Q. My friend is constantly cracking her knuckles. Is it bad for you to do this?
A. The most popular explanation for the the mechanics of what is happening during the process of “popping your knuckes” is called “cavitation”. When a manipulation is performed of the knuckles, the applied force separates the joint surfaces of a fully encapsulated 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. 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 joint fluid.
The long-term consequences of this practice have not been studied thoroughly, and the scientific evidence is inconclusive. The common parental advice “cracking your knuckles gives you arthritis” is not supported by any evidence. However, some doctors would argue that habitual knuckle crackers are more likely to have hand swelling and reduced grip strength attributed to stretched tendons. It is unknown whether these effects are caused by knuckle cracking or if knuckle cracking is a symptom, as it relieves excess pressure in joints.
So to answer the question simply, it is probably not a legitimate reason to tell somebody to stop “cracking their knuckles” because it is “bad for them.” A more legitimate reason would be to ask them to stop because it annoys you.
Brian Smith M.D.
Board Certified Orthopedic Hand Surgeon
Center for Sports Medicine and Orthopaedics
2415 McCallie Avenue
Chattanooga, TN 37404