Search

Objective: 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)., Methods: 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., Results: 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)., Conclusions: 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.

Study Design: Retrospective radiographic analysis., Objectives: Evaluation of the anatomic features of the craniovertebral junction in patients with occipitalization with and without atlantoaxial dislocation (AAD)., Summary of Background Data: Atlas occipitalization is a common feature of congenital AAD and usually requires surgical intervention. However, not all instances of occipitalization necessarily lead to AAD. No study has specifically examined and compared the craniovertebral bony morphology in occipitalization with, and without, AAD., Materials and Method: We reviewed computed tomography (CT) scans of 2500 adult outpatients. Occipitalization cases without AAD (ON) were selected. Meanwhile, a series of 20 inpatient occipitalization cases with AAD (OD) were obtained in parallel. Another 20 control cases without occipitalization were also included. Multi-directional reconstructed CT images of all cases were analyzed., Results: A total of 18 adults with ON were found in all 2500 outpatients (0.7%). Both anterior height and posterior height of C1 lateral mass in the control group were significantly larger than those in both the ON and OD groups, whereas posterior height in the OD group was significantly less than that in the ON group. Three morphologic types of the occipitalized atlas posterior arch were identified: Type I, bilateral sides were unfused with opisthion; Type II, unilateral side was unfused with opisthion, whereas the other side was fused; and Type III, bilateral sides were fused with opisthion. In the ON group, three cases were type I (17%), six cases were type II (33%), and nine cases were type III (50%). In the OD group, all 20 cases were type III (100%)., Conclusions: Atlas occipitalization with, and without, AAD results from a distinctly different bony morphology at the craniovertebral junction. The novel classification system based on reconstructed CT images may be useful in prognosticating AAD in the setting of atlas occipitalization., Competing Interests: The authors report no conflicts of interest., (Copyright © 2023 Wolters Kluwer Health, Inc. All rights reserved.)

Background: Occipitocervical fusion is an important surgical procedure to treat instability of the upper cervical and craniocervical junction. Fixation to the dense cortical bone of the occiput, contemporaneously typically accomplished with a plate and screws, is known to be strong and durable, but there are many competing methods used to secure an adequate number of fixation points of sufficient strength at the cervical end. Extension of hardware to the midcervical region to acquire additional fixation points, however, results in loss of subaxial motion segments and additional potential morbidity. The C2 vertebra is unique in that its morphology and dimensions permit fixation with longer screws than are typically possible to place in the midcervical lateral masses. Translaminar and pars screw techniques, both commonly used to achieve C2 fixation, are not mutually exclusive, as their respective trajectories are considerably different and engage different portions of the bony anatomy., Methods: We describe a novel, 4-point C2 fixation technique for OC fusion that may avoid the need to extend fusion to the subaxial spine., Results: This technical note illustrates how 4-point C2 fixation can be employed in occiptocervical fusion., Conclusions: 4-point fixation of C2 combining translaminar and pars screw placement is technically feasible and may be a suitable strategy to spare subaxial motion segments in OC fusion procedures. Futher investigation may establish its applicability to additional surgical procedures., (Copyright © 2021 Elsevier Inc. All rights reserved.)

The complex Chiari, characterized by abnormal craniocervical bony anatomy in addition to Chiari tonsillar herniation, is a relatively recent addition to the concepts surrounding the Chiari literature. The primary findings of complex Chiari include craniocervical kyphosis and retroflexed odontoid, both of which can be described with radiographic measurements. This manuscript will outline the background literature regarding Chiari craniocervical morphometrics and supply an algorithm for the general management of complex Chiari patients.

