Posterior C1 Research Articles

Segmental Surface Referencing during Intraoperative Three-dimensional Image-Guided Spine Navigation: An Early Validation with Comparison to Automated Referencing.

Study Design Interventional human cadaver study. Objective Intraoperative three-dimensional (3-D)-guided navigation improves spine instrumentation accuracy. However, image acquisition may need to be repeated with segment hypermobility or distant target from reference frame (RF). The current study evaluates the usefulness of internal metal fiducials (IMFs) as surface references in enhancing registration accuracy and avoiding repeating imaging. Methods Six fresh-frozen cadaveric human torsos were utilized. Posterior C1–T2 exposure was done, and three IMFs were inserted per level; intraoperative 3-D images were then acquired. Two registration methods were utilized: autoregistration (AR, group 1) and point registration using IMF (IMFR, group 2). Registration accuracy was checked by identifying IMFs in both groups. Pedicle screws inserted into C2, C4, C5, and C7 based on the two registration methods (three cadavers each) with RF on C7 and then on C2. Results The mean registration error was lower with IMFR compared with AR (0.35 ± 0.5 mm versus 2.02 ± 0.85 mm, p = 0.0001). Overall, 34 pedicle screws were inserted (AR, 18; IMFR, 16). Final screw placement was comparable using both techniques (p = 0.58). Lateral screws violations were observed in four IMFR screws (1 to 2 mm) as compared with five in AR group (2 to 3 mm). Reregistration after moving RF to C2 was possible using surface screws in IMFR group, thus avoiding new 3-D image acquisition. Conclusion During intraoperative 3-D navigation in spine procedures, surface fiducial registration using IMF provided superior accuracy over automated registration. It allowed repeat registration without repeating radiation during long spine segment instrumentations. More studies are needed to clarify both practical and clinical application of this method.

Distraction Arthrodesis of the Atlantoaxial Facet Joint with Preservation of the C2 Root for the Management of Intractable Occipital Neuralgia Caused by C2 Root Compression

Introduction Vertical collapse of the C1-C2 facet joint may cause narrowing of the C2 root foramen with root compression, resulting in severe occipital neuralgia. The purpose of this study was to evaluate the prospectively collected outcomes data of a distraction arthrodesis surgical group (Study group) in comparison to a Control group in a non-randomized design. Material and Methods The Study group underwent intraoperative skeletal traction, preservation of the C2 nerve roots, facet joint distraction and insertion of a bone block and cancellous bone into the joint along with posterior fusion, and segmental screw fixation using posterior C1 arch screws instead of lateral mass screws. The Control group had C2 root transection with C1-C2 segmental screw fixation and arthrodesis. Inclusion criteria for both groups were (1) occipital neuralgia caused by C2 root compression confirmed by clinical manifestation and imaging studies including radiographs, CT scan, and MRI, (2) intractable pain (VAS≥7) unresponsive to nonoperative treatment, and (3) follow-up period ≥12 months. We compared the preoperative and postoperative 10-point VAS scores for occipital neuralgia and neck pain; NDI; and JOA scores and recovery rates. Results There were 15 patients in the Study group and 8 in the Control group. All had facet joint destruction and/or collapse caused by underlying disorders including rheumatoid arthritis (Study group: 5 ; Control group: 3), rheumatoid arthritis with odontoid nonunion (2, 0), odontoid nonunion (3, 1), unifacet spondylosis (3, 2), os odontoideum (2, 1), and cerebral palsy (0, 1). There was no significant difference in age (61 ± 6, 62 ± 9), gender (4 and 3 men, respectively), and the number of cases with accompanying myelopathy (5, 2) between the 2 groups. The follow-up period averaged 21 ± 12 versus 33 ± 25 months, respectively. There was no significant difference in the VAS score for the preoperative occipital neuralgia (8.2 ± 0.9, 7.9 ± 0.6, p = 0.39). However, it was significantly lower in the Study group at 1, 3, 6, and 12 months postoperatively (p = <0.01, respectively). At 12 months, the VAS was 0.4 ± 0.6 versus 2.5 ± 2.6 ( p = 0.01). In the Study group, all patients had little or no pain (VAS ≤2) while 2 patients (25%) in the Control group were still on medication (Gabapentin) with moderate to severe pain (VAS 4 and 8 respectively). There was no significant difference in preoperative and postoperative VAS scores for neck pain, NDI, and JOA scores and recovery rate, since these values are minimally influenced by occipital neuralgia. Conclusion Our results suggest that our novel technique of distraction arthrodesis can be an effective option for the management of intractable occipital neuralgia caused by C2 root compression. Prospective randomized studies are required for better evaluation.

