Surgical instrument (500) comprising: a handle part (510)； a body part (512) extending distally from the handle part and defining a first longitudinal axis； an articulated tool assembly (17) defining a second longitudinal axis and having a proximal end, the articulated tool assembly being arranged at a distal end of the body part and being able to move from a first position, in which the second longitudinal axis is substantially aligned with the first longitudinal axis, up to at least a second position, in which the second longitudinal axis is arranged at an angle to the first longitudinal axis； and an articulation mechanism that includes an articulation connecting rod for articulating the tool assembly, and an articulation button (402) for rotating an interface element, the articulation connecting rod having a groove at a proximal end functionally connected to the element of interface, the rotational movement of the articulation button (402) becoming an axial movement of the articulation rod, thereby articulating the articulated tool assembly； The articulation mechanism also includes a housing block (410), a piston (436) and an articulation spindle (404), the housing block (410) being configured to receive the articulation spindle (404), the fixing being fixed articulation spindle to the articulation button (402) to rotate with it； characterized in that the articulation spindle defines a plurality of notches (434) and that the articulation spindle is configured to rotate in predetermined increments； and the plurality of notches (434) being configured to mechanically interact with the plunger (436), which is preloaded to engage the articulation spindle, such that when one of the notches is aligned with the plunger, the plunger is engaged only to that notch.Instrumento quirúrgico (500) que comprende: una parte de mango (510)； una parte de cuerpo (512) que se extiende distalmente desde la parte de mango y que define un primer eje longitudinal； un conjunto de herramien
