Arch Of Atlas Research Articles

Craniospinal space reduction and malalignment due to atlas assimilation in Basilar Invagination–A case–control study

IntroductionType I Basilar invagination is associated with the assimilation of the anterior arch of the atlas. Observation suggests that the assimilation of the atlas does not allow the development of the normal space between the skull and C1 and displaces the high cervical spine towards the neural structures, posteriorly positioned. Purpose: The objective of this work is to evaluate craniospinal alignment in patients with type I Basilar invagination and AOA in comparison with normal subjects (Type I). MethodsMagnetic resonance images and / or CT SCAN with reconstruction in the midline, in acquisitions at t1 and or t2, from 30 normal subjects and 27 patients with type I Basilar invagination were evaluated. The position of Anterior arch of Atlas and odontoid process in relation to the Basion and distances between C1 and C2 to the anterior border of foramen magnum were compared between groups. ResultsThe distance from C2 to the Basion was significantly higher in the BI group than in the control group (t test: t = 4.18; p = 0) and the space between the skull and Atlas was reduced. All normal subjects had the Atlas anteriorly located in relation to the Basion. In AOA, all patients had Atlas in line with or posteriorly dislocated in relation to the Basion and the Odontoid process occupying the foramen magnum space. Conclusiondata revealed that AOA prevents a normal position of skull in relation to the Atlas and a presumed “slip-back” cranio-spinal displacement during developmental period.

The role of occipital condyle and atlas anomalies on occipital cervical fusion outcomes in Chiari malformation type I with syringomyelia: a study from the Park-Reeves Syringomyelia Research Consortium.

Congenital anomalies of the atlanto-occipital articulation may be present in patients with Chiari malformation type I (CM-I). However, it is unclear how these anomalies affect the biomechanical stability of the craniovertebral junction (CVJ) and whether they are associated with an increased incidence of occipitocervical fusion (OCF) following posterior fossa decompression (PFD). The objective of this study was to determine the prevalence of condylar hypoplasia and atlas anomalies in children with CM-I and syringomyelia. The authors also investigated the predictive contribution of these anomalies to the occurrence of OCF following PFD (PFD+OCF). The authors analyzed the prevalence of condylar hypoplasia and atlas arch anomalies for patients in the Park-Reeves Syringomyelia Research Consortium database who underwent PFD+OCF. Condylar hypoplasia was defined by an atlanto-occipital joint axis angle (AOJAA) ≥ 130°. Atlas assimilation and arch anomalies were identified on presurgical radiographic imaging. This PFD+OCF cohort was compared with a control cohort of patients who underwent PFD alone. The control group was matched to the PFD+OCF cohort according to age, sex, and duration of symptoms at a 2:1 ratio. Clinical features and radiographic atlanto-occipital joint parameters were compared between 19 patients in the PFD+OCF cohort and 38 patients in the PFD-only cohort. Demographic data were not significantly different between cohorts (p > 0.05). The mean AOJAA was significantly higher in the PFD+OCF group than in the PFD group (144° ± 12° vs 127° ± 6°, p < 0.0001). In the PFD+OCF group, atlas assimilation and atlas arch anomalies were identified in 10 (53%) and 5 (26%) patients, respectively. These anomalies were absent (n = 0) in the PFD group (p < 0.001). Multivariate regression analysis identified the following 3 CVJ radiographic variables that were predictive of OCF occurrence after PFD: AOJAA ≥ 130° (p = 0.01), clivoaxial angle < 125° (p = 0.02), and occipital condyle-C2 sagittal vertical alignment (C-C2SVA) ≥ 5 mm (p = 0.01). A predictive model based on these 3 factors accurately predicted OCF following PFD (C-statistic 0.95). The authors' results indicate that the occipital condyle-atlas joint complex might affect the biomechanical integrity of the CVJ in children with CM-I and syringomyelia. They describe the role of the AOJAA metric as an independent predictive factor for occurrence of OCF following PFD. Preoperative identification of these skeletal abnormalities may be used to guide surgical planning and treatment of patients with complex CM-I and coexistent osseous pathology.

Radiological Study of Atlas Arch Defects with Meta-Analysis and a Proposed New Classification.

