C1 lateral mass screw placement in occipitalization with atlantoaxial dislocation and basilar invagination: a report of 146 cases

Novel MRI signs of the atlantodental space in patients with atlantoaxial dislocation

OBJECTIVES

The type of atlantodental space tissue in patients with atlantoaxial dislocation (AAD) can help doctors understand the possibility of reduction before surgery. However, relevant research on this topic is lacking. In this study, we aimed to summarise the atlantodental space classification of patients with AAD using magnetic resonance imaging (MRI) and explore their clinical characteristics.

MATERIALS AND METHODS

Preoperative 3T cervical MR images of patients who underwent posterior reduction and fixation surgery for non-traumatic AAD between 1 September 2012 and 31 July 2023 were collected. Two radiologists read and recorded the MRI results based on the standard protocol. The kappa value was used to evaluate intra- and inter-observer agreements. The patient's age, sex, body mass index, clinical symptoms, Japanese Orthopaedic Association (JOA) score, and visual analogue scale information were obtained from medical records.

RESULTS

A total of 135 patients with AAD (mean age, 51.3 ± 14.0 years, 52 men) were included in the analysis. The inter-observer agreement between the two readers was 0.818 (P < 0.0001). The intra-observer consistencies were 0.882 (P < 0.0001) and 0.896 (P < 0.0001). Patients with inflexible tissue signs exhibit more irreducible in hyperextension position, and their range of motion of ADI is smaller. These patients were older and had a higher incidence of abnormal spinal cord signals and JOA scores.

CONCLUSIONS

Novel MRI signs exhibited high inter- and intra-observer consistency and were associated with patient age, abnormal spinal cord signals, reducibility, range of motion of ADI, and symptoms.

Posterior realignment of basilar invagination with facet joint distraction technique

PURPOSE

We describe our experience with management of basilar invagination (BI) with the atlantoaxial dislocation (C1/C2) joint reduction technique, including posterior atlantoaxial internal fixation.

MATERIALS AND METHODS

From 2008 to 2018, eleven patients with atlantoaxial dislocation (AAD) and BI underwent surgical reduction using C1/C2 the joint reduction technique with a fibular graft/peek cage placement followed by C1 lateral mass/C2 pedicle screw fixation. In two cases that we originally planned to perform C1/C2 joint reduction, occiput-C2 pedicle screw fixation was performed instead due to intraoperative challenges. Post-operative course and surgical complications will be discussed.

RESULTS

A total of 13 patients, with an average age of 30.46 ± 13.23 years (range 12-57), were operated. In one patient, iatrogenic vertebral artery injury occurred without any neurological complication. JOA score improved from 10.45 ± 1.128 to 15.0 ± 1.949 (p < 0.0001, paired t-test). All radiological indices were improved (p at least < 0.001). No construct failure was seen in any of the patients with C1-2 facet joint distraction technique during follow-up, and no additional anterior decompression surgery was required.

CONCLUSIONS

C1/C2 joint reduction technique with fibular graft/cervical PEEK cage of BI patients together with AAD seems to be an effective and safe surgical method of treatment.

Characteristics and evaluation of C1 posterior arch variation for transpedicular screw placement between patients with and without basilar invagination

BACKGROUND

C1 transpedicular screw (C1TS) placement provided satisfactory pullout resistance and 3D stability, but its application might be limited in patients with basilar invagination (BI) due to the high incidences of the atlas anomaly and vertebral artery (VA) variation. However, no study has explored the classifications of C1 posterior arch variations and investigated their indications and ideal insertion trajectories for C1TS in BI.

PURPOSE

To investigate the bony and surrounding arterial characteristics of the atlas, classify posterior arch variations, identify indications for C1TS, evaluate ideal insertion trajectories for C1TS in BI patients without atlas occipitalization (AO), and compare them with those without BI and AO as control.

METHODS

A total of 130 non-AO patients with and without BI (52 patients and 78 patients, respectively) from two medical centers were included at a 1:1.5 ratio. The posterior arch variations were assessed using a modified C1 morphological classification. Comparisons regarding the bony and surrounding arterial characteristics, morphological classification distributions, and ideal insertion trajectories between BI and control groups were performed. The subgroup analyses based on different morphological classifications were also conducted. In addition, the factors possibly affecting the insertion parameters were investigated using multiple linear regression analyses.

