An apparatus is provided for the internal fixation of the spine. The apparatus comprises two sets of implants (8) each consisting of a rod (18) and a plurality of vertebral anchors (16). The rod (18) is secured to the vertebral elements by the vertebral anchors (16). The anchor (16) includes a transpedicular screw (21) which is secured to a vertebrae. The anchor (16) further includes an anchor seat (23) which captures the screw (21) and permits micromotion between the anchor seat (23) and screw (21). This seat (23) has a rod-receiving channel (51,52) which captures the rod (18). A cap (25) cooperates with the seat (23) to secure the rod (18) in the anchor (16). A nut (27) screws down from the top of the assembly onto the seat (23) to cause rod (18) receiving flanges (46,47) in the cap (23) to apply a compressive force to the rod (18 ). A method of therapy is presented in which the present implants (8) are inserted surgically into a patient.