A guide wire (50) includes a plurality of segments (60-80) which can interlock rotatably relative to one another. A locking element (240) extends through a lumen of the segments (60-80). When the locking element (240) is in an unlocked condition the segments (60-80) are able to rotate relative to one another. In this mode, the guide wire (50) is very flexible. The locking element (240) can be tightened to cause the segments to lock in engagement with one another and to fix the guide wire (50) in position. In practice, the guide wire can be fixed in a curved or bent configuration, which enables the guide wire (50) to provide a rigid support for a microcatheter or other element of an introducer assembly. The guide wire (50) therefore can exhibit both extreme flexibility and stiffness.
