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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., (© 2024 The Author(s). Journal of Morphology published by Wiley Periodicals LLC.)

An in-depth understanding of the anatomy of the craniocervical junction (CCJ) is indispensable in skull base neurosurgery. In this paper, we discuss the osteology of the occipital bone, the atlas (C1) and axis (C2), the ligaments and the muscle anatomy of the CCJ region and their relationships with the vertebral artery. We will also discuss the trajectory of the vertebral artery and review the anatomy of the jugular foramen and lower cranial nerves (IX to XII). The most important surgical approaches to the CCJ, including the far lateral approach, the anterolateral approach of Bernard George and the endoscopic endonasal approach, will be discussed to review the surgical anatomy., (Copyright © 2023 Elsevier Masson SAS. All rights reserved.)

Aim: To provide a comprehensive analysis for accurate screw size selection and insertion angle during surgical procedures., Material and Methods: In this retrospective study, a total of 120 patients participated, resulting in the analysis of 240 occipital condyles using coronal, sagittal, and axial planes on CT scans. Statistical evaluation was performed using the Wilcoxon rank-sum test, with p < 0.05 considered statistically significant., Results: The mean sagittal length and height were measured at 17.2 ± 1.7 mm and 9.1 ± 1.5 mm, respectively. The average condyle angle, a crucial factor for screw insertion, was assessed at 38.0 ± 5.5 mm in length, 19.6 ± 2.6 mm in width, and 9.5 ± 1.0 mm in height. Condyle height in the anterior and posterior hypoglossal canals was measured at 10.8 ± 1.4 mm and 9.0 ± 1.4 mm, respectively. Screw angle and condyle width were statistically smaller in females compared to the male population., Conclusion: The OC is a significant anatomical structure in the craniovertebral junction, playing a crucial role in stability. The obtained morphological values are applicable to the Turkish population and offer statistically significant findings for preoperative planning involving occipital condyle screw instrumentation.

The craniovertebral junction (CVJ) involves the atlas, axis, and occiput along with the atlanto-occipital and atlantoaxial joints. The anatomy and neural and vascular anatomy of the junction render the CVJ unique. Specialists treating disorders that affect the CVJ must appreciate its intricate anatomy and should be well versed in its biomechanics. This first article in a three-article series provides an overview of the functional anatomy and biomechanics of the CVJ., (Copyright © 2023 Elsevier Inc. All rights reserved.)

This paper aimed to better describe the anatomy of the superficial anterior atlanto-occipital ligament of the craniocervical junction and discuss this ligament's potential function and clinical implications. A broad literature review on the anatomical features and findings of the superficial anterior atlanto-occipital ligament was performed. The superficial anterior atlanto-occipital ligament is located anterior to the anterior atlanto-occipital membrane. However, the physiological role of the superficial anterior atlanto-occipital ligament is still unclear due to a lack of anatomical and biomechanical studies although one study has suggested that this ligament is a secondary stabilizer of the craniocervical junction. Further studies are needed to clarify the function and anatomy of the superficial anterior atlanto-occipital ligament.

This article presents the results of a dissection series investigating a previously neglected ligamentous structure attached to the human occipital bone, the Ligamentum condylicum posterius or posterior condylar ligament, and relates these results to the manifestation of a likewise poorly recognized occipital bony variation, the Processus condylicus posterior. The dissection of 50 human cranio-cervical junctions revealed the existence of the posterior condylar ligament in 98% of all cases, sometimes containing free elongated ossicles and osseous spurs at the insertion points at the occipital bone. In two cases the osseous formation of a Processus condylicus posterior became apparent (4%), which further provided the opportunity to study the behaviour of the ligament in these cases. In this article, we show and discuss that the posterior condylar ligament and osseous structures possibly derive from tissue that originates from the material of the dorsal arch of the Proatlas, a rudimentary vertebra between occipital bone and atlas. For this purpose, the Ponticulus atlantis posterior as another Proatlas-manifestation, whose origin from the dorsal Proatlas-arch is widely accepted in literature, is considered. This bony variant was found in 11 specimens (22%) in the present study and further served to classify and interpret the findings of the much rarer Processus condylicus posterior. As a result of this dissection series and a review of literature on this understudied topic, a typology of manifestations of the posterior condylar ligament, Processus condylicus posterior and related structures like free ossicles has been introduced., (© 2021 Anatomical Society.)

The myodural bridge (MDB) is a dense connective tissue structure that connects the subocciptal musculature to the spinal dura mater. The purpose of this study was to clarify morphological evolution characteristics and compositional changes in the fibrous structures of MDB during its growth and development in the atlanto-occipital interspace. For this, histological sections from Sprague-Dawley (SD) rats (age, E17 to adulthood) were stained with Masson's Trichrome and Picrosirius Red. The results demonstrated that at age E18, the posterior arch of the atlas was completely closed and MDB fibers had already begun to form. In rat embryos (E18-E21), only few fibers and muscles were present in the suboccipital region, and these were lightly stained. In postnatal rats, an obvious increase in the amount of fibers and muscle tissues was noted. At age P1, MDB fibers originated from the rectus capitis posterior minor muscle and merged into the atlanto-occipital membrane, which was closely attached to the spinal dura mater. As rats matured, MDB fibers gradually became denser and more organized. This study also showed that in postnatal rats, MDB was mainly composed of type I collagen fibers. By observing the development of MDB in SD rats, the function of MDB can be further understood. This study provides a morphological basis for future functional studies involving the MDB., (© 2020 American Association for Anatomy.)

Recent studies have evidenced that the anatomical structure now known as the myodural bridge (MDB) connects the suboccipital musculature to the cervical spinal dura mater (SDM). In humans, the MDB passes through both the posterior atlanto-occipital and the posterior atlanto-axial interspaces. The existence of the MDB in various mammals, including flying birds (Rock pigeons and Gallus domesticus) has been previously validated. Gentoo penguins are marine birds, able to make 450 dives per day, reaching depths of up to 660 feet. While foraging, this penguin is able to reach speeds of up to 22 miles per hour. Gentoo penguins are also the world's fastest diving birds. The present study was therefore carried out to investigate the existence and characteristics of the MDB in Gentoo penguin (Pygoscelis papua), a non-flying, marine bird that can dive. For this study, six Gentoo penguin specimens were dissected to observe the existence and composition of their MDB. Histological staining was also performed to analyze the anatomic relationships and characteristic of the MDB in the Gentoo penguin. In this study, it was found that the suboccipital musculature in the Gentoo penguin consists of the rectus capitis dorsalis minor (RCDmi) muscle and rectus capitis dorsalis major (RCDma) muscle. Dense connective tissue fibers were observed connecting these two suboccipital muscles to the spinal dura mater (SDM). This dense connective tissue bridge consists of primarily type I collagen fibers. Thus, this penguin's MDB appears to be analogous to the MDB previously observed in humans. The present study evidences that the MDB not only exists in penguins but it also has unique features that distinguishes it from that of flying birds. Thus, this study advances the understanding of the morphological characteristics of the MDB in flightless, marine birds., Competing Interests: Haichang Ocean Park Holding Co., Ltd. is responsible for the breeding of Gentoo Penguin (Pygoscelis Papua) and provides the basic data related to the penguin specimens for this research group. Another part of their work is the study and popularization of science related to penguins. The authors have declared that no competing interests exist. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

The paracondylar process is an exostosis, situated lateral to the occipital condyles, which expands towards the transverse process of the atlas. The epitransverse process of the atlas is a bony outgrowth that extends from the transverse process towards the occiput. Ponticulus posterior is a bony bridge that spans from the lateral mass of the atlas towards the posterior extremity of the vertebral artery groove. They are important anatomical variations. In this article, we analyze a rare situation of concomitant presence of ponticulus posterior, foramen arcuate, paracondylar process and epitransverse process, all of them situated on the right side of an individual with artificial cranial deformation from the fifth century AD. The paracondylar process and the epitransverse process form an accessory atlantooccipital joint. The expression of these variations, though under genetic influence, might have also been influenced by artificial cranial deformation. To our knowledge, this association has not been reported. The epitransverse process and the ponticulus posterior are important because of the positional relationship with the vertebral artery on which they may exert compression effects generating blood flow disorders. The paracondylar process is located at the insertion of rectus capitis lateralis, an important surgical landmark, which could be affected by the presence of the paracondylar process, thus leading to possible difficulties in orientation and iatrogenic trauma. This case contributes to extending the knowledge regarding anatomical variations, being of great use to the contemporary medical field, especially surgery.

