Atlantoaxial Fixation for Basilar Invagination without Obvious Atlantoaxial Instability (Group B Basilar Invagination): Outcome Analysis of 63 Surgically Treated Cases

A Staged Approach for Surgical Management of Basilar Invagination

BACKGROUND AND OBJECTIVES

Patients with basilar invagination (BI) can be treated with several surgical options, ranging from simple posterior decompression to circumferential decompression and fusion. Here, we aimed at examining the indications and outcomes associated with these surgical strategies to devise a staged algorithm for managing BI.

METHODS

We conducted a retrospective cohort study in 2 neurosurgical centers and included patients with a BI, as defined by a position of the dens tip at least 5 mm above the Chamberlain line. Other craniovertebral junction anomalies, such as atlas assimilation, platybasia, and Chiari malformations, were documented. C1-C2 stability was assessed with a dynamic computed tomography scan.

RESULTS

We included 30 patients with BI with a mean follow-up of 56 months (min = 12, max = 166). Posterior decompression and fusion (n = 8) was only performed in cases of obvious atlanto-axial instability (eg, increased atlanto-dental interval or hypermobility on flexion/extension), while anterior decompression (transoral or transnasal) was reserved to patients with lower cranial nerves deficits (eg, swallowing dysfunction) and irreducible anterior compression (n = 9). Patients with posterior signs (eg, Valsalva headaches) or myelopathy but without C1-C2 instability nor anterior signs were managed with an isolated foramen magnum decompression, with or without duraplasty (n = 13). Complications were more frequent for combined procedures, including neurological deterioriation (n = 4) and tracheostomy (n = 2), but reinterventions were more likely in patients undergoing posterior decompression alone (n = 3).

CONCLUSION

Patient selection is key to determine the appropriate surgical strategy for BI: In our experience, combined approaches are only needed for patients with irreducible and symptomatic anterior compression, while fusion should be restricted to patient with obvious signs of atlanto-axial instability. Other BI patients can be managed by foramen magnum decompression alone to minimize surgical morbidity.

Biomechanical differences of three cephalic fixation methods for patients with basilar invagination and atlantoaxial dislocation in the setting of congenital atlas occipitalization: a finite element analysis

BACKGROUND CONTEXT

In cases of basilar invagination-atlantoaxial dislocation (BI-AAD) complicated by atlas occipitalization (AOZ), the approach to cranial end fixation has consistently sparked debate, generally falling into two categories: C1-C2 fixation and occipitocervical fixation. Several authors believe that C1-C2 fixation carries a lower risk of fixation failure than occipitocervical fixation.

PURPOSE

To study the biomechanical differences among 3 different cranial end fixation methods for BI-AAD with AOZ.

STUDY DESIGN

This was a finite element analysis.

PATIENT SAMPLE

A 35-year-old female patient diagnosed with congenital BI-AAD and AOZ.

OUTCOME MEASURES

range of motion (ROM), peak von Mise stress (PVMS), cage micro-subsidence, cage micro-slippage METHOD: Four finite element models were constructed, including unstable group (BI-AAD with AOZ), C1 lateral mass screw group, occipital plate group, occipitocervical rod group. The flexion and extension (FE), lateral bending (LB) as well as axial rotation (AR) were simulated under a torque of 1.5 Nm. Parameters include C1-C2 ROM, PVMS on screw-rod construct, cage micro-subsidence, cage micro-slippage.

RESULTS

The ROM of the C1 lateral mass screw group was smaller than that of the other fixation groups in LB and AR, but not FE. Compared with the occipitocervical rod group, the ROM in LB and AR of the occipital plate group was higher, but not in FE. The PVMS of C1 lateral mass screw group was significantly higher than that of the other groups. The ROM and PVMS of the occipitocervical rod group were in between the other 2 groups. Regarding the screws at the cranial end, the PVMS of the 4-screw occipitocervical rod group was significantly lower than that of the other groups. In general, the cage micro-motion follows the ascending order: C1 lateral mass group < occipitocervical rod group < occipital plate group.

CONCLUSION

In cases of BI-AAD with AOZ, the C1 lateral mass screw group provided the least ROM and cage micro-motion, but the screw-rod PVMS was the largest. The advantage of occipital plate fixation lies in the lowest screw-rod PVMS, but the ROM and cage micro-motion is the highest. Four-screw fixation at the cranial end of occipitocervical rod group helps to reduce the PVMS and may prevent screw failure at the cranial end.

Biomechanical Study of Atlanto-occipital Instability in Type II Basilar Invagination: A Finite Element Analysis

OBJECTIVE

Recent studies indicate that 3 morphological types of atlanto-occipital joint (AOJ) exist in the craniovertebral junction and are associated with type II basilar invagination (BI) and atlanto-occipital instability. However, the actual biomechanical effects remain unclear. This study aims to investigate biomechanical differences among AOJ types I, II, and III, and provide further evidence of atlanto-occipital instability in type II BI.

METHODS

Models of bilateral AOJ containing various AOJ types were created, including I-I, I-II, II-II, II-III, and III-III models, with increasing AOJ dysplasia across models. Then, 1.5 Nm torque simulated cervical motions. The range of motion (ROM), ligament and joint stress, and basion-dental interval (BDI) were analyzed.

RESULTS

The C0-1 ROM and accompanying rotational ROM increased progressively from model I-I to model III-III, with the ROM of model III-III showing increases between 27.3% and 123.8% indicating ultra-mobility and instability. In contrast, the C1-2 ROM changes were minimal. Meanwhile, the stress distribution pattern was disrupted; in particular, the C1 superior facet stress was concentrated centrally and decreased substantially across the models. The stress on the C0-1 capsule ligament decreased during cervical flexion and increased during bending and rotating loading. In addition, BDI gradually decreased across the models. Further analysis revealed that the dens showed an increase of 110.1% superiorly and 11.4% posteriorly, indicating an increased risk of spinal cord impingement.

CONCLUSION

Progressive AOJ incongruity critically disrupts supportive tissue loading, enabling incremental atlanto-occipital instability. AOJ dysplasia plays a key biomechanical role in the pathogenesis of type II BI.

Effect of the Basilar Invagination (Type B) on Cervical Spine: A Case-control Study with MRI

OBJECTIVE

To evaluate the effect of the basilar invagination (BI) type B on cervical spine.

