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!

How Does Alberta, Canada, Stay Rat-Free?

Francisco Martins/iStock via Getty Images
Francisco Martins/iStock via Getty Images

David Moe:

Alberta is the only province in Canada that does not have any rats and is, in fact, the largest inhabited area on the planet that is rat-free. Rats had to come from Eastern Canada, and it’s a long walk, so it was not until the 1950s that they finally reached Alberta. When they did, the Alberta government was ready for them: They instituted a very aggressive rat control program that killed every single rat that crossed the Alberta/Saskatchewan border.

The Agricultural Pests Act of Alberta, 1942 authorized the Minister of Agriculture to designate as a pest any animal that was likely to destroy crops or livestock; every person and municipality had to destroy the designated pests. Where their pest control was not adequate, the provincial government could carry it out and charge the costs to the landowner or municipality.

Rats were designated as pests in 1950. An amendment to the act in 1950 further required that every municipality appoint a pest control inspector. In 1951, conferences on rat control were held in eastern Alberta, and 2000 posters and 1500 pamphlets titled "Rat Control in Alberta" were distributed to grain elevators, railway stations, schools, post offices, and private citizens.

Between June 1952 and July 1953, [more than 140,000 pounds] of arsenic trioxide powder were used to treat 8000 buildings on 2700 farms in an area 12 to 31 miles wide and 186 miles long on the eastern border. Some residents were not informed that arsenic was being used and some, allegedly, were told that the tracking powder was only harmful to rodents. Consequently, some poisoning of livestock, poultry, and pets occurred. Fortunately, Warfarin—the first anticoagulant rodent poison—became available in 1953; Warfarin is much safer than arsenic, and in fact is prescribed to some heart patients as a blood thinner.

The number of rat infestations in the border area increased rapidly from one in 1950 to 573 in 1955. However, after 1959, the numbers of infestations dropped dramatically.

The provincial share of rat control expenses increased to 100 percent in 1975. All premises within the control zone from Montana to Cold Lake are now inspected at least annually. Rat infestations are eliminated by bait, gas, or traps. Buildings are occasionally moved or torn down, and in some cases, rats are dug out with a backhoe or bulldozer. In the early days they also used shotguns, incendiaries, and high explosives to control rats. It was something of a war zone.

Hundreds of suspected infestations are reported each year, but most sightings turn out to be muskrats, pocket gophers, ground squirrels, bushy-tailed wood rats, or mice. However, all suspected infestations are investigated.

A few white rats have been brought in by pet stores, biology teachers, and well-meaning individuals who did not know it was unlawful to have rats in Alberta, even white lab rats or pet rats. White rats can only be kept by zoos, universities, colleges, and recognized research institutions in Alberta. Private citizens may not keep white rats, hooded rats, or any of the strains of domesticated Norway rats. Possession of a pet rat can lead to a fine of up to $5000.

In 2004 someone released 38 rats in Calgary. By the time the rat control officers arrived, most of them were dead. The local residents had formed a posse and killed them with brooms, 2x4s, and shovels. If the authorities had caught the culprit, he could have faced a $190,000 fine (38 x $5000)—assuming his neighbors didn’t get to him with brooms, 2x4s, and shovels first. Albertans don’t want rats.

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

Why Do Students Get Summers Off?

Iam Anupong/iStock via Getty Images
Iam Anupong/iStock via Getty Images

It’s commonly believed that school kids started taking summers off in the 19th century so that they’d have time to work on the farm. Nice as that story is, it isn’t true. Summer vacation has little to do with tilling fields and more to do with sweaty, rich city kids playing hooky—and their sweaty, rich parents.

Before the Civil War, farm kids never had summers off. They went to school during the hottest and coldest months and stayed home during the spring and fall, when crops needed to be planted and harvested. Meanwhile, city kids hit the books all year long—summers included. In 1842, Detroit’s academic year lasted 260 days.

But as cities got denser, they got hotter. Endless lanes of brick and concrete transformed urban blocks into kilns, thanks to what was known as the “urban heat island effect.” That’s when America’s swelling middle and upper class families started hightailing it to the cooler countryside. And that caused a problem. School attendance wasn’t mandatory back then, and classrooms were being left half-empty each summer. Something had to give.

Legislators, in one of those if-you-can’t-beat-‘em-join-‘em moments, started arguing that kids should get summers off anyway. It helped that, culturally, leisure time was becoming more important. With the dawn of labor unions and the eight-hour workday, working adults were getting more time to themselves than ever before. Advocates for vacation time also argued (incorrectly) that the brain was a muscle, and like any muscle, it could suffer injuries if overused. From there, they argued that students shouldn’t go to school year-round because it could strain their brains. To top it off, air conditioning was decades away, and city schools during summertime were miserable, half-empty ovens.

So by the turn of the century, urban districts had managed to cut about 60 schooldays from the most sweltering part of the year. Rural schools soon adopted the same pattern so they wouldn’t fall behind. Business folks obviously saw an opportunity here. The summer vacation biz soon ballooned into what is now one of the country’s largest billion-dollar industries.

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