A catheter assembly is provided having an inner member and an outer member extending along a longitudinal axis, the inner member and the outer member having a coaxial configuration and dimensioned for relative axial movement. The outer member has a wall defining an opening such as a longitudinal slot; an expanding member such as a leaf spring is connected to the inner member, the leaf spring being adapted to engage with the longitudinal slot so as to maintain rotational alignment between inner member and outer member.