A pedicle screw assembly includes a fastener (30) whose head (34) has a recess (46), and is slotted (50) allowing expansion of the head. The assembly also has an insert (56) having an outer dimension that is greater than the unexpanded inner dimension of the recess (46). A locking element (96) is adapted to be forced against an orthopedic rod (92) arranged in rod receiving opening (94) of a coupling element (70), to in turn force the insert (56) into the recess of the expandable head (34) thereby expanding the outer surface (44) of the head against the seat (88) of the coupling element (70) for locking the fastener (30) from further pivotal movement relative to the coupling element (70). In other preferred embodiments, the head is expandable by virtue of the material of which it is made such as carbon fiber.
