Abstract: A system for osteosynthesis of the spine. The system includes at least two pedicular screws and a linking plate for linking the screws together in an essentially rigid manner. Each screw has a bone anchoring threaded part, a non-circular section head, and a threaded end shank adapted to cooperate with a nut. The plate has at least one opening adapted to have the threaded end shank of a screw passed through it and be trapped between the screw head and the nut. A locking member is also provided for preventing relative angular movement between the heads of the screws and the linking plate. The locking member is adapted to be inserted between the plate and the screw head and includes a bore through which the threaded end shank of the screw passes, and further includes a first locking cooperation of shapes with the screw head and a second cooperation of shapes with the plate.