It sounds like your surgeon used an arthroscope to enter the joint. This long, slender tool pokes through the skin and tissue right into the knee joint. A tiny TV camera on the
end allows the physician to see inside the joint.
There's a special part of the arthroscope called a cannula. The cannula can be a rigid or flexible tube. It's used to drain fluid or guide other instruments into the joint.
New tools have been made for arthroscopic surgery. There are forceps, shavers, measuring rods, and even tiny drills that can pass through the cannula. Once inside, the doctor uses special foot pedals and hand held devices to guide the camera and operate the tools. Frayed tissue can be shaved smooth. Torn cartilage can be sewn or glued back down. Bone chips can be removed and so on.