Novel reconstruction of the anterior craniocervical junction using an expandable cage with integrated fixation after total C2 spondylectomy for chordoma

Chordoma is a locally aggressive malignant tumor that generally occurs in the clivus, mobile spine and sacrum. While en bloc resection with wide margins has been advocated as the only cure for chordomas, tumor characteristics and violation of critical anatomical boundaries may preclude pursuing this treatment option in the cervical spine. We present a C2 chordoma in a 35-year-old man with epidural and prevertebral extension that was treated with a single stage anterior–posterior total C2 spondylectomy with novel reconstruction using an expandable cage with integrated fixation followed by stereotactic radiosurgery. Single stage intralesional total C2 spondylectomy via anterior transoral and posterior approaches was performed. The anterior column was reconstructed using an expandable cage with integrated fixation from the clivus to C3. The patient maintained his intact neurological status at 6 month follow-up with full resumption of activities of daily living without any significant morbidity.

Evaluation of the Efficacy of Titanium Mesh Cages with Posterior C1 Lateral Mass and C2 Pedicle Screw Fixation in Patients with Atlantoaxial Instability

Atlantoaxial fusion is a surgical technique that is performed for the treatment of atlantoaxial instability. The standard surgical procedure is fixation of the atlantoaxial complex via a C1 lateral mass and C2 pedicle screw with posterior wiring. Bone grafting material may still be biomechanically suboptimal, such as autologous bone obtained from osteoporotic patients, and may result in collapse and loosening of posterior wiring. Fourteen patients with C1 lateral mass and C2 pedicle fixation as a result of atlantoaxial instability were included in this study. All patients were treated by a single surgeon using a titanium mesh cage with demineralized bone matrix packing. Patient clinical history, imaging data, and medical records were reviewed. To evaluate bony fusion, measurement of the atlantodental interval and computed tomography were performed in the preoperative period, immediate postoperative period, andat 1, 3, 6, and 12 months postoperatively. The Wilcoxon signed-rank test was used to compare differences in theradiologic evaluation at 1 and 12 months postoperatively. Bone fusion was achieved in all patients (100%). Of the 14 patients, 11 had rheumatoid arthritis and 3 had trauma. The mean atlantodental interval of patients with rheumatoid arthritis was 1.85 mm in the immediate postoperative period, 1.96 mm at 1 month postoperatively, 1.98 mm at 3 months postoperatively, 1.96 mm at 6 months, and 1.93 mm at 12 months. Hardware failure and other complications were not observed. The titanium mesh cage has several advantages compared with bone autografts, including reduced donor-site morbidity, immediate rigid fixation, and successful bone fusion.

New entry point for C2 screw, in posterior C1-C2 fixation (Goel-Harm’s technique) significantly reducing the possibility of vertebral artery injury

Objective: To reduce the chance of vertebral artery injury in posterior C1 lateral mass and C2 pedicle/pars screw–rod fixation (Goel–Harms technique ).Method: 49 patients, 30 males and 19 females, 12years - 82 years, underwent posterior C1–C2 fixation from February 2007 till June2013. A new entry point for the posterior C2 screw, 3mm below the midpoint of the C1–C2 joint which is directed medially and downwards into the C2 body , probably avoids the vertebral artery. As the screw now bypasses the pedicle/ pars , the chance of injuring the vertebral artery is probably reduced.Results: No case of intra-operative vertebral artery injury.Conclusion: The new technique of C2 screw fixation allows rigid immobilization of the C1–C2 joint without significant risk of vertebral artery injury.

A Clinical and Kinematical Evaluation of Trajectory Planning Software for Posterior Atlantoaxial Transarticular Screw Fixation Surgery

Atlantoaxial instability is a progressive cervical spine condition that often requires surgical intervention. The posterior C1-2 transarticular fixation has been a great advancement for the management of atlantoaxial instability as it provides improved biomechanical stability. However, the surgical risks of serious neurovascular injury associated with this technique remain an obstacle for its wider adoption. The goal of this study is to evaluate the surgical outcome of C1-2 transarticular screw fixation utilizing a lab-designed trajectory planning software (TPS) system and to investigate the likely kinematical impact of deviated screw trajectory. The TPS system was applied to 19 patients (mean age: 61.1 years, range: 35–71 years; 14 males and 5 females) that underwent C1-2 transarticular fixation at our institution. A total of 32 transarticular screws were inserted. Pre-operative computed tomography images were used to render a three-dimensional bone tissue model as well as the corresponding multi-planar digitally reconstructed radiographs. The pre- and post-operative positions of C1 and C2 were also compared. Overall, only one malpositioned screw was identified and no major complications occurred for any of the patients. A comparison of the planned and actual screw insertion trajectories indicated that the vertical angle was the only parameter to have a statistically significant difference. Moderate negative correlation was found between the vertical entry point and the vertical angle, and moderate positive correlation was found between the horizontal entry point and the horizontal angle. The TPS system is a cost-effective clinical implementation that can potentially reduce the associated complication rates for C1-2 transarticular fixation. The system should be viewed as a useful assistive device as well as a potential training and auditing tool for institutions where more expensive navigational systems are not readily available.

