intelligence creates to interact with the matter. So, the
different properties of chemical elements, for instance, do not derive so much
from the matter of which those atoms are composed -- all atoms are proposed to
be made from the same building blocks -- but instead from the pattern of
organization, the number and distribution of the subatomic particles. With
increasing levels of complexity, the same pattern is true -- the organization
of constituent parts, which is an expression of the information being created
within the structure, gives the structure its properties and functions.
Theory development
A subluxation theory arises at a very basic level from this major
premise, and starts with the abstract notion that information flow is necessary
to maintain the function and organization of complex organisms.
Essentially, it is remarked here that information flow is critical to the
proper functioning of higher organisms. Information allows the organism to
perceive internal and external changes in the environment and to devise and
execute appropriate adaptive responses. Hence the matter of the organism can be
reorganized to meet new challenges.
Distortion of information, then, would be expected to lead to some degree
of dysfunction in the organism. If we think of the central nervous system as
one of the main generators and conduits of information in the body, any factor
that effects nerve function could distort the information content in the
system.
A host of factors can interfere with nerve function, including adverse
metabolic, chemical and mechanical states. Chiropractors have carved a niche by
considering the mechanical effects in the area of spinal joints that might have
a negative impact on nerve function.
Hence, the present authors arrive at a definition of vertebral
subluxation with the first hypothesis in the theory development to deal
directly with the spine. This is a very general definition and does not specify
the way in which the mechanical influences the neurological.
Just as it is proposed that interference to information processing or
transmission is, in and of itself, deleterious to the human, the vertebral
subluxation is seen as a distinct phenomenon worthy, in and of itself, of
research independent of any disease process to which it may be related.
The hypothesis tree takes an interesting turn here: it could not be
decided which was the primary component at this level, distortion of the
information content, or the mechanical disturbance. Indeed, by the present
definition, the vertebral subluxation does not exist unless both components are
present simultaneously. Hence the tree split into two branches, one in which
the distortion of information leads to adverse mechanical effects, and another
in which adverse mechanical effects lead to nerve interference. It was also
noticed that in such a state where the cause can also be an effect, a positive
feedback loop was being described.
This is a positive feedback loop because the initial conditions lead to
an effect that tends to reinforce those initial conditions. The feedback loop
helps to answer the question beginning chiropractic students always ask, "Why
can't innate intelligence correct the suxblaxation?" Maybe it sometimes can,
but if the information that the body needs in order to perceive the subluxation
is lacking or distorted, then the adaptive response will not be appropriate or
sufficient. Even if the adaptive response is appropriate, if the neuromuscular
impulses are distorted or interfered with, then, again, the corrective response
will be insufficient. Hence, the subluxation can exist as a self-perpetuating
phenomenon in the body.
At this stage of hypothesis development, while it may not be able to be
said exactly what is a vertebral subluxation, some of its critical features can
be seen: it is significant in the deleterious effects it may have on the
nervous system, it may be initiated by unknown factors, but once present is
self-perpetuating. It may also be able to be said at this level what a
vertebral subluxation is not. It is not equated with joint dysfunction alone,
but must include a wider effect on the nervous system. For example, a fixation
of C5 might be noted with respect to C6 with palpation or on videoflouroscopy.
By the present definition, this would not necessarily be a vertebral
subluxation, unless some other signs of the fixation's effect on physiology or
neurology could be detected as well. In an inverse example, a sensation loss
might be noted over the region of the deltoid muscle during a neurological
exam. Would this be a sign of vertebral subluxation? Only if a vertebral
articular problem could be detected that might reasonably be related to the
nerve supply of that area of the body.
Figure 1 shows the current development of the hypothesis tree. Note that
the tree begins at the bottom, and rises in stages. At the center of the tree
can be seen the two parallel statements that comprise the positive feedback
loop. Notice also at this level that the "Adverse chemical...,"
extra-mechanical influences on nerve function can re-enter the tree here, if
the interference can produce mechanical loading on the vertebrae. The present
authors were thinking particularly of metabolic influences that might produce
muscular hyper- or hypotonus.
