US Patent 8740854 Stopper and plunger rod for a pre-filled syringe

A plunger rod adapted for attachment with a stopper for use with a syringe barrel is disclosed. The plunger rod includes an elongated member having a front end and a back end, the plunger rod extending along a longitudinal axis. The plunger rod includes at least one deflecting arm associated with the front end of the elongated member. The deflecting arm is capable of deflecting radially inward during insertion of the plunger rod into a stopper, and deflecting outward into contact with an inner surface of the stopper after insertion to lock the plunger rod within the stopper.