RESULTS

The BI group was associated with significantly smaller lateral mass height and width, sagittal length of posterior arch, pedicle height, vertical height of posterior arch, and distance between VA and VA groove (VAG) than control group. Four types of posterior arch variations with indications for different screw placement techniques were classified; Classifications I and II were suitable for C1TS. The BI cohort showed a significantly lower rate of Classification I than the control cohort. In the BI group, the subgroup of Classification I had significantly larger distance between the insertion point (IP) and inferior aspect of the posterior arch. In addition, it had the narrowest width along ideal screw trajectory, but a significantly more lateral ideal mediolateral angle than the subgroup of Classification II. Multiple linear regression indicated that the cephalad angle was significantly associated with the diagnosis of BI (B = 3.708, P < 0.001) and sagittal diameter of C1 (B = 3.417, P = 0.027); the ideal mediolateral angle was significantly associated with BMI (B = 0.264, P = 0.031), sagittal diameter of C1 (B =  - 4.559, P = 0.002), and pedicle height (B =  - 2.317, P < 0.001); the distance between the IP and inferior aspects of posterior arch was significantly associated with age (B =  - 0.002, P = 0.035), BMI (B =  - 0.007, P = 0.028), sagittal length of posterior arch (B =  - 0.187, P = 0.032), pedicle height (B =  - 0.392, P < 0.001), and middle and lower parts of posterior arch (B = 0.862, P < 0.001).

CONCLUSION

The incidence of posterior arch variation in BI patients without AO was remarkably higher than that in control patients. The insertion parameters of posterior screws were different between the morphological classification types in BI and control groups. The distance between VA V3 segments and VAG in BI cohort was substantially smaller than that in control cohort. Preoperative individual 3D computed tomography (CT), CT angiography and intraoperative navigation are recommended for BI patients receiving posterior screw placement.

Strategies to avoid internal carotid artery injury in “sandwich” atlantoaxial dislocation patients during surgery

PURPOSE

To elucidate the anatomic relationship between the internal carotid artery (ICA) and the bony structures of the craniovertebral junction among "sandwich" atlantoaxial dislocation (AAD) patients, and to analyze the risks of injury during surgical procedures.

METHODS

The distance from the medial wall of ICA to the midsagittal plane (D1), the shortest distance between the ICA wall and the anterior cortex of the lateral mass of atlas (LMA) (D2) on the most caudal and cranial levels of LMA and the angle (A) between the sagittal plane passing through the screw entry point of C1 lateral mass(C1LM) screw and the medial tangent line of the vessel passing through the entry point were measured. Besides, the location of ICA in front of the atlantoaxial vertebra was divided into 4 categories (Z1-Z4).

RESULTS

There was a statistically difference between the male and female patients regarding D1, and the difference between D2 at level a and level b as well as angle A between the left and right sides were statistically different (p < 0.05). Ninety-two ICAs (57.5%) were anteriorly located in Z3, 50 (31.3%) were located in Z4, 17 were located in Z2, and only one ICA was located in Z1 in all 80 patients.

CONCLUSIONS

In "sandwich" AAD patients, particular attention should be paid to excessively medialized ICA to avoid ICA injury during trans-oral procedures, and the risk of injuring the ICA with more cranially and medially angulated C1LM screw placement was relatively less during posterior fixation procedures. A novel classification of ICA location was used to describe the relationship between ICA and LMA.

The Classification of Axial Deformity in Patients with Basilar Invagination

OBJECTIVE

To summarize the variation types of the axis in patients with basilar invagination (BI), then propose a classification scheme of the axis deformity.

METHODS

From December 2013 to September 2020, 92 patients (male 42, female 50) who were diagnosed with BI were studied retrospectively. Based on the imaging data of CT, the width and height of the axis pedicle and the sagittal diameter of the lateral mass were measured in each patient. According to the development of axis pedicle and lateral mass, the types of axis variation were summarized, and then the classification scheme of axis deformity was put forward.

RESULTS

All cases were analyzed and axis deformities were divided into four types. Type I: the axis is basically normal (53 cases, 57.6%). Type II: axis lateral mass is dysplasia (eight cases, 8.7%), which includes two subtypes: type IIA, the axis unilateral lateral mass is dysplasia (three cases); type IIB, the axis bilateral lateral masses are all dysplasia (five cases). Type III: axis pedicle is dysplasia (11 cases, 12%), which is subdivided into two subtypes: type IIIA, the axis unilateral pedicle is dysplasia (six cases); type IIIB, the axis bilateral pedicles are all dysplasia (five cases). Type IV: axis pedicle and lateral mass are all dysplasia (20 cases, 21.7%), this type contains the following four subtypes: type IVA, the unilateral axis pedicle and unilateral lateral mass (contralateral or ipsilateral) are all hypoplasia (four cases); type IVB, the unilateral axis pedicle and bilateral lateral masses are all hypoplasia (five cases); type IVC, the bilateral axis pedicles and unilateral lateral mass are all dysplasia (seven cases); type IVD, the bilateral axis pedicles and bilateral lateral masses are all dysplasia (four cases). The left and right abnormal lateral mass sagittal diameter (Type II) was (7.23 ± 1.39) mm and (5.96 ± 1.37) mm, respectively, the left and right abnormal pedicle width (Type III) was (2.61 ± 1.01) mm and (3.23 ± 0.66) mm, respectively, left and right abnormal pedicle height (Type III) was (5.43 ± 2.19) mm and (4.92 ± 1.76) mm, respectively. Moreover, the classification scheme has good repeatability and credibility.

