A medical instrument comprises at least one frame and one jointed device 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 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 , suitable to allow the sliding of at least one portion of said tendon (90; 190) over it; characterized in that : said sliding surface 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 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 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 , suitable to allow the sliding of at least one portion of said tendon (90; 190) over it; characterized in that : said sliding surface 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 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 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 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. <EOS>