Objective To compare biomechanical properties of cortical bone trajectory (CBT) screw and traditional trajectory screw for fixing upper-middle thoracic spine. Methods The tomography images were obtained by CT scanning of normal T7 and T8 segments, and the three-dimensional (3D) model of T7-8 was reconstructed by Mimics software. The finite element model of upper-middle thoracic spine was established by optimizing FreeForm model and pre-processing function of ANSYS software. On this basis, the CBT screw and pedicle screw fixation models after discectomy were established, and 5 N·m flexion, extension, lateral bending and rotation loads were applied to the two model groups, respectively. The displacement and peak stress of vertebrae and implants under different working conditions were compared and analyzed. Results Under different loading conditions, the maximum displacement of CBT screw group was lower than that of pedicle screw group, and the range of motion of CBT screw group was lower than that of pedicle screw group. The stress level of both models was close, and the stress of CBT screw group was slightly lower than that of pedicle screw group. Under the load of flexion, extension and rotation, the maximum vertebral stress of pedicle screw group decreased by 31%, 17% and 18% compared with that of CBT screw group, and under lateral bending load, the vertebral stress of CBT screw group was 20% lower than that of pedicle screw group. Under the load of flexion and rotation, the maximum stress of pedicle screw group decreased by 2% and 11%; however, the maximum stress of CBT screw group was 11% and 1% lower than that of pedicle screw group. Conclusions The stability of CBT screw was better than that of pedicle screw, and the overall stress distribution was similar to that of pedicle screw. However, the vertebral stress distribution of CBT group was slightly inferior. The research findings provide a theoretical basis for the clinical application of cortical screw fixation after the failure in pedicle screw fixation for the upper-middle thoracic vertebrae.

Objective:To evaluate the feasibility of using cortical bone trajectory (CBT) screws in the osteoporotic thoracolumbar fixation by comparing the bone CT values at the bone-screw interface between traditional trajectory (TT) screws and CBT screws in patients with different bone densities.Methods:The high-resolution CT imaging data of thoracolumbar segments following thoracic or lumbar spine fractures from April 2020 to October 2022 were collected at The Second Hospital Affiliated to Wenzhou Medical University for retrospective analysis. They were divided into 3 groups: a normal bone mass group, an osteopenia group and an osteoporosis group. From each group 30 cases were chosen (90 cases in total, 36 males and 54 females). All the data were imported into Mimics 18.0 for three-dimensional bone reconstruction in which placement of TT and CBT screws was simulated on the vertebrae from T10 to L2 (non-fractured vertebrae). Regions of interest (ROI) where each simulated screw intersected the bone were segmented to measure their CT bone values. For each vertebra in each group, the relative difference percentage in average CT value of ROI between TT and CBT screws was calculated. The CT values of ROI were compared in the same group between TT and CBT screws from T10 to L2; the CT values of ROI were compared in the same screws among the 3 groups from T10 to L2; the CT values of ROI were compared between the CBT screws in the osteopenia and osteoporosis groups and the TT screws in the normal bone mass group; the relative difference percentages in average CT value of ROI between CBT and TT screws were compared between the 3 groups from T10 to L2.Results:The average CT value of ROI for CBT screws was significantly higher than that for TT screws from T10 to L2 in every group ( P< 0.001); as for the CT values of ROI for CBT and TT screws from T10 to L2, the osteoporosis group0.05). At T10, T12, and L1, the relative difference percentage in average CT value of ROI between CBT and TT screws was significantly higher in the osteopenia and osteoporosis groups than that in the normal bone mass group ( P<0.05), but there was no such a difference between the osteopenia and the osteoporosis groups ( P>0.05). At T11 and L2, there was no significant difference between the 3 groups in the relative difference percentage in average CT value of ROI between CBT and TT screws ( P>0.05). Conclusions:As bone mass decreases, both CBT and TT screws lead to a significant decrease in the bone density at the bone-screw interface. In patients with osteoporosis, CBT screws can still lead to a higher bone density at the bone-screw interface than TT screws, thus providing a higher strength at the bone-screw interface.

Objective:To introduce a novel technique note about anterior decompression through transoral axis slide and rotation osteotomy (ASRO) and identify its imaging parameters related to osteotomy, and to explore its clinical application value.Methods:CT data of cervical spine of 90 subjects were collected, including 54 males and 36 females. The age ranged from 26 to 72 years, with an average age of 48.7 years. The Mimics software was used to reconstruct the atlantoaxial three-dimensional model. We plan to perform osteotomy on both sides of the axis of the vertebral body in the anteroposterior direction and the ASRO related anatomical parameters were measured, including the minimum osteotomy angle, the maximum osteotomy angle, the minimum and maximumdistance between the osteotomy trajectory and the inner side of the articular surface, the length of the upper articular surface of the axis side mass, the depth of osteotomy at the highest point and lowest point of the axial osteotomy surface and the minimum osteotomy depth. A 56-year-old female patient was admitted to the hospital due to atlantoaxial dislocation with failure of occipital-cervical fusion, difficulty walking, weakness and hypoaesthesia in four limbs. Imaging revealed that narrow space between the transversal walking wire and upper-posterior of the odontoid process, compressing the spinal cord from the front and the back respectively. The ASRO technique was performed on the patient under neuro-electrophysiological monitoring, and the osteotomy angle, osteotomy depth, narrowest width of the upper cervical spinal canal, the medullary, spinal cord angle were measured and Japanese Orthopaedic Association Scores (JOA) cervical myelopathy evaluation were performed after the operation to evaluate the surgical treatment effect.Results:The minimum osteotomy angle and the maximum osteotomy angle was 14.7°± 4.36° and 33.0°± 8.67°. The minimum and maximumdistance between the osteotomy trajectory and the inner side of the articular surface, and the length of the upper articular surface of the axis side mass was 6.0±1.80 mm, 12.2±3.17 mm, and 17.2±1.90 mm, the ratio of the former two to the latter was 34%±8.7% and 70%± 15.0%. The depth of osteotomy at the upper edge, lower edge and narrowest place of the axial osteotomy surface were 6.0±1.80 mm, 12.2±3.17 mm and 17.2±1.90 mm. The postoperative imaging of the patient showed that the osteotomy angle was 17.1° on left side and 16.5° on right side, and the depth of osteotomy at the upper edge, lower edge and narrowest place of the axial osteotomy surface were 17.1 mm, 13.2 mm, and 9.1 mm on left side, and 17.4 mm, 11.8 mm, 8.46 mm on right side. All measured values met the ranges which were shown in the imaging anatomical study. The narrowest width of the upper cervical spinal canal increased from 6.58 mm to 15.28 mm, the medullary spinal cord angle increased from 131.7° to 153.8°postoperatively, and the cervical spine JOA score recovered from 6 points to 14 points, suggesting that the postoperative spinal canal space is obvious increased, the compression on the front of the spinal cord was significantly reduced. The patient's symptoms improved significantly.Conclusion:ASRO technique is a good choice for salvage of failed posterior occipitocervical fusion and some irreducible atlantoaxial dislocation because of the anterior bony fusion. It could direct decompress the spinal cord anteriorly, avoid the odontoid resection, which is a safe and feasible new technique.