What is the danger of floating cartlidge, in the knee?

Loose knee cartilage. Moving around freely inside knee joint may eventually become lodged in the joint space & restrict joint motion. Arthroscopic surgery can locate the piece & remove it as well as smooth out areas of rough cartilage. Surgery done thru 3 holes so recovery is relatively quick.
More wear and tear. Loose pieces of cartilage, especially large pieces can get stuck or can rub on other areas creating increased wear and pain. If the piece is large enough or if there are multiple pieces, your surgeon may recommend arthroscopic removal.