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STUDY DESIGN Retrospective descriptive study. OBJECTIVE 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 venous sinus 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 venous sinus presence in cervical spine CT angiograms. These measurements were used to create topographical maps of occipital bone thickness and likelihood of venous sinus presence, which we then compared to the screw hole configurations of four occipital plates. RESULTS 100 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 venous sinus presence ranging from 8-33%.Level of Evidence: 5.

Observational and morphological study with three-dimensional (3D) computed tomography (CT) analysis.To discover the morphology and configuration deformities of craniovertebral junction (CVJ) and upper cervical spine in children with unilateral hemifacial microsomia (HFM). To determine whether there are specific HFM patients who are at higher risk of certain cervical vertebral anomaly.The evaluation for cervical vertebrae anomaly in HFM children, especially in CVJ region, is underreported.Eighty-eight unilateral HFM children (64 males, 24 females) with four Pruzansky-Kaban types (I, Ila, Ilb, and III) underwent cranial and cervical CT scanning from skull to C5 in neutral position. The 3D morphology and configuration of the occipital condyle, atlas, and axis, etc. were evaluated on the presence of deformed detailed structures of CVJ region.No C1 deformation was found in type I group. Six (14.3%) type Ila cases, seven (33.3%) type IIb cases, and six (37.5%) type Ill cases had lateral masses asymmetry of C1 (P 0.05). Five (55.6%) type I cases, 17 (40.5%) type Ila cases, 12 (57.1%) type Ilb cases, and 10 (62.5%) type Ill cases had C2 anomaly (P 0.05). The incidence rate of C1-C2 instability for four groups were 33.3% (type I), 33.3% (type IIa), 33.3% (type IIb), and 31.3% (type Ill), respectively (P 0.05).For HFM children, the incidence of C1 deformation increased from type I to type Ill. The probability of C2 anomaly and C1-C2 instability in children with different types of HFM is nearly the same. The craniovertebral junction of every HFM child must be monitored carefully for C1-C2 instability before any surgical procedure to avoid atlantoaxial dislocation and spinal cord injury.Level of Evidence: N/A.

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.

A retrospective analysis of collected data.Our study aims to present the morphology of cranial-cervical spinal canal in basilar invagination (BI) patients.BI is characterized by protrusion of the odontoid process into the foramen magnum (C0), leading to compression of the cervicomedullary junction. However, no study has ever clarified the anatomical diameters of spinal canal in patients with BI.The study retrospectively examined computed tomography (CT)-based anatomical characteristics in a cohort of 84 patients with and without BI. We measured the anteroposterior diameter (APD) and transversal diameter (TVD) of spinal canal from C0 to C4, together with the area of vertebral canal (Area). Independent samples t test was used for statistical analysis.The APD in the BI group was shorter than the control group from C0 to C2 (C0: 27.98 vs. 35.11 mm, P 0.001; C1: 11.87 vs. 16.91 mm, P 0.001; C2: 12.91 vs. 14.84 mm, P 0.001), but it became longer from C3 to C4. The TVD of the BI group was significantly wider from C0 to C3 (C0: 30.59 vs. 28.54 mm, P 0.001; C1: 31.31 vs. 25.98 mm, P 0.001; C2: 21.56 vs. 20.40 mm, P = 0.01; C3: 22.45 vs. 21.23 mm, P = 0.013), and it had no significance at C4. The Area showed no difference between the two groups from C1 to C2, but it turned larger at C3 and C4 in BI patients.BI patients may have shorter APD from C0 to C2, which could be the leading cause of neurological compression, necessitating decompression on sagittal plane. Below the pathological levels, BI patients have larger spinal canal than general population.3.

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

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

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 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 Review and grade the morphology of the C1-C2 neural foramina, from the MR images of patients who underwent C1-C2 spinal surgery, and determine the relationship with ON. Objective To evaluate the feasibility of MRI for C1-C2 neural foramen evaluation with a new grading system and to correlate the C1-C2 neural foramen grade with ON. Summary of background data There have been no MRI studies of patients with and without ON in relation to C2 nerve root ganglion findings. Methods Among the registry of 124 patients who underwent C1-C2 spinal surgery between July 2004 and May 2012 in Seoul National University Bundang Hospital, we enrolled 101 patients who had information about ON and a relevant preoperative cervical spine MR image. A total of 202 neural foramina were evaluated with our new C1-C2 neural foramen grading system (grade, 0-3) using consensus reading by 2 experienced radiologists who were blinded to the clinical information. The relationship between the C1-C2 grading system and ON was assessed using a χ test and Fisher exact test. Inter- and intraobserver reliability agreement was assessed using the κ statistic. Results All C1-C2 neural foramina were delineated on T2 parasagittal images. Among 202 C1-C2 neural foramina, grade zero was found in 49 foramina (24.3%), grade 1 in 95 (47.0%), grade 2 in 30 (14.9%), and grade 3 in 28 (13.9%). Grade 1 stenosis was most frequently noted. The grade 2 group had the most frequent prevalence of ON (43.3%), followed by grade 3 (35.7%), grade zero (30.6%), and grade 1 (29.5%). However, the relationship between the grade and ON was not statistically significant. Inter- and intraobserver agreements were substantially high. Conclusion C1-C2 neural foramina can be depicted on MR image. However, the relationship between the new grading system for C1-C2 neural foramina and ON was not statistically significant. Level of evidence 4.

