
Figure 1
OVERVIEW OF THE VSC MODEL
Kinesiopathology is a functional component which is the end product of the synergistic activity of the various tissue level components. The tissue level components are presented in Figure 1 as supporting structures for kinesiological functions. Bones provide the structural rigidity required for the efficient transmission of forces generated by muscles. Fibrous connective tissue allows the formation of joints which permit movement while the circulatory system nourishes and cleanses the tissues. The nervous system, through its action on the muscles controls movement.
The inflammatory response is a process common to all tissues and is a critical factor in tissue remodeling after injury. Histopathology represents the cellular description of the degenerative process. Each tissue component is recognized by its own characteristic histology, and degenerative processes are described by their patterns of histopathology. The dorsal root ganglia (DRG), for example, have a unique and distinctive histological appearance. Wallerian degeneration on the other hand is the histopathological description of injured nerve fibers. Descriptions of nerve degeneration must be included in any complete description of subluxation as should a thorough understanding of normal cellular structure and architecture. In previous descriptions of the VSC, however, the term histopathology has been reserved exclusively for connective tissue.
Biochemistry is fundamental to all life processes and any complete description of subluxations must address biochemical mechanisms. This is found primarily in the biochemical dynamics of connective tissue and the biochemistry of inflammation [23]. Other aspects of biochemistry are involved as well, such as nutrition [24], certain aspects of drug usage [25] and neurohumoral elements such as trophic substances and neurotransmitters [26]. Recent investigations into the effects of chiropractic adjustments on hormonal responses [27] also bring endocrinological aspects of biochemistry into the realm of chiropractic theory.
Each major component of the VSC will be discussed individually in the remainder of this series in order to establish the concept of subluxations as a dynamic and functional model for the theory and practice of chiropractic. It is not possible, in a brief article such as this, to present an exhaustive description of each of the components of the model. Each is presented in sufficient detail, however, to provide definition and direction for the reader and to allow for integration of the various components into the more generalized model of subluxations.
ELEMENTS OF THE MODEL
KINESIOPATHOLOGY
Kinesiology is the study of human movement, and kinesiopathology would represent any alteration from normal movement. It is a common adage that movement is life, and a corollary of that would be that the lack of movement is death. It is well known that the lack of movement in a joint leads initially to joint stiffness (loss of flexibility) [28, 29], with associated pain [29]. This is followed by degeneration of the joint [6], and ultimate fusion by bony ankylosis [30]. Videman states [31] "All situations that lead to immobilization can cause some degree of degenerative change in the musculoskeletal system. Early mobilization, traction and continuous passive motion overcome the harmful effects of immobilization." The idea that joint restriction or "fixation" is an integral component of subluxations was first proposed by Smith et al. [32]. More recently, the basic concepts of the diagnosis of spinal fixations by motion palpation of the spine were formalized by Gillet [33] and organized by Faye [34] and others into a system of joint palpation called motion palpation of the spine and extremities. This represents but one of many palpation systems used in chiropractic today, including scanning palpation of the cervical spine [35].
In the movement of any joint, there is a range of active physiological motion which is under voluntary control. The passive range of movement adds an additional increment of motion beyond the active range which can be reached only with assistance, as provided by an examiner or a doctor. At the end of this passive range of motion there exists a resistance to further movement which is referred to as the elastic barrier. It is at this barrier that an examiner begins to experience what is referred to as joint play, a springiness and rebound in the joint movement. Beyond this barrier is an additional space in which movement can occur, and this is referred to as the paraphysiological space. As described by Sandoz [36] movement into this space is accomplished by the chiropractic adjustment which he defines as:
"a passive, manual manoeuvre during which an articular element is suddenly carried beyond the usual, physiological limit of movement without, however, exceeding the boundaries of anatomical integrity. The usual but not obligate characteristic of an adjustment is the thrust which is a brief, sudden and carefully dosed impulsion at the end of the normal passive range of movement and which is usually accompanied by a cracking noise."
The boundaries of anatomical integrity, referred to by Sandoz, are found at the end of the paraphysiological space. Movement of a joint beyond this barrier will result in sprain, strain and dislocation (luxation) accompanied by stretching and/or tearing of the associated ligamentous and capsular structures.
