OBJECTIVETo evaluate the biomechanical effects of the anterior cervical transpedicular-screw system (ACTPS), compared to the anterior cervical screw plate system (ACLP), in the subaxial cervical spine after 2-level corpectomy.

METHODSA verified intact finite element subaxial cervical (C3-C7) model was established and analyzed by Mimics 10.0, Rapidform XOR3, Hypermesh 10.0, CATIA5V19, ANSYS 14.0 softwares based on the CT data (C1-T1) was collected from a 28 years old male volunteer. The axial force of 75 N and moment couple of 1N·m was loaded on the upper surface of C3, which made the model movement in flexion extension, lateral bending, rotating direction, respectively. Then, recorded the range of motion, and compared the results with the in vitro biomechanical experimental data to verify the effectiveness of the model. The ACTPS model and the ACLP model were analyzed using the finite element method. The range of motion at the operation segments (C4-C7), the range of motion at the adjacent segment (C3-C4) and stress distribution under flexion, extension, lateral bending, and axial rotation were calculated, and compared the range of motion with intact model.

RESULTSThere were 85,832 elements and 23,612 nodes in the intact model of subaxial cervical spine (C3-C7) in this experiment,and the range of motion of intact model validated with the reported cadaveric experimental data. In ACTPS group the stress was been well-distributed, but the stress concentrated on the interface between screw and the titanium plate in ACLP group. There were obvious differences of the maximum stress value between the two groups. The range of motion of fixed segments in ACTPS group was smaller than ACLP group, however adjacent segment range of motion showed no significant difference. Compared with the intact group, the range of motion in flexion extension, lateral flexion, rotation direction was decreased respectively about 25°, 20° and 8°, the range of motion at adjacent segment (C3-C4) was correspondingly compensated about 0.3°, 3° and 0.1°.

CONCLUSIONSACTPS is better than ACLP in terms of biomechanical properties. It offers rigid stability, and may be more suitable for reconstruction stability of 2-level and more than 2 levels corpectomy in the subaxial cervical spine. Meanwhile, the risk of fracture of ACTPS system is lower than that of the ACLP system.

Adult ; Biomechanical Phenomena ; Bone Screws ; Cervical Vertebrae ; surgery ; Finite Element Analysis ; Humans ; Male ; Models, Anatomic ; Range of Motion, Articular ; Rotation

Objective To evaluate the accuracy in placement of cervical anterior transpedicular screws (ATPS) under the guidance of our modified drilling template.Methods Eight wet cadaveric specimens of adult cervical spine,4 male and 4 female ones,were used for this experiment.Data of CT thin layer scanning of the cervical specimens in DICOM format were imported into software Mimics 17.0.After 3D models of the cervical vertebrae were reconstructed,the optimal trajectory was designed for ATPS placement in the transparent mode of the 3D models.Normal and our modified drilling templates for ATPS placement were designed and manufactured by 3D printing.The 2 kinds of drilling templates were used to assist ATPS placement onto one cervical vertebra,with laterality randomized.Altogether 64 pieces of ATPS were placed,with 32 ones for each drilling template.Postoperative CT scanning was conducted to evaluate the accuracy in ATPS placement.The 2 kinds of ATPS template were compared in terms of the deviations between actual and ideal trajectories in direction (caudal-angle and extroversive-angle) and position (X and Y axes) of the entry point.Results Our modified drilling template led to one screw penetrating the pedicle cortical bone while the normal drilling template led to 4 screws penetrating the pedicle cortical bone,yielding an accuracy rate of 96.9％ and of 87.5％ respectively.The extroversive-angle deviation (0.72°±0.69°),caudal-angle deviation (0.91°±0.70°),X axis shift (0.53 ±0.40 mm) and Y axis shift (0.54 ±0.42 mm) related to the modified template were all significantly smaller than those related to the normal template (1.16° ± 0.70°,1.49°±0.68°,0.88±0.40mm,1.22±0.42mm,respectively) (P ＜0.05).Conclusion Compared with a normal ATPS template,our modified drilling template for ATPS may be advantageous in better fitness,greater stability,increased accuracy in screw placement,and protection of adjacent discs.