Background: In situations in which posterior atlanto-occipital fixation might not be possible or might require supplemental fixation, anterior fixation might add stability in obtaining arthrodesis. The present study aimed to provide a radiographic evaluation of the safety and feasibility in the anterior approach., Methods: The bilateral craniocervical computed tomography slices of 60 patients were examined. The anterior screw entry point was the lowest point at the middle anterior aspect of C1 (atlas) lateral mass. To avoid hypoglossal canal and craniocerebral injury, the height of the hypoglossal canal and occipital condyle and occipital condyle width were obtained. The mandible occlusion angle (MOA), anterior screw trajectory above, under, and distal to the hypoglossal canal (AHA, UHA, and DHA) relative to the tangent line of C1 front border were measured, together with the maximum screw length under each angle (AHL, UHL and DHL). An independent samples t test was used for statistical analysis., Results: The height of the hypoglossal canal and occipital condyle and occipital condyle width were all larger in the men than in the women. The MOA, AHA, UHA, and DHA were 55.0°, 18.7°, 41.0°, and 55.0°, respectively, and were similar between genders. The AHL, UHL, and DHL were 34.5, 30.9, and 31.3 mm, with the measurements for the men generally longer than those for the women by 3-4 mm. A total of 10 of 120 bilateral measurements showed the possibility of mandible occlusion, and the potential success rate of the anterior approach could reach 91.7%., Conclusions: The ideal entry angle for anterior atlanto-occipital fixation ranges from 41.0° to 55.0°, with a safe screw length from 30.9 to 31.3 mm. The potential success rate could reach >90%., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Background: Proatlas segmentation anomalies represent a rare subset of congenital craniovertebral junction anomalies. In this condition, the structures originating from the proatlas, such as the clivus, occipital condyles, foramen magnum rim, and odontoid tip, may demonstrate congenital anomalies, usually without any spinal instability. Elongated clivus, as a result of nonsegmentation of the odontoid tip from the rest of the proatlas, has been reported before to cause ventral spinal cord compression. We report such a case with certain unreported other associations and explore the pathoembryology and management options of such complex anomalies., Case Description: An 8-year old girl presented with a 2-year history of progressive spastic quadriparesis. On neuroimaging, the anterior arch of the atlas was deficient, the odontoid process was foreshortened, and the clivus was elongated, encroaching into the spinal canal leading to ventral spinal cord compression. Additionally, there was rotatory posterior dislocation of the occipital condyles onto the posterior atlantal arch and vertebral artery anomaly. This patient underwent transoral decompression followed by occipitocervical fusion using rods and screws with satisfactory results., Conclusions: Proatlas anomalies are rare, varied, and often subtle enough to go unrecognized. Knowledge of the embryology and its aberrations is necessary to understand these anomalies. Our case describes a rare form of bony anomalies pertaining to the fate of the proatlas with accompanying atlanto-occipital dislocation., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Background: The arcuate foramen is an anatomic variant that is thought to arise from ossification of the posterior atlanto-occipital membrane. Owing to potential entrapment of the vertebral artery segment that traverses the foramen, vertebrobasilar ischemia may occur, and the person may experience vertigo, headache, or neck pain., Methods: We reviewed the literature regarding anatomy (both human and comparative), embryology, nomenclature, pathology, and surgery of the arcuate foramen., Results: Surgically, the presence of an arcuate foramen is important when placing screws into lateral masses of the atlas. In these cases, the screws can damage the V3 segment of the vertebral artery and/or the suboccipital nerve., Conclusions: It is important to review the current literature on the arcuate foramen to further understand its morphology and clinical relevance., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Objective: To study the craniovertebral junction and determine the anatomic characteristics of occipitalization of the atlas (OC) by computed tomography (CT) imaging., Methods: We retrospectively reviewed 80 cases of patients with OC who underwent cervical CT scanning between March 2012 and March 2014. Forty healthy subjects were recruited as a control cohort. Fusion pattern and associated osseous anomalies were recorded. Fifteen linear quantitative parameters were measured to study the outlet of the foramen magnum, angular dimension of the skull base, posterior cranial fossa, and height of the odontoid process., Results: The most common fusion pattern was the complete osseous fusion (83.75%). Fifty-four patients (67.5%) presented with other osseous anomalies. Measurements of the OC group, such as the length of the clivus, cranial canal angle, and height of the odontoid process, were significantly different than those of the control group. The correlation analysis showed that the C1 lateral facet inclination was significantly correlated with the age of onset., Conclusions: The outlet of the foramen magnum is severely impaired in patients with OC, and the presence of other osseous anomalies is common. Deformity is not confined to the region of the assimilated atlas; the clivus and odontoid process are also shorter than normal. The lateral facet inclination likely influences disease progression., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Purpose: Cranio-vertebral junction fixation is challenging due to the complex topographical anatomy and the presence of important anatomical structures. There are several limitations to the traditional occipital squama fixation methods. The purpose of this work is to assess the safety and feasibility of a new optimum trajectory of occipital condyle (OC) screws for occipitocervical fixation via a free-hand technique., Methods: Eight different parameters of OC morphology were studied in fifty adult skulls. Free-hand placement of OC screws was performed in five cadavers using 3.5-mm titanium polyaxial screws and a 3-mm rod construct (C0-C1-C2). Postoperative computed tomography was performed to determine the success of the screw placement and their angulation, length and effect on hypoglossal canal volume., Results: The average length, width and height of the OC were 24.2 ± 3.6, 14.2 ± 1.9, and 10.7 ± 2 mm, respectively. The average medio-lateral, hypoglossal canal and atlanto-occipital joint angles were 38.8° medially ±5°, 7.4° rostrally ±1.9° and 23.4° caudally ±3.5°, respectively. The ten screws were successfully inserted using a free-hand technique with bicortical purchase. There was no vertebral artery injury or breach of the hypoglossal canal in any specimen. The average screw length was 22.2 ± 3.9 mm. The average medio-lateral angle was 30° medially ±6.7°. The average cranio-caudal angle was 4° caudally ±6.2°., Conclusions: The free-hand technique of OC screw placement is a safe and viable option for occipitocervical fixation and may be a preferred alternative in selected cases. However, further studies are needed to compare its safety and reliability to other more established methods.

