The popping sound in the knee when bending is commonly caused by the release of gas bubbles in the joint fluid, a process called cavitation. This is normal and usually harmless, similar to cracking knuckles. Changes in joint pressure during bending cause gas bubbles in the synovial fluid to rapidly collapse, creating a popping or cracking noise. Other causes can include patellar tracking issues where the kneecap moves out of alignment, cartilage wear or damage (as seen in osteoarthritis), or ligament and meniscus injuries that cause clicking or popping with pain or instability. If the popping is painless and not accompanied by swelling or difficulty moving the knee, it is often nothing serious. However, if there is pain, swelling, or instability, consulting a healthcare professional is advised to check for possible injuries or conditions like ligament tears, meniscus tears, or arthritis. In summary, knee popping when bending is often due to harmless gas bubble release in the joint fluid, but can also be caused by mechanical issues or injuries that may require medical evaluation if symptomatic.
