Measurement of anatomical parameters of anterior transpedicular root screw intervertebral fusion system of cervical spine.

OBJECTIVE: This study aims to investigate the feasibility of the anterior transpedicular root screw (ATPRS) intervertebral fusion system for the cervical spine and provide a basis for the design of the ATPRS intervertebral fusion system. METHODS: A total of 60 healthy adult cervical spine CT images examined from our hospital were selected, including 30 males and 30 females, with an average age of 39.6 ± 4.8 years. The image data was imported into Mimics 21.0 software in DICOM format for 3D model reconstruction. Simulated screw insertion was performed on both sides of the midline of the intervertebral space. The entry point (P1) was determined when the upper and lower screw paths did not overlap. When the screw was tangent to the medial edge of the Luschka joint, the insertion point was determined as the entry point (P2). Measurements were taken and recorded for the following parameters: distance from the screw entry point to the midline of the intervertebral space (DPM), the simulated screw length, inclination angle, cranial/caudal tilted angle, the anterior-posterior (AP) and mediolateral (ML) diameters of the cervical intervertebral space, the heights of the anterior, middle, and posterior edges of the cervical intervertebral space, and the curvature diameter of the lower end plate of the cervical vertebral body. Statistical analysis was performed on the measurement results. RESULTS: The screw entry area (P1P2) showed an increasing trend from C3-C7 in both male (2.92-6.08 mm) and female (2.32-5.12 mm) groups. There were statistical differences between men and women at the same level (P < 0.05). The average screw length of men and women was greater than 20 mm, and the upper and lower screw lengths showed an increasing trend from C3 to C7. In the area where screws could be inserted, the range of screw inclination was as follows: male group upper screw (47.73-66.76°), lower screw (48.05-65.35°); female group upper screw (49.15-65.66°) and lower screw (49.42-63.29°); The range of cranial/caudal tilted angle of the screw was as follows: male group upper screw (32.06-39.56°), lower screw (29.12-36.95°); female group upper screw (30.97-38.92°) and lower screw (27.29-37.20°). The anterior-posterior diameter and mediolateral diameter of the cervical intervertebral space showed an increasing trend from C3 to C7 in both male and female groups. The middle height (MH) of the cervical intervertebral space was greater than the anterior edge height (AH) and posterior edge height (PD), with statistical differences (P < 0.05). CONCLUSIONS: Through the study of CT images of the cervical spine, it was determined that the ATPRS intervertebral fusion system has a feasible area for screw insertion in the cervical intervertebral space.

Sting is a critical regulator of spinal cord injury by regulating microglial inflammation via interacting with TBK1 in mice.

Spinal cord injury (SCI) is a devastating neurological condition that results in progressive tissue loss, secondary to vascular dysfunction and inflammation. Lack of effective pharmacotherapies for SCI is mainly attributable to an incomplete understanding of its pathogenesis. Stimulator of interferon gene (Sting), also known as Transmembrane protein 173 (TMEM173), activates the type I interferon-regulated innate immune response, playing crucial role in modulating inflammation. However, the mechanism underlying Sting activation in SCI is still unclear. Here, we reported that Sting functioned as a positive regulator of SCI. Sting expression was increased in the injured spinal cord samples of SCI mice, along with significantly up-regulated levels of pro-inflammatory cytokines including tumor necrosis factor α (TNF-α), interleukin (IL)-1ß and IL-6. Suppressing Sting expression in lipopolysaccharide-incubated mouse microglia markedly reduced the activation of nuclear factor-κB (NF-κB) and mitogen activated protein kinases (MAPKs) signaling pathways, as illustrated by the decreased phosphorylation of IKKß, IκBα, NF-κB/p65, p38, ERK1/2 and JNK. Furthermore, LPS-stimulated release of pro-inflammatory cytokines in microglial cells was also reversed by Sting knockdown. In contrast, LPS-induced inflammation was further accelerated in microglial cells with Sting over-expression through potentiating NF-κB and MAPKs signaling. Mechanistically, Sting directly interacted with the TANK-binding kinase 1 (TBK1), thus promoting its phosphorylation and the activation of down-streaming NF-κB and MAPKs signaling pathways. Notably, the effects of Sting on SCI progression were verified in mice. Consistently, Sting knockout alleviated inflammatory response and facilitated recovery after SPI in mice through blocking TBK1 activation and subsequent NF-κB and MAPKs phosphorylation. In summary, our findings may provide a novel strategy for prevention and treatment of SCI by targeting Sting.

