How does Chiropractic really work!
The "Pain Gate Theory" has been accepted as a viable explanation for the benefits of Chiropractic treatment.
Canadian orthopedic surgeon WH Kirkaldy-Willis, MD (1)notes :
“Spinal manipulation is essentially an assisted passive motion applied to the spinal joints.”
Since 1965, Melzack and Wall's proposed Pain Gate Theory has “withstood rigorous scientific scrutiny.”
“The transmission of pain can be impeded by increased proprioceptive input.” Pain is increased by “lack of proprioceptive input.” This is why it is so important to regain early movement in joints after an injury.
The facet joints in the spine are densely populated with mechanoreceptors. How Chiropractic works is by increasing proprioceptive input in the form of spinal adjustments to decrease the central transmission of pain from adjacent spinal structures by closing the "Pain Gate".
By the Chiropractor applying a stretch into the facet joint capsule, the aim is to fire capsular mechanoreceptors which will “inhibit facilitated motoneuron pools” which are responsible for the muscle spasms that commonly accompany low back pain.
Mechanoreceptors are considered the most important source of the “non-nociceptive” afferents that control pain. Therefore improving their function closes the pain gate and in turn reduces pain.
The increased muscle spasm that often accompanies spinal pain also reduces spinal motion and results in opening the pain gate and in turn increasing the patients pain.
Our muscles become a key player in chronic spinal pain conditions because of overlapping feedback loops:
1) Pain leads to increased muscle tone.
2) Increased muscle tone leads to more inflammation and more pain.
3) An increase in muscle tone reduces joint range of motion.
4) Reduced range of motion leads to reduced mechanoreception.
5) Reduced joint mechanoreception opens the pain gate.
6) The “open” pain gate leads to more pain and further increased muscle tone (again, a feedback loop).
This feedback loop mechanism was eloquently reviewed by Yale’s Manohar Panjabi, PhD (2):
The theoretical basis for Panjabi’s model was based on the animal studies carried out by Aage Indhal, MD, and colleagues from Norway (3). The studies clearly showed the relationship between spine pain and contraction of the segmental muscles, leading to reduced movement of that region of the spine.
Indahl was also able to show that by stimulating the mechanoreceptors of the facet joint they could inhibit the spinal cord reflex to the spinal muscles causing the spasm and also decrease pain.
Dr. Indahl’s experiments and Dr. Panjabi’s models are perfect matches to how Chiropractic spinal adjusting works.
Raymond Brodeur is a Chiropractor and Engineer working at Michigan State University (4). Dr. Brodeur’s basic premise is that the cavitation ( popping noise) associated with the audible adjusting of a spinal segment has sufficient speed to fire off high-threshold mechanoreceptors,decreasing muscle spasm and improving joint motion.
The primary research by Orthopedic Surgeon WH Kirkaldy-Willis, MD was clearly able to show that Chiropractic spinal adjusting was capable of decreasing both muscle spasm and pain (1). Dr. Kirkaldy-Willis used 283 patients with chronic, severe, treatment resistant low back pain and documented that Chiropractic spinal adjusting was able to fix the condition in 81% of the patients.
Dr. Kirkaldy-Willis’ explanation for the observed improvement in clinical status was the firing of facet capsule mechanoreceptors, which decreases muscle spasm and closes the pain gate.
1) Kirkaldy-Willis WH; Cassidy JD; Spinal Manipulation in the Treatment of Low back Pain; Canadian Family Physician; March 1985, Vol. 31, pp. 535-540.
2) Panjabi MM; A hypothesis of chronic back pain: ligament subfailure injuries lead to muscle control dysfunction; Eur Spine J. 2006 May;15(5):668-76.
3) Indahl A, Kaigle A, Reikerås O, Holm S; Electromyographic response of the porcine multifidus musculature after nerve stimulation; Spine (Phila Pa 1976). 1995 Dec 15;20(24):2652-8.
4) Brodeur R; The audible release associated with joint manipulation; J Manipulative Physiol Ther. 1995 Mar-Apr;18(3):155-64.