Finite element analysis of the biomechanical effects of anterior and posterior cervical fusion surgery for bilateral cervical dislocation

Lower cervical spine injuries often manifest as lower cervical vertebral fractures and dislocations, as well as lower cervical facet joint dislocations. Especially in cases of bilateral facet joint dislocations, it is important to rapidly and effectively relieve spinal cord and nerve root compression to prevent secondary spinal cord injury, while also providing reliable and long-lasting stability to the injured segment after surgery. Combined anterior and posterior approaches have the advantages of both pure anterior or posterior approaches, but the actual situation is complex and variable, making systematic theoretical analysis crucial. This study, with bilateral facet joint dislocation of the C6 segment and cervical spinal cord injury as the research background, established a three-dimensional model of the cervical spine C3-C7 after implementing four types of anterior-posterior combined surgeries. The four surgical approaches consist of four combinations: anterior parallel or inclined screw placement combined with posterior Margel or Anderson method screw insertion. Through finite element method, a systematic comparative analysis of the theoretical effects of the four combined surgeries in treating bilateral facet joint dislocation of the cervical spine was conducted. The conclusion was that the variations in the four combined fixation methods have a certain impact on the biomechanical characteristics of the intervertebral disc nucleus. There is a clear mutual influence relationship among anterior and posterior fixation instruments. Based on the model used in this study, it is recommended to use a torque greater than 2.1 nm to tighten the locking nut of the posterior rod to ensure reliable internal fixation.