The above description does not apply to all types of adjustments nor to other less conventional chiropractic procedures, but it does represent a well-defined and widely used procedure in the practice of chiropractic. It should be pointed out here that the delivery of an adjustment is an art which is developed through years of practice. Although the basic mechanics of delivery are simple, the analysis of where and when to deliver an adjustment can be complex and subtle. It should also be pointed out that improper administration of an adjustment can be harmful [37, 38] and in extreme cases, fatal [39].
MOTION SEGMENT
The basic unit of spinal mobility is the motion segment [40], previously known as the spinal motor unit [41], motor segment [42], functional spinal unit [43] or basic spinal unit [44]. The term motor unit was often confused with the neurological motor unit, consisting of a single motor neuron and all muscle fiber bundles innervated by it [45]. The term motion segment avoids this confusion and is recommended whenever the motion of adjacent vertebrae is described. The motion segment consists of two adjacent vertebrae joined by an intervertebral disc (IVD), two posterior articulations and a number of ligaments [44], including capsules, intraspinous ligaments and intertransverse ligaments. Parke [42] also includes the muscles and segmental contents of the vertebral canal and the intervertebral foramen (IVF).
Functionally, the motion segment is viewed as a three-joint complex [46], but may be considered as a single, compound joint with three articulations [18], analogous to the wrist. Limitation of the motion segment to these basic elements is a necessary simplification for biomechanical studies. For chiropractic applications, such as those suggested by the work of Sato and Swenson [47], a broader concept of the spinal unit is needed.
The term Integrated Segmental Unit (ISU) refers to the basic motion segment along with associated spinal structures, such as the segmental nerves, nerve roots and dorsal root ganglion, sinu- vertebral nerves, muscles, and vascular structures, such as the radicular arteries and veins. It would also include meningeal structures, such as the dural funnel, and segmental spinal circuitry and reflex arcs. It must be recognized, too, that regional differences exist in the spine. In the cervical spine, for example, the ISU would include the vertebral arteries, and the joints of Lushka, while in the thoracic spine, it would include the costal articulations, capsules and associated ligaments.
Joint movement is a complicated phenomenon, and more so in the spine than in any other organ system
[48]. In addition to the three planes of physiological movement: flexion/extension, lateral flexion & rotation, there are also long axis traction and joint play, a springiness in the joint when it is taken to tension.
It is difficult to discuss the kinesiology of joints, or kinesiopathology, without considering the role played by ligaments, capsules and muscle/tendon systems. In the spine, the dural sac, along with its contents, may also be considered as structural components that impact on the kinetics of movement [49-50]. The spine is further complicated in its kinesiology in that it responds as an integral unit in which restrictions of movement at one level can lead to compensatory hypermobility in other areas [51-52]. The most succinct statement of this interrelatedness is found in Rothman & Simeone's "The Spine" [42] in which it is stated that no disorder of a single major component of a segmental unit can exist without affecting first the functions of the other components of the same unit and then the functions of other levels of the spine.
As an example, with degeneration of the IVD, paraspinal ligamentous laxity occurs which predisposes the spinal articulations to degeneration [53]. In other situations, spasticity can lead to joint contracture which can, in turn, increase the degree of spasticity and muscle contracture, thereby creating a vicious cycle [54]. To prevent the development of this cycle, it is essential to maintain the full range of motion of all joints [54]. Similarly, immobilization of a joint can lead to contracture [55]. Another related aspect of this problem is the clinical observation that in athletes there is an increased tendency to re-injure extremities that have been previously immobilized due to injury [56].
It has been conclusively shown that when a joint is immobilized it undergoes a degenerative process which ultimately leads to bony ankylosis [57-63]. The extent and progress of degeneration, however, are dependent upon the position in which the joint is immobilized [57, 64, 65]. Whereas most of these observations were made on extremities and on experimental animals, clinical studies suggest the same process occurs in the human spine [36, 76, 77, 52, 66]. Patients with tuberculosis of the spine underwent vertebral fusion by discectomy, thereby effectively eliminating movement between the two vertebrae [67]. Within six months, fusion of the zygapophyseal joints was also observed in these same patients. While this is an extreme example of spinal immobilization, it can be inferred from studies in animals that complete immobilization is not required for the degenerative process to occur [57]. It would appear, in fact, that any alteration of the range of motion of a joint, either restriction or facilitation, is accommodated for by alteration of the structure and composition of the connective tissues of the joint.