This study is a computed tomographic (CT)-based morphometric analysis of the pediatric occipital condyles as related to occipital condyle screw placement.To quantify reference data concerning the dimensions of the immature occipital condyles to guide the placement of occipital condyle screw.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.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.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).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.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 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 Observational and quantitative study with 3-dimensional (3D) computerized tomographic (CT) analysis. Objective To establish the 3D configuration and morphometric data of obliquity of the lateral atlantoaxial articulations (LAA) in congenital anomaly with occipitalization. Summary of background data Plane radiographs and normal CT scans cannot clearly demonstrate the configuration of LAA as the hindrance of circumambient bony structures. The morphology of anomalous LAA with occipitalization is underreported. Methods A series of 63 cases with occipitalization and 20 control subjects underwent thin-slice CT scanning. The 3D configuration of LAA were analyzed and categorized based on the degree of olisthy and inclination orientation of the atlantoaxial articular facets (AAF). The obliquity of the AAF was measured in reconstructed sagittal and coronal planes, respectively. Results Four types of configuration of LAA with occipitalization were found: type I, characterized by slight anteversion of LAA without olisthy of the inferior and superior facets (16% of 126 sides); type II, characterized by partial olisthy of the 2 facets and evident anteversion of LAA (48%); type III, defined by the separation or complete olisthy of the 2 facets (13%); and type IV, wherein the articular facets sloped dorsally (23%). Forty-eight of 49 cases in the former 3 types wherein AAF sloped ventrally had atlantoaxial dislocation (AAD). All type IV cases wherein AAF sloped dorsally had no AAD. In control subjects, LAA had no evident obliquity of anteversion or retroversion. Conclusion Instability at the C1-C2 junction in congenital anomaly with occipitalization is likely a direct result of the anteversion of LAA and bony malformation of this region, and it aggratates with the increasing obliquity of anteversion of the AAF. Demonstrating 3D morphological changes of LAA may provide a new means to diagnosis instability in congenital anomaly at craniovertebral junction and a basis for rational surgical treatment.

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 Case report and literature review. OBJECTIVE To discuss the diagnosis, limitations, and treatment of combined occipital-cervical and atlantoaxial disassociation with normal neurologic function. SUMMARY OF BACKGROUND DATA Injuries to the craniocervical junction can lead to devastating neurologic deficits. Occipital-cervical disassociation is a well-documented injury pattern that can lead to pain, spinal cord injury, and death. Early diagnosis and treatment can preserve neurologic function. Combined injuries to both the occipital-cervical and atlantoaxial segments are less common and, to date, have only been described with severe neurologic injury. METHODS Retrospective review of a case. Literature review was performed through Medline and Pubmed searches. RESULTS This is the first case to present a combined occipital-cervical and atlantoaxial disassociation with a neurologically intact patient. Initial physical examination was limited, but early imaging revealed evidence of instability. Early diagnosis and early (< 24) surgical stabilization was performed with no complications and neurologic preservation. One-year follow-up visit revealed normal neurologic examination with neck pain VAS = 2/10 and neck disability index = 6. CONCLUSION Combined injuries to the occipital-cervical and atlantoaxial can result in upper cervical instability. Despite previous reports, neurologic preservation remains a possibility in this injury pattern. Limitations in physical examination and radiographic imaging persist, but early diagnosis and surgical stabilization may improve neurologic outcomes.

