If you have been to your Chiropractor or a therapist that performs manipulation you may have already had this subject explained to you briefly. However, this post will hopefully provide you with a little more detail and understanding about why you hear this unfamiliar noise and also reveal whether or not it is even significant!.
If you have not heard of a manipulation before I shall now briefly explain. A manipulation is where a practitioner (such as a Chiropractor) takes a joint that is not moving as it should be and applies a quick thrust to encourage the joint further into the direction in which it is having problems moving. They use this technique so as to:
break adhesions that have formed within the joint
increase the spinal segment’s ability to move and therefore increases that area of the spine’s movement.
increase the brain’s awareness of the manipulated segment so that if there is no problem at the treated level, the brain gets told!. A result of this is a loosening of the muscles in the local area which will then also lead to an increase in movement.
inhibit the pain being felt at the joint, very useful! 🙂
The professional term for the cracking or popping noise that is heard during a manipulation is called an ‘audible release’ and the most commonly followed theory is that this occurs as a result of a ‘cavitation’. A basic definition of a ‘cavitation’ simplified in my own words is “the formation and collapse of bubbles as a result of a change in pressure within a liquid”. The liquid, in the case of your body and of course your spine, is the synovial fluid found between the facet joints. (see pictures below)
Facet Joints can be found between the vertebrae of the spine, the angle of the facets of an individual vertebra will determine its limitations with regard to which directions the vertebra can move.
There are usually two pairs of facets that connect each segment of the spine two on top and two on the bottom.
The synovial fluid is contained by the facet’s capsule acting as a lubricant and buffer for the facet joint during movement
The best way I can have you visualise what is happening during a cavitation is if you imagine a propellor blade under water, when it spins, bubbles appear seemingly out of nowhere. This is due to a rapid pressure change in the water around the blades as a result of the propellor spinning quickly. in the facet joint It is the rapid change in pressure of the synovial fluid as a result of the quick manipulation separating the joint that causes the bubble formation.
The theories behind the noise or audible release (as we call it) vary somewhat. However, the most commonly followed theory by Unsworth et al (1971) is that it is the noise made from the rapid formation of carbon dioxide bubbles within the synovial fluid of the joint during the manipulation. an example which may help is when you have two suction cups stuck together and then take them apart rapidly, the pressure change results in a ‘crack’ or ‘pop’ noise.
Used in combination with other therapeutic techniques, manipulation is a very effective tool in getting you and your spine back to your working best.
Now, Interestingly, research has found that the ‘audible release’ is actually not significant with regards to the outcome and success of a manipulation. So don’t be upset if you don’t hear anything during a manipulation as it isn’t even necessary!. There are multiple irrelevant factors that can affect whether a manipulation will result in a pop or crack from one day to another, even crazy factors such as a change in the barometric pressure of the weather outside!!!. So don’t expect to hear them all the time but also don’t be surprised if you do, they are pretty common ;-).
References: Unsworth, A., Dowson, D., Wright, V., “Cracking joints”. A bioengineering study of cavitation in the metacarpophalangeal joint. Ann Rheum Dis. 1971;30:348-358.
Pictures adapted from (in order): http://www.physioadvisor.com.au/8339150/facet-joint-sprain-facet-joint-pain-back-sprai.htm http://rozeklaw.com/whiplash-neck-injury.htm http://sundialchiropractic.wordpress.com/2010/07/02/what-causes-joint-clicking