An anatomic consideration of C2 vertebrae artery groove variation for individual screw implantation in axis

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.

Morphometric Analysis of the Neural Arch of C2 Vertebra in Indian Population

BACKGROUND AND OBJECTIVE

The most common injuries to upper cervical spine are fractures of the second cervical vertebrae. The study aims to evaluate the morphometry of the neural arch of the second cervical vertebrae in the South Indian population.

MATERIALS AND METHODS

Sixty-three second cervical vertebrae of undetermined gender and age without any gross defect were used for the study. The dimensions of neural arch, including superior articular facet, inferior articular facet, pediculoisthmic component, lamina, spinous process, foramen transversarium, and vertebral foramen, were measured by two independent observers using digital vernier caliper accurate to 0.1 mm and the data was analyzed. Descriptive statistics were obtained for the variables. Paired t-test was done to compare the measurements between right and left sides.

RESULTS

There was no statistical difference between the right and left sides of the dimensions of superior articular facets, foramen transversarium, and the transverse diameter of inferior articular facet. The anteroposterior diameter of the inferior articular facets was more on the right side (P = 0.009). The width of the pediculoisthmic component in both the superior and inferior aspects was found to be less on the right side than that of the left (P = 0.006 and P = 0.031, respectively). The thickness in the middle one-third of laminae was optimum for bilateral safe screw insertion (≥4.0 mm) in 77% specimens.

CONCLUSION

In summary, measurements of the transverse diameter of superior articular facet and thickness of lamina differed significantly from those reported in literature. This should be kept in mind while doing neurosurgery procedures in the Indian population.

C1-C2 Facet Joint Penetration by C2 Pedicle Screws: Influence of Local Anatomy, Bone Mineral Density, and Screw Length

BACKGROUND

A challenge of C2 pedicle screw placement is to avoid penetration into the C1-C2 facet joint, as this may alter normal biomechanics and accelerate joint degeneration. Our objective was to clarify how local anatomy and surgical technique may relate to C2 pedicle screw penetration into the C1-C2 facet joint.

METHODS

C2 pedicle screws were inserted using a fluoroscopically assisted freehand technique. Independent fellowship-trained spine surgeons blindly reviewed intraoperative fluoroscopic and postoperative computed tomography (CT) images for evidence of facet joint penetration (FJP). C2 pedicle morphometry, the sagittal angle of the facet joint, axial and sagittal pedicle screw angles, and screw length were measured on the relevant CT images.

RESULTS

A total of 34 patients fulfilled the study criteria, and a total of 68 C2 pedicle screws were placed. Eight screws (16%) penetrated the C1-C2 facet joint. The mean sagittal angle of the C1-C2 facet joint was significantly lower in the FJP group compared with the non-FJP group. The mean sagittal angle of the screws was significantly higher in the FJP group compared with the non-FJP group. The mean screw length was significantly greater for screws causing FJP compared with the non-FJP group. The mean axial screw angle was significantly lower in the FJP group compared with the non-FJP group. Pedicle width, length, height, and transverse angle were not significantly associated with FJP. Independent reviewers were able to identify FJP on intraoperative fluoroscopic imaging in 2 out of 8 cases.

CONCLUSION

Lower sagittal angle of the facet joint, higher sagittal angle of the pedicle screw, and screw length >24 mm are associated with higher risk of C1-C2 FJP. When placing C2 pedicle screws under these conditions, caution should be taken to avoid FJP.

CLINICAL RELEVANCE

Several anatomical and technical factors may increase the risk of C1-C2 FJP during placement of C2 pedicle screws using a fluoroscopically assisted freehand technique, underscoring the importance of preoperative planning and limiting screw length.

LEVEL OF EVIDENCE: 3

A comprehensive analysis and literature review of vertebral artery variation in craniovertebral junction using three-dimensional computed tomography angiography

PURPOSE

To describe vertebral artery (VA) variation in patients with or without osseous anomalies at congenital craniovertebral junction (CVJ).