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 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 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 Immunohistochemical analyses on the axial skeleton from wild type mice. OBJECTIVE In the clinic, we have previously observed cervical spine defects associated with deviations in the posterior part of the occipital bone and with morphologic and functional variations in the craniofacial skeleton. As examples, cervical spine fusions occurred frequently in patients with mandibular overjet and even more frequently and more caudally in the cervical spine in patients with sleep apnoea. The aims of the present study were to elucidate this association between the spine and the cranium by comparing gene expression domains of important developmental genes known to be involved in vertebral column formation with gene expression in the craniofacial region. SUMMARY OF BACKGROUND DATA This is the first study looking specifically on gene expression in the basilar part of the occipital bone that is formed around the cranial part of the notochord, thus connecting the spine and the craniofacial skeleton. METHODS The material consisted of 4 mouse embryos p.c. day 13.5, NMRI wild-type mice, from the same litter. The body axis, the cranial base, and the craniofacial area were studied by immunohistochemical analyses using Collagen II, Pax9, Pax1, and Noggin antibodies. RESULTS Pax1 expression was highly similar in the posterior part of the occipital bone and in the vertebral column, indicating that the basilar part of the occipital bone from a developmental standpoint can be considered the uppermost vertebra. Pax9 and Noggin expression domains were in accordance with those described previously. CONCLUSION The present study supports that the basilar part of the occipital bone may be regulated by similar developmental mechanisms as the vertebral column and may thus be regarded the uppermost vertebra. Thus, the clinically observed association between the cervical column and the craniofacial area has been proved by immunohistochemical methods.

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.

Conventional and phase-contrast magnetic resonance (MR) imaging were used to evaluate the morphology and cerebrospinal fluid (CSF) flow dynamics at craniocervical junction in adolescent idiopathic scoliosis (AIS).To determine the morphology of cerebellar tonsil, foramen magnum, and dynamic flow of CSF at the craniocervical junction in AIS patients versus normal controls and their correlation with somatosensory cortical evoked potentials (SSEP).Previous studies have documented obstructed CSF flow in patients with Chiari I malformation. Low-lying cerebellar tonsils and syringomyelia are also observed in AIS patients. We sought to investigate whether disturbed CSF flow is also evident in AIS subjects at the foramen magnum level and its association with level of cerebellar tonsils and dimensions of foramen magnum.Conventional and phase-contrast MR were performed in 105 adolescent girls (69 AIS subjects and 36 age-matched controls). Measurements of cerebellar tonsillar level related to the basion-opsithion (BO) line, anteroposterior (AP), transverse (TS) diameter, and area of foramen magnum, and peak velocity of CSF flow in both the anterior and posterior subarachnoid space through foramen magnum were obtained. Correlations were made among different parameters and SSEP findings.A total of 42% of subjects in the AIS group had the cerebellar tonsillar tip positioned 1 mm below the BO line. The cerebellar tonsillar level in AIS subjects was significantly lower than the median tonsillar level in normal controls (P0.01). The AP diameter and area of foramen magnum were significantly larger in AIS subjects when compared with normal controls (P0.05), but the peak CSF velocities through foramen magnum showed no significant difference (P0.05).Peak CSF velocities through foramen magnum were not significantly different in AIS subjects despite the presence of low-lying cerebellar tonsils. This might be explained by the compensatory effect of larger foramen magnum in AIS subjects.

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 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 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. Retrospective study of 146 patients with the diagnosis of occipitalization, atlantoaxial dislocation (AAD) and basilar invagination, using a novel surgical treatment strategy. Objective. To introduce a novel fixation and reduction technique. Summary of Background Data. Atlas occipitalization associated with basilar invagination often result in fixed AAD that need reduction and occipitocervical fixation. The widely used occipitocervical fixation with suboccipital screws has several limitations such as the poor screw purchase in maldevelopment of the occipital bone, limited area available for implants in previous suboccipital craniectomy. The placement of occipitalized C1 lateral mass screw is an alternative option. Methods. From June 2007 to June 2013, 146 patients of occipitalized atlas with fixed AAD and basilar invagination, underwent fixation and reduction via C1 lateral mass and C2 pars/pedicle screw. Results. A total of 143 patients achieved the follow-up in the range from 6 months to 4 years (average, 30 mo). Neurological improvement was seen in all the 143 patients, with the averaged Japanese Orthopedic Association scores increasing from 11.6 to 15.5. Radiographical evaluation showed that solid bony fusion was achieved in all patients, and complete reduction was attained in 95 patients, and partial reduction (>60%) in 40 patients, and no effective reduction in 8 patients who had additional transoral decompression. Magnetic resonance imaging demonstrated that the ventral cervicomedullary compression was relieved in all patients. Conclusion. Although technically demanding, the C1 lateral mass placement in occipitalization is very useful in the rescue situation where more conventional stabilization alternatives are not technically possible, or as routine occipitocervical stabilization. It provides firm stabilization offering an optimum situation for bony fusion, and meanwhile the effective reduction of fixed AAD and basilar invagination. An extremely high fusion rate can be expected with minimal complications and minimal postoperative immobilization with this technique. Conclusion. Level of Evidence: 4

