For many years now, there has been a claim that cracking your knuckles leads to arthritis in the future. Although this is a common belief, I still question if it is actually true. I’ve cracked my knuckles for years, despite my mom constantly telling me not to. My mom even went as far as to tell my doctor to tell me to not crack my knuckles. To my surprise though, my doctor said that cracking your knuckles has no correlation with arthritis. Although that made me happy to know, it made me question why such a common idea that arthritis can be caused by knuckle cracking was so easily rebuked by my doctor.
First of all, let me explain why people crack their knuckles and what they are actually doing when they crack them. Amanda Montell, author of the article The Real Reason You’re Addicted to Cracking your Knuckles explains that cracking your knuckles is basically a way to relieve pressure. After sitting in a position for a while, you want to stretch, and this is just a way some people do it. It’s similar to stretching your entire body, but instead it’s your joints. It gives the person a nice feeling, making it habitual and sometimes addictive (Montell 2016). That nice feeling is felt when the person stretches their bones apart, popping the bubble of fluid that builds up between the bones according to Harvard Health Publications’ article called Does knuckle cracking cause arthritis?
If cracking your knuckles is a pressure reliever than why do people associate it with such a bad thing like arthritis? That made me wonder whether if the correlation with arthritis is actually causal or not. There are four possibilities:
- Cracking knuckles directly causes arthritis.
- Arthritis causes one to crack their knuckles (reverse causation).
- There is a third variable that causes both arthritis and the cracking of the knuckles. For example, having a family history of arthritis might cause your arthritis and also stress you out, causing you to crack your knuckles.)
- The correlation between knuckle cracking and arthritis is due to chance alone.
According to Steve Mirsky, author of Crack Research: Good news about knuckle cracking, Donald Unger published a study in 1998 to see if knuckle cracking really causes arthritis. He cracked his left knuckles in his hand twice a day for fifty years. He used the right hand as the control. After all those years, he found that both of his hands were fine, despite the difference in knuckle cracking. This study that he conducted earned him an Ig Nobel Prize (Mirsky 2009.) This study ruled out the direct and reverse correlation between knuckle cracking and arthritis. He established that there is no correlation between the two. Here, Unger failed to reject the null hypothesis, that nothing was going on. Similar to smoking, a person might not smoke but still get lung cancer. Having it only being tested on one person can make the results ultimately due to chance alone. Still though, it is possible that a third variable could cause arthritis and knuckle cracking in another person. Although Unger’s study was long, it was only experimented on one person, himself. If he had conducted it on more than one person, he may have had different results. That being said, although this was experimental, it wasn’t large enough to 100% conclude anything.
That being said, after researching more into this topic, I found a study conducted in 1990 by Jorge Castellanos and David Axelrod. In the study, they gathered 300 people 45 years old or older. They took into consideration third variables like evidence of possible muscular diseases, making sure no participants had them. Of the 300 tested, 226 did not crack their knuckles habitually and the other 74 were knuckle crackers. They took into consideration sex, smoking history, strength and other factors. After taking in all the factors, they concluded that there wasn’t a greater chance of arthritis in the habitual knuckle crackers over the non-knuckle crackers. They did do a further study that found habitual knuckle crackers had greater hand swelling, less strength, did more laborious things, were more likely to be smokers and drink alcohol. They did find that more non-knuckle crackers bite their nails (Castellanos, Azelrod 1990). The fact that non-knuckle crackers were found to bite their nails more may indicate that biting their nails is a way to relieve stress in imposition to relieving stress by cracking their knuckles. This study was observational because they didn’t ask certain people to crack their knuckles, but instead they just observed the effects.
Since the studies above are either observational or experimental but lacking enough evidence, I would want to conduct my own study. The study would be experimental, allowing me to manipulate the x variable. In the experiment, I would randomly select 1,000 students from Penn State. Each of the students would be asked the question, “Do you habitually crack your knuckles?” Based on that question, I would allocate the students into two groups. I would record the students age, history of arthritis, gender and muscular strength. I would then have them crack their knuckles every day for the next seven months. After the seven months, I would record the students hand strength again and also see if there are any possible signs of arthritis. I have to take into consideration though that not all the students may follow the instructions completely. Also I must keep in mind that signs of arthritis will probably not show up, that’s why I will make sure to look for decreasing muscular strength and any swelling that may appear in addition. Although this study is not perfect, you must keep in mind that the correlation between knuckle cracking and arthritis is like cancer and smoking. You won’t see any of the effects right away. That being said, it’s extremely hard to conduct an experiment over many years with many participants. You can’t trust that all the participants will follow the experiment’s rules or even stay in the experimental study for its entirety.
From these studies, I can conclude that knuckle cracking does not directly cause arthritis. Although reverse causation is unlikely, it is still a possibility. There isn’t enough information conducted to conclude that reverse causation is not possible. Both arthritis and knuckle cracking also may be both caused by a third variable like family history that indicates arthritis. Although this has been concluded, I still think that if one can, stopping or decreasing knuckle cracking is a good idea. Although knuckle cracking does not cause arthritis directly, it does cause other things. In an article by Mr. Mercola called Is Cracking Your Knuckles Harmful? he mentions the 1990 study mentioned above. He further explains that knuckle cracking can lead to swelling in the hands and essentially a decrease in grip strength (Mercola 2014). If possible, I think it’s best that one chances their habits to avoid hand issues in the future.
Source 5 (make sure to click the PDF on the right side to view)