A disposable surgical kit for fixing the vertebrae using a posterior or postero-lateral route has at least one pedicle screw or vertebral screw and an assembly tube cooperating with the screw. The assembly tube is composed of two independent rigid half-shells. Each of the half-shells has, on the inner face of its proximal end, a shoulder with a shape complementing a recess formed on each side of the screw head in order to permit the gripping or the release of the screw by spreading apart the distal ends of the half-shells The kit additionally has a retractable securing element for securing the half-shells. The retractable securing element has longitudinal fastening means designed as a dovetail for engaging with complementary slides formed in the rigid half-shells.