Only 6 cases of isolated unilateral rupture of the alar ligament have been previously reported. The authors report a new case and review the literature, morbid anatomy, and pathogenesis of this rare injury. The patient in their case, a 9-year-old girl, fell head first from a height of 5 feet off the ground. She presented with neck pain, a leftward head tilt, and severe limitation of right rotation, extension, and right lateral flexion of the neck. Plain radiographs and CT revealed no fracture but a shift of the dens toward the right lateral mass of C-1. Magnetic resonance imaging of the cervical spine showed signal hyperintensity within the left dens-atlas space on both T1- and T2-weighted sequences and interruption of the expected dark signal representing the left alar ligament, suggestive of its rupture. After 12 weeks of immobilization in a Guilford brace, MRI showed lessened dens deviation, and the patient attained full and painless neck motion. Including the patient in this case, the 7 patients with this injury were between 5 and 21 years old, sustained the injury in traffic accidents or falls, presented with marked neck pain, and were treated with external immobilization. All patients had good clinical outcome. The mechanism of injury is hyperflexion with rotation. Isolated unilateral alar ligament rupture is a diagnosis made by excluding associated fracture, dislocation, or disruption of other major ligamentous structures in the craniovertebral junction. CT and MRI are essential in establishing the diagnosis. External immobilization is adequate treatment.

Introduction: Occipitalization of the atlas is the most common malformation of the craniovertebral junction. It can be diagnosed on lateral teleradiography and its finding imposes screening for associated atlantoaxial instability. In case of instability, brisk movements of the cervical spine during surgery may result in compression and distortion of the spinal chord and vertebro-basilar vascular system., Observation: An 18 year-old female patient was referred to our department for facial dysmorphosis and extraction of the third molars. A lateral teleradiography revealed an occipitalization of the atlas and the fusion of the second and third cervical vertebral body. Further pre-operative investigations allowed ruling out any joint instability or associated craniovertebral junction malformations., Discussion: Occipitalization of the atlas is not usually well-known by maxillofacial surgeons. It may be diagnosed with a lateral teleradiography. Its diagnosis imposes screening for other spinal malformations (spinal fusion, hemivertebra, spina bifida occulta). The major risk is compression and distortion of the spinal chord and vertebro-basilar vascular system, during surgery or anesthesia., (Copyright © 2013 Elsevier Masson SAS. All rights reserved.)

Atlantooccipital dislocation (AOD) is a rare and often fatal injury. In cases of survival, residual deficits are severe and often include cranial nerve palsy, quadriplegia, or respiratory issues. Occipitalization is defined as partial or complete congenital fusion of the occiput to the atlas and is exceptionally rare. The authors present a rare case of AOD superimposed on a congenital occipitalization of the atlas. This 39-year-old man had AOD following a motor vehicle collision. On examination, his overall motor score on the American Spinal Injury Association scale was 5/100, and his rectal tone was absent. Computed tomography demonstrated AOD in an area of occipitalization. Magnetic resonance imaging revealed ligamentous injury leading to C1-2 instability. Intervention included occipital cervical instrumentation fusion from the occiput to C-3. Six months postoperatively, imaging revealed fusion of the graft and consolidation of the fractured occipitalization. At the 2-year follow-up, the patient's strength was 3/5 for wrist extension and handgrip on the right side and full strength in the rest of the myotomes. Bladder and bowel function was also normalized. A high-velocity collision led to disruption of the atlantooccipital ligaments and fracture of the occipitalized lateral masses in this patient. Internal fixation and fusion led to good fusion postoperatively. Occipitalization probably led to abnormal joint mechanics at the C1-occiput junction, which might have altered the amount of force required to fracture the occipitalization and produce AOD. This difference may partially account for the favorable neurological outcome in the featured patient compared with traditional cases of AOD.

Study Design: Prospective radiographic analysis., Objective: This study aimed to characterize the relationship between the alignment of the occipitoaxial (OA) and the subaxial spine, establish normal parameters, and to determine the influence of upper cervical spine alignment on subaxial degenerative disc disease (DDD) and clinical outcomes in this population., Summary of Background Data: Previous studies reported that the alignments of the upper and lower cervical spine are closely interrelated in patients with atlantoaxial dislocations of a rheumatoid etiology. None have focused on congenital etiologies or included patients with OA kyphosis. The influence of the upper cervical alignment on subaxial (DDD) and outcomes is also unclear., Methods: Fifty-eight patients with congenital AAD undergoing surgical reduction and fusion were included. C0-C2 and C2-C7 angles were measured and DDD was assessed using plain radiographs. The relationship between the alignment of the OA joint and the subaxial cervical spine was evaluated, as well as the relationships between the cervical alignment, outcomes, and cervical DDD., Results: C0-2 improved from a mean of 1.59±17.3 degrees preoperatively to a mean of 15±9.8 degrees postoperatively (P<0.001). C2-7 changed from a mean of 25.55±19.6 degrees to a mean of 14.2±14.4 degrees postoperatively (P<0.001). The OA and subaxial alignment were negatively correlated in this population both before (r=-0.84; P<0.001) and after (r=-0.64; P<0.001) surgical treatment. There was an increased incidence of DDD postoperatively (P<0.01), which was positively correlated with the postoperative C0-2 angle (r=0.54; P<0.001), but negatively correlated with the postoperative C2-7 angle (r=-0.79; P<0.001)., Conclusions: Changes in OA alignment before and after surgery are associated with changes in the subaxial spine. There is a high incidence of postoperative DDD in the subaxial spine that seems to be related to sagittal alignment after surgery.

