By: Sophie Gabreldar
The joints in our bodies can make a variety of different noises, from popping all the way to cracking. The technical term for these noises is “crepitus”, from the Latin word of “to rattle.” People of all age can experience crepitus, but it becomes more common with old age.
What Causes Crepitus?
Air bubbles forming in the joint spaces are usually the cause of the popping noises. This noise occurs at the joints where there is a layer of fluid separating the two bones. Joints can move apart through everyday movements, or deliberately by the hands of a professional. When this happens, the low pressure in the joint space causes gases within the synovial fluid (a natural lubricant in the joint) to form a gas cavity, which contains oxygen, nitrogen and carbon dioxide.
When the formation of the cavity, that is what causes your joints to crack. While the noises this makes may be alarming, this usually perfectly normal.
Historically, there has been lots of debate about how this air bubble causes the popping noise. A study done in 1947 was the first time researchers attempted to understand it. They concluded that the bubbles were formed after a cracking noise was produced. In contrast, another study claimed that the noise actually resulted from the bubble bursting.
The scientific conflict produced much debate and was not resolved until a 2015 real-time medical imaging study of joint spaces proved that it is the formation of the bubble that creates the noise. It then takes a while for the gases to re-accumulate, which is why you cannot immediately crack your knees or knuckles again.
Another study created a mathematical model of a knuckle that helped confirm that the noise comes from collapsing gas bubbles.
Any Cause For Concern?
People are often told in childhood that if you crack your joints, you will give yourself arthritis. One study published in 1990 found that among 74 people who regularly cracked their knuckles, their average grip strength was lower and there were more instances of hand swelling than among 226 people who did not crack their knuckles. However, the incidence of arthritis was the same in both groups.
If there is no pain, swelling, or other joint symptoms, there is probably nothing to be concerned about.
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