The history of chiropractic, like all healing arts, is largely one in which empirical process has preceded theoretical formulation. In other words, from the earliest days practitioners have applied new manual treatment methods on an intuitive, empirical basis, noted that some are more effective than others, and theorized on the basis of these findings as to the underlying mechanisms.

When certain methods have demonstrated their effectiveness over a period of time, they, along with the theories used to explain them, become part of what we might call the "chiropractic corpus," the body of tradition, evidence, and practice which is the contribution of the chiropractic school of knowledge to the healing arts as a whole.

Not until the late Twentieth Century was this accumulated body of chiropractic knowledge sufficiently grounded in scientific research to allow wide recognition across professional boundaries. Fortunately, that point has now been reached. It therefore seems timely to review the nature of the chiropractic diagnostic and therapeutic model, so that it can be well understood by the public and other health professionals.

Part of this review is an examination of chiropractic theory past and present. It is important to sift out ideas which may have been state of the art in 1910 or 1950, but which are no longer fully tenable. Chief among these is the idea that the chiropractic adjustment works primarily by physically moving a vertebra that is out of place back into place.

The Bone-Out-of-Place Theory
The early chiropractors assumed that their adjustments worked by moving misaligned vertebrae back into line, thereby relieving pressure caused when those bones impinged directly on spinal nerves. The standard explanation given to patients was the analogy of stepping on a garden hose if you step on the hose the water canât get through, and then if you lift your foot off the hose, the free flow of water is restored. Similarly, the explanation went, the chiropractic adjustment removes the pressure of bone on nerve, thus allowing free flow of nerve impulses.

Based on the information available in the early years, such a theory was plausible. Chiropractors were able to feel interruptions in the symmetry of the spinal column with their well-trained hands, and in many cases could verify this on x-ray (discovered in 1895, the same year as chiropractic). They would then adjust the vertebra with manual pressure, attempting to move it back into line. More often than not, patients reported significant functional improvements and healing effects.

But there are problems with the theory. This can most simply and directly be illustrated by noting the fact that, after an adjustment resulting in dramatic relief from headaches or sciatica, an x-ray will rarely show any discernible change in alignment. (Such comparative x-rays are now considered inappropriate, because of the unnecessary radiation exposure). Long-term positive health changes have not been definitively shown to correlate with symmetrical alignment of spinal bones on any consistent basis.

Though much excellent work has been done by chiropractors whose understanding of their healing art was based on the bone-out-of-place theory, the theory has not stood the test of time. This does not mean that chiropractic is invalid, only that this late nineteenth century explanation has been overtaken by later developments.

While misalignments may play a role in the interpretation of spinal subluxations, they are no longer believed to play the central role. But if the old explanation of misaligned bones pressing on nerves is inadequate, what new theory has replaced it? To answer this question, we need to move beyond the essentially two-dimensional viewpoint of the misalignment theory, and include motion as an added dimension.

The Intervertebral Motion Theory
In the 1930s, Belgian chiropractor Henri Gillet developed a theory of intervertebral motion and fixation, in which he asserted that it was loss of normal spinal joint movement, rather than misalignment, that was the underlying explanation for the vertebral subluxation. He agreed with the bone-out-of-place adherents that the interplay between the skeletal system and the nervous system was crucial, but parted ways with them regarding the causal process underlying the abnormal nerve signaling. Rather than attributing the subluxationâs effects to direct pressure of misaligned bone on nerve, Gillet theorized that loss of proper joint dynamics was the underlying issue.

Later work by medical researchers Schmorl and Junghans, and many more who followed, verified the complex role of the "vertebral motor unit," consisting of bones, muscles, ligaments, blood vessels, and nerves. This model is now widely accepted.

All of these structural components are involved in the subluxation complex. Bypassing the old argument of whether the causative factor in the vertebral subluxation is the bone or the muscle, the work of Gillet, Schmorl, Junghans, and others allowed the problem to be seen from a broader, multi-faceted perspective, in which all components of the intervertebral joint are involved in an elaborate interplay. This model first achieved profession-wide attention among chiropractors in the 1980s, and now enjoys broad acceptance in chiropractic college curricula throughout the world.[1]

Jerome McAndrews, D.C., an early advocate of motion theory and practice who later served as president of Palmer College of Chiropractic, translated this model into visual terms when I spoke with him during preparation of this book.

"View it as a mobile hanging from the ceiling," Dr. McAndrews said. "As it hangs there, it is in a state of dynamic equilibrium. Then, if you cut one of the strings, the whole mobile starts moving, because its balance has been upset. Eventually, it slows down and reaches a new state of dynamic equilibrium."

The bodyâs musculoskeletal system works in much the same way, Dr. McAndrews explained. If its normal balance is disrupted, it has no choice but to compensate. Structural patterns will be altered to a greater or lesser degree, depending on the nature and intensity of the forces that threw off the old pattern of balance.