Hypothesis formulation
The next step in hypothesis development is to take the left and right
branches of the feedback loop and elaborate on particular, more specific
mechanisms by which the vertebral subluxation could be observed. The goal of
the hypothesis development is two-fold here: to try to open up the vertebral
subluxation definition to include several of the currently held theories of
subluxation mechanism, and generate concrete testable hypotheses, with proposed
measures and outcomes.
Kent surveyed the extant vertebral subluxation hypotheses for the
inaugural issue of JVSR in 1996.(18) He describes five major divisions of
models: the component approach, subluxation degeneration, nerve root
compression, dysafferentation and neurodystrophic models. Several elements of
these models were used as general hypotheses in the next level of the tree
development. Note in figure 1 that four general hypotheses are presented on
each side of the tree as darkened boxes.
Direct mechanical influences on the nervous system include the
possibility of compressive and tensile effects either on nerve roots or the
spinal cord, or both. The manner in which restricted joint mobility can reduce
segmental mechanoreceptor output leading to disturbed nerve information
processing is another possible direct mechanical influence to consider.
To render any of these hypotheses researchable, they must be refined into
more specific testable forms. For instance, if it is suggested that vertebral
misalignment is an important aspect of the model, then the misalignment must be
able to be quantified, perhaps with a particular type of x-ray analysis.
Similarly, ways of measuring specific changes in nerve function, such as
conduction rates, must be investigated.
When neurologic dysfunction is considered as an initiating mechanism for
vertebral subluxation (the right branch in figure 1), hypotheses develop around
the effects of neurological disturbance reflecting back on the articulations.
The general hypotheses envisioned so far derive from effects on the muscles and
their control of joint position or movement. Distortion of sensory and motor
information as well as the integration of that information in the central
nervous system could play a role in these subluxation models. Following these
branches to create testable hypotheses is a matter of developing techniques for
measuring such things as muscle tone, joint position sense, coordination and
postural strain.
Most of the hypotheses depicted so far have been looking at the
mechanisms relating articular function and nerve function. Another class of
hypotheses can also be developed that are less related to possible subluxation
mechanisms and more devoted to real-life outcomes. Study in this area is
crucial to establish the impact of the correction of vertebral subluxation on
the lives of patients. These hypotheses would be amenable to testing using
practice-based studies and clinical case series. The measures used might
include patient surveys of quality of life or specific tests of physical
performance, for instance.
Subluxation detection methods
Much of the work at higher levels in this hypothesis tree will lead to
development and testing of subluxation detection measures. There are already
many methods that have been developed for use in many of the named chiropractic
techniques. Various techniques have particular methods for determining the
presence of nerve interference and related articular dysfunction. Perhaps the
most often used analysis techniques are palpatory, relying on the doctor's
sense of vertebral mobility or position, tissue texture and muscle tone. Leg
checks, the estimation of functional leg length inequality, is also very
common. Not as well recognized are procedures for measuring vertebral alignment
using x-ray analysis, and assessments of skin temperature or galvanic
resistance patterns.
Reliability and validity testing needs to be done on all of these methods
in order to determine their objectivity, sensitivity and specificity in
locating vertebral subluxations. Some methods have passed recent tests of
reliability: leg length difference measurement,(19) and an upper cervical x-ray
line drawing procedure in particular.(20)
Reliability is a necessary condition for validity, but is not sufficient
to guarantee it. Validity is most often assessed by comparing the results of
testing to a known standard. Since we are hampered in this respect by the lack
of a gold standard against which to compare our methods, other tests of
validation need to be agreed upon. Perhaps validation can be found by looking
at our definition of vertebral subluxation itself. The definition requires both
an articular dysfunction and a neurological component. You would not expect
measures of two dissimilar phenomena to covary in a population over time unless
there were some underlying mechanism linking them. When a tight linkage is
found between two measures of subluxation, perhaps this can be used as evidence
for the concurrent validity of the measuring system.
