Back Cracking? What makes that “Clicking" noise?

Patients often ask chiropractors what makes that noise when having their spine adjusted. They also make the most interesting comments after having a chiropractic treatment such as “I love the sound of my neck cracking", whilst the terms of endearment for the noises coming from backs and necks with a chiropractic manipulation are interesting and make for good stories around the barbie, there is a lot more to it than a neck "crack" and the source of the sound may surprise you. 

When asked most people believe that the noise heard when having an adjustment comes from the bones rubbing against each other or from tendons gliding over the joint.

The "crack" or cavitation as it is scientifically known is in fact thought to come from the movement of gases within the joint during a manipulation.

To understand this let us run through some very basic anatomy. 

A typical vertebral joint where a cavitation is thought to come from is made of two joint surfaces, these are surrounded by a capsule that helps to support the joint and increase its stability. Inside this capsule there is a substance called synovial fluid which provides lubrication and nutrition to the joint surfaces. The biggest thing to take note however is that the pressure inside the joint is lower than the pressure outside (the joint is at a negative pressure), this is where it gets interesting, as your Chiropractor provides an adjustment to the joint a gap is produced between the two surfaces of the joint causing a vacuum (a space were the pressure is less), this pressure change in the joint causes gas that is normally dissolved in the synovial fluid to rush out of the fluid and into this joint space, this happens at a rapid speed and causes the “pop”. Think like opening a soft drink, just not as unhealthy. The gas is made up of CO2 and is slowly reabsorbed back into the synovial fluid as the pressure changes return to normal. This is the most widely accepted theory for what makes your back go click, with the human body being so complicated its nice to have a small understanding of what's going on sometimes. 

Written by Dr Rory Lester

Brodeur R. The audible release associated with joint manipulation. J Manipulative Physio Ther. 1995 Mar-Apr;18(3):155-64. PMID: 7790795.