CT analysis of the axis for transarticular screw fixation of rheumatoid atlantoaxial instability

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.

Ideal entry point and trajectory for C2 pedicle screw placement in basilar invagination patients with high-riding vertebral artery based on 3D computed tomography

BACKGROUND

C2 pedicle screw placement in patients with basilar invagination (BI) is fraught with risks because of a high incidence of anatomical variations and high-riding vertebral artery (HRVA). However, no study can be found in the literature that attempted to identify the ideal entry point and trajectory through the C2 pedicle in BI patients with HRVA.

PURPOSE

To investigate the parameters of ideal entry point and trajectory for C2 pedicle screw placement in BI patients with HRVA and compare them with those in BI patients without HRVA and patients without BI as control. These parameters would serve as a guide to pedicle screw placement.

STUDY DESIGN

A retrospective comparative study.

PATIENT SAMPLE

A total of 396 patients (198 consecutive BI patients and 198 matched patients without BI as control) and 792 unilateral pedicles from April 2017 to October 2021 at two medical centers were included.

OUTCOME MEASURES

The insertion parameters of mediolateral angle, surface distance, cephalad angle, and vertical distance from the superior border of the lamina were the primary outcome measures for the reference of C2 pedicle screw placement. Furthermore, factors that affect the primary insertion parameters were assessed via multiple linear regression analyses.

METHOD

According to the diagnosis of BI and HRVA, the unilateral pedicles were assigned into HRVA of BI, non-HRVA of BI, HRVA of control, and non-HRVA of control groups. Subgroup analyses based on Goel types A and B were also performed. Moreover, vertebral artery (VA) anomalies that might result in potentially serious complications were identified and systematically compared.

RESULTS

The measurements of insertion parameters in BI patients with HRVA indicated a mean mediolateral angle of 27.42°, a mean cephalad angle of 43.02°, a mean surface distance of 9.74 mm, and a mean vertical distance from the superior border of the lamina of 3.85 mm. Compared with that in BI patients without HRVA, the measurements suggested that the entry point in BI patients with HRVA should be shifted upward by 0.38 mm and the trajectory should be angled cephalad by 6.05° and medially by 4.78°. In the control group, changes in the insertion parameters between HRVA and non-HRVA showed a similar trend to the BI group. Multiple linear regression showed that mediolateral angle was significantly associated with the male gender (B=-0.930, p=.017) and the diagnoses of HRVA (B=6.964, p<.001), Goel type A (B=-1.656, p=.003), and Goel type B (B=0.981, p=.030). Moreover, cephalad angle was significantly associated with the length of lateral mass (B=-0.319, p=.001) and the diagnoses of HRVA (B=3.254, p<.001) and Goel type A (B=6.924, p<.001). The VA anomalies were significantly higher in the BI group than in the control group.

CONCLUSIONS

The insertion parameters of the ideal entry point and trajectory for C2 screw placement in BI patients with HRVA were remarkably different from those of non-HRVA of BI, HRVA of control, and non-HRVA of control cohorts. Preoperative 3D computed tomography (CT) and CT angiography are highly recommended in such patients to improve intraoperative safety and reduce postoperative complications.

Differences in fixation strength among constructs of atlantoaxial fixation

OBJECTIVE

To avoid jeopardizing an aberrant vertebral artery, there are three common options in placing a C2 screw, including pedicle, pars, and translaminar screws. Although biomechanical studies have demonstrated similar strength among these C2 screws in vitro, there are limited clinical data to address their differences in vivo. When different screws were placed in each side, few reports have compared the outcomes. The present study aimed to evaluate these multiple combinations of C2 screws.

METHODS

Consecutive adult patients who underwent posterior atlantoaxial (AA) fixation were retrospectively reviewed. Every patient uniformly had bilateral C1 lateral mass screws in conjunction with 2 C2 screws (1 C2 screw on each side chosen among the three options: pedicle, pars, or translaminar screws, based on individualized anatomical consideration). These patients were then grouped according to the different combinations of C2 screws for comparison of the outcomes.

