The Role of Chiropractic in Pain Management
Dr. Connie D'Astolfo, B.A., B.S., DI hom. D.C.

Besides restoring structure and function, pain modulation is central to chiropractic therapy. Conventional approaches to pain management, although sometimes necessary, presents a much greater risk of side effects, i.e. peripheral nerve blocks, which may result in iatrogenic complications such as dysaesthesia or persistent numbness or analgesic drugs, which can lead to tolerance, dependency, systemic disturbances or diminished mental acuity if administered long term.

Definition of Pain:

There are two categories of pain; sensory and neurogenic pain. Sensory pain can be described as "an unpleasant sensory experience which evokes an adversive emotional reaction." Sensory pain occurs as a consequence of injury, damage or potential damage of the skin, subcutaneous tissues or internal organs. When damage to a tissue occurs, peripheral sensory detectors ( nociceptors) are excited and activate their sensory nuclei and second order neuron pain pathways at their appropriate spinal cord level. These receptors are free nerve endings which are stimulated by excessive heat, mechanical stimuli, or chemicals such as prostaglandin and bradykinin as a result of cell damage. These pain receptors also respond to excessive distention of an organ, dilation of a blood vessel, prolonged muscle contractions or inadequate blood flow. Nociceptive afferent fibers, after synapsing in the dorsal horn of the spinal cord, ascend to the reticular formation, thalamus, sensory cortex and autonomic centres. The final perception of pain will depend on the interactions and modulation of the sensory message that take place at all relay stations within the nervous system. Sensory pain, originating either from visceral organs or deep somatic tissues, may be felt in a surface area distant from the damaged/stimulated tissue. This is known as referred pain. Pain originating from deep somatic tissues of joints, for example, often refers to its corresponding scleratome. Referred pain occurs because the anatomic sites of referred pain share the same segmental innervation as the original site of tissue damage.

    Neurogenic pain is not a consequence of the activation of a sensory nociceptive channel via peripheral nociceptors but the result of altered nervous function at a central or peripheral level and is associated with a lesion or disease of a neural pathway. Examples include thalamic pain, trigeminal neuralgia (compressive neuralgias) or radiculopathy, RSD (reflex sympathetic dystrophy), phantom limb pain and chronic pain syndromes.  

To understand the role of chiropractic manipulative therapy in modulation of pain, one must have a basic understanding of articular neurology. Vertebral synovial joints are innervated by a variety of neuroreceptors all derived from the dorsal and ventral rami as well as the recurrent meningeal nerve of each segmental spinal nerve. Information from these receptors cross many segmental levels because of multilevel ascending and descending primary afferents.

     Type I mechanoreceptors are confined to the outer layers of the joint capsule and are stimulated by active or passive joint movements. Stimulation of type I receptors is involved with:

1. reflex modulation of posture and movement

2. perception of posture and movement

3. tonic effects on neck, eye, limbs, jaw and eye muscles

4.inhibition of pain from receptors via an enkephalin interneuron transmitter

     Type II mechanoreceptors are found within the deeper layers of the joint capsule. They are stimulated when minor changes in tension within the inner joint occurs. Type II receptors are likely to achieve the following:

1. inhibition of pain from receptors via an enkephalin interneuron transmitter

2. monitoring for reflex actions

3. phasic effects on neck, eye, limbs, jaw and eye muscles

     Type III mechanoreceptors are located only in ligaments of the peripheral joints and like GTOs, impose an inhibitory effect on motorneurons. These receptors:

1. monitor direction of movement

2. create a reflex effect on segmental muscle tone

3. recognize potentially harmful joint movements

     Type IV nociceptors are free nerve endings located throughout the fibrous portion of the joint capsule and ligaments. Type IV receptors are absent from articular cartilage and synovial linings but have been found in synovial folds and within the annulus fibrosis of the disc. These receptors are associated with the following:

1. evoke pain

2. tonic effects on neck, limb, jaw and eye muscles

3. central reflex connections for pain inhibition and autonomic effects

Spinal Dysfunction: Mechanical Effects

     The manipulable spinal disorder, traditionally termed "subluxation" in chiropractic, is now characterized as a spinal joint strain/sprain with associated local and referred pain and muscle spasm. The function of the joint is impeded by static misalignment and/or reduction of motion (i.e., "fixation," "blockage," or "hypomobility"). Mechanisms that have been proposed for spinal dysfunction, include:

1. Entrapment of a zygapophyseal joint meniscoid (synovial fold), which have been shown to be heavily innervated by nociceptors. (Giles, 1987; Bogduk, 1985).

2. Stiffness caused by adhesions and scar tissue from previous injury and/or degenerative changes and adaptive shortening of myofascial tissues. (Arkuszewski, 1988; Lantz, 1995).

3. Entrapment of annular material from the intervertebral disc, which is innervated by nociceptors. (Bogduk, 1981, 1985).

