A medical instrument (60, 160, 260, 360) comprises at least one frame and one jointed device (70, 170, 270) comprising at least one first joint member, suitable to connect to at least one portion of said frame, and at least a second joint member, wherein said first joint member is connected via a rotational joint to said second joint member; said rotational joint being suitable to permit a relative moment of rotation between said two joint members around a first axis of joint movement (P-P); said medical instrument (60, 160, 260, 360) also comprises at least one tendon (90; 190), suitable for moving at least said second joint member with respect to said first joint member, by pulling it; wherein at least one of said first joint member and said second joint member comprises at least a sliding surface (40, 80, 140, 180), suitable to allow the sliding of at least one portion of said tendon (90; 190) over it; characterized in that: said sliding surface (40, 80, 140, 180) is a ruled surface formed by a plurality of portions of straight lines all parallel to each other and substantially parallel to the first axis of joint movement (P-P); and wherein the jointed device (70, 170, 270) is obtainable as according to a method of manufacturing comprising the steps of: providing a machining fixture on an electro discharge machine having a an electrical discharge wire and arranging a plurality of workpieces on said machining fixture, and cutting the desired geometry on said workpieces with cutting lines parallel to each other. said first joint member is connected via a rotational joint to said second joint member; said rotational joint being suitable to permit a relative moment of rotation between said two joint members around a first axis of joint movement (P-P); said medical instrument (60, 160, 260, 360) also comprises at least one tendon (90; 190), suitable for moving at least said second joint member with respect to said first joint member, by pulling it; wherein at least one of said first joint member and said second joint member comprises at least a sliding surface (40, 80, 140, 180), suitable to allow the sliding of at least one portion of said tendon (90; 190) over it; characterized in that: said sliding surface (40, 80, 140, 180) is a ruled surface formed by a plurality of portions of straight lines all parallel to each other and substantially parallel to the first axis of joint movement (P-P); and wherein the jointed device (70, 170, 270) is obtainable as according to a method of manufacturing comprising the steps of: providing a machining fixture on an electro discharge machine having a an electrical discharge wire and arranging a plurality of workpieces on said machining fixture, and cutting the desired geometry on said workpieces with cutting lines parallel to each other. said sliding surface (40, 80, 140, 180) is a ruled surface formed by a plurality of portions of straight lines all parallel to each other and substantially parallel to the first axis of joint movement (P-P); and wherein the jointed device (70, 170, 270) is obtainable as according to a method of manufacturing comprising the steps of: providing a machining fixture on an electro discharge machine having a an electrical discharge wire and arranging a plurality of workpieces on said machining fixture, and cutting the desired geometry on said workpieces with cutting lines parallel to each other.