Biomechanical comparison of C1-C2 posterior arthrodesis techniques

Abstract

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.