Extension device for a bone screw and screwdriver instrument

Abstract

The invention refers to an extension device () for a bone screw () and to a screwdriver instrument () connectable to the extension device (); it is proposed that the screwdriver instrument () comprises a toggle lever mechanism () having a first and a second lever arm (), which are pivotally connected to each other through a common articulation point (), that the first lever arm () may be removably applied, in the area of its free end (), at a first pivot bearing point () on the extension device () and is pivotally mounted and axially supported in the applied state, and that the second lever arm () is pivotally mounted and axially supported at a second pivot bearing point () on the shank, that the first lever arm () is elastically and longitudinally extendable, and that this longitudinal extensibility and a distance between the second pivot bearing point () and the common articulation point () of the lever arms () are adapted to each other in such a way that when manually pivoting the second lever arm () in the direction of a parallel alignment with the axial longitudinal direction (), a dead center is overcome, and the toggle lever mechanism () reaches a tilt-stable position (), in which the shank of the screwdriver instrument () is forced in the axial direction () against the tool application point of the bone screw.