Our joints contain synovial fluid, a sac of liquid which acts as a lubricant, protecting bones from grinding against each other. When someone cracks their knuckles, they increase the space in the joint, causing bubbles of gas (think oxygen, nitrogen and carbon dioxide) to form in the fluid. It’s the popping of these bubbles that make the cracking noise.
While it may sound worrying, there isn’t actually much evidence to suggest this is dangerous – or increases the risk of getting arthritis. The most important risk factors for developing arthritis are family history, age, gender, joint injury, and lifestyle elements such as smoking and obesity.
It is true that people with arthritis sometimes find their joints crack, but this is because their cartilage has already been damaged. Cracking isn’t usually the most common symptom of arthritis, either.
Although there are isolated reports of self-injury caused from cracking knuckles, such as sprained ligaments, these are very rare. You’re much more likely to harm yourself by cracking joints in your spine and neck, which are surrounded by important blood vessels.
All in all, if you want to stop someone cracking their knuckles, you need to give a better excuse than worrying about their arthritis odds.
Asked by: Katy Wilkins, Aberdeen
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