Embryology, classification, and surgical management of bony malformations of the craniovertebral junction

Imaging of Craniovertebral Junction Instability, Fixation, and Stenosis in Children

Craniovertebral junction (CVJ) instability, fixation, and stenosis in children are closely related conditions that are often challenging to diagnose and are associated with significant morbidity. Groups at higher risk for CVJ abnormalities include children with trisomy 21, juvenile idiopathic arthritis, upper respiratory infection or other inflammatory conditions of the head and neck, and certain skeletal dysplasias. Radiography, CT, and MRI play complementary roles in the evaluation of pathologic conditions of the CVJ. CVJ morphometry is helpful in characterizing osseous relationships and suggesting potential instability and/or neural compression. CT with multiplanar and three-dimensional volume-rendered reconstructions may be helpful in identifying (a) congenital anomalies associated with instability and/or neural canal narrowing; (b) disorders predisposing to atlantoaxial rotatory fixation (AARF), such as retropharyngeal inflammation in Grisel syndrome; and (c) acquired osseous abnormalities associated with irreducibility in children with chronic AARF (eg, facet deformity or new bone formation). Dynamic CT is particularly helpful for evaluating children with persistent torticollis that is refractory to initial conservative therapy. Early diagnosis and treatment of AARF are essential in reducing the likelihood of progression to chronic AARF. Performing CT angiography before C1-C2 fixation may help identify vascular variations that increase surgical risk and provide an opportunity for modification of the surgical plan. MRI is preferred for assessment of the hindbrain; upper cervical spinal cord; and nonossified structures such as cartilage, ligaments, and paravertebral soft tissues. The authors discuss normal development and anatomy, imaging evaluation, and disorders associated with CVJ instability, fixation, and stenosis in children. Imaging-related treatment considerations are also discussed. ©RSNA, 2025 Supplemental material is available for this article.

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.

Clinical effect and prognosis of transoral or endoscope-assisted transoral release for irreducible atlantoaxial dislocation: A retrospective cohort study

Background

The clinical applications of endoscope-assisted transoral release for irreducible atlantoaxial dislocations are limited. This study aimed to investigate the clinical effect and prognostic factors of traditional and endoscope-assisted transoral release, as well as posterior reduction and fixation, in treating irreducible atlantoaxial dislocations.

Materials and methods

We conducted a retrospective study on 59 patients with irreducible atlantoaxial dislocation who underwent either traditional or endoscope-assisted transoral release, posterior fixation, and fusion between January 2018 and January 2023. Various data, including surgical time, blood loss, drainage volume, oral intake, hospital stay, complications, and neurological status (assessed by the Japanese Orthopedic Association [JOA] score and Oswestry Disability Index [ODI]), were recorded. Imaging parameters such as the atlantodontoid interval (ADI), space available for the cord (SAC), and cervicomedullary angle (CMA) were analyzed and compared. In addition, the correlation between ODI, JOA and patient age, course of disease, preoperative ADI, SAC and CMA were analyzed.

Results

No significant differences were observed in age, sex, BMI, preoperative ADI, preoperative SAC, or preoperative CMA. All patients achieved excellent reduction with no significant differences between the two groups. Patients in the endoscopic group experienced significantly reduced blood loss, earlier oral intake, and shorter hospital stays compared to those in the open group (P < 0.05). The ODI and JOA scores improved significantly in both groups at 1, 6, 12, 18, and 24 months postoperatively (P < 0.05). Postoperative ADI, SAC, and CMA values in both groups were significantly better than preoperative values (P < 0.001). The patient age, course of disease and the preoperative ADI were negatively correlated with the postoperative ODI and the JOA improvement ratio (P < 0.01), and the preoperative SAC and preoperative CMA had positive correlations with the postoperative ODI and the JOA improvement ratio (P < 0.01) at 6, 12 and 24 months postoperatively.

Conclusion

Patient age, course of disease, preoperative ADI, SAC and CMA are correlated with the operative prognosis of irreducible atlantoaxial dislocation. The endoscope-assisted transoral approach, compared to the traditional transoral approach, is minimally invasive, resulting in less operative blood loss, earlier oral intake and a shorter length of hospital stay, which could be offered as an alternative for irreducible atlantoaxial dislocation.

