The most accepted theory to explain the benefits of chiropractic in the treatment of pain is the Gate Theory of Pain, originally presented by Melzack and Wall in 1965. The June 2002 issue of the British Journal of Anaesthesia presents a modern review of the Gate Theory in an article titled:
Gate Control Theory of pain stands the test of time
Key Points from this article include:
1) “In 1965, Pat Wall (who died August 8, 2001) and Ron Melzack published their paper in Science, entitled a ‘New Theory of Pain’.”
2) The GATE THEORY “has stood the test of time.”
3) The GATE THEORY notes that “pain could be controlled by modulation—reduce excitation or increase inhibition.”
4) The Gate Theory proposed:
- Small “C” fiber nociceptors activate excitatory pain systems.
- This pain system excitation is “controlled by the balance of large fiber [mechanoreceptors]” which are “under the control of descending systems.”
[This is the neurological basis for chiropractic adjustments helping with pain. Chiropractic adjustments increase the firing of large diameter mechanoreceptors, which neurologically inhibits pain.]
Neurology reference texts that contain sections on pain cite the principles of the Gate Theory. A few such citations are included below:
The perception of pain is dependent upon the balance of activity in large (mechanoreceptor) and small (nociceptive) afferents.
John Nolte, The Human Brain, Mosby Year Book, 1993, p. 139.
If large myelinated fibers (mechanoreceptors) were selectively stimulated, then normal “balance” of activity between large (mechanoreceptor) and small (nociceptive) fibers would be restored and the pain would be relieved.
John Nolte, The Human Brain, Mosby Year Book, 1999, p. 203.
“Pain is not simply a direct product of the activity of nociceptive afferent fibers but is regulated by activity in other myelinated afferents that are not directly concerned with the transmission of nociceptive information.”
Eric Kandel, James Schwartz, Thomas Jessell, Principles of Neural Science, McGraw-Hill, 2000, pp. 482-3.
“The idea that pain results from the balance of activity in nociceptive and nonnociceptive afferents was formulated in the 1960s and was called the gate control theory.”
Eric Kandel, James Schwartz, Thomas Jessell, Principles of Neural Science, McGraw-Hill, 2000, pp. 482-3.
“Simply put, nonnociceptive afferents ‘close’ and nociceptive afferents ‘open’ a gate to the central transmission of noxious input.”
Eric Kandel, James Schwartz, Thomas Jessell, Principles of Neural Science, McGraw-Hill, 2000, pp. 482-3.
“The balance of activity in small- and large-diameter fibers is important in pain transmission...”
Eric Kandel, James Schwartz, Thomas Jessell, Principles of Neural Science, McGraw-Hill, 2000, pp. 490.
There is little doubt that reductions of normal motion are a common factor in pain syndromes. A representative study to support this concept was published
June 26, 2001 in the journal Neurology, and titled:
Handicap after acute whiplash injury
A 1-year prospective study of risk factors
Key Points from this article include:
1) Exposure to a whiplash injury implies a risk for development of chronic disability and handicap, with reported frequencies ranging from 0% to 50% in follow-up studies. The exact risk for development of chronic whiplash syndrome is not known.
2) This study prospectively determined the sensitivity and specificity of five possible predictors for handicap following a whiplash injury in 141 whiplash-injured patients and in 40 and control subjects.
3) The whiplash-injured patients and the controls were assessed after 1 week and 1, 3, 6, and 12 months. After 3 to 4 years, participants with whiplash injury were questioned about legal issues.
4) “Of 141 patients with whiplash injury, 8% had not returned to daily activity after injury and an additional 4% had returned only to modified job functions 1 year after trauma.”
5) “The best single estimator of handicap was the cervical range-of-motion test, which had a sensitivity of 73% and a specificity of 91%. Accuracy and specificity increased to 94% and 99% when combined with pain intensity and other complaints.”
6) Initiation of lawsuit within first month after injury did not influence recovery.
7) The authors concluded that reduced “cervical range-of-motion test has a high sensitivity in prediction of handicap after acute whiplash injury.”
