Comparison of the anatomic risk for vertebral artery injury associated with percutaneous atlantoaxial anterior and posterior transarticular screws

Anterior Transarticular Crossing Screw Fixation for Atlantoaxial Joint Instability: A Biomechanical Study

OBJECTIVE

To evaluate the biomechanical stability of anterior transarticular crossing screw (ATCS) and compare it with anterior transarticular screw (ATS) which may provide basic evidence for clinical application.

METHODS

Eight human fresh cadaveric specimens (occiput-C4) were tested with 5 conditions including the intact status, the injury status (type II odontoid fracture), the injury+ATS fixation status (traditional bilateral ATS fixation); the injury+unilateral ATCS fixation status; and the injury+bilateral ATCS fixation status. Specimens were applied to a pure moment of 1.5 Nm in flexion-extension, lateral bending, and axial rotation, respectively. The range of motions (ROMs) and the neutral zones (NZs) of C1 to C2 segment were calculated and compared between 5 status.

RESULTS

ATS and ATCS fixations significantly reduced the motions in all directions when compared with the intact and injury statues (p < 0.05). In flexion-extension, the ROMs of ATS, unilateral ATCS, and bilateral ATCS were 4.7° ± 2.5°, 4.1° ± 1.9°, and 3.2° ± 1.2°, respectively. Bilateral ATCS resulted in a significant decrease in ROM in flexion-extension when compared with ATS and unilateral ATCS (p = 0.035 and p = 0.023). In lateral bending and axial rotation, there was no significant difference in ROM between the 3 fixations (p > 0.05). Three fixations resulted in similar NZs in all directions (p > 0.05).

CONCLUSION

ATCS is a biomechanically effective alternative or supplemental method for atlantoaxial instability.

Degenerative cervical myelopathy caused by posttraumatic severe atlantoaxial dislocation over 10 years in patients with right vertebral artery hypoplasia: A case report of successful management

INTRODUCTION

Degenerative cervical myelopathy caused by long-standing neglected AAD is rare, especially in severe cases. Combined with the exceptional right vertebral artery hypoplasia condition, treatment must be integrated into multitherapy to avoid fatal complications.

CASE

A 55-year-old man presented with degenerative cervical myelopathy caused by posttraumatic severe atlantoaxial dislocation for more than 10 years in patients with right vertebral artery hypoplasia. After treatment with halo traction and C1 lateral mass, as well as C2 pedicle screw fixation combined with bone autoplasty, the condition was resolved.

CONCLUSION

This is an extremely rare and severe condition (anatomical damage, long-term sequelae, degree of paralysis on admission, and complete hypoplasia of the right vertebral artery). The treatment strategy is consistent with early favorable outcomes.

Design a novel integrated screw for minimally invasive atlantoaxial anterior transarticular screw fixation: a finite element analysis

PURPOSE

To design a new type of screw for minimally invasive atlantoaxial anterior transarticular screw (AATS) fixation with a diameter that is significantly thicker than that of traditional screws, threaded structures at both ends, and a porous metal structure in the middle. The use of a porous metal structure can effectively promote bone fusion and compensate for the disadvantages of traditional AATSs in terms of insufficient fixation strength and difficulty of bone fusion. The biomechanical stability of this screw was verified through finite element analysis. This instrument may provide a new surgical option for the treatment of atlantoaxial disorders.

METHODS

According to the surgical procedure, the new type of AATS was placed in a three-dimensional atlantoaxial model to determine the setting of relevant parameters such as the diameter, length, and thread to porous metal ratio of the structure. According to the results of measurement, the feasibility and safety of the new AATS were verified, and a representative finite element model of the upper cervical vertebrae was chosen to establish, and the validity of the model was verified. Then, finite element-based biomechanical analysis was performed using three models, i.e., atlantoaxial posterior pedicle screw fixation, traditional atlantoaxial AATS fixation, and atlantoaxial AATS fixation with the new type of screw, and the biomechanical effectiveness of the novel AATS was verified.

RESULTS

By measuring the atlantoaxial parameters, the atlantoaxial CT data of the representative 30-year-old normal adult male were selected to create a personalized 3D printing AATS screw. In this case, the design parameters of the new screw were determined as follows: diameter, 6 mm; length of the head thread structure, 10 mm; length of the middle porous metal structure, 8 mm (a middle porous structure containing an annular cylinder ); length of the tail thread structure, 8 mm; and total length, 26 mm. Applying the same load conditions to the atlantoaxial complex along different directions in the established finite element models of the three types of atlantoaxial fusion modes, the immediate stability of the new AATS is similar with Atlantoaxial posterior pedicle screw fixation.They are both superior to traditional atlantoaxial anterior screw fixation.The maximum local stress on the screw head in the atlantoaxial anterior surgery was less than those of traditional atlantoaxial anterior surgery.

