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Background: Little attention has been given to the retroverted dens within the existing medical literature. However, this finding can have a clinical impact, especially in patients with Chiari malformation type I (CM1), as it can have consequences for further treatment., Methods: Using standard search engines, we performed a literature review of anatomical, radiologic, and clinical studies as well as pathologic and surgical considerations related to the retroverted dens. Key words for our search included retroverted dens; retroflexed dens; odontoid retroflexion; posterior inclination; and tilted dens., Results: A retroverted dens is most commonly found in the pediatric population in relation to CM1. Research has demonstrated that high degree of dens angulation can result in significant anterior brain stem compression with the need for both anterior and posterior decompression in patients with symptomatic CM1., Conclusions: A greater degree of dens angulation can lead to neurologic symptoms secondary to spinomedullary compression. Therefore, correct measurements are essential as such findings can influence presurgical planning., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Background: The odontoid process is a critical component of the cranio-cervical junction. Therefore, clinicians who diagnose, treat, or operate this region need a strong background in regard to the embryology, anatomy, and anatomical variations that may be seen for the odontoid process., Methods: A literature review was performed, using standard search engines, to explore the morphology, embryology, and anatomical variants of the odontoid process., Conclusions: A sound understanding of the development of the odontoid process, both in normal and in variant forms, as well as its phenotypical morphology is a prerequisite for the diagnosis and treatment of patients presenting with disorders affecting the cranio-cervical spine.

The aim of this study was to determine any correlation between natural head position and cranio-cervical growth direction and if natural head position influences facial growth direction. One hundred sixty (160) cephalometric radiographs were examined and cranio-cervical inclinations determined (angles: NS-Ver, NS-OPT, NS-CVT). On the basis of the NS-ML angle, radiographs were divided into two groups: mandibular anteriorotation and posteriorotation. On the basis of the SGo/NMe index, two groups were formed: short-faced and long-faced subjects. The angles NS-Ver, NS-OPT, and NS-CVT describe cranio-cervical inclination. Subjects with anterior mandible growth do position their heads more vertically and have a shorter face, and those with posterior mandible growth tilt their heads more backwards and have a longer face. An adaptive head position can be a factor in altering the direction of facial growth. Determination of head position and mandible growth direction can be an important indicator in patients with TMD treatment.

Background: Knowledge of biomechanics and the cervical spine's anatomy has become more topical as the incidence of whiplash neck disorders has increased. Unfortunately, injuries after traffic accidents are often brought to court, where the medical expert's knowledge is of utmost importance to ensure a correct medical evaluation., Material and Methods: The article is based on information identified through non-systematic searches of PubMed and on the author's experience as a professor of anatomy., Results: The cervical spine is particularly vulnerable to forces perpendicular to the length axis. Stability depends largely on the soft tissue. Injuries of soft tissue (especially in ligaments and intervertebral discs) may lead to instability and periosteal reaction with subsequent new formation of bone., Interpretation: The cervical spine is a relatively weak and vulnerable part of the body. One should consider locally restricted new formations of tissue with corresponding height reduction of the intervertebral disc as a sign of genuine injury.

Background: The aim of the study was to evaluate the results of instrumented rod and wire fusion in children with craniovertebral junction (CVJ) instability and os odontoideum., Methods: We evaluated seven children (mean age 9.85 years) with Down and Morquio's syndromes and primary os odontoideum. X-ray, computerized tomography (CT) scan and magnetic resonance (MR) imaging of the CVJ showed reducible instability in all of the cases but one. All the children underwent surgical correction by means of posterior wiring, instrumentation, fusion and external orthosis. A posterior wiring technique was also utilized in the only child with irreducible preoperative atlantoaxial instability, which, however, proved to be reducible under general anesthesia., Findings: At maximum follow-up (observation range 28 to 106 months, mean 59.42 months), the clinical picture was improved in all the patients. The postoperative neuroradiological investigations demonstrated satisfactory bony fusion with neural decompression in all patients., Conclusions: A wiring technique to correct atlantoaxial instabilities has been shown to be more relevant in these children with syndromic atlantoaxial dislocation and os odontoideum due to its simplicity, safety (continuous fluoroscopic assistance is not necessary and there is no risk of neuro-vascular injuries) and lower costs (no complex hardware devices; no neuronavigation systems are required). Preoperative irreducibility of the C1-C2 shift is not an absolute criterion for transoral decompression in children since os odontoideum can be reduced under general anesthesia.

