What makes the sound when we crack our knuckles?
Your joints, including those in your knuckles, are surrounded by a membrane called the synovial membrane. Inside this membrane is synovial fluid, which acts as a lubricant and shock absorber so that your bones don’t grind together when you move.
When you 'crack' your knuckles or any other joint, it expands the space between your bones, creating negative pressure that draws synovial fluid into the new gap.
This influx of synovial fluid is what causes the popping sound and feeling when you crack a knuckle. If you continually crack your knuckles, it may cause some injuries.
