Biomechanical Test and Assessment on three Internal Fixations on Spine Subaxial Cervical

Objectives:To evaluate the primary stabilities of 3 different instrumentations in the subaxial cervical spine and to provide a theory basis for the selection internal fixations reasonably in clinical.Methods:Five fresh human cadavers cervical specimens(C3～C7)were loaded nondestructively with 2.0Nm pure moments.A decompression laminectomy instability was created in C4～C5 and the motion at C4～C6 was measured in nexion-extension,lateral bending,and axial rotation.The five specimens were instrumented by the following fixation techniques,respectively,1.the intact state 2.after the C4～C5 decompression laminectomy 3.facet wiring with bone graft 4.lateral mass screws.5.pedicle screws.Data analysis was performed by calculating the ranges of motion,and statistical differences were determined by the test for group comparison.Results:No significant difference was observed in nexion-extension between pedicle screws and lateral mass screws.Pedicle screw showed a significantly higher stabilitv in torsion.No difference was found between facet wiring with bone graft and lateral mass screws in lateral bending,in other load directions the stability was even worse.Conclusions:The major investigation of the current study was the higher stability of pedicle screws over lateral mass fixation and facet wiring with bone graft with respect to primary stability and stability.From the biomechanical point of view the use of pedicle screws in the subaxial cervical spine seems justified.In decompression laminectomy,lateral mass screws could meet the need in clinics.The stability of facet wiring with bone graft was worse.