For over a hundred years, the cause of the sound produced when a joint cracks or pops (known as a cavitation) has been poorly understood. Many theories were proposed, but no hard evidence regarding the mechanism was supplied.
In 2015, a team of researchers published a study (known affectionately as the “Pull My Finger” study) that used MRI video to visualize a knuckle as it cracks. They found that as the surfaces of the joint were pulled apart, a cavity was formed. This produced the characteristic “pop” that is heard when joints are cracked.
This means that the current evidence suggests that the chiropractic adjustment is the breaking of a vacuum between the two surfaces of a joint. Chiropractic adjustments have previously been shown to be very effective at decreasing joint pain, increasing range of motion, and decreasing muscle pain and tonicity.
Pull My Finger: Why Joints Crack