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Study Design: Retrospective descriptive study., Objective: The aim of this study was to create topographical maps of occipital bone thickness and venous sinus (VS) presence to assess the risks of screw insertion in four commercially available occipital plates., Summary of Background Data: Craniocervical junction instability and deformity are serious pathological conditions that require posterior fixation of the occipital bone to the cervical vertebrae. Insertion of occipital bone screws requires evaluation of both occipital bone thickness for effective internal fixation and intracranial VS presence for vascular injury prevention. Despite the surgical risks, there is a paucity of research on safe screw placement., Methods: We created a matrix of 231 standardized measurement points to analyze the occipital bone thickness and VS presence in cervical spine CT angiograms. These measurements were used to create topographical maps of occipital bone thickness and likelihood of VS presence, which we then compared to the screw hole configurations of four occipital plates., Results: Hundred patients were assessed. Maximum occipital bone thickness of 13.9 ± 3.3 mm was midline in the occipital bone, 45 mm from the foramen magnum, around the external occipital protuberance (EOP). Regions with thicknesses >8 mm were 2 cm lateral to the EOP at the level of the superior nuchal line and 2.5 cm inferior to the EOP. The area with the highest VS presence rate was around the EOP and the superior nuchal line. The right transverse VS was more prominent in both sexes., Conclusion: There is a limited area of the occipital bone with thicknesses for enough screw purchase. Previous studies have shown 8 mm as the minimum screw length to reduce the risk of implant failure. In our analysis, only "T"-shaped plates had configurations with thicknesses >8 mm for each screw hole. For every screw hole in the analyzed occipital plates, there was a possibility of VS presence ranging from 8% to 33%.Level of Evidence: 5., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)

Study Design: Retrospective review., Objective: Evaluate radiographic and clinical outcomes for infants and children, who underwent rigid occipito-cervical fixation for traumatic craniocervical dissociation (tCCD)., Summary of Background Data: Traumatic craniocervical dissociation is devastating. Children are at high risk but make up a large number of survivors. Non-rigid fixation has traditionally been favored over screw and rod constructs due to inherent challenges involved with instrumenting the pediatric craniocervical junction. Therefore, outcomes for rigid occipito-cervical instrumentation in infants and young children with tCCD remain uncertain., Methods: Retrospective review of children who survived tCCD between 2006 and 2016 and underwent rigid occipito-cervical fixation., Results: Fifteen children, from 8 months to 8 years old (mean, 3.8 yr), were either a passenger (n = 11) or a pedestrian (n = 4) in a motor vehicle accident. Seven patients had weakness: five with quadriplegia, one with hemiparesis, and one with bilateral upper extremity paresis. Ten patients had concurrent C1-2 instability. At last follow-up, four patients had improved motor function: one with bilateral upper extremity paresis and one with hemiparesis regained full strength, one with quadriplegia regained function on one side while another regained function in bilateral upper extremities. All underwent rigid posterior occipito-cervical fixation, with two patients requiring additional anterior and posterior fixation at non-contiguous levels. Fourteen patients were stable on flexion-extension x-rays at a mean follow-up of 31 months (9-1 yr or longer, 7-2 yr or longer). There were no cases of deformity, growth disturbance, or subaxial instability., Conclusion: Children who survive tCCD may regain function after stabilization. Rigid internal rod and screw fixation in infants and young children safely provided long-term stability. We advocate using C2 translaminar screws to exploit the favorable anatomy of pediatric lamina to minimize the risks of occipitocervical (OC) instrumentation., Level of Evidence: 4.

Study Design: Retrospective study., Objective: To investigate whether clivodens angle (CDA) could diagnose basilar invagination (BI) at computed tomography (CT)., Summary of Background Data: Over the years, multiple craniometric methods such as Chamberlain line, McGregor line, McRae line, Wackenheim clivus baseline, and Welcher basal angle have been described for evaluation of craniovertebral junction anomalies, initially with radiography and later with CT. However, such a variety of measurements in turn reflects the difficulty in making a definite diagnosis of BI and there is a certain disadvantage in all of these criteria because the anatomic landmarks vary within a normal range., Methods: CDA, described an angle formed at the intersetion of a line that runs along the long axis of the clivus and one that runs along the long axis of the dens, was measured on mid-sagittal reconstructed CT images from 63 BI patients and 100 control participants to compare the two groups by using independent-sample t test. Interobserver reliability was evaluated with Kendall correlation coefficient. For evaluating the diagnostic performance and determining the cutoff value of CDA, receiver operating characteristic curve was utilized., Results: The measurement of CDA showed good interobserver agreement (KCC = 0.891). Compared with control participants whose mean value was 135.8 degrees ± 9.2 (range, 118-156°), BI patients had a significantly smaller one (P < 0.001), 110.4 degrees ± 15.8 (range, 55-140°). The area under receiver operating characteristic curve was 0.937 (95% confidence interval: 0.901, 0.973), and the cutoff value of 125 degrees had the largest Youden index (J), 0.715., Conclusion: Having a better diagnostic performance than clivoaxial angle, CDA can be utilized for diagnosing BI., Level of Evidence: 3.

Study Design: A finite element analysis., Objective: The aim of this study was to determine the biomechanical differences between atlantoaxial fusion cage combined with transoral atlantoaxial reduction plate fixation (TARP + Cage, modified TARP technique) and that combined with C1 lateral mass screw and C2 pedicle screw fixation (C1LS + C2PS + Cage, modified Goel technique) in the treatment of basilar invagination (BI) by finite element analysis., Summary of Background Data: Clinical studies have shown that transoral anterior atlantoaxial release followed by TARP fixation can achieve reduction, decompression, fixation, and fusion of C1-C2 through a transoral-only approach. Although cage has been used to reduce the BI through posterior approach, there are no studies referred to the cage combined with TARP for C1-C2 fusion., Methods: A finite element model was used to investigate and compare the stability between TARP + Cage fixation and C1LS + C2PS + Cage fixation in the treatment of BI. Vertical load of 40  N was applied on the C0, to simulate head weight, and 1.5  Nm torque was applied to the C0 to simulate flexion, extension, lateral bending, and rotation., Results: In comparison with the C1LS + C2PS + Cage model, the TARP + Cage model reduced the ROM by 44.7%, 30.0%, and 10.5% in extension, lateral bending, and axial rotation, while the TARP + Cage model increased the ROM by 30.0% in flexion, and the TARP + Cage model also led to lower screw stress in all motions with one exception (anterior C2PS stress in extension)., Conclusion: Our results indicate that the TARP + Cage fixation may offer higher stability to C1LS + C2PS + Cage in extension, lateral bending, and axial rotation but lower stability in flexion. Compared with modified Goel technique, the modified TARP technique not only has the capability of transferring the load and distributing the stress but also can provide neural decompression, stabilization and fusion, and restore C1-C2 normal fusion angle., Level of Evidence: N/A.

Study Design: A retrospective analysis of 11 cases., Objective: The aim of the study was to evaluate the effectiveness of anterior cervical and retropharyngeal debridement combined with posterior occipital-cervical fusion in treatment of upper cervical spinal tuberculosis., Summary of Background Data: The anterior approach simply could not provide strong fixation whereas the posterior treatment could not clear up the lesions completely. The method combining anterior and posterior approaches to treat the upper cervical tuberculosis is advisable., Methods: The clinical data of 11 patients with upper cervical tuberculosis who underwent an upper cervical operation in our hospital were retrospectively analyzed. All 11 patients underwent the surgery of anterior cervical and retropharyngeal approaches to debridement, and then, according to the different degrees of patient pedicle destruction and deformity, different occipitocervical approaches were used (either through pedicle screw or laminar screw fixation). After surgery, antituberculosis drugs were administered for 18 months. During the follow-up, neurological function, clinical symptoms, fusion, reducible degree, and complications were all evaluated and documented., Results: Surgeries for 11 patients were performed successfully; anatomical reduction was achieved in nine cases, bony fusion was achieved in all 11 patients, and all cases with tuberculosis were clinically cured in the 18 months after the operation. The Japanese Orthopaedic Association score increased from 8.4 ± 1.3 preoperative to 15.0 ± 1.3 in the last follow-up (P < 0.05). The occipitocervical visual analog scale decreased from 6.7 ± 0.6 preoperative to 0.6 ± 0.6 at the last follow-up (P < 0.05). No serious complications were documented during follow-up., Conclusion: The approach of anterior cervical and retropharyngeal debridement combined with posterior occipitocervical fusion has been proved to be an effective treatment of upper cervical tuberculosis, which plays an important role in removing the lesions, restoring stability, and anatomical reduction., Level of Evidence: 4.