RESULTS

A total of 63 patients were analyzed, with a mean follow-up of 34.3 months. There were five kinds of construct combinations of the C2 screws: 2 pedicle screws (the Ped-Ped group, n = 24), 2 translaminar screws (the La-La group, n = 7), 2 pars screws (the Pars-Pars group, n = 6), 1 pedicle and 1 pars screw (the Ped-Pars group, n = 7), and 1 pedicle and 1 translaminar screw (the Ped-La group, n = 19). The rate of successful fixation in each of the groups was 100%, 57.1%, 100%, 100%, and 78.9% (Ped-Ped, La-La, Par-Par, Ped-Par, and Ped-La, respectively). The patients who had no translaminar screw had a higher rate of success than those who had 1 or 2 translaminar screws (100% vs 73.1%, p = 0.0009). Among the 5 kinds of construct combinations, 2 C2 pedicle screws (the Ped-Ped group) had higher rates of success than 1 C2 pedicle and 1 C2 translaminar screw (the Ped-La group, p = 0.018). Overall, the rate of successful fixation was 87.3% (55/63). There were 7 patients (4 in the Ped-La group and 3 in the La-La group) who lost fixation/reduction, and they all had at least 1 translaminar screw.

CONCLUSIONS

In AA fixation, C2 pedicle or pars screws or a combination of both provided very high success rates. Involvement of 1 or 2 C2 translaminar screws in the construct significantly lowered success rates. Therefore, a C2 pars screw is recommended over a translaminar screw.

Late Subaxial Lesion after Overcorrected Occipitocervical Reconstruction in Patients with Rheumatoid Arthritis

Study Design

Retrospective case-control study, level 4.

Purpose

To clarify the risk factors for late subaxial lesion after occipitocervical (O-C) reconstruction. We examined cases requiring fusion-segment-extended (FE) reconstruction in addition to/after O-C reconstruction.

Overview of Literature

Patients with rheumatoid arthritis (RA) frequently require O-C reconstruction surgery for cranio-cervical lesions. Acceptable outcomes are achieved via indirect decompression using cervical pedicle screws and occipital plate–rod systems. However, late subaxial lesions may develop occasionally following O-C reconstruction.

Methods

O-C reconstruction using cervical pedicle screws and occipital plate–rod systems was performed between 1994 and 2007 in 113 patients with RA. Occipito-atlanto-axial (O-C2) reconstruction was performed for 89 patients, and occipito-subaxial cervical (O-under C2) reconstruction was performed for 24 patients. We reviewed the cases of patients requiring FE reconstruction (fusion extended group, FEG) and 26 consecutive patients who did not require FE reconstruction after a follow-up of >5 years (non-fusion extended group, NEG) as controls.

Results

FE reconstructions were performed for nine patients at an average of 45 months (range, 24–180 months) after O-C reconstruction. Of the 89 patients, three (3%) underwent FE reconstruction in cases of O-C2 reconstruction. Of the 24 patients, five (21%) underwent FE reconstruction in cases of O-under C2 reconstruction (p=0.003, Fisher exact test). Age, sex, RA type, and neurological impairment stage were not significantly different between FEG and NEG. O-under C2 reconstruction, larger correction angle (4° per number of unfixed segment), and O-C7 angle change after O-C reconstruction were the risk factors for late subaxial lesions on radiographic assessment.

Conclusions

Overcorrection of angle at fusion segments requiring O-C7 angle change was a risk factor for late subaxial lesion in patients with RA with fragile bones and joints. Correction should be limited, considering the residual mobility of the cervical unfixed segments.

Anatomical variations of vertebral artery and C2 isthmus in atlanto-axial fusion: Consecutive surgical 100 cases

