A shaft having an axis and a distal end portion is adapted to be deployed inside a vertebral body through a cannula. A filament is carried by the distal end portion. A surface on the filament is movable between a collapsed condition sized and configured to be deployed with the shaft through the cannula and an extended position that extends radially from the shaft. A mechanism is coupled to the filament to extend the filament in situ radially from the shaft into contact with cancellous bone within the vertebral body. The surface, when extended, defines a structure capable of forming a cavity wholly within the vertebral body in the cancellous bone.