Scientists(ˈsīəntist) have spent 60 years agonizing(ˈagəˌnīziNG) over how our knuckles(ˈnəkəl) crack(krak)

Scientists(ˈsīəntist) have spent 60 years agonizing(ˈagəˌnīziNG) over how our knuckles(ˈnəkəl) crack(krak)

By Katherine Ellen Foley(ˈfōlē)

Knuckle-cracking. Aside from worrying about whether it leads to arthritis(ärˈTHrītis) (it doesn’t), most of us do it mindlessly to get ourselves in the mood to start a project—or while we fret(fret) about it.

Scientists have been struggling(ˈstrəgəl) with an explanation(ˌekspləˈnāSHən) for the pops our finger joints(joint) are capable(ˈkāpəbəl) of making for upwards of 60 years. Much of the early theories(ˈTHi(ə)rē,ˈTHēərē) have been disproven or unreproducible. Knuckles don’t seem to have a uniform(ˈyo͞onəˌfôrm) refractory period(ˈpi(ə)rēəd) in between snaps, for example(igˈzampəl), and the noise(noiz) doesn’t come from vibrations(vīˈbrāSHən) in nearby tissues(ˈtiSHo͞o) or a fibrous(ˈfībrəs) snap as a result of the quick movement.

Scientists got close to cracking the case in 2015, when researchers from the University of Alberta(alˈbərtə) published a paper in which a test subject cracked his knuckles in an MRI machine, and they confirmed that bubbles in the joints pop as they’re pulled apart. (The released(riˈlēs) air is still trapped within us, and eventually dissolves(diˈzälv) back into the normal fluid(ˈflo͞oid) in our knuckles, allowing us to repeat the process shortly afterward.)

But Vineeth Chandran Suja, formerly a graduate students at École Polytechnique in France(frans,fräNs), had been working on the same problem for a few years with his advisor(ədˈvīzər) Abdul Barakat when the 2015 paper came out. They weren’t entirely(enˈtīrlē) convinced(kənˈvinst).

A crack occurs in just about a third of a second—far too quickly to get a good idea with an imprecise(ˌimpriˈsīs) picture. “Mathematical(ˌmaTH(ə)ˈmatikəl) modeling is particularly useful because [real-time] imaging(ˈimij) is not sufficiently(səˈfiSHənt) rapid(ˈrapid) to capture the phenomena(fəˈnɑmənə) involved(inˈvälvd),” Bakarat told Gizmodo. So, the duo(ˈd(y)o͞o-ō) created a model of the hand’s metacarpophalangeal(ˈmetə) joint and played with it to account for all sorts of factors that affect fingers, like the thickness(ˈTHiknis) of the surrounding fluid(ˈflo͞oid), or the speed at which the joints move.

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https://qz.com/1240783/scientists-may-have-solved-the-mystery-behind-the-sounds-of-knuckle-cracking/