METHODS

In the present study, we retrospectively analyzed 258 patients with VA variation who underwent three-dimensional computed tomography angiography (3D CTA) in our hospital from March 2017 to October 2019.

RESULTS

Among 258 patients, 180 were accompanied by skeleton structural malformation, including 105 cases of occipital ossification of the atlas, 8 cases of the bipartite atlas, 7 cases of hypoplasia of the posterior arch of the atlas, 45 cases of C2/3 congenital fusion, 2 cases of C2/3/4 congenital fusion, and 13 cases of congenital os odontoid. VA variation was divided into type A (VA variation in the CVJ area without osseous anomalies) and type B (VA variation in the CVJ area with osseous anomalies). There are totally 10 subtypes, including type A1 (atlas occipitalization with VA entrance approach close to middle line, 20.2%); type A2 (atlas occipitalization with VA entrance approach far from middle line, 30.2%); type A3 (first intersegmental VA in C1-C2, 1.9%); type A4 (fenestration of the VA, 2.3%); type A5 (VA bulging type, 6.6%); type A6 (VA exposures with the absence of the posterior atlas arch, 2.3%); type A7 (C2 inner wall type, 0.4%); type A8 (single vertebral artery, 2.3%); type B1 (posterior ponticuli, 2.7%); and type B2 (high-riding VA, 31.4%).

CONCLUSION

This study is expected to take the lead in the most comprehensive classification of VA variation.

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.

Prevalence of Vertebral artery anomaly in upper cervical and its surgical implications: a systematic review

BACKGROUND

The presence vertebral artery (VA) abnormalities in the upper cervical may be a potential cause of catastrophic complication in the posterior approach of the upper cervical spine surgery. The aim of this study was to demonstrate the real incidence of the V3 segment anomaly in patients who need upper cervical surgery, and tried to find out the risk factors of V3 segment anomaly to evaluate the necessary of computed tomographic angiography (CTA) for upper cervical surgery.

METHOD

This systematic review was conducted following the preferred reporting items for systematic reviews and meta-Analyses (PRISMA). Retrospective studies and reports of case series involving human subjects with data on anomalies of vertebral artery in upper cervical spine were included. Data on the prevalence of persistent first intersegmental artery (PIA), fenestration of the VA (FA), posterior inferior cerebellar artery (PICA) were extracted.

RESULTS

A total of 16 articles involving 5927 subjects met the inclusion criteria. The total incidence of V3 segment anomaly in the patients with bony abnormalities was 25.9% (74/286): PIA was 17.5%, FA was 6.6% and PICA was 1.8%. The total incidence of V3 segment anomaly in the patients without bony abnormalities was 2.7% (152/5671): PIA was 1.76%, FA was 0.4% and PICA was 0.5%. The total incidence of V3 segment anomaly in Asian population without bony abnormalities was 5.8%, while in European and American population was 0.8 and 0.6%, respectively.

CONCLUSION

Patients with bone abnormalities are high risk factor for VA abnormalities, CTA is of paramount importance to evaluate the variant VA anatomy. However, regarding to the low incidence of V3 variation in normal population, we do not recommend preoperative CT angiography as mandatory part of preoperative.

Suitability of the Subaxial Cervical Laminae for Laminar Screws in the Pediatric Population: A Radiologic Anatomical Study

INTRODUCTION

The laminar screw method was popularized during recent years. Since no data exist in the literature on its suitability for subaxial levels in the pediatric population, a radiologic anatomical study was planned to evaluate the suitability of the laminae for laminar screws in children.

METHODS

The laminar thicknesses from C3 to C7 were measured in axial sections in 120 pediatric patients using computed tomography. The patients were divided into 3 age-groups: ages 4-6, 7-9, and 10-12. Each age-group consisted of 20 boys and 20 girls. The suitability of the laminae was evaluated for 3.5-mm-thick commercially available screws and also for the 3-mm screws that could be produced in the future. If the height of the base of the spinous process is ≥ 9 mm, the segment was accepted as suitable for the bilateral screw, and ≥5 mm is for the unilateral screw. Additionally, laminar thickness and length were measured for possible short screws longer than 15 mm in the laminae that were distally thin but proximally thick.

