When patients come for chiropractic treatment they often ask us if we are cracking their bones.
The short answer is no. The crack or popping noise often heard from an adjustment is from the joints; synovial joints to be exact.
Let us explain.
Synovial joints are the most flexible in the body and contain a viscous fluid called synovial fluid. This fluid is the texture of egg yoke and its job is to lubricate and cushion joints allowing them to gently glide past one another.
Like gasses dissolving into blood there are gasses dissolved in the synovial fluid. When you stretch a joint further than normal, you increase the joint space. There is however the same amount of synovial fluid, therefore you cause a decrease pressure in the joint. This decrease in pressure pulls the dissolved gas out of the fluid and into a bubble (much like taking the cork of a champagne bottle). The fluid then puts pressure on the bubble until it pops into smaller bubbles making the ‘popping’ sound.
These small bubbles then sit around in the joint and take 20 minutes to slowly dissolve back into the fluid. This is the reason why once you’ve popped a joint you can’t get another pop for a while.
Interestingly, Dr Donald Unger carried out a self experiment after his mother told him not to crack his knuckles as he would get arthritis. Dr Unger popped only the joints of his left hand for 50 years which equated to 36500 times! The findings of his study show no arthritis in either hand.
This won Dr Unger a Noble prize, a parody of a noble prize for crazy but interesting scientific accomplishments!