Anatomy and mobility in the adult cadaveric craniocervical junction

Genetic diseases with craniofacial malformations can be associated with anomalies of the craniocervical joint (CCJ). The functions of the CCJ are thus impaired, as mobility may be either limited by abnormal bone fusion causing headaches, or exaggerated in the case of hypermobility, which may cause irreparable damage to the spinal cord. Restoring the balance between mobility and stability requires surgical correction in children. The anatomy and biomechanics of the CCJ are quite unique, yet have been overlooked in the past decades. Pediatric evidence is so scarce, that investigating the adult CCJ is our best shot to disentangle the form-function relationships of this anatomical region. The motivation of the present study was to understand the morphological and functional basis of motion in the CCJ, in the hope to find morphological features accessible from medical imaging able to predict mobility. To do so, we have quantified the in-vitro kinematics of the CCJ in nine cadaveric asymptomatic adults, and estimated a wide range of mobility variables covering the complexity of spinal motion. We compared these variables with the shape of the occipital, the atlas and the axis, obtained using a dense geometric morphometric approach. Morphological joint congruence was also quantified. Our results suggest a strong relationship between bone shape and motion, with the overall geometry predicting best the primary movements, and the joint facets predicting best the secondary movements. We propose a functional hypothesis stating that the musculoligamental system determines movements of great amplitude, while the shape and congruence of joint facets determine the secondary and coupled movements, especially by varying the geometry of bone stops and the way ligaments are tensioned. We believe this work will provide valuable insights in understanding the biomechanics of the CCJ. Furthermore, it should help surgeons treating CCJ anomalies by enabling them to translate objectives of functional and clinical outcome into clear objectives of morphological outcome.

Knockdown of best1 Gene in Zebrafish Caused Abnormal Neuronal and Skeletal Development - A Subtype of Craniovertebral Junction Malformation?

OBJECTIVE

To investigate the developmental defects caused by knockdown of best1 gene in zebrafish as a model for a subtype of craniovertebral junction (CVJ) malformation.

METHODS

Two antisense morpholinos (MOs) were designed targeting zebrafish best1 to block translation (ATG-MO) or to disrupt splicing (I3E4-MO). MOs were microinjected into fertilized one-cell embryos. Efficacy of splicing MO was confirmed by reverse transcription-polymerase chain reaction. Phenotypes were analyzed and quantified by microscopy at multiple developmental stages. Neuronal outgrowth was assessed in transgenic zebrafish expressing green fluorescent protein in neurons. Skeletal ossification was visualized by Calcein staining.

RESULTS

Knockdown of best1 resulted in zebrafish embryos with shorter body length, curved axis, low survival rate, microcephaly, reduced eye size, smaller head and brain, impaired neuronal outgrowth, and reduced ossification of craniofacial and vertebral bone.

CONCLUSION

Best1 gene plays critical roles in ophthalmologic, neurological and skeletal development in zebrafish. A patient with a premature stop codon in BEST1 gene exhibited similar phenotypes, implying a subtype of CVJ malformation.

A Global Bibliometric and Visualization Analysis of Craniovertebral Junction Bony Abnormalities Based on VOSviewer and Citespace

OBJECTIVE

Recent years have witnessed a rapidly growing interest in CVJ bony abnormalities, and a qualitative and quantitative analysis of relevant literatures is necessary. This study aims to identify and summarize the published articles related to craniovertebral junction bony abnormalities, to analyze and visualize the current research trends and major contributors.

METHODS

We collected data from Web of Science, excluding certain article types. Two researchers screened articles for relevance. Data were organized with EndnoteX9, and analyzed using VOSviewer and CiteSpace for co-authorship, co-occurrence, keyword burst, and co-citation analyses to identify research trends and collaborations.

RESULTS

A total of 2,776 articles were included, revealing an increasing trend in annual publications of CVJ bony abnormalities. The USA was the leading country. King Edward Memorial Hospital was the most prolific institution, and Seth GS Medical College had the most citations. The Spine is the most popular journal with the highest number of publications and citations. Professor Goel Atul from India emerged as the most influential pioneer in this field. Keyword analysis highlighted surgical techniques, diagnosis, and anatomy as the primary research hotspots and Fixation, Placement, and Basilar invagination gradually become the new research trend. However, there is a relative weakness in basic research and epidemiology.

