An implantable fixation device comprises a support bar (1) having right-hand threads on the one end and left-hand threads on the opposite end, and having jaw supports (5, 6) threadingly mounted on the respective threaded ends. The jaw supports have secured thereto bolt jaws by means of a respective clamping screw (7), which bolt jaws are (adapted to be) fixed to intact vertebral bodies of the spiral column by means of bone (screw) bolts (13). Further, the bolt jaws are provided with receiving holes (16) permitting the insertion of rod-shaped repositioning instruments (17). By means of this structure, setting of the vertebral elements or segments is possible irrespective of the length of the bone bolts. The repositioning rods (17) can be easily removed; subsequent shortening of the bone bolts (17) is not necessary.