How Does Chiropractic Manipulative Therapy Work?
Each and every joint has a range of motion that it can move through. If it didn't, it wouldn't be a joint. We know that muscles move bones, and thus joints, and there is a certain range of motion that the muscles surrounding a joint can move the joint through. This is called the physiological range of motion. All of the joints can be moved a bit further, passively, that is, by external force, such a doctor examining the joint and moving it through it's full range of motion. This is called the anatomical range of motion. Between the physiological and anatomical ranges there is a "para-physiological space". The adjustment pushes the joint into this space, which helps to free it from restriction and allows the joint to move more easily.
The sound that one hears when getting adjusted, the "pop" or "crack" is referred to as "cavitation". This is an indication that the joint has not only moved, but that it has gapped momentarily. Not every adjustment causes a cavitation; sometimes, the joint is either too "stuck" due to muscle spasm or other factors, or the joint is too hypermobile, and does not have normal biomechanics. In any event, cavitation is best understood as an analogy. The surfaces of a joint are smooth and in close contact with each other. They are surrounded by a lubricating fluid called synovial fluid. This fluid has a number of gases dissolved in it, such as carbon dioxide, oxygen and nitrogen.
When the two joint surfaces are gapped by an adjustment, for a split second there is a vacuum created by the space between the joint surfaces. In that split second, the dissolved gases in the synovial fluid leave the fluid and fill in the space. This all happens very quickly, but it seems to be responsible for the noise. The analogy is that of two suction cups that are pressed together. If one pulls them apart quickly, the vacuum that is created by the space between them, quickly fills with air. That is responsible for the sound that one hears when pulling apart the two suction cups.
Neurological Effects of Chiropractic Manipulative Therapy
You have a sixth sense that you probably didn't even know you had. This sense is called "Proprioception" and is the sense of where your body parts are in space. If you can touch your nose with your eyes closed, your proprioceptive sense is working. Joints are surrounded by a tough capsule that holds in the synovial fluid that lubricates the joint surfaces, and protects the joint from trauma.
The joint capsule contains many tiny nerve receptors called "proprioceptors" that tell the brain where that joint is, and how much the joint is moving. Proprioception is so important to your brain that the nerves that carry the proprioceptive information back to your brain are the largest, fastest conducting nerves in your body. Proprioceptive information from your big toe actually gets to your brain in about 1/3 of the time that it takes your eyes to send visual information to the back of your brain.
Pain receptors in the body also send information back to the brain, but they send it along thin, slow, junky nerve fibers that take a long time to transmit information. When you are experiencing pain, nerve signals are sent along the slow pain fibers in the body, up the spinal cord and into the brain. Due to the way that nerves enter the spinal cord, and interconnect, it is possible to "gate" the pain with a stronger nerve impulse from larger and faster nerves. If you've ever banged your arm on something and rubbed it to make the pain go away, then you've experienced pain gating.
With chiropractic manipulative therapy, we cause an enormous nerve impulse to be transmitted along the proprioceptive nerves back up the spinal cord and to the brain. This impulse is so great, that it can overwhelm the slower, weaker pain signal and prevent pain from being felt. This effect happens quickly, but it can last quite a long time. In addition, the adjustment also stimulates the release of endorphins, which are morphine-like compounds that the body excretes in response to certain stimuli. These endorphins also help to stop pain transmission.
Mechanical Effects of Chiropractic Manipulative Therapy
Motion is life. It is the common trait that almost all animals share. Your body was meant to move, and in order to do that, you need joints that move correctly. Your spinal joints, in particular need to be able to move through their range of motion without restriction. With a few exceptions, the bones in your spine, the vertebrae, form three joints with the one above, and three more with the one below. Above and below the vertebrae are discs, which act as shock absorbers for the spine. The disc consists of a jelly-like substance called "nucleus pulposus", which is surrounded by a tough fibrous covering made up of concentric rings called the "annulus fibrosus".
After about age 30, the blood supply to the discs begins to dry up, and the source of oxygen and glucose, the two things that cells need for energy, start to diminish. When this happens, the only way that the disc gets nutrition is through a process called "imbibition" -- literally, "drinking". In a manner similar to a sponge that is compressed and placed in water; when it expands, it absorbs a great deal of water, the disc when compressed and allowed to recoil, will drink in nutrients from the surrounding tissues. The only way that the disc is allowed to experience compression and expansion, is if the other two joints between that vertebrae and the adjacent one are moving properly.
With time, a joint that is allowed to be immobilized will fuse solid. Many things can immobilize a joint. Usually though, joint immobilization is the result of a spasm of the muscles surrounding the joint. Whether the spasm is the result of damage to the joint or surrounding tissues, or due to another issue, such as emotional stress or chemical irritation, immobilizing the joint for any period of time has been shown to lead to the formation of adhesions within the joint. If these adhesions are not broken by means of an adjustment to the joint, then they will continue to grow, becoming thicker and more numerous, and eventually calcifying, resulting in a fusion of the joint.
Periodically having the joint adjusted, in addition to resolving the cause of the immobilization will help to prevent this degenerative process, and will keep the joint healthy. Further, by keeping the joints moving, the disc is allowed to experience compression and expansion, and this slows down the degeneration of the disc, helping to prevent loss of height with age.
Immune Effects of Chiropractic Manipulative Therapy
Your immune system actually consists of several subsystems including a variety of specialized cells called white blood cells. There are several types of white blood cells or WBCs. Two in particular, Polymorphonuclear Cells (PMNs) or Neutrophils, and Monocytes, act as "Pac-Man", eating bacteria and preventing infection. As seen in the video to the right, they chase bacteria around and eventually engulf and destroy them. A well designed study conducted by Ronald Pero, Ph.D., at New York Preventative Medicine Institute, showed that in a population of those who had been chiropractic patients for at least 5 years, Neutrophils and Monocytes were up to 2-4 times as active as those who had never been adjusted.
There are a number of potential mechanisms for explaining this effect. But underlying all of them is that the central nervous system, the brain and the spinal cord, are involved in the regulation of all other systems of the body. By stimulating the nervous system with spinal manipulation, it is thought that the other systems in the body can be upregulated as well. It is thought that this is the mechanism behind the beneficial effect of chiropractic manipulative therapy on asthma and allergies.
There are two main types of joint manipulation, Low-velocity/High-amplitude or LVHA and High-velocity/Low-amplitude or HVLA. Chiropractic manipulative therapy generally falls under the category of HVLA. This means that chiropractic manipulation therapy is applied using a very fast but very shallow thrust. Osteopathic manipulation or OMT (Osteopathic Manipulative Therapy) is generally LVHA. HVLA manipulation tends to be less painful, puts less stress on the joint, and is usually more effective than low-velocity manipulation. HVLA manipulation is more difficult to do and requires a lot more training to perform safely. Drs. Press and Geleta have completed 5 academic years of training after university, including an extensive clinical internship in order to safely and competently perform HVLA manipulation.