A segmented piston rod for an injection device for delivering a medication from a reservoir having a stopper, the piston rod comprising multiple segments that each are joined together via a hinge located on the lateral side of each segment. The piston rod can be bent in one direction by articulating subsequent hinges while an axial force can be transmitted by the segmented piston rod to the stopper when the subsequent hinges are closed and the segments abut each other opposite to the lateral side of the hinge. The segmented piston rod is being secured against rotation with respect to the housing around the longitudinal axis of the segmented piston rod. The segmented piston rod has a last element which abuts the stopper in the reservoir and a first segment which is opposite to the last segment. The segmented piston rod is characterized by that the at least first segment of the segmented piston rod is equipped with an internal thread matching an external thread of a drive sleeve wherein rotation of the drive sleeve by a drive mechanism advances the piston rod towards the stopper of the reservoir.
