A guide wire 50 includes a plurality of interconnecting segments 60, 70, 80 which can rotate relative to one another, and a locking element. When the locking element 240 is unlocked the segments 60-80 are able to rotate relative to one another and the guide wire 50 is very flexible. The locking element 240 can be locked to cause the segments to engage and not rotate relative to one another, fixing the guide wire 50 in position. In this way the flexibility of the guide wire 50 is controllable and can be altered between extreme flexibility and stiffness. The guide wire can be fixed in a curved or bent configuration. The locking element may extend through a lumen of the segments 60-80 and may be engaged by pulling a handle (224, see figure 9), which compresses the elements together to increase the stiffness. The segments may interconnect along a common line parallel to the longitudinal axis of the guidewire, or along different lines (see figure 4).