An RCT study on the feasibility of anterior transpedicular screw fixation in the cervicothoracic junction.

STUDY DESIGN: We evaluated the trajectory and the entry points of anterior transpedicular screws (ATPS) in the cervicothoracic junction (CTJ). OBJECTIVE: This study aimed at investigating the feasibility of ATPS fixation in the CTJ. Application of an ATPS in the lower cervical spine has been reported; however, there were no reports exploring the feasibility of anterior transpedicular screw fixation in the CTJ. METHODS: CT scans were performed in 50 cases and multiplanar reformation was used to measure the related parameters on pedicle axis view at C6-T2. Transverse pedicle angle, outer pedicle width, pedicle axis length, distance transverse intersection point (DtIP), sagittal pedicle angle, anterior vertebral body height, outer pedicle height, and distance sagittal intersection point (DsIP) were measured. The prozone of CTJ was divided into three different regions, which were named as the "manubrium region", the region "above" and "below" the manubrium. The distribution of the trajectory of sagittal pedicle axes was recorded in the three regions and the related data were statistically analyzed. RESULTS: There was no statistical difference in gender (P > 0.05). The transverse pedicle angle decreased from C6 (46.77° ± 2.72°) to T2 (20.62° ± 5.04°). DtIP increased from C6 to T2. DsIP was an average of 7.17 mm. The sagittal pedicle axis lines of the C6 and C7 were located in the region above the manubrium. T1 was mainly in the manubrium region followed by the region above the manubrium. T2 was mainly located in the manubrium region followed by the region below the manubrium. CONCLUSION: Implantation of ATPS at C6, C7, and some T1 is feasible through the low anterior cervical approach, while it is almost impossible to approach T2 that way.

Anterior transpedicular screws in conjunction with plate fixation and fusion for the treatment of subaxial cervical spine diseases.

OBJECTIVE: This study aimed at exploring the clinical application of anterior transpedicular screw (ATPS) and plate in the reconstruction of subaxial cervical spine. METHODS: 8 cases were reconstructed by ATPS and plate in the subaxial cervical spine from Jan 2009 to Dec 2011. X-rays and computed tomography images were collected to evaluate the position of ATPS. Magnetic resonance imaging was also included to evaluate the result of decompression, the existence of epidural hematoma and the morphology of the cervical spinal cord. Japanese Orthopaedic Association scores were observed before and after operation as a functional estimation. RESULTS: All of the eight cases were followed up from 3 to 36 months with the average of 15.5 months. A total of 16 ATPS were implanted in the subaxial cervical spine in the eight patients. All the screws were inserted smoothly. Bone fusion was found in all the subjects 4.5 months after operation on average. No loosening or breakage of the internal fixation was observed in our study. Hoarseness was observed in one case due to distraction injury of the recurrent laryngeal nerve, which disappeared after 3 weeks' conservative treatment. Dysphagia was complained by two patients after surgery, which was alleviated 3 months later. There were four screws deviating less than 1 mm (Grade 1), two medially and two laterally. All the anterior compressions were removed completely in this group. Only a small amount of epidural hematoma was found in four cases on MRI images before discharge. The average JOA scores were significantly improved from 5.6 ± 1.4 before surgery to 14.5 ± 0.8 at discharge (P < 0.01), which decreased to 13.2 ± 1.2 at 3 months after operation, but improved again to 15.2 ± 0.8 at 1 year after operation. CONCLUSION: Although there are some complications, ATPS with plate is an effective and safe technique for anterior reconstruction in the subaxial cervical spine. Only those spine centers with sufficient experience in complex cervical spine reconstruction surgery can conduct this technique according to strict indications.

[Three-dimensional finite-element study on anterior transpedicular screw fixation system of the subaxial cervical spine].

OBJECTIVE: To 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. METHODS: A 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. RESULTS: There 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°. CONCLUSIONS: ACTPS 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.

Radiological studies on the best entry point and trajectory of anterior cervical pedicle screw in the lower cervical spine.

