Most of us have heard myths about how it can cause our joints harm. But what exactly happens when we crack our knuckles and why is there a sound? Between our joints, there is a lubricant known as synovial fluid, which contains nitrogen, oxygen and carbon dioxide. When you pull or crack your joint, they separate slightly and there is more space between the joints. Extra space means reduced pressure, which causes a small gas bubble to appear. This is similar to how opening a can of soda causes gas bubbles on the surface. Previous scientific studies have had differing conclusions about how the crack sound is created. While some believe that this is due to the formation of the gas bubbles others argued that it is due to the gas bubbles collapsing instead. Some Canadian scientists from the University of Alberta decided to settle the dispute once and for all with the help of an MRI scanner—which allowed them to see the entire knuckle-cracking process in detail. The conclusion is that the crack sound you hear is due to the formation of the gas bubble between your joints.
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