Study Design: This study is a computed tomographic-based morphometric analysis of the pediatric occipital bones as related to pediatric occipitocervical fusion., Objective: To quantify reference data concerning the thicknesses of the immature occipital bones to guide the pediatric occipitocervical fusion., Summary of Background Data: To the best of our knowledge, no published study has provided insight into the thicknesses of pediatric occiputs with different age groups., Methods: 80 pediatric patients were divided into 4 age groups, and their occiputs were studied on Philips Brilliance 256 iCT scan., Results: The mean thickness ± standard deviations of the pediatric occipital bones with different age groups is shown. The median and the paramedian regions are always thicker than the more lateral regions at each age group and the thickest point in the occiputs is mostly at the external occipital protuberance. The mean thickness of occiputs showed an obvious significant difference between each 2 age groups and no significant difference between male and female in different age groups except the group 4., Conclusion: Our investigation provides insight into the anatomy of occiputs in pediatric population and preoperative CT evaluation must be required to further decrease the risk of occipitocervical fusion.

Study Design: A case report., Objective: To describe a unique craniocervical junction anomaly and its implications both on mobility and stability of the skull base., Summary of Background Data: Congenital variations in the craniocervical junction (CVJ) are rare and frequently symptomless. Mild traumas may commonly rouse symptoms which help to unveil such anomalies through radiological investigations., Methods: A 73-year-old woman developed a monoparesis of the right arm after a mild craniofacial trauma. Neurological examination revealed hyper-reflexia in the upper limbs, confirming the strength impairment in the right one. Radiology showed a post-traumatic bulbo-medullary contusion sustained by a unique and unstable association of the first occipital condyles congenital dislocation ever reported with a rare condylus tertius. The patient underwent posterior decompression and occipitocervical screw-rod fixation and fusion. Clinico-radiological follow-up highlighted a gradual recovery of the neurologic impairment and the posterior decompression with resolution of the spinal cord contusion., Results: Although apparently stable the hyperostosis and the irregularly shaped condylar surfaces behind the 3-points mechanism of skull base support played a critical role in determining axial instability. The imbalance due to skull-cervical spine malpositioning may consequently trigger a vicious cycle of development of osteophytes leading to spinal cord narrowing with neurologic decline. A surgical strategy providing for posterior decompression and fixation satisfied the need to solve both bulbo-medullary constriction and skull base instability., Conclusion: Clinical evidences about CVJ anomalies are lacking and symptoms, when present, tend to be vague. Although extremely rare clinicians should be aware of CVJ variations by engaging to improve their knowledge of imaging anatomy, embryology, CVJ basic craniometry and anatomic relationships. Studies on developmental control genes may offer future perspectives of early diagnosis and targeted treatments., Level of Evidence: 4.

Study Design: Retrospective cohort study., Objective: This study describes clinical and radiological results of a new cable technique for occipitocervical fusion (OCF) in children with skeletal dysplasia (SD)., Summary of Background Data: Anatomical variability and poor bone quality make upper cervical surgery technically challenging in patients with SD. We present a new cable technique for OCF in children with SD when the posterior elements are not of a size or quality for other types of instrumentation., Methods: Retrospective review of 24 patients with SD (8 boys, 16 girls) who underwent OCF between 2001 and 2011. In this technique, cables provide compression across a bone graft that is prevented from entering the canal and the graft resists excessive lordosis. Demographic and radiographical data are presented. All patients were followed for initial outcomes of surgery, and 20 patients (83%) were followed for 2 years or more for mid- and long-term outcomes., Results: Mean age at surgery was 6.5 years and mean follow-up was 4.1 ± 2.4 years. This technique was used as a primary procedure in 20 and a revision procedure in 4 patients. Diagnoses included Morquio syndrome (6), spondyloepiphyseal dysplasia (9), spondyloepimetaphyseal dysplasia (5), metatropic dysplasia (3), and Kniest syndrome (1). Ten patients had upper cervical instability and features of cervical myelopathy, and the remaining 14 patients had instability and signal changes on magnetic resonance image. Fusion extended from occiput to C2 in 71% patients, and upper cervical decompression was needed in 92% patients. Postoperatively, all patients were immobilized in a halo vest for mean duration of 12 weeks. Fusion was achieved in all patients. Complications included halo pin-tract infections (7), junctional instability (2), and extension of fusion (4)., Conclusion: This new cable technique is a good alternative for OCF in patients with SD who have altered anatomy at the craniocervical junction not amenable to rigid internal fixation., Level of Evidence: 4.

Study Design: This study is a computed tomographic (CT)-based morphometric analysis of the pediatric occipital condyles as related to occipital condyle screw placement., Objective: To quantify reference data concerning the dimensions of the immature occipital condyles to guide the placement of occipital condyle screw., Summary of Background Data: To the best of our knowledge, no published study has provided insight into the anatomy of occipital condyle of the pediatric population with different age groups., Methods: Sixty-nine pediatric patients were divided into 4 age groups, and their occipital condyles were studied on CT scans. Condylar length, width, height, sagittal angle, and sagittal angle lengths were measured on Philips Brilliance 16 CT., Results: The mean pediatric coronal height, sagittal length, and axial width noted statistically significant age-related differences were 9.0 mm, 21.3 mm, and 9.8 mm, respectively. The mean sagittal angle for all patients was 27.2 ± 5.1° (range, 15.1-41.0°). In 82.6% (114/138) of the occipital condyles, the anatomy could accept the occipital condyle screw (width ≥8 mm and height ≥6.5 mm)., Conclusion: Our investigation provides insight into the anatomy of occipital condyle of the pediatric population with different age groups. As the pediatric occipital condyles have sufficient occipital bone for appropriate fixation or fusion, the occipital condyle screws fixation is a feasible technique for children. Even so, given the evolution of this technique being still in its infancy and the complexity inherent to the craniovertebral junction, a careful radiological analysis of occipital condyle must be required in preoperative planning and feasibility determination., Level of Evidence: N/A.

Study Design: Prospective descriptive study., Objective: To verify the feasibility and utility of evaluating venous sinuses (VSs) using computed tomography venography (CTV) concomitant with preoperative CT angiography (CTA) for safe occipital screw fixation., Summary of Background Data: Preoperative evaluation of the vertebral artery by CTA is indispensable in occipitocervical spinal instrumentation surgery. Despite accumulating evidence showing the potential of CTV, no studies have reported the usefulness of concomitant use of CTV and CTA before placement of occipital plate-screw constructs., Methods: We analyzed 30 consecutive patients who underwent CTV simultaneously with CTA. First, we investigated VS anatomy in individual cases and classified the continuity patterns of relevant VSs. Subsequently, we evaluated the probable risk zones for VS injury, from the viewpoint of occipital screw insertion., Results: VSs can be clearly visualized using CTV simultaneously with CTA examination without significant increase of radiation exposure or extra workload for radiographical technicians. VS continuity was classified into 4 categories: the confluence type (n = 9), bifurcation type (n = 8), transverse type (n = 11), and others (n = 2). The confluence of sinuses and their relevant VSs were greatly variable between individuals, and occasionally, some cases with high-risk morphology for VS injury in occipital screw placement were observed., Conclusion: Our findings indicate that there is no universal position for safe insertion of occipital screws that is applicable to all individuals. It is risky to determine optimal screw placement, only on the basis of traditional cadaveric information such as occipital bone thickness and several external bony landmarks. Spine surgeons must recognize that VS injury may occasionally lead to life-threatening complications. The detailed information on VSs obtained by preoperative CTV examination combined with CTA in individual cases can be useful in preoperative planning and can contribute greatly to the improvement of surgical safety., Level of Evidence: 2.

Study Design: Retrospective case series., Objective: The aim of this study was to describe the clinical outcomes of cervical reduction and occipital-C2 transarticular (OCTA) fixation with an assistance of intraoperative 3-dimensional navigation system (ITNS) during the treatment of reducible occipitocervical instability (OCI) in patients with Klippel-Feil syndrome (KFS) with occipitalization of the atlas and fusion of C2-C3., Summary of Background Data: Patients with KFS have congenital fusions of at least 2 cervical segments and may gradually develop symptoms at the hypermobile articulations adjacent to the cervical synostosis. This is particularly common in patients with KFS with occipitalization of the atlas and C2-C3 fusion. These patients may be at risk for instability and neurological complications of the occipitocervical junction that require occipitocervical reconstruction and fusion. Numerous treatment techniques are available for this pathological condition. However, there has yet to be a study of reducible OCI, showing successful treatment with intraoperative reduction and posterior OCTA fixation using ITNS., Methods: From 2006 to 2011, 9 patients with KFS with reducible OCI attributed to occipitalization of the atlas and C2-C3 fusion were surgically treated. After a limited foramen magnum decompression, reduction of the OCI was conducted by intraoperative cervical traction and extension, followed by OCTA fixation using a direct posterior approach and with the assistance of ITNS. The follow-up period ranged from 6 to 60 months (mean, 31 mo)., Results: Good decompression and bone fusion were achieved in all the patients. The clinical symptoms had improved for all patients. There were no intraoperative or postoperative complications., Conclusion: In patients with KFS with occipitalization of the atlas and C2-C3 fusion, manual cervical traction in tandem with cervical extension, followed by posterior OCTA fixation and fusion provides a safe, effective treatment of OCI and ventral brainstem impingement. IFTN is a feasible tool for monitoring cervical reduction and OCTA screw insertion in patients with KFS with this pathological condition.

