Surgical device for aligning an extramedullary alignment rod in a knee joint replacement operation, having a supporting section with at least two supporting geometries (S, S', Sa, Sa'), which are spaced apart from one another along a supporting line (SG) that extends in a proximodistal direction and are each configured for supporting on an anterior edge (K) of a tibia (T), and a reference section , which projects in an anterior direction from the supporting section and has at least two reference geometries (R1, R1', R2, R2'), which are spaced apart from one another along a reference line (RG1, RG2) that extends in a proximodistal direction, wherein the reference line (RG1, RG2) is spaced apart from the supporting line (SG) by an anterior distance (A1, A2) and extends parallel to the supporting line (SG), wherein the at least two reference geometries (R1, R1', R2, R2') and/or the reference line (RG1, RG2) are used, instead of the anterior edge (K) of the tibia (T), as a reference for aligning the extramedullary alignment rod , and wherein the at least two reference geometries (R1, R1', R2, R2') are each configured for the at least mediolaterally form-fit mounting of the extramedullary alignment rod , characterized in that the reference section has at least two first reference geometries (R1, R1'), which are spaced apart from one another along a first reference line (RG1), and two second reference geometries (R2, R2'), which are spaced apart from one another along a second reference line (RG2), wherein the first reference line (RG1) is spaced apart from the supporting line (SG) by an anterior first distance (A1), and wherein the second reference line (RG2) is spaced apart from the supporting line (SG) by an anterior second distance (A2). a supporting section with at least two supporting geometries (S, S', Sa, Sa'), which are spaced apart from one another along a supporting line (SG) that extends in a proximodistal direction and are each configured for supporting on an anterior edge (K) of a tibia (T), and a reference section , which projects in an anterior direction from the supporting section and has at least two reference geometries (R1, R1', R2, R2'), which are spaced apart from one another along a reference line (RG1, RG2) that extends in a proximodistal direction, wherein the reference line (RG1, RG2) is spaced apart from the supporting line (SG) by an anterior distance (A1, A2) and extends parallel to the supporting line (SG), wherein the at least two reference geometries (R1, R1', R2, R2') and/or the reference line (RG1, RG2) are used, instead of the anterior edge (K) of the tibia (T), as a reference for aligning the extramedullary alignment rod , and wherein the at least two reference geometries (R1, R1', R2, R2') are each configured for the at least mediolaterally form-fit mounting of the extramedullary alignment rod , characterized in that the reference section has at least two first reference geometries (R1, R1'), which are spaced apart from one another along a first reference line (RG1), and two second reference geometries (R2, R2'), which are spaced apart from one another along a second reference line (RG2), wherein the first reference line (RG1) is spaced apart from the supporting line (SG) by an anterior first distance (A1), and wherein the second reference line (RG2) is spaced apart from the supporting line (SG) by an anterior second distance (A2). <EOS>