Anterior occiput-to-axis screw fixation: part I: a case report, description of a new technique, and anatomical feasibility analysis

Anterior atlanto-occipital transarticular screw fixation: a biomechanical comparison with posterior fixation techniques

OBJECTIVE

Atlanto-occipital instability is commonly treated with posterior fixation. However, in patients with congenital or acquired factors, posterior fixation may not be possible. For these situations, a novel anterior atlanto-occipital transarticular screw (AATS) fixation technique has been introduced recently. However, biomechanical study of this technique is lacking. This study was designed to evaluate the biomechanical stability of AATS fixation for the atlanto-occipital joint and compare it with conventional posterior occipitocervical fixation (POCF).

METHODS

Six cadaveric specimens (occiput-C4) were tested in four conditions, including intact, injury, injury + AATS, and injury + POCF states. A pure moment of 1.5 Nm was applied to specimens in flexion, extension, lateral bending, and axial rotation. The range of motion (ROM) and neutral zone (NZ) were calculated and compared from the occiput to C1.

RESULTS

The AATS fixation constrained ROMs to 0.4° in flexion (p < 0.001), 0.4° in extension (p < 0.001), 1.0° in lateral bending (p < 0.001), and 0.7° in axial rotation (p < 0.001) when compared with the injury state. In all directions, there was no statistically significant difference observed in ROMs and NZs between AATS fixation and POCF (p > 0.05).

CONCLUSIONS

This study identified that the novel AATS fixation, as stand-alone anterior fixation, was equivalent to POCF in all directions. The results suggest that anterior transarticular screw fixation is a biomechanically effective salvage technique for posterior atlanto-occipital fixation, and may also serve as supplemental fixation.

Biomechanical comparison of anterior axis-atlanto-occipital transarticular fixation and anterior atlantoaxial transarticular fixation after odontoidectomy: A finite element analysis

Background: Anterior axis-atlanto-occipital transarticular fixation (AAOF) and anterior atlanto-axial transarticular fixation (AAF) are two common anterior screw fixation techniques after odontoidectomy, but the biomechanical discrepancies between them remain unknown. Objectives: To investigate the biomechanical properties of craniovertebral junction (CVJ) after odontoidectomy, with AAOF or AAF. Methods: A validated finite element model of the intact occipital-cervical spine (from occiput to T1) was modified to investigate biomechanical changes, resulting from odontoidectomy, odontoidectomy with AAOF, and odontoidectomy with AAF. Results: After odontoidectomy, the range of motion (ROM) at C1-C2 increased in all loading directions, and the ROM at the Occiput-C1 elevated by 66.2%, 57.5%, and 41.7% in extension, lateral bending, and torsion, respectively. For fixation models, the ROM at the C1-C2 junction was observably reduced after odontoidectomy with AAOF and odontoidectomy with AAF. In addition, at the Occiput-C1, the ROM of odontoidectomy with AAOF model was notably lower than the normal model in extension (94.9%), flexion (97.6%), lateral bending (91.8%), and torsion (96.4%). But compared with the normal model, in the odontoidectomy with AAF model, the ROM of the Occiput-C1 increased by 52.2%, -0.1%, 92.1%, and 34.2% in extension, lateral bending, and torsion, respectively. Moreover, there were no distinctive differences in the stress at the screw-bone interface or the C2-C3 intervertebral disc between the two fixation systems. Conclusion: AAOF can maintain CVJ stability at the Occiput-C1 after odontoidectomy, but AAF cannot. Thus, for patients with pre-existing atlanto-occipital joint instability, AAOF is more suitable than AAF in the choice of anterior fixation techniques.

Atlanto-Occipital Transarticular Screw Fixation for the Treatment of Traumatic Occipitocervical Instability in the Pediatric Population

BACKGROUND

Atlanto-occipital transarticular screw fixation (AOTSF) has rarely been reported for fixation of the craniovertebral junction (CVJ).