OBJECTIVE: To explore the best entry point and trajectory of anterior cervical transpedicular screws in the lower cervical spine by radiological studies, and provide reference for clinical application. METHODS: Fifty patients were scanned by computed tomography and confirmed no obvious defect of the cervical spine. On horizontal axis, camber angle (α) and axial length (AL) were measured from C3 to C7. On sagittal view, the cranial or caudal angle (ß) and sagittal length (SL) were also measured from C3 to C7. On the sagittal and horizontal planes vertebrae were respectively divided into four areas, ordered 1-4, on the anterior side of the pedicle. The areas and angles of pedicle intersect into the vertebral body were recorded. We inserted six anterior pedicle screws into the lower cervical spine of three patients by this technique. RESULTS: On transverse plane, camber angle (α) of C3-C5 increased gradually, while it decreased from C5 to C7. On sagittal view, C3 and C4 pedicles showed cranial tilting, while C5 to C7 were caudally tilted. AL and SL values increased gradually from C3 to C7. The number of the intersections of C3-C7 in each area was also different. Six pedicle screws of three cases were inserted into the lower cervical spine with proper placement and no complications. CONCLUSION: Anterior transpedicular screw (ATPS) is a theoretically feasible option for internal fixation. The technique described in this paper was subsequently used in three patients without complication. Future improvement of ATPS insertion remains necessary for this technically demanding procedure.

[Feasibility of a novel type of complex anterior cervical fixation by using Mimics software].

OBJECTIVE: To investigate the feasibility of mimics software in analyzing a new type of complex anterior cervical fixation -- anterior transpedicular screw fixation+zero notch internal fixation. METHODS: From January 2021 to September 2022, 50 normal pedestrians who underwent cervical spine CT scanning were selected for C1-C7 segment scanning, including 27 males and 23 females, aged from 25 to 65 years old with an average of (46.0 ± 9.0) years old. The dicom format is exported and engraved into the CD, and use the mimics software to perform 3D reconstruction of each segment. A simulated screw is placed on the image according to the critical value of zero notch screw (head and tail angle 44°, internal angle 29°). The position of zero notch screw in each segment is observed to determine the feasibility of anterior transpedicular screw fixation plus zero notch internal fixation. RESULTS: For the upper zero notch screws the three-dimensional images of the cervical spine across all 50 subjects within the C3-C7 segments demonstrated safe position, with no instances of intersection with ATPS. For the lower zero notch screw, in C3-C4 and C4-C5, 4 out of 50 subjects are in the safe position in the three-dimensional images of cervical vertebrae, and 46 cases could achieve secure screw placement when the maximum caudal angle is(32.3±1.9) ° and (36.1±2.2) °, respectively. In C5-C6 and C6-C7 segments, no lower zero notch screws intersected with ATPS, and all screws are in safe positions. CONCLUSION: Lower cervical anterior pedicle screw fixation plus zero notch internal fixation can achieve successful nail placement through the selected entry point and position.

Biomechanical study of anterior transpedicular root screw intervertebral fusion system of lower cervical spine: a finite element analysis.

Background: The cervical anterior transpedicular screw (ATPS) fixation technology can provide adequate stability for cervical three-column injuries. However, its high risk of screw insertion and technical complexity have restricted its widespread clinical application. As an improvement over the ATPS technology, the cervical anterior transpedicular root screw (ATPRS) technology has been introduced to reduce the risk associated with screw insertion. This study aims to use finite element analysis (FEA) to investigate the biomechanical characteristics of a cervical spine model after using the novel ATPRS intervertebral fusion system, providing insights into its application and potential refinement. Methods: A finite element (FE) model of the C3-C7 lower cervical spine was established and validated. After two-level (C4-C6) anterior cervical discectomy and fusion (ACDF) surgery, FE models were constructed for the anterior cervical locked-plate (ACLP) internal fixation, the ATPS internal fixation, and the novel ATPRS intervertebral fusion system. These models were subjected to 75N axial force and 1.0 Nm to induce various movements. The range of motion (ROM) of the surgical segments (C4-C6), maximum stress on the internal fixation systems, and maximum stress on the adjacent intervertebral discs were tested and recorded. Results: All three internal fixation methods effectively reduced the ROM of the surgical segments. The ATPRS model demonstrated the smallest ROM during flexion, extension, and rotation, but a slightly larger ROM during lateral bending. Additionally, the maximum bone-screw interface stresses for the ATPRS model during flexion, extension, lateral bending, and axial rotation were 32.69, 64.24, 44.07, 35.89 MPa, which were lower than those of the ACLP and ATPS models. Similarly, the maximum stresses on the adjacent intervertebral discs in the ATPRS model during flexion, extension, lateral bending, and axial rotation consistently remained lower than those in the ACLP and ATPS models. However, the maximum stresses on the cage and the upper endplate of the ATPRS model were generally higher. Conclusion: Although the novel ATPRS intervertebral fusion system generally had greater endplate stress than ACLP and ATPS, it can better stabilize cervical three-column injuries and might reduce the occurrence of adjacent segment degeneration (ASD). Furthermore, further studies and improvements are necessary for the ATPRS intervertebral fusion system.