Background: We herein outline the experience matured in our equipped Cranio-Vertebral Junction Laboratory for anatomic dissection., Methods: An extreme lateral approach (ELA) was performed on 4 fresh cadavers and submandibular approach was performed on 5. An endoscope and navigation-assisted far lateral approach (FLA) was performed in 5 injected specimens. In these specimens, a transoral approach was also performed, as well as a neuronavigation-assisted comparison between transoral and transnasal explorable distances., Results: As calculated with neuronavigation, statistically significant differences both in the explored craniocaudal (P = 0.003) and lateral (P = 0.008) distances were observed between the transoral approach and endoscopic endonasal approach. In FLA, neuronavigation facilitated identification and partial removal of the occipital condyle; in one case, during endoscopic intradural exploration, tearing of the emerging roots of the 11th cranial nerve occurred. In ELA, the site where the accessory nerve pierces into the sternocleidomastoid muscle was found at a distance from the tip of the mastoid between 3 and 4 cm., Conclusions: During dissections, as in the clinical setting, endoscope and image guidance give the surgeon a constant orientation, increasing the accuracy and the safety of the approach. Nonetheless, the encumbrance of the endoscope could represent a limit in deep and narrow corridors as those running across the craniovertebral junction, especially in "oblique" FLA and ELA, in which the surgical target is often hidden by a delicate tangle of nerves and vessels. Its use appears more suitable and safer in "straight" approaches as transoral and transnasal in which there are no neurovascular structures interposed., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Introduction: There are many craniometric measurements that are used in evaluating craniovertebral junction (CVJ) pathologies such as basilar invagination, atlantoaxial dislocation and platybasia. Therefore, it is important to determine the normal reference range of the craniometric measurements. This study aims to determine the morphometric reference values of the bony structures in the CVJ from cone-beam computed tomography (CBCT) images of a group of South Eastern Anatolian population., Materials and Methods: The CBCT images of 300 individuals were retrospectively evaluated. 14 parameters on midsagittal and 2 parameters on the coronal plane were studied. The data were statistically evaluated., Results: Measurement results were found as follows; the distances between odontoid process (OP) and McGregor line as 0.31 ± 3.22 mm, OP and Chamberlain line 1.06 ± 3.22 mm, OP and McRae line 5.30 ± 1.59 mm, OP and Fischgold digastric line 8.70 ± 4.12 mm, OP and Fischgold bimastoid line - 5.15 ± 4.86 mm, length of McRae line 35.58 ± 2.52 mm, atlantodental interval 1.28 ± 0.48 mm, posterior atlantodental interval 19.54 ± 2.24 mm, basion axial interval 4.01 ± 1.83 mm, basion dental interval 4.92 ± 1.77 mm, length of Modified Ranawat line 28.66 ± 2.38 mm, length of Redlund-Johnell line 35.11 ± 4.09 mm, clivus canal angle 157.62° ± 11.85°, Welcher basal angle 130.83° ± 6.29°, craniocervical tilt 126.98° ± 12.24° and Powers ratio as 0.72 ± 0.06., Conclusion: In this study, the morphometric values were evaluated according to age and gender in individuals who did not have any radiologic anomalies. The normal reference ranges may be useful for researchers who are researching pathology in this region. It is recommended to conduct further studies with different populations to determine the normal reference range.

Purpose: The connective tissue between suboccipital muscles and the cervical spinal dura mater (SDM) is known as the myodural bridge (MDB). However, the adjacent relationship of the different connective tissue fibers that form the MDB remains unclear. This information will be highly useful in exploring the function of the MDB., Methods: The adjacent relationship of different connective tissue fibers of MDB was demonstrated based upon three-dimensional visualization model, P45 plastinated slices and histological sections of human MDB., Results: We found that the MDB originating from the rectus capitis posterior minor muscle (RCPmi), rectus capitis posterior major muscle (RCPma) and obliquus capitis inferior muscle (OCI) in the suboccipital region coexists. Part of the MDB fibers originate from the ventral aspect of the RCPmi and, together with that from the cranial segment of the RCPma, pass through the posterior atlanto-occipital interspace (PAOiS) and enter into the posterior aspect of the upper cervical SDM. Also, part of the MDB fibers originate from the dorsal aspect of the RCPmi, the ventral aspect of the caudal segment of the RCPma, and the ventral aspect of the medial segment of the OCI, enter the central part of the posterior atlanto-axial interspace (PAAiS) and fuse with the vertebral dura ligament (VDL), which connects with the cervical SDM., Conclusions: Our findings prove that the MDB exists as a complex structure which we termed the 'myodural bridge complex' (MDBC). In the process of head movement, tensile forces could be transferred possibly and effectively by means of the MDBC. The concept of MDBC will be beneficial in the overall exploration of the function of the MDB.

Purpose: The occipital condyles (OCs) are crucial anatomical structures in the cranial base. To our knowledge, there is no cone beam computed tomography (CBCT)-based study on the morphometric analysis of OCs. The aim of this study was to evaluate the morphometric analysis of OCs using CBCT., Methods: CBCT images of 200 OCs from 100 patients of which 39 males and 61 females in the age group of 18-67 years were included in the study population. Linear and angular measurements of OCs were performed., Results: The average OC width, length, height, sagittal angle, and effective height were 10.3 ± 1.3 mm, 19.6 ± 2.0 mm, 9.1 ± 1.4 mm, 7.4 ± 1.7 mm, and 35.3 ± 5.2 mm. Condylar width and sagittal angle measurements were found significantly different between the right and left sides; and were not found significant difference between the right and left sides in the measurements of condylar height, length, and effective height. Also the average intercondylar anterior distance (ICAD), intercondylar posterior distance (ICPD), distance between the basion and the anterior apex of the occipital condyle (B-AAOC), distance between the basion and posterior apex of the occipital condyle (B-PAOC), distance between the opisthion and anterior apex of occipital condyle (O-AAOC), and distance between the opisthion and posterior apex of occipital condyle (O-PAOC) were 20.9 ± 1.5 mm, 44.0 ± 2.0 mm, 12.3 ± 1.9 mm, 34.5 ± 4.2 mm, 29.8 ± 1.7 mm, and 27.0 ± 2.1 mm. There was not significant difference in the morphometric measurements among age groups. All morphometric measurements showed a significant difference depending on gender., Conclusions: The morphometric evaluation of OCs may be effectively examined using CBCT. Linear and angular measurements data of OCs in the present study may be used as a reference database for future morphometric and surgical investigations.

