Source
The physical mechanism is uncertain, and cracking may possibly arise from several different causes. Suggested causes include:
- Cavitation within the joint—small cavities of partial vacuum form in the fluid and then rapidly collapse, producing a sharp sound. This explains the popping that can occur in any joint, such as during spinal manipulation. Synovial fluid cavitation is the most likely theory and substantial evidence exists in support of it.
- Rapid stretching of ligaments.
- Intra-articular (within-joint) adhesions being broken.
Of these hypotheses, perhaps the most popular is cavitation. When a manipulation is performed, the applied force separates the articular surfaces of a fully encapsulated synovial joint, which in turn creates a reduction in pressure within the joint cavity. In this low-pressure environment, some of the gases that are dissolved in the synovial fluid (which are naturally found in all bodily fluids) leave the solution, making a bubble, or cavity, which rapidly collapses upon itself, resulting in a "clicking" sound. This process is known as cavitation. The contents of the resultant gas bubble are thought to be mainly carbon dioxide. The effects of this process will remain for a period of time known as the "refractory period", which can range from a few seconds to some hours while it is slowly reabsorbed back into the synovial fluid. There is some evidence that ligament laxity may be associated with an increased tendency to cavitate.
Read more about this topic: Cracking Joints
Famous quotes containing the word source:
“It has lately been drawn to your correspondent’s attention that, at social gatherings, she is not the human magnet she would be. Indeed, it turns out that as a source of entertainment, conviviality, and good fun, she ranks somewhere between a sprig of parsley and a single ice- skate. It would appear, from the actions of the assembled guests, that she is about as hot company as a night nurse.”
—Dorothy Parker (1893–1967)
“Concupiscence and force are the source of all our actions; concupiscence causes voluntary actions, force involuntary ones.”
—Blaise Pascal (1623–1662)
“The act of birth is the first experience of anxiety, and thus the source and prototype of the affect of anxiety.”
—Sigmund Freud (1856–1939)