The association between atlantoaxial instability and anomalies of vertebral artery and axis

Radiological features and internal fixation strategies of atlantoaxial dislocation combined with atlas occipitalization

BACKGROUND

Patients with atlantoaxial dislocation combined with atlas occipitalization often present with variations in the anatomy of the vertebral artery and bone, posing potential risks during the implantation of the C2 pedicle screws during surgery.

OBJECTIVE

Based on comprehensive preoperative imaging evaluation, this study investigates the blood supply, course, and relationship with bone of the vertebral artery in patients with atlantoaxial dislocation combined with atlas occipitalization, aiming to provide reference for safe implantation of internal fixation.

METHODS

Imaging data of 77 patients with atlantoaxial dislocation combined with atlas occipitalization from October 2015 to December 2023 at the First Affiliated Hospital of the University of Science and Technology of China were collected, including CT, CT angiography, and MRI. The blood supply, course, and relationship with surrounding structure of the vertebral artery were analyzed using PACS and RadiAnt software.

RESULTS

There were 18 males and 59 females, with an average age of 48.5 ± 10.5 years (range: 17-71 years). Forty-one cases (53.2%) were associated with congenital C2-3 fusion(Klippel-Feil syndrome). Vertebral artery blood supply was predominantly unilateral (including single blood supply) in 56 cases (72.7%), with left-sided predominance (62.5%). Segment V3 course variations of the vertebral artery were common, with 47 cases (35.6%) not entering the transverse foramen of C1. High-riding vertebral arteries were present in 36 cases (46.8%), with 22 cases (61.1%) associated with congenital C2-3 fusion. The average width of the axis pedicle on the high-riding side was 2.13 ± 1.2 mm, and the height of the isthmus was ≤ 5 mm, with an average of 2.55 ± 1.07 mm. There was a loose gap on the lateral side of the vertebral artery within the transverse foramen, with an average of 2.1 mm, and the corresponding width of the subarachnoid space on the inner side of the axis pedicle was 3.48 mm.

CONCLUSION

Comprehensive preoperative imaging evaluation can reduce the risk of vertebral artery injury during surgery in patients with congenital atlantoaxial dislocation combined with atlas occipitalization, and provide feasible and optimized internal fixation solutions.

Types of high-riding vertebral artery: a classification system for preoperative planning of C2 instrumentation based on 908 potential screw insertion sites

BACKGROUND CONTEXT

Our recent studies indicated that a high-riding vertebral artery (HRVA) is a common variant posing a risk of injuring the vessel during C2 instrumentation. However, several different types fit in the current definition of HRVA, which may require a different strategy for C2 screw placement.

PURPOSE

To classify HRVA and provide a clinical aid for preoperative planning of C2 instrumentation. A secondary goal was to estimate coexistence of each HRVA type with the ipsilateral narrow C2 pedicle (NP).

STUDY DESIGN

A retrospective observational study involving radiologic measurements of the estimated number of anonymized cervical computed tomography (CT) scans. STROBE checklist was applied.

PATIENT SAMPLE

A total of 908 potential screw insertion sites (PSIS) of 454 consecutive cervical CT scans were analyzed. The sample size was estimated using ScalaR SP function in RStudio.

OUTCOME MEASURES

Three types of HRVA based on a series of C2 vertebral morphological parameters including the C2 isthmus height (C2IsH) and C2 internal height (C2InH). Also, the prevalences of each HRVA type and coexisting NP based on the C2 pedicle width (C2PW).

METHODS

HRVA was defined as C2IsH of ≤5 mm and/or C2InH of ≤2 mm measured 3 mm lateral to the lateral border of the spinal canal. A narrow pedicle was defined as C2PW of ≤4 mm. Measurements were done using Syn.govia software. Interobserver, intraobserver, and inter-software agreement coefficients for C2IsH, C2InH, and C2PW parameters were adopted from our previous study. K-means cluster analysis was applied.