The aim of this study is to evaluate the anatomical relationship between the bony structures and ventral neurovascular structures around craniovertebral junction (CVJ). Eleven fresh-frozen cadaveric specimens were dissected around CVJ. The anatomical relationships were evaluated between C1 bony structures (midline, lateral margin of the C1 lateral mass (LM) and C1 transverse process (TP)) and ventral neurovascular structure such as ICA and HN. Morphometric evaluation of occipital condyle was also performed. The diameter of the HN and the ICA was 2.4 ± 0.5 mm and 5.1 ± 0.2 mm. The ICA was located lateral to the C1 LM in 44.4% (ICA Group 1) and in front of lateral half of the C1 LM in 55.6% (ICA Group 2). The HN was located lateral to the C1 LM in 85% (HN Group 1) and in front of lateral half of the C1 LM in 15% (HN Group 2). HN Group 2 was significantly more common in ICA Group 2 (p < 0.05, OR = 2.00, 95% CI: 1.07-3.71). There was significant correlation between ICA and HN in terms of the distance from the midline, C1 LM and TP (r = 0.67, 0.87 and 0.76 respectively, P < 0.01). In conclusion, the HN location is related with ICA location and the medially located ICA is a risk factor of the HN located ventral to the C1 LM. These results demonstrate the vulnerability of the neurovascular structures during CVJ surgery and suggest that preoperative 3D-CTA or enhanced CT scan can be useful in guiding surgical technique., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Within many institutional collections are skeletal and mummified human remains representing a part of our species' adaptation and evolution to various biocultural environments. Archaeologically recovered individuals come from deep into our past, and possess information that provides insight into population history, genetics, diet, health and other questions relevant to all living peoples. Academic concerns have been raised regarding the reinterment of these collections due to the rise of the international repatriation movement, the passage of various laws and implementation of institutional policies. While all potential research questions cannot be anticipated, the proactive documentation of collections is one way to ensure primary data are maintained for future study. This paper explores developments in digitization technology that allow the archive of virtual copies of human remains, and an example of how anatomical and archaeological collections can be digitized towards pragmatic research goals. The anatomical variability of the human atlanto-occipital (AO) articular surfaces was studied using non-metric categorical shape, 2D measurement and 3D morphometric analyses to provide reference standards for the reassociation of individuals from commingled skeletal remains, such as found in some archaeological sites or forensic investigations including mass grave or mass disaster recovery scenes. Results suggest that qualitative shape observations and caliper-derived measurements of the articulating AO condyles tend to display significant sexual dimorphism and biological ancestry-related size and shape differences. Variables derived from a scanned 3D mesh, such as condylar angle and articular surface curvature, quantify biomechanical variation and display a stronger congruency within individuals. It is recommended that a two-stage approach involving initial screening and identification of possible reassociation candidates is accomplished with a linear osteometric approach, followed by 3D laser scanning of the candidate joint surfaces for morphometric analyses to confirm reassociations when destructive DNA typing is not allowed or otherwise impractical due to cost or other resource restrictions., (© 2016 Anatomical Society.)

Background: Imaging of the craniocervical junction (CCJ) after trauma is crucial for injury detection and description. Of all the anatomic measurements of the CCJ, the normal value of atlanto-occipital interval (AOI) is not yet well established in adults. The aim of our study is to determine the normal values of the AOI in Nigerians aged between 21 and 60 years using multidetector computed tomography (MDCT) scan and to determine racial, age, and sex differences., Methods: This was a prospective observational study done at Memfys Hospital for Neurosurgery, Enugu, Nigeria, between May 2016 and April 2017. There were 240 subjects (120 men and 120 women) divided into the following age groups: 21-30, 31-40, 41-50, and 51-60 years. Non-Nigerians and those with preexisting CCJ abnormalities were excluded. Normal values were those within the 95% confidence interval. Results were analyzed for possible sex and age variations and compared with the available literature for racial differences. Ethical approval was obtained for this study., Results: The measured normal computed tomography value of the AOI in adult Nigerians was 1.181 ± 0.018 mm. The values in the age groups of 21-30, 31-40, 41-50, and 51-60 years were 1.279 ± 0.038, 1.164 ± 0.033, 1.151 ± 0.029, and 1.133 ± 0.033 mm, respectively (P < 0.05). The average normal values in men and women were 1.188 ± 0.025 and 1.174 ± 0.026 mm, respectively. The interobserver reliability test using the Cronbach α was 0.938., Conclusions: AOI values in this study were higher than previous MDCT-based values in non-African populations. The AOI decreased linearly with age and did not show any sex difference., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Purpose: During routine dissection of the anterior craniocervical junction (CCJ), a variant ligament just anterior to the articular capsule of the atlantooccipital joint was observed. To our knowledge, no literature has previously described this ligament. Therefore, the aim of this study was to clarify the anatomy, incidence, and biomechanics of this undescribed structure of the anterior atlantooccipital joint., Methods: Twenty-six sides from 13 fresh-frozen adult cadavers were used for this study and the morphology of the variant ligament examined. When present, its length, width, thickness, and the angle from the midline of the CCJ were measured., Results: The variant ligament identified, when present, is distinct and located anterior to the atlantooccipital joint capsule traveling between the occipital bone and the transverse process of the atlas. The ligament was found on 12 of 26 sides (46.2%). The mean length of the ligament was 32.0 ± 5.5 mm. The ligament became taut with contralateral lateral flexion and the ipsilateral rotation of the atlantooccipital joint., Conclusions: We propose that this ligament may be termed the lateral oblique atlantooccipital ligament. To date, this structure has not been described in any textbooks or reports in the extant medical literature. Although its function is not clear, based on its course and connections, it might function as a secondary stabilizer of the atlantooccipital joint. As the stability of the craniocervical junction is of paramount importance, knowledge of normal and variant anatomical structures in this region is important for the surgeon treating patients with pathology of this region. These slides can be retrieved under Electronic Supplementary Material.

The myodural bridge (MDB) is a dense connective tissue that connects muscles with the cervical spinal dura mater via the posterior atlanto-occipital and atlato-axial interspaces. To date, the physiological function of the MDB has not been fully elucidated. Recent studies have identified the presence of the MDB in mammals, but very little information is available on the existence of the MDB in avifauna. We selected Gallus domesticus to explore the existence and the fiber property of the MDB in avifauna. We found that in this species, fibers originating from the ventral aspect of the rectus capitis dorsal minor are fused with the dorsal atlanto-occipital membrane and that numerous trabeculae connect the dorsal atlanto-occipital membrane with the cervical spinal dura mater. Furthermore, the occipital venous sinus is located between the trabeculae. The MDB is mainly composed of collagen type I fibers. Our results show that the MDB is present in G. domesticus and lead us to infer that the MDB is a highly conservative evolutionary structure which may play essential physiological roles.

Context: Disorders of the rectus capitis posterior minor (RCPm) muscles have been associated with chronic headache. Magnetic resonance (MR) imaging protocols currently used in clinical settings do not result in image sets that can be used to adequately visualize the integrity of occipitoatlantal structures or to definitively quantify time-dependent functional morphologic changes., Objective: To develop an MR imaging protocol that provides the superior image quality needed to visualize occipitoatlantal soft tissue structures and quantify time-dependent pathologic changes., Methods: Asymptomatic participants were recruited from the Michigan State University College of Osteopathic Medicine student body. Magnetic resonance imaging data were collected from each participant at enrollment and 2 weeks after enrollment using a 3T magnet. A conventional spin-echo pulse sequence was used to construct 24 axial, T1-weighted images with the following measurement parameters: repetition time, 467 milliseconds; echo time, 13.5 milliseconds; number of excitations, 4; slice thickness, 3.0 mm; and in-plane resolution, 0.625×0.625 mm. Image planes were aligned approximately perpendicular to the long axes of the RCPm muscles to facilitate the authors' ability to accurately draw regions of interest around the specific muscle boundaries. Cross-sectional area (CSA) of the right and left RCPm muscles was quantified for each participant at the 2 points in time. The null hypothesis was that there would be no significant difference between mean values of muscle CSA collected at enrollment and 2 weeks after enrollment for a given participant and a given side of his or her body., Results: Thirteen participants were enrolled. No significant difference was found between mean values of either right or left RCPm muscle CSA for any of the participants measured at enrollment and 2 weeks after enrollment (all P>.05)., Conclusion: The protocol achieves the superior image quality necessary to compare the functional form of occipitoatlantal structures at progressive points in time.

