Biomechanics of C-7 transfacet screw fixation

Laboratory investigation

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Object

The small diameter of the pedicle can make C-7 pedicle screw insertion dangerous. Although transfacet screws have been studied biomechanically when used in pinning joints, they have not been well studied when used as part of a C7–T1 screw/rod construct. The authors therefore compared C7–T1 fixation using a C-7 transfacet screw/T-1 pedicle screw construct with a construct composed of pedicle screws at both levels.

Methods

Each rigid posterior screw/rod construct was placed in 7 human cadaveric C6–T2 specimens (14 total). Specimens were tested in normal condition, after 2-column instability, and once fixated. Nondestructive, nonconstraining pure moments (maximum 1.5 Nm) were applied to induce flexion, extension, lateral bending, and axial rotation while recording 3D motion optoelectronically. The entire construct was then loaded to failure by dorsal linear force.

Results

There was no significant difference in angular range of motion between the 2 instrumented groups during any loading mode (p > 0.11, nonpaired t-tests). Both constructs reduced motion to < 2° in any direction and allowed significantly less motion than in the normal condition. The C-7 facet screw/T-1 pedicle screw construct allowed a small but significantly greater lax zone than the pedicle screw/rod construct during lateral bending, and it failed under significantly less load than the pedicle screw/rod construct (p < 0.001).

Conclusions

When C-7 transfacet screws are connected to T-1 pedicle screws, they provide equivalent stability of constructs formed by pedicle screws at both levels. Although less resistant to failure, the transfacet screw construct should be a viable alternative in patients with healthy bone.

Abbreviations used in this paper: ROM = range of motion; LZ = lax zone; SZ = stiff zone.

Article Information

Address correspondence to: Neil R. Crawford, Ph.D., Neuroscience Publications, 350 West Thomas Road, Phoenix, Arizona 85013. email: neuropub@chw.edu.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    Schematics showing (A) lateral and (B) posterior views of the C-7 transfacet screw trajectory. Reproduced with permission from Horn et al.: J Neurosurg Spine 9:200–206, 2008. Figure provided courtesy of Indiana University.

  • View in gallery

    Configurations for flexibility and load-to-failure tests. Left: In the flexibility test, adjustable pulleys were used in conjunction with a standard servohydraulic test frame, enabling 2 equal and opposite forces separated by a small distance (pure moment) to be applied through a looped string when the piston advanced upward. Optical markers on each level are visible for tracking vertebral motion. Right: In the failure test, a posterior force was applied to the entire hardware construct, using a cable with looped ends in conjunction with the servohydraulic test frame. Each cable end was routed around both the C-7 and T-1 screws under the rods so that both rostral and caudal screws were loaded equivalently. The piston of the servohydraulic frame pulled the cable posteriorly while a load cell in line with the piston measured applied load.

  • View in gallery

    Bar graphs showing mean angular motion for the normal (A), destabilized (B), and instrumented (C) conditions of the specimens. Columns represent ROM. On each column the horizontal line denotes the division between the LZ and SZ. Error bars show SDs of the ROM.

  • View in gallery

    Bar graph demonstrating mean ultimate strength for the entire construct (C7–T1) in specimens with C-7 transfacet screws compared with specimens with C-7 pedicle screws. In both groups, the C-7 screw head was interconnected bilaterally by longitudinal rods to pedicle screws at T-1. Error bars show SDs.

References

1

An HSCoppes MA: Posterior cervical fixation for fracture and degenerative disc disease. Clin Orthop Relat Res 335:1011111997

2

Barrey CMertens PJund JCotton FPerrin G: Quantitative anatomic evaluation of cervical lateral mass fixation with a comparison of the Roy-Camille and the Magerl screw techniques. Spine 30:E140E1472005

3

Crawford NRBrantley AGDickman CAKoeneman EJ: An apparatus for applying pure nonconstraining moments to spine segments in vitro. Spine 20:209721001995

4

Crawford NRDickman CA: Construction of local vertebral coordinate systems using a digitizing probe. Technical note. Spine 22:5595631997

5

Crawford NRPeles JDDickman CA: The spinal lax zone and neutral zone: measurement techniques and parameter comparisons. J Spinal Disord 11:4164291998

6

Crawford NRYamaguchi GTDickman CA: A new technique for determining 3-D joint angles: the tilt/twist method. Clin Biomech (Bristol Avon) 14:1531651999

7

Daubs MDKim YJLenke LG: Pedicle screw fixation (T1, T2, and T3). Instr Course Lect 56:2472552007

8

Ebraheim NAXu RChallgren EYeasting RA: Quantitative anatomy of the cervical facet and the posterior projection of its inferior facet. J Spinal Disord 10:3083161997

9

Horn EMTheodore NCrawford NRBambakidis NCSonntag VK: Transfacet screw placement for posterior fixation of C-7. J Neurosurg Spine 9:2002062008

10

Jeanneret BMagerl FWard EHWard JC: Posterior stabilization of the cervical spine with hook plates. Spine 16:S56S631991

11

Karaikovic EEKunakornsawat SDaubs MDMadsen TWGaines RW Jr: Surgical anatomy of the cervical pedicles: landmarks for posterior cervical pedicle entrance localization. J Spinal Disord 13:63722000

12

Klekamp JWUgbo JLHeller JGHutton WC: Cervical transfacet versus lateral mass screws: a biomechanical comparison. J Spinal Disord 13:5155182000

13

Ludwig SCKowalski JMEdwards CCHeller JG: Cervical pedicle screws: comparative accuracy of two insertion techniques. Spine 25:267526812000

14

Ludwig SCKramer DLBalderston RAVaccaro ARFoley KFAlbert TJ: Placement of pedicle screws in the human cadaveric cervical spine: comparative accuracy of three techniques. Spine 25:165516672000

15

Pal GPRoutal RVSaggu SK: The orientation of the articular facets of the zygapophyseal joints at the cervical and upper thoracic region. J Anat 198:4314412001

16

Panjabi MM: Biomechanical evaluation of spinal fixation devices: I. A conceptual framework. Spine 13:112911341988

17

Panjabi MM: The stabilizing system of the spine. Part II. Neutral zone and instability hypothesis. J Spinal Disord 5:3903961992

18

Roy-Camille RSaillant GLaville CBenazet JP: Treatment of lower cervical spinal injuries–C3 to C7. Spine 17:S442S4461992

19

Takayasu MHara MYamauchi KYoshida MYoshida J: Transarticular screw fixation in the middle and lower cervical spine. Technical note. J Neurosurg 99:1321362003

20

Xu REbraheim NAKlausner TYeasting RA: Modified Magerl technique of lateral mass screw placement in the lower cervical spine: an anatomic study. J Spinal Disord 11:2372401998

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