Biomechanical Evaluation of Five Different Occipito-Atlanto-Axial Fixation Techniques

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Study Design.The stabilizing effects of five different occipitocervical fixations 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 reconstruction stability and no studies to date have investigated anterior-posterior translational stiffness.Methods.A total of 21 human cadaveric spines were used. After testing intact spines (CO-C2), a type II dens fracture was created and five different reconstructions were performed: 1) occipital and sublaminar wiring/rectangular rod, 2) occipital screws and C2 lamina claw hooks/rod, 3) occipital screws, foramen magnum screws, and C1-C2 transarticular screws/rod, 4) occipital screws and C1-C2 transarticular screws/Y-plate, and 5) occipital screws and C2 pedicle screws/rod. Biomechanical testing parameters included axial rotation, flexion/extension, lateral bending, and anterior-posterior translation.Results.Pedicle screw fixation demonstrated the highest stiffness among the five reconstructions (P< 0.05). The two types of transarticular screw methods provided greater stability than hook or wiring reconstructions (P< 0.05). The C2 claw hook technique resulted in greater stability than sublaminar wiring fixation in anterior-posterior translation (P< 0.05). However, the wiring procedure did not significantly increase the stiffness levels beyond 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 transarticular 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 transarticular 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 fivereconstructions.

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