Background: The available literature on the anatomy and imaging of the craniovertebral junction (CVJ) focusses on the osteometric indices described for the detection of abnormal relationships between the components of CVJ. However, a knowledge of the normal osteometry of this region in the Indian population is critically important for the operating surgeon as it may influence the surgical technique as well as the choice, size and configurations of the implants. It is also important to determine whether critical differences exist between the osteometric data of Indians and the rest of the world for this part of the anatomy. Accordingly, the present study is an attempt to quantitate the osteometric indices for the anatomically normal CVJ in Indian subjects., Materials and Methods: We retrospectively studied the imaging data of 49 consecutive adult patients (31 males, 18 females) who underwent a computed tomographic (CT) angiogram for suspected vascular conditions unrelated to the craniovertebral junction. Several parameters related to the atlanto-dental relationship, foramen magnum, atlas and axis vertebrae were recorded, including the dimensions of the commonly instrumented bony regions and also the indices related to the CVJ bony relationships. The data was also compared between the two genders, statistically through the Student's t-test using the statistical program "R"., Results: No patient had an atlanto dens interval >2.5 mm. The mean distance of the odontoid tip from the McRae line in this series was 5.11 mm and no patient had the odontoid tip above the McRae line. Female subjects had significantly smaller diameters of C1 lateral masses and odontoid screw trajectory length when compared to males. Additionally, in the Indian population, the length range of odontoid screw trajectory and the thickness of the narrowest part of the C2 pedicles was smaller with respect to similar data from other geographical regions. However, the rest of the parameters resembled the data from studies conducted on populations with other ethnicities., Conclusion: The osteometric parameters of the CVJ in the Indian population are largely similar to those described globally. However, there are some important differences too which can influence the design of surgical implants suited to the Indian population., Competing Interests: There are no conflicts of interest

Objective: A precise anatomical description of the alar ligaments is important to better understand their biomechanical and pathologic implications. Although there are several studies regarding their anatomy, the literature is inconsistent. To our knowledge, there are no reports that compare cadaveric morphologic findings with computed tomography (CT) images of the alar ligaments., Methods: Eight sides from 4 fresh-frozen cadaveric specimens were used in this study. After routine dissection of the craniocervical junction, the alar ligaments were exposed. We carried out measurements of the alar ligaments, their position within the craniovertebral junction, and their relation to the dens and adjacent structures. Fine-cut CT of the specimens was performed, and the measurements were later compared with the original cadaveric dissections., Results: Alar ligaments were attached to the upper half of the lateral surface of the dens and ran laterally to its insertion just medial to the occipital condyle. The ligaments were found to have an ovoid cross-sectional area with a nearly horizontal caudocranial trajectory and comparable diameters in both anteroposterior and superoinferior directions between the CT and cadaveric measurements., Conclusions: There were small but not statistically significant differences in the measurements between the cadaver specimens and the CT images. There was however, a strong correlation between the proximal and distal insertions, as well as the orientation of the fibers, that suggests CT images can be an appropriate approach to the study of the anatomical and 3-dimensional features of the alar ligaments., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Background: Descriptions of intracranial extensions of vertebral venous plexuses are lacking., Objective: To identify vertebral venous plexuses at the craniocervical junction in cadavers and describe them., Methods: The authors dissected 15 ink-injected, formalin-fixed, adult cadaveric heads and measured cranial extensions of the spinal venous plexuses., Results: All specimens had vertebral venous plexuses at the craniocervical junction composed of multiple interwoven vessels concentrated anteriorly (anterior vertebral plexuses), posteriorly (posterior vertebral venous plexuses), and laterally (lateral vertebral venous plexuses). Veins making up the plexus tended to be largest for the anterior internal vertebral venous plexus. On 33%, a previously unnamed lateral internal vertebral venous plexus was identified that connected to the lateral marginal sinus. The anterior external vertebral venous plexus connected to the basilar venous plexus via transclival emissary veins in 13%; remaining veins connected either intracranially via small perforating branches through the anterior atlanto-occipital membrane (33%) or had no direct gross connections inside the cranium (53%). The anterior internal vertebral plexus, which traveled between layers of the posterior longitudinal ligament, connected to the anterior half of the marginal sinus in 33% and anterolateral parts of the marginal sinus in 20%. The posterior internal venous plexus connected to the posterior aspect of the marginal sinus on 80% and into the occipital sinus in 13.3%. The posterior external venous plexus connected to veins of the hypoglossal canal in 20% and into the posterior aspect of the marginal sinus in 13.3%., Conclusion: Knowledge of these connections is useful to neurosurgeons and interventional radiologists., (Copyright © 2017 by the Congress of Neurological Surgeons)

Objective: Various authors have described the morphology of the alar ligaments; however, there are no reports of a cadaveric study focusing on their attachments onto the dens. The purpose of this study was to use fresh cadaveric specimens to describe in detail different attachment patterns of the alar ligaments onto the dens., Methods: This study used 22 sides from 11 fresh frozen cadaveric heads. Specimens were obtained from 8 men and 3 women who were 67-99 years old at death. Dissection of the exact attachment of the alar ligaments onto the dens was observed from posterior, superior, and anterior views under the surgical microscope., Results: From a posterior view, 6 alar ligaments passed over the tip of the dens, and 16 alar ligaments attached onto the posterolateral part of the dens; the right and left ligaments had no continuity. From a superior view, the alar ligament was classified in 2 ways: depending on the covered area of the dens (entirely or posterior two thirds) and continuity of the alar ligament (transversely, separately, or combination). Fourteen alar ligaments covered the posterior two thirds of the dens. From an anterior view, in 1 specimen, the alar ligament extended to the anterior surface of the dens., Conclusions: Wide posterolateral anchoring to the dens coupled with the nearly horizontal trajectory explains the biomechanical advantage of the alar ligaments in undertaking a stabilizing function in limiting head rotation that would otherwise be ineffective in the case of weaker attachments or a more vertical orientation., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Objective: The alar ligaments are among the primary ligamentous structures contributing to craniovertebral stability. The purpose of this study is to clarify the morphology of the alar ligament using fresh cadaveric specimens., Methods: Twenty-two fresh, frozen cadaveric alar ligaments were used in this study. The occiput, C1, and C2 were removed en bloc from each specimen, and various measurements and observations including variations were documented., Results: The angle formed by both alar ligaments was measured in a neutral position (149 ± 24.19 degrees), as well as during forced flexion (134.18 ± 27.08 degrees) and extension (163.81 ± 24.54 degrees)., Conclusions: The current cadaveric evaluation offers an interesting window into better understanding the anatomy of the alar ligaments., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Objective: Four layers of ligamentous stabilizers comprise the craniocervical junction, and the second layer is composed of apical and paired alar ligaments. The purpose of this study is to establish the tensile strength of the alar ligaments for better understanding the implications that can arise from trauma and other pathologies in the craniocervical region., Methods: Nineteen sides from 10 fresh frozen adult cadaveric Caucasian heads were used in this study. The specimens were derived from 6 males and 4 females, and the age of the cadavers at death ranged from 67-90 years old. To measure the tensile strength, a tensile testing machine (M2-200, Mark-10 Corporation, Copiague, New York, USA) was used in this study., Results: The force (N) necessary until failure for all alar ligaments ranged from 87-346 N with a mean of 186.9 ± 69.7 N. There was a significant difference when comparing tensile strength between males and females., Conclusions: Further studies will be necessary to determine their importance as secondary stabilizers and measure their ability to support similar forces when subject to rotation and lateral bending forces, as well as with flexion-extension., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Objective: Distal branches of the C1 nerve that travel with the hypoglossal nerve have been well investigated but relationships of C1 and the hypoglossal nerve near the skull base have not been described in detail. Therefore, the aim of this study was to investigate these small branches of the hypoglossal and first cervical nerves by anatomic dissection., Methods: Twelve sides from 6 cadaveric specimens were used in this study. To elucidate the relationship among the hypoglossal, vagus, and first and cervical nerve, the mandible was removed and these nerves were dissected under the surgical microscope., Results: A small branch was found to always arise from the dorsal aspect of the hypoglossal nerve at the level of the transverse process of the atlas and joined small branches from the first and second cervical nerves. The hypoglossal and C1 nerves formed a nerve plexus, which gave rise to branches to the rectus capitis anterior and rectus capitis lateralis muscles and the atlanto-occipital joint., Conclusions: Improved knowledge of such articular branches might aid in the diagnosis and treatment of patients with pain derived from the atlanto-occipital joint. We believe this to be the first description of a branch of the hypoglossal nerve being involved in the innervation of this joint., (Copyright © 2017 Elsevier Inc. All rights reserved.)