RESULTS

The C4 and C5 levels had the thinnest (2.77 ± 0.6 mm and 2.81 ± 0.6 mm, respectively) and C7 had the thickest laminae (4.66 ± 0.6 mm) in all age-groups. No significant differences were found between boys and girls and right and left laminae. According to the age-groups, an increase in laminar thickness was possible by growing, but only C7 laminae thickness was statistically different between 10-12 and 4-6 age-groups (p < 0.001). The last rate of the suitability was 9.1% for the 3.5-mm-thick screws and 13.75% for the 3-mm-thick screws after deletion of the bilateral insertion due to the short base of the spinous process and adding the possible short screws in the distally thin but proximally thick laminae. The rates increased with age, but the only statistically significant difference was found between 4-6- and 10-12-year-old age-groups (p < 0.001).

CONCLUSIONS

Laminar screws may be suitable for some levels of C7, C6, and C3 even in the young pediatric population. The use of thinner screws (3 mm) may increase the suitability rate. Therefore, laminar screw choice may be considered as a salvage method in pediatric patients, and all laminae may be evaluated individually for suitability. This study did not evaluate the safety and efficacy of the method in children, and these issues must be studied further.

C2 partial transpedicular screw technique for atlantoaxial dislocation with high-riding vertebral artery: A technique note with case series

OBJECTIVE

Although the C2 pedicle screw (C2PS) is currently the most biomechanically robust option for C2 fixation, the high-riding vertebral artery (HRVA) precludes safe C2PS placement. However, unintentional partial C2 pedicle perforation and vertebral foramen violation due to C2PS placement without neurovascular complications occurred frequently in clinic. Therefore, we have attempted to apply C2 partial transpedicular screw (C2PTS) in patients with HRVA with satisfactory preliminary outcomes. The aim of the present study is to introduce the C2PTS technique and report the preliminary radiological and clinical outcomes of application of C2PTS.

PATIENTS AND METHODS

The data of 15 patients with atlantoaxial dislocation underwent atlantoaxial arthrodesis with posterior screw-rod construct were retrospectively reviewed. All patients had unilateral or bilateral HRVA that precluded safe C2PS placement and C2PTS was used as an alternative. In this technique, a Penfield dissector was used to properly mobilize the HRVA inferiorly to preclude vertebral artery injury and pave the way for C2PTS placement. The C2PTS travelled under the superior border of the isthmus and toward the ipsilateral atlantoaxial articulation. The implant position and atlantoaxial reduction were evaluated using computed tomography (CT) scans and vertebral artery (VA) was assessed using CT angiography postoperatively.

RESULTS

Satisfactory C2PTS placement and atlantoaxial reduction were achieved in all patients. Postoperatively, no vertebral artery injury and implant failure were observed, and bone fusion was achieved in all the patients. Additionally, there were no VA occlusion or stenosis due to screws demonstrated on VA CT angiography.

CONCLUSION

C2PTS can achieve three-column fixation of axis and is an efficient alternative to C2PS which is prohibited due to HRVA; also, gently mobilizing the HRVA inferiorly is mandatory to prevent vertebral artery injury during C2PTS placement.

A possible novel technique for intraoperative imaging of the vertebral artery during arthrodesis of the upper cervical spine