CONCLUSIONS

By measuring relevant atlantoaxial data, we found that screws with a larger diameter can be used in AATS surgery, and the new AATS can make full use of the atlantoaxial lateral mass space and increase the stability of fixation. The finite element analysis and verification revealed that the biomechanical stability of the new AATS was superior to the AATS used in traditional atlantoaxial AATS fixation. The porous metal structure of the new AATS may promote fusion between atlantoaxial joints and allow more effective bone fusion in the minimally invasive anterior approach surgery.

Biomechanical evaluation of C1 lateral mass and C2 translaminar bicortical screws in atlantoaxial fixation: an in vitro human cadaveric study

BACKGROUND CONTEXT

Atlantoaxial fixation with C1 lateral mass-C2 translaminar bicortical (C1LM-C2TB) screws has been reported to afford good stability with the least risk of injury to vertebral artery. However, no comparative in vitro studies have been conducted to evaluate the biomechanical stability of this method.

PURPOSE

This study aimed to compare in vitro biomechanics of fixation with C1LM-C2TB with fixation with C1 lateral mass-C2 translaminar unicortical screws (C1LM-C2TU) and with C1 lateral mass-C2 pedicle screws (C1LM-C2PS).

STUDY DESIGN

This is an in vitro biomechanical study.

METHODS

Fifteen fresh-frozen human cadaveric cervical spines (C1-C3) were tested after destabilization by transverse-alar-apical ligament disruption. Instrumentation was performed with three fixation constructs: C1LM-C2PS, C1LM-C2TU, and C1LM-C2TB. Flexion, extension, lateral bending, and axial rotation were tested. Range of motion and neutral zone pre-fatigue and post-fatigue values were measured.

RESULTS

No significant differences were observed in flexion-extension among the three groups. However, C1LM-C2TB fixation was superior to C1LM-C2TU fixation in lateral bending and axial rotation.

CONCLUSION

C2 translaminar bicortical screws are biomechanically superior to C2TU screws for fixation of the atlantoaxial complex, and it is equivalent to C2PS fixation. C2 translaminar bicortical screws or C2PS should be preferred over C2TU screws.

"Inline" Axial Reconstructed CT Scans Provide a Significantly Larger Assessment of C2 Pedicle Diameter for Screw Placement Compared With "Standard" Axial Scans: Implications for Surgical Planning

STUDY DESIGN

Radiologic analysis.

OBJECTIVE

The objective was to compare C2 pedicle diameter and screw feasibility on reconstructed axial computed tomography (CT) cuts created "Inline" (IL) with the intended pedicle screw tract versus unaltered "Standard" (STD) axial cuts.

BACKGROUND DATA

Axial CT cuts through the C2 pedicle are commonly evaluated when planning pedicle screw fixation as medial aberrancies of the vertebral artery can significantly narrow pedicle diameter. STD axial CT cuts provided by radiology departments are typically formatted orthogonal to the long axis of the neck or the vertical plumb, which is often not IL with the axis of the intended C2 pedicle screw tract.

MATERIALS AND METHODS

A total of 89 cervical spine CT scans obtained by a single radiology department over 2 years (35 male, 54 female; mean age 64.9 y) were reviewed. STD axial cuts were not manipulated but were assessed as provided. IL axial cuts were created along the intended C2 pedicle screw tract using free, open-source DICOM viewer software. Inner and outer pedicle diameters were measured on axial cuts most closely approximating the isthmus of the intended tract.

RESULTS

On STD cuts, the mean outer and inner pedicle diameters were 5.05±1.45 and 2.01±1.31 mm, respectively. By contrast, IL measurements yielded significantly larger outer and inner diameters: 5.85±1.78 and 2.68±1.47 mm (P<0.01). IL measurement predicted a higher number of pedicles amenable to insertion of a 3.5 mm screw with safety margins of 1 to 3 mm.

