A surgical guide device, intended to be placed against a patient's bone, for assisting an opening wedge osteotomy technique, said surgical guide device being characterized in that it comprises: - a rear face adapted to be positioned against a surface of said bone, and - a window for guiding a cut line intended to be made into said bone, wherein said guide window is delimited by an upper edge and a lower edge, arranged opposite to each other and spaced apart from each other, wherein said surgical guide device comprises two parts (4, 5) that are assembled to each other through detachable fastening means, i.e.: - a proximal part, having a lower edge defining at least one portion of said upper edge of said guide window, and - a distal part, having an upper edge defining at least one portion of said lower edge of said guide window, wherein said proximal and distal parts are each provided with several through-orifices (42, 56) opening through the rear face, adapted to receive elements temporarily implantable into said bone and/or adapted to guide a drilling of holes into said bone, the distal part comprises tubulars ducts that are adapted to guide the insertion of a rod within the bone, characterized in that the distal part comprises at least two distal tubular ducts (582, 583) that are arranged remote from the guide window and that are directed in such a manner that their respective longitudinal axes (582', 583') intersect the plane of the guide window in order to each position a cut stop and/or hinge indication rod (82, 84). said surgical guide device being characterized in that it comprises: - a rear face adapted to be positioned against a surface of said bone, and - a window for guiding a cut line intended to be made into said bone, - a rear face adapted to be positioned against a surface of said bone, and - a window for guiding a cut line intended to be made into said bone, wherein said guide window is delimited by an upper edge and a lower edge, arranged opposite to each other and spaced apart from each other, wherein said surgical guide device comprises two parts (4, 5) that are assembled to each other through detachable fastening means, i.e.: - a proximal part, having a lower edge defining at least one portion of said upper edge of said guide window, and - a distal part, having an upper edge defining at least one portion of said lower edge of said guide window, - a proximal part, having a lower edge defining at least one portion of said upper edge of said guide window, and - a distal part, having an upper edge defining at least one portion of said lower edge of said guide window, wherein said proximal and distal parts are each provided with several through-orifices (42, 56) opening through the rear face, adapted to receive elements temporarily implantable into said bone and/or adapted to guide a drilling of holes into said bone, the distal part comprises tubulars ducts that are adapted to guide the insertion of a rod within the bone, characterized in that the distal part comprises at least two distal tubular ducts (582, 583) that are arranged remote from the guide window and that are directed in such a manner that their respective longitudinal axes (582', 583') intersect the plane of the guide window in order to each position a cut stop and/or hinge indication rod (82, 84).