CONCLUSIONS

The classification about axis deformity could provide personalized guidance for axis screw placement in the BI and other upper cervical surgery, and axis screw placement errors would be effectively avoided.

Suitability of 3.5-mm screw for the atlas in children: a retrospective computed tomography analysis

BACKGROUND

The growth and development of the atlas in children has not been studied to date using a large sample size.

OBJECTIVE

To study whether a 3.5-mm screw is suitable for the atlas in children, to explore the anatomical size and development of the atlas in 0-14-year-old children, and to provide morphological basis for lateral mass screw internal fixation.

METHODS

A Computed Tomography (CT) morphometric analysis was performed on 420 pediatric atlases. In the atlas, D1, D2, D3, D4, and α of the atlas lateral mass were measured. Statistical analysis was performed using one-way ANOVA and Students' t test. The least square method was used for the regression analysis of the change trend in anatomical structure. The curve with the greatest goodness of fit was used as the anatomic trend regression curve.

RESULTS

D1, D2, D3, and D4 generally showed an increasing trend with age. The ranges of averages of D1, D2, D3, D4, and α in 0-14 year-old children were as follows: 4.576-9.202 mm, 9.560-25.100 mm, 3.414-10.554 mm, 11.150-27.895, and 12.41°-20.97°, respectively. The trends of the fitting curves of L1 and L3 were power functions, and those of L2 and L4 were logarithmic curves.

CONCLUSIONS

CT examination could help in preoperative decision-making, and 3.5-mm screw was found to be suitable for lateral mass screw internal fixation in children aging 2 years and older. D1-D4 increased with age. This provided a certain reference to perform posterior atlantoaxial fusion in children and is of great significance to design posterior atlantoaxial screw in children.

Feasibility of 3.5mm C2 pedicle screws in children: Part II, a computerized tomography analysis

BACKGROUND

There have been no studies with large sample sizes on growth of the pedicle of C2 in children. In the present study we measured the pedicle of C2 through computed tomography (CT) imaging in children aged less than 14 years and evaluated the suitability of the 3.5-mm screw for the pedicle in such children.

METHODS

The study was conducted on CT morphometric images of 420 children in our hospital between June 2018 and June 2020. The width (D1), length (D2), height (D3), inclination angle (α), and tail angle (β) of the C2 pedicle were measured. One-way analysis of variance and Student's t test were used for statistical analyses. The least-square method was used to analyze the curve fitting the trend of anatomical change in the pedicle. The largest degree of goodness of fit determined the best-fitting curve.

RESULTS

The size of the pedicle of C2 increased with age. The median ranges of D1, D2, D3, α, and β were 3.312-5.431 mm, 11.732-23.645 mm, 3.597-8.038 mm, 32.583°-36.640°, and 24.867°-31.567°, respectively. The curves fitting the trends of D1 and D3 were power functions, whereas D2 was fitted by a logarithmic curve. However, no curve fitted α or β.

CONCLUSION

A 3.5-mm screw can be placed in the pedicle of C2 in children aged more than one year. The growth and development trend of this pedicle can provide an anatomical reference for deciding on posterior cervical surgery and for selecting and designing pedicle screws for children.

Can C1 lateral mass and C3 pedicle screw fixation be used as an option for atlantoaxial reduction and stabilization in Klippel-Feil patients? A study of its morphological feasibility, technical nuances, and clinical efficiency