New Radiographic Index for Occipito-Cervical Instability.

Study DesignRetrospective study.PurposeTo propose a new radiographic index for occipito-cervical instability.Overview of LiteratureSymptomatic atlanto-occipital instability requires the fusion of the atlanto-occipital joint. However, measurements of occipito-cervical translation using the Wiesel-Rothman technique, Power's ratio, and basion-axial interval are unreliable because the radiologic landmarks in the occipito-cervical junction lack clarity in radiography.MethodsOne hundred four asymptomatic subjects were evaluated with lateral cervical radiographs in neutral, flexion and extension. They were stratified by age and included 52 young (20–29 years) and 52 middle-aged adults (50–59 years). The four radiographic reference points were posterior edge of hard palate (hard palate), posteroinferior corner of the most posterior upper molar tooth (molar), posteroinferior corner of the C1 anterior ring (posterior C1), and posteroinferior corner of the C2 vertebral body (posterior C2). The distance from posterior C1 and posterior C2 to the above anatomical landmarks was measured to calculate the range of motion (ROM) on dynamic radiographs. To determine the difference between the two age groups, unpaired t-tests were used. The statistical significance level was set at p<0.05.ResultsThe ROM was 4.8±7.3 mm between the hard palate and the posterior C1, 9.9±10.2 mm between the hard palate and the posterior C2, 1.7±7.2 mm between the molar to the posterior C1, and 10.4±12.1 mm between the molar to the posterior C2. There was no statistically significant difference for the ROM between the young- and the middle-aged groups. The intra-observer reliability for new radiographic index was good. The inter-observer reliability for the ROM measured by the hard palate was low, but was better than that by the molar.ConclusionsROM measured by the hard palate might be a useful new radiographic index in cases of occipito-cervical instability.

Electrophysiological correlates of top-down effects facilitating natural image categorization are disrupted by the attenuation of low spatial frequency information

The modulatory effects of low and high spatial frequencies on the posterior C1, P1 and N1 event-related potential (ERP) amplitudes have long been known from previous electrophysiological studies. There is also evidence that categorization of complex natural images relies on top-down processes, probably by facilitating contextual associations during the recognition process. However, to our knowledge, no study has investigated so far how such top-down effects are manifested in scalp ERPs, when presenting natural images with attenuated low or high spatial frequency information. Twenty-one healthy subjects participated in an animal vs. vehicle categorization task with intact grayscale stimuli and images predominantly containing high (HSF) or low spatial frequencies (LSF). ERP scalp maps and amplitudes/latencies measured above occipital, parietal and frontocentral sites were compared among the three stimulus conditions. Although early occipital components (C1 and P1) were modulated by spatial frequencies, the time range of the N1 was the earliest to show top-down effects for images with unmodified low spatial frequency spectrum (intact and LSF stimuli). This manifested in ERP amplitude changes spreading to anterior scalp sites and shorter posterior N1 latencies. Finally, the frontocentral N350 and the centroparietal LPC were differently influenced by spatial frequency filtering, with the LPC being the only component to show an amplitude and latency modulation congruent with the behavioral responses (sensitivity index and reaction times). Our results strengthen the coarse-to-fine model of object recognition and provide electrophysiological evidence for low spatial frequency-based top-down effects within the first 200ms of visual processing.

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

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

Vertebral Artery Injury during Routine Posterior Cervical Exposure: Case Reports and Review of Literature

Study Design Case series. Objective We report the unusual occurrence of vertebral artery injury (VAI) during routine posterior exposure of the cervical spine. The importance of preoperative planning to identify the course of the bilateral vertebral arteries during routine posterior cervical spine surgery is emphasized. Methods VAI is a rare but potentially devastating complication of cervical spinal surgery. Most reports of VAI are related to anterior surgical exposure or screw placement in the posterior cervical spine. VAI incurred during posterior cervical spinal exposure surgery is not adequately addressed in the existing literature. Two cases of VAI that occurred during routine posterior exposure of the cervical spine in the region of C2 are described. Results VAI was incurred unexpectedly in the region of the midportion of the posterior C1–C2 interval during the initial surgical exposure phase of the operation. An aberrant vertebral artery course in the V2 anatomical section in the region between C1 and C2 intervals was identified postoperatively in both patients. A literature review demonstrates a relatively high incidence of vertebral artery anomalies in the upper cervical spine; however, the literature is deficient in reporting vertebral artery injury in this region. Recommendations for preoperative vertebral artery imaging also remain unclear at this time. Conclusions Successful management of this unexpected complication was achieved in both cases. This case report and review of the literature highlights the importance of preoperative vertebral artery imaging and knowledge of the course of the vertebral arteries prior to planned routine posterior exposure of the upper cervical spine. In both cases, aberrancy of the vertebral artery was present and not investigated or detected preoperatively.