A fertile ground for subluxation measures is the `pattern' analysis
developed by BJ. Palmer, and taught at several chiropractic colleges. In
pattern analysis, the physiology of the body is considered to represent an
optimally adaptive state when it is constantly changing in response to changes
in the environment. When a pattern of consistent unchanging findings in a set
of measures appears, the physiological system is considered to be in a
maladaptive state. In pattern analysis, the detection of a static pattern of
responses indicates that the nervous system is not functioning properly, the
first condition for a possible vertebral subluxation. Further analysis is used
to detect spinal anomalies that might be related to the aberrant physiology.
Paraspinal skin temperature is the classic measure used in pattern
analysis, particularly in upper cervical chiropractic techniques. Any
physiological factor, however, can potentially be used in pattern analysis.
Functions directly related to the spinal column (for example, intrinsic heat
patterns, electromyography, and muscle tone patterns) may be particularly
relevant and may also simultaneously provide other useful information regarding
spinal function.
Practical application of the model
Ultimately, clinical verification of the validity of specific subluxation
detection/analysis systems will need to be done, comparing the reduction or
elimination of subluxation indicators through adjustment with clinical
outcomes. A time-series experimental design would be appropriate for this type
of clinical study.(21,22) Blinded assessments of some specific set of
functional measures in conjunction with chiropractic analysis of spinal and
articular function can be performed on three or more occasions before care is
begun. This establishes a baseline for the functional and vertebral subluxation
measures. The baseline period is followed by the actual chiropractic care,
during which time both the functional and subluxation measures are monitored on
a regular basis. After correction of any structural aberrance, the patient can
be monitored for improvement or degradation of function, whether continued
adjustment is indicated or not. Here, the functional measures could be of
neurological or physiological function, performance measures on standard
cognitive tests, or perhaps sports performance.
A time-series analysis would allow inferences to be drawn between the
presence of vertebral subluxation as indicated by chiropractic measures, and
the changes in function. If researchers use a common set of vertebral
subluxation measures, it may be possible to compare results of a number of such
studies, regardless of what chiropractic adjustive techniques are used.
Further development
The hypothesis tree could benefit by the addition of more limbs. As it
is, only eight different types of mechanisms are represented here. Each of the
perhaps 200 or more chiropractic techniques has at its core a hypothetical
framework regarding how its indicators relate to vertebral subluxation, and how
best to correct the varieties of articular dysfunction detected. Many of those
technique systems will fit within this vertebral subluxation hypothesis
framework.
The process of researching a particular vertebral subluxation hypothesis
should start with systematic literature reviews to uncover basic and clinical
science that might support or refute the hypothesis. Research programs then
could be directed at further testing of the hypothesis, by applying
experimental and descriptive methods. In the tree shown in figure 1, note that
only one experimental approach is offered for each of the eight general
hypotheses shown. In practice, each general hypothesis should be the source of
several null hypotheses that each needs to be falsified in order to support the
major hypothesis. The research task is daunting and will certainly take time to
accomplish. This formulation is just one way of approaching the whole process
in an organized manner.
Ultimately, the scientific investigation of vertebral subluxation should
be of use to practitioners. The goal is not simply to justify existing methods
of chiropractic practice, but to determine the effectiveness of that work as it
is done now. Future developments, then, could be compared with the status quo
to find out if changes in technique provide improvements in outcome. It would
also be useful to survey chiropractors for hypotheses that arise from a
clinical perspective, and that might be overlooked utilizing a philosophically
driven theory development. Certainly a theory is only good if it helps explain
reality, and reality in this case is what happens when a person undertakes a
program of chiropractic care aimed at detection and correction of those spinal
dysfunctions that impact on the function of the nervous system -- namely
vertebral subluxations.
References
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