Biomechanical evaluation of five different occipito-atlanto-axial fixationtechniques

Study Design. The stabilizing effects of five different occipitocervical fi xations were compared. Objectives. To evaluate the construct stability provided by five different occipito-atlanto-axial fixation techniques. Summary of Background Data. Few studies have addressed occipitocervical rec onstruction stability and no studies to date have investigated anterior-pos terior translational stiffness. Methods. A total of 21 human cadaveric spines were used. After testing inta ct spines (CO-C2), a type II dens fracture was created and five different r econstructions were performed: 1) occipital and sublaminar wiring/rectangul ar rod, 2) occipital screws and C2 lamina claw hooks/rod, 3) occipital scre ws, foramen magnum screws, and C1-C2 transarticular screws/rod, 4) occipita l screws and C1-C2 transarticular screws/Y-plate, and 5) occipital screws a nd C2 pedicle screws/rod. Biomechanical testing parameters included axial r otation, flexion/extension, lateral bending, and anterior-posterior transla tion. Results. Pedicle screw fixation demonstrated the highest stiffness among th e five reconstructions (P < 0.05). The two types of transarticular screw me thods provided greater stability than hook or wiring reconstructions (P < 0 .05). The C2 claw hook technique resulted in greater stability than sublami nar wiring fixation in anterior-posterior translation (P < 0.05). However, the wiring procedure did not significantly increase the stiffness levels be yond the intact condition under anterior-posterior translation and lateral bending (P> 0.05). Discussion. C2 transpedicular and C1-C2 transarticular screws significantly increased the stabilizing effect compared to sublaminar wiring and lamina hooks. The improved stability afforded by C2 pedicular and C1-C2 trans arti cular screws offer many potential advantages including a high rate of bony union, early ambulation, and easy nursing care. Conclusion. Occipitocervical reconstruction techniques using C1-C2 transart icular screws or C2 pedicle screws offer biomechanical advantages compared to sublaminar wiring or lamina hooks. Pedicle screw fixation exhibited the highest construct stiffness among the five reconstructions.