Laboratory Products

  • Why Do Your Knuckles Crack?

Why Do Your Knuckles Crack?

Apr 16 2018 Read 1013 Times

For some people the sound of cracking knuckles is cringe-worthy. For others it's a daily, if not hourly habit. Whatever your inclination, new research has revealed why knuckles make that signature "crack" when the joint between the fingers and the hand bones is released.

According to science student Vineeth Chandran Suja, it all boils down to a trio of mathematical equations. Together with his lecturer Dr Abdul Barakat, Chandran Suja devised a model that explains how cracking the knuckles triggers a pressure change which forces tiny air bubbles to collapse in joint fluid.

"The first equation describes the pressure variations inside our joint when we crack our knuckles," explains Chandran Suja in an interview with BBC News. "The second equation is a well-known equation which describes the size variations of bubbles in response to pressure variations," he adds. "And the third equation that we wrote down was coupling the size variation of the bubbles to ones that produce sounds."

A combination of bubbles, fluid and pressure

Together, the three equations offer a mathematical explanation that describes why releasing the knuckle joints is accompanied by such a dramatic sound effect. The study was published in the journal Scientific Reports and explains how a combination of bubbles, fluid and pressure has created what some people consider one of humankind's most annoying habits. 

"When we crack our knuckles we're actually pulling apart our joints," says Chandran Suja. "And when we do that the pressure goes down. Bubbles appear in the fluid, which is lubricating the joint - the synovial fluid. During the process of knuckle cracking there are pressure variations in the joint which causes the size of the bubbles to fluctuate extremely fast, and this leads to sound, which we associate with knuckle cracking."

Bridging the gap between previous studies

While the findings are a breakthrough, it's not the first time scientists have explored the mystery of knuckle cracking. The bubble collapsing theory was first put forward in 1971 and was challenged 40 years later when new research suggested that air pockets remain in synovial fluid long after the joints have been pulled apart.   

The new model bridges the gap between the two conflicting theories and indicates that only a partial bubble collapse is needed to produce the "crack" sound. It also explains why some people are unable to crack their knuckles. If the space between the knuckle bones is too small fluid pressure levels don't drop low enough to trigger a bubble collapse, and hence create a sound.  

As well as human physiology, modern laboratories also delve into the complexities of birds and mammals. Introducing FLIR thermal imaging cameras, 'Investigating the Thermal Physiology of Birds and Mammals' offers a behind the scenes glimpse at the latest work from Glasgow's Institute of Biodiversity, Animal Health and Comparative Medicine.

Reader comments

Do you like or dislike what you have read? Why not post a comment to tell others / the manufacturer and our Editor what you think. To leave comments please complete the form below. Providing the content is approved, your comment will be on screen in less than 24 hours. Leaving comments on product information and articles can assist with future editorial and article content. Post questions, thoughts or simply whether you like the content.

Post a Comment




Digital Edition

Lab Asia April 2019

April 2019

In This Edition Articles - Mobile Affinity Sorbent Chromatography Of Proteins - Integration of MS and UV Data for Peak Tracking in HPLC Method Development - VMXm takes its First Users 'wher...

View all digital editions

Events

Analitika Expo 2019

Apr 23 2019 Moscow, Russia

InformEx

Apr 30 2019 Chicago, IL, USA

Making Pharmaceuticals Exhibition & Conference 2019

Apr 30 2019 Ricoh Arena, Coventry, UK

AOCS Annual Meeting & Expo

May 05 2019 St. Louis, MO, USA

ISCC & GCxGC 2019

May 13 2019 Fort Worth, Tx, USA

View all events