What comes to mind when you think of rehabilitation? Physical therapy for a knee surgery, back surgery, or joint replacement? Do you think of chiropractic or neurology? An injury does affect local structures and tissues. It affects local nerves, but can also have an effect on surrounding tissues and the central nervous system as well. The whole body is connected, and it is important to consider every aspect of the body when rehabilitating an injury.
Neurology is the main factor in determining how our bodies perceive the world, how it communicates with our brains, and how the brain then communicates back to the body to interact with the world. Chiropractors constantly talk about how altered joint function within the spine interferes with the ability of the brain to communicate with the body, therefore affecting normal bodily function. However, the afferent aspect of brain/body communication is critical. In a review by Seaman & Winterstein, they discuss how joint dysfunction or restricted joint mobility in the spine can cause alteration in afferent input to the CNS. These vertebral joint dysfunctions can lead to chronic changes in nociception, including increased firing of A-delta and C fibers1.
These peripheral nerves typically have a high threshold for stimulation under normal conditions. This is important because not every touch or contact should elicit a response from the body. Only noxious stimuli should be able to reach the threshold to create a response. However, when a tissue is injured, it doesn’t take as much stimulus to depolarize a nerve. As a result, any stimulus, even a light one, can cause a sensation of pain. This is also known as peripheral sensitization, and can be caused by inflammatory mediators, or sympathetic release of norepinephrine 1. As chiropractors, we may be able to address this peripheral sensitization through an adjustment. There are different regions of the spine associated with the two branches of the autonomic nervous system. The cervical and sacral regions are considered sympathetic, while the thoracic region is considered to be sympathetic. If peripheral sensitization is heightened under sympathetic influence, by acting on the cervical or sacral regions, we might be able to negate the sympathetic effects and restore normal peripheral function.
This peripheral sensitization can also lead to central sensitization. Overactive nociceptors can lead to hyperexcitability in the brain and spinal cord. When afferent neurons are overactive, there is increased stimulus to the brain, making it easier to reach a threshold, increasing sensitivity to afferent input, and causing the brain to remain in an excited state. This increased sensitization in nociception and the central nervous system causes increased pain1. The central nervous system has a bigger role on pain perception than we might think. When there is noxious stimuli from a peripheral afferent nerve, it creates a pain pathway in the brain which remains, even when the noxious stimulus is removed. This has been demonstrated in a study reviewed by Melzack et al. Injection of capsaicin in the skin creates hyperalgesia, however even after anesthetization of the area of injection, pain is still experienced 2. This shows that the peripheral system does not need to be active in order for someone to feel pain.
Another example of this is phantom limb pain. Melzack et al. discuss how after amputation, many people can still experience the same pain, even though the body part has been removed. This shows just how strong that central pain pathway is. How can you feel pain in your hand, if you don’t have a hand anymore? Researchers found that by acting on the central nervous system to block or remove the patient’s pain in a limb before amputation resulted in decreased pain post- surgery 2.
As chiropractors, we work closely with the nervous system every day. When you injure a tissue, you often think of rehabbing just that area. If you sprain an ankle, you’re going to do ankle exercises. If you hurt your back, you might do back stretching and core strengthening. But we can’t forget about the spine during rehab. Damaged tissues in the periphery have a profound effect on the central nervous system as well. It can cause inflammation, hyperexcitation, and sympathetic activation.
We can use the power of a chiropractic adjustment to regulate and normalize peripheral afferent nerve function. By finding and correcting vertebral joint dysfunction, we can prevent increased stimulation of noxious receptors, thereby reducing sensations of pain.
This article first appeared in the February 2020 issue of Lifelines, the Life West student magazine.
Seaman DF, Winterstein JF. Dysafferentation: a novel term to describe the neuropathophysiological effects of joint complex dysfunction. A look at likely mechanisms of symptom generation. Journal of Manipulative & Physiological Therapeutics. 1998;21(4):267-280.
Melzack R, Coderre TJ, Katz J, Vaccarino AL. Central neuroplasticity and pathological pain. Annals New York Academy of Sciences. 2001:933:157-170