This study consists of a retrospective cohort study, a systematic review, and a meta-analysis which were separately conducted. This study aimed to investigate the prevalence of atlas arch defects, generate an evidence-based synthesis, and propose a common classification system for the anterior and combined atlas arch defects. Atlas arch defects are well-corticated gaps in the anterior or posterior arch of the atlas. When both arches are involved, it is known as a combined arch defect. Awareness of these defects is essential for avoiding complications during surgical procedures on the upper spine. The prevalence of arch defects was investigated in an open-access OPC-Radiomics (Radiomic Biomarkers in Oropharyngeal Carcinoma) dataset comprising 606 head and neck computed tomography scans from oropharyngeal cancer patients. A systematic review and meta-analysis were performed to generate prevalence estimates of atlas arch defects and propose a classification system for the anterior and combined atlas arch defects. The posterior arch defect was found in 20 patients (3.3%) out of the 606 patients investigated. The anterior arch defect was not observed in any patient, while a combined arch defect was observed in one patient (0.2%). A meta-analysis of 13,539 participants from 14 studies, including the present study, yielded a pooled-posterior arch defect prevalence of 2.07% (95% confidence interval [CI], 1.22%-2.92%). The prevalences of anterior and combined arch defects were 0.00% (95% CI, 0.00%-0.10%) and 0.14% (95% CI, 0.04%-0.25%), respectively. The anterior and combined arch defects were classified into five subtypes based on their morphology and frequency. The present study showed that atlas arch defects were present in approximately 2% of the general population. For future studies, larger sample sizes should be used for studying arch defects to avoid the small-study effect and to predict the prevalence accurately.

Posterior arch reconstruction in cervical surgery to restore the global biomechanics of the Atlas: a technical note

The posterior arch of the atlas is usually not considered one of the main stabilizers of the cranio-cervical junction, allowing surgeons to its removal when needed with a relative certainty to preserve the stability of the atlo-axial segment. However, these considerations do not reflect the importance to examine the integrity of the posterior arch in the whole biomechanics of the atlas. Authors like Gebauer and Panjabi revealed, respectively in experimental and clinical conditions, how the atlas responds to an axial loading force, proving that the whole atlas is involved into horizontal conversion of axial forces and providing evidence supporting the preservation of the posterior arch. Other authors evaluated the risk for anterior arch fracture following C1 laminectomy. In this technical note three different techniques of posterior atlas arch reconstruction after surgical iatrogenic disruption are presented, considering both neoplastic and degenerative disease.

Posterior and lateral ponticles of atlas: An osteological study at Fatima Jinnah Medical University, Lahore

Background: Among the cervical vertebrae, atlas is known to have many variations, posterior ponticle being the commonest. It may completely or incompletely covers the groove of vertebral artery leading to ischemia of posterior circulation. Therefore, vertebral artery is at greater risk of injury during neurological and spinal surgeries. Prevalence of posterior ponticles varies widely among different populations, for instance in Turkish population it was 10.8%, in American 22.1%, Kenyan 14.7%, Brazilian and Indian 16.7%. The prevalence of lateral ponticle in Kenyan population was reported to be 3.9% and in Indians it was 2%. However, the data regarding the prevalence of these ponticles is largely lacking in Pakistan. Therefore, this research was designed to determine the prevalence of posterior and lateral ponticle in atlas vertebrae of Pakistani population.&#x0D; Materials and methods: A total of 47 human atlas vertebrae of unknown age and gender from bone bank of Department of Anatomy Fatima Jinnah Medical University, Lahore were studied for the presence of complete and incomplete posterior and lateral ponticles. The bones studied were completely intact and did not have any pathology.&#x0D; Results: Total incidence of ponticles was 38 % in this study, of which 36% were posterior ponticles and 2% were lateral ponticles. Bilateral incomplete posterior ponticles/were found in 8 (17%) atlas vertebrae whereas bilateral complete posterior ponticles/foramen arcuale were found in only 1 (2%) atlas vertebrae. Unilateral incomplete posterior ponticle was identified on right side in 5 (11%) and left side in 2 (4%) atlas vertebrae. Unilateral complete posterior ponticle was found in only 1 (2%) atlas on the left side whereas no such finding was identified on right side in any vertebra. Unilateral complete lateral ponticle was found in only 1 (2%) atlas on the right side but not on left side. No bilateral complete lateral ponticle and incomplete unilateral or bilateral lateral ponticles were identified in this study.&#x0D; Conclusion: Presence of posterior and lateral ponticles pose a risk of vertebrobasilar vascular insufficiency and may cause variety of symptoms. Vertebral artery may be at risk during neurosurgical procedures when having a foramen arculae and may give a false impression of much wider posterior arch of atlas. Knowing the prevalence of this can help neurosurgeons, general surgeons, radiologists, and chiropractors in management of the patients.

