It creates a sound that sets teeth on edge and, we’re often told, raises the risk of arthritis¹.

掰指关节的声音让人很不舒服，而且我们常被告知，掰指关节会增加患关节炎的风险。

But people who can crack their knuckles² may actually have healthier joints⁴ than others.

但实际上，那些“咔咔”地掰指关节的人比其他人拥有更健康的关节。

Scientists say that the force involved in making fingers ‘pop’ is more than enough to cause damage.

科学家称，让关节发出“咔”的一声的力量足以给关节带来损伤。

Yet, studies show that regular knuckle³-cracking doesn’t seem to do any harm.

然而，一些研究显示，经常掰指关节并不会对关节有伤害。

This suggests it is actually a sign of very healthy joints.

这意味着，关节发出响声是显示关节非常健康的迹象。

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.

这一理论出自加拿大的研究员，他们用磁共振扫描仪观察手指内部，记录在指关节发出响声时里面发生了些什么。

One of the team, a ‘gifted knuckle-cracker’, put one finger at a time into a tube connected to a cable.

研究团队中有一个人很擅长掰指关节，他每次将一个手指放入一个和电缆相连的试管中。

This wire was then slowly pulled until the joint in large knuckle in the middle of each finger popped.

然后电缆慢慢拉伸手指，直到每根手指中间的大关节发出响声。

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.

电缆被拉大约6秒后，两块骨头突然分离，在关节内部的液体中形成一个空洞或者说是泡泡。

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.

据PLOS ONE杂志报道，掰指关节的响声——响声持续时间不到三分之一秒——准确地与泡泡形成的时间吻合。

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.

这项研究的主要作者是来自亚伯达大学的Greg Kawchuk教授，他说：“我们称之为‘拉我的手指研究’(pull my finger study)，实际上的确是拉伸某人的手指并用核磁共振观察发生了什么。”

‘When you do that, you can see very clearly what is happening inside the joints.

“当你用核磁共振观察的时候，你可以非常清楚地看到关节内部发生了什么。”

‘It is a bit like forming a vacuum.

“它像是形成了一个真空。”

‘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.’

“当关节接合处突然分开，液体无法流入不断增大的关节真空处，因此形成了一个气泡，这就是响声的来源。”

The scans also showed a mysterious white flash occurs just before the noise is heard.

扫描仪还显示，就在听到响声之前有一道神秘的白光闪过。

Further research is needed into this streak⁵ of light – and why the cracking sound is so loud.

为什么会出现这道白光，以及为什么掰指关节会发出这么大的声音，还有待进一步研究。

However, the researchers are happy to have shown that the noise is created when a bubble forms inside the knuckle.

不过能够向众人展示响声的背后是指关节内部的泡泡，研究人员已经很高兴了。

Although this was first suggested more than 100 years ago, recent thinking has been that the crack is created when a bubble bursts.

虽然这个猜想最早在100多年前就提出了，不过不久前曾有人认为指关节发出响声是因为气泡破裂。

Previous studies have shown that between 25 and 54 per cent of us crack our knuckles – with men doing it more than women.

先前的研究显示，25%到54%的人掰指关节，掰指关节的男性比女性多。

And despite the common wisdom that the habit raises the risk of arthritis, previous studies have failed to prove this.

尽管所谓的普世真理认为这个习惯会增加患关节炎的风险，但是过去的研究并未证明这一点。

One comparison of Los Angeles nursing home residents found those who had regularly cracked their knuckles were actually less likely to have damaged joints.

对洛杉矶私人疗养院居民的比较研究发现，那些经常掰指关节的人关节比较不容易受到损伤。

The US researchers behind that study concluded: ‘The chief morbid⁶ consequence⁷ of knuckle cracking would appear to be its annoying effect on the observer.’

这项研究的美国研究员总结道：“掰指关节的主要不良后果在于，关节的响声会让周围的人感到不舒服。”