What Happens When You Crack Your Knuckles?

By Ehren Allen, DPT/Certified Orthopedic Manual Therapist

Cracking Your Knuckles

What happens when you crack your knuckles? It may be background noise, or it may be like nails on a chalkboard, but there is nothing quite like hearing the sound of someone cracking their knuckles.  As a child, I was a habitual knuckle cracker.  My parents constantly fussed at me about it.  “It’s not good for you” and “you’ll get arthritis,” they would say.  But I couldn’t resist.  It felt good.  I grew up thinking this was a bad habit.  But I never really understood what actually happens when you crack your knuckles.

Image of a happy woman cracking her knuckles at a desk. JOI Rehab

Happy woman cracking her knuckles

What Are The Knuckles?

“Knuckle” is a common term to describe joints in the hands and fingers.  A common joint that people tend to crack is the Metacarpophalangeal joint or MCP.  Some people crack every joint in their fingers.

There are many joints in the hands and fingers.  The bones of those joints are connected by ligaments that allow movement.  A joint capsule also connects the joints.  The capsule is a closed space between the joint’s surfaces that contain a lubricant called synovial fluid.  The lubricant allows for smooth movement as the joint moves during activity.  It also contains nutrients to supply the surfaces of the joint.

Illustration showing the bones of the hand. JOI Rehab

Illustration of the bones of the hand

What Happens When You Crack Your Knuckles?

The quick answer is that cracking your knuckles causes a reaction inside the joint.  The joint capsule houses the lubricant for the joint.  The capsule is a closed structure and does not allow the lubricant out.  The lubricant in the capsule is a thick and viscose material.  As it moves inside the capsule, it can build up little bubbles of nitrogen, oxygen, and carbon dioxide gases.  When you quickly pull, stretch, or flex a joint in the fingers, the joint capsule stretches, and those bubbles can pop.  This is what creates the “cracking” sound.

Does Cracking Your Knuckles Cause Arthritis?

There have been numerous studies performed to determine whether cracking your knuckles causes arthritis.  Many of the studies used ultrasound imaging and MRIs to determine the difference in joints’ health in the hand between those who crack their knuckles and those who do not.  Overwhelmingly, studies show no significant difference in the incidence of osteoarthritis between knuckle crackers and non-knuckle crackers.  So the answer is NO, cracking your knuckles does not cause arthritis.

Click here to read more about Arthritis of the Hand.

Image of elderly hands that have arthritis in the hand bones. JOI Rehab

Arthritis of the Hands

Is Cracking Your Knuckles a Bad Habit?

Knuckle cracking is definitely a habit for many.  One reason is that it feels good.  When the bubbles are popped, there can be an immediate increase in the movement of the joint.  This is because the gas bubbles take up space.  When they release, there is more room for movement, at least temporarily.  The bubbles re-form, and the joint can be popped again soon.

But there may also be a chemical reason that it feels good.  When the joint pops, natural chemicals can be release call endorphins.  Endorphins are “feel good” chemicals in your body.  This chemical release may also be part of what makes cracking your knuckles a habit.

But is it a bad habit?  It depends on who you ask.  Cracking your knuckles can be an annoyance to others, but there is no significant evidence that it causes any harm to the joints of the hands and fingers.

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