A syringe for use with a powered injector includes an elongated body having an interior surface, a plunger movably mounted in the elongated body for pressurizing the fluid medium, and a plunger extension connected to the plunger and extending rearward from the plunger. The plunger extension includes at least one spine member operable to engage at least one engagement member on the interior surface of the elongated body. The at least one spine member and the at least one engagement member cooperate to prevent relative rotation between the plunger extension and the elongated body.