Anatomy

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What Causes Your Knuckles to “Crack”?

Last Modified Date: February 08, 2024

Cracking your knuckles can be a pleasurable experience, as it can create a feeling of looseness and increased mobility for a short period of time, but it can also be a source of extreme annoyance for other people in the room. Have you ever wondered what causes this sound? Turns out, the cracking sound made by knuckles and other joints is caused by the popping of nitrogen gas bubbles in synovial fluid.

Dr. Robert Klapper, orthopedic surgeon and co-director of the Joint Replacement Program, explains that many joints contain small gaps or pockets that are filled with synovial fluid, which helps bones connected to joints glide close to each other without any grating or friction. When a person cracks their knuckles, the volume of space between their joints expands. Synovial fluid fills this space. Gas is rapidly released, creating nitrogen bubbles. Klapper states that it takes 20 minutes for these bubbles within the synovial fluid to reform before a person can "crack" the joint again.

The cracking sound made by knuckles and other joints is caused by the popping of nitrogen gas bubbles in synovial fluid.

There have long been myths and superstitions about cracking your knuckles, including the myth that it will cause arthritis. In truth, it will not cause any serious harm. If someone does experience pain while cracking their knuckles, it could be a sign of a preexisting condition that requires medical attention.

Take a crack at it:

In a recent study, radiologist Robert D. Boutin from the University of California oversaw an ultrasound imaging study conducted on a group of participants that recorded audio and visual evidence of knuckle cracking. During the cracking of a person’s knuckle, a bright light on the ultrasound flashed, like a firework inside the joint.

Boutin concluded, “We’re confident that the cracking sound and bright flash on ultrasound are related to the dynamic changes in pressure associated with a gas bubble in the joint.”

According to research, men are more likely to crack their knuckles than women.

While cracking your knuckles has no correlation with arthritis, some studies have indicated that habitually cracking your knuckles can cause soft-tissue swelling and loss of grip strength over time.