One of the biggest barriers to people coming to see a chiropractor about their back problems are the stories that circulate about the sound that occurs when a manipulation (or adjustment) is applied to a joint.
Chinese whispers are where people tell a sequence of repetitions of a story, each one differing slightly from the previous version until final versions have little resemblance to the original story. Sometimes the story becomes so embedded into society that it almost becomes an urban myth. Much has been told about the ‘cracking ‘ ‘popping ‘ or ‘clicking’ sound that occurs when a manipulation takes place to a joint, so I thought it would be good to add a little clarity.
From the diagram below, you can see that a joint in the human body consists of two bones that come
close to each other. At the end of each bone surface there is a layer of protective cartilage (articular cartilage). The articular cartilage then becomes the synovial membrane which attaches to each bone forming a synovial cavity. Now, synovial cavities are surrounded and attached to each bone by a more fibrous layer called the joint capsule. Finally, ligaments surround the joint capsule to give the whole structure some strength.
Movement of any joint causes the synovial membrane to secrete a fluid (called synovial fluid) which helps ‘lubricate the bony surfaces and cartilage of the joint. ‘That’s fine and dandy’ I hear you say to yourself, but what’s that got to do with ‘clicking’ or ‘popping’ of a bone when chiropractors perform a manipulation?
Poor movement of the joint (if it is misaligned) results in poor secretion of the lubricating synovial fluid. The joint begins to dry out and a small ‘gas bubble forms in the synovial cavity. When chiropractors manipulate a joint there are a series of events that take place (some of which are for discussion in later blogs). At the basic level, a controlled force, at the right time, in the right direction applied by the hands of a chiropractor will cause sudden pressure changes in the synovial cavity and the collection of ‘gas’ will escape creating the characteristic ‘crack, ‘click’ or ‘pop’ – just as it would if you pressed on a piece of bubble wrap.
It was never the sound of ‘bone moving on bone’. That’s just an urban myth