In Klippel-Feil patients with atlantoaxial dislocation, narrow C2 pedicles are often encountered preventing pedicle screw placement. Alternative techniques, including translaminar screws, pars screws, and inferior process screws could not achieve 3-column rigid fixation, and have shown inferior biomechanical stability. The present study aimed to evaluate the feasibility, safety, and efficacy of C3 pedicle screws (C3PSs) as an option for atlantoaxial stabilization in Klippel-Feil patients, and to introduce a freehand technique, the "medial sliding technique," for safe and accurate C3PS insertion. Thirty-seven Klippel-Feil patients with congenital C2-3 fusion who have received atlantoaxial fixation were reviewed. Preoperative CT and CT angiography were acquired to evaluate the feasibility of C3PS placement. C1 lateral mass and C3PS constructs were used for atlantoaxial stabilization. The "medial sliding technique" was introduced to facilitate C3PS insertion. Clinical outcomes and complications were evaluated, and screw accuracy was graded on postoperative CT scans. Morphological measurements showed that more than 80% C3 pedicles could accommodate a 3.5-mm screw. Fifty-eight C3PSs were placed in 33/37 patients using the medial sliding technique. Overall, 96.7% screws were considered safe and there was no related neurovascular complications; 27/33 patients exhibited neurological improvement and 30/33 patients had a solid bone fusion at an average 19.3-month follow-up. Therefore, the C3PS was a feasible option for atlantoaxial fixation in Klippel-Feil patients. The clinically efficiency of C3PS was satisfied with high fusion rates and low complications. The medial sliding technique we used could facilitate safe and accurate placement of C3PSs in Klippel-Feil patients with fused C2-3 vertebra.

A novel surgical protocol for safe and accurate placement of C1 lateral mass screws in patients with atlas assimilation, basilar invagination and atlantoaxial instability: technical details, accuracy assessment and perioperative complications

PURPOSE

To introduce a novel surgical protocol for safe and accurate placement of C1 lateral mass screws in patients with atlas assimilation, basilar invagination and atlantoaxial instability, and to categorize the screw accuracy and perioperative complications regarding this technique in a large case series.

METHODS

Between January 2015 and January 2020, patients who had atlas assimilation, basilar invagination and atlantoaxial instability, and underwent atlantoaxial fixation using C1 lateral mass screws were reviewed. C1 lateral mass screws were placed with a novel surgical protocol following a series key steps, including posterior para-odontoid ligament release, panoramic exposure of the invaginated lateral mass, and diligent protection of the abnormal VA. Screw accuracy and related complications were specifically evaluated.

RESULTS

A total of 434 C1 lateral mass screws were placed. Fifteen screws (3.5%) were classified as unacceptable, 54 screws (12.4%) were classified as acceptable, and 365 screws (84.1%) were classified as ideal. Overall, 96.5% of screws were deemed safe. There were no cases of vascular injury or permanent neurological defects. One patient with an unacceptable screw presented with hypoglossal nerve paralysis and recovered after an immediate revision surgery. Thirty-seven patients complained about occipital neuralgia and were successfully managed with medication.

CONCLUSION

Placement of C1 lateral mass screws in patients with atlas assimilation, basilar invagination and atlantoaxial instability following this surgical protocol is safe and accurate. Thorough para-odontoid ligamental release, wide exposure of the invaginated lateral mass, and diligent protection of the vertebral artery are critical to maximize the chances of successful screw placement.

Three-Dimensional Evaluation and Classification of the Anatomy Variations of Vertebral Artery at the Craniovertebral Junction in 120 Patients of Basilar Invagination and Atlas Occipitalization

BACKGROUND

Patients with basilar invagination and atlas occipitalization usually present abnormal anatomy of the vertebral arteries (VAs) at the craniovertebral junction (CVJ).

OBJECTIVE

To describe and further classify different types of VA variations at the CVJ with 3D visualization technology.

METHODS

One hundred twenty patients with basilar invagination and atlas occipitalization who had undergone 3-dimensional computed tomographic angiography (3D-CTA) were retrospectively studied. Imaging data were processed via the separating, fusing, opacifying, and false-coloring-volume rendering technique. Abnormal anatomy of the VA at the CVJ was categorized and related anatomic parameters were measured.

RESULTS

Seven different types were classified. Type I, VAs enter the cranium after leaving VA groove on the posterior arch of atlas (26.7% of 240 sides); Type II, VAs enter an extraosseous canal created in the assimilated atlas lateral mass-occipital condyle complex before reaching the cranium (53.3%); Type III, VA courses above the axis facet or curves below the atlas lateral mass then enter the cranium (11.7%); Type IV, VAs enter the spinal canal under the axis lamina (1.3%); Type V, high-riding VA (31.3%); Type VI, fenestrated VA (2.9%); Type VII, absent VA (4.2%). Distance from the canal of Type II VA to the posterior facet surface of atlas lateral mass (5.51 ± 2.17 mm) means a 3.5-mm screw can be safely inserted usually. Shorter distance from the midline (13.50 ± 4.35) illustrates potential Type III VA injury during exposure. Decreased height and width of axis isthmus in Type V indicate increased VA injury risks.

CONCLUSION

Seven types of VA variations were described, together with valuable information helpful to minimize VA injury risk intraoperatively.

