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.
Some examples of mechanical problems that can cause knee pain include: 1  Loose body. Sometimes injury or degeneration of bone or cartilage can cause a piece of bone or cartilage to break off and float in the joint space. 2  Iliotibial band syndrome.