RESULTS

Prevalence of at least 1 HRVA was 24.9% (n=113 subjects) and 16.2% of PSIS (n=147 sites). Based on the measurements and K-means clustering, the following 3 types of HRVA have been distinguished: type 1-isthmic with only C2IsH being reduced and normal C2InH; type 2-internal with only C2InH being reduced and C2IsH within normal limits; type 3-isthmo-internal with both C2IsH and C2InH being reduced. Kruskal-Wallis test followed by unadjusted and Bonferroni-adjusted posthoc multiple comparison analysis detected significant differences across the types. The prevalences of the newly identified types were as follows: 78.2%, 8.8%, and 12.9% for type 1, type 2, and type 3, respectively. 73.9% of type 1 HRVA, 53.8% of type 2 HRVA, and 100% of type 3 HRVA had a concomitant ipsilateral NP. Prediction of the HRVA types by the K-means clustering has been evaluated. Screw placement techniques for each type are proposed and discussed.

CONCLUSIONS

We present the first classification system for the high-riding vertebral artery distinguishing 3 types based on the large homogenous cohort, which may serve as an adjunct to preoperative planning of C2 instrumentation. External validation of this classification scheme shall determine its further clinical utility.

Effect of High-Riding Vertebral Artery on the Accuracy and Safety of C2 Pedicle Screw Placement in Basilar Invagination and Related Risk Factors

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

To investigate the effect of HRVA on the intrapedicular accuracy of C2PS placement through the freehand method in patients with BI and analyse the possible risk factors for C2PS malpositioning.

METHOD

A total of 91 consecutive patients with BI who received 174 unilateral C2PS placements through the freehand method were retrospectively included. The unilateral pedicles were assigned to the HRVA and non-HRVA groups. The primary outcome was the intrapedicular accuracy of C2PS placement in accordance with the Gertzbein-Robbins scale. Moreover, the risk factors that possibly affected intrapedicular accuracy were assessed.

RESULTS

The rate of intrapedicular accuracy in C2PS placement in patients with BI was 23.6%. Results showed that the non-HRVA group had remarkably higher rates of optimal and clinically acceptable C2PS placement than the HRVA group. Nevertheless, the HRVA group exhibited similar results for grade B classification as the non-HRVA group. Moreover, in the HRVA and non-HRVA groups, the most common direction of screw deviations was the lateral direction. Furthermore, the multivariate analyses showed that the obliquity of the lateral atlantoaxial joint in the sagittal plane ≥15°, and that in the coronal plane ≥ 20°, isthmus height < 4.3 mm, and distance from the skin to the spinous process ≥ 2.8 cm independently contributed to a high rate of screw malpositioning in BI patients.

CONCLUSION

The presence of HRVA in BI patients contributed to the high rate of malpositioning in C2PS placement via the freehand method. However, the rates of intrapedicular accuracy in patients with BI with and without HRVA were considerably low.

Impact of craniocervical junction abnormality on vertebral artery hemodynamics: based on computational fluid dynamics analysis

Background and purpose

A three-dimensional reconstruction and data analysis of the vertebral artery (VA) with craniocervical junction abnormality (CJA) was performed by computational fluid dynamics (CFD) based on images to assess the impact of CJA on vertebral artery hemodynamics.

Methods

Retrospective analysis of combined head and neck computed tomography angiography (CTA) images of 60 patients with CJA and 60 normal patients admitted to our department from January 2018 to June 2022. The VA was reconstructed in three dimensions using CFD-related software, and the results were visualized to derive vertebral artery lumen diameter (D), peak systolic velocity (PSV), mean blood flow velocity (MV), wall pressure (P), wall shear stress (WSS), normalized WSS (NWSS), etc. Statistical analysis was used to analyze whether the data related to hemodynamics in the CJA group and the control group were statistically significant.

