My knees crack when I stretch my legs

The sound made by joints is not unfamiliar to people. We often hear crackling sounds in our finger joints when we clench our fists. When we stretch or yawn after sitting in front of the computer for a long time, our neck and cervical spine may also make some sounds. The knees may also "pop" when we stretch our legs. This is not a serious disease. It is just caused by too little lubricating fluid between the joints, which increases the friction in the joints, so there is no need to worry too much.

Generally speaking, if there is only a clicking sound without any redness or swelling on the surface, or pain, and no movement disorder, it is physiological clicking and does not require special treatment, nor is there any need to be overly anxious about it. When the joints move, friction and sound will always occur between the articular surfaces, between the cartilage pads and the articular surfaces, between the tendons and the joint capsules, etc.

In most people, this sound is not obvious, but in some people it is clearer. Especially for those who sit for a long time, less lubricating fluid is produced between the joints, which increases the friction loss of the joints and makes it more likely to hear the popping sound. When accompanied by pain or limited joint movement, you need to go to the hospital to determine whether the joint is dislocated or damaged.

People who work at a desk all year round, such as teachers, editors, secretaries, and computer data entry operators, often complain about "pops" in the cervical spine. The popping sound is precisely a reminder for people not to maintain the same posture for too long, but to exercise more. It is best to get up and move around for 15 to 30 minutes.

In fact, the sound produced by the joints can be amplified and recorded by a microphone. Many years ago, domestic doctors developed a joint sound wave recorder that can be used clinically to "listen" to knee joint lesions. The sound of the joints is so loud that it can sometimes scare people. Some recent studies have provided the answer. It turns out that when the joint first moves, the force of the tendon (such as tension, etc.) will instantly cause the joint to deform, which can increase by up to 7%. The deformation creates negative pressure in the joint cavity. Although this negative pressure is small, it is enough to cause the joint capsule to collapse (be sucked in), and to partially vaporize the nitrogen, oxygen, carbon dioxide and other gases dissolved in the synovial fluid into bubbles. When the movement is about to be completed, the bubbles and synovial fluid are compressed, and there is a "pop" sound like popping champagne, which bounces the depressed joint capsule back to its original shape, and the gas dissolves back into the liquid. Also, because it takes time for the gas to dissolve back, the knuckle cracking sound can be repeated but not continuously. Although the study pointed out that these noises are not enough to cause cartilage damage (less than 15% of the energy can damage cartilage), there is no need to worry about it. However, another 35-year follow-up of 350 people who cracked their knuckles for a long time found that these people generally had enlarged knuckles but weakened grip strength. From this it can be seen that those who enjoy doing this should exercise some restraint.

Of course, in addition to this mechanism, noises coming from the knee, ankle or back may also be caused by the taut tendons moving slightly and then bouncing back to their original position when the joints move; or there may be greater friction with the joint protrusions, causing the noises. If there is no redness, swelling, heat or pain, it should generally be no problem.