C1 Lateral Mass Research Articles

CT-based morphometric analysis of C1 laminar dimensions: C1 translaminar screw fixation is a feasible technique for salvage of atlantoaxial fusions.

Background:Translaminar screw fixation has become an alternative in the fixation of the axial and subaxial cervical spine. We report utilization of this approach in the atlas as a salvage technique for atlantoaxial stabilization when C1 lateral mass screws are precluded. To assess the feasibility of translaminar fixation at the atlas, we have characterized the dimensions of the C1 lamina in the general adult population using computed tomography (CT)-based morphometry.Methods:A 46-year-old male with symptomatic atlantoaxial instability secondary to os odontoideum underwent bilateral C1 and C2 translaminar screw/rod fixation as C1 lateral mass fixation was precluded by an anomalous vertebral artery. The follow-up evaluation 2½ years postoperatively revealed an asymptomatic patient without recurrent neck/shoulder pain or clinical signs of instability. To better assess the feasibility of utilizing this approach in the general population, we retrospectively analyzed 502 consecutive cervical CT scans performed over a 3-month period in patients aged over 18 years at a single institution. Measurements of C1 bicortical diameter, bilateral laminar length, height, and angulation were performed. Laminar and screw dimensions were compared to assess instrumentation feasibility.Results:Review of CT imaging found that 75.9% of C1 lamina had a sufficient bicortical diameter, and 63.7% of C1 lamina had sufficient height to accept bilateral translaminar screw placement.Conclusions:CT-based measurement of atlas morphology in the general population revealed that a majority of C1 lamina had sufficient dimensions to accept translaminar screw placement. Although these screws appear to be a feasible alternative when lateral mass screws are precluded, further research is required to determine if they provide comparable fixation strength versus traditional instrumentation methods.

A new technique of C1 lateral mass screw insertion via posterolateral approach

A new technique of C1 lateral mass screw insertion via posterolateral approach

A Review of Os Odontoideum in Children

Study Background: Os odontoideum is an anomaly of the cervical axis characterized by an independent ossicle of variable size separated from the hypoplastic dens that can present as an incidental radiographic finding to severe neck pain, torticollis, myelopathy, as well as seizures and syncope. Diagnosis is primarily made based on clinical presentation and extensive radiologic evaluation. In this review, we discuss the etiology, treatment, and management of this rare condition in the pediatric population and propose a treatment algorithm. Methods: We performed a comprehensive retrospective review of English literature in PubMed on surgical approaches to treatment and stabilization of Os osontoideum in children. Results: Asymptomatic children, who are diagnosed with Os odontoideum, but lack overt neurologic deficits, are advised to continue radiologic monitoring with lateral flexion-extension X-rays once a year and MRI evaluation once every five years. For symptomatic patients with significant atlantoaxial instability, neurologic deficits, or myelopathy, surgical treatment is recommended. In cases where the atlantoaxial joint is aligned properly without any kyphotic deformities and vertebral arteries abnormalities, transarticular C1-C2 screw fixation should be considered. If these requirements are not met, C1 lateral mass screws with C2 pars/pedicle screws method are advised. The transoral approach, odontoid screw fixation, and minimally invasive techniques are possible alternatives, but have not been studied enough to be considered standard treatments in pediatric population. Conclusions: These recommendations are meant to initiate a “best practices” strategy for treatment of Os odontoideum in children. We anticipate further refinement of these recommendations as new research and reports arise in the field of minimally invasive neurosurgery.

Placement of C1 Pedicle Screws Using Minimal Exposure: Radiographic, Clinical, and Literature Validation.

Traditional C1-2 fixation involves placement of C1 lateral mass screws. Evolving techniques have led to the placement of C1 pedicle screws to avoid exposure of the C1-C2 joint capsule. Our minimal dissection technique utilizes anatomical landmarks with isolated exposure of C2 and the inferior posterior arch of C1. We evaluate this procedure clinically and radiographically through a technical report. Consecutive cases of cranial-vertebral junction surgery were reviewed for one fellowship trained spinal surgeon from 2008-2014. Information regarding sex, age, indication for surgery, private or public hospital, intra-operative complications, post-operative neurological deterioration, death, and failure of fusion was extracted. Measurement of pre-operative axial and sagittal CT scans were performed for C1 pedicle width and C1 posterior arch height respectively. 64 patients underwent posterior cranio-vertebral junction fixation surgery. 40 of these patients underwent occipital-cervical fusion procedures. 7/9 (77.8%) C1 instrumentation cases were from trauma with the remaining two (22.2%) from oncologic lesions. The average blood loss among isolated C1-C2 fixation was 160cc. 1/9 patients (11.1%) suffered pedicle breech requiring sub-laminar wiring at the C1 level. On radiographic measurement, the average height of the C1 posterior arch was noted at 4.3mm (range 3.8mm to 5.7mm). The average width of the C1 pedicle measured at 5.3mm (range 2.8 to 8.7mm). The patient with C1 pedicle screw failure had a pedicle width of 2.78mm on pre-operative axial CT imaging. Our study directly adds to the literature with level four evidence supporting a minimal dissection of C1 arch in the placement of C1 pedicle screws with both radiographic and clinical validation. Justification of this technique avoids C2 nerve root manipulation or sacrifice, reduces bleeding associated with the venous plexus, and leaves the third segment of the vertebral artery unexplored. Pre-operative review of imaging is critical in the placement of C1-C2 instrumentation.

