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What goes ‘CRACK’?

Spinal Manipulative Therapy or the ‘manual chiropractic spinal adjustment’ is one of the many treatment techniques we use. It is also known as a High Velocity Low Amplitude (HVLA) adjustment. This means moving the joint a very small distance VERY quickly. Sometimes a ‘cracking’ sound is heard. This is called ‘joint cavitation’.

So, what happens during the spinal adjustment?

First a little bit of anatomy is required. The most common joint type in the body is a synovial joint. Every spinal bone (vertebra) has four of these (called spinal facet joints) and you have 24 vertebrae, so that is lot of joints.

The general anatomy of a synovial joint is illustrated here:

For this article the important bits are joint ends of the bones, the joint capsule and the synovial cavity, which contains the cartilage lined joint surfaces and the synovial fluid.

When you move around your healthy joints work in their normal functional range within the physiological zone, limited by the ‘elastic barrier’. Mobilisation or stretching will challenge and bounce on this barrier but it stops short of breaking through it. Beyond the elastic barrier lies the paraphysiological space, which is the safety zone before the joint is damaged. You cannot yourself move a joint into this zone but the chiropractic adjustment does.

As well as applying the correct amount of movement it is equally important that the chiropractic adjustment  is fast enough to beat the stretch reflex, which every muscle possesses. As an example, try tapping your knee just below your knee cap. This stretches your thigh muscles very suddenly causing them to contract. If your lower leg hangs loosely when this is done the lower leg will kick out - the knee jerk reflex. If the chiropractic adjustment is too slow the spinal muscles will start contracting before the adjustment is complete potentially damaging the muscle. I hope that you now can see why it is so important that whoever treats you using HVLA knows what they are doing.


The ‘crack’, which sometimes is heard during the adjustment is thought to occur when the joint surfaces are suddenly gapped and the pressure inside the joint decreases in order to compensate, releasing the gases dissolved in the synovial fluid into the joint cavity and the joint capsule recoils. Once the cavitation has happened the range of movement increases. It takes a little while for the joint fluid to normalise so it can not cavitate for another 30-40 minutes.

Current evidence suggests that some or all of the following mechanisms may be responsible for the observed effects of joint manipulation:

So what other noises may a joint make?

Other noises that may be heard from a joint include tendons of muscles snapping over bony prominences as you move. Most commonly this happens in the wrists, shoulders, hips and ankles. It is not actually occurring in the joint itself but outside it and is usually totally harmless. Another cause of joint noise is more ominous; Arthritis, particularly the wear-and-tear type, Osteoarthritis, can cause grinding gravelly noises, which often lessen with repetitive movement. The noise is caused by wear and tear of the joint surfaces making them rough and unable to glide as easily and as silently as before. A bit like rubbing together two sheets of sand paper.

Is deliberately clicking my joints bad for me?

You may have come across people who keep clicking their joints. Clicking associated with normal movements has never been identified as a cause of arthritis. If you are a regular finger clicker this too is unlikely to be bad for you. One survey in a retirement home found regular finger clickers were less likely to have arthritis.

Some people feel that they can release tension in their shoulders or in their back by regularly contort themselves causing a ‘click’. Rarely does this have a lasting effect and whereas it may be safe to do we have found that people often need to do it more and more frequently with less and less effect. We have also found that advising people to stop clicking themselves (however tempting) in areas they are having treatment more often results in a successful treatment outcome that lasts.

Some people worry that regular chiropractic adjustments may cause joint damage. This has never been shown and in fact the reverse is likely to be true. Joint stiffness which chiropractic treatment removes can cause wear-and-tear changes in as little as 2 weeks.

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