Unstable atlas fracture treatment by anterior plate C1-ring osteosynthesis using a transoral approach.

STUDY DESIGN: A retrospective study was conducted to evaluate anterior plate fixation of unstable atlas fractures using a transoral approach. OBJECTIVE: To further investigate the safety and efficacy of this surgical technique, as there is currently a paucity of available data. While most atlas fractures can be managed by external immobilization with favorable results, surgery is usually preferable in highly unstable cases. Surgical stabilization is most commonly achieved using a posterior approach with fixation of C1-C2 or C0-C2, but these techniques usually result in loss of joint function and cannot fully stabilize anterior arch fractures of the atlas. Although a transoral approach circumvents these issues, only nine cases were described in the literature to our knowledge. METHODS: Twenty patients with unstable atlas fractures were treated with this technique during a 6-year period. Screw and plate placement, bone fusion, and integrity of spinal cord and vertebral arteries were assessed via intraoperative and follow-up imaging. Neurologic function, range of motion, strength, pain levels, and signs of infection were assessed clinically upon follow-up. RESULTS: There were no incidents of screw loosening or breakage, plate displacement, spinal cord injury, or vertebral artery injury. A total of 20 plates were placed and all 40 screws were inserted into the atlas lateral masses. CT scans demonstrated that two screws were placed too close to the vertebral artery canal, but without clinical consequences. Imaging demonstrated that bone fusion was achieved in all cases by 6 months postoperatively, without intervertebral instability. No plate-related complications were observed in any patients during the follow-up period. CONCLUSIONS: C1 anterior plate fixation using a transoral approach appears to be a safe, reliable, and function-preserving surgical method for the management of unstable atlas fractures. For this type of fracture, a transoral approach with anterior fixation should be considered as an alternative to posterior approaches or conservative treatments.

Anatomical and Imaging Study on the Optimum Entry Point and Trajectory for Anterior Transpedicular Root Screw Placement into the Lower Cervical Spine.

Objective: To study the optimum entry point and trajectory for anterior transpedicular root screw (ATPRS) placement into the lower cervical spine (LCS), so as to provide a basis for clinical application. Methods: A retrospective analysis of cervical CT images of patients who underwent cervical CT examination in the Spinal Surgery of Ningbo No. 6 Hospital from January 2020 to August 2021 was conducted. The data were obtained and modeled. On the coronal plane, the vertebral body (VB) between the anterior midline of cervical vertebral segments C3-7 and the left P line (by drawing the line parallel to the anterior midline of the VB at the intersection of the anterior edge of the Luschka's joint and the upper endplate) was equally divided into 9 zones (a-i). The ideal entry point and path of cervical ATPRS were designed and recorded. Additionally, 7 cadaveric specimens were selected, and the screw placement parameters were regenerated according to the above methods for screw placement. Results: Zone i of each segment, with the longest screw length, was the best area for screw placement. In all patients, the horizontal angles of vertebrae C3-7 in zones a, d, and g, zones b, e, and h, and zones c, f, and i showed a gradually decreasing trend. The sagittal angle range of C3-7 in all patients showed a gradually increasing trend in zones a-c, d-f, and g-i. The distance from the anterior midline of C3-7 to the P line increased in all patients, and the distance was longer in males than in females, with statistical significance. Pedicle screws were successfully inserted in all the 7 cadaveric specimens. Conclusions: ATPRS placement can be used for LCS internal fixation, and the precise screw placement parameters can be simulated by the software, which provides theoretical basis for its future clinical application.