STUDY DESIGN: Blinded comparison of 5 methods to diagnose atlanto-occipital dislocation (AOD) on plain radiographs and computerized tomography (CT) of the cervical spine. OBJECTIVE: To determine the best method to diagnose AOD. SUMMARY OF BACKGROUND DATA: Several methods are proposed for the diagnosis of AOD, including the Power's ratio, X-line method, basion-dens interval, condylar gap, and Harris method. No blinded comparison of the results of these methods has been compared to patient outcome, and there is no information available regarding the accuracy of these methods applied to CT scans. METHODS: Plain lateral radiographs and CTs of the cervical spine were reviewed in 104 patients, including 6 with AOD. Images underwent a blinded review by a board certified neurosurgeon (D.K.R.), orthopedist (P.A.A.), radiologist (J.C.), and emergency physician (D.B.B.). Each diagnostic method for AOD was applied for determination of sensitivity, specificity, and positive and negative predictive values. The ability to identify relevant anatomic landmarks was also tabulated. RESULTS: Average values for sensitivities, specificities, positive and negative predictive values for each method applied to plain radiographs are: 0.4625-1.0, 0.8933-0.9725, 0.2775-0.45, and 0.975-1.0, respectively. These values for each method applied to CT scans are: 0.7075-1.0, 0.8725-0.9775, 0.3175-1, and 0.98-1.0, respectively. Identification of relevant anatomic landmarks occurred 99.75% of the time when these methods were applied to CT scans compared to 39% to 84% of the time on plain radiographs. CONCLUSIONS: Sensitivity, specificity, positive and negative predictive values of these methods improve when applied to CT scans because of better visualization of anatomic landmarks. This result suggests CT scans of the cervical spine may be warranted in all trauma patients suspected of having cervical spine injury.

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

STUDY DESIGN: A case report is presented. OBJECTIVES: To describe the diagnostic procedure, treatment, and outcome of a 56-year-old man with posterior atlanto-occipital dislocation and concomitant discoligamentous C3-C4 instability. CASE REPORT: A 56-year-old male seat-belted driver of a car was involved in an accident. After initial spontaneous breathing and weak movements of all his extremities, artificial respiration became necessary because of increasing respiratory insufficiency. Radiologic diagnostics, including computed tomography scans, showed a posterior atlanto-occipital dislocation and a Grade 2 craniocerebral trauma with occipital subarachnoidal bleeding. Further examination showed a serial rib fracture with concomitant hemopneumothorax. After stabilization of the patient, magnetic resonance imaging of the cervical spine showed a contusion of the upper cervical spinal cord. Additionally, rupture of the interspinal ligaments and the posterior longitudinal ligament could be seen, as well as a rupture of the intervertebral C3-C4 disc. Operative stabilization was performed by posterior fusion of C0-C4 using the CerviFix-System and autogenous bone grafts taken from the iliac crest. At 12 months after the operation, the patient had only slight weakness of the left arm and a 70% limitation in the range of motion of the cervical spine. CONCLUSIONS: With improvements in advanced trauma life support, the number of patients with atlanto-occipital dislocation admitted to hospital alive is increasing, so this particular lesion must be kept in mind. When the patient survives the accident, the long-term prognosis is quite good, with a high rate of recovery after initial neurologic deficits. Language: en

STUDY DESIGN: The significance of occipitoaxial angle in the development of subaxial subluxation after occipitocervical fusion was determined in a minimum 5-year follow-up study performed retrospectively. OBJECTIVE: To clarify the association between the position of the fixed occipital bone and axis and the development of subaxial subluxation. SUMMARY OF BACKGROUND DATA: There have been few reports describing the association between the position of fixation of the occipital bone and axis and subaxial lesion in occipitocervical fusion. MATERIALS AND METHODS: Thirty-eight patients with rheumatoid arthritis who underwent occipitocervical fusion for irreducible atlantoaxial dislocation were reviewed. The angle between the McGregor line and the inferior surface of the axis (O-C2) was measured in healthy volunteers and patients who had undergone occipitocervical fusion. The association between any changes in the alignment of the cervical vertebrae and the development of subaxial subluxation during follow-up periods was studied. RESULTS: The number of the patients in whom postoperative kyphosis and swan neck deformity developed was only five, but in four (80%) of them, retroversion of the occipital bone was used to increase the O-C2 angle. In 14 patients, in whom anteversion of the occipital bone against the axis was excessive, 12 (86%) patients experienced subaxial subluxation after surgery. In the patients in whom fixed O-C2 angles were in normal range, only one patient developed such abnormal changes in the middle and lower cervical vertebrae. CONCLUSION: It is necessary to give attention to the position of the fixed occipital bone and axis during procedures of occipitoaxial fusion for patients with rheumatoid arthritis.

