A variable-stiffness guidewire system which comprises an elongated flexible guidewire. The guidewire has a body and a tensioning head coupled to the body. The tensioning head is slidably moveable with respect to a guidewire collar coupled to the body via a tensioning wire to adjust a stiffness of the guidewire. The guidewire includes one or more protrusions within a conduit of the guidewire collar which applies a frictional force to the tensioning wire to maintain the tensioning head a desired distance from the collar, thereby maintaining the desired stiffness in the guidewire. A tool can be utilized with the guidewire to engage the guidewire head and move the guidewire head a desired distance from the guidewire collar to achieve a desired stiffness.
