Whenever I'm asked why I recommend custom-made, flexible orthotics to many of my patients, my reply is simple: Orthotics enhance the proprioceptive response of the entire lower extremity (including the foot), and help to stabilize the pelvis and spine.
When joints in the feet (or any joints, for that matter) misalign/subluxate/fixate or are somehow irritated, a neurological event I refer to as "proprioceptive noise" occurs. A brief overview of the model known as dysafferentation explains why a variety of symptoms (some not usually associated with dysfunctional joints) are eliminated or reduced with attention to extravertebral/extremity joints.
The two main types of sensory receptors that innervate joint structures are nociceptors and mechanoreceptors. Nociceptors (type 4 mechanoreceptors) depolarize (fire) via noxious mechanical stimuli and the chemical mediators released in response to injured tissue. Mechanoreceptors (types 1, 2 and 3) depolarize solely via mechanical stimuli, such as that associated with touch and normal body movements. Nociceptors are located in nearly every tissue of the body, while examples of mechanoreceptors are golgi tendon organs, muscle spindles, Meissner's/Pacinian/Ruffini corpuscles and Merkel's receptors.1
The neurological research of Hooshmand demonstrates how restricted joint motion causes an increase in nociceptive axons (A-delta and C fibers) and a decrease firing of large-diameter mechanoreceptor axons (A-beta fibers).2 It is important to remember that a chief function of mechanoreceptor input is to inhibit nociception at the level of the spinal cord.
Simply stated, proprioceptive noise is the excessive firing of nociceptors due to decreased mechanoreception. If one restricts normal joint motion, nociceptors excessively fire, since mechanoreception is decreased. This is the main reason I believe rigid orthotics are not optimal for most patients - they have the potential to restrict normal joint motion and thus create excessive nociceptor firing. As we know, when a joint is restricted at one level, it can create hypermobility in the joint/joints above. Therefore, mechanically, when foot motion is restricted, the potential for hypermobility in knees, hips and sacroiliac joints increases.
With joint subluxation/hypomobility, nociceptors will excessively fire, potentially creating a pain sensation and/or a variety of symptoms. First, let's discuss the conscious sensation of pain. Furman and Gallo write, "While the brain can process several trillion bits of information per second, it appears that we are perhaps only consciously aware of 50 bits of information per second at any given time."3 Since pain is a conscious sensation, it is understandable why a prominent chiropractor writes, "A clear indication that using the conscious perception of pain to determine the need for care is hugely inadequate and inaccurate. How can any scientist knowingly rely on less than 50/3 trillionths of the information and claim it to be a valid analysis?"4 Again, simply put, most subluxated feet are not painful.
Next, let's look at the potential symptomatology created by excessive nociceptor firing. Dysafferent input can and does produce a variety of symptoms that one would not usually associate with dysfunctional joints. Cabell authored research stating that "nociceptor activity reflexively activates the sympathetic nervous system."5 Research by Nansel and Szlazak suggests that nociceptive input from dysfunctioning joints can cause symptoms such as sweating, pallor, nausea, vomiting, abdominal pain, sinus congestion, dyspnea, cardiac palpitations, and chest pain that mimics heart disease.6
Turning Down the Noise
As chiropractors, we deal with the neurological integrity of the human body. In addition to relieving symptoms classically associated with joint dysfunction/subluxation, we can and do affect the autonomic nervous system. As Patterson states, "Adjustments to decrease nociceptor input to the spinal cord seem to be an effective way to decrease the hyperexcitable central state."7 The hyperexcitable central state is the reflexively activated sympathetic nervous system.
So, as a chiropractor, anything I can do to decrease the nociceptive bombardment of the spinal cord (proprioceptive noise) ultimately will benefit the patient by decreasing the potential for pain and inhibiting the sympathetic nervous system. That is why I use custom-made, flexible orthotics.
- Guyton A. Basic Neuroscience (2nd edition). Philadelphia: W.B. Saunders, 1991.
- Hooshmand H. Chronic Pain: Reflex Sympathetic Dystrophy, Prevention and Management. Boca Raton, FL: CRC Press, 1993:33-35.
- Furman ME, Gallo FP. The Neurophysics of Human Behavior: Explorations at the Interface of the Brain, Mind, Behavior, and Information. Boca Raton, FL: CRC Press, 2000.
- Chestnut J. The 14 Foundational Premises for the Scientific and Philosophical Validation of the Chiropractic Wellness Paradigm, 2002.
- Cabell J. "Sympathetically Maintained Pain." In: Willis W, ed. Hyperalgesia and Allodynia. New York: Raven Press, 1992.
- Nansel D, Szlazak M. Somatic dysfunction and the phenomena of visceral disease simulation: a probable explanation for the apparent effectiveness of somatic therapy in patients presumed to be suffering from visceral disease. J Manip Physiol Ther 1995;18:379-397.
- Patterson M. The spinal cord: participant in disorder. J Manip Physiol Ther 1993;9(3):2-11.
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