The use of the hybrid fixator should involve a certain trade-off between the protection of the transition segment and the deterioration of the adjacent segments. This trade-off stiffness, which largely depends on both fixator design and disc degeneration, provides the improved rigidity and flexibility of the transition and adjacent segments.

Background: This study was designed to derive the theoretical formulae to predict the pullout strength of pedicle screws with an inconstant outer and/or inner diameter distribution (conical screws). For the transpedicular fixation, one of the failure modes is the screw loosening from the vertebral bone. Hence, various kinds of pedicle screws have been evaluated to measure the pullout strength using synthetic and cadaveric bone as specimens. In the literature, the Chapman's formula has been widely proposed to predict the pullout strength of screws with constant outer and inner diameters (cylindrical screws).

No abstract