METHODS

The research protocol used head magnetic resonance imaging (MRI) exams from 41 participants with BI type B and 158 controls. The criterion for BI was the distance of the odontoid apex to Chamberlain's line (DOCL) equal to or greater than 7 mm. The clivus length (CLI), clivus canal angle (CCA), Welcker's basal angle (WBA), Boogaard's angle (BOA), upper cervical lordosis angle (UCL), and total cervical lordosis angle (CL) were evaluated. The descriptive analysis, group comparisons, and correlations between skull base and cervical spine parameters were performed at the 95% CI.

RESULTS

Participants with BI type B showed shorter clivus length (CLI: 25.7 ± 7.3 mm); greater angulation of the skull base (WBA: 126.5 ± 10.4); greater inclination foramen magnum (BOA: 151.5 ± 14.5); decrease in the value of the CCA (131.6 ± 15); and greater angulations of UCL (17.9 ± 13.8) and CL (29.7 ± 19.9) in comparison to the control group (P < 0.05). Clivus length and CCA correlated inversely with UCL and CL, while BOA correlated directly with UCL and CL. The WBA did not correlate with CL (P < 0.05).

CONCLUSIONS

The deformation of skull base in the BI of type B caused, on average, a hyperlordosis of almost 30° in the C2-C6 segment. This change was approximately 17° in the C2-C4, with the clivus hypoplasia being a risk factor for cervical hyperlordosis.

Treatment of Chiari malformations with craniovertebral junction anomalies: Where do we stand today?

Background

Chiari malformation type 1 (CM-1) is characterized by cerebellar tonsil herniation through the foramen magnum and can be associated with additional craniovertebral junction anomalies (CVJA). The pathophysiology and treatment for CM-1 with CVJA (CM-CVJA) is debated.

Objective

To evaluate the trends and outcomes of surgical interventions for patients with CM-CVJA.

Methods

A systematic review of the literature was performed to obtain articles describing surgical interventions for patients with CM-CVJA. Articles included were case series describing surgical approach; reviews were excluded. Variables evaluated included patient characteristics, approach, and postoperative outcomes.

Results

The initial query yielded 403 articles. Twelve articles, published between 1998-2020, met inclusion criteria. From these included articles, 449 patients underwent surgical interventions for CM-CVJA. The most common CVJAs included basilar invagination (BI) (338, 75.3%), atlantoaxial dislocation (68, 15.1%) odontoid process retroflexion (43, 9.6%), and medullary kink (36, 8.0%). Operations described included posterior fossa decompression (PFD), transoral (TO) decompression, and posterior arthrodesis with either occipitocervical fusion (OCF) or atlantoaxial fusion. Early studies described good results using combined ventral and posterior decompression. More recent articles described positive outcomes with PFD or posterior arthrodesis in combination or alone. Treatment failure was described in patients with PFD alone that later required posterior arthrodesis. Additionally, reports of treatment success with posterior arthrodesis without PFD was seen.

Conclusion

Patients with CM-CVJA appear to benefit from posterior arthrodesis with or without decompressive procedures. Further definition of the pathophysiology of craniocervical anomalies is warranted to identify patient selection criteria and ideal level of fixation.

Basilar Invagination With Chiari Type I Malformation and Atlanto-Axial Instability: A Rare Case Report

Basilar invagination (BI) and Chiari malformation type I (CM-I) are important anomalies involving the craniovertebral junction (CVJ) involving the skull base and occipitocervical region. The incidence of BI is rare involving < 1% of the general population worldwide. They present with varied and complex clinical-radiological features. We present a 36-year-old male who displayed complaints of persistent reeling sensation at our center. Clinical examination revealed bilateral cerebellar signs along with nystagmus and restricted neck movements. Imaging revealed evidence of BI with cerebellar tonsil herniation of ~14.7 mm. Atlantodens interval of 6 mm was noted. The unexpected findings of C1-C2 fusion and instability were also noted. We describe a rare case of BI with C1 prolapse into the foramen magnum along with CM-1 malformation and congenital fusion of C1-C2. We conclude that the treatment algorithm for these rare cases is not very well established and is individually dependent.

Intra-articular Distraction Versus Decompression to Treat Basilar Invagination Without Atlantoaxial Dislocation: A Retrospective Cohort Study of 54 Patients

OBJECTIVE

The surgical management of basilar invagination without atlantoaxial dislocation (type B basilar invagination) remains controversial. Hence, we have reported the use of posterior intra-articular C1-2 facet distraction, fixation, and cantilever technique versus foramen magnum decompression in treating type B basilar invagination as well as the results and surgical indications for this procedure.

METHODS

This was a single-center retrospective cohort study. Fifty-four patients who underwent intra-articular distraction, fixation, and cantilever reduction (experimental group) and foramen magnum decompression (control group) were enrolled in this study. Distance from odontoid tip to Chamberlain's line, clivus-canal angle, cervicomedullary angle, craniovertebral junction (CVJ) triangle area, width of subarachnoid space and syrinx were used for radiographic assessment. Japanese Orthopedic Association (JOA) scores and 12-item Short Form health survey (SF-12) scores were used for clinical assessment.

RESULTS

All patients in the experimental group had a better reduction of basilar invagination and better relief of pressure on nerves. JOA scores and SF-12 scores also had better improvements in the experimental group postoperation. SF-12 score improvement was associated with preoperative CVJ triangle area (Pearson index, 0.515; p = 0.004), cutoff value of 2.00 cm2 indicating the surgical indication of our technique. No severe complications or infections occurred.

CONCLUSION

Posterior intra-articular C1-2 facet distraction, fixation, and cantilever reduction technique is an effective treatment for type B basilar invagination. As various factors involved, other treatment strategies should also be investigated.

Confronting historical legacies of biological anthropology in South Africa-Restitution, redress and community-centered science: The Sutherland Nine

We describe a process of restitution of nine unethically acquired human skeletons to their families, together with attempts at redress. Between 1925-1927 C.E., the skeletonised remains of nine San or Khoekhoe people, eight of them known-in-life, were removed from their graves on the farm Kruisrivier, near Sutherland in the Northern Cape Province of South Africa. They were donated to the Anatomy Department at the University of Cape Town. This was done without the knowledge or permission of their families. The donor was a medical student who removed the remains from the labourers' cemetery on his family farm. Nearly 100 years later, the remains are being returned to their community, accompanied by a range of community-driven interdisciplinary historical, archaeological and analytical (osteobiographic, craniofacial, ancient DNA, stable isotope) studies to document, as far as possible, their lives and deaths. The restitution process began by contacting families living in the same area with the same surnames as the deceased. The restitution and redress process prioritises the descendant families' memories, wishes and desire to understand the situation, and learn more about their ancestors. The descendant families have described the process as helping them to reconnect with their ancestors. A richer appreciation of their ancestors' lives, gained in part from scientific analyses, culminating with reburial, is hoped to aid the descendant families and wider community in [re-]connecting with their heritage and culture, and contribute to restorative justice, reconciliation and healing while confronting a traumatic historical moment. While these nine individuals were exhumed as specimens, they will be reburied as people.

