In vitro biomechanical comparison of transpedicular versus translaminar C-2 screw fixation in C2–3 instrumentation

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Object

In instrumentation of the upper cervical spine, placement of pedicle screws into C-2 is generally safe, although there is the potential for injury to the vertebral arteries. Owing to this risk, translaminar screws into C-2 have been used. The aim of this study was to compare the stability of the in vitro cadaveric spine using C-2 laminar compared with C-2 pedicle screws in C2–3 instrumentation.

Methods

Eight fresh frozen human cadaveric cervical spines (C1–6) were potted at C1–2 and C5–6. Pure moments in increments of 0.3 Nm to a maximum of 1.5 Nm were applied in flexion, extension, right and left lateral bending, and right and left axial rotation. Each specimen was tested sequentially in three modes: 1) intact; 2) C2 pedicle screw–C3 lateral mass fixation; and 3) C2 laminar screw–C3 lateral mass fixation. The sequence of fixation testing was randomized. Motion was tracked with reflective markers attached to C-2 and C-3.

Results

Spinal levels with instrumentation showed significantly less motion than the intact spine in all directions and with all loads greater than 0.3 Nm (p < 0.05). Although there was no significant difference between C2 pedicle screw–C3 lateral mass fixation and C2 laminar screw–C3 lateral mass fixation, generally the former type of fixation was associated with less motion than the latter.

Conclusions

When pedicle screws in C-2 are contraindicated or inappropriate, laminar screws in C-2 offer a safe and acceptable option for posterior instrumentation.

Abbreviations used in this paper:ROM = range of motion; VA = vertebral artery.

Article Information

Address correspondence to: Patrick W. Hitchon, M.D., Department of Neurosurgery, University of Iowa Hospitals and Clinics, 200 Hawkins Drive, Room BT3023, Iowa City, Iowa 52242. email: patrick-hitchon@uiowa.edu.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Anteroposterior (left) and lateral (right) radiographs of C2–3 instrumentation with C-2 pedicle screws and C-3 lateral mass screws.

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    Anteroposterior (left) and lateral (right) radiographs of C2–3 instrumentation with C-2 laminar screws and C-3 lateral mass screws.

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    Graph showing C2–3 flexion/extension in intact, C2 transpedicular–C3 lateral mass fixation, and C2 laminar–C3 lateral mass fixation. With pure moments greater than 0.3 Nm, both instrumented constructs had significantly (p < 0.05) less motion than the intact state.

  • View in gallery

    Graph showing C2–3 lateral bending in intact, C2 transpedicular–C3 lateral mass fixation, and C2 laminar–C3 lateral mass fixation. For pure moments greater than 0.3 Nm, both instrumentation constructs had significantly (p < 0.05) less motion than the intact state. LLB = left lateral bending; RLB = right lateral bending.

  • View in gallery

    Graph showing C2–3 axial rotation in intact, C2 transpedicular–C3 lateral mass fixation, and C2 laminar–C3 lateral mass screw fixation. Both types of instrumentation were associated with significantly (p < 0.05) less motion than the intact state. LAR = left axial rotation; RAR = right axial rotation.

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