METHODS

A retrospective chart review of all pediatric patients (less than 18 years of age) with an attempt of AOTSF for fixation of traumatic CVJ instability was conducted.

RESULTS

A total of 4 patients (2 boys and 2 girls; ages 2, 3, 5, and 8 years) who suffered from acute traumatic CVJ instability managed during 2007-2018 underwent an attempted AOTSF. In 2 patients, this method was technically successful. In the other 2 instances, we were not able to engage the screw into the occipital condyle. These were converted to standard occipital plate, rod, and screw fixation. All were placed in a halo subsequently for a minimum of 3 months. Three patients were fused at last follow-up (range, 17-48 months). One patient after successful AOTSF did not fuse. There were no surgical complications or revision procedures.

CONCLUSIONS

AOTSF was feasible in half of pediatric patients suffering from traumatic CVJ instability. Therefore, intraoperative salvage options and strategies should be on hand readily. In the pediatric population, where bony anatomy may pose challenges to fixation, this technique may offer a viable first-line option in selected cases, despite the overall modest success rate.

Occipital Condyle Screw Placement in Patients with Chiari Malformation: A Radiographic Feasibility Analysis and Cadaveric Demonstration

OBJECTIVE

Patients who undergo decompression surgery for Chiari malformation frequently require occipitocervical fixation. This is typically performed with occipital plates, which may cause intracranial injuries due to multiple fixation points. We undertook this study to assess the feasibility of occipital condyle (OC) screw placement as an alternative method of occipitocervical fixation in this patient population.

METHODS

Using a cadaveric model with navigational assistance, we performed the complete surgical procedure for occipitocervical fixation with OC screws. We then performed a morphometric analysis using measurements from computed tomography scans of 49 patients (32 adult, 17 pediatric) who had undergone occipitocervical fusion with instrumentation following decompression surgery for Chiari malformation. Bilateral morphometric data were analyzed for the adult and pediatric subgroups separately, as well as for the overall group.

RESULTS

The surgical procedure was successfully performed in the cadaveric model, demonstrating the feasibility of the proposed method. Ninety-eight OCs were studied in the morphometric analysis, and 80 (81.6%) met our eligibility criteria for OC screw placement. However, in 14.1% of adult OCs and 26.5% of pediatric OCs studied, placement of condylar screws would have been challenging or unsafe, according to our criteria.

CONCLUSIONS

Our findings suggest that OC screws provide a useful option for occipitocervical fixation in a substantial proportion of patients with Chiari malformation. However, rigorous preoperative analysis would be essential to identify appropriate candidates for this technique and exclude those in whom it should not be attempted. Additional study is warranted.

Surgical, clinical, and radiological outcomes of occipitocervical fusion using the plate-screw-rod system with allograft in craniocervical instability

Objective:

We evaluated surgical, clinical, and radiological outcomes of posterior occipitocervical fusion (OCF) using plate–rod–screw construct supplemented with allograft in cases of occipitocervical instability.

Study Design:

This was a retrospective analysis of prospective collected data.

Methods:

Data of 52 patients who underwent posterior OCF using plate–screw–rod construct supplemented with allograft at a single institute from 2009 to 2014 were analyzed. Demographics, clinical parameters (Visual Analog Score [VAS], ODI, and mJOA score), functional status (McCormick scale), radiological parameters – mean atlantodens interval, posterior occipitocervical angle, occipitocervical 2 angle, and surgical parameters (operative time, blood loss, hospital stay, and fusion) with complications were evaluated.

