When people crack their knuckles, they experience a release of pressure in the joints and relaxation in the surrounding muscles. It can make the joint feel more mobile and is unlikely to cause arthritis or other problems.

Joints can make popping, cracking, creaking, grinding, and snapping sounds — especially the joints in the knuckles, knees, ankles, back, and neck.

The sounds can stem from several factors, and they can be startling. Some people wonder whether cracking joints, especially those in the knuckles, can cause or worsen arthritis.

Over time, various researchers have found that 25–54% of people crack their knuckles and that men are more likely to do it habitually than women. It is sometimes a nervous habit.

In this article, learn whether knuckle-cracking has any link with arthritis, what the sounds actually indicate, and why people do it.

Experts have several theories about what causes the noises when joints crack or pop.

Synovial fluid bubbles

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One theory involves gas bubbles popping. When a person extends a joint, this lowers the pressure inside it, releasing any gases, such as carbon dioxide. This gas is released as a bubble.

Cracking joints may create a vacuum that the gases then fill. And when a person pulls a finger to crack their knuckle, for example, the sudden, dramatic increase in surrounding pressure pops the gas bubbles, partially or totally, making a sound.

This formation and collapse of bubbles is called “cavitation.” Synovial fluid is fluid within joints.

Cavity formation

The authors of one 2015 study concluded that the cracking or popping sound results from the formation of cavities. They came to this conclusion after looking at what happens when joints crack on MRI scans.

The scientists inserted volunteers’ fingers into a flexible tube that they used to apply traction to the joint. They then cracked the joint while taking images at 3.2 frames per second.

The results showed the rapid creation of a cavity in the joint at the point of separation, and the cavity remained visible after the noise had stopped.

Tendons snapping over joints

Tendons keep muscles attached to bones, while ligaments connect bones to other bones. Ligaments can make popping noises when they tighten while the joint is moving. Tendons can make a popping noise when they move out of place and snap back into position as the joint moves.

People often hear these noises in their knee and ankle joints when they stand up from sitting or while walking up or down the stairs.

Joint instability

A popping sound in a joint such as the elbow may result from instability or looseness, the American Association of Orthopedic Surgeons points out. A person might also find that the joint catches as they move.

If the sound of a joint cracking occurs with any pain, this may indicate damage to the joint and possibly a tear in the cartilage that cushions it. Anyone experiencing this should consider contacting a healthcare professional.

Knuckles may be the joints that people crack the most often. A person might do this by:

  • bending their knuckles backward or forward
  • turning them sideways
  • pulling on the bones around the joint

While a person might be concerned that this causes arthritis, several studies have concluded that any association is unlikely.

One physician researched his own knuckle cracking, in response to complaints from his family. He cracked the knuckles of his left hand at least twice a day for 50 years, but not those of his right hand.

The doctor did not develop arthritis in either hand, and he reported that there were no differences between the two hands. He concluded that knuckle cracking was not linked to arthritis.

A 2011 study tracked the development of arthritis in 215 people, 20% of whom cracked their knuckles regularly. Among this group, 18.1% of the participants developed arthritis in their hands, compared with 21.5% of the participants who did not crack their knuckles. The researchers concluded that the risk of developing arthritis is roughly the same, whether or not a person cracks their knuckles.

Joint manipulation stimulates a set of nerve endings, called the Golgi tendon organs, which are involved in the sense of motion.

These sit where the tendons join the muscles, and they respond to changes in muscle load. When a person cracks their joints and these nerve endings are stimulated, the person experiences a sense of release of pressure in the joints. This can also cause the muscles around the joint to feel more relaxed and the joint to feel more mobile.

Cracking or popping joints does not seem to be linked to any health issue — unless the person also has pain and swelling in the area. In this case, it may be a good idea to contact a healthcare professional.

Otherwise, as one group of doctors put it, “The chief morbid consequence of knuckle cracking would appear to be its annoying effect on the observer.”

Because it stimulates nerve endings, cracking or popping joints may cause a feeling of released muscle tension and increased mobility.

There is no evidence that manipulating the joints in this way causes any health issue, such as arthritis. However, if a joint pops, clicks, or cracks, and there is pain or swelling in the area, it may be a good idea to seek medical advice.