Introduction: Cervical vertebrae shape has been proposed as a diagnostic factor for assessing skeletal maturation in orthodontic patients. However, evaluation of vertebral shape is mainly based on qualitative criteria. Comprehensive quantitative measurements of shape and assessments of its predictive power have not been reported. Our aims were to measure vertebral shape by using the tools of geometric morphometrics and to evaluate the correlation and predictive power of vertebral shape on skeletal maturation., Methods: Pretreatment lateral cephalograms and corresponding hand-wrist radiographs of 98 patients (40 boys, 58 girls; ages, 8.1-17.7 years) were used. Skeletal age was estimated from the hand-wrist radiographs. The first 4 vertebrae were traced, and 187 landmarks (34 fixed and 153 sliding semilandmarks) were used. Sliding semilandmarks were adjusted to minimize bending energy against the average of the sample. Principal components analysis in shape and form spaces was used for evaluating shape patterns. Shape measures, alone and combined with centroid size and age, were assessed as predictors of skeletal maturation., Results: Shape alone could not predict skeletal maturation better than chronologic age. The best prediction was achieved with the combination of form space principal components and age, giving 90% prediction intervals of approximately 200 maturation units in the girls and 300 units in the boys. Similar predictive power could be obtained by using centroid size and age. Vertebrae C2, C3, and C4 gave similar results when examined individually or combined. C1 showed lower correlations, signifying lower integration with hand-wrist maturation., Conclusions: Vertebral shape is strongly correlated to skeletal age but does not offer better predictive value than chronologic age.

Introduction: The purpose of this study was to evaluate the validity of the cervical vertebral maturation (CVM) method as an indicator of skeletal age in the circumpubertal period by correlating it to the hand-wrist method (HWM)., Methods: Hand-wrist and lateral cephalometric radiographs of 400 Chinese subjects were randomly selected. Their ages were 10 to 15 years for girls and 12 to 17 years for boys, so they were within the circumpubertal period. Skeletal ages were assessed according to the CVM method and the HWM., Results: The CVM was significantly correlated with HWM skeletal age (Spearman r = 0.9521 [boys] and 0.9408 [girls]). All patients in cervical vertebral stage 3 of the CVM corresponded to stages MP3-FG or MP3-G (around the peak of the growth spurt) in the HWM., Conclusions: The CVM is a valid indicator of skeletal growth during the circumpubertal period, providing information for timing of growth modification.

Aim: The aims of this clinical study were to describe the segments and the inferior boundaries of the odontoid process as regards the embryological development of C2 based on the magnetic resonance imaging finding., Material and Methods: Cranial and cervical magnetic resonance images including occiput, C1, and C2, and those obtained for different reasons such as evaluation of cranial and upper cervical pathology were re-evaluated for this study. Synchondroses around the odontoid process were accepted as the boundaries between the neural arch and the body of C2., Results: Thirty cases were included for this study. Fifteen of these were adult cases and the remaining 15 were in pediatric cases. Apicodental, dentocentral, neurocentral, and dentoneural synchondrotic articulations were clear, especially under the ages of 3 years. The dentocentral synchondrosis was found well below the line drawn through the level of superior articulating facets., Conclusion: This study demonstrated that the inferior boundary of the odontoid process is not located at the level of superior articulating facets. The real border between the odontoid process and the body of C2 is located well below the level of the superior articulating facets because of the location of the dentocentral synchondrotic articulation. This level should be considered in the classification of C2 fractures.

The odontoid process of C2 projects upward from the superior roof of the body of C2. There is a confusion about the inferior border of the odontoid. The aims of this clinical study were to describe the inferior border of the odontoid process based on the remnant of dentocentral synchondrosis in adults, and the estimation of the odontoid/body ratio in pediatric and adult ages. Sixty-six cases were included for this study. Forty-four of them were in adult ages and the remaining 22 of them were in pediatric ages. The region of occiput, C1, C2, and C3, was examined with the magnetic resonance imaging (MRI) in all cases. The length of the odontoid process was estimated by using radiological images of MR from the tip of the odontoid to the remnant of dentocentral synchondrosis. The portion located under the level of synchondrosis was considered as the body of C2. The average length of the odontoid was 18. 6 mm in pediatric and 21. 3 mm in adult cases. In adult females, the length of the odontoid process (19. 1 mm in length) was smaller than those of adult males (23. 6 mm in length). The average ratio of odontoid/body was two in pediatric and 1.8 in adult cases. This study demonstrated that the neck of the odontoid segment at the level of superior articulating facets is not the synchondrosis between the odontoid process and the body of C2. The synchondrosis is located well below the level of superior articulating facets. It can be demonstrated with sagittal and coronal images of MR in both of pediatric and adult individuals.