Biomechanical analysis of atlantoaxial intraarticular fusion cages with posterior pedicle screws fixation using finite element method.

BACKGROUND: Cadaveric biomechanical studies indicated that atlantoaxial intraarticular fusion cages with posterior pedicle screws fixation could increase the multi-axial rigidity. However, the stress distribution of the fixation construct is still unclear. METHODS: From computed tomography images, a nonlinear intact three-dimensional C0-2 finite element model was developed and validated. Four finite element models were reconstructed: intact model, unstable model, bilateral atlantoaxial pedicle screws combined bilateral cages model, bilateral atlantoaxial pedicle screws model. The range of motion and maximum von Mises stresses were compared under flexion, extension, lateral bending, and axial rotation. FINDINGS: Compared with unstable model, both bilateral atlantoaxial pedicle screws combined bilateral cages model and bilateral atlantoaxial pedicle screws model fixation techniques reduced range of motion by >99% in extension, flexion, lateral bending and axial rotation. For bilateral atlantoaxial pedicle screws combined bilateral cages model, the maximum von Mises stress was in the base of the C2 screw head site. In the bilateral atlantoaxial pedicle screws model was stressed at the rod linked C1 and C2 screws. Compared with bilateral atlantoaxial pedicle screws model, bilateral atlantoaxial pedicle screws combined bilateral cages model reduced the maximum von Mises stress on the implants by >90% in extension, flexion, lateral bending and axial rotation. INTERPRETATION: The finite element model study indicated that, compared with posterior C1-C2 pedicle screws fixation, atlantoaxial intraarticular fusion cages with posterior pedicle screws fixation could not only significantly restore stability to the atlantoaxial junction, but also dramatically reduce the maximum von Mises stress in the C1-C2 pedicle screws.

Anterior cervical transpedicular screw fixation system in subaxial cervical spine: A finite element comparative study.

Multilevel cervical corpectomy has raised the concern among surgeons that reconstruction with the anterior cervical screw plate system (ACSPS) alone may fail eventually. As an alternative, the anterior cervical transpedicular screw (ACTPS) has been adopted in clinical practice. We used the finite element analysis to investigate whether ACTPS is a more reasonable choice, in comparison with ACSPS, after a 2-level corpectomy in the subaxial cervical spine. These 2 types of implantation models with the applied 75 N axial pressure and 1 N • m pure moment of the couple were evaluated. Compared with the intact model, the range of motion (ROM) at the operative segments (C4-C7) decreased by 97.5% in flexion-extension, 91.3% in axial rotation, and 99.3% in lateral bending in the ACTPS model, whereas it decreased by 95.1%, 73.4%, 96.9% in the ACSPS model respectively. The ROM at the adjacent segment (C3/4) in the ACTPS model decreased in all motions, while that of the ACSPS model increased in axial rotation and flexion-extension compared with the intact model. Compared to the ACSPS model, whose stress concentrated on the interface between the screws and the titanium plate, the stress of the ACTPS model was well-distributed. There was also a significant difference between the maximum stress value of the 2 models. ACTPS and ACSPS are biomechanically favorable. The stability in reducing ROM of ACTPS may be better and the risk of failure for internal fixator is relatively low compared with ACSPS fixation except for under lateral bending in reconstruction the stability of the subaxial cervical spine after 2-level corpectomy.

[Establishment of finite element model of anterior cervical transpedicular system for reconstruction of cervical stability after subtotal resection of two segments of lower cervical spine].

OBJECTIVE: To establish the fixation model of anterior cervical transpedicular system (ACTPS) after subtotal resection of two segments of lower cervical spine(C3-C7) in order to provide a finite element modeling method for anterior cervical reconstruction. METHODS: The CT data of the cervical segment (C1-T1) of a 30-year-old adult healthy male volunteer was collected. Used Mimics 10.0, Rapidform XOR3, HyperMesh 10.0, CATIA5V19 and ANSYS 14.0 to establish the three-dimensional nonlinear complete model of lower cervical spine(C3-C7) as the intact group. The number of units and nodes of the complete model were recorded. After the effectiveness of the complete model was verified, the C5 and C6 vertebral subtotal resection was performed, and the ACTPS model was established as the ACTPS group. The axial force of 75 N and moment couple of 1N·m was loaded on the upper surface of C3 in intact group and ACTPS group, the range of motion(ROM)and stress distribution in states of flexion extension, lateral flexion, rotation was compared between two groups. RESULTS: There were 85 832 elements and 23 612 nodes in the complete model of lower cervical spine(C3-C7) which was established in this experiment. The stress distribution of ACTPS internal fixation model was relatively uniform. Comparing with the intact group, the overall range of motion in ACTPS group was decreased in flexion extension, lateral flexion and rotation directions, and the corresponding compensation of adjacent C3,4 segment was increased slightly. CONCLUSION: The stress distribution of ACTPS fixation system is uniform, there is no stress concentration area at the joint of screw and titanium plate, and the fracture risk of internal fixation is low. It is suitable for stability reconstruction after anterior decompression of two or more cervical segments.

