A surgical kit for fastening vertebrae via the posterior approach or via the posterolateral approach, comprising: at least one vertebral or pedicle screw, and a fitting tube co-operating with the screw the fitting tube having two rigid branches, each of the two branches having, on the inside face of its proximal end, at least one shoulder the kit further comprising a retractable securing insert for securing together the branches wherein the screw head has at least two longitudinal extensions, extending in the distal direction, each of said extensions being configured to enable said screw head to be inserted into a space of complementary shape formed between the inside surface of the proximal end of one of the rigid branches and the outside surface of the proximal end of said retractable insert, when the retractable insert is fully engaged in the fitting tube.
