Abstract: The invention relates to an orthopaedic surgical instrument (1) for positioning a tibial cutting guide (2) including: at least a medial or a lateral cutting guide (3) and a vertical cutting guide (4) formed in a guide body (10); an arm or beam (11) supporting said guide body (10); a supporting rod (8) having a proximal end (18) coupled to said guide body (10) through said arm or beam (11). The arm (11) has a structure that is supported in a rotably and cantilever manner at the proximal end (18) of said rod (8); a locking mechanism (20) is provided in the proximity of said proximal end (18) for locking the arm (11) in a desired position; and a bistable mechanical switch (9) is active in said locking mechanism (20) for manually activating the locking position.

Abstract: The invention relates to an orthopaedic surgical instrument (1) for positioning a tibial cutting guide (2) including: at least a medial or a lateral cutting guide (3) and a vertical cutting guide (4) formed in a guide body (10); an arm or beam (11) supporting said guide body (10); a supporting rod (8) having a proximal end (18) coupled to said guide body (10) through said arm or beam (11). The arm (11) has a structure that is supported in a rotably and cantilever manner at the proximal end (18) of said rod (8); a locking mechanism (20) is provided in the proximity of said proximal end (18) for locking the arm (11) in a desired position; and a bistable mechanical switch (9) is active in said locking mechanism (20) for manually activating the locking position.