Everything about Cracking Joints totally explained
Cracking joints is the practice of manipulating one's
joints such that they produce a sharp
sound, likened to cracking (also likened to popping, etc.). The most common form of this occurs during
knuckle cracking, a process different from
snapping one's
fingers. It is possible to crack other joints, such as vertebrae.
Causes
clicking sounds, many people bend their
fingers into unusual positions. These positions are usually ones that their own muscles are unable to achieve, and which are not commonly experienced in everyday use. For example, bending a finger backwards away from the palm (into
extension), pulling them away from the
hand (distraction), compressing a finger
knuckle toward the palm (into
flexion), or twisting a finger about the first bone's axis (torsion).
Cracking within the body may also be caused by a
breaking bone.
The snapping of tendons or scar tissue over a prominence (as in
snapping hip syndrome) can also generate a loud snapping or popping sound.
Source
The physical mechanism is as yet unproven, but suggested theories include:
- Cavitation within the joint—small cavities of partial vacuum form in the fluid 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. (Discussed in detail below.)
- Rapid stretching of ligaments.
- Intra-articular (within-joint) adhesions being broken.
Of these theories 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 creating 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
nitrogen. The effects of this process will remain for a period of time known as the "
refractory period", which can range from a few minutes to some hours while it's slowly reabsorbed back into the
synovial fluid. There is some evidence that ligament laxity may be associated with an increased tendency to cavitate.
Repercussions
A single event isn't enough to cause damage to the joint, although there's a hypothesis that prolonged joint stress due to cracking knuckles may eventually lead to a higher risk of joint damage. However, the long-term consequences of this practice have not been studied thoroughly, and the scientific evidence is inconclusive. In a letter to the editor, Dr. Donald L. Unger reported to have spent fifty years cracking the knuckles of only his left hand twice daily. After this time his hands were found to have no noticeable differences and no arthritis had developed. (Note that this isn't a serious scientific study, and results can be only generalized to "knuckle-cracking physicians with a lot of time on their hands" as the article states half-jokingly). The common parental advice "cracking your knuckles gives you
arthritis" isn't supported by any evidence, but habitual knuckle crackers are more likely to have hand swelling and lower grip strength attributed to stretched tendons.
Further Information
Get more info on 'Cracking Joints'.
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