Abstract: BACKGROUND: Improper treatment of the lamina and facet joints during the cervical spine fenestration decompression can easily lead to cervical structure transformation, which causes segmental biomechanical change, and in turn results in cervical vertebra degeneration acceleration and instability in the long run. Clinically, we need to understand how the endoscopic cervical spine fenestration decompression affects the segmental biomechanics and the related anatomic relevance.
OBJECTIVE: The finite element reverse engineering technology is used to accurately simulate the three-dimensional finite element model for the treatment of cervical spondylotic myelopathy with endoscopic cervical spine fenestration decompression, in order to study the biomechanics of cervical spine under physiological conditions.
METHODS: A volunteer’s cervical vertebrae CT data were obtained and imported into MIMICS 20.0 software to establish C4-7 finite element model M. The model M was imported into 3-matic software to simulate unilateral C4-5 fenestration model M1 and bilateral C4-5 fenestration model M2. ANSY Sworkbench 18.0 software was used to apply same physiological conditions’ pressures and torques for the above three models, and the biomechanical changes under six different working conditions, i.e., left/right bending, forward bending, backward extension and left/right rotation, were analyzed.
RESULTS AND CONCLUSION: (1) Compared with the intervertebral disc stress in model M, the stress value increased by 10% to 16% at intervertebral disc region B and D in model M1 at right bending, while increased by 10% to 15% in model M2 at right bending and increased by 10% to 14% at intervertebral disc region A and C at left bending. Compared with the intervertebral disc displacement in model M, the displacement of the intervertebral disc in model M1 increased by 10%-17% at left bending, and in model M2, the displacement of intervertebral disc increased by 10%-18% at left/right bending. The stress and displacement values of the C4-5 intervertebral discs in the three models showed no significant difference under other working conditions. (2) The results showed that the treatment of cervical spondylotic myelopathy with endoscopic cervical spine fenestration decompression could achieve accurate control, and there have little impact on the biomechanical stability of the surgical segment in both unilateral or bilateral decompressiom when removing partial lamina and facet joint within 1/2, and thus no auxiliary internal fixation is required to reconstruct segmental stability.  

Key words: bone, cervical spondylotic myelopathy, spinal endoscopy, minimally invasive surgery, fenestration decompression, finite element analysis, biomechanics