A tourniquet in knee surgery is an inflatable wrapping which goes around the upper thigh to stop blood flow during an operation.
Tourniquets and exsanguinators: a potential source of infection in the orthopedic operating theater? Brennan SA, Walls RJ, Smyth E, Al Mulla T and O'Byrne JM. Acta Orthop. 2009 Apr 29; 80(2): 251–255.