¹ that brought forward the idea that the cracking sound from a knuckle was due to the formation of a cavity within the joint. It wasn’t until 1971 when another researcher by the name of Unsworth ², challenged this cavity formation idea with a study explaining that the sound was from a cavity collapsing phenomenon.

The collapsing cavity theory remained the best explanation until we conducted an MRI study in 2015 ³ that challenged the sound source was related, again, to the formation of cavity, resorting back to what Roston had proposed in 1947.  However, in our conclusions, tribonucleation, which is the formation of a cavity from the rubbing of structures, did not have strong supporting references contributing to the magnitude of the classic cracking sound. That is, when some cracks their knuckles, people can often hear it from across the room. Tribonucleation has not been shown to create such loud sounds.

This is what got the researchers of this recent publication curious. They used a mathematical model study using the Rayleigh-Plesset equation in the attempt to resolve the debate of whether the cracking sound is related to the formation or the collapse of a cavity. In their calculations, they believe it is to be related to a partial collapse.

Again, like with our PLOS One study, the media has gone wild with this publication. But the truth is, the plot has only thickened. The debate gets even more intense.

Quietly, I have developed a physical model that may settle the debate once and for all. Data collection is underway at UBC. I look forward to contributing to the science of sounds from our joints.