8) “Risk for long-term handicap was increased by a factor of 2.5 in persons with reduced cervical mobility after 1 year, and by 2.1 in those with reduced mobility after 6 months.”
9) “This prospective study showed that long-term handicap after whiplash injury is predictable by measuring neck mobility in a standardized manner, by means of a CROM device.”
10) These authors, in a study in SPINE (2001), showed that patients with whiplash injury have reduced neck mobility, which is inversely related to neck pain intensity. [This is a GATE THEORY article, and it is reviewed below.]
11) “From the current quantitative assessment, it was shown that poor prognosis is related to reduced neck mobility and high initial pain intensity.”
12) The current study indicates that testing of CROM in patients with acute whiplash injury predicts subsequent handicap in terms of reduced daily activity.
13) A 1998 study showed that randomly assigned patients, with acute whiplash injury, to soft collar or early mobilization, reduced long-term pain and complaints was observed in the early mobilization group.
[Borchgrevink GE, Kaasa A, McDonagh D, et al. Acute treatment of whiplash neck sprain injuries. A randomized trial of treatment during the first 14 days after car accident. Spine 1998; 23: 25–31.]
14) A 2000 study showed that mobilization within 96 hours could reduce whiplash pain significantly more than mobilization initiated after 2 weeks.
[Rosenfeld M, Gunnarsson R, Borenstein P. Early intervention in whiplash-associated disorders. A comparison of two treatment protocols. Spine 2000; 25: 1782–1787.]
15) These authors found a significant inverse relationship between pain and reduced CROM and between nonpainful complaints and increased CROM in patients with acute whiplash. [Again, the GATE THEORY.]
Another similar study indicating that reduced motion is associated with chronic pain was published in the October 1, 2001 issie of the journal Spine, and titled:
Cervical Range of Motion Discriminates Between symptomatic Person and Those With Whiplash
Key Points from this article include:
1) This study evaluated 114 patients with persistent [3 months - 2 years] whiplash-associated disorders and 89 asymptomatic controls. Range of cervical motion was measured in flexion, extension, left and right lateral flexion, and left and right rotation.
2) Results showed that cervical range of motion was reduced in all primary movements in patients with persistent whiplash-associated disorder. Sagittal plane movements were proportionally the most affected.
3) On the basis of primary and conjunct range of motion, age, and gender, 90.3% of study participants could be correctly categorized as asymptomatic or as having whiplash.
4) The authors concluded that cervical range of motion was capable of discriminating between asymptomatic persons and those with persistent whiplash-associated disorders.
5) “Assessment of range of motion (ROM) forms a basic tenet of clinical examination of the cervical spine.”
6) In whiplash-associated disorders (WAD), cervical ROM is commonly used as an outcome measure after treatment or to quantify disability.
7) Cervical ROM is an important component of the American Medical Association Guides to the Evaluation of Permanent Impairment.
8) In 1997, Gargan et al found that reduced cervical ROM 3 months after whiplash injury was a good predictor of persistent pain and disability 2 years after injury.
[Gargan M, Bannister G, Main C, et al. The behavioural response to whiplash injury. J Bone Joint Surg [Br] 1997; 79B: 523–6.]
9) Also in 1997, Jordan et al noted a reduction in cervical ROM in persons with whiplash injury when compared to matched asymptomatic persons.
[Jordan A, Mehlsen J, Ostergaard K. A comparison of physical characteristics between patients seeking treatment for neck pain and age-matched healthy people. J Manipulative Physiol Ther 1997; 20: 468–75.]
10) “The results of the analyses support previous assertions that individuals with persistent WAD have reduced primary ROM.”
11) “The results of the present study indicate that ROM was a significant discriminator between asymptomatic persons and those with persistent WAD.”
