When an adjustment is delivered to a joint, there is a brief expansion of the volume of this closed-volume space. The negative pressure created, briefly, by this procedure can result in the formation of a nitrogen gas bubble from the synovial fluid that lubicates the joint/cartilage surface. The formation of this bubble produces the cracking noise. This is similar to what happens when a person “cracks” their knuckles. This nitrogen gas bubble resorbs into the synovial fluid within 15-20 minutes.