Study Design: Consecutive case series and literature review., Objective: To describe the utility of 3-dimensional computed tomographic angiography (3D CTA) for evaluating vertebral artery (VA) anomalies before surgery., Summary of Background Data: Recent advances in instrumentation surgery at the craniovertebral junction (CVJ) enable us to perform rigid internal fixation. However, the risk of VA injury as a complication of the surgery has become a major problem. Thus, the importance of preoperative evaluation of the VA course has been emphasized., Methods: Cases of 100 consecutive patients who underwent CVJ instrumentation surgery since July 1998 were analyzed. Occipitocervical/thoracic or C1-C2 posterior fusion was performed for atlantoaxial subluxation (AAS) in 59 patients and cervical fixation including C2 was required for middle-to-lower cervical lesions in 41 patients. Twenty-seven patients with AAS had a congenital skeletal anomaly (CSA) at the CVJ including os odontoideum and occipitalization of C1 (AAS-CSA[+] group). Anomalous VAs at the extra- and intraosseous regions were evaluated by 3D CTA., Results: No neurovascular injury occurred during surgery. Abnormal courses of the VA at the extraosseous region were detected in 10 cases: 2 had fenestration and 8 had a persistent first intersegmental artery. All 10 cases were in the AAS-CSA(+) group. A high-riding VA was detected in 31 cases. Fourteen out of the 31 cases were in the AAS-CSA(+) group, indicating 51.9% of the AAS-CSA(+) group had high-riding VA. In the AAS-CSA(+) group, a C1-C2 transarticular screw and C2 pedicle screw were actually inserted in 58% and 31% of the planned insertions, respectively., Conclusion: The present findings suggest that the frequency of an abnormal VA at the extra- and intraosseous regions is increased when patients have AAS and CSA at the CVJ. Using preoperative 3D CTA, we can precisely identify anomalous VAs and thereby reduce the risk of their intraoperative injury.

Study Design: In vitro human cadaveric biomechanical study., Objective: The objective was to evaluate and compare the construct stability of occiput-C1-C2 fixation provided by C0-C1 transarticular screws or occipital condyle screws., Summary of Background Data: The placement of an occipital plate is commonly recommended in occipitocervical fixation surgery. However, there are unique clinical situations in which the placement of the occipital plate may not be possible or may have already failed. For these situations, 2 novel techniques that use the occipital condyle have been recently introduced: (1) C0-C1 transarticular screws fixation and (2) direct occipital condyle screws and C1 lateral mass screws fixation. However, there is a lack of thorough biomechanics studies of these techniques., Methods: Nondestructive kinematic tests and destructive tests were conducted in 16 fresh frozen cadaveric spines. As a nondestructive kinematic test, a pure moment of up to 2.0 N·m was applied in smooth continuous flexion/extension, lateral bending, and axial rotation motions. In addition to an intact-state case, a total of 5 different constructs (standard occipital plate, C0-C1 transarticular screws with/without occipital plate, and occipital condyle screws with/without occipital plate) were tested after destabilization of C0-C1 and C1-C2. All constructs had C2 pedicle screws fixation, and occipital condyle screws were incorporated with C1 lateral screws., Results: All fixation techniques significantly reduced ranges of motion compared with the intact state. In comparison with the standard occipital plate construct, the 2 novel techniques showed higher stability in axial rotation and lower stability in lateral bending. In both nondestructive and destructive tests, there were no statistical differences between C0-C1 transarticular screw construct and occipital condyle screw construct., Conclusion: The C0-C1 transarticular screw technique and direct occipital condyle screw with C1 lateral mass screw technique can be salvage fixation methods when occipital plate fixation is not feasible.

Study Design: Evaluation by simulation of screw insertion using fine-cut computed tomographic (CT) scans and screw trajectory software., Objective: To evaluate the feasibility and optimal trajectory of the occipital condylar screw., Summary of Background Data: To the best of our knowledge, no large series examining the feasibility and optimal trajectory of occipital condylar screws have been published., Methods: We simulated unicortical placement of a 4 × 18-mm screw using 1-mm sliced CT scans and 3-dimensional screw trajectory software in 314 occipital condyles of 157 patients. With the screw tip directed toward a point just below the tip of the basion on lateral fluoroscopy, 3 entry points were compared in view of success rate of screw placement, safe range of medial angulation in an axial plane, and maximum screw length., Results: The lateral entry point had the highest success rate (93.0%) of screw placement, mean safe range of the medial angulation (10.9°), and maximum screw length (20.7 mm), followed by the middle (92.0%, 10.8°, and 20.6 mm, respectively) and medial (74.2%, 7.7°, and 19.7 mm, respectively) entry points. While the lateral and the middle entry points did not have any statistically significant difference in the 3 parameters, they were significantly better than the medial entry point. All 3 entry points had highly variable ranges of safe medial angulation, making it difficult to provide a single recommended value., Conclusion: Screw placement is feasible in up to 93% of the occipital condyles. The lateral and the middle entry points are significantly better than the medial entry point. Selection between the middle and the lateral entry points should be individualized taking into account local anatomic variation. Because the medial angulation of these screws is highly variable, preoperative 3-dimensional CT evaluation and possibly even intraoperative navigation may be required.

Study Design: This retrospective study was conducted to analyze the radiographic and clinical results in seven patients with primary basilar invagination who accepted a combination of continuous cervical traction before operation and posterior screw/rod system reduction together with occipitocervical fusion., Objective: To evaluate the radiographic and clinical outcomes of this treatment regimen in combination of continuous cervical traction and posterior instrumented reduction with pedicle screw/rod system., Summary of Background Data: Primary basilar invagination poses considerable difficulties in the surgical management regarding surgical approach, reduction, and decompression. A variety of methods have been described to treat primary basilar invagination and all methods existed limits., Methods: There were four male and three female patients, and the ages ranged from 12 to 40 years (average age, 22.3 yr). Six patients presented neurologic deficits. The Nurick scale was from 1 grade to 4 grades (average, 2.7 grades). The distance of the odontoid tip in relation to Wackenheim line, atlantodental interval, Klaus height index, craniospinal angle, modified Omega angle, and cervicomedullary angle were measured pretreated and after surgery. When the tip of odontoid process was inferior or approximate to Wackenheim line and McRae line after cervical traction, the operation of reduction and fixation should be accepted., Results: After surgery, the mean Wackenheim value and atlantodental distance were reduced 9.3 mm and 2.0 mm, respectively. The mean Klaus height index, craniospinal angle, Omega angle, and cervicomedullary angle improved 6.5 mm, 17.0°, 11.6°, and 27.4°, respectively. All postoperative data had a significance compared with pretreatment data (P < 0.05). There was a tendency that younger patients were able to obtain more ideal reduction than adults. Of six patients with neurologic symptoms, five patients were normal or nearly normal. All patients achieved solid fusion., Conclusion: This case series demonstrates a safe, easy, and effective treatment regimen for the patients with primary basilar invagination.

Study Design: Radiologic evaluation of computed tomography (CT) scans using screw insertion simulation software., Objective: To investigate the optimal entry point and trajectory of atlantooccipital transarticular screws., Summary of Background Data: To our knowledge, no large series focusing on the placement of atlantooccipital transarticular screws have been published., Methods: We used 1.0-mm sliced CT scans and 3-dimensional screw trajectory software to simulate 4.0-mm screw placement. Four entry points were evaluated. Screw placement success rate, safe range of medial angulation, and screw length using each entry point were determined., Results: CT scans of 126 patients were evaluated, for a total of 252 screws for each entry point. On simulation, the 2 lateral entry points showed significantly higher success rates and safe range of medial angulation than the 2 middle points. The 2 lateral entry points had similar success rates (98.0% for anteriolateral (AL) point and 97.6% for posteriolateral (PL) point). Although the safe range of medial angulation was significantly wider for the AL point (26.1 degrees) than for the PL point (23.7 degrees), the screw lengths were significantly longer for the PL point (32.6 mm) than for the AL point (29.4 mm). For both points, 30 degrees of medial angulation led to highest rate of successful screw placement, but the rate was only 79.4% and 80.2%, respectively., Conclusion: Although there was no significant difference in success rates between AL and PL points, PL is likely the best entry point. Although 30 degrees medial and approximately 5 degrees upward angulation led to the highest rate of successful screw placement, the rate was only around 80%. Given the wide individual variation, we recommend that a preoperative 3-dimensional CT scan be obtained when attempting atlantooccipital transarticular screw fixation.