An important and related study regarding neck pain, the Gate Theory of pain, and manual therapy was published in the May 21,2002 issue of the Annals of Internal Medicine, and titled:
Manual Therapy, Physical Therapy, or Continued Care by a General Practitioner for Patients with Neck Pain
A Randomized, Controlled Trial
Key Points from this article include:
1) This was a 7 week randomized clinical trial evaluating 183 patients, 18 to 70 years of age, who had had nonspecific neck pain for atleast 2 weeks.
2) The results at 7 weeks showed the success rates were 68.3% for manual therapy, 50.8% for physical therapy [exercise], and 35.9% for continued [physician/analgesic] care.
3) “Manual therapy scored consistently better than the other two interventions on most outcome measures.”
4) The authors concluded “in daily practice, manual therapy is a favorable treatment option for patients with neck pain compared with physical therapy or continued care by a general practitioner.”
5) Clinical Implications: “Primary care physicians should consider manual therapy when treating patients with neck pain.”
6) Between 10% and 15% of the general population have neck pain.
7) Neck pain peaks at about 50 years of age.
8) Neck pain is more common in women than in men.
9) Neck pain can be severe and disabling.
10) Neck pain can be accompanied with headache, arm pain, and dizziness.
11) “According to the International Federation of Orthopedic Manipulative Therapies, ‘Orthopedic manipulative (manual) therapy is a specialization within physical therapy and provides comprehensive conservative management for pain and other symptoms of neuro-musculo-articular dysfunction in the spine and extremities’.”
12) The manual therapy was defined as the “use of passive movements to help restore normal spinal function” including muscular mobilization techniques, specific articular mobilization techniques to improve joint function and decrease restrictions in movement at single or multiple segmental levels in the cervical spine, and stabilization techniques to improve postural control and movement patterns.
13) Joint mobilization was defined as “a form of manual therapy that involves low-velocity passive movements within or at the limit of joint range of motion.”
14) The physical therapy used consisted primarily of active exercise, therapy exercises, postural exercises, and stretching.
15) “At 3 weeks, more patients worsened with continued [physician] care (n = 9) than with physical therapy (n = 3) or manual therapy (n = 0).”
16) “The success rates for manual therapy were statistically significantly higher than those for physical therapy.”
17) “Manual therapy scored better than physical therapy on all outcome measures…”
18) “Range of motion improved more markedly for those who received manual therapy or physical therapy than for those who received continued care.”
[Key Point]
19) “Patients receiving manual therapy had fewer absences from work than patients receiving physical therapy or continued [physician] care.”
20) “Manual therapy and physical therapy each resulted in statistically significantly less analgesic use than continued [physician] care.”
21) “Manual therapy was more effective than continued [physician] care, and our results consistently favored manual therapy on almost all outcome measures.”
22) “Although physical therapy scored slightly better than continued [physician] care, most of the differences were not statistically significant.”
23) “The postulated objective of manual therapy is the restoration of normal joint motion, was achieved, as indicated by the relatively large increase in the range of motion of the cervical spine.” [Key Point]
24) “In the physical therapy and manual therapy groups, the hands-on approach, frequent visits, and opportunities for intensive patient–therapist interaction may have contributed to the observed [superior] effects.” [Key Point]
25) “In our study, mobilization, the passive component of the manual therapy strategy, formed the main contrast with physical therapy or continued care and was considered to be the most effective component.”
Importantly, Dr. ManoharM.Panjabi, from the Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, published a supportive theoretical hypothesis on the origins of chronic back pain in the May 2006 issue of the European Spine Journal, titled
A hypothesis of chronic back pain:
Ligament subfailure injuries lead to muscle control dysfunction
Key points from this article include:
1) 70–85% of the population in industrialized societies experience low back pain at least once in their lifetime.
2) 30% of the population has low back pain at any given point in time.
3) The total cost of low back pain in the US is more than $50 billion per year.
4) Abnormal mechanics of the spine has two causes:
- Degenerative changes of the spinal column
- Injury of the spinal ligaments
5) The most likely cause is spine trauma, from:
- A single trauma due to an accident
- Microtrauma caused by repetitive motion over a long time
- Both of these events cause spinal ligament injury.
