This invention relates to a surgical instrument, a guide tool for cartilage repair at an articulating surface of a joint, and also to the design method of the guide tool. More specifically the invention concerns a guide tool equipped with a positioning body comprising a guide body comprising at least two guide channels and a cartilage contact surface and wherein the cartilage contact is designed to fit the individual contour of the cartilage or subchondral bone in the joint in a predetermined area surrounding the site of diseased cartilage and the guide channels has a cross-sectional profile that is designed to correspond to the cross-section of the insert tools and the guide channel has a muzzle on the cartilage contact surface at a position facing the site of the diseased cartilage, characterized in that； -At least one of said guide channels has an outer portion and an inner portion and that said outer portion is larger in volume than said inner portion and between the outer portion and the inner portion is a stop function - The guide channels are placed within the guide body in a predetermined pattern, wherein the position and angle of the guide channels are designed to fit the individual cartilage damage site.