In elderly, the fractures in C1-C2 are a common entity. Poor bone quality and wide range of motion hamper the natural bone fusion, thus making surgery often the only possible way to deal with the underlying pathology. The proximity to important neurovascular structures represents the stabilization in this segment a challenge to the surgical team. There are two major techniques, which are used to achieve a dorsal fusion in the C1-C2 Segment: Goel/Harms and Magerl techniques. The reported risk for damaging the vertebral artery in both techniques lies between 8% and 9,5% using a C-Arm. In Goel/Harms technique lateral mass screws in C1 and pedicle screws in C2 are placed. A transarticular screw is placed on both sides C1-C2 in Magerl technique in order to achieve stabilization of the C1-C2 Segment. By using the new navigational methods for a better imaging of the bony structures (O-Arm), this risk could be reduced further down. The risk for injury of the vertebral artery using the O-Arm navigation depends on the pathology, which is operated, ranging from 0, 3% to 2%. A further problem represents the anatomical variations of the vertebral artery, of which the high-riding vertebral artery being the most important one, reported between 10 and 14,5% of the cases according to the literature review. The novel technique for intraoperative imaging of the vertebral artery represents a fusion between an intraoperative O-Arm and intraoperative application of contrast, thus intraoperatively seeing the exact way of the vertebral artery. Also, after the insertion of the screws, a second CT scan with the O-Arm could be performed, yet again with contrast, to see whether the perfusion of both vertebral arteries is preserved. The significance of this method could bring the injuries of the vertebral artery to 0% independently on the technique, which has been used. This method could be used not only for craniocervical stabilization but also for removal of complex tumors in craniocervical junctions, whereas the vertebral artery is encompassed.

Posterior C2 Fixation Using Trans-C2 Inferior Articular Process Screws: A Case Series and Technical Note

OBJECTIVE

Upper cervical fixation with C2 pedicle screw insertion may predispose patients to vertebral artery injury, in particular, patients with craniovertebral junction anomalies. The aim of this study was to describe an alternative technique with trans-C2 inferior articular process screw (C2IAPS) insertion for rigid C2 fixation, which can be used to anchor the C2 vertebra for upper cervical fixation.

METHODS

Records of 19 patients who underwent posterior atlantoaxial fixation using C2IAPS combined with C1 lateral mass screw were retrospectively reviewed. Efficacy was assessed by postoperative imaging and Japanese Orthopaedic Association scores.

RESULTS

There were 22 C2IAPSs successfully implanted (3 on both sides and 16 on 1 side). With the exception of 2 screws that had intruded into the outlet of the intervertebral foramen, all screws were safely implanted. Average Japanese Orthopaedic Association scores improved from 11.8 ± 1.9 preoperatively to 15.3 ± 1.3 postoperatively. Bony fusion rate was 100%.

CONCLUSIONS

For patients who are not eligible for C2 pedicle screw fixation, C2IAPS fixation can be considered as an alternative technique for upper cervical fixation of C2.

Occiput-axis crossing translaminar screw fixation technique using offset connectors: An in vitro biomechanical study

OBJECTIVE

Fixation with the axis vertebra (C2) using pedicle screws is commonly used to treat an unstable occipitocervical junction; however, it is accompanied by a risk of vertebral artery injury. The occiput-C2 (OC2) crossing translaminar screw fixation technique may avoid this risk, but rod implantation is difficult. Offset connectors can help facilitate this construct. This study aimed to evaluate the stability of a technique for OC2 crossing translaminar screw fixation using offset connectors (C2LAM + OF) in comparison with other methods.

PATIENTS AND METHODS

Six fresh-frozen human cadaveric occipital-cervical spines were tested intact under flexion, extension, lateral bending, and axial rotation. These were then made into a type II odontoid fracture model, instrumented with an occipital plate, and tested in the following modes: C2 bilateral pedicle screws (C2P), a single C2 pedicle screw and bilateral C3 lateral mass screws (C2P + C3M), C2 crossing translaminar screws (C2LAM), and C2LAM + OF. The OC2 range of motion (ROM) for each construct was obtained and compared using a repeated-measures analysis.

RESULTS

The ROM of the C2LAM + OF construct was found not to be significantly different from that of the C2P and C2P + C3M fixations in every direction (p > 0.05). However, the C2LAM + OF construct was superior to the C2LAM construct in axial rotation (p < 0.05).

CONCLUSIONS

OC2 crossing translaminar screw fixation using offset connectors offers similar stability to C2 pedicle screw fixation and is an effective alternative method for treating an unstable occipitocervical junction.