6) “The role played by the injury to the mechanoreceptors embedded in the ligaments of the spinal column has not been explored by any hypothesis.”
7) The [neurological] transducer function of the spine provides the information needed to precisely characterize the spinal posture, vertebral motions, spinal loads etc. to the neuromuscular control unit [spinal cord] via the innumerable mechanoreceptors present in the spinal column ligaments, facet capsules and the disc annulus. [VERY IMPORTANT: mechanoreceptors in the spinal ligaments, facet capsules, and annulus of the disc provide the afferent input to the spinal cord to control the precise coordination of posture and segmental motions].
8) Mechanoreceptors provide information to the neuromuscular control unit to generate appropriate muscular spinal stability.
9) “If the structural function is compromised, due to injury or degeneration, then the muscular stability is increased to compensate for the loss.” [This results in a reduction of ACTIVE range of motion].
10) Injured muscles heal relatively quickly due to abundant blood supply and therefore are not the main cause of chronic back pain. In contrast, ligament injuries heal poorly and therefore lead to tissue degeneration over time. “Thus, the ligament injuries are more likely to be the major cause of the chronic back pain.” [Key Point]
11) “The incoming corrupted transducer data may never become normal, even though the ligaments, incorporating the injured mechanoreceptors, may heal/scar over time.” [The Fibrosis Of Repair]
12) “The hypothesis proposes that the dysfunction of the muscle system over time may lead to chronic back pain via additional mechanoreceptor injury, and neural tissue inflammation.”
A SUMMARY OF DR. PANJABI’S MODEL FOLLOWS:
1) The spinal ligaments, disc annulus and facet capsules are innervated with mechanoreceptors.
2) Degenerative spinal disease, single trauma, or cumulative microtrauma causes subfailure injuries of the spinal ligaments, disc and facet capsules, causing abnormal firing of the embedded mechanoreceptors.
3) There is increased nerve ingrowth into diseased intervertebral discs.
4) Subfailure injury of spinal ligaments is defined as an injury caused by stretching of the tissue beyond its physiological limit, but less than its failure point.
5) Chronic whiplash patients have decreased active neck range of motion, but an increase in passive neck range of motion.
6) Injured muscles heal relatively quickly due to an abundant blood supply and therefore they are not the main cause of chronic back pain. [Important]
7) Ligament and disc injuries heal poorly and therefore lead to tissue degeneration over time.
8) “Thus, the ligament injuries are more likely to be the major cause of the chronic back pain.” [KEY POINT]
9) The subfailure ligament injuries may heal with scar tissue over time, resulting in long-term or permanent mechanoreception. [The Fibrosis Of Repair]
10) “Subfailure injuries of the ligaments. The injured mechanoreceptors send out corrupted transducer signals to the neuromuscular control unit, which finds spatial and temporal mismatch between the expected and received transducer signals, and, as a result, there is muscle system dysfunction and corrupted muscle response pattern is generated. Consequently, there are adverse consequences: higher stresses, strains, and even injuries, in the ligaments, mechanoreceptors, and muscles. There may also be muscle fatigue, and excessive facet loads. These abnormal conditions produce neural and ligament inflammation, and over time, chronic back pain.”
This article by Dr. Panjabi generated the following [unpublished] letter to the editor:
Dear Dr. Panjabi:
Congratulations on your article “A hypothesis of chronic back pain: ligament subfailure injuries lead to muscle control dysfunction” European Spine Journal, May 2006.
The hypothesis you presented is consistent with the perspective offered within the chiropractic community for decades. In the parlance of the chiropractic profession you have expertly and vividly described what is referred to as a vertebral subluxation. The chiropractic community has been studying, writing about and modifying its perspective on the phenomenon you articulated for more than a century.
Our present hypothesis suggests that the altered mechanoreceptive afferent driven motor mismatch can be corrected by the firing of the mechanoreceptors of the facet joint capsules which are activated by means of a chiropractic adjustment (1). The hypothesis you articulated, explains why chiropractic spinal adjustments have proven to be more effective in treating chronic spinal pain when compared to medication, exercise, and needle acupuncture (2, 3, 4, 5, 6, 7, 8, 9).