CONCLUSIONS

Reformatted IL axial cuts through the intended path of C2 pedicle screws provide significantly larger assessments of C2 pedicle diameter than those obtained on STD cuts. IL measurements predict C2 screw insertion feasibility in a substantially higher number of pedicles. As assessment of IL cuts may alter surgical decision-making at no added cost or radiation exposure, we suggest that they be obtained whenever considering C2 pedicle screw placement.

Percutaneous anterior C1/2 transarticular screw fixation: salvage of failed percutaneous odontoid screw fixation for odontoid fracture

BACKGROUND

The objective of this study is to investigate the outcomes and safety of using percutaneous anterior C1/2 transarticular screw fixation as a salvage technique for odontoid fracture if percutaneous odontoid screw fixation fails.

METHODS

Fifteen in 108 odontoid fracture patients (planned to be treated by percutaneous anterior odontoid screw fixation) were failed to introduce satisfactory odontoid screw trajectory. To salvage this problem, we chose the percutaneous anterior C1/2 transarticular screw fixation technique in treatment of these patients. The visual analogue score (VAS) of neck pain and Neck Disability Index (NDI) of all patients were scored at pre-operation, 3 months after operation, and final follow-up. Additional, technique-related complications were recorded and collected.

RESULTS

Percutaneous C1/2 transarticular screw fixation was performed successfully in all 15 patients whose odontoid screw fixation failed. No technique-related complications (such as nerve injury, spinal cord injury, and esophageal injury) occurred. The VAS of neck pain and NDI score improved significantly (P = 0.000) after operation, and no significant differences were found when compared to 93 non-salvage patients who successfully performed the percutaneous anterior odontoid screw fixation. No screw loose or breakage occurred, all of the odontoid fractures achieve radiographic fusion, bony fusion bridge could be observed at the C1/2 lateral articular facet on 9/15 patients.

CONCLUSIONS

We suggest that percutaneous anterior C1/2 transarticular screw fixation is a good alternative salvage technique if percutaneous odontoid screw fixation failed, and it is a minimally invasive, feasible, and safe technique.

A novel computed method to reconstruct the bilateral digital interarticular channel of atlas and its use on the anterior upper cervical screw fixation

Purpose. To investigate a novel computed method to reconstruct the bilateral digital interarticular channel of atlas and its potential use on the anterior upper cervical screw fixation.

Methods. We have used the reverse engineering software (image-processing software and computer-aided design software) to create the approximate and optimal digital interarticular channel of atlas for 60 participants. Angles of channels, diameters of inscribed circles, long and short axes of ellipses were measured and recorded, and gender-specific analysis was also performed.

Results. The channels provided sufficient space for one or two screws, and the parameters of channels are described. While the channels of females were smaller than that of males, no significant difference of angles between males and females were observed.

Conclusion. Our study demonstrates the radiological features of approximate digital interarticular channels, optimal digital interarticular channels of atlas, and provides the reference trajectory of anterior transarticular screws and anterior occiput-to-axis screws. Additionally, we provide a protocol that can help make a pre-operative plan for accurate placement of anterior transarticular screws and anterior occiput-to-axis screws.

Percutaneous atlantoaxial anterior transarticular screw fixation combined with mini-open posterior C1/2 wire fusion for patients with a high-riding vertebral artery

CONTEXT/OBJECTIVE

To describe the technique and clinical results of percutaneous atlantoaxial anterior transarticular fixation combined with limited exposure posterior C1/2 arthrodesis in patients with a high-riding vertebral artery.

DESIGN SETTING

Zhejiang Spine Center, China.

PARTICIPANTS

Five patients with a high-riding vertebral artery and an upper cervical fracture.

INTERVENTIONS

Percutaneous atlantoaxial anterior transarticular screw fixation combined with limited exposure posterior C1/2 wire fusion.

OUTCOME MEASURES

Computed tomography scans were used to assess the high-riding vertebral artery and feasibility of anterior transarticular screw fixation preoperatively. A Philadelphia collar was used to immobilize the neck postoperatively. Anteroposterior (open-mouth) and lateral views were obtained at pre/postoperation and at the follow-up.

RESULTS

The operation was performed successfully on all of the patients, and no intraoperative operation-related complications such as nerve injury, vertebral artery, and soft tissue complications occurred. The mean follow-up period was 33.8 months (range: 24 to 58 months). No screw breakage, loosening, pullout, or cutout was observed. Bone union was achieved in all patients at the last follow-up.

CONCLUSIONS

Our small case series results suggested that percutaneous anterior transarticular screw fixation combined with mini-open posterior C1/2 wire fusion is a technically minimally invasive, safe, feasible, and useful method to treat patients with a high-riding vertebral artery.

