The outer tube (1) of the trochar contains a movable boss (2) with a point (8) at the forward end. A concentric chamber in the forward end of the boss contains a sliding protective sleeve (12) spring-loaded into the forward protective position enclosing the boss point. The spring can be a coil one, acting between the inner end of the chamber and the rear end of the sleeve, distorting elastically under the back-pressure from the layers of tissue. Its diameter can be roughly half the external diameter of the boss.
