Biomechanical comparison of C1-C2 posterior arthrodesis techniques.

STUDY DESIGN Biomechanical comparison of 5 atlantoaxial posterior arthrodesis techniques. OBJECTIVE To assess the relative value of different posterior wire constructs when one or two transarticular screws are used. SUMMARY OF BACKGROUND DATA A combination of Gallie or Brooks techniques and 2 posterior transarticular screws has been shown to be effective for atlantoaxial arthrodesis. Anatomic constraints may preclude the insertion of a transarticular screw unilaterally or bilaterally. METHODS Ten adult human cadaveric upper cervical spine specimens were used. The specimens were tested intact, after odontoidectomy and transverse and capsular ligament section and after stabilization with each of the 5 techniques: 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. Pure moments were applied in flexion-extension, lateral bending, and torsion within physiologic limits (<1.5 Nm). RESULTS In flexion-extension and lateral bending, the range of motion (ROM) and neutral zone (NZ) increased significantly after the specimens were injured as compared with intact spines (P < 0.001). After stabilization, the ROM and NZ were significantly lower than in injured and intact spines in all motions (P < 0.01) except lateral bending in the intact spine. Among the 5 instrumented techniques, the ROM for the Gallie construct with 1 screw was significantly higher than for the Brooks-Jenkins construct with 1 or 2 screws in flexion-extension (P < 0.05). In axial torsion, the Gallie construct with 1 screw displayed a larger NZ and ROM than any of the other 4 constructs (P < 0.05). CONCLUSIONS Gallie or Brooks-Jenkins cable fixation alone may not be adequate for atlantoaxial arthrodesis. If 2 supplemented transarticular screws can beinserted, there is no difference between the Gallie or Brooks techniques. If only a single screw can be inserted, the Brooks-Jenkins technique is recommended rather than a Gallie technique.