The Role of Transverse Connectors in C1-C2 fixation for Atlantoaxial Instability: Is It Necessary? A Biomechanical Study

OBJECTIVE

To investigate the biomechanical effect of C1 lateral mass-C2 pedicle screw-rod (C1LM-C2PS) fixation with and without transverse connectors (TC) in an atlantoaxial instability (AAI) model.

METHODS

Ten freshly frozen cadaveric specimens were tested using an industrial robot under the following conditions: intact model, AAI model, C1-C2 model, C1-C2 with one TC model, and C1-C2 with two TCs model. Three types of motion, flexion-extension (FE), lateral bending (LB), and axial rotation (AR), were applied (1.5 Nm) to the specimens. The range of motion (ROM) and neutral zone (NZ) between C1 and C2 in all directions were measured.

RESULTS

Compared with those of the intact and AAI models, the C1-C2 ROM and NZ of all instrumented groups were decreased significantly in each direction of loading motion (P < 0.05). The mean FE ROM in the no TC, 1 TC, and 2 TC groups was 2.12° ± 0.41°, 2.29° ± 0.42°, and 2.04° ± 0.69°, respectively (P = 0.840, 0.981, 0.628, respectively); the mean LB ROM in the 3 intervention groups was 1.26° ± 0.67°, 1.02° ± 0.51° and 1.03° ± 0.57°, respectively (P = 0.489, 0.501, 1.000, respectively). During AR, the ROM and NZ of the no TC group (3.19° ± 0.89° and 1.51° ± 0.42°) were significantly reduced by more than 60% compared with those in the 1 (0.98° ± 0.28° and 0.40° ± 0.11°) and 2 TC groups (1.17° ± 1.69° and 0.42° ± 0.61°) (P < 0.001). Two TCs were equivalent for all loading motions to 1 TC (P > 0.05).

CONCLUSIONS

Adding TCs to C1LM-C2PS can effectively decrease the axial rotation ROM and enhance the stability of C1-C2 segment. Therefore, it is necessary to use TC-strengthened C1 lateral mass -C2 pedicle screw-rod fixation in patients with instability of C1-C2.

Effects of transverse connector on reduction and fixation of atlantoaxial dislocation and basilar invagination using posterior C1-C2 screw-rod technique

BACKGROUND CONTEXT

The mechanical strength provided by internal fixation is crucial for maintaining reduction and facilitating bony fusion. Though satisfactory results with the C1-C2 technique have been acquired in most clinical reports, the related problems of fusion delay and pseudarthrosis still exist. To increase the chance of bony fusion, a transverse connector (TC) is frequently used to augment torsional stiffness of thoracolumbar screw/rod constructs. Nevertheless, the clinical implication of TC in the management of atlantoaxial dislocation (AAD) and basilar invagination (BI) remains largely unknown.

PURPOSE

To evaluate the effects of TC application on C1-C2 screw-rod constructs based on consecutive adult patients with AAD and BI in a single institution over a 10-year period.

STUDY DESIGN

A retrospective study.

PATIENT SAMPLE

Patients with AAD and BI, who were treated with posterior C1-C2 screw-rod technique with or without TC usage from June 2007 to June 2017 at a single institution.

OUTCOME MEASURES

The radiological measurements included the anterior atlantodental interval (AADI), posterior atlantodental interval (PADI), height of odontoid process above Chamberlain line, and cervicomedullary angle (CMA). Patients' neurologic status was evaluated with the Japanese Orthopaedic Association (JOA) score. Fusion status was evaluated at different follow-up periods.

METHODS

We compared the difference of clinical, radiological, and surgical outcomes between the TC and NTC groups postoperatively.

RESULTS

In total, there were 149 consecutive patients in the TC group and 168 patients in the NTC group. On average, 1.2 TCs per patient were used in the TC group. No significant differences were identified for operative time and blood loss between groups. There was also no statistical difference in the radiological measurements of AADI, PADI, Chamberlain line, and CMA between the TC and NTC groups preoperatively and postoperatively. A significantly higher JOA score was obtained in the TC group than that in the NTC group postoperatively. The fusion rates were higher in the TC group than those in the NCT group at the early stage postoperatively (3 and 6 months; p<.01).

CONCLUSIONS

Use of TCs seems to improve bony fusion and neurologic outcomes in the treatment of AAD and BI with C1-C2 screw-rod technique.

Can Posterior Reduction Replace Odontoidectomy as Treatment for Patients With Congenital Posterior Atlantoaxial Dislocation and Basilar Invagination?

BACKGROUND

For patients with odontoid process protrusion and basilar invagination, posterior screw–rod fixation can usually achieve satisfactory horizontal reduction, but in some cases satisfactory reduction in the vertical direction cannot be achieved at the same time.

