By Kaelie Rivers Breiter
My husband does it, my son does it, my daughter does it. Snap, crackle, pop, it’s annoying and like nails on a chalkboard. Cracking knuckles is absolutely my number one pet peeve. I constantly bark, “Knock it off! It's going to give you arthritis, please stop!”—half saying it to scare them but half thinking I swear I've heard that somewhere before. It's an annoying habit that I wish my family would realize and stop. So I wondered, What exactly happens when the knuckle is “cracked”? Are there any long term effects? Why do people do it?
First, the medical term for cracking your knuckles is defined as manipulating one’s joints to produce a distinct cracking or popping sound. During my investigation, I found when the finger is pushed forward or backward (doctors call this hyper-flexion or hyper-extension at the metacarpophalangeal joint) or pulled hard outwards, the space between the finger joints are stretched and cause the “cracking” noise. More specifically, these movements cause a negative or decrease in pressure change in the joint. The pressure change causes tiny gas bubbles to form in the fluid around the joints, which are called synovial joints and are surrounded by fluid-filled capsules. The cushioning synovial fluid—which is located between your synovial joints—is there for lubrication and is made up of dissolved gases: mostly nitrogen. The fluid lubricates your joints like motor oil in a car’s engine, reducing friction and preserving cartilage as it allows your fingers to move in different directions without causing pain. When you crack your knuckles, you stretch the space between your finger joints, which causes the bubbles in the fluid to collapse and create a popping sound. When the bubbles collapse they give off carbon dioxide. The gases take about 20 minutes—also known as the refractory period, or the amount of time that needs to pass until a person can crack their knuckles again—to reform back into the synovial fluid before a person can begin cracking again. A person may feel like he or she has more mobility in his or her fingers as it feels like the pressure has been relieved, but there is no evidence to support this.
How do we know if cracking knuckles has any effects on your hands? Is it harmless? Yes, it is harmless for the most part as there is plenty of scientific research to back it up. A 2011 study published in the Journal of the American Board of Family Medicine looked at 215 people between ages 50 and 89 with an examination of their right hand over the past five years. The researchers found a similar incidence of knuckle osteoarthritis in any one joint among people who said they cracked their knuckles and those who didn’t, no matter how frequently or for how many years the person cracked their knuckles. I also found in my research that there was an experiment a California doctor did on himself where he regularly cracked the knuckles on only one hand for 60 years. He checked his X-rays on his hand after years of this behavior and found no difference in arthritis between his hands. Similarly, there are other studies that have come to the same conclusion. But at the same time in my investigation, I found that there are a few rare medical supports that suggest some problems with this habit that may relate to how much force is applied and a person’s specific technique. For example, joint dislocation and tendon injuries have been described after attempts to crack knuckles. A study published in 1990 found that 74 people who regularly cracked their knuckles, found that their average grip strength was lower and there were more instances of hand swelling than among 226 people who did not crack their knuckles. The incidence of arthritis was the same in both groups. I also found that bending the fingers to crack them can wear away the cartilage over time if a person does it repeatedly.
So why does my husband do it, my daughter and my son? I have asked them and they don’t have a great reason other than to say it is a habit they cannot seem to break. I looked into why people do it and found there were some definitely interesting reasons. The sound it makes is something people like to hear when they do it. Others say they like the way it feels. People claim it relieves tension in their joints and that it feels like they can move their fingers easier. Like I stated previously, there is no evidence supporting this, but that might be hard to verify. Next others say it is a way to occupy their hands when they are nervous, like bouncing your leg up and down, or twirling your hair. Stress is another explanation, as it’s something to take it out on. Or cracking your knuckles can be a diversion from the real stress you are experiencing. Lastly, once you start doing it and not realizing it, it becomes a bad habit. When you find yourself unconsciously cracking your knuckles many times a day, it becomes a habit; people who crack their knuckles five times a day or more are consequently called habitual knuckle crackers.
My original motive for investigating this topic was to get my family to stop cracking their knuckles. I cannot, however, tell them anymore that it causes arthritis, as it does not. To reiterate, the popping or cracking noise is due to the collapse of nitrogen bubbles in the joints, and there are many reasons why people might do it. I believe for my family it is a nervous act for my daughter, a stress reliever for my husband, and an annoying habit for my son. I can still tell them, though, to “Quit cracking your knuckles! You can strain your tendons, which might cause weakness or swelling, or you can dislocate your fingers!”
Supplementary Questions:
Why do knuckles crack?
What is the synovial fluid?
Does cracking knuckles cause arthritis?
Name a reason why people crack their knuckles?
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