In 1922, Paul Hecker, a French physician and Head of Anatomy at the Medical College of Strasbourg, published a sentinel thesis on the ligaments of the craniocervical junction based on a study of comparative anatomy. Unfortunately, this dissertation has been lost to history and until now, was unavailable in the English language. Herein, we present a translation of Hecker's work with an update in its nomenclature, which with modern imaging capabilities of the craniocervical junction is germane and timely. Clin. Anat. 30:322-329, 2017. © 2017 Wiley Periodicals, Inc., (© 2017 Wiley Periodicals, Inc.)

Purpose: Our study highlights the morphometry of the partial and complete atlas occipitalization (AOZ), its coexistence with fusions of the 2nd and 3rd cervical vertebrae and morphological and morphometric abnormalities of the posterior cranial fossa that are of paramount neurological importance., Methods: One hundred and eighty adult dry skulls, the atlas and axis vertebrae were examined., Results: Four skulls (2.2 %) showed AOZ. Two of them (1.1 %) presented a partial AOZ, one male skull (0.6 %) a complete AOZ and a female skull (0.6 %) had a fused left hemiatlas with the occipital bone and a fusion of the 2nd and 3rd cervical vertebrae. The inner anteroposterior and transverse diameters of the foramen magnum (FM) in the control group were 34.6 ± 3.46 and 29.3 ± 3.47 mm. Only the skull with the complete AOZ had a reduced outer anteroposterior diameter of the FM (29.8 mm), while no specimen was found with a reduced transverse diameter. A wide total decrease (range 13.1-50.9 %) in the surface area of the FM in skulls with AOZ was detected. Extracranial, the clivus length in two skulls with AOZ was smaller than the normal range. No skull was detected with a reduction in the intracranial length of the clivus. All skulls with the AOZ had a vermian fossa., Conclusions: The study adds important morphometric details about the partial and complete AOZ and correlates the phenomenon of synostosis with the narrowing of the FM, particularly in the case of complete AOZ. Awareness of the AOZ and other fusions of the upper cervical vertebrae and their topographical relations and attendant problems are of paramount importance to surgeons, when operate to the craniocervical junction, or interpret imaging studies to plan a safe surgery for nerve or spinal tissue decompression.

Background and Purpose: Widening of the occipital condyle-C1 interval is the most specific and sensitive means of detecting atlanto-occipital dislocation. Recent studies attempting to define normal measurements of the condyle-C1 interval in children have varied substantially. This study was performed to test the null hypothesis that condyle-C1 interval morphology and joint measurements do not change as a function of age., Materials and Methods: Imaging review of subjects undergoing CT of the upper cervical spine for reasons unrelated to trauma or developmental abnormality was performed. Four equidistant measurements were obtained for each bilateral condyle-C1 interval on sagittal and coronal images. The cohort was divided into 7 age groups to calculate the mean, SD, and 95% CIs for the average condyle-C1 interval in both planes. The prevalence of a medial occipital condyle notch was calculated., Results: Two hundred forty-eight joints were measured in 124 subjects with an age range of 2 days to 22 years. The condyle-C1 interval varies substantially by age. Average coronal measurements are larger and more variable than sagittal measurements. The medial occipital condyle notch is most prevalent from 1 to 12 years and is uncommon in older adolescents and young adults., Conclusions: The condyle-C1 interval increases during the first several years of life, is largest in the 2- to 4-year age range, and then decreases through late childhood and adolescence. A single threshold value to detect atlanto-occipital dissociation may not be sensitive and specific for all age groups. Application of this normative data to documented cases of atlanto-occipital injury is needed to determine clinical utility., (© 2016 by American Journal of Neuroradiology.)

OBJECT There is a significant deficiency in understanding the biomechanics of the pediatric craniocervical junction (CCJ) (occiput-C2), primarily because of a lack of human pediatric cadaveric tissue and the relatively small number of treated patients. To overcome this deficiency, a finite element model (FEM) of the pediatric CCJ was created using pediatric geometry and parameterized adult material properties. The model was evaluated under the physiological range of motion (ROM) for flexion-extension, axial rotation, and lateral bending and under tensile loading. METHODS This research utilizes the FEM method, which is a numerical solution technique for discretizing and analyzing systems. The FEM method has been widely used in the field of biomechanics. A CT scan of a 13-month-old female patient was used to create the 3D geometry and surfaces of the FEM model, and an open-source FEM software suite was used to apply the material properties and boundary and loading conditions and analyze the model. The published adult ligament properties were reduced to 50%, 25%, and 10% of the original stiffness in various iterations of the model, and the resulting ROMs for flexion-extension, axial rotation, and lateral bending were compared. The flexion-extension ROMs and tensile stiffness that were predicted by the model were evaluated using previously published experimental measurements from pediatric cadaveric tissues. RESULTS The model predicted a ROM within 1 standard deviation of the published pediatric ROM data for flexion-extension at 10% of adult ligament stiffness. The model's response in terms of axial tension also coincided well with published experimental tension characterization data. The model behaved relatively stiffer in extension than in flexion. The axial rotation and lateral bending results showed symmetric ROM, but there are currently no published pediatric experimental data available for comparison. The model predicts a relatively stiffer ROM in both axial rotation and lateral bending in comparison with flexion-extension. As expected, the flexion-extension, axial rotation, and lateral bending ROMs increased with the decrease in ligament stiffness. CONCLUSIONS An FEM of the pediatric CCJ was created that accurately predicts flexion-extension ROM and axial force displacement of occiput-C2 when the ligament material properties are reduced to 10% of the published adult ligament properties. This model gives a reasonable prediction of pediatric cervical spine ligament stiffness, the relationship between flexion-extension ROM, and ligament stiffness at the CCJ. The creation of this model using open-source software means that other researchers will be able to use the model as a starting point for research.

OBJECTIVE The microscopic transoral, endoscopic transnasal, and endoscopic transoral approaches are used alone and in combination for a variety of craniovertebral junction (CVJ) pathologies. The endoscopic transoral approach provides a more direct exposure that is not restricted by the nasal cavity, pterygoid plates, and palate while sparing the potential morbidities associated with extensive soft-tissue dissection, palatal splitting, or mandibulotomy. Concerns regarding the extent of visualization afforded by the endoscopic transoral approach may be limiting its widespread adoption. METHODS A dissection of 10 cadaver heads was undertaken. CT-based imaging guidance was used to measure the working corridor of the endoscopic transoral approach. Measurements were made relative to the palatal line. The built-in linear measurement tool was used to measure the superior and inferior extents of view. The superolateral extent was measured relative to the midline, as defined by the nasal process of the maxilla. The height of the clivus, odontoid tip, and superior aspect of the C-1 arch were also measured relative to the palatal line. A correlated clinical case is presented with video. RESULTS The CVJ was accessible in all cases. The superior extent of the approach was a mean 19.08 mm above the palatal line (range 11.1-27.7 mm). The superolateral extent relative to the midline was 15.45 mm on the right side (range 9.6-23.7 mm) and 16.70 mm on the left side (range 8.1-26.7 mm). The inferior extent was a mean 34.58 mm below the palatal line (range 22.2-41.6 mm). The mean distances were as follows: palatal line relative to the odontoid tip, 0.97 mm (range -4.9 to 3.7 mm); palatal line relative to the height of the clivus, 4.88 mm (range -1.5 to 7.3 mm); and palatal line relative to the C-1 arch, -2.75 mm (range -5.8 to 0 mm). CONCLUSIONS The endoscopic transoral approach can reliably access the CVJ. This approach avoids the dissections and morbidities associated with a palate-splitting technique (velopharyngeal insufficiency) and the expanded endonasal approach (mucus crusting, sinusitis, and potential lacerum or cavernous-paraclival internal carotid artery injury). For appropriately selected lesions near the palatal line, the endoscopic transoral approach appears to be the preferred approach.

