What are the Effects of Spinal Manipulation?
"Research into the effects of spinal manipulation has escalated over the past decade, partly due to increased understanding of articular neurology and pain modulation. Melzack and Wall first proposed the gate theory of pain in 1965. Since that time, the basic principles of this theory have withstood rigorous scientific scrutiny-even if the precise mechanisms and anatomical details are not fully understood. In essence, they proposed a spinal gating mechanism within the substantia gelatinosa (Rexed's lamina II) of the dorsal horn of the spinal cord. This gate theory controls the central nervous system including pain, touch, temperature and proprioception. They have shown that the central transmission of pain can be blocked by increased proprioceptive input and facilitated by a lack of proprioceptive input. This concept explains why rubbing an acute injury alleviates the pain and the importance of early mobilization to control pain after musculoskeletal injury.
Wyke has shown that the articular capsules of the spinal facet joints are densely populated by mechanoreceptors. These encapsulated nerve endings relay proprioceptive information on the joint position and mobility through large myelinated fibers to the substantia gelatinosa of the spinal cord. These impulses then compete for central transmission with impulses from the smaller unmyelinated pain fibers from adjacent tissues. Hence, increased proprioceptive input in the form of spinal mobility tends to decrease the central transmission of pain from adjacent spinal structures by closing the gate. Any therapy, which induces motion into articular structures, will help to inhibit pain transmission by this means.
Wyke and others have also shown that articular mechanoreceptor stimulation has a reflexogenic effect on motor unit activity in the muscles operating over the joint being stimulated. Stretching apophyseal joint capsules can therefore reflexly inhibit facilitated motorneuron pools, which are responsible for the increased muscle excitability and spasms that commonly accompany low back pain. In more chronic cases, there is shortening of periarticular connective tissue and intra-articular adhesions may form. We believe that in some cases, manipulation will stretch or break these adhesions. In fact in most cases of chronic low back pain, there is an initial increase in symptoms after the first few manipulations. In almost all cases, however, this increase in pain is temporary and can be easily controlled by local application of ice. However, the gain in mobility must be maintained during this period to prevent further adhesion formation. Through these mechanisms, spinal manipulation can break the cycle of pain, muscle spasm and immobility which predominates in many cases of low back pain." - W.H Kirkaldy-Willis, J.D Cassidy. "Spinal Manipulation in the Treatment of Low Back Pain"; Can Fam Physician, 1985; 31:535-40.
How Adhesions Form in Cases of Vertebral Subluxation Complex (VSC):
Much of the information concerning the connective tissue component of the VSC involves the major biochemical components of collagen, proteoglycan and hyaluronic acid. Collagen is known to consist of about 21% lysine and hydroxylysine residues, and these can undergo biochemical alterations which allow them to form chemical cross linkages which hold adjacent collagen molecules together and stabilize the overall fibrillar structure of collagen. It is further known that the numbers of these cross-linkages increase with advancing age and in states of degeneration. Not only do these linkages form with collagen fibrils, they may form between fibrils within the same fiber, or between fibers. This is, no doubt, involved in the formation of connective tissue adhesions as are known to form between the nerve root sheath and the articular capsule of the spinal zygapophyseal articulations.
In order for such bonds to form, the collagen molecules must be close enough to each other for the chemical reactions to form between lysine residues on adjacent collagen monomers. Thus, in fibrils, there is considerable cross-linking of this nature. Between fibrils, however, there is usually a critical distance, which is maintained by the presence of proteoglycan (PG) molecules. The sulfated glycosaminglycan (GAG) residues of the PG's draw water into the spaces between individual collagen fibrils. The water contributes to the space-filling properties of the PG's but also provides for lubrication between adjacent collagen fibrils, especially in fibrous connective tissue. Upon immobilization of a joint, the first measurable biochemical change is a decrease in proteoglycan; a change which occurs in all connective tissue components of the joint. Thus, when a joint is immobilized, the proteoglycan from the connective tissue components allow the collagen fibers to approximate each other more closely and this facilitates the formation of more collagen cross-linkages. It has been demonstrated that movement of a previously immobilized joint leads to a disruption of collagen cross-linkages, and it is possible that this provides a mechanism whereby these cross-linkages might be disrupted by the high-velocity, low amplitude thrust which is characteristic of the chiropractic adjustment. The longer a joint is immobilized, the more collagen cross-linkages are formed.
This would appear to be a mechanism for stabilizing the joint in its new range of motion. Thus the adjustment could restore the tissue to a state of pliability, and actually allow the tissue to rejuvenate itself. Obviously, the effectiveness of an adjustment program would depend upon the duration of immobilization. The longer a joint is immobilized, the longer it takes to restore the joint to normal movement. Beyond a certain point, of course, the changes are irreversible. Thus a chronically immobilized joint would require a longer period of chiropractic adjustment to restore the connective tissue to optimal function than would be necessary with an acutely immobilized or subluxated articulation. - Charles A. Lantz, Ph.D., DC. "The Vertebral Subluxation Complex." ICA International Review of Chiropractic, 1989; Sept/Oct: 37-61.