Study Design: Case report., Objective: To report a new surgical technique of the primary cervical osteosarcoma in the atlas., Summary of Background Data: Primary osteosarcoma of the atlas is extremely rare. This is the first report that describes a surgical treatment of the primary osteosarcoma in the atlas. Resection of an osteosarcoma in the atlas is very difficult because of the complex and important anatomic structures that surround it, and secure reconstruction of the atlas is difficult as well., Methods: A 48-year-old man was referred to our institute with a 10-month history of a palpable painful mass on the right posterior neck. His neck mass was diagnosed as chondroblastic osteosarcoma by open bone biopsy. The plain radiograph of the lateral cervical spine revealed the osteoblastic lesion of the vertebra and an extraosseous mass formation from the C1 to C3 vertebrae. Computed tomography of the cervical spine revealed approximately a 7 × 3 × 7 cm-sized extraosseous calcified mass that originated from the right lateral mass of the atlas. The magnetic resonance imaging of the cervical spine did not show any spinal cord compression., Results: The patient underwent excision of this tumor using the direct lateral approach and reconstruction of the lateral mass of the atlas. On gross examination of the mass, there was a reactive thin membrane ("pseudomembrane") between soft tissue and tumor. At 3 months after surgery, the computed tomographic scan showed the solid fusion state of the occipitocervical joint. He rarely complained of any problems except for mild limitation of neck motion., Conclusion: We report a rare case of complete excision of an osteosarcoma of the C1 lateral mass in our patient via a direct lateral and posterior approach to secure additional fixation of occipitocervical joint. We describe our technique for reconstructing the lateral mass of the atlas. This reconstruction technique will also be applicable to other resection surgeries involving the occipitocervical junction.

Background: Tumors at the craniovertebral junction are difficult to remove because of their location and complex anatomic relations. The lateral transcondylar approach is a versatile approach to this area and allows access to a variety of intra- and extradural tumors. The lateral transcondylar approach has been used for a series of chordomas in this location., Objective: The nuances of this operation and its effectiveness in this group of patients are presented., Methods: There were 29 chordomas (1991-2007) in this region treated by one of the authors (CS) that were retrospectively reviewed. The imaging studies and medical records were evaluated. The location and extent of the tumor were defined, and the postoperative images were studied to determine the degree of resection., Results: There were 11 male and 18 female patients; their age range was 7 to 67 years. Headache and neck pain were the predominant presenting symptoms, and hypoglossal nerve palsy was the most common cranial nerve palsy. Twelve patients had previous surgery and 9 had previous radiation. Anterior midline and lateral approaches were used independently or in combination to treat these patients. Dural invasion was found in 27 patients requiring resection of the dura. Surgery was performed in 1 stage in 19 patients, and the tumor resection in the remaining patients was done in 2 stages. The lateral transcondylar approach was used in 19 patients. The occipital condyle was involved in all these patients. Radical tumor resection was achieved in 17 patients. Patients who had complete removal of the occipital condyle required occipitocervical fusion (20 patients) in the immediate postoperative period., Conclusion: The lateral transcondylar approach is an effective approach to chordomas in this region. Most of the tumors were large and extended into multiple anatomic compartments. The approach allowed resection of all the involved tissues, intra- and extracranial, and afforded excellent neurovascular control.

Background: Defining the anatomic zones for the placement of occiput-C1 transarticular screws is essential for patient safety., Objective: The feasibility and accuracy of occiput-C1 transarticular screw placement were evaluated in this anatomical study of normal cadaveric specimens., Material and Methods: Sixteen measurements were determined for screw entry points, trajectories, and lengths for placement of transarticular screws, as applied in the technique described by Grob, on the craniovertebral junction segments (occiput-C2) of 16 fresh human cadaveric cervical spines and 41 computed tomographic reconstructions of the craniovertebral junction. Acceptable angles for screw positioning were measured on digital x-rays., Results: All 32 screws were placed accurately. As determined by dissection of the specimens, none of the screws penetrated the spinal canal. Screw insertion caused no fractures, and the integrity of the hypoglossal canal was maintained in all the disarticulated specimens., Conclusion: Viable transarticular occiput-C1 screw placement is possible, despite variability of the anatomy of the occipital condyle.

Occipitoatlantal dislocation (OAD) can be devastating. This injury may be fatal in many cases, but more survivors are reported because of improvements in diagnosis and treatment. This article describes the diagnosis and treatment of OAD. To diagnose and treat OAD appropriately, neurosurgeons must have a detailed understanding of the anatomy of the craniocervical junction. Various radiographic criteria are used to establish the diagnosis of OAD. A destabilizing injury such as OAD requires surgical fixation. Many surgical techniques are available for fixation of the craniocervical junction. Future studies will continue to refine the diagnostic criteria for OAD and to develop improved methods for craniocervical stabilization.

