What's The Crack

The cracking or popping sound that is sometimes produced when joints are manipulated, (or as we chiropractors like to say 'adjusted'), seems to evoke strong emotions from some people. I'm often asked what causes the sound. Patients sometimes think it is caused by bones rubbing together or something snapping. Some have had relatives or friends tell them that clicking their joints will cause arthritis. Such misconceptions seem to generate a certain degree of fear of the cracking sound. This fear is slightly irrational when you consider that many of us experience a click from our knees when we squat down to pick something up or even clicks from our ankles or toes when we take our first steps of a morning.

To help us understand what is happening during an adjustment it might be useful to know what joints look like. Most of the joints in our bodies are called 'synovial joints'. These joints normally provide free movement between the bones they join. They are encapsulated by ligaments and contain a lubricating fluid called synovial fluid.

Research over many years has tried to answer the question - 'What causes the crack?' It has been shown in various studies that there is a sudden change in the pressure within a joint when it is stretched. When a chiropractor 'adjusts' a joint, the joint is essentially being stretched very quickly. This rapid stretch and the resulting pressure change within the joint capsule (because there is suddenly more space inside the adjusted joint) appears to cause gas which was previously dissolved within the synovial fluid, to vapourize to fill the increased joint space. The 'crack' (sometimes called an audible release) seems to be associated with this process. The vapourized gas remains contained within the the joint capsule and will be slowly resorbed back into the synovial fluid over a period of 20-30 minutes. During this time it is unlikely that the joint will crack again.

Investigations into the safety of cracking joints have looked at the effects of habitual knuckle cracking. They did not find any increase in the incidence of osteoarthritis in the hands. It appears that very frequent knuckle cracking does reduce grip strength. It has also been shown that spinal manipulation that results in an audible release can lead to greater muscle relaxation than manipulation that does not prouce a crack. Pain reduction after an adjustment however does not seem to be dependent on there being an audible pop.

So what does all this mean? Firstly it suggests that cracking or popping joints need not be feared. It is a common occurrence that doesn't only take place when a chiropractor adjusts a joint but can happen spontaneously when joints are stretched. Secondly, the evidence does not link it with arthritis. Finally, there does not necessarily need to be a click when a joint is adjusted in order for a pain reduction to occur.