The purpose of this study is the biomechanical comparison of five C1 – C2 posterior arthrodesis techniques. Ten adult human cadaveric upper cervical spine specimens were sectioned at the C3 level. The occiput and C3 vertebra were potted in PMMA. The specimens were tested intact; after destabilizing with odontoid transection and sectioning of the transverse and capsular ligaments; and after stabilization with Brooks-Jenkins cable fixation, Brooks-Jenkins with unilateral transarticular screw, Gallie posterior wire construct with unilateral transarticular screw, Brooks-Jenkins with bilateral screws, and Gallie with bilateral screws. Data were analysed with special attention paid to the motion at C1 – C2. The neutral zone (NZ) and range of motion (ROM) were measured in the main plane of each motion, as well as in coupled planes. In flexion / extension and lateral bending, the ROM and NZ increased significantly in the injured specimens as compared to the intact (p< 0.0001).

In axial torsion, there was no significant difference between the intact and injured spines at C1 – C2 level. In the different fixation systems, the ROM and NZ were significantly lower than in injured and intact spines in all motions (p< 0.01), except the lateral bending in intact spine. Among the 5 instrumentations, the NZ and ROM in flexion / extension for the Gallie construct with one screw were significantly higher than for the Brooks-Jenkins construct with one or two screws (p< 0.05). In axial torsion, the Gallie construct with one screw displayed a larger NZ and ROM than any of the other four constructs (p< 0.05).