Respectfully,
Daniel J. Murphy, DC
Practice of Chiropractic
Faculty, Life Chiropractic College West
References
1) Indahl A, Kaigle AM, Reikeras O et al (1997) Interaction between the porcine lumbar intervertebral disc, zygapophysial joints, and paraspinal muscles. Spine 22:2834–2840
2) WH Kirkaldy-Willis and JD Cassidy, Spinal manipulation in the treatment of low back pain, Canadian Family Physician, Vol. 31, March 1985, pp536-40.
3) TW Meade, S Dyer, W Browne, J Townsend, AO Frank. Low back pain of mechanical origin: randomised comparison of chiropractic and hospital outpatient treatment. British Medical Journal, June 2, 1990;300: 1431-7.
4) The Lancet, Chiropractors and low back pain, July 28, 1990, p. 220.
5) TW Meade, S Dyer, W Browne, AO Frank. Randomised comparison of chiropractic for low back pain: results from extended follow up. British Medical Journal, August 5, 1995;311: 349-51.
6) Woodward MN, Cook JC, Gargan MF, Bannister GC. Chiropractic treatment of chronic 'whiplash' injuries. Injury. 1996 Nov;27(9):643-5.
7) S Khan, J Cook, M Gargan, G Bannister. A symptomatic classification of whiplash injury and the implications for treatment. Journal of orthopaedic Medicine 21(1) 1999:22-5.
8) Lynton GF Giles and Reinhold Muller, Chronic Spinal Pain: A Randomized Clinical Trial Comparing Medication, Acupuncture, and Spinal Manipulation, Spine, July 15, 2003; 28(14): 1490-1502
9) Reinhold Muller, PhD, Lynton G.F. Giles, DC, PhD, Long-Term Follow-up of a Randomized Clinical Trial Assessing the Efficacy of Medication, Acupuncture, and Spinal Manipulation for Chronic Mechanical Spinal Pain Syndromes, Journal of Manipulative and Physiological Therapeutics, January 2005, Volume 28, Number 1.
Lastly, Helene M. Langevin from the Department of Neurology, University of Vermont, College of Medicine, published a supportive article in the June 2006 issue of the journal Medical Hypothesis, titled:
Connective tissue: A body-wide signaling network?
Key points from this article include:
1) Unspecialized “loose” connective tissue forms an anatomical network throughout the body.
2) Connective tissue functions as a body-wide mechanosensitive signaling network that is separate from the nervous system, yet it also influences and is influenced by the nervous system.
3) Connective tissue signals include electrical, cellular and tissue remodeling. Each of these are responsive to mechanical forces that occur subsequent to changes in movement or posture, and to pathological conditions such as injury or pain.
4) Connective tissue function as a whole body communication system.
5) Since connective tissue is intimately associated with all other tissues, including the viscera, connective tissue signaling may influence the normal or pathological function of a wide variety of organ systems.
6) The existence of a connective signaling network may profoundly influence our understanding of health and disease.
7) Dividing the human body into separate systems for research and medical specialization is a mistake because all of the systems are integrated through the nervous system and connective tissue.
8) The musculoskeletal system does not physiologically function in isolation from the rest of the body. [Key Point]
9) “Unspecialized connective tissue not only forms a continuous network surrounding and infiltrating all muscles, but also permeates all other tissues and organs.”
10) The connective tissue matrix allows “cells to perceive and interpret mechanical forces.”
11) “Since connective tissue plays an intimate role in the function of all other tissues, a complex connective tissue network system integrating whole body mechanical forces may coherently influence the function of all other physiological systems.” [Key Point]
12) There is direct communication between the connective tissues within the matrix, and also indirect communication via the nervous system.
13) Connective tissue is richly innervated with mechanoreceptors and nociceptors.
19) Sensory information from connective tissue is integrated in the central nervous system.