Study Design: A method for evaluating occipitocervical neutral position is described., Objective: To describe and measure a posterior occipitocervical angle (POCA) in normal subjects that can be used to guide contouring of fusion implants to achieve occipitocervical neutral fusion and for use in standardized testing of occipitocervical constructs., Summary of Background Data: The goal of occipitocervical fusion is to fuse the head in an ideal functional position. Several methods of estimating occipitocervical neutral position have been described and tested, yet none has been proven superior. An ideal method would easily and reproducibly aid in evaluating occipitocervical position intraoperatively and potentially aid in the design and testing of implant constructs., Methods: Fifteen adult lateral cervical spine radiographs taken in occipitocervical neutral position and interpreted as normal by an experienced radiologist were studied. Analysis consisted of measurement of the POCA. The POCA is defined as the angle formed by the intersection of a line drawn tangential to the posterior aspect of the occipital protuberance and a line determined by the posterior aspect of the facets of the third and fourth cervical vertebrae., Results: The mean POCA was 109.7 degrees with a SD of 5.7 degrees. Compilation of the data revealed a normal distribution of measurements where 80% of the POCA values were between 101 and 119 degrees., Conclusions: POCA is a simple measurement that may be valuable as an intraoperative tool during occipitocervical fusion and may aid the design and testing of fusion implants and their application in the operating room.

STUDY DESIGN.: Observational study with 3-dimensional computed tomography angiography analysis. OBJECTIVE.: To examine the course of the vertebral artery (VA) at the craniovertebral junction (CVJ) in individuals with occipitalization of the atlas. SUMMARY OF BACKGROUND DATA.: The anatomy of the VA at the CVJ should be completely understood to decrease the risk of iatrogenic injury. Although quantitative anatomic studies have focused on the normal VA, the anomalous VA with occipitalization of the atlas has not been fully explored. METHODS.: A consecutive series of 36 cases with occipitalization of the atlas underwent 3-dimensional computed tomography angiography. Seventy-two vertebral arteries were analyzed. In this setting, the safety of placing lateral mass screws (LMS) was studied. RESULTS.: Four different pathways of the VA at the CVJ with occipitalization of the atlas were found. Type I, wherein the VA enters the spinal canal below the C1 posterior arch, and the course of the VA is below the occipitalized C1 lateral mass (8.3% of 72 vertebral arteries); Type II, the VA enters the spinal canal below the C1 posterior arch, and the course of the VA is on the posterior surface of the occipitalized C1 lateral mass, or makes a curve on it (25%); Type III, wherein the VA ascends externally laterally after leaving the axis transverse foramen, enters an osseous foramen created between the atlas and occipital bone, then into the cranium (61.1%); and Type IV, in which the VA is absent (5.6%). CONCLUSION.: Four types of VA with occipitalization of the atlas are confirmed. Type-I and type-IV VA have relatively low risks for C1 LMS perforation. Type-II and type-III anomalies will probably increase the risk of VA injury during C1 LMS placement. Definite caution should also be taken during the procedure on the contralateral side of a type-IV VA.

Stabilization of the occipitocervical junction and fixation of the occiput is challenging. Rigid fixation with plates and screws has reduced dependence on external immobilization and improved fusion rates. The strength of the occipital fixation can be compromised as plates constrain the ability to place occipital screws along the midline. Bilateral contoured rods with medial offset connectors allow placement of 6 occipital screws in the thickest and strongest bone along the midline, while easily connecting to screws in the cervical spine. The purpose of this study is to review complications and fusion rates in a patient series using this new technique to stabilize the occipitocervical junction. A retrospective review was performed at 2 years of 20 patients who underwent occipitocervical fusion for instability using bilateral contoured rods with medial offset connectors. Six occipital screws were successfully placed in 17 patients. The caudal screw on one side was abandoned in 3 patients due to insufficient occipital thickness. Sixteen patients fused. Four patients died in the perioperative period secondary to polytrauma complications. There were no hardware-related complications nor failure of occipital fixation. Bilateral rods with medial offset connectors allow parasagittal placement of 6 bicortical screws in the thickest and strongest bone along the occipital midline. The use of 6 occipital screws has been shown to be biomechanically advantageous. Using this technique, 6 occipital screws were easily placed in each of 17 patients, while 5 strong points of fixation were obtained in the other 3 patients. We experienced no failure of occipital fixation, and all surviving patients went on to fusion.

Study Design: Cadaveric specimens were measured to determine appropriate placement for C1 lateral mass screws. Instrumentation guidelines were developed and used to instrument a series of cadaveric specimens. Clinical experience with C1 lateral mass fixation was reviewed to evaluate results. Postoperative computed tomographic (CT) scans were reviewed to evaluate screw placement., Objectives: The cadaveric study measured the dimensions of the atlas and determined ideal trajectory for screw placement. This technique was applied clinically, and 50 cases were retrospectively reviewed for fixation difficulties, neurologic or vascular injuries, and perioperative complications. Postoperative CT scans were reviewed when available., Summary of Background Data: Halo application, posterior wiring, and C1 to C2 transarticular screws have been used to stabilize the upper cervical spine. Each technique has disadvantages, and C1 lateral mass fixation recently has gained popularity as a potential alternative. Recent anatomic studies have documented the dimensions of the C1 lateral mass and its ability to accommodate screw fixation. Small clinical series have documented early success with this technique., Methods: Fifteen specimens were stripped of soft tissue and measured by using calipers and CT scans. Guidelines were formulated for C1 lateral mass screw fixation. Additional specimens with intact soft tissue were instrumented without difficulty. A clinical series was reviewed to evaluate for complications related to this technique. Postoperative CT scans were reviewed to evaluate screw placement., Results: The C1 lateral mass safely accommodated screw fixation. Trajectory of 10 degrees medial and 22 degrees cephalad was preferred. The technique was safely applied in a series of 50 patients. Postoperative CT scans showed the ability of the surgeon to achieve the intended goals for starting point and safe trajectory., Conclusions: C1 lateral mass fixation is a safe alternative for upper cervical fixation with several potential advantages versus other techniques, but further clinical evaluation is warranted.