A METHOD FOR REMOVAL OF BRAIN, BRAIN STEM WITH SPINAL CORD AS ONE UNIT FROM HUMAN CADAVERS FOR ANATOMICAL STUDY AND MUSEUM PURPOSES

After successful embalming of the 05 human adult cadavers, removals of brain, brain stem with spinal cord were done as a single unit. The removal of bilateral laminectomy of vertebrae helps in viewing of spinal cord with its coverings and spinal nerve roots, dorsal root ganglion and cauda equina. It is followed by removal of vault of skull, squamous part of occipital bone and posterior arch of atlas, helps in viewing of brain, brain stem along with dural sheath and venous sinuses. This approach helps in total removal of brain, brain stem and spinal cord with its covering with large venous sinuses remaining intact however small venous sinuses are sacrificed in this process. The specimen thus obtained can be used for anatomical study and museum display.&#x0D; Keywords: Removal of brain, brain stem, spinal cord, anatomical study.

89. 3D evaluation and classification of the anatomy variations of vertebral artery at the craniovertebral junction

BACKGROUND CONTEXT Patients with basilar invagination (BI) and atlas occipitalization usually present abnormal anatomy of the vertebral arteries (VAs) at the craniovertebral junction (CVJ). PURPOSE To describe and further classify different types of VA variations at the CVJ with 3D visualization technology. STUDY DESIGN/SETTING To display the 3D structures of the VA and bone with different colors to summarize different types of VA variations. PATIENT SAMPLE A total of 120 patients with BI and atlas occipitalization who had undergone 3D-CTA were retrospectively studied. OUTCOME MEASURES Abnormal anatomy of the VA at the CVJ was categorized and related anatomic parameters were measured. METHODS Imaging data were processed via the separating, fusing, opacifying and false coloring-volume rendering (SFOF-VR) technique. RESULTS Seven different types were classified. Type I, the VA enters the cranium after leaving the VA groove on the posterior arch of atlas (26.7% of 240 sides). Type II, the VA enters an extraosseous canal created in the assimilated atlas lateral mass-occipital condyle complex before reaching the cranium (53.3%). Type III, the VA course above the axis facet or curves below the atlas lateral mass then enters the cranium (11.7%). Type IV, the VA enters the spinal canal under the axis lamina (1.3%). Type V, high-riding VA (31.3%). Type VI, fenestrated VA (2.9%). Type VII, absent VA (4.2%). Distance from the canal of Type II VA to the posterior facet surface of atlas lateral mass(5.51±2.17mm) means a 3.5 mm screw can be safely inserted usually. Shorter distance from the midline (13.50±4.35) illustrates potential Type III VA injury during exposure. Decreased height and width of axis isthmus in Type V indicate increased VA injury risks. CONCLUSIONS The courses of VA variations in patients with BI and atlas occipitalization were described and classified into seven different types utilizing the SFOF-VR technique, which is highly recommended as a convenient and concise method for the preoperative evaluation. This new classification system and related anatomical parameters allow for improved understanding of the 3D relationship between the course of VA variations and CVJ anatomy, which is important for minimizing the risk of intraoperative VA injury in patients with congenital anomalies at the CVJ. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

Anatomical study in exposed area and operating space of extended endonasal approach to the ventral region of cranio-cervical junction

