There are really several reasons that our knuckles crack. But before we get into the details, let’s get a better understanding of just what knuckles are.

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The body is made up of hundreds of bones, many of which are connected at the joints. The knuckle is a joint. These joints must move to allow us to bend, stretch, reach etc. In a healthy person the joints have padding and a small amount of lubrication that allows them to move without causing pain or extensive damage.

The skeleton is held in place by tendons and ligaments that change position when we move. If a joint moves because of bending or reaching, the connecting tendons and ligaments must move also. For example, when we bend our fingers, small connecting tendons move slightly out of position and then must return to the original spot. Some studies show that these tendons making a snapping sound sometimes.That may be one reason we actually hear knuckles and other joints make a cracking sound.

Over the course of several decades, scientists have also discovered that joints have a fluid that helps us move smoothly and lubricates our joints to reduce wear and tear. Like all materials in nature, this liquid contains different gases, such as nitrogen, carbon dioxide and oxygen.

Movement causes changes in the position of the liquids and even compresses the liquid and gases. The bubbles of gas pop. This is a major reason for the sound of knuckles “cracking, especially when someone does this on purpose.

One more element comes into play when our joints, including the knuckles, make this cracking sound. As we get older our joints aren’t lubricated as well as they were when we were young. As the padding (cartilage) wears away and the tendons/ligaments stretch, the bones develop rough edges and rub together. This can add to any sound we hear when we move.

It isn’t necessary to be concerned about occasional “popping” and “cracking” from the joints. But if we feel consistent pain when moving, it may be time to talk to a doctor or other medical professional. The cracking sound from our knuckles is usually not an indication of any serious problems. However, some people crack their knuckles on purpose and this may damage the joints.

We have established that the sound of knuckles “cracking” and other joints “popping” and “creaking” is due to three basic things: quick movement of tendons, gas bubbles popping after being compressed and rough surfaces that come with aging that grind when we move.

The knuckle is one of the joints that bends smoothly in a healthy person. The knuckle isn’t design to rotate as the shoulder and hip joints might. But even the simple task of bending in one direction and returning to the original position is enough to cause gases to compress and tendons to snap. If a person tries to pop his or knuckles on purpose, the gases are forced out of the liquid lubricant. It must be absorbed back into the liquid again before we can hear the popping/cracking sound again the next time we “crack” our knuckles.


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Lucas Beaumont
Generalist. Wikipedia contributor. Elementary school teacher from Saskatchewan, Canada.

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