Study Design: An index for measuring the vertical relationship of atlas and axis is described., Objective: Deduction and application of vertical atlantoaxial index (VAAI) for quantifying the vertical atlantoaxial relationship of atlas and axis and classifying basilar invagination (BI) based on the VAAI., Summary of Background Data: A number of craniospinal parameters have been described to quantify the amount of BI in relation to herniation of odontoid into the cranium. Successful treatment of BI by distraction of atlantoaxial facet joint, placement of a spacer to maintain the distraction, and lateral mass fixation has been described recently. The treatment is based on the understanding that BI is in fact a disease of the atlantoaxial facet joints and is a result of progressive vertical instability. With this new concept and technique that involves preserving all bony elements and reduction of BI in the form of reducing the vertical atlantoaxial subluxation, we thought it was prudent to formulate an index to quantify the relation of atlas and axis in the sagittal plane., Method: Mid-sagittal computerized tomography (CT) scan films of 90 cases of BI treated by us between October 1999 and May 2005 with distraction and lateral mass plate and screw fixation were analyzed before and after surgery. The age of the patients ranged from 8 to 55 years and the male:female ratio was 2.5:1. Additionally, mid-sagittal CT scan films of hundred normal subjects in the same age group were analyzed as a control group. The VAAI was measured in all cases. VAAI is an index that measures the vertical relationship of the atlas and axis. The images were compiled and copies of the compilation were made. Two observers independently performed the measurements and intraobserver as well as interobserver agreement was assessed using the intraclass corelation (ICC) ) test (SigmaStat)., Results: The preoperative mean and mode values of VAAI in this series of patients were 0.53 (0.20 to 0.67) and 0.61, respectively. The postoperative mean and mode values of VAAI are 0.78 (range, 0.60 to 0.89) and 0.80, respectively. The mean and mode values of VAAI in general population were 0.80 (range, 0.76 to 0.85) and 0.80, respectively. The results in preoperative patients with BI demonstrated excellent intraobserver (ICC=0.96 and 0.98) and interobserver corelation coefficient (ICC=0.96). The results in normal subjects and postoperative CT scans of operated patients with BI also showed excellent intraobserver (ICC=0.97 and 0.98) and interobserver corelation coefficient (ICC=0.97)., Conclusions: VAAI can be an excellent measurement tool for the assessment of relationship of atlas and axis. Nonrheumatoid BI can be graded and classified depending on the value of VAAI.

Background: Occipitalization is defined as a congenital fusion of the atlas to the base of the occiput. We are not aware of any previous studies addressing the morphologic patterns of occipitalization or the implications of occipitalization in children. We present data on what we believe is the largest reported series of children with occipitalization studied with computed tomography and/or magnetic resonance imaging, and we provide a description of their clinical characteristics., Methods: We retrospectively reviewed all cases of occipitalization in children included in our spine database. Patient charts and imaging studies were reviewed. A new morphologic classification of occipitalization was developed from the two-dimensional sagittal and coronal reformatted computed tomographic reconstructions and/or magnetic resonance images. The classification includes four patterns according to the anatomic site of occipitalization (Zones 1, 2, and 3 and a combination of those zones), and it was applied to this group of patients. Imaging studies were also reviewed for evidence of cervical instability and for other anomalies of the craniovertebral junction., Results: Thirty patients with occipitalization were identified. There were twenty-four boys and six girls with a mean age of 6.5 years. The morphologic categorization was Zone 1 (a fused anterior arch) in six patients, Zone 2 (fused lateral masses) in five, Zone 3 (a fused posterior arch) in four, and a combination of fused zones in fifteen. Seventeen patients (57%) had atlantoaxial instability, and eight of them had an associated C2-C3 fusion. Eleven patients (37%) had spinal canal encroachment, and five of them had clinical findings of myelopathy. The highest prevalence of spinal canal encroachment (63%) was noted in patients with occipitalization in Zone 2., Conclusions: Occipitalization is associated with abnormalities that lead to narrowing of the space available for the spinal cord or brainstem. The risk of atlantoaxial instability developing is particularly high when there is an associated congenital C2-C3 fusion. Two-dimensional sagittal and coronal reformatted computed tomographic reconstructions and/or magnetic resonance images can help to establish the diagnosis and permit categorization of occipitalization in three zones, each of which may have a different prognostic implication.