Results:

The mean age of the patients was 54.56 ± 16.21 years with male: female was 28:24. The mean operative time was 142.2 min (90–185 min) and mean blood loss was 250.8 ml. The mean duration of hospital stay was 6.7 days and mean follow-up period was 65.17 ± 5.39 months. There was significant improvement in clinical parameters (modified JOA score, VAS, and Oswestry Disability Index values) postoperatively. Forty patients showed recovery in neurological status at least in Grade 1 in McCormick scale with no neurological deterioration in any patient. Furthermore, radiological parameters at cervicomedullary junction got into acceptable range. Implant-related complications noted in 1 patient and 1 patient had vertebral artery injury. We had dural tear in 3 patients and infection in 2 patients. Fusion was achieved in 46 cases with mean time for fusion was 11.039 months.

Conclusion:

Patients with occipitocervical instability can successfully undergo posterior OCF using plate–screw–rod construct supplemented with allograft with high fusion rate, good clinical and functional outcomes, and low complication rate.

Anterior Atlantooccipital Transarticular Screw Fixation: A Cadaveric Study and Description of a Novel Technique

STUDY DESIGN

Retrospective analysis of collected data and operative experiment on human cadavers.

OBJECTIVE

To describe a novel technique of the anterior atlantooccipital (AC) transarticular screw fixation, and to analyze the pertinent anatomy with cadaveric and radiographic assessment of the feasibility, safety, and general applicability of this technique.

SUMMARY OF BACKGROUND DATA

In some situations, the posterior AC fixation techniques may not be possible, or may require supplemental fixation, which include the congenital hypoplasia, absence of the bony elements, and even revision surgery. However, an anterior screw fixation technique may add stability to further attempts at obtaining an arthrodesis.

METHODS

A detailed description of the surgical technique was presented. Three-dimensional (3D) CT reconstruction of the cranioverteral region of 30 patients were performed to determine screw entry points, target points, and proposed screw trajectories. Following screw insertion in eight fresh frozen human cadaver spine specimens, dissection verified screw location relative to structures at risk.

RESULTS

The ideal entry point is located caudal to the C1 superior facet joint in line with the medial third of the C1 superior facet. The ideal screw is directed 41.7° posteriorly in the sagittal plane and 11.6° laterally in the coronal plane with a length around 30.4 mm. The feasibility of anterior AC screw fixation was 92% (35/38 cases). There is a risk of injury to the vertebral artery and the hypoglossal nerve.

CONCLUSION

Anterior AC transarticular screw fixation is feasible and can be considered as a salvage technique or an alternative for the posterior AC fixation, as well as the supplement to the anterior occipitocervical fixation.

LEVEL OF EVIDENCE

3.

Anterior Atlanto-Occipital Transarticular Screw Fixation: A Radiological Evaluation

BACKGROUND

In situations in which posterior atlanto-occipital fixation might not be possible or might require supplemental fixation, anterior fixation might add stability in obtaining arthrodesis. The present study aimed to provide a radiographic evaluation of the safety and feasibility in the anterior approach.

METHODS

The bilateral craniocervical computed tomography slices of 60 patients were examined. The anterior screw entry point was the lowest point at the middle anterior aspect of C1 (atlas) lateral mass. To avoid hypoglossal canal and craniocerebral injury, the height of the hypoglossal canal and occipital condyle and occipital condyle width were obtained. The mandible occlusion angle (MOA), anterior screw trajectory above, under, and distal to the hypoglossal canal (AHA, UHA, and DHA) relative to the tangent line of C1 front border were measured, together with the maximum screw length under each angle (AHL, UHL and DHL). An independent samples t test was used for statistical analysis.

RESULTS

The height of the hypoglossal canal and occipital condyle and occipital condyle width were all larger in the men than in the women. The MOA, AHA, UHA, and DHA were 55.0°, 18.7°, 41.0°, and 55.0°, respectively, and were similar between genders. The AHL, UHL, and DHL were 34.5, 30.9, and 31.3 mm, with the measurements for the men generally longer than those for the women by 3-4 mm. A total of 10 of 120 bilateral measurements showed the possibility of mandible occlusion, and the potential success rate of the anterior approach could reach 91.7%.