VA anomalies in extra- and intraosseous regions of the craniovertebral junction (CVJ) is considered very carefully during the posterior screw fixation for the atlantoaxial instability (AAI). This study aims to compare the incidence and variations of VA anomalies, isthmus and pedicle size of C2 in 100 patients with AAI due to congenital skeletal anomaly (CSA) and acquired disease by using three-dimensional CT angiograms (3D CTA) before surgery. The CSA group contained 48 patients and the acquired disease group consisted of 52. In the CSA group, Os odontoideum was the major cause with 43 patients. The causes of acquired disease were RA in 16 patients and OA in 36 patients. Five patients had the anomalous VA in only CSA group; fenestration 2 patients and persistent first intersegmental (PFIS) artery 3 patients. Between CSA and acquired disease groups, no significant differences were found in the isthmus height, internal height, and pedicle width of C2 except the right internal height that is bigger in CSA group. The high-riding VA (isthmus height <4 mm or internal height <2 mm) had no significant difference between CSA group (27.1%) and acquired disease group (34.6%). However, in acquired disease group, patients with rheumatoid arthritis had smaller left internal height (4.21 ± 1.63 vs. 5.51 ± 1.83 mm) and pedicle width (4.11 ± 1.05 vs. 5.05 ± 1.66 mm) of C2 than those of patients with degenerative osteoarthritis. Therefore, in the case of atlantoaxial fusion, we should contemplate VA anomaly and the high-riding VA, especially in patients with CSA and RA.

Canine atlantoaxial optimal safe implantation corridors - description and validation of a novel 3D presurgical planning method using OsiriX™

Background

Canine ventral atlantoaxial (AA) stabilization is most commonly performed in very small dogs and is technically challenging due to extremely narrow bone corridors. Multiple implantation sites have been suggested but detailed anatomical studies investigating these sites are lacking and therefore current surgical guidelines are based upon approximate anatomical landmarks. In order to study AA optimal safe implantation corridors (OSICs), we developed a method based on computed tomography (CT) and semi-automated three-dimensional (3D) mathematical modelling using OsiriX™ and Microsoft®Excel software. The objectives of this study were 1- to provide a detailed description of the bone corridor analysis method and 2- to assess the reproducibility of the method. CT images of the craniocervical junction were prospectively obtained in 27 dogs and our method of OSIC analysis was applied in all dogs. For each dog, 13 optimal implant sites were simulated via geometrical simplification of the bone corridors. Each implant 3D position was then defined with respect to anatomical axes using 2 projected angles (ProjA). The safety margins around each implant were also estimated with angles (SafA) measured in 4 orthogonal directions. A sample of 12 simulated implants was randomly selected and each mathematically calculated angle was compared to direct measurements obtained within OsiriX™ from 2 observers repeated twice. The landmarks simulating anatomical axes were also positioned 4 times to determine their effect on ProjA reproducibility.

Results

OsiriX could be used successfully to simulate optimal implant positions in all cases. There was excellent agreement between the calculated and measured values for both ProjA (ρ_c = 0.9986) and SafA (ρ_c = 0.9996). Absolute differences between calculated and measured values were respectively [ProjA = 0.44 ± 0.53°; SafA = 0.27 ± 0.25°] and [ProjA = 0.26 ± 0.21°; SafA = 0.18 ± 0.18°] for each observer. The 95 % tolerance interval comparing ProjA obtained with 4 different sets of anatomical axis landmarks was [−1.62°, 1.61°] which was considered appropriate for clinical use.

Conclusions

A new method for determination of optimal implant placement is provided. Semi-automated calculation of optimal implant 3D positions could be further developed to facilitate preoperative planning and to generate large descriptive anatomical datasets.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0824-3) contains supplementary material, which is available to authorized users.

Ipsilateral arcuate foramen and high-riding vertebral artery: implication on C1-C2 instrumentation

BACKGROUND CONTEXT

Several methods for C1-C2 stabilization have been described in the literature. These include C1-C2 transarticular and C1 lateral mass screws. In patients with aberrant anatomy such as a high-riding vertebral artery (VA) or the presence of an arcuate foramen at C1, there exists a higher risk of VA injury. This may lead to excessive bleeding, stroke, and possibly death. There have been several studies determining the incidence of arcuate foramen and high-riding VA occurring individually in the general population, but none have determined their occurrence simultaneously.

PURPOSE

To determine the prevalence of ponticulus posticus and high-riding VA occurring simultaneously in the general population.

STUDY DESIGN

Radiological study.

METHODS

One hundred consecutive computed tomography (CT) scans of the cervical spine were reviewed. Scans that contained an arcuate foramen were identified, and it was indicated whether the foramen was right sided, left sided, or bilateral. In the same group, the thickness of the isthmus and the internal height of the lateral mass of C2 were measured. The VA was considered high riding if the isthmus thickness was less than 5 mm or the isthmus internal height was less than 2 mm.

