The invention discloses a screw-rod instrument specially used for posterior atlantoaxial vertebrae fixation, comprising two pulling-screws (2), two supporting-screws (1), two variable cross section fixing rods (3), two lock nuts (4) and a bracing beam (5). Each of the variable cross section fixing rods (3) is configured to connect a supporting-screw (1) and a pulling-screw (2), the bracing beam (5) is configured to connect both of the variable cross section fixing rods (3)； wherein each of the supporting-screws (1) comprises a first tail (11) and a first head (12), and each of the pulling-screws (2) comprises a second tail (21) and a second head (22)； both the first tail (11) and the second tail (21) are provided with nail grooves, with U-shaped grooves on the sides； wherein each of the nail grooves is provided with internal thread inside, and the lock nut (4) is connected with the nail groove； each of the variable cross section fixing rods (3) passes through the U-shaped grooves and is fastened by the lock nut (4)； the bottoms of the nail grooves of the supporting-screws (1) are 2-6 mm higher than the bottoms of the nail grooves of the pulling-screws (2). The aforementioned screw-rod instrument not only increases the safety and convenience of a surgery, but also improves the function of spondylolisthesis reduction of the screw-rod system through raising the bottoms of the nail grooves 2-6 mm higher.
