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.
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.
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.
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.
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