Objective To explore the scope, feasibility and indications of extended neuroendoscopic endonasal approach to reveal the region of cranial-cervical junction. Methods Ten (20 sides) intact frozen adult cadaveric heads were used to simulate the extended neuroendoscopic endonasal approach to remove the anterior tubercle of atlas, part of the atlas anterior arch, odontoid and part of the slope. In the cranial-cervical junction area, we observed the exposed range and measured the distance from the nostril to the anterior tubercle of atlas, the height and width of the anterior arch of the atlas, the distance of bilateral medial margin of occipital condyle, the distance of bilateral medial margin of the foramen lacerum, the vertical distance from the occipital condyle to the homolateral foramen lacerum, and the height, anteroposterior diameter and transverse diameter of the odontoid. Results The exposed range of the extended neuroendoscopic endonasal approach was as follows: when the lesion was located at the foramen magnum, the medial margin of the occipital condyle was the boundary of both sides, the root of the odontoid was the lower boundary, and the lower edge of the occipital bone was the upper boundary. When the lesion was located at the region of cranial-cervical junction, the upper edge of the foramen lacerum on both sides was the upper boundary, and the foramen lacerum and the outer edge of the occipital condyle were the boundaries of both sides of the bone window. By measurement, the distance from the nostril to the anterior tubercle of atlas was 8.9-9.7 cm, with an average of 9.3±0.3 cm. The height of the anterior arch of the atlas was 2.3-3.0 cm, with an average of 2.7±0.3 cm; the width was 1.5-2.0 cm, with an average of 1.8±0.2 cm; the distance of bilateral medial margin of occipital condyle was 1.5-2.0 cm, with an average of 1.8±0.2 cm; the distance of bilateral medial margin of the foramen lacerum was 2.1-2.9 cm, with an average of 2.4 ±0.3 cm; the vertical distance from the occipital condyle to the homolateral foramen lacerum was 1.6-2.2 cm, with an average of 1.9±0.3 cm; the height of the odontoid was 0.9-1.3 cm, with an average of 1.1±0.2 cm, its length was 0.8-1.3 cm, with an average of 1.1±0.2 cm; the transverse diameter of the dentate was 0.9-1.2 cm, with an average of 1.0±0.1 cm.The maximum exposed area of cranio-cervical junction was 6.4-9.8 cm2, with an average of 8.6±1.6 cm2. Conclusion The extended neuroendoscopic endonasal approach with removal of the anterior tubercle of atlas and part of the atlas anterior arch could effectively reveal the cranial-cervical junction area which is suitable for the treatment of odontoid deformity, skull base depression and atlantoaxial joint dislocation as well as resection of epidural tumors in the cranial-cervical junction and ventral and ventral midline tumors. Key words: Natural orifice endoscopic surgery; Anatomy; Cranio-cervical junction; Extended endonasal approach

Quantitative study of the effect of atlas posterior arch resection on cervical posterior decompression

Objective To quantitatively compare the effect of preservation or removal of atlas posterior arch on cervical posterior decompression, so as to provide a basis for reasonable selection of upper cervical spine decompression range and determination of surgical indications for atlas posterior arch resection. Methods The data of 45 patients with posterior decompression of upper cervical spine were retrospectively analyzed. According to the decompression range, the patients were divided into C2-C7 group and C1-C7 group. There were 25 cases in the C2-C7 group, 19 males and 6 females, with an average age of 56.3 years (40-71 years), 4 cases of cervical spondylotic myelopathy and 21 cases of ossification of the posterior longitudinal ligament of cervical spine. All of the 25 patients underwent open-door laminoplasty: 20 cases with hinge side anchoring procedure and 5 cases with preservation of the unilateral posterior muscular-ligament complex procedure (titanium cable procedure). There were 20 cases in C1-C7 group, 12 males and 8 females, with an average age of 58.4 years (44-75 years). All of the 20 cases underwent atlas posterior arch resection as well as C2-C7 open-door laminoplasty, including anchoring procedure in 1 case, titanium miniplate procedure in 4 cases, and titanium cable procedure in 15 cases. Standardized vertebral-cord distance (SVCD) at each level from atlas to level C6,7 was measured on T2-weighted images of MR on the mid-sagittal plane in the neutral position performed 3-12 months postoperatively at each individual level. As the main outcomes, the SVCD values obtained at the same level of the two groups were compared between the two groups. Shapiro-Wilk normality test was performed on the SVCD values at C1,2 and C2 levels of two groups. The area under the normal distribution curve of SVCDs was used to calculate the corresponding residual compression rate with different magnitude of compression mass to further discover the difference of the decompression effect between the two groups. Results The SVCD obtained at the level of the anterior arch of atlas (C1), the junction of odontoid process and axis (C1,2) and the middle part of axis body (C2) in the C2-C7 group was 9.91±1.34 mm, 8.35±1.27 mm, and 8.22 ±1.43 mm, respectively. The SVCD at the same levels was 11.02±1.60 mm, 9.72±1.24 mm, and 9.12±1.11 mm, respectively. SVCDs differed significantly in the above range between the two groups. However, from level C2,3 to C6,7, there was no significant difference in SVCDs between the two groups. The JOA score of group C2-C7 was 11.8±2.7 preoperatively and increased significantly to 14.7±1.8 at 12 months postoperatively(t=-7.006, P<0.001) with a recovery rate of 57.0%±32.2%. The JOA score of group C1-C7 was 11.7±2.8 preoperatively and increased significantly to 14.2±2.3 at 12 months postoperatively(t=-6.177, P<0.001) with a recovery rate of 51.9%±32.1%. Conclusion Atlas posterior arch resection can significantly increase the decompression effect of posterior cervical surgery from the anterior arch of atlas to the middle part of axis body, but it would not increase the decompression effect at level C2,3 or below. When the magnitude of the ventral compression factor exceeds the decompression limit (8.5 mm) available with C2-C7 decompression in the range from atlas to the middle of the axis body, extending the decompression range by atlas posterior arch resection is an effective means to achieve adequate decompression. Key words: Cervical atlas; Axis; Ossification of posterior longitudinal ligament; Spinal cord compression; Decompression, surgical