Background: This study describes the ultrasonographic appearance of the atlanto-occipital space and ultrasound-guided collection of cerebrospinal fluid (CSF) in cattle. The atlanto-occipital space of 73 euthanized cattle (group A) and 14 live cattle with neurological disorders (group B) was examined in the sagittal and transverse planes using a 5.0-MHz convex transducer. Optimal ultrasonograms were frozen on the screen and various variables were measured in both planes using the electronic cursors. Puncture of the subarachnoid space was achieved using a spinal needle introduced in the median plane in a caudoventral direction while the spinal cord was viewed in longitudinal section. The examination of cerebrospinal fluid (CSF) was limited to gross evaluation and a red blood cell count., Results: The spinal cord and the subarachnoid space were seen in the sagittal plane in all cattle. In group A, the mean distance between the skin and subarachnoid space was 38.6 mm, the mean depth of the subarachnoid space dorsal and ventral to the spinal cord was 8.9 mm and 8.4 mm, respectively, the mean diameter of the spinal cord was 9.9 mm and the mean diameter of the dural sac was 26.9 mm. These measurements were similar on transverse images. For collection of CSF from the subarachnoid space, the spinal cord was viewed in longitudinal section. All CSF samples from group A were colourless and clear and the median erythrocyte count was 2.5/μl. Ultrasonographic findings and results of CSF analysis were similar in group B., Conclusions: Ultrasonography is useful for the visualisation of the spinal cord and facilitates the safe collection of CSF from the atlanto-occipital space in cattle.

The transcondylar variation of the far-lateral, retrosigmoid approach is intended for pathologies in the anterolateral portion of the foramen magnum. That area is more clearly visualized when a fraction of the ipsilateral occipital condyle is removed. In this study, the biomechanical effect of this approach on occiput-C2 rotation was investigated. Our hypothesis was that the biomechanical characteristics are significantly altered following the transcondylar approach. Five human cadaveric upper cervical spine specimens (occiput-C7) were used in the study. Torsional moments were applied from zero to a maximum of 1.5 N m to the left and to the right using a mechanical testing machine. The resulting rotational motions of the O-C1, C1-2, and O-C2 segments were measured in the intact specimen and after a simulated right-sided transcondylar approach with resection of 2/3 of the condyle, confirmed by CT scanning and visual inspection. After the posterior two-thirds of the occipital condyle were removed, the neutral zone (NZ) increased 1.3° to the left and 2° to the right at C0-C1, and 7.4° to the left and 6.2° to the right at C1-2. The cumulative increase in NZ between O and C2 was 8.7° to the left and 8.2° to the right. The transcondylar approach also resulted in significant increases in range of motion (ROM) in axial rotation to both sides in all segments. ROM increased 2.8° to the left and 2.4° to the right between C0 and C1, 7.3° to the left and 5.4° to the right between C1 and C2, and 10.1° to the left and 7.8° to the right between CO and C2. Upon inspection, the area of the occipital condyle where the alar ligament attaches had been completely removed in three of the five specimens. Removing the posteromedial two-thirds of one occipital condyle alters the normal axial rotational movements of the craniovertebral junction on both sides. The insertion of the alar ligament can be inadvertently removed during condylar resection, and this could contribute to atlanto-axial instability. There is a biomechanical substrate to cranio-cervical instability following a transcondylar approach; these patients may need to be followed over several years to ensure it does not progress and necessitate occipito-cervical fusion., (© 2015 Wiley Periodicals, Inc.)

The craniovertebral junction (CVJ) has unique anatomical structures that separate it from the subaxial cervical spine. In addition to housing vital neural and vascular structures, the majority of cranial flexion, extension, and axial rotation is accomplished at the CVJ. A complex combination of osseous and ligamentous supports allow for stability despite a large degree of motion. An understanding of anatomy and biomechanics is essential to effectively evaluate and address the various pathological processes that may affect this region. Therefore, the authors present an up-to-date narrative review of CVJ anatomy, normal and pathological biomechanics, and fixation techniques.

Cisternal puncture in dogs and cats is commonly carried out. This article describes the percutaneous ultrasound anatomy of the cisternal region in the dog and the cat and an indirect technique for ultrasound-guided cisternal puncture. Ultrasound images obtained ex vivo and in vivo were compared with anatomic sections and used to identify the landmarks for ultrasound-guided cisternal puncture. The ultrasound-guided procedure was established in cadavers and then applied in vivo in seven dogs and two cats. The anatomic landmarks for the ultrasound-guided puncture are the cisterna magna, the spinal cord, the two occipital condyles on transverse images, the external occipital crest and the dorsal arch of the first cervical vertebra on longitudinal images. Using these ultrasound anatomic landmarks, an indirect ultrasound-guided technique for cisternal puncture is applicable in the dog and the cat., (© 2014 Blackwell Verlag GmbH.)

Objective: To evaluate objectively the anatomic areas of the cranial base exposed by a three-dimensional (3D) endoscope-assisted far lateral approach., Methods: A series of far lateral approaches with only condyle resection, with only jugular tubercle resection, with both partial condyle and total jugular tubercle resection, and without occipital condyle and jugular tubercle resection were performed on 10 cadaveric heads (20 sides). To assess properly the exposure of major anatomic and neurovascular structures, the intradural anatomy of the exposed craniocervical junction was divided into 8 compartments, including 3 superior cranial compartments, 3 inferior cranial compartments, and 2 spinal compartments., Results: The anteromedial compartments toward the midline were difficult to explore using the microscope and required the aid of the endoscope. The 3D endoscope provided general circumferential visualization of the anatomic structures, even without resection of the jugular tubercle, and afforded good visualization of the more lateral compartments. Safe and optimal surgical corridors for insertion of the endoscope were also identified., Conclusions: Use of a 3D endoscope allows for minimal resection of the condyle and jugular tubercle, better visualization of the surgical compartments toward the midline, and better in-depth surgical exploration of each intradural compartment. However, the 3D probe is still too large and restricts surgical maneuverability., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Unlabelled: Classic anatomical studies describe two membranes - atlanto-occipital and atlanto-axial in the posterior aspect of the craniocervical region. During many surgical procedures in this area, however, we have not found such membranes., Objective: To clarify the anatomical aspects and structures taking part of the posterior atlanto-occipital and atlanto-axial area., Method: Analysis of histological cuts of three human fetuses and anatomical studies of 8 adult human cadavers., Results: In both atlanto-occipital and atlanto-axial areas, we have observed attachment between suboccipital deep muscles and the spinal cervical dura. However, anatomical description of such attachments could not be found in textbooks of anatomy., Conclusion: Our study shows the absence of the classical atlanto-occipital and atlanto-axial membranes; the occipito-C1 and C1-C2 posterior intervals are an open area, allowing aponeurotic attachment among cervical dura mater and posterior cervical muscles.

