Biomechanical comparison of anterior and posterior stabilization methods in atlantoaxial instability

Object. The authors compared the biomechanical stability of two anterior fixation procedures-anterior C1-2 Harms plate/screw (AHPS) fixation and the anterior C1-2 transarticular screw (ATS) fixatiom and two posterior fixation procedures-the posterior C-I lateral mass combined with C-2 pedicle screw/rod (PLM/APSR) fixation and the posterior C1-2 transarticular Screw (PTS) fixation after destabilization. Methods. Sixteen human cervical spine specimens (Oc-C3) were tested in three-dimensional flexion-extension, axial rotation, and lateral bending, motions after destabilization by using an atlantoaxial C1-2 instability model. In each loading mode, moments were applied to a maximum of 1.5 Nm, and the range of motion (ROM), neutral zone (NZ), and elastic zone (EZ) were determined and values compared using the intact spine. the destabilized spine, and the postfixation spine. The AHPS method produced inferior biomechanical results in flexion-extension and lateral bending modes compared with the intact spine. The lateral bending NZ and ROM for this method differed significantly from the other three fixation techniques (p < 0.05), although statistically significant differences were not obtained for all other values of ROM and NZ for the other three procedures. The remaining three methods restored biomechanical stability and improved it over that of the intact spine. Conclusions. The PLM/APSR fixation method was found to have the highest biomechanical stiffness followed by PTS, ATS. and AHPS fixation. The PLM/APSR fixation and AATS methods can be considered good procedures for stabilizing the atlantoaxial joints, although specific fixation methods are determined by the proper clinical and radiological characteristics in each patient.