Part 1: CBCT EVALUATION OF ATLANTOAXIAL/ATLANTO-OCCIPITAL JOINTS FOR CERVICAL INSTABILITY RISK ASSESSMENT

Background In dental radiography, the vertical atlantoaxial index (VAAI)1 measures the vertical relationship of the atlas and the axis. Based on prior studies, value less than 0.8 might present a predisposition toward cervical instability. The Powers ratio (PR) is the ratio between the distance of 2 lines: (B–P): from basion to posterior arch of C1 (O–A): from opisthion to the anterior arch of atlas. The normal ratio is 1:1, if the ratio exceeds 1, it indicates atlanto-occipital instability. The basion–axial interval (BAI) is the horizontal distance between basion and posterior dens.4 The basion–dens interval (BDI) is the distance between the basion and the tip of the dens.4 Objective The objective of this study was to determine the potential risk for atlantoaxial/atlanto-occipital instability2 in patients who underwent cone beam computed tomography (CBCT) imaging of the head. The research was conducted at the Oral and Maxillofacial Radiology clinic of the University of Pennsylvania School of Dental Medicine (Philadelphia, PA). Materials and Methods After institutional review board approval, a preliminary study was performed on patients undergoing either preimplantation assessment of jaws or evaluation of atypical facial pain, and measurements were recorded. A total of 50 CBCT volumes were identified for the selected craniocervical cephalometric measurements. Analysis of the CBCT volumes and cephalometry were performed to record various craniocervical measurements and determine the potential risk of atlantoaxial atlanto-occipital instability. The measurements were done by using the midsagittal-view CBCT images. These measurements included BAI, BDI, VAAI, and PR. It was anticipated that these measurements would provide a risk estimate for cervical instability that could potentially result in spinal cord injury. All CBCT volumes were acquired by using the Carestream CS9300 machine (Carestream, Atlanta, GA). Results Based on the preliminary results, the average VAAI measurement was 0.7626, the average BAI was 4.970 mm, the average BDI was 5.043 mm, and the average PR was 0.6961. Discussion Apart from VAAI, BDI, and BAI, the PR3 was utilized in this study to find out the atlantoaxial dissociation (normal PR = 1:1). A ratio over 1 indicates atlanto-occipital dissociation (AOD. BAI is the horizontal distance between basion and the posterior cortex of the axis (normal ≤12 mm). BDI is the distance between the basion and the tip of the dens (normal ≤8.5 mm). Both BAI and BDI are used to diagnose AOD injuries.

Morphometric multislice computed tomography examination of the craniovertebral junction in neck flexion and extension.

Detailed study of the craniovertebral junction (CVJ) is necessary to completely understand the mechanism of its flexion and extension. One cadaver head was sectioned in the sagittal plane. Also, in 22 volunteers, examined using the multislice computed tomography (MSCT), 14 parameters and 2 angles were measured in the neutral position, flexion and extension. The obtained measurements showed the anterior part of the occiput to move inferiorly in flexion, and the anterior atlas arch and the tip of the dens to get closer to the basion. At the same time, the opisthion moves superiorly, but the cervical spine bends anteriorly. Consequently, the dens-opisthion diameter and the opisthion-posterior atlas arch distance slightly decrease in length, whilst the arches of the atlas (C1), axis (C2) and C3 vertebra become more distant. Following extension, the posterior part of the occiput moves inferiorly, so that the basion-dens tip, the basion-axis arch, and the basion-posterior atlas arch distances increase in length. In contrast, the distances of the C1-C3 arches decrease in length. The angle between the foramen magnum and the dens tip decreases 1.620 on average in flexion, but increases 3.230 on average in extension. The angle between the axis body and the opisthion also decreases in flexion (mean, 3.360) and increases in extension (mean, 6.570). Among the congenital anomalies, a partial agenesis of the posterior atlas arch was revealed (4.5%), as well as an anterior dehiscence of the C1 foramen transversarium (13.6%). The mentioned measurements improved our understanding of the CVJ biomechanics. The obtained data can be useful in the evaluation of the CVJ instability caused by trauma, congenital anomalies and certain spine diseases.

