Book 10, Question 5
Why Does Cracking Knuckles Make Noise?
Knuckles can make a popping noise because of tiny gas bubbles in the fluid inside your joints! When a joint stretches, a bubble can pop, and you hear a little crack. It is a gas pop, not bones smashing together.
More fun facts
- When you crack a knuckle, the bones separate and a gas bubble forms in the fluid inside the joint.
- X-rays taken after cracking show a gas bubble inside the joint.
- A math model suggests the sound comes from tiny bubbles collapsing as the pressure changes.
- Experiments showed that bubbles can stay in the joint fluid long after the crack.
- Studies going back to 1998 found no link between cracking knuckles and arthritis in the hands.
- Doctors say big joints like the neck and spine need careful handling and should not be cracked roughly.
Sources: Smithsonian Magazine, Scientific American, BBC, National Geographic
Questions kids ask
Does cracking knuckles cause arthritis?
Studies have found no link between cracking knuckles and arthritis in the hands.