Study Design. Reconstructive computed tomography (CT) study of occipito-atlanto and atlantoaxial joints in RA patients. Summary of Background Data. The occipitocervical region is one of the most common sites of rheumatoid arthritis (RA). Although lateral radiography has been used for the diagnosis of atlantoaxial subluxation and vertical subluxation, reconstructive CT imaging of the occipito-atlanto and atlantoaxial joints is more sensitive in detecting morphologic changes in this region. We investigated this region in RA patients, using coronal-view reconstructive CT images, and examined the relationship between the morphology and other radiographic parameters. Methods. The occipitocervical region was examined in 58 female RA patients by reconstructive CT, plain radiography, and MRI. The degree of destructive change on reconstructive CT was compared to that on other radiographic evaluations. Results. Coronal-view reconstructive CT revealed primary destructive changes before detection by lateral radiography, using Redlund-Johnell or Ranawat values. A Redlund-Johnell value less than 34 mm was diagnostic for occipitocervical subluxation in female RA patients. Conclusion. Coronal-view reconstructive CT is useful for the diagnosis of occipitocervical joint subluxation in RA.

STUDY DESIGN: The study defines the occipitocervical neutral position using cervical radiographs from 30 subjects. OBJECTIVE: To identify reproducible radiographic measures of the occipitocervical neutral position that can be used during surgery to optimize fusion position. SUMMARY OF BACKGROUND DATA: When performing rigid internal fixation of the occiput to the cervical spine, the ability to determine that the occiput is in a neutral position in relation to the cervical spine is important. Currently, no objective radiographic measures for the occipitocervical neutral position exist. METHODS: Thirty flexion, extension, and neutral lateral cervical spine radiographs radiographs interpreted as normal by an experienced radiologist were studied. The occipitocervical angle and occipitocervical distance were defined and calculated. Two investigators, an orthopedic resident and an experienced orthopedic spine surgeon, measured the occipitocervical angle and occipitocervical distance independently on all radiographs in a blinded manner. Correlation coefficients were obtained to determine interobserver reliability. RESULTS: The mean occipitocervical angles were 24.2 degrees, 44.0 degrees, and 57.2 degrees in flexion, neutral, and extension, respectively. The mean occipitocervical distances were 21.5 mm in neutral, 28.0 mm in flexion, and 14.8 mm in extension. The differences in the occipitocervical angle and occipitocervical distance in neutral, flexion, and extension were statistically significant (P < 0.05 and < 0.001, respectively). There were no significant interobserver differences in any of the measurements. CONCLUSIONS: The radiographic measures of the occipitocervical neutral position reported in this study are reliable, repeatable, and simple to determine on routine lateral radiographs. These measurements should be a valuable intra-operative tool for achieving occipitocervical fusion in appropriate alignment.

STUDY DESIGN A report of three cases of pyogenic osteomyelitis of the occipitocervical junction. OBJECTIVE To describe the conservative management of pyogenic osteomyelitis of the occipitocervical junction. SUMMARY OF BACKGROUND DATA The therapeutic approach to inflammation of the upper cervical spine is controversial. METHODS Pyogenic osteomyelitis of the occipitocervical junction is rare. In the orthopedic literature, only a few case reports with variable treatment methods are available. Three patients with pyogenic osteomyelitis of the occipitocervical junction were treated nonoperatively. Intravenous antibiotic therapy was begun after direct cultures or blood cultures were obtained. Early mobilization was accomplished by application of a halo vest. RESULTS Two patients recovered by spontaneous fusion of the occipitocervical junction. Instability developed in the spine of one patient, but she refused further treatment. CONCLUSIONS Diagnosis of osteomyelitis of the upper cervical spine is difficult. In cases with absence of neurologic symptoms or spinal abscess formation, treatment can be nonoperative.

