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.

Biomechanical evaluation of posterior screw fixation in cadaveric cervical spines.

Sixteen fresh-frozen spines from cadavers (C4-T1) were randomized on the basis of dual energy xray absorptiometry analysis of bone mineral density. The specimens were subjected to physiologic loads (

Biomechanical evaluation of new posterior occipitocervical instrumentation system.

Twelve fresh-frozen cadaveric occipitocervical specimens were randomized based on dual energy xray absorptiometry analysis of bone mineral density. The specimens were subjected to physiologic loads in a device that applied pure unconstrained flexion and extension, lateral bending, and axial rotational moments. The spines were tested intact and after major injury simulating transoral decompression of the dens. Biomechanical testing using pure moments with physiologic loads (< 1.5 N-m) was used to compare stability of posterior occipitocervical plates and screws, loop and cable construct, and new cervical rod and screw system. The injury created significantly less stiffness and greater range of motion and neutral zone at C1-C2 in flexion and extension and lateral bending and greater range of motion and neutral zone in axial rotation than the intact state. In lateral bending, the new rod construct had significantly lower mean values for range of motion than the loop and the plate construct. In axial rotation, the rod construct had a significantly higher mean value for stiffness than the other two devices and a significantly lower mean value for range of motion than the loop. The new rod-based instrumentation system for occipitocervical fixation is biomechanically equivalent or superior to a plate and screw construct and a rod and cable system.