Study Design: Technique note., Objective: To describe a modified minimally invasive approach for the treatment of irreducible atlantoaxial dislocation (IAAD)., Summary of the Background Data: Currently, the most frequently used route for the treatment of symptomatic IAAD is transoral-transpharyngeal approach. Although it provides the most direct route to the atlantoaxial joint, potential problems may arise because of traverse oral cavity, such as the potential risks of infection, postoperative disturbances of breathing, and swallowing. The aim of this study was to describe a less-invasive approach for IAAD., Methods: Four consecutive patients with IAAD underwent the combined video-assisted atlantoaxial transcervical release (VAAT) procedure and posterior occipital-cervical fusion or C1-C2 screw fixation at Tongji Hospital. Clinical characteristics, images data, operative variables, and follow-up data were recorded., Results: Four cases presented with signs and symptoms of spinal cord dysfunction caused by IAAD underwent 1-stage anterior release, reduction, and posterior fixation. Three cases received C1-C2 screw fixation, and 1 case with occipitocervical fixation. Postoperative imaging studies showed that complete decompression was achieved in all the cases. No systemic infections, cerebrospinal fluid leaks, or adverse neurologic sequelae were found. None of the patients required prolonged intubation, tracheostomy, or enteral tube feeding. All patients started to oral intake after anesthesia. Neurologic status in 1 case remained at baseline whereas it improved in the others. The mean follow-up period was 9 months (6 approximately 12 months). All cases achieved solid fusion, without implants failure., Conclusion: Our initial experience showed that the VAAT procedure for IAAD is a safe supplement and alternative to conventional and transcervical procedures.

Study Design: A case report of traumatic atlantooccipital dislocation (AOD) managed by intraarticular-posterior fusion from a posterior approach at the C0-C1 level with preservation of C1-C2 motion., Objective: To present a new technique for atlantooccipital fusion with long-term follow-up., Summary of Background Data: There is an increasing number of patients with AOD who have preservation of neurologic function. The most frequent method used to treat this condition is occipitocervical fusion. There has been a tendency in recent years to minimize the extent of stabilization, performing occipitoatlantal fusion only. However, it is difficult to achieve a solid fusion between C0 and C1, and the long-term effect of the insufficiency of lig. alaria on C0-C2 stability is unknown. The authors present a modified technique of C0-C1 fusion that aims to enhance fusion and achieve greater stability., Methods: A 11-year-old child with AOD was initially treated unsuccessfully with a halo device for 3 months. As instability persisted, an isolated C0-C1 fusion was performed from a posterior approach. This anatomically based intraarticular fusion technique comprises removal of the articular cartilage of the atlantooccipital joints, and cancellous bone autografting at the atlantooccipital joints and between the occiput and posterior arch of C1, supported by an occipital plate linked by rods to lateral mass screws in the atlas., Results: This technique of increased bony fusion surface and internal fixation provided an excellent result with full recovery of minor neurologic deficits. At long-term follow-up, 9 years after surgery, the patient was free of signs and symptoms; solid fusion of the C0-C1 joint, and normal values for rotation of the C1-C2 segment were recorded., Conclusion: Intraarticular and posterior fusion of the atlantooccipital joint was able to provide an excellent long-term clinical outcome in the treatment of traumatic AOD in a child. This is the first report of an intraarticular fusion of the C0-C1 segment and the longest follow-up published on isolated C0-C1 stabilization.

Study Design: A human cadaveric biomechanical study comparing craniocervical fixation techniques., Objective: To quantitatively compare the biomechanical stability of a new technique for occipitocervical fixation using the occipital condyles with an established method for craniocervical spine fusion., Summary of Background Data: Stabilization of the occipitocervical junction remains a challenge. The occiput does not easily accommodate instrumentation because of access and spatial constraints. In fact, the area available for the implant fixation is limited and can be restricted further when a suboccipital craniectomy has been performed, posing a challenge to current fixation techniques. Occipital screws are also associated with the potential for intracranial complications., Methods: Six fresh frozen cadaveric specimens occiput-C4 were tested intact, after destabilization and after fixation as follows: (1) occipital plate with C1 lateral mass screws and C2 pars screws and (2) occipital condyle screws with C1 lateral mass screws and C2 pars screws. Specimens were loaded in a custom spine testing apparatus and subjected to the following tests, all performed under 50-N unconstrained axial preload: flexion, extension, lateral bending, and axial rotation at 1.5 Nm. The constructs were statistically compared with a one-way analysis of variance and compared with the intact condition., Results: Motions were reduced by approximately 80% compared with the intact condition for both configurations under all motions. There were no statistically significant differences in the range of motion (ROM) between the 2 instrumentation conditions. The mean values indicated decreased ROM with the novel occipital condyle screw construct in comparison with the standard occipital plate and rod system., Conclusion: Craniocervical stabilization using occipital condyle screws as the sole cephalad fixation point is biomechanically equivalent with regard to the modes tested (ROM and stiffness) to the standard occipital plate construct.

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.

Study Design: Technical note., Objective: To introduce the application of navigation system with software for brain surgery to the upper cervical spine of patients who have previously had occipitocervical (O-C) fusion., Summary of Background Data: The anterior approach to the spine using a navigation system with software for spine surgery is difficult because the registration tends to be inaccurate. However, after O-C fusion, the upper cervical spine is considered part of the skull, and a navigation system with software for brain surgery in which the registration is performed using the head with several markers attached to it can be applied., Methods: Three patients with previous O-C fusion-2 with upper cervical chordoma and 1 with a disc herniation at C2/3-were treated using this technique., Results: In the first case, with a huge retropharyngeal C1 chordoma, this technique was very helpful in blindly dissecting the nonvisible parts of the tumor. In the second case, with a C2 chordoma, the vertebral arteries were successfully exposed under the guidance of the navigation system at both primary and revision surgery. In the third case, with disc herniation at C2/3, the herniated disc was removed successfully with the totally fused spine. In this application, computed tomography images can be merged freely with magnetic resonance images, which is helpful to clarify the soft tissues such as tumor, disc herniation, or the dural tube., Conclusion: This technique greatly supports surgeons inexperienced in the anterior approach to the upper cervical spine or surgeons at revision surgery who may be lost in and daunted by an unfamiliar operation field surrounded by important structures. Although an anterior approach to the upper cervical spine in the patient with O-C fusion may rarely be required, this application should be considered.

Study Design: Biomechanical evaluation of occipitocervical instrumentation techniques., Objective: Compare methods of occipital instrumentation by quantifying load sharing of occipital screws and measuring motion across instrumented occipitocervical spines., Summary of Background Data: Newer occipitocervical plate/screw systems that attach to longitudinal rods have been developed to improve fixation. These devices place screws in the center of occipital bone or off-midline. Midline plates offer screw purchase in thicker bone. Off-midline systems may increase the effective moment arm for torsional and lateral bending control. Measurement of screw loads within occipital plates is useful for determining optimal plate configuration., Methods: Ten cadaveric specimens (occiput-C4) were tested in flexion/extension (FE), lateral bending (LAT), and axial rotation (ROT) over +/-3 Nm pure moment. After intact testing, 4 occipitocervical fixation constructs were tested using washer load cells to assess loading across screws used to fix the plates to the occiput. Parasagittal occipital plates were positioned either convex or concave side facing medially. Each plate was first fixed using 3 screws (rostral, middle, caudal), then with the caudal screw eliminated (simulated failure). Range of motion (ROM) and peak screw loads are reported., Results: ROM decreased from intact to any of the 4 fusion plate configurations in FE, LAT, and ROT (P << 0.05), but not between plate configurations. Screw load significantly decreased from medially convex to medially concave configurations in LAT, but no significant changes were observed in FE or ROT. With caudal screws removed, middle screws peak loads significantly increased in FE and LAT (P < 0.05), but not ROT., Conclusion: Occipital screw placement off-midline improves screw loads under lateral bending forces on occipitocervical constructs, though loads for FE and ROT are unchanged. As screws pullout, the loads may be redistributed, resulting in increased screw pullout forces above. Despite the improvement in screw loads for laterally based plates during lateral bending, overall ROM across the occipitocervical junction is unchanged.

Study Design: A retrospective clinical study., Objective: To confirm the impact of the O-C2 angle on dyspnea and dysphagia after posterior occipitocervical (O-C) fusion., Summary of Background Data: Dyspnea and dysphagia are complications of posterior O-C fusion with malalignment, and may be prolonged or occasionally serious. However, it is difficult to select a safe alignment during surgery, and no indicators of the appropriate alignment have been available to preclude these complications., Methods: The authors retrospectively reviewed 29 consecutive patients who had undergone O-C or occipitocervicothoracic fusion between 2003 and 2008. Data were analyzed for O-C2 angles on plain radiographs and the axial computed tomographic cross-sectional areas of the oropharynx just cranial to the epiglottis before and after surgery. The patients were grouped according to whether they developed postoperative dyspnea and/or dysphagia (group A) or not (group B)., Results: After surgery, 4 patients complained of dysphagia, and 1 patient had dyspnea and dysphagia, although they had all undergone short O-C fusions. The difference in the O-C2 angle (dOC2A = postoperative O-C2 angle--preoperative O-C2 angle) and the percentage change in the cross-sectional area of the oropharynx (S) before and after surgery (% dS) were linearly correlated. Both dOC2A and % dS were significantly lower in group A than in group B. All patients with dOC2A of less than -10 degrees showed % dS of less than -40%, and developed dyspnea and/or dysphagia after surgery. Conversely, no patients with positive dOC2A developed these complications., Conclusion: The O-C2 angle has considerable impact on dyspnea and/or dysphagia after O-C fusion. The O-C2 angle is easily measured during surgery and can be a practical index with which to avoid postoperative dyspnea and dysphagia.

