A spinal fixation system (1) for use in the fixation of a spine comprising: a coupling element (2) having a pair of opposed longitudinal apertures (17) through a wall (35) thereof; a longitudinal slot (8) in a coupling element (2) interior surface (3); a hole (13) through the bottom end (5) of the coupling element (2); and a securing element (18) dimensioned for insertion into the coupling element (2), the securing element (18) having an outwardly extending wing (26) dimensioned for riding in the coupling element slot (8), for preventing a rotation of the securing element (18) about a longitudinal axis (7) thereof.