CONCLUSIONS

The ideal entry angle for anterior atlanto-occipital fixation ranges from 41.0° to 55.0°, with a safe screw length from 30.9 to 31.3 mm. The potential success rate could reach >90%.

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.

Correction of clivoaxial angle deformity in the setting of suboccipital craniectomy: technical note

A subset of patients with Chiari Type I malformation may develop neurological dysfunction secondary to an abnormally obtuse clivoaxial angle (CXA) and clivoaxial deformity causing deformative stress injury to the neural axis. Clivoaxial deformity can occur after initial standard suboccipital craniectomy, duraplasty, and C-1 laminectomy for brainstem compression, or severe clivoaxial deformity may be present in conjunction with a Chiari malformation. Clivoaxial deformity and abnormal CXA can be treated with an occipitocervical fusion (OCF). Performing OCF in the setting of a cranial defect can be challenging with currently available instrumentation. The authors describe their recent experience and outcomes in 3 consecutive pediatric patients using the "inside-out" technique for treating clivoaxial deformity and abnormal CXA in the setting of a craniectomy defect to restore stability to the craniocervical junction, while correcting the CXA.

The radiological feature of anterior occiput-to-axis screw fixation as it guides the screw trajectory on 3D printed models: a feasibility study on 3D images and 3D printed models

Anterior occiput-to-axis screw fixation is more suitable than a posterior approach for some patients with a history of posterior surgery. The complex osseous anatomy between the occiput and the axis causes a high risk of injury to neurological and vascular structures, and it is important to have an accurate screw trajectory to guide anterior occiput-to-axis screw fixation. Thirty computed tomography (CT) scans of upper cervical spines were obtained for three-dimensional (3D) reconstruction. Cylinders (1.75 mm radius) were drawn to simulate the trajectory of an anterior occiput-to-axis screw. The imitation screw was adjusted to 4 different angles and measured, as were the values of the maximized anteroposterior width and the left-right width of the occiput (C0) to the C1 and C1 to C2 joints. Then, the 3D models were printed, and an angle guide device was used to introduce the screws into the 3D models referring to the angles calculated from the 3D images. We found the screw angle ranged from α1 (left: 4.99±4.59°; right: 4.28±5.45°) to α2 (left: 20.22±3.61°; right: 19.63±4.94°); on the lateral view, the screw angle ranged from β1 (left: 13.13±4.93°; right: 11.82±5.64°) to β2 (left: 34.86±6.00°; right: 35.01±5.77°). No statistically significant difference was found between the data of the left and right sides. On the 3D printed models, all of the anterior occiput-to-axis screws were successfully introduced, and none of them penetrated outside of the cortex; the mean α4 was 12.00±4.11 (left) and 12.25±4.05 (right), and the mean β4 was 23.44±4.21 (left) and 22.75±4.41 (right). No significant difference was found between α4 and β4 on the 3D printed models and α3 and β3 calculated from the 3D digital images of the left and right sides. Aided with the angle guide device, we could achieve an optimal screw trajectory for anterior occiput-to-axis screw fixation on 3D printed C0 to C2 models.

Three-dimensional finite element analysis of occipitocervical fixation using an anterior occiput-to-axis locking plate system: a pilot study

BACKGROUND CONTEXT

Although there are many techniques for occipitocervical fixation, there have been no reports regarding occipitocervical fixation via the use of an anterior anatomical locking plate system.

PURPOSE

The biomechanics of this new system were analyzed by a three-dimensional finite element to provide a theoretical basis for clinical application.

STUDY DESIGN

This was a modeling study.

PATIENT SAMPLE

We studied a 27-year-old healthy male volunteer in whom cervical disease was excluded via X-ray examination.

OUTCOME MEASURES

The states of stress and strain of these two internal fixation devices were analyzed.