Dystopic Os Odontoideum: A Rare Cause of Atlantoaxial Instability

Os odontoideum is a relatively common developmental anomaly of the craniovertebral junction (CVJ), which is usually an incidental finding on spine imaging. But the dystopic variety of os odontoideum is uncommon and can be baleful. This anomaly can be a cause of atlantoaxial instability requiring surgical fixation. But the diagnosis of this variety requires considerable knowledge of anatomy of the CVJ as this unfamiliar entity needs to be differentiated from other CVJ anomalies like persistent os terminale, accessory ossicle of anterior arch of atlas, assimilation of atlas, and, most importantly, from orthotopic variety of os odontoideum. Here, we present a 34-year-old lady who presented with gradual-onset weakness of right side of the body. A computed tomography scan of the cervical spine revealed dystopic os odontoideum.

Cortical bone thickening in Type A posterior atlas arch defects: experimental report

Background ContextTo date, no information about the cortical bone microstructural properties in atlas vertebrae with posterior arch defects has been reported. PurposeTo test if there is an increased cortical bone thickening in atlases with Type A posterior atlas arch defects in an experimental model. Study DesignMicro-computed tomography (CT) study on cadaveric atlas vertebrae. MethodsWe analyzed the cortical bone thickness, the cortical volume, and the medullary volume (SkyScan 1172 Bruker micro-CT NV, Kontich, Belgium) in cadaveric dry vertebrae with a Type A atlas arch defect and normal control vertebrae. ResultsThe micro-CT study revealed significant differences in cortical bone thickness (p=.005), cortical volume (p=.003), and medullary volume (p=.009) values between the normal and the Type A vertebrae. ConclusionsType A congenital atlas arch defects present a cortical bone thickening that may play a protective role against atlas fractures.

ДОСЛІДЖЕННЯ ЛІНІЙНИХ РОЗМІРІВ ТА ЩІЛЬНОСТІ ТІЛ ХРЕБЦІВ ШИЙНОГО ВІДДІЛУ ХРЕБТА У ОСІБ РІЗНОЇ СТАТІ ЮНАЦЬКОГО ВІКУ

ДОСЛІДЖЕННЯ ЛІНІЙНИХ РОЗМІРІВ ТА ЩІЛЬНОСТІ ТІЛ ХРЕБЦІВ ШИЙНОГО ВІДДІЛУ ХРЕБТА У ОСІБ РІЗНОЇ СТАТІ ЮНАЦЬКОГО ВІКУ

A case of midline defect of posterior arch of atlas in a cadaver

AbstractDuring a routine osteology class for undergraduate students in Government Medical College, Kozhikode, Kerala, a median defect of posterior arch was found in the atlas of a cadaver. It was not a fracture as the edges were regular, round and smooth.There was no associated anomalies. These midline defects of posterior arch of atlas are sub divided both morphologically (types A-E) and clinically (sub groups 1-5) depending on the extent of absence of posterior arch and presence or absence of the posterior tubercle.The author presents a rare anomaly of a posterior arch partial aplasia which could be congenital. Since major neurologic deficits can be produced by a minor trauma, it is crucial to recognize this anomaly.

Craniovertebral junction 360°: A combined microscopic and endoscopic anatomical study.