Study Design: Case presentation and literature review., Objective: To review the safety of using INFUSE bone graft (recombinant human bone morphogenetic protein-2 applied to an absorbable collagen sponge) in occipitocervical (OC) fusion., Summary of Background Data: Although INFUSE bone graft is currently approved for use in certain tibial fractures, oral maxillary procedures, and anterior lumbar interbody fusion, it has been extensively used "off-label" in posterolateral lumbar and anterior cervical fusions. INFUSE is highly effective in promoting cervical spine fusion via an anterior approach, but its potential role in promoting bony fusion in posterior cervical or OC fixation has not been studied., Methods: A 53-year-old woman with basilar invagination underwent OC fixation using INFUSE bone graft. Three days after surgery she experienced neurologic decline associated with significant tissue swelling and a large postoperative seroma under significant pressure. She made excellent recovery after reoperation and drainage. An extensive review of the literature was performed to propose a modified approach to the use of INFUSE in OC fixation., Results: Proper dosing and delivery of INFUSE for posterior cervical/OC fixation is not currently known. Previously published experience with anterior cervical fusion suggests that INFUSE can have potent inflammatory effects on paraspinal soft tissue., Conclusion: INFUSE should only be used for OC fixation in patients at elevated risk of nonunion. To prevent complications due to soft tissue swelling, consideration should be given to preventing direct exposure of INFUSE to paraspinal musculature, prolonged soft tissue drainage, and prophylactic treatment with perioperative steroid therapy.

Study Design: Case series., Objective: To describe survival and outcomes after occipitocervical dissociation injuries., Summary of Background Data: Historically, occipitocervical dissociation injuries have a high rate of associated neurologic deficit with a relatively high incidence of mortality., Methods: Six patients with occipitocervical dissociation injuries are reported and their management and imaging findings reviewed. Possible contributory factors for survival are discussed., Results: All patients had upper neck and head dissociation injuries. The pattern of injury in all of these cases included a distraction type mechanism. All cases demonstrated soft tissue disruption in the zone of injury, which was consistent and apparent on all imaging studies. In these patients, the extent and severity of injury was more apparent on magnetic resonance imaging (MRI) than on radiograph or computed tomography scan. Management of these injuries included immobilization followed by surgery with particular care taken to avoid application of distraction forces to the neck., Conclusion: Patients with occipitocervical dissociation injuries may survive their injury and even retain neurologic integrity. Initial in-line head stabilization is emphasized to prevent catastrophic neurologic injury. The resting osseous relationships and vertebral alignment at the time of imaging evaluation may be deceivingly normal, and the damage often primarily or exclusively involves disruption of the perivertebral soft tissue structures. Prevertebral soft tissue swelling was apparent in all cases. For these injuries that involve primarily damage to the ligamentous structures, MRI seems to be the optimal test for revealing the magnitude of the injury.

Study Design: Case report and clinical discussion., Objective: To describe a case of persistent posttraumatic headache associated with the presence of a paracondylar process, and the result of surgical resection of this osseous anomaly., Summary of Background Data: The paracondylar process is one of a group of congenital anomalies of the craniovertebral junction. This heterogenic group is classified in the literature based on embryologic origin. In general, the paracondylar process has little or no clinical significance. There are some cases reporting symptoms related to the paracondylar process, especially after head trauma. Few report improvement after surgery., Methods: We describe a case of a 21-year-old woman who was seen for severe persistent daily headache and neck pain after minor head- and neck injury. Clinical examination revealed tenderness and an abnormal structure in the right cervico-occipital region by palpation. A conventional radiograph and computed tomography scan of the craniovertebral junction revealed a paracondylar process on the right side of the skull., Results: After resection of the paracondylar process, headache and cervical pain were substantially reduced., Conclusion: This case underlines the possible clinical significance of congenital anomalies of the craniovertebral junction. They can become symptomatic after head trauma, causing headache and/or cervical pain. Surgical extirpation can relieve these symptoms.

Study Design: Case report., Objective: To stress the importance of the fusion angle of the occipitocervical spine based on an unusual case of upper-airway obstruction after a posterior fusion from the occipital bone to the second cervical vertebra (O-C2) in a flexed position., Summary of Background Data: It is well known that cervical malalignment after occipito-cervicothoracic fusion may cause dysphagia or, rarely, dyspnea. However, to the best of our knowledge, there have been no previous English reports of prolonged upper-airway obstruction after an O-C2 fusion., Methods: We present the case of a 77-year-old woman with rheumatoid arthritis, who developed an upper-airway obstruction immediately after an O-C2 fusion. She was reintubated immediately and extubated the next day. She again suffocated suddenly 3 days after surgery, and a tracheotomy was performed. Suspecting that the main cause of the airway obstruction was not only pharyngeal edema, but also the fixture of the upper cervical angle in a flexed position, we changed the angle to the neutral position 14 days after surgery., Results: After revision surgery, the upper-airway obstruction disappeared., Conclusion: An adequate fixation angle is necessary to avoid airway obstruction after an occipitocervical fusion, even for short upper cervical fusions, especially in patients with rheumatoid arthritis.

Study Design: A case report., Objective: To report the first myotonic dystrophy case in which cervical kyphosis had been surgically corrected., Summary of Background Data: Myotonic dystrophy is an autosomal dominant disease that shows myotonia, progressive muscle atrophy, and other various symptoms. Instability of the neck is expected to cause disorders of the cervical spine; however, there are no detailed reports on deformity of cervical spine associated with this disease., Methods: A 43-year-old man with cervical kyphosis due to myotonic dystrophy had undergone an occiput-T2 fusion with autogenous iliac bone using spinal instrumentation., Results: The activity of daily life of the patient had improved markedly, and the good results continued to be preserved for 5 years. There were not any major perioperative complications., Conclusions: Surgical correction of cervical spine is not necessarily a contraindication for myotonic dystrophy.

Study Design: Retrospective case series., Objective: Evaluate the change in lordosis at the occipitocervical junction occurring during growth in skeletally immature children treated with posterior occipitocervical arthrodesis versus patients skeletally mature at arthrodesis., Summary of Background Data: Posterior occipitocervical arthrodesis is often indicated for children who have instability of the upper cervical spine develop. Theoretically, in skeletally immature children, this approach retards the growth of the posterior spinal elements but allows the anterior spinal column to continue to grow with the risk of excessive lordosis of the cervical spine developing., Methods: There were 21 children, younger than 11 years (range 1.9-10.9) at surgery and expected to have normal spinal growth, followed radiographically for an average of 6.3 years (range 2.0-12.4). Postoperative lateral neutral radiographs were compared to those at most recent follow-up to measure the change in occipitocervical angle. These results were then compared to a series of control patients who were skeletally mature at surgery., Results: Average overall change in lordosis at the occipitocervical junction was -4.6 degrees (range -12.8 degrees to +6.5 degrees). Average annualized change was -0.28 degrees per vertebral level per year (range -1.13 degrees to +0.67 degrees). This annualized change in angle was statistically significant compared to the average change of +0.01 degrees (range -0.09 degrees to +0.11 degrees) measured in the control series of patients skeletally mature at surgery (P = 0.01)., Conclusions: Increasing lordosis occurs at the occipitocervical junction following fusion in skeletally immature children. If occipitocervical arthrodesis is indicated in a skeletally immature child, fusion in excessive extension and overtightening of posterior wires should be avoided.

Study Design/setting: Independent computer-based literature review of articles pertaining to instrumentation and fusion of junctional injuries of the cervical spine., Objective: To review and discuss the evolution of instrumentation techniques and systems used in the treatment of cervical spine junctional injuries., Summary of Background Data: Instrumentation of junctional injuries of the cervical spine has been limited historically by failure to achieve rigid internal fixation in multiple planes. The evolution of these techniques has required increased insight into the morphology and unique biomechanics of the structures to be instrumented., Methods: Computer-based literature search of Ovid and PubMed databases., Results: Extensive literature search yielded insights into the evolution of systems initially based on onlay bone graft combined with wiring techniques. Such techniques have come to include systems incorporating rigid, longitudinal struts that accommodate multiplanar screws placed in the lateral masses, pedicles, transarticular regions, and occipital bone., Conclusions: Despite a rapid evolution of techniques and instrumentation technologies, it remains incumbent on the physician to provide the patient with a surgical procedure that balances the likelihood of a favorable outcome with the risk inherent in the implementation of the procedure.

