What that sound is NOT: 

The sound that can occur during a chiropractic adjustment is NOT the bones cracking, grinding together or anything scary like that! It is actually a natural phenomenon that occurs within a specific type of joint – a synovial joint. Synovial joints are found within the spine, but other examples are in the fingers/toes and TMJ.

The phenomenon behind the sound:

Medically the noise that occurs during an adjustment is called cavitation. Or it was called cavitation)¹… The mechanism behind this was believed to be the formation of an empty space (a bubble) within the synovial fluid of the joint. 

However, recent research is indicating that the phenomenon is not cavitation but instead tribonucleation. Watch out, big words here! According to Kawchuk et al., “joint cracking is associated with cavity inception rather than collapse of a pre-existing bubble.”² This study used real time MRI to visualize what occurs within a joint at the time of a chiropractic adjustment. This study provides direct experimental evidence to support tribonucleation versus the previously termed cavitation.

In short. That noise is the sound of a gas bubble forming instead of a gas bubble collapsing – which makes sense since a chiropractic adjustment typically provides a gapping of a joint to allow for improved motion instead of a compression of a joint that would “pop” a bubble. Science is often still catching up to mechanisms that occur within our body and may not be settled quite yet on this phenomenon.

What does the noise mean?

Essentially, not much! The sound associated with an adjustment is nothing more than a noise, “ear candy” if you will. It does not indicate that an adjustment was successful or that a joint “moved” into position. The chiropractic adjustment is meant to restore alignment and motion of a joint NOT to make a “crack” sound. That is why chiropractors recheck joint motion following an adjustment, to be sure of success.

There is some side benefit to tribonucleation within a joint as it is associated with an increase in endorphins (‘feel-good’ hormones) and a decrease in prostaglandins (hormone-like inflammation modulators).^3,4

Read about why a person shouldn’t adjust themselves in our blog.

Resources:

1. Brodeur R. J Manipulative Physiol Ther. 1995 Mar-Apr;18(3):155-64. The audible release associated with joint manipulation.

2. Kawchuk GN, Fryer J, Jaremko JL, Zeng H, Rowe L, Thompson R (2015) Real-Time Visualization of Joint Cavitation. PLoS ONE 10(4): e0119470. https://doi.org/10.1371/journal.pone.0119470

3. Vernon HT, Dhami MS, Howley TP, Annett R. J Manipulative Physiol Ther. 1986 Jun;9(2):115-23. Spinal manipulation and beta-endorphin: a controlled study of the effect of a spinal manipulation on plasma beta-endorphin levels in normal males.