Pain is our perception of discomfort and is an important, adaptive response of our nervous system which helps protect us from further injury. Pain sensitivity increases after an injury due to the chemical responses in the target tissue (tissue that is disturbed or injured). This increased sensitivity is normal and an important part of the recovery process.
Pain triggers inflammation which directs healing cells to the area of injury. The pain message is carried on nerve fibers called A fibers which are large in diameter, which allows messages to travel quickly. After the pain message reaches the central nervous system (brain and spinal cord), a response is generated that creates new ion channels along the C nerve fibers. The more ion channels the C fiber has, the more sensitive we are to pain. So in a sense, pain begets more pain, and that is how we become sensitive to any touch in our toe after we stub it. Over time, as the inflammatory process completes and healing occurs, the target tissue begins sending “normal” messages back up the nerve and the central nervous system responds by telling the C fibers to decrease the number of ion channels, which decreases our sensitivity to pain. The process just described is best know as the acute pain cycle.
The process just described is what happens in the ideal world, but in some cases the pain message lingers despite adequate healing time, and this process is known as chronic pain. Healing may be slowed due to physiological changes such as inadequate circulation, and poor immune response, both which can make someone more likely to develop chronic pain. In the past, the literature described chronic pain as any pain lasting more than 3 months; however, a movement is beginning in which we are understanding pain as more of a continuum rather than separate categories. The more stress we have on our system whether it be continued overuse of an injured area, or whether it be mental stress or fear of our injury, the more likely the pain message will continue and develop into chronic pain. In the case of physical stress to the tissue, the inflammatory process is stimulated to continue, which results in continued increased sensitization of the nervous tissue and if left unchecked can result in target tissue changes including fibrosis (tissue changes from its original formation such as muscle to fibrous connective tissue). In the case of mental stress, there is more overflow of nerve impulses from the brain to the body (think of our stress tolerance like a bucket that when full spills over in the form of nerve impulses that travel down our nerves from our brain to our spinal cord and out to our body) and the nerve impulses create excessive traffic that results in increased firing of the nerve and use of the ion channels. The body thinks if the ion channels are all being used, that we must need them, so the body keeps the sensitivity of the nerves elevated by hanging on to the excessive ion channels.
In order to tell the central nervous system that we no longer need the extra pain sensitizing ion channels, we need to send messages from the body to the brain that everything is alright. In physical therapy, we do this by moving the body in ways that are not painful, but that are significant enough to send a message to rewrite the pain sensitization response. The good news is that ion channels only live for 2-10 days before they are either replaced or just eliminated, so rewriting our pain response can begin after only 2 days. We usually notice improvement in overall pain with physical therapy by 2 weeks of starting on an appropriate exercise program. If the exercises are too difficult, then the body may perceive pain, and the pain cycle continues. If the exercise is a novel motion not normally associated with pain, but using muscles and joints that are usually painful, then we can successfully disrupt the pain cycle.
Generally, the longer the pain has been around, the longer it takes to completely break the pain cycle. In some cases of chronic pain the brain has created a pattern of pain message activity that becomes perceived as normal, and the brain will continue generating pain messages to fill in the “normal” message of pain despite our efforts to rewrite the messages. In these cases, we find that patients must continue on a long term exercise program to continue the positive input to the system and to continually re-write the pain message to keep it at bay. In some cases even when everything is being done correctly, the pain message is not completely eliminated, and we then educate the patient in how to work around their pain and pace their activities to prevent the pain from flairing up beyond acceptable levels. These patients are sometimes directed to a pain management doctor who can discuss medication that can assist with correcting the chemical process of chronic pain in the brain and nervous system.
We also concern ourselves with the general state of the brain’s firing (factors such as sleep, stress, production of endorphins which are our natural pain killers best produced during outdoor cardiovascular activity).
In physical therapy, we design a program to address all aspects of the pain cycle. We treat the target tissue (muscle, fascia, joint, nerve, tendon, ligament, etc) with manual therapy/hands on treatments and exercises. We rewrite the nerve firing pattern by incorporating movements in a novel, pleasant, and positive environment. We also use electrical machines to send impulses along the nerves to electrically disrupt the pain message or to trigger normal firing in a muscle. We treat the brain by educating patients in how they can control their pain which decreases their stress about their condition and decreases overflow to the body. We educate patients in proper sleep habits/hygiene, stress management techniques, and in the basics of proper nutrition and hydration to keep the physiologic anti-pain processes working at their optimum. We introduce appropriate levels of cardiovascular exercise and whenever we can, humor, to assist with production of the brain’s natural pain killer, endorphin.
For more information, check out Explain Pain (2003) by David Butler and Dr. Lorimer Moseley, Noigroup, Adelaide.