Exploring the Pathogenesis of Atlanto-Occipital Instability in Chiari Malformation With Type II Basilar Invagination: A Systematic Morphological Study

BACKGROUND

Our previous study suggested that atlanto-occipital instability (AOI) is common in patients with type II basilar invagination (II-BI).

OBJECTIVE

To further understand the pathogenesis of AOI in Chiari malformations (CM) and CM + II-BI through systematic measurements of the bone structure surrounding the craniocervical junction.

METHODS

Computed tomography data from 185 adults (80 controls, 63 CM, and 42 CM + II-BI) were collected, and geometric models were established for parameter measurement. Canonical correlation analysis was used to evaluate the morphological and positional relationships of the atlanto-occipital joint (AOJ).

RESULTS

Among the 3 groups, the length and height of the condyle and superior portion of the lateral masses of the atlas (C1-LM) were smallest in CM + II-BI cases; the AOJ had the shallowest depth and the lowest curvature in the same group. AOJs were divided into 3 morphological types: type I, the typical ball-and-socket joint, mainly in the control group (100%); type II, the shallower joint, mainly in the CM group (92.9%); and type III, the abnormal flat-tilt joint, mainly in the CM + II-BI group (89.3%). Kinematic computed tomography revealed AOI in all III-AOJs (100%) and some II-AOJs (1.5%) but not in type I-AOJs (0%). Morphological parameters of the superior portion of C1-LM positively correlated with those of C0 and the clivus and significantly correlated with AOI.

CONCLUSION

Dysplasia of the condyle and superior portion of C1-LM exists in both CM and II-BI cases yet is more obvious in type II-BI. Unstable movement caused by AOJ deformation is another pathogenic factor in patients with CM + II-BI.

Interfacet Distraction for Type B-Basilar Invagination Assisted by a Novel Sliding-Traction Head Holder: 2-Dimensional Operative Video

Type B basilar invagination (BI) refers to odontoid process prolapse into skull base without dislocation, which is often associated with Chiari malformation and syringomyelia.1 Its pathogenesis and treatment are in controversy. Posterior fossa decompression has been introduced to treat the associated Chiari malformation; however, it may not be effective for symptoms with severe ventral nerve compression.2 C1-2 in situ fixation has been reported to treat minor instability in type B BI,3 yet the assessment of minor instability has not been widely accepted. We believe that the pathogenesis is chronic ventral compression of the brainstem. Transoral odontoidectomy is a classic surgical procedure to treat the pathogenesis, but it is associated with high risks of infection, velopharyngeal incompetence, and airway obstruction and often requires posterior surgery for fusion.4 Thus we use an interfacet distraction technique to move the odontoid process down and relieve ventral brainstem compression.5 Therefore interfacet structural support is necessary to maintain the distance of the interfacet. The reason for fixation is that interfacet distraction disrupts atlantoaxial stability. We designed a novel sliding-traction head holder, which can quantitatively tract and stabilize the head without support for the head or face, avoiding the risk of eyeball compression. It adapts to a variety of surgical methods and allows intraoperative changes in the patient's position. Assisted by the device, a satisfied interfacet distraction and a correction of BI were obtained. Video 1 describes how the interfacet distraction technique assisted by a sliding-traction head holder was performed in an illustrative case. The patient consented to the procedure.

Risk Factors of Postoperative Cerebrospinal Fluid Leak After Craniovertebral Junction Anomalies Surgery: A Case-Control Study

Objective: To identify potential risk factors for cerebrospinal fluid (CSF) leakage after craniovertebral junction (CVJ) anomaly surgery and to provide a reference for clinical practice.Methods: Sixty-six patients who underwent elective CVJ anomaly surgery during a 6-year period (April 2013 to September 2019) were retrospectively included. Research data were collected from the patients’ medical records and imaging systems. Patients were divided into CSF leak and no CSF leak groups. Univariate tests were performed to identify potential risk factors. For statistically significant variables in the univariate tests, a logistic regression test was used to identify independent risk factors for CSF leakage.Results: The overall prevalence of CSF leakage was 13.64%. Univariate tests showed that a basion-dental interval (BDI) > 10 mm and occipitalized atlas had significant intergroup differences (p < 0.05). Multivariate analysis indicated that a BDI > 10 mm was an independent risk factor for CSF leakage, and patients with CVJ anomalies with a BDI > 10 mm were more likely to have postoperative CSF leaks (odds ratio, 14.67; 95% confidence interval, 1.48–30.88; p = 0.004).Conclusion: It is necessary to maintain vigilance during CVJ anomaly surgery in patients with a preoperative BDI > 10 mm to avoid postoperative CSF leaks.

Evolving Concepts of Craniovertebral and Spinal Instability

Weakness of the muscles of the nape of the neck and back of the spine and its related instability is the nodal point of pathogenesis of a number of clinical and pathological events at the craniovertebral junction and the spine. Whilst acute instability results in sudden and relatively severe symptoms, chronic or long-standing instability is associated with a range of musculoskeletal and structural spinal alterations. Telescoping of the spinal segments results in "vertical" spinal instability in the subaxial spine and central or axial atlantoaxial instability (CAAD) at the craniovertebral junction. Instability in such cases might not be observed on dynamic radiological imaging. Chiari formation, basilar invagination, syringomyelia, and Klippel-Feil alteration are some of the secondary alterations as a result of chronic atlantoaxial instability. Radiculopathy/myelopathy related to spinal degeneration or ossification of posterior longitudinal ligament appears to have their origin from vertical spinal instability. All the secondary alterations in the craniovertebral junction and subaxial spine that are traditionally considered pathological and to have compressive and deforming role are essentially protective in nature, are indicative of instability, and are potentially reversible following atlantoaxial stabilization. Stabilization of unstable spinal segments is the basis of surgical treatment.

