1727, from Japanese samurai warrior, knight, originally the military retainer of the daimio, variant of saburai, nominal form of sabura(h)u to be in attendance, to serve..
The bubbles make a noise when they burst. This is called cavitation. Another cause for painless popping in the knee is when the ligaments and tendons catch as they go over a bony lump and pop when they snap back into place. Or the clicking and popping may be caused by catching on soft tissue or scar tissue within the knee.
Finding the Cause. 1  Location: Where on the knee the patient feels pain can offer some clues about what type of injury or condition is causing the pain. For instance, pain on the inside or medial side of the knee (the side closest to the other knee) can be caused by medial meniscus tears, MCL injuries, and arthritis.