Anterior Retropharyngeal Reduction and Sequential Posterior Fusion for Atlantoaxial Rotatory Fixation With Locked C1-C2 Lateral Facet.

Retrospective case series. To introduce a new type of atlantoaxial rotatory fixation (AARF) with a locked C1-C2 lateral facet and evaluate its therapeutic strategy. AARF presenting with torticollis and limited neck motion is commonly seen in teenagers. Fielding and Hawkins' classification is generally applied to AARF. Although conservative treatment is effective for acute AARF, it is often unsuccessful for chronic AARF, which ultimately requires surgery. We introduce a new type of chronic AARF with a locked C1-C2 lateral facet that does not fit into Fielding and Hawkins' classification and describe the appropriate treatment. Eight patients who had chronic AARF with a unilaterally locked C1-C2 lateral facet were referred to our clinic. Reduction had failed after traction for 3 to 4 weeks. After open release and reduction using the anterior retropharyngeal approach, we applied posterior C1-C2 transpedicular screw fixation with an autologous iliac bone graft for stage I or II. The anterior retropharyngeal approach provided direct access to the C1-C2 locked lateral facet. The patient in an overall poor condition (stage II) underwent delayed posterior C1-C2 arthrodesis. The others (stage I) underwent immediate posterior C1-C2 arthrodesis. All patients were followed up for an average of 14.8 months (5-37 mo). Three-dimensional computed tomography revealed C1-C-2 arthrodesis bone graft fusion after an average of 3.1 months (2-4 mo). There was no recurrence of symptoms and no dislocations or internal fixation device loosening or breakage. AARF with a locked C1-C2 lateral facet is a new type of AARF that cannot be classified using Fielding and Hawkins' classification. The anterior retropharyngeal approach for the release and reduction of AARF, followed by posterior C1-C2 arthrodesis is an effective therapeutic strategy for AARF with a locked C1-C2 lateral facet. 4.

Unilateral C-1 posterior arch screws and C-2 laminar screws combined with a 1-side C1-2 pedicle screw system as salvage fixation for atlantoaxial instability.

OBJECT Atlantoaxial instability often requires surgery, and the current methods for fixation pose some risk to vascular and neurological tissues. Thus, new effective and safer methods are needed for salvage operations. This study sought to assess unilateral C-1 posterior arch screws (PASs) and C-2 laminar screws (LSs) combined with 1-side C1-2 pedicle screws (PSs) for posterior C1-2 fixation using biomechanical testing with bilateral C1-2 PSs in a cadaveric model. METHODS Six fresh ligamentous human cervical spines were evaluated for their biomechanics. The cadaveric specimens were tested in their intact condition, stabilization after injury, and after injury at 1.5 Nm of pure moment in 6 directions. The 3 groups tested were bilateral C1-2 PSs (Group A); left side C1-2 PSs with an ipsilateral C-1 PAS + C-2 laminar screw (Group B); and left side C1-2 PSs with a contralateral C-1 PAS + C-2 LS (Group C). During the testing, angular motion was measured using a motion capture platform. Data were recorded, and statistical analyses were performed. RESULTS Biomechanical testing showed that there was no significant difference among the stabilities of these fixation systems in flexion-extension and rotation control. In left lateral bending, the bilateral C1-2 PS group decreased flexibility by 71.9% compared with the intact condition, the unilateral C1-2 PS and ipsilateral PAS+LS group decreased flexibility by 77.6%, and the unilateral C1-2 PS and contralateral PAS+LS group by 70.0%. Each method significantly decreased C1-2 movements in right lateral bending compared with the intact condition, and the bilateral C1-2 PS system was more stable than the C1-2 PS and contralateral PAS+LS system (p = 0.036). CONCLUSIONS A unilateral C-1 PAS + C-2 LS combined with 1-side C-1 PSs provided the same acute stability as the PS, and no statistically significant difference in acute stability was found between the 2 screw techniques. These methods may constitute an alternative method for posterior atlantoaxial fixation.

Posterior Reduction of Fixed Atlantoaxial Dislocation and Basilar Invagination by Atlantoaxial Facet Joint Release and Fixation: A Modified Technique With 174 Cases.

