Finite element method to study cervical postoperative stability

A cervical spine model built by means of the finite element method was used to determine the risk of postoperative cervical instability in relation to the type of discectomy, in cervical disc herniation. Furthermore, this model was employed to check whether, at the adjacent levels of the fusion discectomy, the intervertebral translation during cervical movements will maintain the normal amplitude [normal ROM] or its amplitude will decrease. The intervertebral displacement and the tension arising from motion and weight in the cervical vertebral structure were thus determined through computer modelling using the above-mentioned method and the software Abaqus. It resulted in a cervical spine model consisting of 739666 finite elements interacting through 210530 nodes, with biomechanical properties following the vertebral anatomical structures modelled. Two movement situations were studied to determine the behaviour of this model. Firstly, the moment of force for flexion and extension of 1 Nm. Secondly, we aimed to establish the maximum flexion and extension for a normal cervical spine model in order to determine the momentum value of moving forces for each of them. It was showed that both anterior cervical microdiscectomy without fusion and cervical discectomy with cage fusion (used for the surgical treatment of cervical disc herniation at one level), ensure postoperative vertebral stability when performed properly. Both types of surgery reduce the mobility of the cervical spine, although more in the case of fusion discectomy. The intradiscal tension increases in movement in both models, with a higher intensification in the fusion discectomy model. The practical conclusion is that microdiscectomy without fusion is preferable in the case of a single-level cervical disc herniation occurred to a cervical spine without instability.