We often get asked what causes joints to click – either when a chiropractor adjusts a joint or when you do it yourself. The answer is that a gas bubble is released from the synovial fluid within the joint when the joint is stretched. This is an effect called cavitation.
Joints have a sack around the ends of the two bones which make up the joint and this sack, or joint capsule, is filled with lubricating fluid produced by the lining of the capsule itself. As with all fluid there is a certain amount of gas dissolved in it. When the joint is pulled apart rapidly the volume of the joint increases but the joint capsule won’t let any more air in so a vacuum is created. This drop in pressure is what is thought to allow the dissolved gas to escape from the fluid into the joint. At this point the joint volume increases suddenly with snap and this is what we hear. Once a joint has clicked it won’t click again until the gas has dissolved back into the fluid about 20 minutes later.
There are a couple of other causes of apparent noises coming from the joints too. Tendon of muscles can snap over bony prominences as you move. This happens especially in the wrists, shoulders, hips and ankles. It is not actually occurring in the joint itself but outside it and is usually totally harmless. A key difference with true joint clicking is that it will occur repeatedly without the 20 minute wait between clicks as no gas needs to dissolve back into any fluid.
The third causes of joint noise is the most ominous. Arthritis, particularly the wear-and-tear type – osteoarthritis. Here the noise sounds more like ground glass in the joint. It is a crunching, grinding type of noise which may gradually lessen with repetitive movements. It is caused by roughening of the joint surfaces so they are unable to slide over each other silently any more. It is a bit like the non-stick surface coming off a frying pan. The joint becomes a bit sticky.
We notice noise in the joints of the neck more than any others because our ears are nearby. The other big joints like the knees also sound loud because they are so big. Other people will often notice these clicks too but it usually not a sound associated with arthritis.
Can regular joint clicking cause arthritis? When done in moderation is unlikely to cause any harm. If it associated with normal movements then clicking has never been identified as a cause of arthritis. If you are a regular finger clicker this too is unlikely to be bad for you. One survey in a retirement home found regular finger clickers were less likely to have arthritis.
Some people worry that regular chiropractic adjustments may cause joint damage. This has never been shown and in fact the reverse is likely to be true. Joint stiffness which chiropractic treatment removes can cause wear-and-tear changes in as little as 2 weeks.