Treatment of fixed atlantoaxial dislocation (AAD) with basilar invagination (BI) is challenging. To introduce a modified technique to reduce fixed AAD and BI through a posterior approach. From 2007 to 2013, 174 patients with fixed AAD and BI underwent surgical reduction by posterior atlantoaxial facet joint release and fixation technique. There was 1 death in the series, and 3 patients were lost to follow-up. The follow-up period ranged from 12 to 52 months (mean: 35.2 months) for the remaining 170 patients. Neurological improvement was observed in 168 of 170 patients (98.8%), and was stable in 1 (0.06%) and exacerbated in 1 (0.06%), with the Japanese Orthopedic Association scores increasing from 11.4 preoperatively to 15.8 postoperatively (P < .01). Radiologically, complete or >90% reduction was attained in 107 patients (62.9%), 60% to 90% reduction was attained in 51 patients (30%), and <50% reduction was attained in 12 patients (7.1%), who underwent additional transoral decompression. Complete decompression was demonstrated in all 170 patients. Solid bony fusion was demonstrated in 167 patients at follow-up (98.2%). This series showed the safety and efficacy of the posterior C1-2 facet joint release and reduction technique for the treatment of AAD and BI. Most fixed AAD and BI cases are reducible via this method. In most cases, this method avoids transoral odontoidectomy and cervical traction. Compared with the occiput-C2 screw method, this short-segment C1-2 technique exerts less antireduction shearing force, guarantees longer bone purchase, and provides more immediate stabilization.

Traumatic atlantooccipital dislocation: comprehensive assessment of mortality, neurologic improvement, and patient-reported outcomes at a Level 1 trauma center over 15 years

Background contextOnly Level 3 evidence exists for the diagnosis and treatment of atlantooccipital dislocation (AOD) with few studies examining mortality, neurologic improvement, and patient-reported outcomes (PROs). PurposeFirst, the aim was to determine: the incidence of AOD, 90-day surgical morbidity and mortality after AOD, patient factors that may be associated with delayed or missed diagnosis, and factors that were associated with mortality and neurologic improvement after AOD. Secondly, the aim was to quantify the pain, disability, and quality of life experienced by patients surviving AOD. Study design/settingThis was a retrospective cohort study. Patient sampleA total of 5,337 consecutive spine computed tomography traumagrams from 1997 to 2012 were included. Outcome measuresMortality, neurologic improvement, complications, EuroQol five dimensions (EQ-5D), Neck Disability Index (NDI), Numeric Rating Scale (NRS)-neck, NRS-arm, and return-to-work were the outcome measures. MethodsPatients were considered to have AOD if they met one of the following radiographic criteria: basion-dens interval greater than 10 mm; basion-axial interval: anterior displacement greater than 12 mm or posterior displacement greater than 4 mm between the basion and posterior C2 line; and condyle to C1 interval greater than 1.4 mm. Linear regression analysis was performed to identify factors associated with 90-day mortality, neurologic improvement, and missed diagnosis. Patient-reported outcomes were assessed via phone interview. ResultsThirty-one patients met radiographic criteria for AOD; an incidence of 0.6% over 15 years. Twenty-one (68%) patients were treated with occipital cervical fusion. At 90 days postoperatively, there were no new neurologic deficits or reoperations. Eight (26%) patients died within 90 days. All patients who died had no documented AOD diagnosis and were not treated surgically. Missed AOD diagnosis was the strongest predictor of mortality. Younger age, lower Glasgow Coma Score, lower Injury Severity Score (ISS) score, and worse initial American Spinal Injury Association (ASIA) score were significantly associated with greater neurologic improvement. Higher ISS score and better ASIA score were significantly associated with missed AOD diagnosis. The average PROs metrics at time of telephone follow-up were as follows: EQ-5D=0.73±0.19, NDI=30.89±18.57, NRS-neck=2.33±2.21, NRS-arm=2.00±2.54. Of the patients with follow-up data, four were employed full-time, and five were receiving disability. ConclusionsOur work suggests that failure to diagnose AOD is a powerful predictor of mortality. Higher ISS scores and better neurologic presentation were significantly associated with missed diagnosis. Craniocervical arthrodesis preserved neurologic function with low complication rate and unexpectedly high PROs and return-to-work. These results must be carefully interpreted because it is unclear whether missed AOD diagnosis accompanies another death-causing injury (eg, traumatic brain injury) or if failure to treat AOD contributes to mortality in a multifactorial manner.

