Why does cracking a joint make a “crack” sound? Is it harmful to do so much?

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2022-02-08 06:47:19

The COVID-19 pandemic is making us more stressed and more sedentary. The corollary: The last two years must have been more than a few “chuckles” around the planet.

Every time someone stood up, relaxed, or cracked their knuckles, the same satisfying and seductive sound came back: Clutter, Clutter. No one does not like them, you can easily find thousands of videos on youtube with millions to tens of millions of views on this topic.

But while joint cracking is an act very familiar to all of us, have you ever dig into it? Something like why is there a rattle in your joints? What happened when you strained your joints? Does it do any harm?

And if the chuckle has existed indefinitely, must it be a product of evolution? Let’s explain all those mysteries in the article below.

1. Why do we crack joints?

Before answering this question, it’s important to agree that the article is only about the joint-cracking behavior we do to ourselves, a kind of “self-manipulatuon” or “selfie”.

If you go to a physical therapy clinic to have your doctor or a chiropractor break your bones for you, even though it’s also a crackling sound, the effect of the therapy will be very different from that of self-cracking. match at home.

So back to the question, why do we like cracking our own joints? Often people say it makes them feel more relaxed, relieves tension in their joints, and ultimately feels satisfied.

Not only humans, animals also often perform a behavior similar to cracking joints after long periods of inactivity.

Similar behavior to joint cracking in Cyclosa argenteoalba . spider

Scientists call it “pandiculate” or involuntary stretching of soft tissues. They’ve seen dogs, cats, elephants, sheep, and even spiders perform this behavior. For example, in the video above, you can see a spider relaxing. its leg joints.

In short, we can understand that joint cracking is an instinctive behavior. Studies show that by stretching, animals including humans can restore balance and joint functions.

2. Where does the chuckle come from?

To explain this, we must know between the joints that are joined together there is a fluid-filled space called synovial fluid. Synovial fluid helps lubricate joints, reducing friction between them every time we move.

But like all liquids in the world, synovial fluid cannot but contain a certain amount of dissolved air (including oxygen, nitrogen and CO2). When you crack or rotate a joint, the force you apply expands the spaces that contain the synovial fluid.

And as space expands, it creates a force of attraction similar to that of a vacuum. Air bubbles in the synovial fluid will appear, they inflate, and they “crack,” which is the crackling sound you hear.


However, there is also another theory that explains that the chuckle is actually caused by air bubbles forming, not exploding. This means that when you stretch your joints, the larger gap causes more air to take up space and bubbles form.

As the balls form, they can also make a rasping sound. Scientists are still debating which theory is correct. They also used ultrasound machines to track bubbles in the joint’s synovial fluid.

The answer now leans more towards the second hypothesis, because the ultrasound detected a clicking sound immediately after the air bubbles formed in the joint, not when they disappeared:

Ultrasound image shows air bubbles forming in the joint when you break it

Interestingly, once you have successfully cracked the joint, you have to wait 20 minutes before cracking the joint a second time. The chuckles won’t appear during that time, no matter what you do. Because 20 minutes is also the time for the air bubbles to dissolve back into your synovial fluid.

3. Is there any harm in breaking joints?

There is a myth that has been passed down from generation to generation, maybe your mother also told you not to crack your knuckles too much because it can cause arthritis. But a series of studies conducted in recent years showed that knuckle cracking did not increase the incidence of arthritis.

Donald Unger, an American doctor even patiently experimented on himself for 60 years. He cracked his left knuckle every day and left his right hand untouched for six decades.

The results showed that such repeated cracking did not cause arthritis and did not harm Unger’s left hand compared to his right hand. This interesting research even earned Unger the 2009 IgNobel.


Donald Unger, who spent 60 years cracking his knuckles to prove it’s harmless.

Exactly one year later, a 2010 study looked at the joint-cracking habits of 215 people to find that the behavior was not a risk factor for developing arthritis.

Even more surprising is that people who do not crack their joints have a higher rate of arthritis than those who do. An earlier study of nursing home patients also found no association between joint cracking and arthritis.

Even so, there was a rather remarkable 1990 study. It was done on 300 people and came to the conclusion that cracking knuckles frequently and for a long time can lead to swelling and loss of strength. hold.

However, since then, no new studies have confirmed this result. There are only a few reports of injuries caused by excessive knuckle cracking. But these cases are usually so mild and don’t happen so often that scientists don’t take them into account.

In short, the act of cracking joints is almost safe and leaves no side effects too significant.

4. Is joint cracking a product of evolution?

Perhaps the most interesting question, why our joints evolved to creak. Jerome Fryer, a Canadian researcher, has raised the interesting idea that synovial structure is a product of evolution.

To demonstrate, Fryer created joints that mimic the joints of humans and animals. He found that if joints contained only water instead of synovial fluid, the space between them would be very easy to widen or even separate.

The bubbles will then be much easier to form, but they are “spray” bubbles, which will not make any rattles.

Simulation of joint cracking in synovial fluid by Jerome Fryer

That all changed when the water in the synovial fluid was treated to become more concentrated, meaning less air soluble and containing only microscopic bubbles, a snap that was followed by a rasping sound as the bubbles appeared. formed.

As such, the synovial fluid has evolved to become more concentrated, helping to better hold the joints together. We will need to apply a stronger force if we want them to expand, and these strong forces create the rattle.

The thick synovial fluid not only aids joint stability, but it also provides the joint with protection from injury.

5. Don’t confuse the crackling sound with other rattle sounds

As we’ve said, crackles when cracking come from the formation or bursting of bubbles in the synovial fluid. But sometimes it can be confused with some other sound also coming from your body, near the joints.

Firstly, it could be the popping of the ligaments. Ligaments act as rubber bands that stretch between muscles and bones to connect them. When you move the joint, the ligaments also move and it can sometimes make a clicking sound but this “pop” is usually deeper than the crackling sound.

You can easily hear the ligaments when turning your ankle, when standing or sitting down, or when climbing stairs.

Don’t mistake the cracking sound for this sound

The second most confusing sound is a chuckle that sounds more hissing than crackling than cracking. In fact, it can sound like a “crack,” which is the sound when bone rubs against cartilage. This friction is most commonly heard in the knees, but they are also harmless.

In short, you don’t need to worry about any “crack” or “crack” sounds coming from your joints. Unless these noises are accompanied by pain, you should go to the hospital.

If not, that’s actually the way your body works, all perfectly normal. Cracking joints is an instinctive behavior and even included in the inventory that has helped you evolve.



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