Patent ID: 7073415

Claim:
An instrument system comprising pedicle screws having an internal thread in their head, said thread accepting a grub screw with an external diameter D 1 in the direction of the screw axis to fixedly clamp a connection part which projects transversely to the screw axis into the head, further comprising: at least two holders with a tubular part, at least one of said holders being provided with projections configured for engaging in a shape matched manner at the head of the pedicle screws; a screwdriver with a diameter D 4 adapted to be positioned at the grub screw, the tubular parts of the at least two holders, being supportable at the head of the pedicle screws; and a centering part adapted to be screwed into the internal thread of the pedicle screws, instead of the grub screw, and to be gripped when one of said holders is mounted on the centering part corresponding in its external diameter D to the diameter D 1 of the grub screw with the tubular parts having an internal diameter D 2 which essentially equals with a loose-fit oversize, the diameter D 1 of the grub screw, in order to position the grub screw with the screwdriver or the centering part guided through the tubular part to the head of the pedicle screw such that threads of the grub screw engage with the internal thread of the pedicle screws in a non-tilted manner, wherein the centering part has a central region in the longitudinal direction which can be elastically deflected up to an angle of 20Â° or more away from the longitudinal axis.