RESULTS

Fourteen out of one hundred (14%) patients had a fully formed arcuate foramen. Of these, six were left sided, three were right sided, and five were bilateral. In addition, there were 24 (24%) patients with partially formed ponticulus posticus. Thirty-two (32%) patients were identified to have a high-riding VA. Of these, 13 were left sided, 9 were right sided, and 10 were bilateral. Five (5%) had an ipsilateral arcuate foramen and high-riding VA.

CONCLUSIONS

The arcuate foramen and high-riding VA are common anomalies that are often not recognized. Although ipsilateral high-riding VA and arcuate foramen rarely occur in the general population, proper identification of these anomalies on preoperative CT scan facilitates planning the safest technique for C1-C2 instrumentation.

The effect of rheumatoid arthritis on the anatomy of the female cervical spine

The effect of rheumatoid arthritis on the anatomy of the cervical spine has not been clearly documented. We studied 129 female patients, 90 with rheumatoid arthritis and 39 with other pathologies (the control group). There were 21 patients in the control group with a diagnosis of cervical spondylotic myelopathy, and 18 with ossification of the posterior longitudinal ligament. All had plain lateral radiographs taken of the cervical spine as well as a reconstructed CT scan. The axial diameter of the width of the pedicle, the thickness of the lateral mass, the height of the isthmus and internal height were measured. The transverse diameter of the transverse foramen (d1) and that of the spinal canal (d2) were measured, and the ratio d1/d2 calculated.

The width of the pedicles and the thickness of the lateral masses were significantly less in patients with rheumatoid arthritis than in those with other pathologies. The area of the transverse foramina in patients with rheumatoid arthritis was significantly greater than that in the other patients. The ratio of d1 to d2 was not significantly different. A high-riding vertebral artery was noted in 33.9% of the patients with rheumatoid arthritis and in 7.7% of those with other pathologies. This difference was statistically significant. In the rheumatoid group there was a significant correlation between isthmus height and vertical subluxation and between internal height and vertical subluxation.

Is rheumatoid arthritis a risk factor for a high-riding vertebral artery?

STUDY DESIGN

A retrospective comparative study on the morphologic characteristics of the axis in patients with or without rheumatoid arthritis (RA).

OBJECTIVE

To compare the morphologic risk of vertebral artery (VA) injury during atlantoaxial transarticular screw fixation between patients with or without RA.

SUMMARY OF BACKGROUND DATA

VA injury is a potentially serious complication during atlantoaxial transarticular screw fixation. Although this operation is frequently performed on RA patients, there have been few comparative studies on the morphologic risk of VA injury between RA and non-RA patients.

METHODS

A total of 107 three-dimensional computed tomography images of the cervical spine including the C1-C2 complex were evaluated. Forty-seven RA patients and 60 non-RA patients were included in the study. The maximum atlantoaxial transarticular screw diameter (MSD) that could be inserted without breaching the cortex was measured 3-dimensionally using a computer- assisted navigation system. A high-riding-VA carrier was defined as a patient with either MSD of 4 mm or less. In RA patients, the space available for the spinal cord in flexion (SAC in flexion), duration of disease, RA stage, and type of disease were examined.

RESULTS

In the RA group, 45 of 94 MSDs (47.9%) were 4 mm or less, and 33 of 47 patients (70.2%) were high-riding-VA carriers. In the non-RA group, 11 of 120 MSDs (9.2%) were 4 mm or less, and 9 of 60 (15.0%) patients were high-riding-VA carriers. MSD, C3 A-P diameter, and the ratio of MSD to C3 A-P diameter were significantly smaller in the RA group than in the non-RA group. Multiple logistic regression analysis showed that SAC in flexion was a significant risk factor for a high-riding-VA carrier in the RA group.

CONCLUSION

RA was a significant risk factor for the presence of a high-riding VA. When performing atlantoaxial transarticular screw fixation, particularly on RA patients, thorough preoperative evaluation of the bony architecture is of great importance to avoid inadvertent VA injury.