I have a daughter who constantly cracked her knuckles when she was younger… and even does it now… mostly to irritate me.
Knuckle cracking is an activity that involves manipulating the finger joints so that a “cracking” sound is created. Sometimes this activity becomes a habit.
The actual physics involved consist of creating negative pressure inside the finger joint by either increasing the bending or straightening of the fingers to the point where the joint space is enlarged. This causes joint fluid (a normal constituent of the finger joint) to travel to the area of negative pressure. Gases that have dissolved in joint fluid form large bubbles. When they are forced into the area of negative pressure inside the joint, the large bubbles collapse into smaller bubbles. This is what creates the cracking sound. The process of creating the cracking sound even has its own name- cavitation!
It has been shown that the amount of force needed to crack the joints is greater than the force required to cause damage to cartilage.
Therefore, the question is… does cracking knuckles lead to arthritis? A recent study reviewed the known data on knuckle cracking (deWeber K, Olszewski L, Ortolano R. J Am Board Fam Med.2011; 24(2): 169-174).
They correlated the duration and total volume of previous knuckle cracking with the frequency of osteoarthritis.
They showed the duration of knuckle cracking, measured in “crack years” had no correlation with either the development or presence of osteoarthritis in the hands.
Despite the warnings issued by generations of mothers to “stop cracking your knuckles!”… it doesn’t appear that this habit is one that leads to significant osteoarthritis in the hands.
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