The Real Reason Behind Knuckle Cracking Explained

Knuckle Cracking

To understand that first, you need a little background about the nature of the joints of the body. The type of joints that you can most easily “crack” is the Diarthrodial Joints. They consist of two bones that contact each other at their cartilage surfaces. These are surrounded by a joint capsule. Inside it is a lubricant; Synovial Fluid. The fluid contains dissolved gases, including oxygen, nitrogen and carbon dioxide. The easiest joints to pop are the ones in your fingers.

What happens when you “crack” your knuckles or any other joint?

When you pull or bend your fingers, you stretch that fluid-filled capsule. This decreases pressure inside the gas-packed fluid, causing a small nitrogen bubble to form and then instantly pop. The collapsing bubble is what causes the audible crack that we hear.

The gases take about 20 minutes to fully dissolve back into the fluid. That’s the refractory period— the amount of time that needs to pass until you can get cracking again. The joint cannot be cracked again until the gases have dissolved back into the synovial fluid, which explains why you cannot crack the same knuckle repeatedly.

How can releasing such a small quantity of gas cause so much noise?

Researchers have estimated the energy levels of the sound by using accelerometers to measure the vibrations caused during joint popping. The amounts of energy involved are very small, on the order of 0.1 milli-joules per cubic millimeter. Studies have also shown that there are two sound peaks during knuckle cracking, but the causes of these peaks are unknown. It is likely that the first sound is related to the gas dissolving out of the solution, whereas the second sound is caused by the capsule reaching its length limit.

Does popping a joint cause any damage?

One study found no correlation between knuckle cracking and osteoarthritis in the finger joints. Another study, however, showed that repetitive knuckle cracking may affect the soft tissue surrounding the joint. Also, the habit tends to cause an increase in hand swelling and a decrease in the grip strength of the hand.


Another source of popping and cracking sounds is the tendons and ligaments near the joint. Tendons must cross at least one joint in order to cause motion. But when a joint moves, the tendon’s position with respect to the joint is forced to change. It is not uncommon for a tendon to shift to a slightly different position, followed by a sudden snap as the tendon returns to its original location with respect to the joint. These noises are often heard in the knee and ankle joints when standing up from a seated position or when walking up or down the stairs.

If you’re committed to leaving your knuckle-cracking habit behind you, a certain level of willpower is also necessary. But know that if you still crack a couple times a day, our docs say you’ll be just fine.

“Like all things in life, moderation is key”, So feel free to crack your knuckle while reading this post.

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