Most people familiar with spinal manipulation as a helpful treatment of spinal problems have experienced a clicking sound during treatment. A doctor of chiropractic presses on your neck or back and, click, something happened. Later when someone asks you what happened at the doctor, you respond, “my neck popped,” or “my back clicked.”
But what is actually happening? Where does the sound come from? The objective of a spinal manipulation (aka chiropractic adjustment) is to increase motion of specific joints in a specific direction. Every joint in our body has a designed amount of motion in a certain direction for healthy functioning of that joint and the joints around it. When a specific joint or group of joints are restricted in their motion from swelling, scarring, capsule tightness, or surrounding muscle tension, the mechanics the kinetic chain are altered. Like links in a chain, if one becomes stuck, the adjacent joints move more than their design allows. The resulting imbalance of joint motion causes joint swelling, muscle tension, and eventually, pain.
The solution, therefore, is to treat the joints that are restricted in a certain motion. When one has a tight muscle, it needs to be stretched, and a series of stretching gives improved length to the muscle. When one has a restricted joint, it needs to be manipulated, and a series of manipulations gives improved motion to the joint.
During manipulation, the sound of a joint clicking is ancillary to the treatment. The inside of most joints are at a negative pressure with fluid holding the joint surfaces together. (This phenomenon is modeled by water between two plates of glass; the plates slide easily but cannot be pulled apart.) Manipulation causes the joint to gap, pulling gas from the solution (like a bubble forming in soda). It takes about 20-30 minutes for the joint fluid to reach equilibrium again; it cannot click during this time. Some manipulation techniques do not cause a click, but all are performed to improve a specific direction of joint motion.