METHODS

A three-dimensional finite element model of normal occiput-C2 was established based on the anatomical data from a Chinese population. An unstable model of occipital-cervical region was established by subtracting several unit structures from the normal model. An anterior occiput-to-axis locking titanium plate system was then applied and an anterior occiput-to-axis screw fixation was performed on the unstable model. Limitation of motion was performed on the surface of the fixed model, and physiological loads were imposed on the surface of the skull base.

RESULTS

Under various loads from different directions, the peak values of displacement of the anterior occiput-to-axis locking titanium plate system decreased 15.5%, 12.5%, 14.4%, and 23.7%, respectively, under the loads of flexion, extension, lateral bending, and axial rotation. Compared with the anterior occiput-to-axis screw fixation, the peak values of stress of the anterior occiput-to-axis locking titanium plate system also decreased 3.9%, 2.9%, 9.7%, and 7.2%, respectively, under the loads of flexion, extension, lateral bending, and axial rotation.

CONCLUSION

The anterior occiput-to-axis locking titanium plate system proved superior to the anterior occiput-to-axis screw system both in the stress distribution and fixation stability based on finite element analysis. It provides a new clinical option for anterior occipitocervical fixation.

Percutaneous anterior occiput-to-axis screw fixation: technique aspects and case series

BACKGROUND CONTEXT

Posterior occipitocervical fusion techniques have been previously described; however, traditional open anterior approaches are plagued by exposure difficulty. A minimally invasive percutaneous anterior occipitocervical fixation approach avoids this difficult exposure procedure.

PURPOSE

This article describes a novel technique of percutaneous anterior occiput-to-axis screw fixation and its clinical outcomes.

STUDY DESIGN

Technique report.

METHODS

Anteroposterior, lateral and open-mouth views, and computed tomography scans are preoperatively obtained to appraise the feasibility of surgery. We extend our experience of using percutaneous anterior transarticular screw fixation to occiput-to-axis screw fixation. This procedure was performed on six patients.

RESULTS

The operation was successfully performed on all patients without technical difficulties, and no vertebral artery, nerve injury or soft tissue (such as esophageal) complications occurred. All six patients followed up 10 to 39 months (averaged 20.5 months). Bone union was achieved in five patients, and the one patient lacking bone union was stable at final follow-up. The syringomyelia of four patients is almost complete reduction. No screw loosening or breakage has occurred.

CONCLUSIONS

With the correct puncture point, angle of insertion, and use of the appropriate tools, we suggest that percutaneous anterior occiput-to-axis fixation technique is a feasible, safe, and minimally invasive procedure.

Evaluation of femoral tunnel positioning using 3-dimensional computed tomography and radiographs after single bundle anterior cruciate ligament reconstruction with modified transtibial technique

BACKGROUND

The purpose of this study is to report a modified transtibial technique to approach the center of anatomical femoral footprint in anterior cruciate ligament (ACL) reconstruction and to investigate the accurate femoral tunnel position with 3-dimensional computed tomography (3D-CT) and radiography after reconstruction.

METHODS

From December 2010 to October 2011, we evaluated 98 patients who underwent primary ACL reconstruction using a modified transtibial technique to approach the center of anatomical femoral footprint in single bundle ACL reconstruction with hamstring autograft. Their femoral tunnel positions were investigated with 3D-CT and radiography postoperatively. Femoral tunnel angle was measured on the postoperative anteroposterior (AP) radiograph and the center of the femoral tunnel aperture on the lateral femoral condyle was assessed with 3D-CT according to the quadrant method by two orthopedic surgeons.

RESULTS

According to the quadrant method with 3D-CT, the femoral tunnel was measured at a mean of 32.94% ± 5.16% from the proximal condylar surface (parallel to the Blumensaat line) and 41.89% ± 5.58% from the notch roof (perpendicular to the Blumensaat line) with good interobserver (intraclass correlation coefficients [ICC], 0.766 and 0.793, respectively) and intraobserver reliability (ICC, 0.875 and 0.893, respectively). According to the radiographic measurement on the AP view, the femoral tunnel angles averaged 50.43° ± 7.04° (ICC, 0.783 and 0.911, respectively).