Central Atlantoaxial Dislocation: Presenting Symptoms, Diagnostic Parameters, and Surgical Treatment from Reports on 15 Surgically Treated Patients

AIM

This chapter reviews the clinical entity of central or axial atlantoaxial instability (CAAD).

MATERIAL AND METHODS

From January 2018 to November 2020, 15 patients were identified as having CAAD, wherein there was no atlantoaxial instability when analyzed by conventional radiological parameters and wherein there was no evidence of neural or dural compression due to the odontoid process. The patients were identified as having atlantoaxial instability on the basis of the alignment of facets on lateral profile imaging and a range of telltale clinical and radiological indicators. The clinical statuses of the patients were recorded both before and after surgical treatment by using the specially designed Goel symptom severity index and visual analog scale (VAS) scores. All patients were treated via atlantoaxial fixation.

RESULTS

There were six men and nine women ranging in age from 18 to 45 years (average: 37 years). The presenting clinical symptoms were relatively subtle and long-standing. Apart from symptoms that are generally related to neural compromise at the craniovertebral junction, a range of nonspecific cranial and spinal symptoms were prominent. The follow-up time after surgery ranged from 6 to 34 months. All patients showed early postoperative and sustained clinical recovery.

CONCLUSIONS

The correct diagnosis and appropriate surgical treatment of CAAD can provide an opportunity for quick and lasting clinical recovery.

Basilar invagination without atlantoaxial dislocation: treatment by correction of clivus canal angle with interfacet distraction and fixation

BACKGROUND

This study reports on the surgical technique used and clinical outcomes obtained during the treatment of basilar invagination (BI) without atlantoaxial dislocation (AAD) through the correction of the clivus canal angle (CCA) using interfacet distraction and fixation.

METHODS

Nineteen cases with BI without AAD treated by the correction of the clivus canal angle were retrospectively analyzed. Pre- and postoperative computed tomography scans and three-dimensional reconstruction views were obtained to measure the size of the CCA, pB-C2 distance, and degree of BI. Chiari malformation and syringomyelia were evaluated by magnetic resonance imaging (MRI). The clinical outcomes for all patients were measured using the Japanese Orthopedic Association (JOA) scale. The CCA was corrected by using interfacet distraction and fixation techniques. The Wilcoxon test was used to compare pre- and postoperative measurements.

RESULTS

All the patients were followed up for 24.95 ± 5.22 months (range 12-36 months); no patient suffered intraoperative nerve or vascular injury. Clinical symptoms improved in 17 patients (89.5%). The mean JOA score increased from 12.32 ± 1.89 to 14.37 ± 1.30 (Z = -3.655, P < 0.001). The mean CCA improved from 129.34 ± 8.52° preoperatively to 139.75 ± 8.86° postoperatively (Z = -3.824, P < 0.001). The mean pB-C2 decreased from 7.47 ± 2.21 to 5.68 ± 3.13 (Z = -3.060, P = 0.002). Syringomyelia was significantly reduced in 10 out of 13 patients by the first follow-up year. All patients achieved bony fusion.

CONCLUSION

Posterior interfacet distraction and fixation to correct the CCA is a feasible and effective method for treating BI without AAD.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Cranio-cervical decompression associated with non-instrumented occipito-C2 fusion in children with mucopolysaccharidoses: Report of twenty-one cases

BACKGROUND

Mucopolysaccharidosis (MPS) is a multisystemic storage disorder of glycosaminoglycan deposits. Infiltration of the dura mater and supporting ligaments caused spinal cord compression and consecutive myelopathy, especially at the cranio-cervical junction (CCJ). Craniocervical instability and posterior decompression often raise the problem of fixation in children. The main purpose of this paper was to report the result of an original technique of occipito-cervical arthrodesis using a cranial halo-cast system in pediatric population.

METHODS

We recorded 21 patients with cervical myelopathy. All of them had spinal cord decompression by enlargement of the foramen magnum, C1 laminectomy, and occipito-C2 fusion using corticocancellous bone graft. Only one child has an extended laminectomy from C1 to C3. The occiput-C2 arthrodesis was stabilized by the cranial halo-cast system. This immobilization was performed preoperatively and kept for three months then switched to rigid cervical collar. Clinical assessment, including the Goel grade and mJOA, radiographs and magnetic resonance imaging were performed before surgery. The occipito-cervical arthrodesis was controlled by standard X-rays and CT scan.

RESULTS

According to the type of mucopolysaccharidosis, the patients were divided into MPS type I: n= 3, II: n=7, IV: n=11. The mean age of patients at surgery was 6.76 years. All mucopolysaccharidoses cases required a foramen magnum decompression by craniectomy, C1 laminectomy and occipito-C2 arthrodesis. As major complications, a child had immediate post-operative paraplegia due to spinal cord ischemia. The postoperative follow-up ranged from 1.5 to 4 years, with an average of 3.3 years. The average preoperative mJOA score was 8.9, and it improved to 14 points at the last follow-up.

CONCLUSIONS

Satisfactory fusion and good clinical results were obtained with the 2-stage approach to CCJ anomalies.

Measurement of Deformity at the Craniovertebral Junction: Correlation of Triangular Area and Myelopathy

OBJECTIVE

Diseases of the craniovertebral junction (CVJ) are commonly associated with deformity, malalignment, and subsequent myelopathy. The misaligned CVJ might cause compression of neuronal tissues and subsequently clinical symptoms. The triangular area (TA), measured by magnetic resonance imaging/images (MRI/s), is a novel measurement for quantification of the severity of compression to the brain stem. This study aimed to assess the normal and pathological values of TA by a comparison of patients with CVJ disease to age- and sex-matched controls. Moreover, postoperative TAs were correlated with outcomes.

METHODS

Consecutive patients who underwent surgery for CVJ disease were included for comparison to an age- and sex-matched cohort of normal CVJ persons as controls. The demographics, perioperative information, and pre- and postoperative 2-year cervical MRIs were collected for analysis. Cervical TAs were measured and compared.

RESULTS

A total of 201 patients, all of whom had pre- or postoperative MRI, were analyzed. The TA of the CVJ deformity group was larger than the healthy control group (1.62 ± 0.57 cm2 vs. 1.01 ± 0.18 cm2, p < 0.001). Moreover, patients who had combined anterior odontoidectomy and posterior laminectomy with fixation had the greatest reduction in the TA (1.18 ± 0.58 cm2).