Comparison of two techniques for transarticular screw implantation in the subaxial cervical spine.

STUDY DESIGN: Cross-sectional study. OBJECTIVE: To compare 2 techniques of transarticular screw placement in the subaxial cervical spine. SUMMARY OF BACKGROUND DATA: Transarticular screws have been used as an alternative method to achieve posterior cervical spine stability. According to current studies there are several techniques for the placement of transarticular screws in the subaxial cervical spine; however, there is no study that has compared these techniques. METHODS: The techniques of transarticular screw placement by Takayasu (group A) and Dalcanto (group B) were used in 8 cervical specimens. The position, number of facet fractures, involvement of the vertebral artery, encroachment of the anterior branches of cervical nerve roots, and instances that failed to go through the facets were observed and analyzed. RESULTS: Sixty-four screws were implanted, 32 for group A and the same for group B. Although no facet fractures were seen in group A, there were 10 in group B (χ=9.6, P<0.01). Eight screws involved the vertebral artery in group A and 0 in group B (χ=22.3, P<0.001). Eleven anterior branches of lower cervical nerve roots were encroached in group A and 2 in group B (χ=22.0, P<0.001). No screws failed to go through the facets in group B whereas 2 screws failed in group A, resulting in no significant difference (χ=0.52, P>0.05). CONCLUSIONS: There was a high risk of injury to the vertebral artery and anterior branches of the cervical nerve roots if the screws were too long and Takayasu technique was used. However, more facets were fractured if Dalcanto technique was applied.

[An anatomic study of posterior C(2) spinous process laminar screw fixation].

OBJECTIVES: To explore the feasibility and the technical parameters in posterior C2 spinous process laminar screw fixation, and discuss the clinic significance of C2 spinous process laminar screws. METHODS: Twenty cervical cadaveric spines of C2 were dissected, with care taken to expose the lamina and spinous process. After the entrance point of spinous process screw were determined, posterior C2 spinous process laminar screw implantation was performed under visual control. On the morphologic CT scan, the angle and length of the spinous process laminar screw trajectory and the distance between the tip of the screw and the spinal cord and the vertebral artery were measured. RESULTS: The C2 spinous process laminar screws were successfully placed, without impingement of the spinal cord and the vertebral artery. There were little differences between superior and inferior screws in the angle, trajectory length and the distance between the tip of the screw and the spinal cord and the vertebral artery, but without significance (P > 0.05). The placed angles of the screws were 76.8° ± 10.6° in the axial plane. The distance between the tip of the screw and the spinal cord and the vertebral artery was (5.3 ± 1.6) mm and (17.4 ± 3.7) mm respectively. The trajectory length was (23.1 ± 3.2) mm. CONCLUSIONS: Posterior C2 spinous process laminar screw fixation is feasible. C2 spinous process laminar screw fixation affords an alternative to standard screw placement for plate fixation and cervical stabilization.

Effectiveness of 2 Types of Drill Templates for Cervical Anterior Transpedicular Screw Placements: A Comparative Study.