4. Excessive hypertonicity (spasm) of the deep spinal musculature (Blunt, 1995; Buerger, 1983).

Spinal Dysfunction: Neurological Effects

     The classical theory of "pinched or compressed nerve" has been replaced with a model that includes both direct and indirect effects on the function of the nervous system resulting from spinal dysfunction.

Direct effects involve compression or irritation of the neural structures in and around the intervertebral foramen. The IVF is an area where entrapment of neural structures responsible for pain, sensation, motor, and autonomic function, commonly occurs. Effects of partial entrapment of a nerve root, such as those that might occur with disc herniation, foraminal stenosis, or spinal instability often result in neurogenic pain and lower motor neuron deficits such as reduced sensation, reduced reflexes and diminished motor strength (radiculopathy). The effects of compression on autonomic structures (nerves, rami, and ganglia), are only just beginning to be understood and chiropractors have theorized that these effects may extend to visceral function (Lantz, 1995).

Spinal dysfunction can also cause indirect effects on the nervous system. Persistent spinal pain and joint hypomobility has shown to increase sensitization of spinal pain pathways and humural mediators in the dorsal horn (increases C-fibre receptor stimulation). The result is long-lasting abberant firing patterns that reinforce pain perception. (Woolf, 1989; Mense, 1993; Gillette, 1995). The current term for such changes at the spinal cord level is "central sensitization" (Coderre, 1993). This increased perception to stimuli can lead to the point where previously innocuous peripheral stimulation is now interpreted as painful. This model is now used to explain the clinical features of chronic pain and autonomic dysfunction resulting from both neuropathic and somatic pain.

Mechanical and Neurological Effects of Chiropractic Adjustive Therapy in Pain Management

Chiropractic manipulative therapy involves inducing a quick (100-300 milliseconds), high velocity, low amplitude impulse into the joint (spinal or extraspinal joints) (Herzog, 1996; Triano, 1992) When a joint is rapidly stretched or separated, cavitation occurs internally and an audible "pop" may be heard. The audible "pop" occurs due to the sudden drop in pressure within the capsule of the joint as it is distracted. The process of cavitation itself is not therapeutic but does represent a physical event that signifies joint separation, stretching of articular tissue and stimulation of mechanoreceptors and nociceptors. These events have been shown to have significant mechanical and neurological effects, including:

1. Increasing range of motion of the joint by breaking up adhesions/scar tissue

• adhesions and scar tissue can occur due to joint immobilization, chronic joint effusion and inflammation. Adjustive therapy can induce a quick distraction and break up intra-articular adhesions. Often, modalities such as moist heat or ultrasound can assist therapy.

  2. Releasing of entrapped synovial or disc tissue by temporarily increasing joint space, thus reducing pain

• distractive adjustive therapy creates a temporary increase in joint space which may permit trapped tissue to release.

  3. Restoring proper tone of musculature and myofascial tissues by resetting muscle spindles and stimulating Golgi Tendon Organs located in the muscle tendon junction

• high velocity adjustments have the ability to produce a strong stretch on the muscle tendon complex, activating the GTO and inducing reflexive muscle relaxation (autogenic relaxation)



• high velocity adjustments also stimulate joint and soft tissue mechanoreceptors providing a bombardment of somatic afferent receptor activity. Stimulation of mechanoreceptors have demonstrated a notable inhibitory effect on segmental motor activity, decreasing muscle spasms and interrupting painful myofascial cycles.

  4. Stimulus produced analgesia

• The Gate Control Theory of Pain. The dynamic stretching produced by manipulation (particularly when a cavitation occurs) induces a barrage of activity in joint and muscular mechanoreceptors and nociceptors that is transmitted along "large-fibre" afferents. This afferent bombardment produces inhibitory effects by stimulating an interneuron at the dorsal horn of a spinal level which presynaptically inhibits pain information to the transmission cells. If all nociceptive information is inhibited from synapsing with the T cell, then ascending spinothalamic pathway is blocked and pain cannot be appreciated. Pain can also be inhibited by descending fibers from the brain and brain stem reticular formation. These descending fibres carry opiod neuro-modulators and terminate in the dorsal horn of the spinal cord where they can inhibit pain sensation. (Gillette, 1995; Le Bars, 1992; Vernon, 1986). Spinal tissues, in particular, the articular capsule, is richly innervated with mechanoreceptors and nociceptors and appears to have a unique pattern of afferent input into the central nervous system, with a high level of convergence existing with other somatic and visceral inputs onto the same spinal tract projection cells (Gillette, 1995; Patterson, 1986; Hu, 1993). This enables afferent input from spinal tissues to have a strong influence on gating somatic and visceral pain sensations.



• Gillet suggests that spinal adjustments may initiate both a short lived phasic response, triggered by stimulation of superficial and deep mechanoreceptors and a longer lived tonic response, triggered by noxious levels of nociceptor receptors. The phasic responsecan initiate a local gating response but the analgesic effect terminates with cessation of therapy (as occurs with massage therapy and mobilization). The tonic response initiated by noxious levels of nociception is extremely powerful and is capable of outlasting therapy. Adjustments that induce cavitation and capsular distraction may be a source of nociceptive stimulation and can initiate a long lasting analgesic effect.