If chiropractic care is sought early, relatively little treatment may be required, because these compensations will not have had time to deeply imbed themselves structurally. Thus, a child injured playing football at age ten might need just one or two adjustments, but if that child waits until age forty before seeking chiropractic care (not an uncommon occurrence), the situation may prove far more complex. Patterns of long-term muscular rigidity, calcium deposits in ligaments, and significant structural shifts of the vertebral column or ribcage, for example, may set in with relative permanence.

In some such circumstances, when much time has passed, the achievable therapeutic goal may be limited to partial restoration of mobility and function. Returning to the once-upon-a-time perfection of the ten-year oldâs pre-injury body becomes impossible somewhere along the way. The theory of dynamic equilibrium, with its emphasis on intervertebral motion and fixation, has the great advantage of allowing, for the first time, a coherent explanation of chiropractic and the subluxation complex that can be communicated in familiar terms to medical practitioners and researchers. This has resulted in clearer lines of communication between chiropractors and medical professionals. While some hold onto the old model and terminology, the stage has been set for completion of this significant shift in perspective, as the new generation of chiropractic and medical practitioners trained after it took hold comes of age.

Wide-Ranging Effects of Spinal Manipulation
Restoring mobility to a joint by manipulation eases the stress at that joint and in the surrounding tissues. Unless complicating factors are present, muscular tension eases in the area that has been adjusted. As joint dysfunction decreases, other secondary symptoms such as pain, tingling, or numbness along the path of the nerves originating at the involved spinal level also improve.

Though the vast majority of chiropractic patients arrive seeking help for musculoskeletal problems like back pain, neck pain, and headaches, spinal adjustments can also have positive effects on other organs and systems. While chiropractic adjustments are directed to restoring motion at specific vertebral joints, the effects of these adjustments extend beyond the local area where the adjustive force is applied. Effects can extend to all structures served by the nerves originating in the spine.

Thus, neck adjustments can affect not only the neck and arms, but also the function of various organs in the head (via sympathetic pathways), and in the chest and upper abdomen (via the parasympathetic vagus nerve). Upper back adjustments can affect not only the upper back, but also the lungs, heart, and parts of the digestive tract. Adjustments of the lower back may influence not only the lower back and legs, but also the kidneys, pelvic organs and lower digestive tract.

The First Chiropractic Adjustment: A Case of Hearing Restored
The first chiropractic adjustment in 1895 was one in which the patient sought help for back pain, and got results far beyond his expectations. Harvey Lillard, a deaf janitor in the building where D.D. Palmer had an office, came to Palmer bent over with back pain. Palmer gave him a spinal adjustment, after which Mr. Lillard stood up straight, was free of back pain, and able to hear for the first time in many years.

At first, it appeared that Palmer might have discovered a cure for deafness, but similar results were not forthcoming when other deaf people heard about Harvey Lillard and sought Palmerâs help. And while there have been other instances through the years of hearing restored through spinal manipulation (including one by Canadian orthopedist J.F. Bourdillion, M.D.)[2] these have been rare, and no predictable pattern has emerged. The story of Lillardâs recovery has been used for many years to disparage chiropractic, with repeated charges by the naysayers (primarily anti-chiropractic MDs) that such an event is impossible, because no spinal nerves supply the ear. Once, when I was testifying as an expert witness in a patientâs automobile accident case, the opposing attorney, his voice dripping with sarcasm, attacked me with this very story. It is important to refute the charge specifically. The underlying physiological mechanism is called the somato-autonomic reflex, fully recognized in all modern medical and chiropractic textbooks. Its name describes the interaction between the muscular and skeletal system (soma, or body), and the autonomic (involuntary) portion of the nervous system. Signals initiated by spinal manipulation are transmitted via autonomic pathways to internal organs.

In the case of Palmerâs first adjustment, the relevant nerve pathway starts in the upper back, coursing up the neck and into the skull along the sympathetic nerves which eventually lead to the blood vessels in the ear. Proper functioning of the hearing apparatus depends on a normal blood supply, which in turn depends on an adequate nerve supply.

While it is true that there are no spinal nerves as such directly supplying the ear, it is absolutely untrue that no nerve pathway links the two areas. The pathway exists, and any claims to the contrary betray ignorance of fully accepted modern physiology research.

Further Examples of Manipulationâs Effects on Internal Organs
Just as there are autonomic pathways supplying the ear, similar pathways lead from the spine to all parts of the body. A broad array of research has verified that these pathways exist, and that in some instances spinal manipulation can positively affect problems caused by them. The work of Czech neurologist Karel Lewit, M.D., American orthopedic surgeon John McMillan Mennell, M.D., and others has been particularly helpful in spreading these concepts beyond the chiropractic community. Dr. Lewit has for many years successfully used spinal manipulation to treat tonsillitis, breathing problems, migraine, vertigo, and much more.[3]