Why does cracking fingers make sound & will it be bad or good for them?

To understand what causes the 『popping』 sound when we crack our knuckles, we must first understand a little bit about the nature of joints that are easy to crack — fingers, wrist, knee, elbow etc.

These 『crack-able』 joints are of the synovial variety. Two characteristics to remember —

The joints are encased by protective joint capsule called synovial membrane.

Within the joint is a lubricant with the color and consistency of egg -white called synovial fluid.

The synovial fluid, besides reducing friction inside the joint and providing nourishment to the cells, has gases dissolved in it — mostly oxygen, carbon dioxide, and nitrogen.

When we twist or turn a joint to 『crack』 it, we are essentially pulling the two bony joint surfaces apart. This maneuver stretches the joint capsule and reduces the pressure within.

When the pressure inside the joint reduces sufficiently, the gases dissolved in the synovial fluid escape rapidly and form multiple bubbles that rest between the two surfaces.

(If one takes an x-ray of hand after cracking knuckles, they』ll be able to see gas bubbles trapped within the joint)

It is thought that the formation of these bubbles/escaping gas is responsible for producing the loud 『popping』 sound. We can think about it as effervescing soft drinks.

(This phenomenon is quite contrary to the popular belief that the friction between the two bones rubbing against each other causes the 『crack』, don』t you think?)

So why does cracking knuckles (or any other joint) feel SO GOOD?

Well, because, the escaping gases and the resulting multiple bubbles temporarily increases the volume of the joint by 15–20%. The increase in volume further stretches the protective capsule leading to an increased range of motion at the joint — That sure should give you the feeling of satisfaction and relaxation!

Typically it takes about 20 minutes for the escaped gases to dissolve back in the synovial fluid making it nearly impossible for anyone to constantly and repeatedly crack their joints over and over again in this refractory period.

So is cracking bad for your joints? No, not really.

Although it is widely believed that long-term popping of joints can lead to or at least increase the predisposition to osteoarthritis, there have not been conclusive evidences to validate the claim.

In fact, many studies conducted in the recent past suggest there being no correlation between cracking of joints and any form of joint damage/arthritis.

Here』s one such study for example:

A study published in 2011 examined the hand radiographs of 215 people (aged 50 to 89) and compared the joints of those who regularly cracked their knuckles to those who did not. The study concluded that knuckle-cracking did not cause hand osteoarthritis, no matter how many years or how often a person cracked their knuckles.

Here』s another (kinda funny one):

Medical doctor Donald Unger cracked the knuckles of his left hand every day for more than sixty years, but did not crack the knuckles of his right hand. No arthritis or other ailments formed in either hand earning him the 2009 Ig Nobel Prize in Medicine, a parody of the Nobel Prize.

So, don』t worry, crack your knuckles away! Besides probably the loud noise annoying the people around you, the popping isn』t doing anybody any harm!

為了弄清楚我們掰指關節時發出「砰砰」聲的原因，我們首先要了解一些容易掰的關節——手指、手腕、膝蓋、肘部等等的性質。

這些「容易掰」的關節是含有滑液的。記住這兩個特點：

關節被稱為滑膜的保護性關節囊所包裹。

在關節內有一種潤滑劑，其顏色與蛋清的顏色一致，稱為滑液。

滑液除了能減少關節內部的摩擦，並為細胞提供營養的功能外，還含有溶解在其中的氣體——主要是氧氣、二氧化碳和氮氣。

當我們扭動或轉動來「掰」關節時，我們實際上是把兩個骨關節表面分開。這個動作可以拉伸關節囊，減少內部壓力。

當關節內的壓力降低時，滑膜液中溶解的氣體迅速逸出，形成多個氣泡存在於在兩個表面之間。

(如果一個人在掰指關節後拍一張x光片，他就能看到關節內的氣泡)

人們認為，這些氣泡/逸出氣體的形成是產生「爆裂」聲音的原因。我們可以把它想像成是「冒泡」的飲料。

(這一現象與人們普遍認為兩根骨頭互相摩擦導致掰指關節產生聲響的說法是截然相反的，你覺得呢?)

那麼，為什麼掰指關節(或其他關節)的感覺這麼好呢?

因為，逃逸的氣體和由此產生的多個氣泡使關節的體積暫時增加了15-20%。體積的增加進一步拉伸了關節囊，導致關節活動範圍的增加——這肯定會給你帶來滿足和放鬆的感覺!

通常情況下，逃逸的氣體需要大約20分鐘的時間才能溶解在滑液中，這使得任何人都幾乎不可能不斷地反覆地在這段不應期內反覆地掰動它們的關節。

那麼，掰關節對你的關節有害嗎?不。

儘管人們普遍認為長時間的掰關節可以導致或至少增加骨關節炎的易感性，但並沒有確鑿的證據證實這一說法。

事實上，最近的許多研究表明，掰關節和任何形式的關節損傷或關節炎都沒有相關性。

這裡有一個這樣的研究:

2011年發表的一項研究對215個人(年齡在50歲至89歲之間的人)的手部X光照進行了研究，並比較了那些經常掰和不經常掰指關節的人。研究得出結論，掰指關節並不會導致手部骨關節炎，無論多少年或多久。

這是另一個(有點好笑):

醫生Donald Unger每天在掰他的左手指關節，已經有60多年了，但他並沒有掰右手的。他因此獲得2009年搞笑諾貝爾醫學獎（對諾貝爾獎的惡搞），而沒有患任何關節炎或其他疾病。

所以，別擔心，大膽地掰指關節吧!除了可能噪音讓你周圍的人感到討厭之外，這個行為對任何人都沒有害處!

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