CONCLUSIONS

This study provides valuable insights into the current research trends and critical contributors in CVJ bony abnormalities, guiding evidence-based decisions and fostering international collaborations to advance knowledge in this field.

Influence of the Head Neck Position on Imaging Measurements Used to Assess the Craniovertebral Junction in Small Breed Dogs: A Cadaveric Study

OBJECTIVE

 The study aimed to determine the influence of head neck position on imaging measurements used to assess the craniovertebral junction (CVJ) and to recommend the most appropriate position for the evaluation of the CVJ.

STUDY DESIGN

 A cross-sectional sample of adult dogs' cadavers was subjected to a computed tomography scan of the cranium and the cranial cervical region in three standardized head positions. Imaging measurements often used to assess the CVJ were measured. The influence of the head neck position, breed, weight and gender on imaging measurements was tested using repeated measures analysis of variance.

RESULTS

 Twenty-eight cadavers of small breed dogs were enrolled in the study. All cadavers examined had occipital dysplasia. All transarticular imaging measurements were dependent on the head neck position. In addition, the breed, weight and gender had an influence on several measurements.

CONCLUSION

 We recommend a standardized head neck position of 50 degrees flexion if quantitative imaging measurements of the CVJ are used to diagnose pathologies in this region. Future studies should focus on the definition of cut-off values for quantitative imaging measurements of the CVJ to differentiate between healthy and diseased small breed dogs. Regarding atlantoaxial instability, a combination of six parameters (C1-C2 angle, C1-C2 overlap, atlantoaxial distance, dens-to-axis length ratio, ventral compression index and clivus canal angle) is promising for its diagnosis.

Posterior fusion of the craniocervical junction in the pediatric spine: Wright's translaminar C2 screw technique provides for more safety and effectiveness

PURPOSE

Posterior fusion of the craniocervical junction (CCJ) has always been challenging in children with rare congenital diseases and malformations. At our institution, the introduction of the translaminar C2 screw technique led to a significant improvement in the quality of treatment.

METHODS

Retrospective analysis of a pediatric cohort at a single institution who underwent CCJ posterior fusion between 2007 and 2018. Patients were divided into group 1 (other posterior fusion techniques, n = 12) and group 2 (translaminar axis screw placement, n = 19). Diagnosis, sex, age at surgery, surgical technique, immobilization, revisions, fusion, reduction, and complications were assessed.

RESULTS

Follow-up ranged from 12 to 145 months (mean 50.7). The initial fusion rate detected at 3 months by CT differed significantly (66, 7% in group 1 vs. 100% in group 2, p = 0.018). Full reduction of C1/C2 malalignments was achieved in 41, 6% of group 1 versus 84, 2% of group 2 (p = 0.007). Immobilization was applied in 83, 3% of group 1 versus 26, 3% of group 2 (p = 0.0032). Ten complications were treated conservatively, and 15 events required revision surgery (80% in group 1 vs. 20% in group 2). Eight complications were related to immobilization.

CONCLUSIONS

The implementation of the translaminar C2 technique resulted in significantly more safety and efficiency regarding pediatric posterior fusion CCJ surgery at our institution, with significantly higher rates of rigid fixation, full reduction, and fusion, and significantly lower rates of complications and immobilization. These slides can be retrieved under Electronic Supplementary Material.

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.

Complex congenital atlantoaxial dislocation in an infant: case report

The authors report the case of congenital atlantoaxial dislocation in a 9-month-old female infant, who presented with progressive quadriparesis and respiratory failure. The problems in management due to such an early age of presentation, including atypical clinical presentation, unique radiological findings, limited management options, and variable clinical outcomes discussed. This is the youngest case of non-syndromic congenital atlantoaxial dislocation, reported to date, and is a unique combination of lateral, rotatory, and antero-posterior atlantoaxial dislocation.

Shape change in the atlas with congenital midline non-union of its posterior arch: a morphometric geometric study

BACKGROUND CONTEXT

The congenital midline non-union of the posterior arch of the atlas is a developmental variant present at a frequency ranging from 0.7% to 3.9%. Most of the reported cases correspond to incidental findings during routine medical examination. In cases of posterior non-union, hypertrophy of the anterior arch and cortical bone thickening of the posterior arches have been observed and interpreted as adaptive responses of the atlas to increased mechanical stress.