Little is known about the chronological changes that occur in the topographical anatomy of the fetal vertebral artery (VA), especially at and above the occipitovertebral junction. We histologically examined paraffin-embedded horizontal, sagittal and frontal sections of the heads of 25 human embryos and fetuses of crown-rump length 20-110 mm, corresponding to 6-15 weeks of gestation. At 6 weeks, the VA ran anterosuperiorly through a large intracranial subdural space filled with loose mesenchymal tissue. This intracranial course was distant from the brain stem, suggesting that the developing brain did not "guide" the VA. Before 8-9 weeks, the VA appeared to take an almost straight upward course at the occipitovertebral junction. Later, however, the atlanto-occipital joint growing along the mediolateral axis caused the VA to curve at the junction area. In specimens before 10 weeks, the terminal of the VA, or the origin of the basilar artery, was on the anterior side of the inferior olive and near the jugular foramen. The fetal posterior inferior cerebellar artery originated at the same caudal site distant from the primitive cerebellum. Later, the terminal or origin moved rostrally to the level of the pons. These findings indicate that the basic branching pattern of the VA-basilar artery is independent of the developing brain, whereas the arterial courses are secondarily "corrected" by the growing brain and atlanto-occipital joint.

Background: The rotation stress test is recommended for assessing alar ligament integrity. Although some authors, in the literature regarding the rotation stress test, accept that rotation will occur during testing, estimates of range occurring with a normal test response vary between 20 and 40 degrees. None of these estimates are based on formal examination of the test., Objective: The purposes of this study were: (1) to examine the range of craniocervical rotation occurring during rotation stress testing for the alar ligaments in individuals who are healthy and (2) to investigate a measurement protocol for quantifying rotation., Design: A within-subject experimental study was conducted., Methods: Sixteen participants underwent magnetic resonance imaging in neutral and end-range rotation stress test positions. Measurements followed a standardized protocol relative to the position of the axis. A line connecting the transverse foramena of the axis created a reference plane. The position of the occiput in the head-neutral position was calculated as the angle formed between a line joining the foramena lacerum and the reference plane. Measurements were repeated at the end-range test position. Total rotation of the occiput was calculated as the difference in angles measured in neutral and test positions. Measurement was performed on 4 occasions, and reliability of measurements was assessed using the standard error of measurement (SEM) and the intraclass correlation coefficient (ICC)., Results: Measurement of rotation of the occiput relative to a stabilized axis ranged between 1.7 and 21.5 degrees (X=10.6, SD=5.1, SEM=1.14, ICC=.96, 95% confidence interval=.90-.98)., Limitations: Sustaining the test position for imaging increased the potential for loss of end-range position and image quality. Testing could be performed only in the neutral position, not in 3 planes as commonly described., Conclusions: The range of craniocervical rotation during rotation stress testing of intact alar ligaments should typically be 21 degrees or less. Rotation may be quantified using the method protocol outlined.

Background Context: In recent literature, a soft-tissue communication between the rectus capitis posterior major (RCPma) muscle and the cervical dura mater has been identified. To the best of our knowledge, this communication has yet to be validated from a histological perspective nor has it been examined for neural tissue., Purpose: The purpose of this study was to examine the composition and true continuity of the communication between the RCPma and the dura mater at a microscopic level. The communication was also inspected for the presence of proprioceptive neurons., Study Design: An anatomical and histological analysis of a novel structure in the atlantoaxial interspace., Methods: Gross dissection was performed on 11 cadavers to remove the RCPma, the soft-tissue communication, and a section of posterior cervical dura mater as one continuous unit. Paraffin embedding and sectioning followed by hematoxylin and eosin staining was conducted to validate the connection. Staining with antineurofilament protein fluorescent antibodies was performed to identify proprioceptive neural tissue on one specimen, and all findings were recorded via photographic documentation., Results: Histological investigation revealed a tendinous matrix inserting into both the RCPma and the posterior aspect of the cervical dura mater in all 11 specimens. In the one specimen examined for neural tissue, antineurofilament protein fluorescence revealed proprioceptive neurons within the communication. Immunoperoxidase staining demonstrated the insertion of these neurons into both the dura mater and the belly of the RCPma., Conclusions: The existence of a true connection between the RCPma and the cervical dura mater provides new insight in understanding the complex anatomy of the atlantoaxial interspace. The presence of a neural component within this connection suggests that it may serve another function aside from simply anchoring this muscle to the dura mater. Such a connection may be involved in monitoring dural tension and may also play a role in certain cervicogenic pathologies. This study also supports previous reports that no true membrane joins the posterior arch of the atlas to the laminae of the axis and contradicts the conventional belief that the ligamentum flavum joins these two structures., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Background: Recent new anatomical and histological features of craniocervical junction in dogs and cats were described providing evidence of differences between the carnivore species. No information on these structures in foxes exists., Results: Two parts of the alar ligaments were found. A longer one aroused from dens of axis to the internal (medial) surface of the occipital condyles and was called apical part. A shorter part originated from the entire length of the lateral edge of the dens of axis and terminated on the internal wall of the vertebral foramen of atlas and thus was called the lateral part. The transverse ligament of the atlas was widened in the mid region, above the dens of axis, and thickened at enthesis. Periosteal fibrocartilage was detected in the transverse ligament of the atlas at the enthesis, and sesamoid fibrocartilage was present on periphery in the middle of the ligament., Conclusions: The craniocervical junction in foxes differs in part from other carnivores such as dogs and cats but resembles that of mesaticephalic dogs. The sesamoid and periosteal fibrocartilage supports the transverse ligament of the atlas whereas the alar ligaments have no cartilage.

Introduction: Objective of this investigation was to evaluate the rotational mobility at the craniocervical junction and changes in the width of the subarachnoid space during head rotation in healthy volunteers using Magnetic Resonance Imaging (MRI)., Materials and Methods: In 30 healthy volunteers axial 3mm Half-Fourier Acquisition Single-Shot Turbo Spin-Echo (HASTE) sequences were obtained with the subject's head in neutral position, and in maximal rotation to the left and right respectively. All MRI examinations were evaluated by two neuroradiologists in consensus. The ranges of axial rotation at C0-C2 as well as the width of the subarachnoid space in neutral, and in maximal rotated position were measured. Student's t-tests were used to compare group differences., Results: Total range of right-to-left-rotation at C0-C2 was 59-183° with mean rotation to the right and left side of 70° (±12.7°) and 75° (±13.0°). Difference between degrees of rotation to both sides was on average 4.9° (±7.1°) with a significantly greater rotational range to the left compared to the right. In neutral position, distance between the dura and the ventral wall of the cervical spinal cord was 1.6-4.2mm. In active rotation interface between dura and myelon was evident in 19 volunteers with unilateral contact in 7, and bilateral contact in 12 cases., Conclusions: High variablity of rotational mobility at the craniocervical junction and attenuation of width of the subarachnoid space during head rotation are frequent findings in an asymptomatic population. Our results indicate that the assessment of these parameters is of limited diagnostic value in patients with whiplash-associated disorders., (Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.)

Our objectives were to establish a magnetic resonance (MR) protocol for the examination of, and then describe, the normal ligaments and the supporting structures of the occipitoatlantoaxial region. This was done in 10 cadaver dogs. In addition, MR images of three patients with cervical pain localized to the occipitoatlantoaxial region are included to provide examples of ligamentous abnormalities. All ligaments were hypointense in all pulse sequences. The apical, dorsal atlantoaxial, and dorsal longitudinal vertebral ligaments were seen best in the sagittal T1W and PD-weighted images. The transverse ligament was best visualized in the transverse plane in all pulse sequences and appeared to be confluent with the dorsal longitudinal vertebral ligament dorsal to the dens in the sagittal plane. A 20° dorsal plane reconstructed image in 0.6-mm slice thickness was necessary to visualize the alar ligaments, which were visible in 9/10 dogs. The dorsal longitudinal vertebral ligament appeared continuous with the apical ligament and tectorial membrane. Abnormalities in clinically affected dogs included thickening of the alar ligaments, absence of transverse ligament and elongation, and irregularity of the apical ligament., (© 2012 Veterinary Radiology & Ultrasound.)

