QUESTION: “Hi Dr. Neal, what happens physically when you crack your knuckles? There's been a lot of debate about it recently. Thank you.”
DR. NEAL: Thank you so much for taking the time to send in your audio question. And thank you so much for listening to the show.
You’re right that there has been quite a debate about what happens when we crack our knuckles and whether it’s harmful to do so. In fact, studies have found that between 25 and 50% of people regularly crack their knuckles.
So, this is definitely a common habit. Now, here’s what happens when we crack our knuckles.
What Happens When We Crack Our Joints
In between our joints, like our knuckles, we have this specialized fluid called synovial fluid. This synovial fluid is important because it acts as a lubricant so the joints can move without rubbing against each other when we move them. This synovial fluid also provides nutrients to those areas. What does this fluid have to do with knuckle cracking? I’m getting there, I promise.
In our finger joints, bubbles can start to form. There’s actually a fancy medical term for this called tribonucleation. Anyhoo, these bubbles come from gases the body creates naturally as part of our metabolisms. After all, we’re constantly exchanging oxygen, carbon dioxide, nitrogen and other gases as part of our daily functioning.
Cracking our knuckles is actually a bursting of these naturally formed gas bubbles. It’s like popping bubble wrap. Now imagine you or someone else cracking their knuckles. They usually extend their fingers in some way, right? They either flex or pull on their fingers. This pulls the bones apart. By pulling the bones apart, it creates negative pressure. Negative pressure creates a vacuum to pull gas into the synovial fluid. This bubble then bursts which creates the popping sound we hear.
Now, have you ever noticed that knuckles can’t be cracked over and over again? It’s like, once you’ve cracked them, you have to wait a while to crack them again.
Why? It’s because it takes time for those bubbles to get pulled into the synovial fluid again. Some estimates say we can’t re-crack our knuckles for at least 15 minutes.
Is It Harmful To Crack Our Knuckles?
Usually, when I talk about knuckle cracking, people want to know if this is a harmful habit. I often get asked whether cracking knuckles will lead to arthritis. Luckily, it doesn’t. In fact, studies show knuckle crackers have the same function, grip strength and range of motion as those who don’t crack their knuckles.
The one potential side effect is that the cartilage around the area can become thicker over time. But basically, cracking knuckles is neither helpful nor harmful to the health of our joints.