It creates a sound that sets teeth on edge and, we’re often told, raises the risk of arthritis.
掰指關節的聲音讓人很不舒服，而且我們常被告知，掰指關節會增加患關節炎的風險。

But people who can crack their knuckles may actually have healthier joints than others.
但實際上，那些“咔咔”地掰指關節的人比其他人擁有更健康的關節。

Scientists say that the force involved in making fingers ‘pop’ is more than enough to cause damage.
科學家稱，讓關節發出“咔”的一聲的力量足以給關節帶來損傷。

Yet, studies show that regular knuckle-cracking doesn’t seem to do any harm.
然而，一些研究顯示，經常掰指關節并不會對關節有傷害。

This suggests it is actually a sign of very healthy joints.
這意味著，關節發出響聲是顯示關節非常健康的跡象。

The theory comes from Canadian researchers who used MRI scanners to peer deep inside the fingers and record just what happens when knuckles are cracked.
這一理論出自加拿大的研究員，他們用磁共振掃描儀觀察手指內部，記錄在指關節發出響聲時里面發生了些什么。

One of the team, a ‘gifted knuckle-cracker’, put one finger at a time into a tube connected to a cable.
研究團隊中有一個人很擅長掰指關節，他每次將一個手指放入一個和電纜相連的試管中。

This wire was then slowly pulled until the joint in large knuckle in the middle of each finger popped.
然后電纜慢慢拉伸手指，直到每根手指中間的大關節發出響聲。

After about six seconds pulling the cable, the two bones suddenly shot apart, creating a cavity, or bubble, within the fluid that bathes the inside of the joint.
電纜被拉大約6秒后，兩塊骨頭突然分離，在關節內部的液體中形成一個空洞或者說是泡泡。

The cracking – which took less than a third of a second - occurred at the precise moment the bubble was formed, the journal PLOS ONE reports.
據PLOS ONE雜志報道，掰指關節的響聲——響聲持續時間不到三分之一秒——準確地與泡泡形成的時間吻合。

Lead author Professor Greg Kawchuk, from the University of Alberta, said: ‘We call it the “pull my finger study” – and actually pulled someone’s finger and filmed what happens in the MRI.
這項研究的主要作者是來自亞伯達大學的Greg Kawchuk教授，他說：“我們稱之為‘拉我的手指研究’(pull my finger study)，實際上的確是拉伸某人的手指并用核磁共振觀察發生了什么。”

‘When you do that, you can see very clearly what is happening inside the joints.
“當你用核磁共振觀察的時候，你可以非常清楚地看到關節內部發生了什么。”

‘It is a bit like forming a vacuum.
“它像是形成了一個真空。”

‘As the joint surfaces suddenly separate, there is no more fluid available to fill the increasing joint volume, so a cavity is formed and that event is what is associated with the sound.’
“當關節接合處突然分開，液體無法流入不斷增大的關節真空處，因此形成了一個氣泡，這就是響聲的來源。”

The scans also showed a mysterious white flash occurs just before the noise is heard.
掃描儀還顯示，就在聽到響聲之前有一道神秘的白光閃過。

Further research is needed into this streak of light – and why the cracking sound is so loud.
為什么會出現這道白光，以及為什么掰指關節會發出這么大的聲音，還有待進一步研究。

However, the researchers are happy to have shown that the noise is created when a bubble forms inside the knuckle.
不過能夠向眾人展示響聲的背后是指關節內部的泡泡，研究人員已經很高興了。

Although this was first suggested more than 100 years ago, recent thinking has been that the crack is created when a bubble bursts.
雖然這個猜想最早在100多年前就提出了，不過不久前曾有人認為指關節發出響聲是因為氣泡破裂。

Previous studies have shown that between 25 and 54 per cent of us crack our knuckles – with men doing it more than women.
先前的研究顯示，25%到54%的人掰指關節，掰指關節的男性比女性多。

And despite the common wisdom that the habit raises the risk of arthritis, previous studies have failed to prove this.
盡管所謂的普世真理認為這個習慣會增加患關節炎的風險，但是過去的研究并未證明這一點。

One comparison of Los Angeles nursing home residents found those who had regularly cracked their knuckles were actually less likely to have damaged joints.
對洛杉磯私人療養院居民的比較研究發現，那些經常掰指關節的人關節比較不容易受到損傷。

The US researchers behind that study concluded: ‘The chief morbid consequence of knuckle cracking would appear to be its annoying effect on the observer.’
這項研究的美國研究員總結道：“掰指關節的主要不良后果在于，關節的響聲會讓周圍的人感到不舒服。”

Vocabulary
sets teeth on edge: 讓人心煩，讓人不舒服
arthritis: 關節炎

（譯者：陳思閩BISTU2012 編輯：陳丹妮）