Science For Everyone: Why Joints Make A Sound When You Crack Them

Science For Everyone: This week, we explain why cracking of joints makes noises such as popping, grinding and snapping. The knuckles, knees, and ankles are the different regions where joints crack. 

Joints cracking sounds: There are various reasons behind why cracking of joints produces a variety of noises. These include the escape of gases, collisions with rough surfaces, and movements of joints, tendons, and ligaments. 

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Joint Cracking Sounds: Welcome back to "Science For Everyone", ABP Live's weekly science column. Last week, we discussed the importance of studying the Sun, how the star helps us, what knowledge we have about the solar system’s only star, and which mysteries still remain. This week, we explain why cracking of joints makes noises such as popping, grinding and snapping. The knuckles, knees, and ankles are the different regions where joints crack. 

There are various reasons behind why cracking of joints produces a variety of noises. These include the escape of gases, collisions with rough surfaces, and movements of joints, tendons, and ligaments. 

Check all the stories appearing in ABP Live's weekly science column here.

Joint fluid, also known as synovial fluid, contains gases such as oxygen, carbon dioxide, and nitrogen. The thick fluid acts as a lubricant and a cushion between the ends of bones, and helps reduce friction when one moves their joints. The joint capsule becomes stretched when one cracks a joint. This causes gaseous particles to be released, and bubbles to be formed. When these bubbles burst, noises are generated. 

Eventually, the gases return to the synovial fluid, and one can crack their joints again.

One cannot crack the same knuckle or joint twice in a row because the gases take some time to return to the synovial fluid.

In most cases, nitrogen bubbles burst, and produce noise. It takes nitrogen bubbles about 20 minutes to return to the synovial fluid. 

The movement of joints also causes a tendon's position to slightly change. When the tendon returns to its original position, one hears a snapping sound. Moving joints also causes ligaments to tighten. These movements usually occur in the knee or ankle. The tightening of ligaments produces a cracking sound. 

An arthritis patient suffers from the loss of smooth cartilage. When the ends of bones collide against each other's rough surface, sounds are produced.

While knuckle cracking is a harmless practice, repetitive cracking can damage the soft tissues of joints. Excessive cracking of knuckles can cause dislocations or tendon injuries, according to Chicago Health. 

For people who suffer from swelling or other joint symptoms, sounds produced by the cracking of joints can be a cause of concern.

When one feels discomfort while cracking, it could indicate a pre-existing condition.

However, if one does not suffer from any pain, swelling or discomfort, they can continue cracking their joints, for this is a "tension-relieving" practice to many, giving them psychological pleasure.