OBJECTIVE: To evaluate effectiveness of regular and modified drill templates used to guide cervical anterior transpedicular screw (ATPS) placement. METHODS: This study included 15 adult cadaveric specimens. Computed tomography images were imported into Mimics software. Three-dimensional modeling of all cervical vertebrae was done, and the ideal trajectories were designed for ATPSs. Models of regular and modified templates were designed for every level on the left or right side randomly. After three-dimensional printing, 2 types of templates were used to guide the insertion. Postoperative computed tomography scans were used to measure deviations between real and ideal trajectories in the direction and positioning of entry points. The deviations in the 2 groups were compared using paired t test. RESULTS: There were 120 templates and ATPSs fabricated and placed. Postoperative images showed that 7 screws perforated pedicles in the regular group, with an accuracy rate of 88.3%. Deviations between real and ideal trajectories in cranially inclined angles and extroversive angles were 1.13° ± 0.61° and 0.97° ± 0.60°, respectively, and deviations of entry point position in the x-axis and y-axis were 0.72 ± 0.38 mm and 0.95 ± 0.47 mm, respectively. In the modified group, there were 2 malposition screws with accuracy rate of 96.7%. Deviations in cranially inclined angles were 0.66° ± 0.53° and 0.66° ± 0.55° in extroversive angles, respectively, and deviations in entry point positions in the x-axis and y-axis were 0.45 ± 0.37 mm and 0.51 ± 0.34 mm, respectively. The differences in deviations between groups were statistically significant. CONCLUSIONS: Compared with regular drill templates, modified drill templates can provide higher accuracy and stronger trajectory control in ATPS insertions.

[Comparative study between 3D guide plate assisted and free-hand insertion of anterior cervical transpedicular screw].

OBJECTIVE: To compare accuracy of anterior cervical pedicle screws between assist of rapid prototyping 3D guide plate and free-hand insertion, and evaluate the safety of two methods. METHODS: Eight adult cervical cadaver specimens after formaldehyde immersion, including 4 males and 4 females, aged 32 to 65(40.3±5.6) years old. After X-ray examination to exclude bone damage and deformity, 4 of them (3D guide plate group) randomly selected were for CT scan to obtain DICOM format data, and the data was imported into Mimics software for model, designed the ideal entry point and nail path for anterior cervicaltranspedicular screw (ATPS). After obtaining the personalized guide plate of the nail channel, it was exported as STL data, and the individual guide plate was printed by rapid prototyping and 3D printing technology. In turn, with the assistance of 3D guide plates, one-to-one personalized ATPS screws were placed on the four lower cervical cadaver specimens. Another 4 (free-hand group) lower cervical cadaver specimens were implanted with ATPS screws using free-hand technique. All specimens were performed CT thin-layer scanning and three-dimensional reconstruction after operation. The Tomasino method was used to evaluate the safety of the screws on the CT cross-sectional and sagittal images, to determine whether there was a cortical puncture of the lower and inner edges of the pedicle. According to the CT rating results, gradeⅠandⅡwere safe, and grade Ⅲ- Ⅴ were dangerous.And the accuracy of screws was recorded and analyzed between two groups. RESULTS: Two screws were inserted in each segment from C3 to C7 in 8 adult cadavers. A total of 80 screws were inserted, 40 in the 3D guide plate group, and 40 in the free-hand group. The Tomasino screw rating method was used to evaluate the safety of screw, 21 screws were gradeⅠ, 14 screws were gradeⅡ, 3 screws were grade Ⅲ, 1 screw was grade Ⅳ, 2 screws were grade Ⅴ in 3D guide plate group, while 14 screws were gradeⅠ, 8 screws were gradeⅡ, 8 screws were grade Ⅲ, 6 screws were grade Ⅳ, 2 screws were grade Ⅴ in free-hand group. The safety rate of 3D guide plate group was 87.5%, and 55.0% of the free hand group (χ2=8.7, P=0.003). CONCLUSION: The 3D printing rapid prototyping guide plate assisted insertion of the anterior cervical pedicle screw can significantly improve the accuracy and safety, and provide a theoretical basis for further clinical application.

Clinical application of C2 laminar screw technique.

C2 laminar screws have become an increasingly used alternative method to C2 pedicle screw fixation. However, the outcome of this technique has not been thoroughly investigated. A total of 35 cases with upper cervical spinal instability undergoing C2 laminar screw fixation were reviewed. All cases had symptoms of atlantoaxial instability, such as craniocervical junction pain, and were fixed with the Vertex cervical internal fixation system. A total of 68 screws were placed and hybrid constructs (a C2 translaminar screw combined with a C2 pars screw) were incorporated in two patients. In this series, there were no intraoperative complications and no cases of neurological worsening or vascular injury from hardware placement. Computed tomographic scans demonstrated a partial dorsal laminar breach in ten patients. None of these resulted in neurological symptoms. None of the patients was found to have a breach of the ventral laminar cortex. All the C2 laminar screws fixations were performed successfully. There was no instability seen on the films with no evidence of hardware failure or screw loosening during the follow-up period in all patients. In conclusion, C2 laminar screw technique is straightforward and easily adopted; it can efficiently and reliably restore upper cervical stability. It is an alternative method to C2 pedicle screw fixation, especially in patients with unilateral occlusion of vertebral artery and pedicle deformity of C2.

