A finite element analysis of the stability of posterior open door extended laminoplasty in cervical spine combined with lateral mass screw fixation

English Keywords:Open door extended laminoplasty  Lateral mass screw  Finite element analysis

English Abstract:

  【Abstract】 Objectives: To construct a multi-segment cervical spinal stenosis with instability model through finite element technology, and to analyze and compare the stability difference of posterior open door laminoplasty combined with unilateral or bilateral lateral mass screw fixations. Methods: A C0-T1 muscular finite element model of the cervical spine was constructed based on the cervical computed tomography(CT) data of an adult healthy male volunteer who visited Ningbo No.6 Hospital in January 2023. The model′s range of motion(ROM) in flexion and extension, lateral bending, and rotation aligned closely with the ROM results reported in relevant literature, showing reasonable stress distribution and high reliability. And based on the complete model, models of cervical multi-segment spinal stenosis and multi-segment spinal stenosis combined with instability were generated using finite element technology. After setting the left side of the two models as the door opening side, removing the full layer of vertebral lamina and fixing with titanium plate, and making a V-shaped groove on the right side as the door axis, an open-door model of multi-segment spinal stenosis (classical open-door group) and an open-door model of multi-segment spinal stenosis combined with instability (unstable open-door group) were established, respectively. On the basis of model of unstable open-door group, unilateral or bilateral lateral mass screws were implanted in C3-C7 segments, generating a unilateral lateral mass screw fixation model(unilateral screw group) and a bilateral lateral mass screw fixation model(bilateral screw group). The ROM and stress distribution in flexion extension, lateral bending, and rotation directions of each group of models were calculated. The ROM results of the unstable open-door group, unilateral screw group, and bilateral screw group were tested using independent sample F, and comparison between groups was made with SNK′s q test. Results: The ROMs in all motion directions of the C3-C7 segment in unilateral screw group and bilateral screw group were smaller than unstable open-door group (P<0.05); The ROMs in flexion, extension, and lateral bending directions at the C3-C7 segments in the bilateral screw group was also smaller than those in the unilateral screw group(P<0.05). The peak stress of the screws in the unilateral screw group was relatively high in the left bending and left rotation directions, with values of 402.9MPa and 450.2MPa, respectively; In the bilateral screw group, the stress peaks of the screw in flexion and extension directions were significantly higher than those in the other directions, at 409.8MPa and 651MPa, respectively. Conclusions: Compared to the open door extended laminoplasty, both unilateral lateral mass screw fixation and bilateral lateral mass screw fixation demonstrate good mechanical stability.