Study Design: A human cadaveric biomechanical study comparing occipital fixation techniques., Objectives: To compare ranges of motion between midline and lateral occipital fixation and between rigid and nonrigid occipital fixation of an unstable craniocervical spine., Summary of Background Data: New fixation techniques using rods and screws increase surgical choice on where fixation is placed onto the occiput. Lateral fixation theoretically gives improved resistance to deformation because of its increased effective moment arm and bilateral purchase. Midline fixation allows significantly longer screw purchase. This study compares these two fixation location., Methods: Cadaveric occipital cervical spine specimens were tested biomechanically intact and under six different fixation techniques. Range of motion between the skull and C2 at 1.5 N-m and 2 N-m bending moments was measured in flexion-extension, lateral bending, and axial rotation. Mechanical testing of different rod diameters and a reconstruction plate was performed and compared with biomechanical testing. Results were compared between the intact condition and all fixations, between the medial and lateral fixations, and between the rigid and nonrigid fixations by analysis of variance., Results: The range of motion of all constructs was significantly reduced compared with intact. Significant differences between groups were only seen in lateral bending in fixation placed laterally. Mechanical testing demonstrated that construct stiffness was predicted by area moment of inertia of the rod and plate to a greater degree than variation in placement of occipital screws or locking of the implant., Conclusion: The choice of location of occipital fixation should be based more on the ease of use and instability pattern. The decreased stiffness of the newer small rod systems should be considered.

Study Design: We describe our surgical experience to remove osteoid osteomas and osteoblastomas of the occipitocervical junction. In this location, vertebral artery vicinity requires special consideration., Objectives: We illustrate our surgical approaches to remove lesions confidently, while minimizing bone resection to preserve stability., Summary of Background Data: Up until now, osteoid osteomas and osteoblastomas of the occipitocervical junction are reported as case reports. Several treatment methods have been described to treat osteoid osteomas. Nevertheless, surgery is the treatment of choice for lesions located in the C0-C2 region., Methods: A retrospective review of 7 patients, including 5 men and 2 women, with a mean age of 21.0 years (range 3.0-38.0) was conducted. Clinical outcomes were evaluated immediately and after a mean follow-up of 27.6 months., Results: There were 6 and 1 patients who underwent surgery with the anterolateral and posterolateral approaches, respectively. In osteoid osteomas, the nidus was removed, and the peripheral condensation was drilled up to normal bone (n = 4) or partially resected (n = 2). One osteoblastoma was removed extensively up to soft tissues. No osteo-arthrodesis was performed. Before surgery, all patients complained of pain, 3 presented with neck stiffness, and 2 with a torticollis. Immediately after surgery, all complaints disappeared. One patient underwent repeat surgery 15 months later for a recurrence. At the end of the follow-up, all patients were symptom-free, and partially resected peripheral condensations were stable on computerized tomography., Conclusions: Removal of osteoid osteomas and osteoblastomas of the occipitocervical junction is safe and efficient. Stability is preserved if more than half the joints are preserved with a proper surgical approach that minimizes bone resection.

Study Design: The study is a retrospective review of 58 patients who underwent occipitocervical fusion between 1997 and 2001., Objectives: Our objective is to study the clinical results after occipitocervical fixation with long-term follow-up and assess factors contributing to clinical success., Methods: Data from patient charts, operative notes, physician office notes, and imaging studies were incorporated in the study. Myelopathy was assessed using a Nurick scale for preoperative and postoperative evaluation. Fusion was assessed using cervical plane films with flexion and extension views., Results: Mean follow-up was 36 months, with all patients having a greater than 1-year follow-up. The most common pathology was congenital cranial settling (41%) followed by trauma (22%) and rheumatoid arthritis (17%). Myelopathy was the most common presentation (62%) followed by pain (28%). A successful fusion occurred in 48 out of 51 patients (94%). Symptoms improved in 86% of patients, whereas 35% improved 1 Nurick grade. Complications occurred in 30% of patients. The cervical wound infection rate was 5%. The rate of adjacent level degeneration was 7%. The mortality rate was 1.7%., Conclusions: Occipitocervical instrumentation allows for very high fusion rates without the need for halo vest immobilization. All patients with successful fixation have pain resolution. Myelopathy improves in most patients, whereas one-third of patients demonstrate dramatic improvement.

Study Design: Case report of a solitary fibrous tumor in the occipitocervical region., Objective: To describe a rare clinical entity and successful management in a patient with solitary fibrous tumor in the occipitocervical region., Summary of Background Data: Solitary fibrous tumor is a rare spindle cell neoplasm of adults that arises most commonly in the pleura. Recently, this tumor has been reported in a number of other sites. However, its occurrence in the occipitocervical region is rare., Methods: The patient presented with a painless mass in the left posterior neck. Resection of the tumor was performed., Results: Histopathological study revealed features of a solitary fibrous tumor. Clinical follow-up review for 2.5 years shows no evidence of recurrence or metastasis., Conclusion: A case of extrapleural solitary fibrous tumor in the occipitocervical region was reported. Solitary fibrous tumor should be considered in the differential diagnosis in a tumoral mass of this region.

Study Design: This is a retrospective review on the application of the authors' technique of atlantoaxial lateral mass plate and screw fixation on a rare subset of patients having mobile and reducible atlantoaxial subluxation in the presence of occipitalized atlas., Objective: Mobile and reducible atlantoaxial dislocation in the presence of an occipitalized atlas is extremely rare. We retrospectively analyzed the management of eight such patients who were treated by lateral mass plate and screw fixation., Summary of Background Data: The authors report their experience with a rare congenital craniovertebral anomaly where there was a mobile and reducible atlantoaxial dislocation in the presence of the occipitalized atlas. The cases were treated by lateral mass plate and screw method of treatment described by the authors in 1994., Methods: Eight patients with occipitalized atlas had a mobile and completely reducible atlantoaxial dislocation. These patients were treated between the years 1996 to 2003 and underwent a direct atlantoaxial lateral mass fixation. The follow-up ranges from 4 months to 6 years (average, 48 months)., Results: All patients underwent a successful fixation and ultimately achieved a solid bony fusion. There were no intraoperative or postoperative complications., Conclusions: Although lateral mass plate and screw fixation in the presence of occipitalized atlas is technically a relatively difficult and anatomically a precise surgical procedure, the firm and segmental stabilization that it provides offers an optimum situation for bony fusion.

Study Design: A retrospective study investigating the clinical outcome of the inside-outside cranial bolt technique for occipitocervical stabilization used to manage rheumatoid arthritis was conducted., Objective: To evaluate the safety and efficacy of the inside-outside technique for occipitocervical stabilization used to manage rheumatoid patients., Summary of Background Data: Achieving occipital cervical fusion for patients with rheumatoid arthritis is a complex and challenging problem. Complications related to placement of occipital screws have been reported., Methods: Occipitocervical stabilization was used for atlantoaxial subluxation or basilar invagination in 21 patients with rheumatoid arthritis. The patients were assessed for pre- and postoperative neurologic status (Ranawat classification), neck pain, fusion and alignment, hardware complications, and continued posterior cranial settling. All the patients underwent stabilization using inside-outside occipital screws. The technique involves bilateral fixation of cervical plates to the occiput using inside-outside screws, and to the cervical spine using pars screws at C2 or lateral mass screws at subaxial levels. Bone grafting was accomplished with autologous rib or iliac crest graft., Results: During the study, 14 women and 7 men with rheumatoid arthritis underwent occipitocervical stabilization and fusion. The average age of the patients was 65 years, and the mean follow-up period was 25.5 months. There were no surgical complications. Neck pain was reduced from an average Ranawat pain score of 2.40 to 0.4 (P < 0.0001). The Ranawat neurologic grade improved in 62% of the patients with preoperative neurologic deficit. Further cranial settling was not observed in any patient. There were no complications from implants and no incidence of instrumentation failure., Conclusions: The "inside-outside" technique is safe and effective for stabilizing the occipitocervical junction in rheumatoid patients. It is associated with significant reduction of neck pain, improved neurologic status, and maintenance of alignment and stability.

Study Design: This biomechanical study used flexibility testing on fresh-frozen human cadaveric specimens (occiput to C3) and compared the range of motion and neutral zone for three occipitocervical fixation techniques., Objectives: To contrast the stabilization provided by a new technique of anterior occipitocervical screw fixation with two other commonly used posterior occipitocervical fixation techniques., Summary of Background Data: There are no published reports describing this novel technique of anterior occipitocervical screw fixation., Methods: Six human occipitocervical spine specimens were mounted in a custom-designed, spine-testing machine that applied a pure moment in flexion-extension, lateral bending, and axial rotation. The specimens were tested intact, after an odontoid osteotomy with capsular injury, and after each of three fixation methods: posterior wiring, posterior plate fixation with C1-C2 transarticular screws, and finally with anterior occipitocervical screws. Intervertebral motion was measured with an optoelectronic measurement system, and the range of motion and neutral zone were the kinematic variables measured and used for analysis., Results: In flexion and extension testing, the posterior plate with transarticular screws provided greater stabilization than posterior wiring or anterior occipitocervical screws. In lateral bending and rotation, the anterior screws were similarly effective to the posterior plate, both of which were more effective than posterior wiring., Conclusion: The anterior screw fixation technique was as effective as a posterior plate with transarticular screws in stabilizing between the occiput and C2 in axial rotation and lateral bending. In extension and flexion, the anterior screw technique was not as effective as a posterior plate with transarticular screws in providing stability.