During skeletal development the two ossification centers of the odontoid process are separated from the corpus of the axis by a subdental synchondrosis. This synchondrosis is thought to close and disappear spontaneously in adolescence although this has never been studied in detail. The basis of the dens is of clinical relevance as type II dens fractures are located here. To characterize the morphological architecture of the axis with particular attention to the subdental synchondrosis, the complete axis was harvested from thirty age-matched and gender-matched patients of the three different age groups at autopsy. The subdental synchondrosis and the bone structure of the dens, the basis of the dens and the body of C2 were analyzed by radiography, histology and quantitative histomorphometry. At the macroscopic level the persistency of the subdental synchondrosis in the adult cervical spine was detected in 87% (26 of 30) of the specimens. Histomorphometry revealed a residual disc blastema with an average size of 25.8% of the sagittal depth of the basis of the dens at this level. Bony integration of the synchondrosis was poor throughout all ages. Histologically a cartilaginous matrix composition of the subdental synchondrosis persisted throughout all groups. The trabecular microarchitecture demonstrated a significant reduction of bone volume and trabecular number as well as an increased trabecular separation within the basis of the dens as compared to the corpus or the dens of C2. This histomorphometric data regarding a poor integration of the synchondrosis into the trabecular network and the reduced bone mass within the basis of the dens might offer a previously underestimated explanation for the occurrence of type II dens fractures and their association with pseudoarthrosis, respectively.

The present study aimed to provide a version of the Cervical Vertebral Maturation (CVM) method for the detection of the peak in mandibular growth based on the analysis of the second through fourth cervical vertebrae in a single cephalogram. The morphology of the bodies of the second (odontoid process, C2), third (C3), and fourth (C4) cervical vertebrae were analyzed in six consecutive cephalometric observations (T1 through T6) of 30 orthodontically untreated subjects. Observations for each subject consisted of two consecutive cephalograms comprising the interval of maximum mandibular growth (as assessed by means of the maximum increment in total mandibular length, Co-Gn), together with two earlier consecutive cephalograms and two later consecutive cephalograms. The analysis consisted of both visual and cephalometric appraisals of morphological characteristics of the three cervical vertebrae. The construction of the new version of the CVM method was based on the results of both ANOVA for repeated measures with post-hoc Scheffé's test (P < .05) and discriminant analysis. The new CVM method presents with five maturational stages (Cervical Vertebral Maturation Stage [CVMS] I through CVMS V, instead of Cvs 1 through Cvs 6 in the former CVM method). The peak in mandibular growth occurs between CVMS II and CVMS III, and it has not been reached without the attainment of both CVMS I and CVMS II. CVMS V is recorded at least two years after the peak. The advantages of the new version of the CVM method are that mandibular skeletal maturity can be appraised on a single cephalogram and through the analysis of only the second, third, and fourth cervical vertebrae, which usually are visible even when a protective radiation collar is worn.

We report seven children (three female, four male) diagnosed with traumatic synchondrotic slip of the odontoid. The clinical records, plain films and CT scans were evaluated retrospectively. The patients ranged in age between 3 and 5 years. Their injuries resulted from a motor vehicle accident in four cases and from a fall from a height in three. The injury was isolated in five; it was associated with a closed head injury in one and with facial and brachial plexus trauma in another. Radiographs showed anterior angulation with or without displacement in all seven cases. Axial CT with sagittal reformation and 3D reconstructions were performed in six cases. This confirmed the synchondrotic slip and, in addition, identified a rotary component to the injury in three cases, with compromise of the canal in two. Other additional injuries were also noted. All cases were treated conservatively and the injuries healed. Only one child had a neurological deficit attributable to her head injury rather than her cervical injury (MR of the cervical cord was normal). The presence of the synchondrosis between the dens and the body of C-2 makes this injury unique to children under 7 years of age; by the age of 7 the synchondrosis has fused.

The development of the second cervical vertebra is complex. The dens (odontoid process) develops two primary ossification centers that usually coalesce within three months following birth. These centers are separated from the primary ossification center of the vertebral centrum by a cartilaginous region--the dentocentral synchondrosis. This synchondrosis is a slow growing, bipolar physis similar to the triradiate cartilage of the acetabulum. It contributes to the overall heights of both the dens as well as the vertebral body. Anatomically the dentocentral synchondrosis is below the level of the C1-C2 articulations. This cartilaginous structure is continuous throughout the vertebral body with similar cartilage in both the facet regions as well as the neurocentral synchondroses. These various cartilaginous continuities progressively close--first, the connections to the facet regions, next the neurocentral synchondroses, and finally the dentocentral synchondrosis. Remnants of the incompletely closed dentocentral synchondrosis must be distinguished from a fracture, which usually propagates along this structure as a physeal injury in infants and children. The cartilaginous epiphysis at the tip of the dens may be transverse or may form a cleft ("V") shape. At eight to ten years, a secondary ossification center--the ossiculum terminale--develops in this proximal dens epiphysis. Fusion of the ossiculum terminale with the rest of the dens occurs between ten and thirteen years.

An analysis of the cervical spine of 508 normal children aged between 3 and 18.9 years provided data for the normal development of the odontoid process and its relationship to the anterior arch of the atlas. In normal children under the age of 9 years, the tip of the odontoid may fall well short of the upper margin of the anterior arch of the atlas. This has important implications for the assessment of atlanto-axial instability in children with Down's syndrome.