Biomechanical Evaluation of the Stabilizing Function of Three Atlantoaxial Implants Under Shear Loading: A Canine Cadaveric Study

OBJECTIVE

To compare the biomechanical properties of a ventral transarticular lag screw fixation technique, a new dorsal atlantoaxial instability (AAI) clamp, and a new ventral AAI hook plate under sagittal shear loading after transection of the ligaments of the atlantoaxial joint.

STUDY DESIGN

Cadaveric biomechanical study.

ANIMALS

Canine cadavers (n = 10).

MATERIALS AND METHODS

The occipitoatlantoaxial region of Beagles euthanatized for reasons unrelated to the study was prepared leaving only ligamentous structures and the joint capsules between the first 2 cervical vertebrae (C1 and C2). The atlanto-occipital joints were stabilized with 2 transarticular diverging positive threaded K-wires. The occipital bone and the caudal end of C2 were embedded in polymethylmethacrylate and loaded in shear to a force of 50 Newtons. The range of motion (ROM) and neutral zone (NZ) of the atlantoaxial joint were determined after 3 loading cycles with atlantoaxial ligaments intact, after ligament transection, and after fixation with each implant. The testing order of implants was randomly assigned. The implants tested last were subjected to failure testing.

RESULTS

All stabilization procedures decreased the ROM and NZ of the atlantoaxial joint compared to transected ligament specimens. Only stabilization with transarticular lag screws and ventral plates produced a significant reduction of ROM compare to intact specimens.

CONCLUSION

Fixation with transarticular lag screws and a ventral hook plate was biomechanically similar and provided more rigidity compared to dorsal clamp fixation. Further load cycling to failure tests and clinical studies are required before making clinical recommendations.

Feasibility and trajectory study of anterior transarticular crossing screw placement for atlantoaxial joint instability: a cadaveric study and description of a novel technique

PURPOSE

In unique clinical situations where C1-C2 anterior transarticular screw (ATS) fixation is not available or has failed, an anterior transarticular crossing screw (ATCS) with transcorporal pathway of the screws inside the contralateral promontory of C2 may enhance the stabilization and achieve atlantoaxial arthrodesis. The present study was to describe a novel technique of ATCS fixation for atlantoaxial joint instability and its applied anatomy, and compared it with ATS fixation method.

METHODS

Direct measurements using digital calipers and a goniometer were conducted on 30 pairs of dried human C1 and C2 vertebrae. The ATS and ATCS with screws (Φ 4.0 mm) were performed on 11 fresh cervical spine specimens. The screw lengths in the C1 and C2, and screw entry angles of the ATS and ATCS were measured, respectively. Cadaver specimens were dissected to observe the incidence of violation to the important structures surrounding the ATS and ATCS fixation technique.

RESULTS

There was enough osseous space for ATCS placement. The lateral and incline angle of the ATCS was 36.2° and 28.7°, respectively. Screw purchase in C2 of the ATCS (25.6 mm) was greater than that of the ATS (11.4 mm). The ATCS C1 purchase (14.8 mm) was similar to the ATS C1 purchase (14.9 mm). No violation to the vertebral artery groove, the spinal canal or the atlanto-occipital joint was observed after the ATCS placement.

CONCLUSION

Anterior transarticular crossing screw is a feasible and viable option for atlantoaxial fixation in selected cases. This technique achieved remarkable longer screw purchase and could enhance the atlantoaxial stability.

Atlantoaxial anterior transarticular screw fixation: a case series and reappraisal of the technique

BACKGROUND CONTEXT

Atlantoaxial instability is commonly treated with C1-C2 fixation performed via posterior approaches. Although anterior transarticular screw (ATS) fixation, performed with a classic retropharyngeal approach, was described more than 10 years ago, the published literature still lacks a comprehensive analysis of the procedure and a real case series.

PURPOSE

We report a series of patients treated with atlantoaxial ATS, describing the surgical procedure in detail and discussing advantages and disadvantages of the technique.

STUDY DESIGN

The study design includes case series and technical report.

METHODS

We prospectively enrolled 15 patients affected by atlantoaxial instability secondary to trauma, degenerative diseases, or inflammatory diseases. Anterior transarticular screw fixation was performed with anteroposterior open-mouth and lateral intraoperative radiographs. All patients were evaluated radiologically at follow-up to identify bone fusion.

