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.
Loosening or Wearing of the Implant. This is most often the cause of pain years or decades after the knee replacement; however, it is seldom the cause of persistent pain right after surgery. Infection. Infection is a serious and worrisome concern. Any increase in pain after knee replacement should raise concerns for infection. Most often, the signs of infection are obvious, but subtle infections may be the cause of persistent discomfort. Kneecap problems are a common cause of knee replacement pain.