The invention relates to a hydraulic traction apparatus for surgery, in particular for knee surgery, having at least one pair of working sections which can be adjusted relative to one another and at least one exchangeable piston in cylinder arrangement made of plastic whose piston is releasably coupled to the one working section and whose cylinder is releasably connected to the other working section and which is stiffened by an outer support mount supporting the cylinder from the outside and by at least one inner reinforcement insert which can be inserted into the cylinder together with the piston.