Results

The lumen diameter of the vertebral artery in the CJA group were less than the control group, and the difference was statistically significant (3.354 ± 0.562 vs. 3.744 ± 0.520, p < 0.05); the PSV, MV, P, WSS, and NWSS of the CJA group were increased compared with the control group, and the difference was statistically significant (1.235 ± 0.182 vs. 1.104 ± 0.145, 0.339 ± 0.063 vs. 0.307 ± 0.042, 24576.980 ± 7095.836 vs. 20824.281 ± 6718.438, 34.863 ± 6.816 vs. 31.080 ± 5.438, 0.272 ± 0.075 vs. 0.237 ± 0.067, p < 0.05).

Conclusion

In the complex CJA, the possibility of hemodynamic variation in the VAs is higher than in the normal population. The hemodynamic aspects of the vertebral artery in patients with CJA, such as diameter, flow velocity, flow, wall pressure and shear force, differ from those in the normal population and may lead to the occurrence of clinical symptoms, such as dizziness, so preoperative examinations such as combined head and neck CTA should be performed to clarify the vascular abnormalities.

Functional and radiological outcomes following craniovertebral junction surgery

Background

Craniovertebral junction (CVJ) pathologies include atlantoaxial instability/deformities resulting in myelopathy, respiratory failure, and even death. Here, we describe the indications, preoperative planning, and intra-operative/postoperative complications following surgical management of CVJ anomalies.

Methods

A prospective analysis of 34 patients with CVJ pathology was evaluated between 2015 and 2022. Their various etiologies included atlantoaxial instability, trauma, tuberculosis, Down's syndrome, Morquio syndrome, os odontoideum, and atlantoaxial abnormalities. Clinical outcomes were assessed using the American spinal injury association (ASIA) impairment scale score and Benzel's modified Japanese Orthopedic Association (mJOA) score. Surgical assessments included length of hospital stay, operative time, blood loss, and intraoperative postoperative complications. Radiological parameters included fusion (i.e., implant loosening/implant failure), preoperative/ postoperative atlanto-dens interval (ADI), clivus canal angle (CCA), and space available for cord (SAC).

Results

Five patients were managed conservatively, while 29 patients had surgery. Operations included occipitocervical fusion (14 patients), C1-2 fusion (10 patients), C1-2 transarticular screw fixation (four patients), and one patient underwent anterior corpectomy decompression/fusion. Seven patients had vertebral artery anomalies, and 13 patients had atlantoaxial abnormalities. At the final follow-up, atlantoaxial instability (i.e., mean preoperative ADI of 6.6 ± 2.3 mm) was restored to 4.2 ± 0.6 mm, significant cord compression (i.e., with mean SAC of 8.3 ± 2.9 mm) was relieved to 17.2 ± 1.6 mm, and the mean preoperative CCA (i.e., 130.2 ± 15.3) was improved to 143.3 ± 8.3°. There was also a statistically significant improvement in the ASIA scale and mJOA score.

Conclusion

Surgical management of CVJ abnormalities requires expertise and meticulous planning to avoid devastating complications such as wound dehiscence and catastrophic vertebral artery injury.

The association between unilateral high-riding vertebral artery and atlantoaxial joint morphology: a multi-slice spiral computed tomography study of 396 patients and a finite element analysis

BACKGROUND CONTEXT

A high-riding vertebral artery (HRVA) can deviate too medially, too posteriorly, or too superiorly to allow the safe insertion of screws. However, it is unknown whether the presence of a HRVA is associated with morphological changes of the atlantoaxial joint.

PURPOSE

To investigate the association between HRVA and atlantoaxial joint morphology in patients with and without HRVA.

STUDY DESIGN

A retrospective case-control study and finite element (FE) analysis.

PATIENT SAMPLE

A total of 396 patients with cervical spondylosis underwent multi-slice spiral computed tomography (MSCT) of cervical spine at our institutions from 2020 to 2022.

