[Stability analysis of an enhanced load sharing dynamic pedicle screw fixation device and its equivalent rigid device].
To compare the stability of an enhanced load sharing dynamic pedicle screw fixation device with its equivalent rigid device and to evaluate biomechanical roles of the dynamic fixation. A model of L(1) body fracture was produced on seven specimens of fresh adult cadaver spine from T(10) to L(4). Both dynamic and rigid devices were applied in the specimens to strength the injured level. Ranges of three dimensional movements and stiffness under flexion-compression were measured in intact, injured and stabilized specimens. Both dynamic and rigid devices were found to provide significant stability for injured segment in flexion-extension and lateral bending. In axial rotation, the devices could restore the stability to levels similar to those in an intact spine. Results indicated 40% increase in range of motion in flexion-extension and 24.1 Nmm reduction in stiffness of flexion-compression for dynamic device, compared with the rigid device. The dynamic device offers a design that may enhance load sharing without sacrificing the stability and will decrease stress-shielding and stress concentration.