Does Cracking Your Knuckles Really Give You Arthritis?

Jaysin Trevino, Flickr // CC BY 2.0
Jaysin Trevino, Flickr // CC BY 2.0

You’ve heard it before. You’re in a quiet room in among a gathering of people, and then—POP!—a little cracking noise rings out, followed by another, and another, and another. For some, cracking knuckles is a habit, while for others that little pop brings relief. And it's not just reserved for tough guys before they beat people up: Between 25 and 54 percent of all people crack their knuckles multiple times a day. But is the old wives’ tale true? Are these knuckle-crackers more likely to hurt their hands and gradually develop arthritis as they get older? 

In short, nope! Despite the rumor that kids constantly hear, it turns out there is no scientific correlation between cracking your knuckles and developing arthritis in your joints, which is when one or more of the points where your bones meet develop inflammation. 

When you crack your knuckles, you're actually doing more bursting than cracking. The popping noise you hear is caused by small bubbles bursting in your synovial fluid, a yolk-like substance that lubricates the areas between bones and reduces friction for ease of movement.

Here's how it works: When you make the motion to crack your knuckles—either by stretching your fingers or bending them backwards—you expand the joint. This causes the pressure between the joint  to decrease, as well as the ligaments that connect the bones and the joint capsule that holds all of it together. That depressurization causes gasses like carbon dioxide, nitrogen, and oxygen that are dissolved in the synovial fluid to form into little bubbles that rush into the empty space. As the joints settle back into place, the fluid also returns to its rightful place and pops those little bubbles, causing that recognizable cracking sound. 

The sensation of cracking your fingers feels good because the stretching of the joint also stimulates nerve endings found along the fingers; joints can’t be cracked more than once within 15 minutes to a half hour, which is about how long it takes for those gasses to dissolve back into your synovial fluid.

Among the scientific studies conducted to prove that there is no correlation between cracking your knuckles and osteoarthritis, one published in the Journal of the American Board of Family Medicine in 2010 found that, among a group of 215 participants between the ages of 50 and 89, arthritis was prevalent in about 18 percent of the people who crack their knuckles and in 21.5 percent who don't, making any correlation inconclusive. Probably the most entertaining study on the subject is by a Dr. Donald Unger who, inspired by his mother’s warnings as a child about getting arthritis by constantly cracking his knuckles, spent more than 60 years cracking only the knuckles on his left hand at least twice a day (in this case, the right hand served as his control). His finding, published in 1998 in a journal called Arthritis & Rheumatism, found there was no discernible sign of arthritis in his left hand as opposed to his right.

So don’t listen to what mom says, everybody—feel free to crack away!

What's the Difference Between Stuffing and Dressing?

iStock
iStock

For carbohydrate lovers, nothing completes a Thanksgiving meal quite like stuffing—shovelfuls of bread, celery, mushrooms, and other ingredients that complement all of that turkey protein.

Some people don’t say stuffing, though. They say dressing. In these calamitous times, knowing how to properly refer to the giant glob of insulin-spiking bread seems necessary. So what's the difference?

Let’s dismiss one theory off the bat: Dressing and stuffing do not correlate with how the side dish is prepared. A turkey can be stuffed with dressing, and stuffing can be served in a casserole dish. Whether it’s ever seen the inside of a bird is irrelevant, and anyone who tells you otherwise is wrong and should be met with suspicion, if not outright derision.

The terms are actually separated due to regional dialects. Dressing seems to be the favored descriptor for southern states like Mississippi, Tennessee, South Carolina, and Georgia, while stuffing is preferred by Maine, New York, and other northern areas. (Some parts of Pennsylvania call it filling, which is a bit too on the nose, but to each their own.)

If stuffing stemmed from the common practice of filling a turkey with carbs, why the division? According to HuffPost, it may have been because Southerners considered the word stuffing impolite, and therefore never embraced it.

While you should experience no material difference in asking for stuffing or dressing, when visiting relatives it might be helpful to keep to their regionally-preferred word to avoid confusion. Enjoy stuffing yourselves.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

Why Do Tires Have to Be Filled With Air?

BookyBuggy/iStock via Getty Images
BookyBuggy/iStock via Getty Images

Paul Misencik:

This is an issue that has perplexed me for most of my life, because pneumatic tires filled with air seem like the last anachronistic, 19th-century component of a modern automobile, and an idea which should have disappeared many decades ago. In an era where even the internal combustion engine itself is giving way to electric motors, and where a new economy hatchback has exponentially more computing power than the Space Shuttle, pneumatic tires don’t seem to make sense any longer.

(And before I get flamed, I know modern tires are vastly more advanced and reliable and capable than their 1930s counterparts. Blowouts, which were a common occurrence when I was a kid, are pretty much unheard of today. Modern tires are great, but they are still vulnerable and maintenance-intensive in a way that doesn’t make any sense to me.)

Companies have experimented with non-pneumatic passenger vehicle tires in the modern age—one of the primary drivers was Michelin. But the tires weren’t filled with solid rubber. In fact, they didn’t even have sidewalls. They were open on the sides, and they had a support lattice of structural polyester ribs, with a ton of air space between the contact patch and the (now deformable) wheel.

One of the big problems with switching from pneumatic tires to non-pneumatic tires is the fact that the current air-filled tire is an important component of the suspension of a vehicle. The flex in the sidewall is a critical part of the compliance of the suspension and substantially affects a vehicle's ride and handling. (Which is why race car drivers sweat tire pressures at each corner of the vehicle so much, as even a small change in tire pressure can have a big effect on the handling and grip of a vehicle.)

If a company like Michelin wants to make a non-pneumatic tire, they'll improve their chances of finding success with it if the new design mimics the compliance and flex characteristics of the outgoing, air-filled models as closely as possible. That way, Michelin would be able to sell the new, non-pneumatic design as a retrofit to older vehicles whose suspensions were originally designed with pneumatic tires in mind. And that is hugely important because if they can’t, it becomes much more difficult to convince manufacturers to change over to the new design—particularly after the mild debacle of Michelin’s failed “TRX” metric tire idea of the 1980s, which required the use of a special wheel and which, despite being by most accounts a superior design in almost every way, never really took off. (Owners of 1980s Ferrari 512 Berlinetta Boxers and some Saab 900 turbos will know what I’m talking about here.)

Non-pneumatic Michelin tires are also rather weird looking, and it’s not clear which manufacturers, if any, would take the risk of being the first to offer them on a new car.

So that is the real issue: Any non-pneumatic tire design must be not only clearly superior to the pneumatic designs of the past, but it must be functionally identical to the outgoing models they would replace, and they must be visually acceptable to consumers.

I hope it happens, though. I hope someone cracks the nut. Pneumatic tires are a 19th-century application still being used on 21st-century vehicles, and at some point that needs to change.

This post originally appeared on Quora. Click here to view.

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