Posterior C2 Instrumentation in the Management of Trauma: Accuracy and Risks Associated with Four Techniques

Introduction Posterior instrumentation of C2 is important in treating occipitocervical, atlanto-axial, and subaxial spinal injuries. The variable C2 anatomy can make instrumentation challenging and prone to potentially severe and even life-threatening complications. The goal of this study was to (1) evaluate a large series of posterior C2 screws to determine accuracy as assessed by computed tomography (CT) scan, (2) assess dimensions of “safe bony windows” with CT, and (3) assess the perioperative complication rate related to errant screw placement. We hypothesize that the evolution of a greater variety of options for C2 fixation and the ability to tailor these techniques to patients' specific anatomy has resulted in decreased complications and increased accuracy. Material and Methods A retrospective review of a single Level I trauma center spine database was assessed to identify all patients with operative management for traumatic conditions with C2 instrumentation between December 2002 and September 2008. Radiographic analysis included evaluation of pre- and postoperative CT scans to quantify the patients' bony anatomy as well as to classify the accuracy of C2 screw placement. All C2 screws were graded using the following definitions: Type I: Screw threads completely within the bony cortex. Type II: Less than half the diameter of the screw violates the surrounding cortex. Type III: Clear violation of the transverse foramen or spinal canal. Results A total of 169 patients (99 males and 70 females) underwent posterior C2 screw fixation for traumatic conditions of the spine, including 23 atlanto-occipital dissociations, 16 unstable C1 ring injuries, 79 dens fractures, 9 Hangman fractures, 8 other C2 fractures, 3 C2 hyperextension injuries, 4 C2–C3 flexion–distraction injuries, 14 subaxial injuries, and 19 odontoid nonunions. Average CT measurements of pedicle height, axial width, and laminar width were 8.1 mm (standard deviation 2.1 mm), 5.8 mm (1.9 mm), and 5.7 mm (1.5 mm), respectively, with males having larger pedicle height ( p &lt; 0.001), pedicle width ( p &lt; 0.001), and laminar width ( p &lt; 0.022). A total of 324 screws underwent CT analysis and chart review. A total of 169 pedicle, 85 trans-articular, 50 laminar, and 20 short pars screws were placed with 80.6, 84.4, 96, and 94.4% accuracy rates (Grade I vs. II and III), respectively. Overall 85% of the screws were rated as being in the ideal location. There were no cases of known vertebral artery injury at the time of surgery. Two pedicle screws were unacceptably placed (Grade III). Both patients had screws encroaching on the vertebral artery foramen: one patient had a vertebral artery occlusion and the other had a Grade I dissection documented on CT angiogram without clinical signs of stroke or emboli as measured on transcranial Doppler. No neurological injuries resulted from instrumentation. Conclusion Our findings demonstrate a lower than previously reported incidence of complications associated with posterior C2 screw placement. In the management of 169 patients with 324 screws, only 2 patients had vascular injuries, neither of whom had any sequelae. The multiple techniques of posterior C2 fixation that are currently available allow for unprecedented flexibility in determining which technique is best suited for a given patient's anatomy.

C2 Subfacetal Body Screw in Posterior Atlantoaxial Fixation (Goel–Harm Technique) to Avoid the Vertebral Artery

Introduction Axis (C2) pedicle/pars screw fixation has a definite risk of injury to the vertebral artery. An alternative trajectory 3 mm below the midpoint of the C2 facet surface, directed, downwards and medially into the C2 body, bypasses the vertebral artery altogether, and still offers adequate bone stock for rigid fixation of the C2 vertebra. Material and Methods Overall, 65 patients, 40 males and 25 females, aged 12 to 82 years, underwent posterior C1–C2 fixation from February 2007 to June 2014. Reducible atlantoaxial instability due to trauma (35), rheumatoid arthritis (20), and infection (tuberculosis) (10), magnetic resonance imaging (MRI), dynamic lateral X-rays of craniovertebral junction (CVJ), 3D CT scan of the craniovertebral region along with dynamic study and CT angiography. The entry point for the C2 screw was 2 to 3 mm below the midpoint of superior facet of the C2 which is also the midpoint C1–C2 joint and directed 10–to 15 degrees medially and downwards into the body of the axis. The same 3-mm drill bit was used incrementally till a depth of 5 mm and, 3.5 mm and 18 to 24mm length self-tapping screw with polyaxial head was used in most cases. Results No case of intraoperative vertebral artery injury. No patient required per operative blood transfusion. Follow-up visits were scheduled at 2, 6 to 8 weeks, and 3 months. Dynamic X-ray imaging was done in all patients at 6 to 8 weeks before discontinuing the collar and after 3 months since the operation. All patients followed up for 3 months. Telephonic follow-up of 30 patients was available for 24 months, 12 patients for 6 months, and remaining 7 patients have not reported and are not contactable after the 3 month visit. One postoperative mortality due to myocardial infarction on 7th day. Seven patients complained of occipital numbness and paresthesia which was not disturbing and responded to reassurance and supportive medication (pregabalin). Two patients had superficial wound infection which responded to appropriate antibiotics. There was no case of implant failure or loss of rigidity of fixation up to 3 months. Conclusion The new entry point offers rigid fixation and avoids the vertebral artery altogether nullifying the chance of arterial injury. Divergent screws (bridge vs. tension band construct) have a greater pull out strength. The new technique of C2 screw fixation allows rigid immobilization of the C1–C2 joint without any risk of vertebral artery injury.

