Fatigue Performance of Cortical Bone Trajectory Screw Compared With Standard Trajectory Pedicle Screw

STUDY DESIGN.Cadaveric biomechanical study. OBJECTIVE.To determine fatigue behavior of cortical bone trajectory (CBT) pedicle screws. SUMMARY OF BACKGROUND DATA.Cortical bone trajectory screws have been becoming popular in spine surgery; however, the long-term fatigue behavior of the new CBT screws remains understudied and limitations not well defined. METHODS.Twelve vertebrae from six cadaveric lumbar spines were obtained. After bone mineral density (BMD) measurements, each vertebral body was instrumented with screws from each group, that is, CBT (4.5 × 25 mm) or standard pedicle screw (6.5 × 55 mm). A load (± 4 Nm sagittal bending) was applied under displacement control at 1 Hz. Each construct was loaded for 100 cycles or until 6° of loosening was observed. After fatigue testing, the screws were pulled out axially at 5 mm/min. RESULTS.The standard pedicle screw showed better resistance against 100 cycle loading compared with the CBT screws (P