OUTCOME MEASURES

A series of atlantoaxial joint morphological parameters, including C2 lateral mass settlement (C2 LMS), C1-2 sagittal joint inclination (C1-2 SI), C1-2 coronal joint inclination (C1-2 CI), atlanto-dental interval (ADI), lateral atlanto-dental interval (LADI), and C1-2 relative rotation angle (C1-2 RRA) were measured, and lateral atlantoaxial joints osteoarthritis (LAJs-OA) was recorded. The stress distribution on the C2 facet surface under different torques of flexion-extension, lateral bending, and axial rotation was analyzed by FE models. A 2-Nm moment was applied to all models to determine the range of motion (ROM).

METHODS

A total of 132 consecutive cervical spondylosis patients with unilateral HRVA were enrolled in the HRVA group, and 264 patients without HRVA matched for age and sex were enrolled in the normal (NL) group. Atlantoaxial joint morphological parameters were compared between two sides of C2 lateral mass within HRVA or NL group, and between HRVA and NL groups. A 48-year-old woman with cervical spondylosis without HRVA was selected for cervical MSCT. A three-dimensional (3D) FE intact model of the normal upper cervical spine (C0-C2) was created. We established the HRVA model by simulating atlantoaxial morphological changes of unilateral HRVA with FE method.

RESULTS

The C2 LMS was significantly smaller on the HRVA side than that on the non-HRVA side in the HRVA group, but C1-2 SI, C1-2 CI, and LADI on HRVA side were significantly larger than those on non-HRVA side. There was no significant difference between left and right sides in the NL group. The difference in C2 LMS (d-C2 LMS) between HRVA side and non-HRVA side in the HRVA group was larger than that in the NL group (P < 0.05). Meanwhile, the differences in C1-2 SI (d-C1/2 SI), C1-2 CI (d-C1/2 CI), and LADI (d-LADI) in the HRVA group were significantly larger than those in the NL group. The C1-2 RRA in the HRVA group was significantly larger than that in the NL group. Pearson correlations showed that d-C1/2 SI, d-C1/2 CI, and d-LADI were positively associated with d-C2 LMS (r=0.428, 0.649, 0.498, respectively, p<.05 for all). The incidence of LAJs-OA in the HRVA group (27.3%) was significantly larger than that in the NL group (11.7%). Compared with the normal model, the ROM of C1-2 segment declined in all postures of the HRVA FE model. We found a larger distribution of stress on the C2 lateral mass surface of the HRVA side under different moment conditions.

CONCLUSIONS

We suggest that HRVA affects the integrity of the C2 lateral mass. This change in patients with unilateral HRVA is associated with the nonuniform settlement of the lateral mass and an increase in the lateral mass inclination, which may further affect the degeneration of the atlantoaxial joint because of the stress concentration on the C2 lateral mass surface.

Clinical application of spinal robot in cervical spine surgery: safety and accuracy of posterior pedicle screw placement in comparison with conventional freehand methods

The novel robot-assisted (RA) technique has been utilized increasingly to improve the accuracy of cervical pedicle screw placement. Although the clinical application of the RA technique has been investigated in several case series and comparative studies, the superiority and safety of RA over conventional freehand (FH) methods remain controversial. Meanwhile, the intra-pedicular accuracy of the two methods has not been compared for patients with cervical traumatic conditions. This study aimed to compare the rate and risk factors of intra-pedicular accuracy of RA versus the conventional FH approach for posterior pedicle screw placement in cervical traumatic diseases. A total of 52 patients with cervical traumatic diseases who received cervical screw placement using RA (26 patients) and FH (26 patients) techniques were retrospectively included. The primary outcome was the intra-pedicular accuracy of cervical pedicle screw placement according to the Gertzbin-Robbins scale. Secondary outcome parameters included surgical time, intraoperative blood loss, postoperative drainage, postoperative hospital stay, and complications. Moreover, the risk factors that possibly affected intra-pedicular accuracy were assessed using univariate analyses. Out of 52 screws inserted using the RA method, 43 screws (82.7%) were classified as grade A, with the remaining 7 (13.5%) and 2 (3.8%) screws classified as grades B and C. In the FH cohort, 60.8% of the 79 screws were graded A, with the remaining screws graded B (21, 26.6%), C (8, 10.1%), and D (2, 2.5%). The RA technique showed a significantly higher rate of optimal intra-pedicular accuracy than the FH method (P = 0.008), but there was no significant difference between the two groups in terms of clinically acceptable accuracy (P = 0.161). Besides, the RA technique showed remarkably longer surgery time, less postoperative drainage, shorter postoperative hospital stay, and equivalent intraoperative blood loss and complications than the FH technique. Furthermore, the univariate analyses showed that severe obliquity of the lateral atlantoaxial joint in the coronal plane (P = 0.003) and shorter width of the lateral mass at the inferior margin of the posterior arch (P = 0.014) were risk factors related to the inaccuracy of C1 screw placement. The diagnosis of HRVA (P < 0.001), severe obliquity of the lateral atlantoaxial joint in the coronal plane (P < 0.001), short pedicle width (P < 0.001), and short pedicle height (P < 0.001) were risk factors related to the inaccuracy of C2 screw placement. RA cervical pedicle screw placement was associated with a higher rate of optimal intra-pedicular accuracy to the FH technique for patients with cervical traumatic conditions. The severe obliquity of the lateral atlantoaxial joint in the coronal plane independently contributed to high rates of the inaccuracy of C1 and C2 screw placements. RA pedicle screw placement is safe and useful for cervical traumatic surgery.