Study Design: A case report of anterior screw fixation from the axis to the occiput is described, as is the surgical technique. The pertinent anatomy is described with a radiographic assessment of the feasibility, safety, and general applicability of this technique., Objectives: To describe a novel technique of anterior occipitocervical fixation and the pertinent anatomy., Summary of Background Data: In unique clinical situations where posterior fixation techniques may not be possible or may have already failed, an anterior screw fixation technique may add stability to further attempts at obtaining a posterior arthrodesis., Methods: A case report is presented, followed by a detailed description of the surgical technique. Ten normal cervical spines had radiographs and computed tomography scans with reformats reviewed to determine screw entry points, target points, and proposed screw trajectories. Following screw insertion in eight fresh frozen human cadaver spine specimens, dissection verified screw location relative to structures at risk., Results: The ideal entry point is located caudal to the C2 superior facet joint in line with the medial third of the C2 superior facet. The screw is directed 25 degrees posteriorly in the sagittal plane and 15 degrees laterally in the coronal plane. The screw tip is located in the posterolateral third of the occipital condyle. Anatomic variation is considerable and makes this technique inadvisable in up to 20% of cases. Structures at risk include the vertebral artery and the hypoglossal nerve., Conclusions: This new technique of anterior fixation of the atlas to the occiput is feasible and safe if meticulous surgical planning is performed.

Study Design: Description of an operative technique with an illustrative case report., Objectives: The technique is presented to provide an alternative to iliac crest graft procedures for achieving occipitocervical fusion in children. This technique is particularly useful in children with instability after extensive decompression or laminectomy and in children with a large protuberant occiput., Summary of Background Data: The majority of techniques previously described for occipitocervical fusion in children rely on corticocancellous iliac crest autograft. Results generally have been promising; however, it can be difficult to harvest enough graft to span large defects after extensive decompression or to contour an iliac crest graft to a protuberant occiput. Structural rib autograft is superior in terms of availability and its unique and modifiable contour. Theoretical benefits of rib graft include superior strength and lower donor site morbidity., Methods: The surgical technique is described. A case of a 2-year-old boy with Down's syndrome and myelopathy secondary to cervical instability is reviewed., Results: The patient underwent occipitocervical arthrodesis using the technique described. The child made a full neurologic recovery, and at the 2-years follow-up evaluation, the graft had incorporated and the spine was stable., Conclusion: A technique of occipitocervical arthrodesis in children is described using autologous rib graft. This procedure was designed to span large defects or to deal with a large protuberant occiput; however, it is also useful for less demanding cases and may offer several advantages compared with procedures relying on iliac crest graft.

Study Design: This retrospective study was conducted to analyze the clinical results in 26 patients with lesions at the craniocervical junction that had been treated by occipitocervical reconstruction using pedicle screws in the cervical spine and occipitocervical rod systems., Objectives: To evaluate the effectiveness of pedicle screw fixation in occipitocervical reconstructive surgery and to introduce surgical techniques., Summary of Background Data: Many methods of occipitocervical reconstruction have been reported, but there have been no reports of occipitocervical reconstruction using pedicle screws and occipitocervical rod systems for reduction and fixation., Methods: Twenty-six patients with lesions at the craniocervical junction underwent reconstructive surgery using pedicle screws in the cervical spine and occipitocervical rod systems. The occipitocervical lesions were atlantoaxial subluxation associated with basilar invagination, which was caused by rheumatoid arthritis in 19 patients and other disorders in 7. The lowest cervical vertebra of fusion in 16 patients was C2, and the remaining 10 patients underwent fusion downward from C3 to C7. Flexion deformity of the occipitoatlantoaxial complex was corrected by application of extensional force, and upward migration of the odontoid process was reduced by application of combined force of extension and distraction between the occiput and the cervical pedicle screws., Results: Solid fusion was achieved in all patients except two with metastatic vertebral tumors who did not receive bone graft for fusion. Correction of malalignment at the craniocervical junction was adequate, and postoperative magnetic resonance imaging showed improvement of anterior compression of the medulla oblongata. There were no neurovascular complications of cervical pedicle screws., Conclusions: Occipitocervical reconstruction by the combination of cervical pedicle screws and occipitocervical rod systems provided the high fusion rate and sufficient correction of malalignment in the occipitoatlantoaxial region. Results of this study showed the effectiveness of cervical pedicle screw as a fixation anchor for occipitocervical reconstruction.

Study Design: A three-group design with consistent pullout strength measures., Objectives: To determine pullout strength of three fixation types (unicortical screws, bicortical screws, wires) and to investigate their correlation with respect to occipital morphology., Summary of Background Data: A secured, multidirectional occipitocervical fusion requires internal fixation. Devices secured at occipital protuberance were suggested to offer the greatest pullout strength because of this region's thickness., Methods: Twelve fresh human cadaveric occiputs were sketched with a grid delineating 21 fixation sites. Each site was drilled and hand-tapped. Four specimens were instrumented with unicortical screws on one side of the midline and bicortical screws on the other. Another four were instrumented with bicortical screws and wires, and the remaining four were instrumented with unicortical screws and wires. Two points on each specimen were secured with identical fixation to examine side-to-side symmetry. An MTS materials testing apparatus (MTS Systems Corporation, Eden Prairie, MN) was used to displace the fixators. Pullout strengths at different anatomic locations were recorded., Results: The greatest pullout strength was at the occipital protuberance for all fixation types. The bicortical pullout strength was 50% greater than unicortical. The wire pullout strength was not significantly different from that of the unicortical screw (P > 0.05). Seventy-eight percent of wires broke at 1100 N. Unicortical pullout strength at occipital protuberance was comparable with that of the bicortical screw at other locations., Conclusions: Unicortical screw fixation at occipital protuberance offers acceptable pullout strength without the potential complications of bicortical screws or wire fixation.

Study Design: The surgically relevant osseous anatomy of the human anatomy was carefully studied and described. The stability of cortical and cancellous screws placed in anatomic sites commonly used for internal fixation of the occiput was tested., Objectives: To define the bony anatomy of the occiput in quantitative terms and to measure the ability of cortical and cancellous screws inserted at sites commonly used for internal fixation., Summary of Background Data: To the authors' knowledge, no previous studies described the gross anatomy of the occiput in specific relation to the internal venous structures in the cranium and to the biomechanical strength of screw fixation in different areas of the occiput., Methods: Thirty-seven human occiputs were carefully measured using calipers. Thin sections from six such specimens were analyzed with specific attention to cortical thicknesses. Stability of screws placed in various locations in the occiput were tested in axial pullout., Results: The thickness of the occiput varied from extremely thin to a 0.1-mm thickness in the region of the cerebellar fossa and increased to a maximum of 8.3 mm at the level of the superior nuchal line and at the transverse sulcus. Results of pullout testing showed that the cancellous screws were as strong as the cortical screws in this area. In areas of the occiput thicker than 7 mm, unicortical fixation was as strong as bicortical fixation., Conclusion: There is a wide variation in thickness of the bone of the occiput. The strength of screw fixation was proportional to the bone's thickness.

Study Design: Dorsal occipitocervical fusion is associated with a high rate of fusion failure and requires an additional surgical site for donor bone graft harvesting. In this series, an autologous occipital calvarial bone graft obtained from the same occipitocervical incision with contoured metal loops was used in 25 adults to achieve craniovertebral stabilization and fusion., Objectives: To study the use of autologous occipital calvarial bone grafts in occipitocervical fusion., Summary of Background Data: Cranial bone grafts have been used successfully in craniofacial reconstruction with good long-term results. In the plastic surgery literature, there are claims that membranous bone grafts are superior to endochondral bone grafts in fusions because of decreased resorption. In recent studies, results have shown successful use of calvarial bone in fusing the upper cervical spine in children. The use of autologous occipital bone in posterior occipitocervical fusions avoids many of the problems associated with traditional donor sites and provides a sufficient quantity of good quality bone for the fusion. This is especially true in the fragile rheumatoid arthritis patient with cranial cervical instability., Method: Split-thickness, autologous calvarial bone grafts with contoured loop and cable instrumentation were used for posterior occipitocervical stabilization and fusion in 25 patients, most of whom had rheumatoid arthritis. The calvarial bone graft was harvested from the occipital skull, using a microair impactor, and was secured next to the loop construct. After surgery, all patients were immobilized with external orthoses., Results: None of the patients had hardware failure or complications from the occipital graft procurement. In 22 patients, good alignment, stability, and bony fusion were shown on radiographs., Conclusions: Occipital calvarial bone graft appears to work as well as other autologous corticocancellous bone grafts routinely used in posterior occipitocervical fusions.