PURPOSE

We sought to determine if the congenital non-union of the posterior arch results in a change in the shape of the atlas.

STUDY DESIGN/SETTING

This study is an analysis of the first cervical vertebrae from osteological collections through morphometric geometric techniques.

METHODS

A total of 21 vertebrae were scanned with a high-resolution three-dimensional scanner (Artec Space Spider, Artec Group, Luxembourg). To capture vertebral shape, 19 landmarks and 100 semilandmarks were placed on the vertebrae. Procrustes superimposition was applied to obtain size and shape data (MorphoJ 1.02; Klingenberg, 2011), which were analyzed through principal component analysis (PCA) and mean shape comparisons.

RESULTS

The PCA resulted in two components explaining 22.32% and 18.8% of the total shape variance. The graphic plotting of both components indicates a clear shape difference between the control atlas and the atlas with posterior non-union. This observation was supported by statistically significant differences in mean shape comparisons between both types of vertebra (p<.0001). Changes in shape were observed in the superior and inferior articular facets, the transverse processes, and the neural canal between the control and non-union vertebrae.

CONCLUSIONS

Non-union of the posterior arch of the atlas is associated with significant changes in the shape of the vertebra.

Surgical Intervention for Unstable Craniovertebral Junction Anomalies with Narrow C2 Pedicle

OBJECTIVE

We sought to investigate and report a novel surgical technique of screws insertion and posterior surgical reduction, as well as explore its clinical results.

METHODS

From September 2008 to September 2012, we treated 41 cases of unstable craniovertebral junction anomalies with a narrow C₂ pedicle at our department. All patients underwent "posterior reduction and internal fixation of the occipital bone with superior or inferior articular process of C₂ and lateral mass of C₃ on the narrowed C₂ pedicle side-for non-narrowed C₂ pedicle side, the screw was only inserted into C₂ pedicle without extending the fixation to C₃ vertebrae-using a titanium screw-rod (plate) fixation system." The preoperative and postoperative atlantodens interval, Chamberlain line, McRae line, and cervicomedullary angle were all measured. In addition, the preoperative and postoperative Japanese Orthopedic Association score was used to evaluate the cervical myelopathy.

RESULTS

A total of 134 screws were inserted into the C₂ pedicle (30 screws), superior (35 screws) or inferior (17 screws) articular process of C₂, and lateral mass of C₃ (52 screws). There was a significant statistical difference between the preoperative and postoperative results in the reduction of the odontoid process, decompression of the upper cervical spinal cord and medulla, as well as the improvement of neurologic functions (P < 0.05). All patients have exhibited a major neurologic improvement and solid bony fusion.

CONCLUSION

This novel surgical technique is safe, feasible, and effective for the treatment of unstable craniovertebral junction anomalies with a narrow C₂ pedicle.

The craniocervical junction: embryology, anatomy, biomechanics and imaging in blunt trauma

Imaging of the blunt traumatic injuries to the craniocervical junction can be challenging but central to improving morbidity and mortality related to such injury. The radiologist has a significant part to play in the appropriate management of patients who have suffered injury to this vital junction between the cranium and the spine. Knowledge of the embryology and normal anatomy as well as normal variant appearances avoids inappropriate investigations in these trauma patients. Osseous injury can be subtle while representing important radiological red flags for significant underlying ligamentous injury. An understanding of bony and ligamentous injury patterns can also give some idea of the biomechanics and degree of force required to inflict such trauma. This will assist greatly in predicting risk for other critical injuries related to vital neighbouring structures such as vasculature, brain stem, cranial nerves and spinal cord. The embryology and anatomy of the craniocervical junction will be outlined in this review and the relevant osseous and ligamentous injuries which can arise as a result of blunt trauma to this site described together. Appropriate secondary radiological imaging considerations related to potential complications of such trauma will also be discussed.

TEACHING POINTS

• The craniocervical junction is a distinct osseo-ligamentous entity with specific functional demands. • Understanding the embryology of the craniocervical junction may prevent erroneous radiological interpretation. • In blunt trauma, the anatomical biomechanical demands of the ligaments warrant consideration. • Dedicated MRI sequences can provide accurate evaluation of ligamentous integrity and injury. • Injury of the craniocervical junction carries risk of blunt traumatic cerebrovascular injury.