Objectives:Craniovertebral junction (CVJ) can be approached from various corridors depending on the location and extent of disease. A three-dimensional understanding of anatomy of CVJ is paramount for safe surgery in this region. Aim of this cadaveric study is to elucidate combined microscopic and endoscopic anatomy of critical neurovascular structures in this area in relation to bony and muscular landmarks.Materials and Methods:Eight fresh-frozen cadaveric heads injected with color silicon were used for this study. A stepwise dissection was done from anterior, posterior, and lateral sides with reference to bony and muscular landmarks. Anterior approach was done endonasal endoscopically. Posterior and lateral approaches were done with a microscope. In two specimens, both anterior and posterior approaches were done to delineate the course of vertebral artery and lower cranial nerves from ventral and dorsal aspects.Results:CVJ can be accessed through three corridors, namely, anterior, posterior, and lateral. Access to clivus, foreman magnum, occipital cervical joint, odontoid, and atlantoaxial joint was studied anteriorly with an endoscope. Superior and inferior clival lines, supracondylar groove, hypoglossal canal, arch of atlas and body of axis, and occipitocervical joint act as useful bony landmarks whereas longus capitis and rectus capitis anterior are related muscles to this approach. In posterior approach, spinous process of axis, arch of atlas, C2 ganglion, and transverse process of atlas and axis are bony landmarks. Rectus capitis posterior major, superior oblique, inferior oblique, and rectus capitis lateralis (RCLa) are muscles related to this approach. Occipital condyles, transverse process of atlas, and jugular tubercle are main bony landmarks in lateral corridor whereas RCLa and posterior belly of digastric muscle are the main muscular landmarks.Conclusion:With advances in endoscopic and microscopic techniques, access to lesions and bony anomalies around CVJ is becoming easier and straightforward. A combination of microscopic and endoscopic techniques is more useful to understand this anatomy and may aid in the development of future combined approaches.

C1–C2 Instability Associated with Periodontoid Inflammatory Tissue Leading to Subarachnoid Hemorrhage: A Case Report and Review of the Literature

The authors present a case of atlantoaxial instability associated with C1–C2 inflammatory tissue leading to subarachnoid hemorrhage. A 65-year-old male patient arrived in June 2011 to the emergency unit for cervical pain and fever. Imaging studies documented periodontoid pseudotumor at C1–C2 level. Infective disease was suspected; the patient was therefore hospitalized and treated with antibiotics. Subsequent computed tomographic (CT) scans revealed C1–C2 instability. In August, the patient showed acute neurological deterioration and coma. Urgent brain CT revealed a hemorrhagic lesion which caused compression on the medulla oblongata, subarachnoid hemorrhage, and ventricular dilatation. An external ventricular drainage was positioned. Angio-CT and angiography did not show any vascular abnormalities. Cervical magnetic resonance imaging documented a solid tissue lesion between the atlas arch and axis. The lesion was associated with an epidural and subdural hematoma, exerting compression on brainstem. The patient underwent posterior decompression and C1–C2 fusion according to Harms technique in October, with significant clinical improvement. The authors present a case of atlantoaxial instability associated with a periodontoid pseudotumor at C1–C2 level determining dural sac compression. The patient showed an acute neurological deterioration caused by bleeding of the solid component of the cervical lesion. Hemorrhage of the solid component of periodontoid masses linked to atlantoaxial instability has not yet been reported in literature. To the best of our knowledge, this is the first case of C1–C2 instability with periodontoid pseudotumor leading to subarachnoid hemorrhage.

Design and biomechanical evaluation of atlantoaxial lateral mass fusion cage

Objective To design an atlantoaxial lateral mass fusion cage and evaluate its biomechanical stability when it is combined with atlantoaxial vertebral pedicle screw fixation. Methods Forty-six sets of CT 3D reconstruction pieces of the normal atlantoaxial junction were chosen to measure sagittal diameter and transverse diameter of atlantoaxial lateral mass joint, sagittal diameter and transverse diameter of epistropheus lateral mass and space height of atlantoaxial lateral mass joint. An atlantoaxial lateral mass fusion cage was designed on this basis. Six fresh human cadaveric cervical spines (C0-C4) were used as samples to measure 3D motion range of C1, and 2 segments under 1.5 N·m load. 3D motion range of samples under the following situations was measured at random: intact state, unstable state (ligament around odontoid process was cut off), fixation with atlantoaxial joint screw+Gallie steel wire, atlantoaxial pedicle screw, atlantoaxial lateral mass joint fusion cage+atlantoaxial vertebral pedicle screw. Results Corresponding width/length of fusion cage is 8/11, 9/12, 10/13 mm, respectively, and the height is designed to 3.5, 4.0, and 4.5 mm, respectively. The motion range of three internal fixation methods is less than that under intact state and unstable state. The difference has statistical significance. The C1+C2+cage fixation produces the least motion range in lateral bending and axial rotation directions and generates the highest motion range in flexion/extension direction. But, the difference has no statistical significance. Conclusion The C1+C2+cage internal fixation technique has similar stability with common atlantoaxial internal fixation method and can provide extra atlantoaxial fusion spots. Thus, it may be a feasible alternative for atlantoaxial fusion when the posterior arch of the atlas is absent. Key words: Biomechanics; Internal fixators; Atlanto-axial joint; Spinal fusion