Characteristics and Comparisons of Morphometric Measurements and Computed Tomography Hounsfield Unit Values of C2 Laminae for Translaminar Screw Placement Between Patients With and Without Basilar Invagination

OBJECTIVE

Patients with basilar invagination (BI) had high incidences of vertebral variations and high-riding vertebral artery (HRVA) that might restrict the use of pedicle or pars screw and increase the use of translaminar screw on axis. Here, we conducted a radiographic study to investigate the feasibility of translaminar screws and the bone quality of C2 laminae in patients with BI, which were compared with those without BI as control to provide guidelines for safe placement.

METHODS

In this study, a total of 410 patients (205 consecutive patients with BI and 205 matched patients without BI) and 820 unilateral laminae of the axis were included at a 1:1 ratio. Comparisons with regard to insertion parameters (laminar length, thickness, angle, and height) for C2 translaminar screw placement and Hounsfield unit (HU) values for the assessment of the appropriate bone mineral density of C2 laminae between BI and control groups were performed. Besides, the subgroup analyses based on the Goel A and B classification of BI, HRVA, atlas occipitalization, and C2/3 assimilation were also carried out. Furthermore, the factors that might affect the insertion parameters and HU values were explored through multiple linear regression analyses.

RESULTS

The BI group showed a significantly smaller laminar length, thickness, height, and HU value than the control group, whereas no significant difference was observed regarding the laminar angle. By contrast, the control group showed significantly higher rates of acceptability for unilateral and bilateral translaminar screw fixations than the BI group. Subgroup analyses showed that the classification of Goel A and B, HRVA, atlas occipitalization, and C2/3 assimilation affected the insertion parameters except the HU values. Multiple linear regression indicated that the laminar length was significantly associated with the male gender (B = 0.190, p < 0.001), diagnoses of HRVA (B = -0.109, p < 0.001), Goel A (B = -0.167, p < 0.001), and C2/3 assimilation (B = -0.079, p = 0.029); the laminar thickness was significantly associated with the male gender (B = 0.353, p < 0.001), diagnoses of HRVA (B = -0.430, p < 0.001), Goel B (B = -0.249, p = 0.026), and distance from the top of odontoid to the Chamberlain line (B = -0.025, p = 0.003); laminar HU values were significantly associated with age (B = -2.517, p < 0.001), Goel A (B = -44.205, p < 0.001), Goel B (B = -25.704, p = 0.014), and laminar thickness (B = -11.706, p = 0.001).

CONCLUSION

Patients with BI had narrower and smaller laminae with lower HU values and lower unilateral and bilateral acceptability for translaminar screws than patients without BI. Preoperative 3-dimensional computed tomography (CT) and CT angiography were needed for BI patients.