Object: Congenital occipitocervical (OC) instability is uncommon in healthy children but can occur in many children with Down syndrome. A simple morphometric method of evaluating the OC joint in children with OC instability is presented, supported by a qualitative image analysis based on computed tomography (CT)., Methods: Thin-cut CT scans of the OC joint were obtained in eight patients with Down syndrome and one patient with congenital OC instability. These patients' CT scans were compared with those of 15 healthy age-matched control individuals. Morphometric analysis was performed by measuring the depth and length of the superior articular surface (SAS) of C-1, and these values were normalized for a comparison between groups. Qualitative data were acquired using a surface-rendering technique for a visual comparison of the C-1 SAS. Morphometric analysis demonstrated an absence of the concave C-1 SAS anatomy in patients with congenital OC instability compared with age-matched control individuals (0.083 compared with 0.202, p < 0.001). Three-dimensional (3D) image analysis of the C-l SAS supported this finding., Conclusions: Congenital differences in the shape of the OC joint are highly associated with atraumatic OC instability in children with Down syndrome. High-resolution CT imaging combined with 3D rendering techniques and surface mapping provides support for this assessment. It appears that abnormal OC joint shape is a contributing factor to congenital OC instability, especially in patients with Down syndrome.

The upper cervical spine includes the articulations of the occiput with atlas and the atlas with the axis, as well as the bony structures of the base of the skull, axis, and atlas. The unique anatomy of the upper cervical spine and the typical mechanisms of injury yield a predictable variety of injury patterns. Injuries to this area include occipital condyle fractures, occipitoatlantal dislocations, subluxations and dislocations of the atlantoaxial articulation, atlas fractures, odontoid fractures, and fractures of the arch of the axis. Injuries to this region are relatively common and can be easily overlooked because patients with the upper cervical injury may have an associated head injury, which can alter their level of consciousness and complicate obtaining an accurate history and physical examination. The complex regional anatomy and overlying structures make plain radiographic images difficult to interpret. Delayed recognition can result in significant disability. A thorough understanding of the clinical presentation, radiographic assessment, and mechanisms of injury can minimize morbidity and enhance treatment effectiveness for the more common upper cervical ligamentous and bony injuries.

Background: The clinical significance of the ponticulus posticus is far from clear. It has been associated with headaches, Barré-Lieou syndrome, photophobia, and migraine. However, little epidemiologic evidence for this exists., Objective: This study investigated the relationship of ponticulus posticus on x-ray studies and headache symptoms in a series of chiropractic patients., Methods: Eight hundred ninety-five patients who visited a chiropractic clinic for the first time and whose conditions required cervical spine x-ray examinations were studied. Complaints were categorized as migraine with aura, migraine without aura, cervicogenic headache, neck pain only, and other conditions. The presence or absence of the ponticulus posticus (whether partial or complete) was determined by means of a lateral cervical film and noted as a positive or negative finding. The data were analyzed by frequency analysis and Pearson's chi 2 test., Results: Forty-six percent of the sample were men and the predominant complaint was neck pain (33%). Most patients were in the fourth decade of life. The frequencies of the other complaints were migraine with aura (7%), migraine without aura (4%), cervicogenic headache (22%), other conditions (33%). An 18% prevalence of ponticulus posticus was found. This finding was significantly associated with migraine without aura (chi 2 = 4.97; P = .03) and not with any other conditions., Conclusion: In a chiropractic patient population that required cervical x-ray examinations, a significant association was found between ponticulus posticus and migraine without aura, with an odds ratio of 2.19:1 in favor of this complaint being present with the osseous anomaly. The mechanism for this remains obscure but may be related to ischemic compression of the vertebral artery or by dural tension at the craniocervical junction.

A rare case of atlanto-axial block vertebra and fusion of anterior arch with the dens, with instability at the atlanto-occipital joint, is reported. The literature is briefly reviewed.

This paper discusses occipitalization of the atlas and its relationship to the chiropractic practitioner. Patients commonly consult a chiropractor with complaint of headache, suboccipital stiffness, restricted motion, dizziness and other symptoms related to the upper cervical region. Differential diagnosis of the exact etiological factor of these symptoms must be made via a thorough history, physical examination, and roentgenological examination. If occipitalization of the atlas is detected on the initial roentgenological examination, then follow-up magnetic resonance imaging, computerized tomography or linear tomographic studies may be warranted to rule out concomitant diverse osseous and/or neural anomalous conditions of the cervical spine which may easily mimic symptoms of disorders commonly treated by the chiropractic practitioner. The chiropractic practitioner must obtain appropriate roentgenological and other diagnostic imaging studies to ensure proper evaluation of the structural integrity of the cervical spine before appropriate treatment can be rendered.

Congenital clefts and aplasias of the atlas vertebra, while rare, are often first encountered in the emergency room setting. Thirty-six patients with atlas malformations and 10 with Jefferson fractures were encountered. Sixteen of the patients with congenital malformations showed bilateral atlantoaxial lateral offset, a finding generally considered to be the result of fracture. The diagnosis of these abnormalities is readily made from plain films by noting their characteristic features. Anomalies produce lateral offset of 1-2 mm. Jefferson fractures produce a greater offset (over 3 mm).