The other side of this issue is the restoration of motion to joints which leads to a restoration of normal joint function and physiology. While the degenerative effects of immobilization may be completely reversed upon remobilization [63, 68, 69], the extent of recovery and the time for maximum recovery are dependent upon the duration of immobilization [70]. In extreme cases of immobilization to the point of fibro-fatty consolidation of the synovial fluid, remobilization of the joint will result in the formation of a new joint cleft and articular cartilage with the histological architecture of an otherwise normal joint [68]. This constitutes some of the strongest evidence available supporting a physiological basis for the effectiveness of chiropractic adjustive procedures. There appears, however, to be a threshold beyond which the degenerative process becomes irreversible, regardless of the cause [71]. Early mobilization in joint trauma is gaining a foot-hold in medical treatment of whiplash [72] and knee surgery [73], conditions which, in the recent past, were treated with braces and casts. Revitalization of the joint following joint remobilization has been documented in every aspect of joint function and structure [6]. Forced motion causes physical disruption of the adhesions between gross structures, such as capsule to cartilage, and leads to a disruption of the intermolecular crossbridging of collagen [60]. It is presumed that intermolecular crosslinking interferes with joint extensibility by inhibiting free gliding of fibers in the nylon hose weave model of the connective tissue matrix [74]. In contrast to these findings, it has been shown in dogs that irreversible degenerative changes occur in the spinal apophyseal joints within two months of traction immobilization using a Harrington rod [75]. In this study, the animals were allowed free movement and activity after removal of the fixation device, but no form of mobilization or adjustment was administered to them.
It is a far simpler matter to evaluate the ranges of motion of the elbow, shoulder or knee than that of the cervical or lumbar spine, and even more difficult to evaluate the movement between adjacent vertebral segments [48, 52]. In studies of the effect of restriction of joint motion on the integrity of the joint, virtually all research is performed on the extremities [6]. Studies on the spine are few [67, 76, 77] and tend to be more clinical than experimental. Animal research is also grossly lacking in this area [75, 78], but the single study of the effect of internal fixation on the zygapophyseal joints in dogs showed that degeneration occurred within two months of immobilization [75]. The mechanisms involved with the degeneration of spinal articulations are qualitatively similar to those in the more movable joints [79] This suggests that certain conclusions made from extremity studies may, by inference, be extended to spinal joint response.
ANALYSIS OF SPINAL MOTION
Kinesiological studies of the spine are extremely difficult, since restrictions of movement in one area can be compensated for by increased movement [52, 47] or degenerative changes [80] in other areas. Since it is difficult to localize specific joints and measure their precise movement [81], the analysis of dysfunction is further complicated. In the clinical setting, spinal movement has been evaluated by goniometry, which evaluates the gross movement of a region of the spine [82]. For example, flexion and extension of the head can be measured in degrees and restrictions noted based on population averages or the patient's prior response. In this analysis, however, we obtain only regional and indirect information regarding the site at which restriction may be occuring.
X-ray analysis is often used in chiropractic [83] and in medicine [84] to evaluate abnormal spinal movement. While there are inherent limitations to plane x-ray analysis of spinal biomechanical abnormalities [77, 85], it is still widely used for such purposes. Modern advances in x-ray technology have led to the development of biplanar radiographic analysis of intervertebral motion [52]. While these techniques still suffer the inherent limitations of static x-ray, they do allow a more precise evaluation of changes in vertebral position. Such studies have shown clearly that the facet joints on opposite sides of the motion segment may behave differently in the same patient [52]. Such asymmetric behavior of the components of the motion segment is consistent with the idea that localized, unilateral splinting by the paraspinal musculature may occur.
One of the newest tools in chiropractic for the analysis of movement between two adjacent spinal segments is videofluoroscopy [86]. It can be used in clinical practice as well as in the laboratory to evaluate a motion segment for hypomobility, hypermobility or abnormal motion [87]. In at least one study, positive findings by videofluoroscopy have been correlated with positive clinical findings and corroborated by magnetic resonance imaging [88]. It has also been shown that fluoroscopic procedures can demonstrate abnormal motion in segments when conventional static radiographs failed to do so [89]. While the applications of videofluoroscopy are just gaining momentum in chiropractic, it promises to be an extremely useful procedure for the analysis and evaluation of specific spinal segmental mobility.
