Why Does Knuckle Cracking Make a Popping Sound?
Our entire body is made of a skeleton of 206 bones. Bones help in giving shape and support to the body and help us move about. Our bones are not too long otherwise we would not be able to bend or grasp things. Bones fit together at joints which is the meeting place between different bones of the skeleton.
Joints are divided into fixed and movable ones. Most of the joints in our face are fixed, with the exception of the bones of lower jaw which are flexible and move up and down like a hinge. Joints in our elbows, knees and ankles are flexible and we use them all the time to move around.
Bones at these joints are held firm by tissues and ligaments. These are tough cords or straps. Inside each joint is a thin membranous bag that secretes a thick fluid called the synovial fluid. Just like oil lubricates an engine to move slickly, the fluid helps in lubrication and helps the joint move smoothly.
When you stretch or bend your finger the bones of the joint are forced apart. As they move apart, the tissues that surround the joint are stretched.
This increases the volume of space between the tissues. With an increase in volume the pressure in the synovial fluid drops forming bubbles. When the joint is stretched far enough the pressure drops so low that these bubbles burst, producing a popping sound.
It takes half an hour for the gas to dissolve back into the synovial fluid. Once the gas is dissolved it is possible to pop the knuckles again. Lots of people are in the habit of popping knuckles but there is no harm or injury associated with knuckle popping.
Scientists however, have seen signs of tissue damage and a decrease in grip strength in certain cases like professional sports-persons. This damage is a result of repeated stretching of the ligaments surrounding the joint.
Knuckle popping however, does have its positive effects. An increase in mobility is seen in the joints immediately afterwards. When joints are stretched certain nerve endings are stimulated and the muscles surrounding the joint relax.