CONCLUSION

In CVJ deformity, the measurement of the cervical TA could indicate the severity of brain stem compression. After surgery, the TA had a varying degree of improvement, which could represent the efficacy of surgery.

Relevance of C1/2 facet configurations and clivus-canal-angles for adult patients with Chiari I malformation with and without basilar invagination

OBJECTIVE

C1/2 facet configurations and clivus-canal angles (CXA) have been proposed as criteria for posterior fusion in Chiari I malformation (CMI).

METHODS

340 adults with CMI without basilar invagination (BI), 111 with CMI with BI and 100 age and sex matched controls were studied using sagittal T2-weighted MRI scans analyzing pre- and postoperative values with their impact on progression-free survival rates.

RESULTS

For CMI without BI, C1/2 facet configurations and CXA were similar to controls (142+11° and 144+10°, respectively) with low rates for posterior C1 displacements (7.1% and 10%, respectively). In CMI with BI, C1 facet displacements were common (54.9%) with lower CXA (120+15°). After foramen magnum decompression (FMD) in CMI without BI (n = 169), 1.8% developed posterior C1 facet displacements without CXA changes and a 97% progression-free survival rate for 10 years. In CMI with BI, patients without ventral compression or instability underwent FMD without fusion (n = 19). 5.3% developed a posterior C1 facet displacement without CXA changes and a 94% progression-free survival rate for 10 years. The remainder of CMI with BI underwent FMD with C1/2 fusion (n = 48). Among these, CXA values increased with 10 year progression-free survival rates of 74% and 93% with and without ventral compression, respectively.

CONCLUSION

For adult CMI without BI, C1/2 facet configurations and CXA are irrelevant. FMD alone provides excellent long-term outcomes. In CMI with BI, anterior C1 facet displacements indicate C1/2 instability. Posterior fusions can be reserved for patients with ventral compression or C1/2 instability.

The management of Chiari malformation type 1 and syringomyelia in children: a review of the literature

In anticipation of the "Chiari and Syringomyelia Consensus Conference" held in Milan in 2019, we performed a systematic literature review on the management of Chiari malformation type 1 (CM1) and syringomyelia (Syr) in children.We aimed to summarize the available evidence and identify areas where consensus has not been reached and further research is needed.In accordance with PRISMA guidelines, we formulated seven questions in Patients-Interventions-Comparators-Outcomes (PICO) format. Six PICOs concerned CM1 children with/without additional structural anomalies (Syr, craniosynostosis, hydrocephalus, tethered cord, and cranio-vertebral junction anomalies), and one PICO Syr without CM1. We searched Medline, Embase, Cochrane, and NICE databases from January 1, 1999, to May 29, 2019. Cohort studies, controlled and randomized clinical trials (CCTs, RCTs), and systematic reviews were included, all pertinent only to patients ≤ 18 years of age.For CM1, 3787 records were found, 460 full texts were assessed and 49 studies (46 cohort studies, one RCT, and two systematic reviews) were finally included. For Syr, 376 records were found, 59 full texts were assessed, and five studies (one RCT and four cohort studies) were included. Data on each PICO were synthetized narratively due to heterogeneity in the inclusion criteria, outcome measures, and length of follow-up of the included studies.Despite decades of experience on CM1 and Syr management in children, the available evidence remains limited. Specifically, there is an urgent need for collaborative initiatives focusing on the adoption of shared inclusion criteria and outcome measures, as well as rigorous prospective designs, particularly RCTs.

Increase of the clivus-canal angle in patients with basilar invagination, without atlantoaxial displacement, treated with a simple maneuver of indirect decompression of the odontoid with the head clamp, during posterior occipitocervical arthrodesis

Background:

Basilar invagination (BI) can be defined as the insinuation of the content of the craniovertebral junction through the foramen magnum toward the posterior fossa. BI is a prevalent condition in Northeast Brazil. The present study describes the changes in the clivus-canal angle (CCA) in the postoperative period in patients with symptomatic BI operated by a posterior approach, using a simple technique of indirect reduction of the odontoid associated with occipitocervical fixation.

Methods:

Patients underwent radiological evaluations by magnetic resonance imaging in the pre and postoperative periods, where the height of the odontoid tip was measured in relation to the Chamberlain line and the ACC. All patients underwent posterior occipitocervical fixation with specific maneuvers of distraction and extension of the cephalic segment with the aid of a head clamp with three fixation points for anterior reduction of the odontoid.

Results:

Among the 8 patients evaluated in the series, all had increased ACC in the postoperative period, with a mean of 14.81 ± 1.54°, and statistically significant difference between the pre and postoperative periods (P < 0.05).

Conclusion:

The indirect surgical reduction of the odontoid process by a posterior approach through the manipulation (distraction-extension) of a “Mayfield” type of head clamp followed by occipitocervical fixation proved to be effective in improving the ACC, being easily reproducible.

Transarticular Fixation Following Mobilization of "High-Riding" Vertebral Artery

BACKGROUND AND IMPORTANCE

The article identifies the feasibility of transarticular screw fixation after mobilizing the vertebral artery in cases where it is in a "high-riding" location.

CLINICAL PRESENTATION

A 42-yr-old male patient had a 4-yr history of progressive quadriparesis. Investigations revealed severe basilar invagination. There was assimilation of atlas and C2-3 fusion. The vertebral artery was "high-riding" into the pedicle-facet of C2 vertebra on both sides. Vertebral artery loop was exposed and mobilized inferiorly on both sides after careful drilling of pedicular bone on the posterior aspect of the dome of the artery. C2 facetal bone on the anterior face of the vertebral artery dome was now available for screw insertion. The C1-2 facets and the articulation were directly in line, making transarticular screw fixation relatively straightforward. The wide bone space available permitted insertion of 2 screws in a transarticular fashion on both sides. The patient had satisfactory clinical improvement. Imaging after 22 mo showed bone fusion across the facets.

CONCLUSION

Mobilization of the high-riding vertebral artery loop can help salvage the surgical procedure of lateral mass stabilization.

The 270° Circumferential Microsurgical Decompression of the Foramen Magnum in Adult Chiari Malformation Type I: Single Surgeon Series of 130 Patients with Syringomyelia, Neurologic, and Headache Outcomes

OBJECTIVE

Chiari malformation type I (CM-I) is a craniocervical junction disorder associated with descent of the cerebellar tonsils >5 mm. The prevalence of CM-I is common, including 0.5%-3.5% in the general population, 0.56%-0.77% on magnetic resonance imaging, and 0.62% in anatomic dissection studies. We sought to measure our surgical outcomes related to resolution/improvement of headaches, neurologic outcomes, and syringomyelia compared with reported adult CM-I studies from 2000-2019.