• afferent input associated with adjustments have also been theorized to increase the levels of neuro-chemical pain inhibitors (opiods), i.e. enkephalins are locally released by stimulation of neurons in the substantia gelatinosa and endorphins are released by stimulation of the hypothalamic pituitary axis.

Undoubtedly, chiropractic manipulation can offer both an alternative to many pain management strategies as well as an effective co-management treatment with many medical therapies. As is common in the U.S., integration of chiropractic services in hospital outpatient centres and multidisciplinary pain clinics can become a reality if administrators, policy makers, medical physicians and the public have a clearer understanding of the chiropractic profession and begin to appreciate its therapeutic benefits and its role in pain management. It is our responsibility as doctors of chiropractic to utilize the full capacity of our training as clinicians, educate our patients and policy makers, cooperate with our medical collegues, and make an attempt to integrate ourselves in arenas chiropractors are not traditionally found, such as hospitals and long term care facilities.

References

1. Arkuszewski Z. Joint blockage: a disease, a syndrome or a sign. Man Med 1988;3:132-4.

2. Bergman et al. Chiropractic Technique, Churchill Livingston Inc. 1993 pp 123-190

3. Blunt KL, Gatterman MI, Bereznick DE. Kinesiology: An Essential Approach Toward Understanding Chiropractic Subluxation. In Gatterman MI (ed). Foundations of Chiropractic: Subluxation. St. Louis, MO: Mosby, 1995.

4. Bodgduk N, Tynan W, Wilson AS. The nerve supply to the human intervertebral discs. J Anat 1981;132:39-56.

5. Bogduk N, Jull G. The theoretical pathology of acute locked back: a basis for manipulative therapy. Man Med 1985;1:78-82.

6. Brunarski DJ: Clinical trials of spinal manipulation: a critical appraisal and review of literature. J Manipulative Physiol Ther 7(4):253, 1984

7. Buerger AA. Experimental neuromuscular models of spinal manual techniques. Man Med 1983;1:10-17

8. Cherkin DC, MacCornack FA: The Management of low Back Pain - a comparison of the beliefs and behaviors of family physicians and chiropractors. West J of Med 149:475, 1988

9. Cherkin DC, MacCormack FA: Health Care Delivery. Patient evaluations low back pain care from family physicians and chiropractors. Zoes J Med 150 (3):351, 1989

10. Gillette RG. Spinal cord mechanisms of referred pain and neuroplasticity. In Gatterman MI (ed). Foundations of Chiropractic: Subluxation. St. Louis, MO: Mosby, 1995.

11. Giles LGF, Harvey AR. Immunohistochemical demonstration of nociceptors in the capsule and synovial folds of human zygapophyseal joint capsule and synovial fold innervation. Br J Rheumatol 1987;26:993-8

12. Herzog W. Mechanical, physiologic and neuromuscular considerations of chiropractic treatments. In Lawrence D, et al. (eds). Advances in Chiropractic, Vol 3. Chicago, IL: Mosby Year Book, 1996.

13. Hu JW, Yu XM, Vernon H, Sessle BJ. Excitatory effects on neck and jaw muscle activity of inflammatory irritant applied to cervical paraspinal tissues. Pain 1993;55:243-50.

14. Lantz CA. The vertebral subluxation complex. In Gatterman M (ed). Foundations of Chiropractic: Subluxation. St. Louis, MO: Mosby; 1995

15. Leach, Robert. The Chiropractic Theories William and Wilkins, Balt. MD. 1994 pp 34-38

16. Le Bars D, Villanueva I, Bouchassira D, Miller JC. Diffuse noxious inhibitory controls (DNIC) in animals and in man. Path Physiol Exp Ther 1992;4:55-65.

17.. Nyiendo J: Chiropractic effectiveness. Oregon Chiropractic Physicians Association Newsletter. April 1991

18. Patterson MM, Steinmetz JE. Long-lasting alterations of spinal reflexes: a potential basis for somatic dysfunction. Man Med 1986;2:38-42.

19. Triano JJ. Studies on the biomechanical effects of a spinal adjustment. J Manipulative Physiol Ther 1992;15:71-75.

20. Vernon HT, Dhami MS, Howley TP, Annett R. Spinal manipulation and beta-endorphin: a controlled study of the effect of a spinal manipulation on plasma beta-endorphin levels in normal males. J Manipulative Physiol Ther 1986;9:115-23.

Dr. Connie D'Astolfo, D.C., is a graduate from National University of Health Sciences. Dr. D'Astolfo recently conducted a presentation on the "Chiropractic Management of Pain" to physicians and staff at a Toronto hospital. Her vision is to see chiropractic physicians fully integrated into the Canadian Health Care System, including hospitals and long term care facilities. She can be reached at (905) 738-1948 or cure4all@yahoo.com.

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