Palpation is the most widely used method for the evaluation of spinal motion in chiropractic. As developed by Gillet [33] and presented by Faye [34] it offers the potential for a highly specific and extremely informative analysis system. A skilled palpator can identify specific vertebral levels of involvement [70]. Additionally, left or right sides of the vertebral joint can be evaluated independently [90] and each spinal articulation can be evaluated clinically for movement in six cardinal directions plus joint play [34].
While the system is a highly refined art of motion palpation, it lacks the rigorous evaluation and analysis necessary to make it an objective science. Clinical trials of spinal palpation are often disappointing [90-93], with intra-examiner reliability relatively high and inter-examiner reliability characteristically low. Some studies, however, provide promising results, and even high inter-examiner reliability [94].While this is by no means meant to discount motion or static palpation, it does point out a need for more in-depth research into this clinical phenomenon.
Not all chiropractors use spinal motion as a criterion for patient treatment. Chiropractors who practice upper cervical techniques may use plain x-ray film analysis exclusively for location of the subluxation and the determination of specific techniques required for its reduction. For these practitioners, the kinesiological component of the subluxation complex is less significant clinically than for others who use some form of motion analysis. Although studies by Harrison [95], Suh [96] and Schram and Hosek [85] suggest that the errors inherent in plain radiographic analysis are substantial, the procedures remain prevalent. While this issue continues to strike heated debate within the profession, a critical and objective analysis of the procedures appears to be far from publication. It should be noted, however, that many upper cervical practitioners do use some form of motion analysis [35]. By and large, it appears that the greater majority of chiropractic practitioners use some form of motion or movement analysis in their evaluation of the patient's need for care.
SUMMARY OF PART I
This article introduces a model of subluxations based on fundamental principles of anatomy, physiology and biochemistry. Building upon the previous 5-component model, the proposed 8-component model of the vertebral subluxation complex provides a framework in which to discuss the "chiropractic lesion" and to develop a more complete theoretical basis of chiropractic. The basic model (See Figure 1) consists of two functional components (kinesiopathology and the inflammatory response), four tissue- level components (neuropathology, myopathology, connective tissue pathology and vascular abnormalities), a structural component (histopathology) and a biochemical component (biochemical abnormalities). While these represent rather broad categories, the specific aspects of each component which are most relevant to chiropractic theory and practice are discussed. In this first article of the series an overview of the model is presented followed by a description of the kinesiopathological component. The second article will discuss neuropathology and myopathology; the third will present the remainder of the components and the fourth will discuss the relevance of the model and propose several directions for research into chiropractic phenomena.
The central concept of the proposed model is immobilization degeneration; when a joint is immobilized every component of the joint undergoes degeneration. This includes muscle, tendon, cartilage, ligaments, articular capsule and bone, to name a few. These changes are reflected in the Kinesiopathological component of the VSC. The scientific literature supporting this concept is reviewed here. It has also been demonstrated that remobilization of a previously immobilized joint can reverse the degenerative process and restore vitality to the tissues of the joint. This provides some of the strongest evidence supporting the clinical practice of chiropractic.
It is the opinion of this author that the kinesiological component of the VSC is the major clinical focus of chiropractic practice and the target of chiropractic treatment. The treatment procedure, invented and developed to a highly refined state by chiropractic, is the adjustive procedure or adjustment [36]. One type of adjustment can be described as an osseous maneuver in which an articulation is manipulated to its limit of functional mobility, i.e. limit of range of motion. When the joint is appropriately stressed, a thrust of high velocity and low amplitude is delivered into the joint. This is often (but not necessarily always) accompanied by a cracking or popping noise. The primary effect, on the body, of this type of chiropractic adjustment is a restoration of movement to restricted or fixated articulations.
While chiropractors employ other therapeutic modalities as well, it is the adjustive procedure which distinguishes the chiropractic profession from all others. This treatment procedure is implicit in the concept of subluxation, since the subluxation itself is presumed to be a manipulable lesion. Indeed, chiropractors have developed elaborate systems of adjustive procedures to correct or forestall the development of subluxations.
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