[Anatomical considerations for the placement of C2 spinous process screws].

OBJECTIVES: To quantitatively anatomically evaluate the C2 spinous process, analyze the anatomical feasibility of the C2 spinous process screws and its clinical significance. METHODS: To dissect and evaluate 30 cervical cadaveric spines of C2 which were taken to expose the lamina and spinous process. Anatomic quantitative evaluation of the C2 spinous process included its height and width. Twenty cervical cadaveric spines of C2 were chosen to the study of the placement of the C2 spinous process screws. The starting point for the C2 spinous process screw insertion was located at the base of the spinous process. After the entrance point of spinous process screws was determined, posterior C2 spinous process screw implantation was performed bilaterally under direct visualization. On the morphologic CT scan, the width of C2 spinous process base, the angle and length of the spinous process screw trajectory, and the distance between the tip of the screw and the spinal cord and the vertebral artery were measured. RESULTS: The average height and width of the C2 spinous process were (12.90 ± 1.30) mm and (18.86 ± 1.17) mm respectively. The C2 spinous process screws were successfully placed without impingement the spinal cord or the vertebral artery and the breakage of the spinous process. On the CT scan, the average width of the base of C2 spinous process was (20.7 ± 1.3) mm. The placed angles of the screws were 1.8° ± 1.0° in the axial plane. The distance between the tip of the screw and the spinal cord or the vertebral artery was (8.3 ± 2.6) mm and (20.2 ± 3.1) mm respectively. There were little differences between superior and inferior screws in the angle, the distance between the tip of the screw and the spinal cord or the vertebral artery, but without significance (P > 0.05). The average trajectory length of the C2 spinous process screws was (19.7 ± 1.1) mm. The average trajectory length of the superior spinous process screws was shorter than that of inferior spinous process screws, with great differences (t = 3.566, P < 0.01). CONCLUSIONS: There is the anatomic feasibility of the C2 spinous process screw fixation which may afford an alternative to standard screw placement for axis fixation. The biomechanical study for the C2 spinous process screw is also necessary.

[Effect of posterior osteotomy on the sagittal parameters of the spinopelvis in patients with lumbar degenerative kyphosis].

OBJECTIVE: To investigate the influence of posterior osteotomy on spinopelvic parameters in lumbar degenerative kyphosis (LDK) patients. METHODS: The clinical data of 21 patients with lumbar degenerative kyphosis who underwent osteotomy from January 2012 to December 2015 were retrospectively analyzed. There were 5 males and 16 females, aged from 55 to 76 years with an average of (66.24±5.13) years. All patients had taken preoperative and postoperative full length spinal X-ray, analyzing the spinopelvic parameters as thoracic kyphosis (TK), lumbar lordosis (LL), sagittal vertical axis (SVA), pelvic incidence (PI), pelvic tilt (PT) and sacral slope (SS). RESULTS: All operations were successful, the average operative time was 190 min (160 to 220 min) and intraoperative blood loss was 1 000 ml (800 to 1900 ml). Parameters of the patients between preoperative and period 1-year follow-up were as follows : preoperative TK increased from (31.67±21.13) ° to (34.67±11.60) °, LL corrected from (4.76±3.17) ° to (37.41±6.28) °, PT reduced from (33.94±5.01) ° to (20.12±5.36) °, and SS improved from (18.47±2.60) ° to (31.71±4.30) °, SVA restored from (13.24±3.60) cm to (2.82±1.33) cm. There were significant differences of spinopelvic parameters between preoperation and postoperation (P<0.05). CONCLUSION: Posterior osteotomy can effectively reconstruct the sagittal balance of spinopelvis in patients with lumbar degenerative kyphosis. The recovery of lumbar lordosis and sacral slope is closely related to the reconstruction of sagittal balance.