METHODS

From December 2003 to June 2018, the first author (K.I.A.) performed 270° circumferential decompression on adult (>18 years) patients with CM-I. At admission and follow-up, all parameters were numerically evaluated; headaches were self-reported on the visual analog scale, neurologic condition was evaluated using Karnofsky Performance Status and European Myelopathy Score, and syrinx width (if present) was measured on magnetic resonance imaging by grades I-IV. All parameters were analyzed, compared, and statistically tested. We compared results with our previously reported and updated systematic review of operative adult CM-I studies (studies from 2000 to 2019).

RESULTS

In our series, 118/121 (98%) experienced headache improvements and 100% experienced neurologic improvements. Complete syrinx resolution was experienced by 35/43 (81%); 8 (19%) showed significant improvement. In data from reported studies (2000-2019), only 79% experienced headache resolution, 77% improvement of neurologic status, and 74% resolution/improvement of syrinx (mean).

CONCLUSIONS

Our modified 270° circumferential microsurgical foramen magnum decompression for adult CM-I appears to be beneficial in improvement of outcomes, namely in resolution of the syrinx, neurologic symptoms, and headaches. We also confirm the association of body mass index with CM-I. Further studies are needed to confirm our results.

Two-Stage Approach for Unstable Pediatric Craniocervical Junction Anomalies with a Halo Vest and Delayed Occipitocervical Fusion: Technical Note, Case Series, and Literature Review

OBJECTIVE

Malformations in the craniocervical junction (CCJ) are rare in the pediatric population but often need surgical treatment. We present a pediatric case series of patients treated with a 2-stage surgical approach with a halo vest and occipitocervical fusion and review complications and outcomes.

METHODS

A retrospective analysis of a single-center case series was performed. Pediatric patients affected by congenital craniocervical junction anomalies and treated with a 2-stage approach were included. A halo vest was implanted in the first surgery, and ambulatory progressive reduction was performed. When a favorable anatomic situation was observed, arthrodesis was performed. Safety analysis was undertaken by analyzing the incidence of complications in both procedures. Effectivity analysis was carried out analyzing radiologic and clinical outcome (Goel grade and modified Japanese Orthopaedic Association score). Student t test was used for statistical analysis.

RESULTS

Sixteen cases were included. Mean age of patients was 9.38 years. Safety analysis showed 2 halo loosenings, 1 pin infection, 2 wound infections, 1 cerebrospinal fluid leak, and 2 delayed broken rods. No major complications were observed. Radiologic analysis showed an improvement in the tip of the odontoid process to the McRae line distance (from -3.26 mm to -6.16 mm), atlantodental interval (from 3.05 mm to 1.88 mm), clival-canal angle (from 134.61° to 144.38°), and cervical kyphosis (from 6.39° to 1.54°). Clinical analysis also showed improvement in mean Goel grade (from 1.75 to 1.44) and modified Japanese Orthopaedic Association score (from 15.12 to 16.41).

CONCLUSIONS

The 2-stage approach was a suitable and effective treatment for craniocervical junction anomalies in pediatric patients.

Evaluation and Surgical Planning for Craniovertebral Junction Deformity

Craniovertebral junction (CVJ) deformity is a challenging pathology that can result in progressive deformity, myelopathy, severe neck pain, and functional disability, such as difficulty swallowing. Surgical management of CVJ deformity is complex for anatomical reasons; given the discreet relationships involved in the surrounding neurovascular structures and intricate biochemical issues, access to this region is relatively difficult. Evaluation of the reducibility, CVJ alignment, and direction of the mechanical compression may determine surgical strategy. If CVJ deformity is reducible, posterior in situ fixation may be a viable solution. If the deformity is rigid and the C1–2 facet is fixed, osteotomy may be necessary to make the C1–2 facet joint reducible. C1–2 facet release with vertical reduction technique could be useful, especially when the C1–2 facet joint is the primary pathology of CVJ kyphotic deformity or basilar invagination. The indications for transoral surgery are becoming as narrow as a treatment for CVJ deformity. In this article, we will discuss CVJ alignment and various strategies for the management of CVJ deformity and possible ways to prevent complications and improve surgical outcomes.

Effectiveness of three-dimensional printed and virtual reality models in learning the morphology of craniovertebral junction deformities: a multicentre, randomised controlled study

OBJECTIVES

To compare the effectiveness of three-dimensional printed (3DP), virtual reality (VR) and conventional normal physical (NP) models in clinical education regarding the morphology of craniovertebral junction (CVJ) deformities.

DESIGN

Prospective, multicentre, randomised controlled study.

SETTING

Three teaching hospitals in China.

PARTICIPANTS

One hundred and fifty-three participants in their first year of a 3-year medical residency programme.

INTERVENTIONS

All participants were randomised to one of the three groups to learn the morphology of CVJ deformities using 3DP, VR or NP models.

PRIMARY OUTCOME MEASURES

The objective outcomes were evaluated using three-level objective testing. In the first-level test, the participants were required to identify 15 anatomical landmarks on radiographs without CVJ deformities. In the second-level test, all participants were asked to identify the same 15 landmarks on radiographs showing classic CVJ deformities. In the third-level test, the participants were required to describe the key features of three classic cases of CVJ deformities depicted on radiographs. Each participant was also asked to answer four subjective questions to evaluate the importance and usefulness of the educational materials.

RESULTS

In the first-level test, the 3DP, VR and NP groups achieved similar correct rates. In the second-level test, the correct rate was higher in the 3DP group (82.1%±13.6%) than the VR and NP groups (76.9%±16.9% and 69.9%±20.0%, p=0.002). In the third-level test, the 3DP group achieved better correct rates regarding the description of key CVJ deformities features (66.2%±20.0%, p=0.049) than the other groups. The subjective tests showed that the 3DP model method was considered the most valuable approach for learning CVJ deformities.

CONCLUSIONS

The objective and subjective results show that the 3DP model is more effective teaching instrument than the NP model for learning the pathomorphology of CVJ deformities. The VR model also showed great efficacy, second to 3DP model, in improving participants' understanding of CVJ deformities.

