Why Knuckles Crack and Joints Creak

Some peoples' bodies play a percussive symphony of cracking and creaking, thanks to the large orchestra of noise-making human joints. But what's behind it all?

The concerto comes from the pop of gas bubbles escaping the joints, snapping tendons and ligaments and rickety arthritic joints.

Joints come in a variety of shapes and sizes. The pivot joint lets us say "No" with our heads, while the hinge joint lets us swing our elbows and knees like a door.

A baseball pitcher uses the tremendous range of motion of the ball-and-socket joint in his shoulder to throw fastballs. And sliding joints in the backbone make gymnasts' backs so flexible.

Releasing gas

A protective fluid cushions most of the joints in our bodies.

Inside a capsule that safeguards bones connected at a joint, synovial fluid keeps the cartilage, tissues and muscles lubricated and well nourished. Nutrients float inside the fluid, along with gases, such as oxygen, nitrogen and carbon dioxide.

As you bend your fingers, the joint capsule stretches. To make more room for the stretch, gases are released from the fluid. The pop of your knuckles is the sound of gas as it bubbles out of the fluid, scientists say. Before your knuckle can crack again, the fluid must reabsorb the gas.

More to it

Tendons and ligaments make a loud racket too.

Tendons are like rubber bands stretched over joints that keep muscles attached to bones. Similarly, ligaments extend to connect bones to other bones. Sometimes, tendons and ligaments slide out of their spot at the joint and then quickly snap back into place.

If your knee cracks when you stand up from sitting on the couch, you're likely hearing your tendons and ligaments popping into proper position around your knee's joints.

Arthritic joints not only cause pain, they can creak as well.

Connecting bones loose their smooth cartilage and grow spurs on their edges. The amount of synovial fluid also increases, making the joint feel stiff and sore.

Okay to crack 'em?

Scientists have conducted few studies on whether cracking your knuckles can cause arthritis or otherwise harm your hands.

Some studies suggest that you can snap your knuckles all you wish, and it won't cause osteoarthritis.

However, other studies indicate that around-the-clock cracking may damage the soft tissue around the joints, make your hand swell and weaken your grip.

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