OBJECTIVE

To propose a method for calculation of the theoretical maximum vertical reduction possible in individual patients.

METHODS

The computed tomography imaging data of patients with occipitalization and basilar invagination who were treated at our institute between January 2013 and June 2016 were retrospectively analyzed. The direction of odontoid reduction was decided by the inclination of the lateral joint. The atlanto-dental distance was assumed to be the maximum possible reduction in the horizontal direction. The maximum vertical reduction possible was calculated based on these values.

RESULTS

A total of 82 patients (34 males and 48 females) were included. The theoretical vertical reduction value was 4.2 ± 3.0 mm, which was significantly smaller than that of the dental protrusion (14.5 ± 3.8 mm, P = .000). Analysis of follow-up data (29 cases) showed that, the difference between the theoretical vertical reduction value H (4.7 ± 3.5 mm) and the actual vertical reduction value Ha (5.6 ± 3.5 mm) was not significant (P = .139).

CONCLUSION

The theoretical calculation method we proposed can well predict the actual degree of vertical reduction. The theoretical vertical reduction value is significantly lower than the odontoid protrusion value, indicating that satisfactory reduction in the vertical direction is difficult with a posterior approach alone.

The Value and Limitation of Cervical Traction in the Evaluation of the Reducibility of Atlantoaxial Dislocation and Basilar Invagination Using the Intraoperative O-Arm

OBJECTIVE

To assess the value and limitation of cervical traction in the evaluation of the reducibility of atlantoaxial dislocation (AAD) and basilar invagination (BI) using the intraoperative O-arm.

METHODS

A total of 22 patients with hyperextensive, irreducible AAD were included. The cervical traction test under general anesthesia was performed, and the degree of reduction was evaluated using the O-arm before the operation started. The traction effects both vertically and horizontally were evaluated. All cases then underwent modified direct posterior reduction and fixation. Clinical outcomes were evaluated using the Japanese Orthopaedic Association (JOA) scale. Radiologic measurements included the anterior atlantodental interval, the distance of odontoid tip above Chamberlain line, and the clivus-canal angle. Magnetic resonance imaging signal changes, size of syringomyelia, and the space ventral to medulla also were used to evaluate the postoperative reduction result.

RESULTS

After the cervical traction test, 7 patients achieved incomplete reduction, 5 achieved only vertical reduction, 6 achieved only horizontal reduction, and 4 achieved complete reduction in both horizontal and vertical orientations as assessed by the O-arm. All patients underwent a direct reduction technique. The mean JOA score increased from 11.1 to 14.5. Complete reduction of AAD and BI were achieved in 19 patients (86.4%), with partial reduction achieved in 3 (13.6%). Sufficient cerebrospinal fluid space anterior to the medulla with improved JOA score was achieved in the 3 partially reduced patients.

CONCLUSIONS

With the innovations of direct posterior reduction techniques, cervical traction under anesthesia may not sufficiently predict the reducibility of BI and AAD. Cervical traction still plays an important role during the direct posterior reduction procedure.

Change of Anatomical Location of the Internal Carotid Artery Relative to the Atlas with Congenital Occipitalization and the Relevant Clinical Implications

INTRODUCTION

The occipitalization of the atlas (OA) is always associated with multiplanar dislocation and olisthy of the C1 over C2 facets, which may change the anatomical relationship between the internal carotid artery (ICA) and the atlas. The purpose of this current study is to identify the location of the ICA relative to the anterior aspect of the atlas in patients with OA and define the clinical implications for screw placement.

METHODS

We retrospectively reviewed the computed tomography angiography data of 86 patients with OA and 86 control subjects. Several parameters were also measured to quantitatively evaluate the mutual relationship.

RESULTS

In the OA group, 25.6% of ICAs were located in area 3 and 74.4% in area 2, whereas the percentages were 57.4% and 42.6%, respectively, in the control group. There were 73 (42.4%) ICAs in which the shortest distance between the dorsal surface of the ICA and the ventral cortex of the atlas was less than 4 mm in the OA group and only 50 (29.1%) in the control group. The ideal angulation of C1 screw trajectory was about 5 degrees more medial in the OA group than that in the control group (P < 0.01).

CONCLUSIONS

The risk of ICA injury is much higher in OA patients than in non-OA patients during the C1 screw placement. A mean medial angulation about 20 degrees will permit a long and safe screw purchase, but should be individualized. We recommend careful preoperative computed tomography angiography evaluation in all patients before surgery.

Vertico-horizontal atlantoaxial index (VHAI): A new craniovertebral radiographic index

OBJECTIVE

The purpose of this study was to develop a new index that can reliably quantify the reduction of basilar invagination with atlantoaxial dislocation.