New entry point for C2 screw, in posterior C1-C2 fixation (Goel-Harm's technique) significantly reducing the possibility of vertebral artery injury

OBJECTIVE

To reduce the chance of vertebral artery injury in posterior C1 lateral mass and C2 pedicle/pars screw-rod fixation (Goel-Harms technique ).

METHOD

49 patients, 30 males and 19 females, 12years - 82 years, underwent posterior C1-C2 fixation from February 2007 till June2013. A new entry point for the posterior C2 screw, 3mm below the midpoint of the C1-C2 joint which is directed medially and downwards into the C2 body , probably avoids the vertebral artery. As the screw now bypasses the pedicle/ pars , the chance of injuring the vertebral artery is probably reduced.

RESULTS

No case of intra-operative vertebral artery injury.

CONCLUSION

The new technique of C2 screw fixation allows rigid immobilization of the C1-C2 joint without significant risk of vertebral artery injury.

Prevalence of High-Riding Vertebral Artery and Morphometry of C2 Pedicles Using a Novel Computed Tomography Reconstruction Technique

Study Design

Cross-sectional, matched-pair comparative study.

Purpose

To determine whether a thin-sliced pedicular-oriented computed tomography (TPCT) scan reconstructed from an existing conventional computed tomography (CCT) scan is more accurate for identifying vertebral artery groove (VAG) anomalies than CCT.

Overview of Literature

Posterior atlantoaxial transarticular screw fixation and C2 pedicle screws can cause vertebral artery (VA) injury. Two anatomic variations of VAG anomalies are associated with VA injury: a high-riding VA (HRVA) and a narrow pedicle of the C2 vertebra. CCT scan is a reliable method used to evaluate VAG anomalies; however, its accuracy level remains debatable. Literature comparing the prevalence of C2 VAG anomalies between CCT and TPCT is limited.

Methods

A total of 200 computed tomography scans of the upper cervical spine obtained between January 2008 and December 2011 were evaluated for C2 VAG anomalies (HRVA and narrow pedicular width) using CCT and TPCT. The prevalence of C2 VAG anomalies was compared using these two different measurement methods via a McNemar's test.

Results

Of the 200 patients studied, 23 HRVA (6.01%; 95% confidence interval [CI], 3.61%–8.39%) were detected with CCT, whereas 66 HRVA (16.54%; 95% CI, 12.85%–20.23%) were detected with TPCT (p<0.001). Sixty-two narrow pedicles (15.58%; 95% CI, 11.99%–19.15%) were detected with CCT, whereas 90 narrow pedicles (22.83%; 95% CI, 18.58%–26.87%) were detected with TPCT (p<0.001).

Conclusions

VAG anomalies are commonly observed. A preoperative evaluation using TPCT reconstructed from an existing CCT revealed a significantly higher prevalence of C2 VAG anomalies than did CCT and showed comparable prevalence to previously published studies using more sophisticated and higher risk techniques. Therefore, we propose TPCT as an alternative preoperative evaluation for C2 screw placement and trajectory planning.

Understanding the Course of Vertebral Artery at Craniovertebral Junction in Occipital Assimilation of Atlas: Made Simplified Using Conventional Angiography

Introduction Preoperative assessment of vertebral artery (VA) is important to avoid its injury during surgery at craniovertebral junction (CVJ). The main concern is the course of third segment of VA (V3) while performing instrumentation at CVJ, that is, segment of VA from its course through transverse foramen of C2 to its course along the posterior arch of C1. This segment of VA includes its passage through C1 transverse foramen as well. This observational study was done to analyze the course, curvature, and termination of VA in patients with occipital assimilation of atlas at CVJ, a complex congenital anomaly, and compared with the normal course for better understanding especially by young neurosurgeons and spine surgeons. Materials and Method This is an observational study that included patients with occipitalized C1 with or without associated anomalies. Out of 30 patients of CVJ anomalies, 16 patients had occipitalized atlas. Digital subtraction angiography was done in all cases. It was done by selectively catheterizing the VA using standard Seldinger's technique and both anteroposterior and lateral projections were taken. Results The course of VA was not identical on either side in any individual. It was lengthened and tortuous in all patients. Different types of anomalous course were encountered like bypassing transverse foramen of C1, close relation with C1-2 facet joints, variable course along the posterior arch of C1, abnormal termination and fenestration of VA. Conclusion Craniovertebral junction anomalies are not only bony or neural, but are vascular too. Complex CVJ anomalies are associated with higher incidence of anomalous course of the VA, an important surgical consideration.