Radiological approach to basilar invagination type B: Reliability and accuracy

OBJECTIVES

This study aims to determine the reliability of the radiological tests used in the diagnosis of basilar invagination (BI).

METHODS

Patients diagnosed with type B basilar invagination, who had both magnetic resonance (MR) and computed tomography (CT) imaging between January 2014 and November 2019 were included in this retrospective reliability study. In this study, distance from odontoid apex to Chamberlain's line (OA-CL) was accepted as a reference method for the diagnosis. Forty-two BI cases and 79 controls were included. Three radiologists with different levels of experience individually evaluated OA-CL, Boogard's angle (BoA), clivo-axial angle (CXA), clivo-dens angle (CDA), and clivo-palate angle (CPA) on midsagittal CT and MR images. Statistical analysis was made with the intraclass correlation coefficient (ICC), t-test, and receiver operating characteristic (ROC) curve.

RESULTS

The ICC for CT and MR were; 0.977-0.973 (OA-CL), 0.912-0.882 (BoA), 0.845-0.846 (CXA), 0.862-0.864 (CDA), and 0.762-0.747 (CPA) respectively (P < 0.001). The areas under the ROC curve were 0.977 (BoA), 0.832 (CXA), 0.852 (CDA), and 0.719 (CPA) (P < 0.001). The cut-off measures were ≥137.84° (BoA), ≤149.25° (CXA), ≤129.58° (CDA), and ≤61.83° (CPA). The diagnostic accuracies were 0.954 (BoA), 0.664 (CXA), 0.704 (CDA), 0.438 (CPA) (P < 0.001).

CONCLUSIONS

OA-CL and BoA express excellent inter-rater agreement than CXA, CDA, and CPA, which are limited due to morphological variations and head spatial position. BoA is the second most reliable diagnostic test. CXA, CDA, should only be used for complementary information. CPA was found inadequate for the diagnosis of BI..

Central atlantoaxial instability as a cause of syringomyelia mimic intramedullary lipoma

A case of a 32-year-old male patient is reported. He was admitted with complaints of burning dysesthesias over his right upper limb and chest and spasticity in the legs. Investigations revealed a long segment intramedullary tumor, image intensity of which matched lipoma. Imaging of craniovertebral junction suggested atlantoaxial “facetal” instability. Atlantoaxial fixation was done, and the intramedullary lipoma was not physically handled or manipulated during surgery. The patient improved in his neurological condition following surgery. The follow-up imaging showed that the intramedullary lipoma reduced significantly in its dimensions. From the case, it appears that the presence of “fat” and “water” in the intramedullary location might have similar pathogenesis.

Atlantoaxial fixation for failed foramen magnum decompression in patients with Chiari formation

Background:

Relationship of atlantoaxial instability with Chiari formation is further analyzed in the report.

Objective:

The outcome of 25 patients who had failed conventional treatment for Chiari formation that included foramen magnum decompression surgery and were treated by atlantoaxial fixation is analyzed.

Materials and Methods:

During the period January 2010 to November 2019, we treated 25 patients who had undergone conventionally described surgical procedures; all included foramen magnum decompression for Chiari formation. None of the patients had any craniovertebral junction anomaly. All patients had syringomyelia. All patients had worsened in their neurological condition following surgery either in the immediate or in the delayed postoperative phase. Atlantoaxial instability was diagnosed on the basis of facetal alignment and on the basis of direct observation of joint status by bone manipulation during surgery. The patients were treated by atlantoaxial fixation. Goel clinical grading scale and Japanese Orthopedic Association Score assessed the clinical status both before and after surgery.

Results:

Following surgery, all patients improved in the clinical condition. The improvement began in the immediate postoperative period and progressed. During the follow-up period that ranged from 4 to 123 months, “significant” neurological recovery and amelioration of presenting symptoms were observed. During the period of follow-up, reduction in the size of syrinx was observed in 14 out of 18 cases where postoperative magnetic resonance imaging was possible.

Conclusions:

Clinical results reinforce the belief that atlantoaxial instability is the nodal point of pathogenesis of Chiari formation. Atlantoaxial fixation is the treatment.

Alternative technique of C1-2-3 stabilization-sectioning of muscles attached to C2 spinous process and C2-3 fixation

Aim:

An alternative technique of C1-2-3 fixation is described that blocks the critical anteroposterior odontoid process movements and retains rotatory movement at the atlantoaxial joint. The technique involves sharp section of the muscles attached to the C2 spinous process and C2-3 transarticular interfacetal screw fixation.

Materials and Methods:

We successfully used this technique of fixation in 14 cases wherein in similar case situation; we earlier advocated inclusion of C1 in the fixation construct. Eleven patients had multisegmental spinal degeneration, 1 patient had Hirayama disease, and 2 patients had ossified posterior longitudinal ligament.

Results and Technical Advantages:

The procedure avoids manipulating C1 vertebra and excludes it from the fixation process, disables movement of C2 vertebra but retains rotation movements of the atlantoaxial joint that are executed by the muscles attached to the transverse process of atlas. The net effect is that the anteroposterior odontoid process movements that threaten the cervicomedullary neural structures are blocked and the critical rotatory atlantoaxial movements are retained.

Conclusions:

The discussed technique can be useful for cases undergoing multisegmental fixation that includes atlantoaxial joint.

Chiari malformation type I and basilar invagination originating from atlantoaxial instability: a literature review and critical analysis

Introduction

Recently, a novel hypothesis has been proposed concerning the origin of craniovertebral junction (CVJ) abnormalities. Commonly found in patients with these entities, atlantoaxial instability has been suspected to cause both Chiari malformation type I and basilar invagination, which renders the tried and tested surgical decompression strategy ineffective. In turn, C1-2 fusion is proposed as a single solution for all CVJ abnormalities, and a revised definition of atlantoaxial instability sees patients both with and without radiographic evidence of instability undergo fusion, instead relying on the intraoperative assessment of the atlantoaxial joints to confirm instability.

Methods

The authors conducted a comprehensive narrative review of literature and evidence covering this recently emerged hypothesis. The proposed pathomechanisms are discussed and contextualized with published literature.

Conclusion

The existing evidence is evaluated for supporting or opposing sole posterior C1-2 fusion in patients with CVJ abnormalities and compared with reported outcomes for conventional surgical strategies such as posterior fossa decompression, occipitocervical fusion, and anterior decompression. At present, there is insufficient evidence supporting the hypothesis of atlantoaxial instability being the common progenitor for CVJ abnormalities. Abolishing tried and tested surgical procedures in favor of a single universal approach would thus be unwarranted.

