The stabilizing effect of posterior fixations in a destabilized atlantoaxial complex model in canines

Purpose: This study was conducted to evaluate the kinematic responses and the restorative effectiveness of three posterior fixations in a canine atlantoaxial (C_1-2) complex model. Methods: Nine canine ligamentous C_1-2 complexes were non-destructively tested in an intact condition, after ligamentous destabilization, and after bilateral stabilization with each of three posterior fixation methods: (1) Halifax inter-laminar clamps; (2) sub-laminar wiring; and (3) individual fixation of the C₁ lateral mass and the C₂ pedicle with screws and plates. Specimens were subjected to a relevantly applied loads through a loading frame rigidly attached to the C₁. Two sets of three markers was separately attached to the mounting jigs of the C₁ and the C₂ to record the spatial locations after each loading step with a Vicron 370 system. The load-deformation data were analyzed. Results: Under a realistic loading paradigm, destabilized canine C_1-2 complex had 3-dimensional motion ranges highly consistent with the corresponding values observed in destabilized cadaveric human C_1-2 complex following a non-destructive loading paradigm. All the three posterior fixations significantly restricted the motion range of axial rotation loads (P < 0.05). However, fixation either with posterior inter-articular screws and plates or inter-laminar clamps also effectively restricted the motion ranges of flexion/extension and lateral bending loads, whereas posterior wiring did not. Conclusion: We described a destabilized canine C_1-2 complex model. Under a realistic loading paradigm, the model had kinematic analogue of destabilized human C_1-2 complex. Our results indicated that posterior stabilization using inter-articular fixation techniques or inter-laminar clamps could effectively restrict hypermotility caused by C_1-2 ligamentous destabilization, and, therefore, appeared to be reliable fixation methods. In contrast, posterior wiring alone would preserve more residual motions, and, thus, might need other adjunctive fixations to offer an optimal condition for solid bony fusion.