Trends in Epidemiology and Management of Traumatic Type II Odontoid Fracture: Experience in Latin America

Introduction Odontoid fractures (OF) are frequent in the trauma population, and there is no universally accepted single method of management. The objective of this study was to evaluate the epidemiology and management of type II OF in Latin America treated either with rigid cervical orthosis or surgery. Patients and Methods A total of 83 patients treated conservatively or by surgery were enrolled in this retrospective study. Medical charts, imaging studies, and outcomes of patients were analyzed in the pretreatment period and at the last medical evaluation. The fractures were assessed using conventional radiographs, three-dimensional computed tomographic (3D-CT) scans, and magnetic resonance images. Fracture gaps, the direction and the degree of displacement of the odontoid process, the fracture line anatomy, the degrees of atlantoaxial instability, the comminuted fracture, and the surface contact area were analyzed. The decision for operative or nonoperative treatment was based on anesthesia risk, and patient's choice of the nonoperative treatment. The nonoperative management generally consisted of a rigid cervical orthosis for 3 months. The type of surgery to be performed was chosen by the surgeon. The solid bony union was defined as the presence of bony bridges and the definite continuity of cortical bone. Fibrous union was considered present when no degree of motion was evident in dynamic radiographs despite persistent cortical bone discontinuity within a fracture gap on 3D CT scans. Nonunion was defined as a definite fracture gap with abnormal motion of the fractured dens on dynamic radiographs and on a 3D CT scan. Results A total of 83 patients were included in this study. The patients were 78.3% men, the mean age = 44.98 ( ± 23.20 years) years. Traffic accidents (66.3%) were the most common cause of trauma. The main symptom was pain (85.5%) in the posterior cervical region. The median time elapsed from accident to surgery was 7 days (P25: 2/P75: 27.5). Median follow-up was 23.66 ( ± 25.43 months) months. Conservative treatment with cervical orthosis, for example, Miami J collar or halo-vest was used in 20.5% of the cases. Odontoid screw technics (57.6%) were the most common surgical treatment adopted as primary surgical treatment. Symptomatic nonunion was observed in two cases with conservative treatment and three cases after odontoid screw fixation. All the patients were referred to posterior C1–C2 fixation. The posterior fixation tended to be used after conservative failed therapy, after nonunion anterior screw surgery, and in fractures with greater displacement. The most common radiological feature was no displacement of the odontoid process in relation to the body of C2, horizontal fracture line, gap fracture &lt; 2 mm, no subluxation across each C1–C2 facet joint and no comminuted fracture. Conclusion The patients treated nonoperatively with a rigid collar may have an overall favorable outcome compared with surgical treatment. A well-designed prospective study is needed to better elucidate optimal treatment algorithms from both an outcomes and cost-effectiveness perspective.

Endoscopic endonasal atlantoaxial transarticular screw fixation technique: an anatomical feasibility and biomechanical study.

OBJECT The primary disadvantage of the posterior cervical approach for atlantoaxial stabilization after odontoidectomy is that it is conducted as a second-stage procedure. The goal of the current study is to assess the surgical feasibility and biomechanical performance of an endoscopic endonasal surgical technique for C1-2 fixation that may eliminate the need for posterior fixation after odontoidectomy. METHODS The first step of the study was to perform endoscopic endonasal anatomical dissections of the craniovertebral junction in 10 silicone-injected fixed cadaveric heads to identify relevant anatomical landmarks. The second step was to perform a quantitative analysis using customized software in 10 reconstructed adult cervical spine CT scans to identify the optimal screw entry point and trajectory. The third step was biomechanical flexibility testing of the construct and comparison with the posterior C1-2 transarticular fixation in 14 human cadaveric specimens. RESULTS Adequate surgical exposure and identification of the key anatomical landmarks, such as C1-2 lateral masses, the C-1 anterior arch, and the odontoid process, were provided by the endonasal endoscopic approach in all specimens. Radiological analysis of anatomical detail suggested that the optimal screw entry point was on the anterior aspect of the C-1 lateral mass near the midpoint, and the screw trajectory was inferiorly and slightly laterally directed. The custommade angled instrumentation was crucial for screw placement. Biomechanical analysis suggested that anterior C1-2 fixation compared favorably to posterior fixation by limiting flexion-extension, axial rotation, and lateral bending (p > 0.3). CONCLUSIONS This is the first study that demonstrates the feasibility of an endoscopic endonasal technique for C1-2 fusion. This novel technique may have clinical utility by eliminating the need for a second-stage posterior fixation operation in certain patients undergoing odontoidectomy.