Case records (523) were chosen at random from the files of J.F. Grostic, D.C. (deceased) for retrospective determination of the effects of chiropractic adjustments on atlas positioning relative to the occiput and axis. For each patient the recorded degrees of (1) atlas rotation and (2) laterality, both before and soon after spinal manipulative therapy, were extracted from the x-ray reports. Frequency histograms were made of pre- and post-adjustment degrees of laterality and rotation and the relative change of values analyzed statistically. Before manipulation, nine patients had zero atlas rotation and none were zero with respect to laterality. The mean deviation from zero degrees of "misalignment," was 2.75 and 2.63 respectively for rotation and laterality. After manipulation the corresponding values were 1.43 and 140, which is a statistically significant change. The numbers of patients who had zero rotations and laterality after adjustment were 156 and 151 respectively. In 63 patients the post-adjustment values were zero for both parameters. Under the circumstances presented in this retrospective study, these data tend to show that spinal manipulative therapy altered the position of atlas in the postulated direction.

Metrical and morphological findings, based on 107 human vertebral columns, related to the variations of the dens are given, and differences in the depth of the superior articular facets of the atlas and specific pertinent details related to the os odontoideum and epitransverse process are also provided and their possible clinical relevance indicated. Findings reveal considerable variation in the height of the dens (11 to 18 mm), but remarkably little in its anteroposterior and transverse diameters at the root. The use of the term "hypoplasia" with reference to the dens is discussed, and a need for more rigid criterian in the use of this term stressed. It is also suggested that there may be sufficient radiological evidence in a lateral radiography to lead one to suspect the presence of an os odontoideum or a separate dens caused by trauma in the distant past.

A new case of sub-occipital Pott's disease is reported: a 26 year old, coloured male patient from Senegal was admitted for: cervical pain of 6 month duration, neck stiffness, dysphagia, left XII paralysis and left hemiparesis. The radiological study found an anterior atlanto-axial subluxation, basilar impression, and increased thickness of the retropharyngeal soft tissue, lysis of the left occipital condyle and the left lateral mass. CT scan study revealed a retropharyngeal mass and an epidural contrast-enhanced lesion at the C2 C3 C4 levels. Chest-X ray showed one tuberculous lesion at the right apex. The research of Acid Fast Bacilli in gastric secretion samples and the results of the retropharyngeal mass puncture were positive. An antituberculous trichemotherapy was started. After early reduction by skull tongs traction, an occipito-cervical arthrodesis by Roy Camille plates was performed, followed by the wearing of a minerva plaster jacket and then a plastic collar. Each one for a 5 month period. One year later, there remained only a left XII paralysis, but the bony reconstruction was not yet obvious on tomography. A survey of the literature of 70 cases of sub-occipital Pott's disease has pointed out these findings: cervical pain (98%), neck stiffness (82%), Atlantoaxial subluxation (68%), thickened prevertebral soft tissue shadow (77%), lateral mass lysis (48%) other tuberculous focus (29%). The main therapeutic trends are: early and long-lasting antituberculous poly-chemotherapy, early reduction of subluxations, prolonged contention for slight osteolytic lesions and for major: lytic lesions, a posterior surgical procedure either by bone graft combined with wires or preferably fusion by means of occipito-cervical plates. The removal of abscess is discussed.

The results of a CT-anatomical correlative study of the main ligaments of the cervico-occipital hinge are reported. CT criteria of normal ligamentous structure of this region are presented in axial, coronal and sagittal views with a special attention to the transverse ligament of the Atlas. Examples of pathological transverse ligaments are illustrated and emphasis is laid upon the better statement CT allows in such cases.

Postmortem radiographic examinations in 312 victims of fatal traffic accidents were analyzed with respect to injuries to the cervical spine. Most fractures and dislocations in this group were found to involve the craniocervical junction and the upper two cervical segments. Over half were flexion injuries, one-fifth caused predominantly by extension. Flexion and extension views were found to be helpful in demonstrating the instability of many injuries.

Occipitoatlantoaxial malformation was diagnosed in a 19-month-old mare of Appaloosa breeding and in a 3-year-old Quarter Horse gelding. Both horses had abnormal head and neck carriage since birth, but neurologic deficits did not become evident clinically until the horses reached 2 and 3 years of age, respectively. Palpation and manipulation of the base of the skull and cervical area proved to be useful diagnostically. Movement could not be elicited at the atlantooccipital joint but, in comparison with clinically normal horses, the range of dorsoventral motion at the atlantoaxial joint was increased. Alternate subluxation and relocation of this joint generated audible clicking sounds. Radiography revealed symmetric atlantooccipital fusion, with modification of the atlas, atlantoaxial joint, and axis. These findings were confirmed at necropsy.

Pyogenic osteomyelitis rarely affects the first and second cervical vertebrae, and when it does it can progress to abscess formation, compressing the spinal cord. If the process is unrecognized, it can be fatal. The cases of five patients are reported. Two patients were treated by anterior débridement and posterior cervical-occipital arthrodesis; one, by transoral drainage; one, by posterior cervical-occipital arthrodesis; and the fifth, by posterior atlanto-axial arthrodesis. The causative organism was Staphylococcus aureus in four patients and Pasteurella multocida in one. In all patients, intravenous antibiotics were used, followed by prolonged administration of oral antibiotics. All five patients recovered.