CONCLUSIONS

Our modified transtibial technique is anticipated to provide more anatomical placement of the femoral tunnel during ACL reconstruction than the former traditional transtibial techniques.

Placement of occipital condyle screws for occipitocervical fixation in a pediatric patient with occipitocervical instability after decompression for Chiari malformation

In cadaveric studies and recently in one adult patient the occipital condyle has been studied as an option to allow bone purchase by fixation devices. In the current case the authors describe the use of occipital condyle screws in a child undergoing occipitocervical fixation. To the best of the authors' knowledge this case is the first reported instance of this technique in a pediatric patient. This girl had a history of posterior fossa decompression for Chiari malformation Type I when she was 22 months of age. When she was 6 years old she presented with neck pain on flexion and extension of her head. Magnetic resonance imaging in flexion and extension revealed occipitocervical instability. She underwent an occiput to C-2 posterior arthrodesis with bilateral screw placement in the occipital condyles, C-2 lamina, and C-1 lateral masses. Postoperatively, she was neurologically intact. Computed tomography demonstrated a stable construct, and her cervical pain had resolved on follow-up.

SURGICAL TREATMENT OF OCCIPITOCERVICAL INSTABILITY

OBJECTIVE

Instability of the occipitocervical junction can be a challenging surgical problem because of the unique anatomic and biomechanical characteristics of this region. We review the causes of instability and the development of surgical techniques to stabilize the occipitocervical junction.

METHODS

Occipitocervical instrumentation has advanced significantly, and modern modular screw-based constructs allow for rigid short-segment fixation of unstable elements while providing the stability needed to achieve successful fusion in nearly 100% of patients. This article reviews the preoperative planning, the variety of instrumentation and surgical strategies, as well as the postoperative care of these patients.

RESULTS

Current constructs use occipital plates that are rigidly fixed to the thick midline keel of the occipital bone, polyaxial screws that can be placed in many different trajectories, and rods that are bent to approximate the acute occipitocervical angle. These modular constructs provide a variety of methods to achieve fixation in the atlantoaxial complex, including transarticular screws or C1 lateral mass screws in combination with C2 pars, C2 pedicle, or C2 translaminar trajectories.

CONCLUSION

Surgical techniques for occipitocervical instrumentation and fusion are technically challenging and require meticulous preoperative planning and a thorough understanding of the regional anatomy, instrumentation, and constructs. Modern screw-based techniques for occipitocervical fusion have established clinical success and demonstrated biomechanical stability, with fusion rates approaching 100%.

C1-C2 arthrodesis after transoral odontoidectomy and suboccipital craniectomy for ventral brain stem compression in Chiari I patients

Chiari I malformations are often associated with congenital craniocervical anomalies such as platybasia, basilar invagination, and retroflexion of the odontoid process. Management of ventral brain stem compression associated with Chiari I malformations remains controversial, but several authors report a significant rate of failure with suboccipital decompression alone in the presence of pronounced ventral brain stem compression (VBSC). Treatment options described in the literature for these patients involve anterior, posterior, or combined decompressions with or without concurrent arthrodesis. A combined anterior and posterior approach provides a definitive circumferential decompression but also significantly disrupts the stability of the occipitocervical junction usually necessitating occipitocervical fixation. We describe an alternative surgical treatment for Chiari I patients with significant ventral brain stem compression where a combined anterior and posterior decompression was considered necessary. We report two patients who underwent transoral odontoidectomy with preservation of the anterior arch of the atlas and suboccipital craniectomy with C1 laminectomy followed by C1-C2 arthrodesis. Preservation of the anterior arch of the atlas in conjunction with C1-C2 arthrodesis stabilizes the occipito-atlanto-axial segments while conserving more cervical mobility as compared to an occipitocervical fusion.