RESULTS

Anterior transarticular screw was performed successfully in 14 patients without complications. The procedure was aborted in a case of vertebral invagination, and one case required revision surgery owing to C2 articular bone fracture. Solid C1-C2 fusion was achieved in all cases (at 10- to 21-week follow-up) except in an elderly patient affected by severe osteoporosis. No complications occurred.

CONCLUSIONS

Although the procedure is still not widely known, ATS allows the effective and safe treatment of C1-C2 instability even in patients with systemic comorbidities. It offers several advantages over posterior approaches.

Fluoroscopically guided anterior atlantoaxial transarticular screws: a feasibility and trajectory study using CT-based simulation software

BACKGROUND CONTEXT

Anterior transarticular screw (ATAS) fixation has been suggested as a viable alternative to posterior stabilization. However, we are not aware of previous reports attempting to establish the usefulness of specific fluoroscopic landmark-guided trajectories in the use of ATAS, and we could find no reference to it in a computerized search using MEDLINE.

PURPOSE

To determine the anatomic feasibility of ATAS placement using defined fluoroscopic landmarks to guide screw trajectory.

STUDY DESIGN

Evaluation using three-dimensional screw insertion simulation software and 1.0-mm-interval computed tomographic scans.

PATIENT SAMPLE

Computed tomographic scans of 100 patients including 50 men and 50 women.

OUTCOME MEASURES

Incidence of violation of the vertebral artery groove of C1 and C2, the spinal canal, and the atlanto-occipital joint and screw lengths and lengths of C1 and C2 purchase.

METHODS

Four screw trajectories were determined: promontory screw (PS), single central facet (CF) screw, and medial (MF) and lateral (LF) double facet screws. Placement of a 4.0-mm screw was simulated using defined fluoroscopic landmarks for each trajectory. The previously mentioned outcome measures were evaluated and compared for the four trajectories. This study was not supported by any financial sources, and there is no topic-specific potential conflict of interest with this study.

RESULTS

No violation of the C1 or C2 vertebral artery groove or of the spinal canal was observed for any of the screw types. Screw lengths and the length of C2 purchase were by far the longest for PS (40.4±2.8 and 25.7±2.1 mm, respectively; p<.001 in all post hoc comparisons). The length of C1 purchase was longer for CF (16.4±2.3 mm) and LF (15.8±1.6 mm) than PS (14.7±2.0 mm) and MF (14.6±2.4 mm) (p≤.001, respectively). There was no atlanto-occipital joint violation if the length of C1 purchase was set at 12 mm for CF and LF and at 10 mm for PS and MF.

CONCLUSIONS

Our results suggest that it may be possible to place ATASs without violating the vertebral artery groove, spinal canal, or the atlanto-occipital joint by using the described entry points, trajectories, and fluoroscopic landmarks.

Deviation analysis of C2 translaminar screw placement assisted by a novel rapid prototyping drill template: a cadaveric study

PURPOSE

The goal of this study is to evaluate the accuracy of patient-specific CT-based rapid prototype drill templates for C2 translaminar screw insertion.

METHODS

Volumetric CT scanning was performed in 32 cadaveric cervical spines. Using computer software, the authors constructed drill templates that fit onto the posterior surface of the C2 vertebrae with drill guides to match the slope of the patient's lamina. Thirty-two physical templates were created from the computer models using a rapid prototyping machine. The drill templates were used to guide drilling of the lamina and post-operative CT images were obtained. The entry point and direction of the planned and inserted screws were measured and compared.

RESULTS

Sixty-four C2 translaminar screws were placed without violating the cortical bone of a single lamina. The bilateral average transverse angle of intended and actual screw for C2TLS was 56.60 ± 2.22°, 56.38 ± 2.51°, 56.65 ± 2.24°, 56.39 ± 2.45°. The bilateral mean coronal angle of the planned and actual screw for C2TLS was 0°, 0°, -0.07 ± 0.32°, 0.12 ± 0.57°. The average displacement of the entry point of the superior and inferior C2TLS in the x, y, z axis was 0.27 ± 0.85, 0.49 ± 1.46, -0.28 ± 0.69, 0.43 ± 0.88, 0.38 ± 1.51, 0.23 ± 0.64 mm.

CONCLUSION

The small deviations seen are likely due to human error in the form of small variations in the surgical technique and use of software to design the prototype. This technology improves the safety profile of this fixation technique and should be further studied in clinical applications.