PATIENTS AND METHODS

Between May 2012 and September 2017, 40 patients with congenital basilar invagination and atlantoaxial dislocation as well as 100 sex-and age-matched control subjects were recruited for this study. All patients underwent direct posterior reduction and fixation. Mid-sagittal computerized tomography scan films were obtained before and after surgery as well as the vertico-horizontal atlantoaxial index (VHAI) was measured in all patients -before and after surgery- and controls. Additionally, the pre-and postoperative Japanese Orthopedic Association (JOA) scores, Nurick grading, European Myelopathy Score (EMS) and Prolo Scale score were used to evaluate the cervical myelopathy.

RESULTS

The mean follow-up was 24.75 months with a range of 6-60 months. The mean value of VHAI in the control group was 87.86 ± 24.98 mm², while the mean values of VHAI before and after surgery were 209.45 ± 96.80 mm² and 95.08 ± 66.95 mm², respectively. Additionally, in the patient group, a negative correlation was observed between JOA, EMS, Prolo Scale scores and VHAI. On the other hand, a positive correlation was found between the Nurick grading and VHAI.

CONCLUSION

The VHAI can be an excellent measurement tool to evaluate the reduction of basilar invagination with atlantoaxial dislocation. There was a negative correlation between VHAI and JOA, EMS and Prolo Scale scores, and a positive correlation with Nurick grading; which indicates the effectiveness of this index.

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.

Surgical Treatment of Occipitocervical Dislocation with Atlas Assimilation and Klippel-Feil Syndrome Using Occipitalized C1 Lateral Mass and C2 Fixation and Reduction Technique

OBJECTIVE

To introduce and assess a surgical treatment of occipitocervical (OC) dislocation with atlas assimilation and Klippel-Feil syndrome (KFS) using occipitalized C1 lateral mass and C2 fixation and reduction technique.

METHODS

From January 2007 to August 2013, 58 symptomatic patients with OC dislocation and KFS of C2-3 congenital fusion and atlas assimilation were surgically treated in our institution via this technique. After opening the C1-2 facet joints via a posterior approach, OC reduction was conducted by intraoperative manipulation and C1 lateral mass and C2 pedicle screw and rod fixation. The instrument position, fusion status, and clinical outcome were analyzed.

RESULTS

The average follow-up was 36 months (range, 18-52 months). Radiologically, effective reduction was achieved in 56 patients (96.6%) and <50% reduction in 2 (3.4%) who had additional transoral decompression. Neurologic improvement and solid bone fusion were achieved in all patients. The clinical symptoms improved for all patients, with the averaged Japanese Orthopedic Association myelopathy scores increasing from 11.5 to 15.6 (P < 0.01).

CONCLUSIONS

In patients with OC dislocation and KFS of C2-3 fusion and atlas assimilation, posterior manipulative reduction combined with occipitalized C1 lateral mass and C2 fixation provides a reliable and effective treatment.

Clinical and Anatomical Features as well as Pathological Conditions of Surgically Treated Adult Patients with Occipitalization of the Atlas

BACKGROUND

This paper intends to clarify clinical and anatomical features as well as pathological conditions of surgically treated adult patients with occipitalization of the atlas.

METHODS

The authors reviewed 12 consecutive adult patients with occipitalization of the atlas who underwent surgery for myleopathy in our hospital. Mainly using preoperative computed tomography and three-dimensional computed tomography angiography, we investigated their anomalies of the osseous structures and vertebral artery at the cervical spine including the craniovertebral junction (CVJ). We also developed a new classification system for occipitalization of the atlas.

RESULTS

Atlantoaxial subluxation (AAS) was detected in 9 patients (75%). The condition of AAS was irreducible in 7 patients. Among these 7 patients, deformity at the lateral atlantoaxial joints was detected in 2 patients. C2-3 fusion was detected in 6 patients (67%) among 9 patients with AAS. Anomalies of the VA were detected in 11 patients (92%). Occipitalization of the atlas was classified into three types according to their pathological conditions. In type 1 (2 patients) the medial atlantoaxial joint is semi-dislocated and the lateral atlantoaxial joints are severely deformed. Type 2 (7 patients) exhibits AAS but the lateral atlantoaxial joints are not deformed. Type 3 (3 patients) is not associated with AAS and therefore does not exhibit osseous stenosis at the CVJ. In type 3 the myelopathy was caused by another coexisting condition.

CONCLUSIONS

Occipitalization of the atlas is classified into three types. The main pathological condition in both types 1 and 2 is AAS. Reduction of AAS is essential in both; however, reduction of AAS in type 1 is more technically demanding than in type 2. The pathological conditions of type 3 are completely different from those of the others, so an accurate diagnosis must be made. The new classification system is a useful guide for surgeons when planning surgical strategies.