The clinical classification and surgical treatment choice of irreducible atlantoaxial dislocation

Objective To investigate the clinical classification and surgical options for bone-fused irreducible atlantoaxial dislocation. Methods From November 2002 to December 2013, 20 cases of irreducible atlantoaxial dislocation were treated, including 8 males and 12 females, aged 22 to 57 years (mean 39 years). There were 6 cases without operation history and 14 cases with operation history, including 1 cases of anterior operation, 11 cases of posterior operation, and anterior and 2 cases of posterior combined approach. In 14 patients with surgery history, 13 cases had internal fixation residual, including 1 case of anterior plate and 12 cases of posterior screw rods. Under general anesthesia, the extensive fusion type was decompressed directly without restoration and immobilization, while the point fusion type was performed using soft tissue release, bone-fused point release, restoration, immobilization and fusion. 1 week, 3, 6, 12 months postoperatively and the annual review of the X-ray, CT and MR were checked, in order to evaluate the reduction, internal fixation, bone graft fusion and decompression of the spinal cord. The JOA scores of preoperative, postoperative and outpatient follow-up review were recorded. Results In all 20 patients, the extensive fusion type accounted for 5 cases, point fusion type 15 cases, while spontaneous fusion 6 cases, iatrogenic fusion 14 cases, including 3 cases of extensive fusion type and 11 cases of point fusion. In 5 cases of extensive fusion treated with anterior resection of anterior arch of atlas and the odontoid process decompression, postoperative MR showed that the spinal cord compression were completely eliminated, and reduction were achieved. The spinal cord and vertebral artery injury were not found. 1 case with cerebrospinal fluid leakage was cured after anterior internal fixation removal and posterior internal fixation. 5 cases of extensive fusion type and 14 cases of punctate fusion were followed up, ranged from 6 to 72 months (mean, 38 months). The JOA score was restored from preoperative average of 11 points to the last follow-up of 14 points. Even though no additional internal fixation was added, all 5 patients with extensive fusion showed no atlantoaxial intervertebral instability in follow-up period, and solid bony fusion of lateral atlantoaxial joint was obtained in 14 point fusion patients 6 months later. Conlusion The point fusion irreducible atlantoaxial dislocation can still get reduction after release and thoroughly removal of bony fusion point, while the extensive fusion irreducible atlantoaxialdislocation may still achieve good outcome by decompression. Key words: Atlanto-axial joint; Dislocations; Spinal fusion; Treatment outcome

How frequent is ponticulus posticus in italian people? A lateral cephalometric study in an orthodontic population

The term “ponticulus posticus” refers to a partial or complete bony arch over the vertebral artery as it crosses the superolateral surface of the posterior arch of the atlas. This anatomical modification is linked to different symptoms, ranging from neckache to headache and migraine (1). This bony arch may also be incorrectly assessed during orthopedic surgery for fixation of C1-C2, with consequent risk of damaging the vertebral artery (2). Its frequency in the general population has been widely analysed by literature in different geographic contexts (3), but an analysis of the prevalence of such feature in the Italian population is still missing. The present investigation aims at providing data concerning the prevalence of ponticulus posticus in a sample of 221 patients. All the patients underwent lateral cephalometry for odontoiatric purposes and none of them was affected by congenital diseases or skeletal deformities. In the analysed sample ponticulus posticus had a prevalence of 7.7% for the complete form, and 9.0% for the incomplete form. Complete and partial forms were observed respectively in 8.8% and 11.0% of males, and in 6.9% and 7.7% of females, without statistically significant differences (chi-square test, p>0.01). Italian prevalence seems lower than that observed in American populations, and higher than that reported in India and Far East countries. The current investigation provided the first data concerning the frequency of posticulus posticus in Italy: further studies are needed in order to widen the sample and improve the analysis by more advanced radiological examinations such as CT and cone beam CT scans.