2008-09-26 / Columnists

Eye On Physical Therapy

Commentary By Dr. Tim Rohrs, DPT

After surgery or injury a joint will swell with fluid and inflammation. Throbbing and aching accompanies the edema. People complain of this pain and aching especially at night while trying to fall asleep. Applying ice to the joint in question for 10 to 15 minutes will help decrease the edema and numb the joint slightly so it is not so painful. This will result in the joint not only feeling better but actually moving better with increased ROM and flexibility. Frequently a patient will ask me if he or she can just apply a product like "Icy Hot," "Ben Gay" or "Biofreeze" to the joint instead of the real ice. The application of ice has a real physiological effect on the joint. It closes down capillaries to the joint as well as cooling the nerves which transmit pain. When cool, they transmit their pain signal much more slowly than they would at regular body temperature. Products such as the ones mentioned above are ones that do not actually decrease swelling, despite the fact that they may feel cold. These products help people "feel" better.

Exactly how does the product make you feel better if it does not have a physiological effect? Meaning, if the product does not affect swelling or healing of living tissues why do we experience decreased pain? How these products work is, they help us experience the pain differently. Pain is transmitted from an injured joint or tissue to the spinal cord on nerve fibers that are different from other nerves in the body.

These nerve fibers that transmit pain signals are smaller in diameter and generally much slower at transmission than other nerves. After the nerve impulse travels to the spinal cord, it travels up to the brain where it is processed as pain. Nerve fibers from the skin travel on different nerve fibers. Theses impulses travel on fibers that are equivalent to the HOV lane. These fibers are bigger in diameter than the pain fibers and much faster. The pain nerve fibers and skin sensation nerve fibers both head to the spinal cord and essentially arrive at the same place. In essence, the nerve impulse which makes it to the spinal cord first is the one transmitted to the brain and the one that our brain will perceive. This race to the spinal cored essentially allows the winner to the close the gate on the other impulse. This theory was proposed by Ronald Melzak and Patrick David Wall in the early 1960s. If you have ever banged your knee on a desk, your initial reaction is to rub your knee really fast and magically your pain starts to subside. That is the theory in action. The knee is hurt, the pain is transmitted on nerves, you start rubbing the skin and the nerves from the skin are activated, the skin activated nerves win the race to the spinal cord and the brain experiences less pain in the knee. The products available on the pharmacy shelf work in the same fashion. They have some product in them that makes the skin feel either hot or cold and activates the nerves of skin sensation and the pain subsides. While there is certainly nothing wrong with experiencing less pain, these products don't have any effect on the swelling, despite the fact that they may feel "cold." As I always say, we are trying to get you better, not just feel better.

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