Anterior cervical fusion: a biomechanical comparison of 4 techniques

Laboratory investigation

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Object

Cervical instrumented fusion is currently performed using several fixation methods. In the present paper, the authors compare the following 4 implantation methods: a stand-alone cage, a cage supplemented by an anterior locking plate, a cage supplemented by an anterior dynamic plate, and a dynamic combined plate–cage device.

Methods

Four finite element models of the C4–7 segments were built, each including a different instrumented fixation type at the C5–6 level. A compressive preload of 100 N combined with a pure moment of 2.5 Nm in flexion, extension, right lateral bending, and right axial rotation was applied to the 4 models. The segmental principal ranges of motion and the load shared by the interbody cage were obtained for each simulation.

Results

The stand-alone cage showed the lowest stabilization capability among the 4 configurations investigated, but it was still significant. The cage supplemented by the locking plate was very stiff in all directions. The 2 dynamic plate configurations reduced flexibility in all directions compared with the intact case, but they left significant mobility in the implanted segment. These configurations were able to share a significant part of the load (up to 40% for the combined plate–cage) through the posterior cage. The highest risk of subsidence was obtained with the model of the stand-alone cage.

Conclusions

Noticeable differences in the results were detected for the 4 configurations. The actual clinical relevance of these differences, currently considered not of critical importance, should be investigated by randomized clinical trials.

Abbreviation used in this paper: ROM = range of motion.

Article Information

Address correspondence to: Fabio Galbusera, M.S.Eng., IRCCS Istituto Ortopedico Galeazzi, via R. Galeazzi 4, 20161 Milan, Italy. email: fabio.galbusera@polimi.it.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Finite element models of the C4–7 segment implanted with a stand-alone cage (a), a cage supplemented by an anterior plate (locking or dynamic; b), and a combined plate–cage device (c).

  • View in gallery

    Illustration demonstrating the geometry of the screw– plate interface in the models including the dynamic plate and the combined plate–cage device. The inclination of the screw head was assumed to be 45°. The clearance between the head and the plate was 0.1 mm.

  • View in gallery

    Graph showing the ROMs calculated with the finite element models in flexion, extension, right lateral bending, and right axial rotation.

  • View in gallery

    Graph showing the fraction of load shared by the cage calculated with the models including the cage supplemented with the anterior locking or dynamic plate and the model including the combined plate–cage device.

  • View in gallery

    Images showing the contact pressures in extension at the cage–C6 endplate interface calculated with the models including a stand-alone cage (a), a cage supplemented by an anterior locking plate (b), cage supplemented by an anterior dynamic plate (c), and a combined plate–cage device (d).

References

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