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 cancerous screws inserted at sites commoniy used for internal fixation. of Background Data. To the authors' knowiedge, 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 at screw fixation in different areas of the occiput. Methods. Thirty-seven human occiputs were carefully measured using canpers. Thin sections from six such specimens were analyzed with specific attention to cortical thicknesses. Stability of screw 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 at the cerebellar fossa and increased to a maximum oi 8.3 mm at the level of the superior nuchal line and at the transverse sulcus. Results of pullout resting 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. 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 haves 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 mused 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 retrospective clinical review of patients with atlanto-occipital dislocations. OBJECTIVES To determine if fusion of the occiput to C1 can be accomplished without extension to the axis. SUMMARY OF BACKGROUND DATA Patients with atlanto-occipital dislocations who have preservation of spinal cord function are quite rare. The standard approach to stabilization has been fusion of the occiput to the axis (C2). This may compromise rotation unnecessarily, however. The authors investigated the success of attempting to fuse only the occiput to C1 in children. METHODS Two children with atlanto-occipital dislocation who had normal neurologic function underwent fusion from the occiput to the atlas after reduction. RESULTS Both cases showed successful fusion with no unwanted extension to lower levels. Full head rotation was preserved. CONCLUSIONS This technique restores stability without restricting rotation.

Study Design. This study compared the reproducibility of three techniques used to measure translation between the occiput and C1 in children with Down syndrome. Objectives. Intraobserver and interobserver variability were computed to determine if there is a reliable way to measure occiput-C1 instability. Summary of Background Data. No studies have been performed comparing measurement techniques in children with Down syndrome. Methods. Powers ratios, basion-axial intervals, and translational anteroposterior motion as described by Wiesel and Rothman were calculated for 60 pairs of flexion-extension lateral cervical radiographs from children with Down syndrome. Calculations were made on two occasions by four reviewers. Results. Mean differences between measurements for two observers were 0.14 for the Powers ratio, 1.3 m for the Wiesel technique, and 1.8 mm for the basion-axial interval. The 95th percentiles of the differences between measurements for two observers were 0.38 for Powers ratios, 3.5 mm for the Wiesel technique, and 5.3 mm for the basion-axial interval. Conclusions. Measurement of atlanto-occipital translation by any of these methods is not reproducible. Although the technique by Wiesel and Rothman is the easiest to apply, confirmation of instability with magnetic resonance imaging should guide management.

STUDY DESIGN The authors present the results of an anatomic study of the human occiput to delineate appropriate screw placement sites. OBJECTIVES Occipital bone morphologic characteristics were evaluated to determine whether significant variability exists and to determine the position of greatest bone thickness for safe and effective internal fixation. SUMMARY OF BACKGROUND DATA New instrumentation and techniques for occipital fixation are being developed in response to concerns about occipital bone variability. Thirty cadaveric occiputs were evaluated to determine if such variability exists and the location of greatest bone thickness. Radial thickness, occipital locations, and gender differences, were determined. METHODS Twenty-six skulls were sectioned sagittally to determine the contributions of the inner, middle, and outer tables to overall occipital thickness. The angle required to gain maximal cortical purchase was determined. Mean values and variance were analyzed statistically to determine variability and thickness. Data was plotted in three dimensions. Variability in morphologic features was minimal. RESULTS The internal occipital protuberance-external occipital protuberance was thickest at 17.55 mm (SD = 3.18 mm) and was consistently located on the superior nuchal line 43 degrees from the horizontal skull base line. Bone thickness decreased radially from the central internal occipital protuberance position. Bone thickness above the superior nuchal line exceeded that below by 2.74 mm (P < 0.05) vertically and at the oblique positions (P < 0.05). Bone to the right of the midline was only 1 mm thicker than that to the left. Gender differences were minimal. The inner table contributed only 10% to overall occipital thickness. As occipital thickness decreased, the optimal purchase angle increased. CONCLUSIONS Unicortical purchase at and above the superior nuchal line is warranted with a low risk of intracranial venous penetration. Internal fixation devices developed in response to occipital bone variability should be considered with respect to occipital bone thickness distributions. Attention to cervical morphologic characteristics should result in higher success rates in occipitocervical arthrodesis.