Study Design: Eight children in whom atlantoaxial dislocation had developed underwent occipitocervical fusion using a rectangular rod. The postoperative results are presented, and the postoperative growth and deformation of the cervical spine were determined radiographically., Objectives: To investigate in a relatively long-term follow-up study whether occipitocervical fusion affects the growth of the cervical spine and induces spinal deformation., Summary of Background Data: It has been reported that children who have undergone C1-C2 posterior fusion are likely to develop abnormal curvature or deformation of the cervical spine as a result of a disturbance of growth of the fused vertebrae. There have been no studies, however, to confirm that these changes occur after occipitocervical fusion in children., Methods: The subjects were one boy and seven girls who had undergone occipitocervical posterior fusion during childhood. The average age at the time of surgery was 8.3 years, and the average follow-up period was 5.9 years. The following were assessed radiographically: redislocation of the atlas, bone union, changes in the curvature of the cervical spine, the height and width of the vertebral bodies, and the anteroposterior diameter of the spinal canal., Results: Solid bone union was achieved in all patients with maintenance of the reduced position at the time of surgery. None of the patients exhibited abnormal curvature of the cervical spine. The rate of increase in height of the C2 vertebral body was significantly less than that of vertebral bodies below C3. The rate of increase in width of the vertebral body and the anteroposterior diameter of the spinal canal of the C2 vertebral body and vertebral bodies below C3 did not differ significantly., Conclusions: Occipitocervical fusion with a rectangular rod is useful for treating atlantoaxial dislocation in children and yields excellent results because of the firm internal fixation it achieves. This surgery induced no apparent postoperative spinal deformations.

Study Design: A biomechanical analysis of the buckling type of alignment on nonfused cervical segments was carried out in patients with occipitocervical fusion for atlantoaxial dislocation., Objectives: To examine whether biomechanical analysis is useful for preoperative prediction of subaxial subluxation after occipitocervical fusion., Summary of Background Data: Rheumatoid arthritis sometimes causes subaxial subluxation after occipitocervical fusion. At present, there are no widely accepted criteria for determining the appropriate extent of fusion to prevent subluxation., Methods: The subjects were 25 patients with rheumatoid atlantoaxial dislocation and 15 patients with nonrheumatoid atlantoaxial dislocation who underwent occipitocervical fusion. Preoperative and postoperative alignment of the cervical spine were analyzed biomechanically, using a specially developed computer program., Results: Five segments of nonfused cervical spine had subluxation after surgery in the rheumatoid group. For these segments, the preoperative value of buckling averaged 13.5 x 10(-4) and exceeded 10 x 10(-4) in all cases. For the segments that showed no subluxation after surgery, the preoperative value of buckling averaged 4.5 x 10(-4). Subluxation of the nonfused segments did not develop in the nonrheumatoid group., Conclusions: In patients with rheumatoid arthritis, segments that show abnormal buckling before surgery are likely to develop subluxation after occipitocervical fusion. Preoperative values of buckling over 10 x 10(-4) constitute a risk factor for subaxial subluxation after occipitocervical fusion.

Study Design: The authors measured the thickness and quality of occipital bone regions to determine screw placement during occipitocervical fusion and described the projection of the posterior dural venous sinuses., Objective: This study provides anatomic data relevant to areas of screw placement into the occiput during occipitocervical fixation., Summary of Background Data: Few reports exist regarding the morphometrics of the occipital bone and intracranial structures relevant to occipitocervical fusion., Method: The thickness of the posterior inferior occipital bone was measured relative to a 10 x 5 cm grid. Sections were evaluated grossly and histologically. The projections of the posterior dural venous sinuses were determined by direct measurements., Results: The maximum thickness of the occipital bone, which ranged from 11.5 to 15.1 mm in males and from 9.7 to 12.0 mm in females, was at the level of the external occipital protuberance. The occipital bone was thicker than 8 mm in an area extending laterally from the external occipital protuberance for 23 mm and consisted of dense cortical bone with little or no diploic bone. The projection of most of the torcula on the external surface of the occipital bone was located superior to the center of the external occipital protuberance (mean, 12.6 mm superior and 4.7 mm inferior to external occipital protuberance), whereas that of the transverse sinus was distributed more evenly above and below the external occipital protuberance (mean, 7.3 mm superior and 6.5 mm inferior)., Conclusions: Screws that are 8-mm long may be inserted in the region of the superior nuchal line (Level 0) extending 2 cm laterally from the center of the external occipital protuberance, 1 cm from the midline at a level 1 cm inferior to the external occipital protuberance (Level 1), and 0.5 cm from the midline at a level 2 cm inferior to the external occipital protuberance (Level 2). The major dural venous sinuses are situated immediately beneath the thickest regions of the occiput and are at risk of penetrative injury during screw placement.

Study Design: In a clinical retrospective study, the authors review long-term results of occipitocervical fusion using a wide diameter, contoured, threaded Steinmann pin., Objectives: To evaluate the clinical and radiographic results of occipitocervical fusion using this technique in a variety of abnormalities including rheumatoid arthritis. SUMMARY OF BACKGROUND DATA. The various surgical techniques and hardware developed for occipitocervical fusion have been associated with mixed results, particularly in patients with rheumatoid arthritis or basilar invagination., Methods: Thirty-nine patients with occipitocervical instability were internally fixed with a wide diameter, contoured, threaded Steinmann pin wired to the occiput and cervical laminae or facets. Fusion was facilitated using autologous iliac crest bone graft and a cervical orthosis. Instability resulted from rheumatoid arthritis (n = 12), congenital anomalies (n = 12), trauma (n = 10), tumor (n = 4), or osteogenesis imperfecta (n = 1). Fifteen patients had radiographic evidence of basilar invagination. Long-term outcome (mean follow-up period, 38.9 months; range, 12-78 months) was based on clinical and radiographic review., Results: Thirty-seven patients (97%) had a stable postoperative occipitocervical construct: there were 35 osseous unions, two fibrous unions, and one nonunion. There was on postoperative death from pulmonary complications. No patient developed evidence of new, recurrent, or progressive basilar invagination., Conclusion: The authors concluded that rigid segmental fixation of the craniovertebral junction using a wide diameter, contoured, threaded Steinmann pin and supplemental autograft creates excellent fusion with minimal complications. This technique is appropriate for a variety of abnormalities including rheumatoid arthritis.

Study Design: In a clinical retrospective study, the results of occipitocervical fusion in patients with rheumatoid arthritis were studied and analyzed., Objectives: The results of two different operative techniques were compared. The advantages of screw fixation compared with wiring techniques in this population of patients were investigated., Summary of Background Data: Numerous different implants have been presented in the literature for occipitocervical fusion in patients with rheumatoid arthritis. The use of wires being the standard fixation technique., Methods: Occipitocervical fusion was performed in patients with rheumatoid arthritis: 26 patients with the wiring technique and 33 patients with a new Y-plate fixation. The results were compared at a follow-up period of 24 months and 50 months, respectively. Clinical and radiologic results were investigated., Results: The atlantodental distance could be significantly better reduced in the group with the Y-plate fixation and the neurologic improvement in the wiring group was 40%, whereas in the Y-plate fixation 86% of neurologic improvement was observed. Pseudarthrosis was seen in 27% of the wiring technique and in 6% in the plate and screw fixation technique., Conclusions: In occipitocervical fusion for patients with rheumatoid arthritis, the screw and plate fixation technique provides superior results than other techniques using wire fixations.

Study Design: Thirty-two patients at one institution underwent occipitocervical fusions with posterior plate and screw instrumentation. The average follow-up was greater than 4 years (50 months)., Methods: AO plates and screws were used and in more than 50% of the cases, the Magerl transarticular C1-C2 screw technique enhanced the occipitocervical instrumentation. In nine patients, cement was used and thus are excluded in evaluation of fusion results. All 23 patients attained solid fusions. No pseudarthrosis occurred. The average time to fusion was 13 weeks. Halos or traction immobilization was not used postoperatively. The average time of the simple orthosis wear was 11 weeks. Patients were out of bed on an average of the second postoperative day with a range of 1-4 days postoperatively. Reduction of the atlantoaxial joint was required in 10 of the 23 patients. At follow-up, nine remain reduced., Results: In one patient, the atlantodens interval approximated the preoperative distance and radiographs demonstrated one transarticular C1-C2 screw was not placed satisfactorily. The average operative time was 172 minutes, and the average blood loss was 956 cc. The neurologic status of the patients improved or remained the same. No patient deteriorated neurologically. A total of 78 occipital screws were placed. No complications resulted from any of these screws. One intraoperative complication occurred secondary to massive bleeding after a transarticular screw hole was drilled. Bone wax was placed over the drill hole and the bleeding ceased. No postoperative problems occurred in this patient. Most specifically, no central nervous system sequela was evident., Conclusions: The conclusions from this study are that posterior occipitocervical fusion can be performed very safely with plate and screw instrumentation. An extremely high fusion rate can be expected with minimal complications and minimal postoperative immobilization. This technique, however, is technically demanding.