Chiropractors get this question all the time… what’s that sound? Are you cracking my bones? Why does my joint pop?
First of all – NO – we’re not cracking your bones! Here’s an explanation of that “pop” or “crack” you might hear with a chiropractic adjustment. The more technical term for this noise is a cavitation.
To start off, I need to give a small anatomy lesson. Many joints in your body, especially the ones targeted by the chiropractic adjustment, are considered synovial joints. This means there is a capsule of connective tissue surrounding the joint and synovial fluid inside to help lubricate the joint.
Now we have to think back to high school science class and remember Boyle’s Law which states that the volume of a given amount of gas held at constant temperature varies inversely with the applied pressure when the temperature and mass are constant. In other words, when volume goes up, pressure goes down. You might remember that in some cases, liquid is just a compressed version of a gas. Lots of pressure can change the state of matter from a gas into a liquid. Alternately, if you reduce that pressure by increasing the volume of the space the liquid is being held, the liquid can change into a gas.
That is what is going on during an adjustment. Many would say that the goal of a chiropractic adjustment is to gap the joints to increase movement in a hypomobile joint (i.e. a joint that isn’t moving as well as we would like it to). With the high-velocity, low-amplitude manipulation, the gapping of the joint creates an increase in the volume of the joint capsule, which in turn reduces the pressure and allows some of that synovial fluid to change states from a liquid into a gas.
THAT is your noise – the change in state from liquid to gas. The formation of this gas bubble in the synovial joint can cause a “pop” or “crack” sound.
Dr. Greg Kawchuk and his colleagues recently did a study where they used an MRI to visualize a joint cavitation in real time. Below is a short video of their findings:
Now you can impress all of your friends with the science the next time they cringe when you crack your knuckles…
For a further explanation and to see if chiropractic adjustments are right for you, book in to see one of our knowledgable practitioners!
Author: Allie Dennis, BSc. Kin (Hons.)
Toronto Chiropractic Intern | CSEP – Certified Personal Trainer
References:
http://chemistry.bd.psu.edu/jircitano/gases.html
Kawchuk GN, Fryer J, Jaremko JL, Zeng H, Rowe L, Thompson R (2015) Real-Time Visualization of Joint Cavitation. PLoS ONE 10(4): e0119470. doi:10.1371/journal.pone.0119470
https://upload.wikimedia.org/wikipedia/commons/thumb/8/8b/907_Synovial_Joints.jpg/250px-907_Synovial_Joints.jpg
http://www.greenhill-osteopath.co.uk/images/cavitationdiagram.jpg
https://saylordotorg.github.io/text_general-chemistry-principles-patterns-and-applications-v1.0/section_14/a433792ac2caa29995f55547b9d15918.jpg