Study Design. In a clinical retrospective study, the authors review long-term results of occipitocervical fusion using a wide diameter, contoured, threaded Stainmann 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 wase 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 diameters, 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 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 This is a report of a prospective case series. OBJECTIVE The purpose of this study was to determine whether evoked potential activity recorded from occipital scalp electrodes in humans is similar to that recorded in animals, and to evaluate the independence of this activity from the classical somatosensory-evoked potential. SUMMARY OF BACKGROUND DATA Intraoperative somatosensory-evoked potentials can be of limited usefulness in predicting spinal cord injury because they are transmitted primarily through the dorsal columns, and therefore do not reflect integrity of important ventral pathways. It recently has been shown in animal studies that a sensory-evoked potential recorded from the cerebellum is mediated via ventral tracts and is useful as an adjunct to the somatosensory-evoked potential in spinal cord monitoring. METHODS Twenty-five patients undergoing spinal or posterior fossa surgery were consecutively entered into the study. Evoked responses were recorded transcranially from over the cerebellar hemispheres and from the vertex. Recordings were made directly from the surface of the cerebellar hemispheres in seven of these patients. RESULTS Waveforms could be recorded and reproduced in all but one of the patients. The overall appearance of the occipital recordings was similar to the appearance of responses obtained in animals. The mean latency of the first negative peak recorded from the ipsilateral occiput was 33.0 msec (standard deviation, 3.7 msec) compared with 52.4 msec (standard deviation, 6.1 msec) for the somatosensory-evoked potential. In addition, the amplitude of this response (0.35 microV; standard deviation, 0.20 microV) was independent of the amplitude of the somatosensory-evoked potential (0.76 microV; standard deviation, 0.69 microV). In five cases, one evoked potential could be recorded in the absence of the other. Recordings from the surface of the cerebellum were of the same morphology, but of greater amplitude than the transcranial recordings. CONCLUSION Evoked responses can be reliably recorded from over the occiput and show characteristics independent of the classical somatosensory-evoked potential. These responses are very similar to the cerebellar-evoked potential recently characterized in animals and may provide a method for assessing the physiologic integrity of the ventral tracts of the spinal cord in humans.

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 A retrospective cohort study. Objective To evaluate the outcomes of patients with occipital condyle fractures (OCFs) treated nonoperatively and establish factors associated with neck disability. Summary of background data The majority of OCFs are treated nonoperatively; however, few studies have reported long-term functional outcomes of these patients. Methods From 1999 to 2007, 103 patients with OCFs were identified. Of this cohort, 28 patients with 32 fractures met the inclusion criteria. Fracture and patient characteristics, including patient age and sex, Anderson and Montesano fracture type, bilaterality, associated head injury, and fracture displacement, were noted. The Neck Disability Index (NDI) was calculated at final follow-up. Results Anderson and Montesano type III fractures were the most commonly observed (54%), followed by type II (43%). The mean NDI was 14.0, which correlates with mild disability, and the NDI headache question showed the highest mean disability score of all questions. There was no statistically significant association between NDI scores and fracture type, displacement of fracture, sex, bilaterality, or presence of head injury. Age was associated with NDI scores, with age range of 40 to 60 years having a mean NDI score of 24.3. Conclusion Anderson and Montessano types I, II, and III OCFs may be treated nonoperatively in the absence of ligamentous instability and concomitant cervical injuries with the expectation of mild neck disability regardless of the displacement, bilaterality, sex, or presence of head injury. Greater disability may be expected in patients aged between 40 and 60 years than in other ages.

Study Design. Case report and clinical discussion. Objective. To describe a rare case of hyperpneumatization of the skull base including the cervical spine with the atlas bone. Summary of Background Data. Initial imaging studies of physically traumatized patients consist of conventional radiographs. An atypical radiolucency is often misdiagnosed as a primary malignancy or a secondary osteolytic metastasis. Further imaging studies may reveal an underlying atypical hyperpneumatization as a very rare benign differential diagnosis. Pathophysiologically, embryological developmental anomalies as well as an elevated pressure to the middle and inner ear are discussed. Methods. We present a symptomatic 40-year-old man with conventional radiographs, after computed tomography and magnetic resonance imaging examinations. Results. Imaging studies reveal an uncommon radiolucency of the skull base including the atlas bone, free air beneath the mastoid bone, stylomastoid foramen, epidural air adjacent to the atlas bone, and surrounding soft-tissue emphysema. Conclusion. Atypical radiolucency may represent a very rare benign hyperpneumatization of the skull base, which may include the craniocervical junction. Because of microfractures of the thinned and consecutive, less stable bones, this also can lead to free air and soft-tissue emphysema, which has not been described previously. Special care should be taken to identify epidural free air because of a possible communication of the epidural space with the external environment. Harmful activities and especially high-speed trauma could result in fractures of the cervical spine due to decreased stability of the hyperpneumatized bones.