Background Context: The craniocervical region is an osteoligamentous complex that provides structural stability and movement by means of numerous ligaments. Fundamental knowledge of these ligaments is important for physicians who treat patients with disorders of this region to reduce morbidity and mortality. There is a paucity of data in the literature regarding the morphology, function, and classification of the transverse occipital ligament (TOL)., Purpose: The purpose of this study was to investigate the prevalence, morphology, and variations of the TOL in a large number of adult human cadavers using dissection, histology, and digital radiography., Study Design: Cadaveric laboratory study., Sample: Thirty-two formalin-fixed human adult cadavers were dissected in the study. Fourteen cadavers were found to have a TOL., Outcome Measures: Measurements using a digital caliper, high-resolution digital photography, histologic staining with bright-field microscopy, and digital radiography., Methods: The posterior musculature and related soft tissues were dissected and underlying bony elements removed. The TOL was identified, isolated, measured, and then removed for histologic preparation with hematoxylin and eosin staining. Anteroposterior open-mouth digital radiographs of the upper cervical spine with monofilament attached to the TOL were used to demonstrate its relations to the occiput, atlas, and axis., Results: The TOL was present in 14 of 32 (44%) of the dissected cadavers (six male and eight female). Three types of TOLs were identified. Type 1 had bilateral connections to the alar ligaments and had fibers inserting onto the dens. Type 2 also had bilateral connections to the alar ligaments but did not have fibers inserting onto the dens. Type 3 neither had any connections to the alar ligaments nor had fibers that connected to the dens. Male cadavers always had a Type 1 TOL compared with 3 of 8 (38%) female cadavers and this difference was significant (p=.031). The TOL consisted of dense regular connective tissue with parallel arrangements of collagen fibers and interposed fibroblasts., Conclusions: Our data suggest that the TOL is not an anatomic variant and can be classified into three types. Future biomechanical studies can be designed to investigate the function of the TOL, although we hypothesize that it may act as a fulcrum during flexion and extension of the head because it is located between the apical ligament and superior crus of the cruciform ligament. Anteroposterior open-mouth digital radiographs revealed the location of the TOL with respect to the upper two cervical vertebrae. Future research should investigate the radiologic characteristics of the TOL using magnetic resonance imaging., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Objective: Knowledge of the anatomy of the ligaments that unite the head to the neck is important to the clinician who treats patients with lesions in this region. Although the anatomy and function of the majority of these ligaments have been well described, some are relatively unknown. One of these includes the anterior atlantodental ligament (AADL). Our goal was to increase knowledge about the AADL., Methods: We dissected the craniocervical junction in sixteen adult cadavers and paid special attention to the presence and anatomy of the AADL., Results: The AADL was found in 81.3% of specimens. The attachment of each ligament was consistent and traveled between the base of the anterior dens to the posterior aspect of the anterior arch of the atlas in the midline and just inferior to the fovea dentis. In 38.5% of specimens, there was some connection between the AADL and the anterior atlanto-occipital membrane. The ligament was roughly 4 × 4 × 4 mm in all specimens. With transection of the transverse ligament, the AADL could be made taut with posterior distraction of the dens. In addition, with left and right rotation of the atlantoaxial joint, the AADL became taut (less than 10°) before any tautness of the alar ligaments in all specimens., Conclusions: The AADL appears to resist posterior displacement of the dens and, with the alar ligaments, resists rotation. When present, the AADL contributes to the predental space. Knowledge of this ligament may aid in further understanding craniocervical stability and help in differentiating normal anatomy from pathology via imaging modalities., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Background: The alar ligaments are integral to limiting occipito-atlanto-axial rotation and lateral flexion and enhancing craniocervical stability. Clinical testing of these ligaments is advocated prior to the application of some cervical spine manual therapy procedures. Given the absence of validation of these tests and the potential consequences if manipulation is applied to an unstable upper cervical spine segment, exploration of these tests is necessary., Objective: The purpose of this study was to examine the direct effect of the side-bending and rotation stress tests on alar ligaments using magnetic resonance imaging (MRI)., Design: This was a within-participant experimental study., Methods: Sixteen participants underwent MRI in neutral and end-range stress test positions using proton density-weighted sequences in a 3-Tesla system. Measurements followed a standardized protocol relative to the position of the axis. Distances were measured from dens tip to the inferior margin of the foramen magnum and from midsubstance of the dental attachment of the ligament to its occipital insertion. Between-side differences were calculated for each measurement to account for inherent asymmetries in morphology. Differences were compared between the test and neutral positions using a Wilcoxon signed rank test., Results: Side-bending stress tests produced a median between-side difference in ligament length of +1.15 mm. Rotation stress tests produced a median between-side difference in ligament length of +2.08 mm. Both results indicate increased measurement of the contralateral alar ligament. Limitations Assessment could be made only in the neutral position due to imaging limitations. Clinical texts state that tests should be performed in 3 positions: neutral, flexion, and extension., Conclusions: Both side-bending and rotation stress testing result in a measurable increase in length of the contralateral alar ligament. This finding is consistent with mechanisms that have been described to support their use in clinical practice.

Study Design: Anatomic study performed on 13 cadaveric specimens focused on muscles of the suboccipital triangle, specifically, the rectus capitis posterior major (RCPma)., Objective: To investigate a connection between the RCPma and the cervical dura mater., Summary of Background Data: In a study of the posterior intervertebral spaces, a connection between the RCPma and the dura mater was briefly described. To the best of our knowledge, no study has been conducted specifically on this communication., Methods: Anatomic dissections were performed in the suboccipital regions of 13 embalmed, adult cadaveric specimens. Findings were recorded via photographic documentation., Results: In 11 of the 13 specimens, the RCPma attached to the spinous process of the axis and then continued to establish a gross anatomical connection with the dura mater in the atlantoaxial interspace. Manual traction of the RCPma resulted in gross dural movement from the spinal root level of the axis to the spinal root level of the first thoracic vertebra., Conclusion: A connection was found to exist between the RCPma and the cervical dura mater. Various clinical manifestations may be linked to this anatomical relationship.

The occipital bone is the upper end of the somatic spine, limited cranially by the tentorium. The bony craniovertebral junction (caudal occiput, atlas, and axis) is interposed between the unsegmented occipital and the intersegmental spinal sclerotomes, separated from the occiput and C3 by the intrasegmental clefts of O4 and C2 sclerotomes, respectively. It retains a primitive segmental hypocentrum (anterior arch of C1) and is unsegmented from caudal O4 to cranial C2 half-sclerotomes (axis). Its morphology relates to the dual function of providing support and mobility (visual/olfactory/auditory pursuit, oral prehension) to the head. The early notochord passes through the odontoid tip to the basiocciput surface before entering the clivus up to the craniopharyngeal canal; later, the rostralmost chordal remnant is the C2/3 nucleus pulposus. Chondrification starts in the second fetal month and ossification in the fetal or postnatal periods depending on the structure.

Surgical approaches to the craniovertebral junction (CVJ) can result in dysfunction of the upper aerodigestive tract. However, few data are available regarding the incidence of complications after such surgery. Evaluation of a CVJ lesion for treatment must establish the biology, transverse and longitudinal extent of the lesion, and the preoperative and postoperative stability of the spine. Endoscopic approaches to the CVJ, which should reduce the expected morbidity of an open transoral approach, have been described recently. This article reviews common pathologies of the CVJ and surgical approaches, and provides an evidence-based analysis of whether endoscopic approaches reduce velopharyngeal insufficiency., (Copyright © 2011 Elsevier Inc. All rights reserved.)

The specialized ligaments of the craniocervical junction must allow for stability yet functional movement. Because injury to these important structures usually results in death or morbidity, the neurosurgeon should possess a thorough understanding of the anatomy and function of these ligaments. To the authors' knowledge, a comprehensive review of these structures is not available in the medical literature. The aim of the current study was to distill the available literature on each of these structures into one offering.