This is such a common question, it is continually being researched and the answer refined. It is so rarely answered well, that I thought it would be good to create a full page to answer. I will also update it periodically? When I do update it I will create a post about the update so that you can be kept up to date, and the information will be all in one place.
In my first post on this topic. I decided to leave out some reasons for space limitations (I try to keep my blogs under 400 words, not that I’m always successful), and some for the lack of research, some for them being controversial, and many others I just don’t know about.
So, here goes…
Chiropractic manipulation is not just joint popping. In fact the audible pop doesn’t even need to occur for a successful manipulation, though it often does, and some patients and doctors like to hear it. Research has found that pop or not, the same benefits are experienced and that trying repeatedly to get a pop can actually cause damage.
The mechanism of why manipulation works is not completely understood. One thing that is understood is that it does work. Most of the simple explanations are incomplete or just plain wrong. The most recent research points to a more complex reason for the therapeutic effects of chiropractic manipulation. It is suggested that many things are occurring at the same time that provide the benefits.
Here are some of the known things that can begin to explain why manipulation works.
1. Positive neuroplastic effects improve the way the brain perceives what is going on in the body and the world around it. The paraspinal muscles are sensors and have more sensors in them per gram than other muscles in the body. These sensors are triggered by adjustments. Interpretation of nervous impulses going to the brain is altered by the manipulation of these joints and muscles, thus expressed sensations such as pain are altered. This alteration can lead to pain relief or other changes in the way that your brain perceives and reacts to reality.
2. Movement provides improved nutrient supply. The cartilage and other structures inside of a joint have no blood supply. These structures get their nutrients through motion. The blood supply goes to the outside of the joint and nutrients move into the synovial fluid of the joint. Joint motion moves this fluid around thus providing fresh nutrients to all parts of the joint, as well as removing waste. If a joint becomes locked down by muscle spasm, scar tissue, a cast, or any other means, for a prolonged period of time the joint begins to feel stiff.You know the feeling of needing to stretch after sitting in the car for a long time.
The facet joints in your spine are particularly vulnerable to this problem because they work in tandem and because of the body’s amazing ability to compensate. Your facet joints all work together, if one is injured it can become locked down to prevent further injury. When this happens you may get the desire to stretch or move your back. This usually works, but if all of the other joints compensate for the problem joint and take that added stress of movement on themselves then the problem joint stays locked down. Specific manipulation induces full range of motion and synovial fluid movement.
3. Manipulation can reduce pressure on the nerves. Your nervous system is the control center of your body, and it is not without weaknesses. Nerves and nerve bundles are soft tissue. They don’t function well under physical pressure. In fact it has been shown that inflammation, a bulging disc, or fragment floating around can interfere with proper nerve conduction. The stuck joint as discussed previously can also physically be stuck pressing on a nerve, causing a disc herniation to press on the nerve, or causing inflammation that is pressing on the nerve, or just be moving in a way that rubs the nerve. In any case. The adjustment can cause a relief of this pressure through movement of the joint to the correct position, or motion. The pressure needed for that is large, and so though it is one effect of the adjustment it is numerically a very small number of chiropractic cases that are treated through this mechanism.
4. Proprioceptive retraining allows for improved function. The brain also records these proprioceptive signals from the joints motion. Especially for chronic conditions the brain is in need of retraining regarding the motion of that joint. Manipulation takes a joint through its full range of motion. This new input is then stored and replayed in the brain, similar to muscle retraining that physical therapists will do, or physical training of athletes, when the body has done the motion enough times it remembers it. This retraining provides a functional correction that may provide pain relief.
5. Proprioceptive stimulation triggers the release of endorphins. These endorphins cause a near instant and temporary relief similar to pain medication making you less aware of the problem. This trick of the body can cause a secondary benefit, that of relaxing local tissues such as trigger points or tight musculature that may be pinching nerves.
Here are some of the more controversial observations, benefits, and mechanisms of chiropractic. (I must note that just because we don’t know how it works doesn’t mean that it doesn’t.)
Somatovisceral effects – That they exist is not so much controversial as is the predictability. We know that the spine can effect the visceral organs, but we can’t really say that if you adjust this level this often in this way that you will get the pancreas to produce this much more insulin. The mechanism, more likely, is one of many things acting on the organs. As with everything else in the body it is more complicated than one single interaction.
Reduced high blood pressure – WebMD research article more research needed, and mechanism unknown.
Improved immune system response – I have yet to see a great side by side study of people who receive chiropractic care next to a control group who doesn’t, to see who gets a cold and how long they last. However there are articles and case studies out there. Even if chiropractic does benefit the immune system, we don’t know the mechanism of how.
Decreased colic in babies – I’ve seen an association, and I’ve read studies that show that there is an effect. I don’t know the mechanism, and I’ve not seen anything more than theories.
I have taken to recording my own observations and creating case studies of the effects of chiropractic that I have seen. Two new and relatively unstudied benefits that I have found are an improvement in vocal performance, and a decrease in bed wetting with chiropractic manipulation. A mechanism for these is not fully understood yet.
Many other benefits have been observed, and still others suspected. Research is still going on and much more is needed. I will add them and any new or additional documentation as I find them, and as my time permits.