Stabilization of the craniocervical junction after an internal dislocation injury: an in vitro study

Background contextReconstructive surgeries at the occipitocervical (OC) junction have been studied in treating degenerative conditions. There is a paucity of data for optimal fixation for a traumatically unstable OC joint. In clinical OC dislocations, segmental fixation may be impossible because of vertebral artery injury or fracture. Segmental fixation of the occiput, C1, and C2 demonstrated maximum biomechanical stability in fixation of an unstable craniocervical dislocation. A biomechanical study comparing various points of cervical posterior screw fixation after recreating traumatic injury would illuminate relative advantages between the various techniques. PurposeTo determine the rigidity lost, if any, of segmental C0–C2 posterior screw fixation versus fixation skipping C1 at the OC junction, with or without a cross-connector. Study designThis study is a cadaveric biomechanical investigation. MethodsIntervertebral motions and translations were recorded in seven specimens under conditions in the following order: intact, OC dislocation model with complete disruption of the cruciate ligaments, alar ligaments, and occipitoatlantal/atlantoaxial capsules (injury), segmental posterior fixation (SPF) with posterior instrumentation (ELLIPSE; Globus Medical, Inc., Audubon, PA, USA) at occiput, C1, and C2 levels, endpoint fixation (EPF) with posterior instrumentation at occiput and C1 level skipping C1, and endpoint fixation with a cross-connector (EPFC). Motion was applied through a custom spine simulator with a pure moment load of 2.5 Nm and measured with motion capture markers attached to occiput (C0), anterior C1 ring, and C2. Flexion-extension (FE), lateral bending (LB), axial rotation (AR), and cranial-caudal (CC) motions were recorded in terms of C0–C2. Results were reported as a percentage of injured motion (injury=100%), unless otherwise stated. ResultsThe injury significantly increased the motion to 165%, 263%, and 130%, during FE, LB, and AR, respectively, of intact. The CC translations increased to 164%, 254%, and 121% during FE, LB, AR, respectively, of intact. Segmental posterior fixation significantly reduced motion to 7%, 8%, and 1%, during FE, LB, and AR, respectively, of injury. Endpoint fixation significantly increased motion in FE, resulting in 12%, 6%, and 4% during FE, LB, and AR, respectively, of injury when compared with SPF. The EPFC construct decreased the motion compared with its counterpart to 8.6%, 5.7%, and 3.2% during FE, LB, and AR, respectively. ConclusionsAll fixation constructs significantly reduced motion in all loading modes and CC translations, compared with intact and injury. The construct with the greatest stability against craniocervical dislocation included SPF with instrumentation at the occiput, C1, and C2. By skipping C1 using the EPF, FE and cephalad-caudal translations significantly increased compared with posterior fixation at every level. The addition of a cross-connector increased the stability but was not statistically significant.

An anatomic study to determine the optimal entry point, medial angles, and effective length for safe fixation using posterior C1 lateral mass screws.

Anatomic study of the C1 lateral mass using fine-cut computed tomographic scans and Mimics software. To investigate the optimal entry point, medial angles, and effective length for safe fixation using posterior C1 lateral mass screws. Placing posterior C1 lateral mass screws is technically demanding, and a misplaced screw can result in injury to the vertebral artery, spinal cord, or internal carotid artery. Although various insertion angles have been proposed for posterior C1 lateral mass screw, no clear consensus has been reached on the ideal medial angle of the C1 lateral mass. The C1 lateral masses were evaluated using computed tomographic scans and Mimics software in 70 patients. The effective width and effective screw length of posterior C1 lateral mass screws were measured at different medial angulations relative to the midline sagittal plane. The height (H) for screw entry point on the posterior surface of C1 lateral mass and the distance (D) between screw entry point and the intersection of the midline sagittal plane and the posterior arch of the atlas were also measured. The mean height (H) for screw entry on the posterior surface of the lateral mass was 4.25 mm, the mean distance (D) between screw entry point and the intersection of the midsagittal plane and the posterior arch of the atlas was 27.62 mm. The optimal medial angle was 20.86° with a corresponding effective width of 10.56 mm and effective screw length of 21.87 mm. This study helps to define the specific anatomy related to C1 posterior lateral mass screw placement in an effort to facilitate instrumentation. However, variation is seen in lateral mass anatomy, and this study must be combined with customized surgical planning that includes advanced imaging for safe and effective instrumentation. 1.