Adjacent-segment "central" atlantoaxial instability and C2-C3 instability following lower cervical C3-C6 interbody fusion: Report of three cases

Aim:

We report adjacent-segment “central” or “axial” atlantoaxial instability and C2–C3 instability as the cause of delayed neurological worsening following multisegmental cervical spinal stabilization.

Materials and Methods:

Three male patients aged 34, 56, and 70 years had been operated earlier for cervical spondylosis by multilevel C3–C6 cervical interbody fusion 6–11 years earlier. After an initial improvement for few years, the patients observed relatively rapid clinical deterioration. When admitted, all the three patients were severely quadriparetic and were brought to the hospital on a wheelchair. Central atlantoaxial instability was diagnosed on the basis of our previously published clinical and radiological parameters. C2–C3 instability was essentially diagnosed on the intraoperative observations. The patients underwent atlantoaxial and C2–C3 fixation.

Results:

All the three patients had rapid clinical recovery that started in the immediate postoperative period. At an average follow-up of 21 months, the patients walked independently.

Conclusions:

Identification and treatment of adjacent-segment central atlantoaxial and C2–C3 instability can lead to gratifying clinical outcome.

Chiari 1 Formation Redefined-Clinical and Radiographic Observations in 388 Surgically Treated Patients

OBJECTIVE

The subject of Chiari formation is revisited and redefined. Results of surgical treatment of patients with Chiari formation by atlantoaxial fixation are presented.

METHODS

Results were analyzed of 388 patients with Chiari formation surgically treated during 2010 to June 2019.

RESULTS

Two hundred and sixty-six patients had syringomyelia. Two hundred and three patients had no craniovertebral bone abnormality and 74 patients had group A and 111 patients had group B basilar invagination. Twenty-nine patients had been earlier treated by foramen magnum decompression surgery with or without duroplasty. Clinical parameters, analysis of video recordings both before and after surgery, and patient self-assessment were included in the analysis of outcome. Immediate postoperative and sustained clinical improvement was observed in 385 patients (99.4%).

CONCLUSIONS

Satisfactory clinical outcome in most patients after atlantoaxial fixation and without any manipulation of neural structures, dura, or bone in the region of foramen magnum consolidates the viewpoint that atlantoaxial instability is the nodal point of pathogenesis of Chiari 1 formation. The study suggests that Chiari 1 formation may be a secondary natural neural alteration in the face of atlantoaxial instability. The role of foramen magnum decompression surgery needs to be reassessed.

External syringomyelia in longstanding benign foramen magnum tumors

BACKGROUND

The effect of benign foramen magnum tumours on cranial and spinal dimensions and cerebrospinal fluid (CSF) spaces is unclear. In this study, we measured alterations in cerebrospinal fluid (CSF) spaces in the spinal canal and in the posterior cranial fossa distant from the site of benign foramen magnum tumors.

METHODS

Twenty-nine magnetic resonance imaging scans of patients with foramen magnum tumors (8 meningiomas and 21 C2 neurinomas) were identified for radiological morphometric analysis and compared with normal control scans. The anterior-posterior distance between the pontomedullary junction and the clivus, the spinal canal diameter, spinal cord diameter, and cord-canal ratios were measured at the C6 and T2 levels.

RESULTS

The mean spinal canal diameter was significantly higher in tumor scans at both the C6 and T2 spinal levels than in controls (13.8 mm vs. 11.4 mm at C6; p<0.0001, and 12.9 mm vs. 11.9 mm at T2; P=0.01). Further, the mean cord:canal ratio was significantly lower in tumor scans at both levels (0.49 vs. 0.64 at C6; P<0.0001, and 0.45 vs. 0.54 at T2; P=0.0009). There was no significant difference in mean anteroposterior distance from the clivus to the pontomedullary junction (10.4 mm vs. 10.3 mm; P=0.91).

CONCLUSION

In the presence of benign foramen magnum tumors, the spinal canal diameter and CSF volume in the spinal canal increased at the C6 and T2 levels, distant from the tumor site, a phenomenon we describe as "external syringomyelia".

Is C2-3 fusion an evidence of atlantoaxial instability? An analysis based on surgical treatment of seven patients

Objective:

The authors analyze the rationale of atlantoaxial fixation in patients presenting with symptoms related to cervical myelopathy and wherein the radiological images depicted C2–3 fusion and presence of single or multiple level neural compression of the subaxial cervical spinal cord attributed to “degenerative” spine.

Materials and Methods:

Seven adult males were analyzed who presented with long-standing symptoms of progressive cervical myelopathy and where imaging showed presence of C2–3 fusion, no cord compression related to odontoid process, and evidence of single or multiple level lower cervical cord compression conventionally attributed to spinal degeneration. There was no other bone or soft tissue abnormality at the craniovertebral junction. There was no evidence of atlantoaxial instability when assessed by conventional radiological diagnostic parameters. Atlantoaxial instability was diagnosed on the basis of clinical understanding, atlantoaxial facetal malalignment, and manual assessment of instability by bone handling during surgery. All the seven patients underwent atlantoaxial fixation and no surgical manipulation at lower cervical spinal levels.

Results:

At an average follow-up of 34 months, all patients have recovered satisfactorily in their neurological function.

Conclusion:

The presence of C2–3 fusion is an indication of atlantoaxial instability and suggests the need for atlantoaxial stabilization. Effects on the subaxial spine and spinal cord are secondary events and may not be surgically addressed.

Hybrid and double insurance atlantoaxial facetal fixation

The authors report a case of a 19-year-old female patient having basilar invagination with complex musculoskeletal abnormalities wherein atlantoaxial fixation was done with a combination of Goel and Magerl techniques on a single articulation on one side and two transarticular screws (Magerl technique) were deployed on the contralateral side articulation. The combination of Goel and Magerl techniques used in a novel fashion resulted in strong fixation and provided an environment for bone fusion. The special joint architecture and location of facet of atlas anterior and rostral to the facet of axis in the form of facetal-spondyloptosis were used to advantage as it provided a direct screw trajectory for transarticular screw insertion. The patient recovered after surgery in her neurological function. Craniovertebral junction realignment could be observed. Solid bone fusion was observed after 8 months of the surgical procedure.