[Are C2 pedicles always screwable? Calibration and planning with a pedicle-lamina angle]

INTRODUCTION

Posterior cervical arthrodesis is associated with osteosynthesis. C2 pedicular screwing affords a good bone anchoring but involves neurological and vascular risks.

PURPOSE

To determine C2 pedicular screwing feasibility from a large cohort of cervical CT scans. To describe the visible anatomical parameters during a surgical procedure in order to plan and secure it.

MATERIALS AND METHODS

Retrospective consecutive series of 100 cervical CT scans was analyzed. Cases with upper cervical fracture were excluded. C2 surgical anatomy was assessed according to maximum length, minimum width and minimum height. Angular parameters were pedicle-transverse angle and sagittal angle. Original pedicle-lamina angle was used as a visible mark during the procedure independent of the patient's position. Pedicular screwing feasibility was evaluated. It was arbitrarily defined by a lower minimum height less than 4mm.

RESULTS

Two hundred C2 pedicles were analyzed with 7.5% that were not screwable. Their mean length was 26.2mm, with a mean width of 5.2mm and a mean height of 9.2mm. Mean pedicle-transverse angle was 36.2°, mean sagittal angle was 25.8° and mean pedicle-lamina angle was 81.3°.

CONCLUSION

C2 pedicle screwing feasibility is inconstant due to anatomical variability. In fact, 13% of patients have at least one non-screwable pedicle. Preoperative planning is essential to achieve this procedure. A pedicle-lamina angle can be used which remains independent from the patient's position.

The efficacy of pedicle screw instrument in treatment of irreducible atlantoaxial dislocation

OBJECTIVE

To explore the effect of pedicle screw instrument in treatment of irreducible atlantoaxial dislocation.

PATIENTS AND METHOD

From June 2003 to February 2009, 14 cases of atlas dislocation with upper cervical cord compression were enrolled and anterior transoral soft tissue release combined with posterior reduction and pedicle screw fixation were performed. CT, MRI and radiograph were used preoperatively, and screw placement and bone graft were administered in all cases intraoperatively. Cervical collars were used for 3 months.

RESULTS

Screws were successfully placed in atlas in all cases. The average follow-up period was 18 months. Bone fusion was observed in all cases without the following complications: neurologic symptoms, internal fixation failure and redislocation. Neurological recovery was observed in all 14 cases.

CONCLUSIONS

Pedicle screw instrument has the following advantages in atlas and axis injury treatment: direct screw placement, short-segment fusion, intraoperative reduction and high fusion rate, which should be a better surgical method for the treatment of atlantoaxial dislocation.

Current Trends in Management of Atlantoaxial Dislocation

Atlantoaxial dislocation (AAD), often caused by trauma, tumors or congenital malformations, is a challenging disorder of the craniocervical junction. Because of its deep location and intricate anatomic structure, the craniocervical junction is always a difficult region for spine surgery. With recent developments in medical science, great progress has been made in the diagnosis and treatment of AAD such that more instructive clinical classifications and efficacious treatment strategies, various novel operation techniques including innovative posterior or transoral anterior reduction, and novel fixation instruments are now widely used in clinical practice for managing AAD. However, surgeons continue to face more special characteristics and difficulty in carrying out upper cervical surgery than they encounter in other regions of the spine. Consequently, this high risk surgery should only be performed by extremely skilled and experienced surgeons and only when stringent indications have been met. Therefore, the aim of this course is to assist surgeons who are dealing with AAD by providing comprehensive information about AAD, including related anatomy, classification, clinical manifestations and diagnosis, imaging examinations and surgical techniques, thus decreasing the occurrence of complications and improving the level of diagnosis and treatment.