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 Radiographic analysis using normal patients. Objective To analyze the relationship between the cervical alignment and the oropharyngeal space. Summary of background data Few clinical studies stress the effect of the occipito-C2 (O-C2) alignment on the oropharyngeal space. A previous study showed dysphagia and/or dyspnea after occipitocervical fusion was caused by oropharyngeal stenosis resulting from O-C2 fixation in a flexed position. Other independent researchers showed that development or improvement of obstructive sleep apnea in rheumatoid arthritis patients was related to the O-C2 alignment. However, there are limited basic data demonstrating the relationship between the O-C2 alignment and the oropharyngeal space. Methods Plain lateral cervical radiographs in five tested positions--neutral, flexion, extension, protrusion, and retraction--of 40 asymptomatic volunteers were collected. The O-C2 angle, the C2-C6 angle, and the anterior-posterior distance of the narrowest oropharyngeal airway space (nPAS) were measured, and the changes in value from the neutral to the other four positions were calculated for each patient. Results According to the multiple regression analysis, there was an extremely strong linear correlation of the change in the O-C2 angle with the percentage change in the nPAS. Referring to the multiple regression analysis, a decrease of 10° in the O-C2 angle caused a 37% reduction in the nPAS in the neutral position. In contrast, no significant correlation was found between the change in the C2-C6 angle and the percentage change in the nPAS. Conclusion Our results show the impact of the O-C2 angle on the oropharyngeal space. This knowledge will be useful for the diagnosis and treatment of the upper cervical lesion combined with the upper airway stenosis, and for the determination of the optimal fixation angle in occipitocervical fusion.

Study design Retrospective medical record review. Objective The purpose of this study was to describe the incidence of other injuries that commonly occur in conjunction with cervical spine fractures and dislocations. Summary of background data Cervical spine fractures are often associated with other significant traumatic conditions, which may also require prompt diagnosis and management. However, the relative incidences of the injuries that occur in conjunction with various cervical spine fractures have not been well documented. Methods The radiographic reports of all patients who underwent CT scans of the cervical spine at a single level 1 trauma center over a 10-year period were reviewed. The medical records of individuals with acute, nonpenetrating fractures of the cervical spine were further assessed for any associated traumatic pathology including noncontiguous spine injuries and those affecting other organ systems (i.e., head and neck, intrathoracic, intra-abdominal/pelvic, and nonspinal orthopedic disorders). Results A total of 13,896 CT scans of the cervical spine were performed during this 10-year period of which 492 revealed acute fractures and/or dislocations. Of these subjects, 60% had sustained at least one additional injury. Overall, 57% were noted to have extraspinal injuries (34% head and neck, 17% intrathoracic, 10% intra-abdominal/pelvic, and 30% nonspinal orthopedic conditions) and noncontiguous spinal trauma was present in 19% of these cases (8% cervical injuries, 8% thoracic, and 6% lumbar). In general, the rates of associated injuries observed with occipital condyle and C7 fractures were significantly higher than those recorded for other cervical segments. Conclusion For patients with a known history of cervical spine trauma, the frequencies of associated injuries were similar across all levels of the cervical spine with the exception of the injuries to the craniocervical junctions. In practice, this means that injuries to the cervical spine can likely be grouped together when considering other possible associated injuries. Further elucidation of these injury patterns will likely be useful for facilitating the expedient evaluation and proper management of these individuals.

STUDY DESIGN In vitro and modeling study of upper cervical spine (UCS) three-dimensional (3D) kinematics and muscle moment arm (MA) during axial rotation (AR) and flexion extension (FE). OBJECTIVE To create musculoskeletal models with movement simulation including helical axis (HA) and muscle features. SUMMARY OF BACKGROUND DATA Integration of various kinematics and muscle data into specific-specimen 3D anatomical models with graphical representation of HA and muscle orientation and MA is not reported for the UCS musculoskeletal system. METHODS Kinematics, anatomical, and computed tomographic imaging data were sampled in 10 anatomical specimens. Using technical markers and anatomical landmarks digitizing, spatial position of segments was computed for five discrete positions of AR and FE using a 3D digitizer. To obtain musculoskeletal model simulation, a registration method was used to combine collected data. Processing was performed using orientation vector and HA computation and suboccipital muscle features (i.e., length and MA) relative to motion angle. RESULTS Range of motion and coupling were in agreement with previous in vitro studies. HA (i.e., location and orientation) showed low variation at the occipitoaxial and atlantoaxial levels for FE and AR, respectively. The main orientation of the HA was vertical at C1-C2 during AR and horizontal at C0-C1 during FE. For muscles MA, absolute peak value (ranging from 20 to 40 mm) occurred at different poses depending on the analyzed muscle and motion. Poor magnitude was found for obliquus capitis inferior and rectus capitis posterior minor in FE and AR, respectively. CONCLUSION On the basis of previous methods, we developed a protocol to create UCS musculoskeletal modeling with motion simulation including HA and suboccipital muscles representation. In this study, simultaneous segmental movement displaying with HA and muscles features was shown to be feasible.