Im often asked by clients, ’What is that cracking noise?” when I correct alignment of various skeletal components – normally followed by “Does it do any damage to the joint?”.
The below diagram shows the typical construction of a (Synovial) joint which has a fluid space encapsulated about the two bones that articulate – such as a knuckle of your hand. Within this Synovial fluid there are dissolved gasses, consisting mainly of Oxygen, Carbon dioxide and Nitrogen.
The action of manipulating the joint releases pressure on the fluid & causes Cavitation (the formation of small bubbles) which are stretched and/or compressed within the Synovial fluid as the joint is adjusted.
It is the compression and bursting of these micro-bubbles that causes the audible ‘crack’, as confirmed in 2015 by MRI video evidence. It is not due to any direct movement of bone against bone — it should be noted that no bone moves directly upon bone unless the joint’s associated cartilage (Hyaline or Fibro) has been badly damaged which is highly unlikely.
The joint actually increases marginally in volume which gives immediate relief from the stiffness that as being experienced by the client. This is why you cannot continuously crack your knuckles as there is insufficient pressure on the joint once corrected alignment is achieved.
The joint size reverts to normal within 20 minutes during which time the joint has stabilised into its normal operating position and pressure.
There is no correlation between cracking of joints and Arthritis or joint damage – in fact a Medical doctor, Donald Unger, cracked the knuckles of his left hand every day for more than sixty years. He did not, however, crack the knuckles of his right hand. No arthritis or other ailments formed in either hand earning him the 2009 ‘Ig Nobel Prize’ in Medicine, a parody of the Nobel Prize.
The chances are that this false claim regarding the damage caused by cracking your knuckles was perpetrated by someone who just didn’t like the noise, and just thought this fable was the best way to prevent the people around them continuing!