What is the reason for the sound which comes when we crack our knuckles? It gives a kind of pleasant and relaxed feeling after having done that. Is it detrimental to the body in any way? Why can’t it be done again before a certain time has passed?
VAIBHAV RATHI, Pune, Maharashtra
The reasons for the sound which comes when we crack knuckles are cavitation within the joint, rapid stretching of ligaments and intra-articular adhesions being broken. In the joint, ligaments connect the bones to one another and a joint capsule surrounds the whole thing which is filled with a natural lubricant called synovial fluid that helps the joint move smoothly.
When we stretch or bend a finger to pop the knuckle, the bones of the joint pull apart and the connective tissue capsule that surrounds the joint is stretched and the space between the joints increases which in turn creates a reduction in pressure within the joint cavity.
In this low pressure condition, some of the gases such as nitrogen and oxygen that are dissolved in the synovial fluid leave the solution ( an event called articular release ) into the empty space to equalise the pressure and make a bubble or cavity through a process called cavitation. These bubbles merge into large bubbles which in turn get popped by additional fluid which rushes in to fill the enlarged space.
The sound heard is just gas bubbles bursting. Thus cracking or popping of joints is the action of joint manipulation to produce a sharp popping sound. The effects of this process will remain for a period of time called refractive period, during which the joint can’t be recracked for another 25-30 minutes. This gives time in the joint space to return to its normal size while the gas gets reabsorbed into the synovial fluid, ready to form bubbles which can then pop all over again. It has been shown that ligament laxity may be associated with an increased tendency to cavitate.
DR.SAINUDEEN PATTAZHY, Associate professor in zoology, S.N.College. Kollam, Kerala