Posterior Reduction of Fixed Atlantoaxial Dislocation and Basilar Invagination by Atlantoaxial Facet Joint Release and Fixation: A Modified Technique With 174 Cases

BACKGROUND:

Treatment of fixed atlantoaxial dislocation (AAD) with basilar invagination (BI) is challenging.

OBJECTIVE:

To introduce a modified technique to reduce fixed AAD and BI through a posterior approach.

METHODS:

From 2007 to 2013, 174 patients with fixed AAD and BI underwent surgical reduction by posterior atlantoaxial facet joint release and fixation technique.

RESULTS:

There was 1 death in the series, and 3 patients were lost to follow-up. The follow-up period ranged from 12 to 52 months (mean: 35.2 months) for the remaining 170 patients. Neurological improvement was observed in 168 of 170 patients (98.8%), and was stable in 1 (0.06%) and exacerbated in 1 (0.06%), with the Japanese Orthopedic Association scores increasing from 11.4 preoperatively to 15.8 postoperatively (P &lt; .01). Radiologically, complete or &gt;90% reduction was attained in 107 patients (62.9%), 60% to 90% reduction was attained in 51 patients (30%), and &lt;50% reduction was attained in 12 patients (7.1%), who underwent additional transoral decompression. Complete decompression was demonstrated in all 170 patients. Solid bony fusion was demonstrated in 167 patients at follow-up (98.2%).

CONCLUSION:

This series showed the safety and efficacy of the posterior C1-2 facet joint release and reduction technique for the treatment of AAD and BI. Most fixed AAD and BI cases are reducible via this method. In most cases, this method avoids transoral odontoidectomy and cervical traction. Compared with the occiput-C2 screw method, this short-segment C1-2 technique exerts less antireduction shearing force, guarantees longer bone purchase, and provides more immediate stabilization.

Chiari I malformation with and without basilar invagination: a comparative study

OBJECT

Chiari I malformation is the most common craniocervical malformation. Its combination with basilar invagination in a significant proportion of patients is well established. This study presents surgical results for patients with Chiari I malformation with and without additional basilar invagination.

METHOD

Three hundred twenty-three patients underwent 350 operations between 1985 and 2013 (mean age 43 ± 16 years, mean history of symptoms 64 ± 94 months). The clinical courses were documented with a score system for individual neurological symptoms for short-term results after 3 and 12 months. Long-term outcomes were analyzed with Kaplan-Meier statistics. The mean follow-up was 53 ± 58 months (the means are expressed ± SD).

RESULTS

Patients with (n = 46) or without (n = 277) basilar invagination in addition to Chiari I malformation were identified. Patients with invagination were separated into groups: those with (n = 31) and without (n = 15) ventral compression by the odontoid in the foramen magnum. Of the 350 operations, 313 dealt with the craniospinal pathology, 28 surgeries were undertaken for degenerative diseases of the cervical spine, 3 were performed for hydrocephalus, and 6 syrinx catheters were removed for cord tethering. All craniospinal operations included a foramen magnum decompression with arachnoid dissection, opening of the fourth ventricle, and a duraplasty. In patients without invagination, craniospinal instability was detected in 4 individuals, who required additional craniospinal fusion. In patients with invagination but without ventral compression, no stabilization was added to the decompression. In all patients with ventral compression, craniospinal stabilization was performed with the foramen magnum decompression, except for 4 patients with mild ventral compression early in the series who underwent posterior decompression only. Among those with ventral compression, 9 patients with caudal cranial nerve dysfunctions underwent a combination of transoral decompression with posterior decompression and fusion.

Within the 1st postoperative year, neurological scores improved for all symptoms in each patient group, with the most profound improvement for occipital pain. In the long term, late postoperative deteriorations were related to reobstruction of CSF flow in patients without invagination (18.3% in 10 years), whereas deteriorations in patients with invagination (24.9% in 10 years) were exclusively related either to instabilities becoming manifest after a foramen magnum decompression or to hardware failures. Results for ventral and posterior fusions for degenerative disc diseases in these patients indicated a trend for better long-term results with posterior operations.

CONCLUSIONS

The great majority of patients with Chiari I malformations with or without basilar invagination report postoperative improvements with this management algorithm. There were no significant differences in short-term or long-term outcomes between these groups. Chiari I malformations without invagination and those with invaginations but without ventral compression can be managed by foramen magnum decompression alone. The majority of patients with ventral compression can be treated by posterior decompression, realignment, and stabilization, reserving anterior decompressions for patients with profound, symptomatic brainstem compression.