Posterior atlantoaxial fixation: A cadaveric and fluoroscopic step-by-step technical guide.

Background:Atlantoaxial surgical fixation is widely employed treatment strategy for a myriad of pathologies affecting the stability of the atlantoaxial joint. The most common technique used in adults, and in certain cases in children, involves a posterior construct with C1 lateral mass screws, and C2 pars or pedicle screws. This technical note aims to provide a step-by-step guide to this procedure using cadaveric and fluoroscopic images.Methods:An embalmed, human, cadaveric, specimen was used for this study. The subject did not have obvious occipital-cervical pathology. Dissections and techniques were performed to mimic actual surgical technique. Photographs were taken during each step, and the critical aspects of each step were highlighted. Fluoroscopic images from a real patient undergoing C1/C2 fixation were also utilized to further highlight the anatomic-radiographic relationships. This study was performed without external or industry funding.Results:Photographic and radiographic pictures and drawings are presented to illustrate the pertinent anatomy and technical aspects of this technique. The nuances of each step, including complication avoidance strategies are also highlighted.Conclusions:Given the widespread utilization of this technique, described step-by-step guide is timely for surgeons and trainees alike.

Neurosurgery Concepts: Key perspectives on C2 nerve root transection following C1 lateral mass screw fixation, choroid plexus cauterization in infants with hydrocephalus, quality of life following treatment of vestibular schwannoma, dynamic magnetic resonance imaging for glioblastoma pseudoprogression, cost-utility analysis of lumbar spinal stenosis treatment

Departments of Neurosurgery, George Washington University School of Medicine and Health Sciences, Washington, D.C, 1Department of Neurosurgery, Northwestern University Feinberg School of Medicine, Chicago, IL, 2Department of Neurosurgery, University of California Los Angeles, David Geffen School of Medicine, Los Angeles, CA, 3Department of Neurosurgery, Baylor College of Medicine, Texas Children’s Hospital, Houston, TX, USA

The Surgical Treatment Principles of Atlantoaxial Instability Focusing on Rheumatoid Arthritis.

Object. This retrospective review was conducted to determine the surgical treatment principle for rheumatoid arthritis (RA) patients with atlantoaxial instability (AAI). Methods. Thirteen patients with AAI, including 5 RA patients, received preoperative computed tomography- (CT-) based image-guided navigation system (IGS) in C1 lateral mass-C2 pedicle screw-rod system fixation (LC1-PC2 fixation). These 13 patients were analyzed for 52 screws inserted into C1 and C2. We defined these patients as non-RA group (8 patients, 32 screws) and RA group (5 patients, 20 screws). The neurological status for RA group was evaluated using the Ranawat classification. The causes of AAI, surgical indications, complications, surgical method revolution, and CT-based navigation application are discussed. Results. None of the 13 patients expressed neurological function deterioration. The non-RA group screw accuracy was 100%. In the RA group, 1 RA patient developed left C2 screw loosening at 1+ months after operation due to screw malposition. The screw accuracy for this group was 95%. Conclusions. Higher intraoperative surgical complication rate was described in RA patients. Preoperative CT-based IGS in LC1-PC2 fixation can provide good neurological function and screw accuracy results. However, for higher screw accuracy in RA patients, intraoperative CT-based IGS application may be considered.

Biomechanical analysis of screw constructs for atlantoaxial fixation in cadavers: a systematic review and meta-analysis.

The unique and complex biomechanics of the atlantoaxial junction make the treatment of C1-2 instability a challenge. Several screw-based constructs have been developed for atlantoaxial fixation. The biomechanical properties of these constructs have been assessed in numerous cadaver studies. The purpose of this study was to systematically review the literature on the biomechanical stability achieved using various C1-2 screw constructs and to perform a meta-analysis of the available data. A systematic search of PubMed through July 1, 2013, was conducted using the following key words and Boolean operators: "atlanto [all fields]" AND "axial [all fields]" OR "C1-C2" AND "biomechanic." Cadaveric studies on atlantoaxial fixation using screw constructs were included. Data were collected on instability models, fixation techniques, and range of motion (ROM). Forest plots were constructed to summarize the data and compare the biomechanical stability achieved. Fifteen articles met the inclusion criteria. An average (±SD) of 7.4±1.8 cadaveric specimens were used in each study (range 5-12). The most common injury models were odontoidectomy (53.3%) and cervical ligament transection (26.7%). The most common spinal motion segments potted for motion analysis were occiput-C4 (46.7%) and occiput-C3 (33.3%). Four screw constructs (C1 lateral mass-C2 pedicle screw [C1LM-C2PS], C1-2 transarticular screw [C1-C2TA], C1 lateral mass-C2 translaminar screw [C1LM-C2TL], and C1 lateral mass-C2 pars screw [C1LM-C2 pars]) were assessed for biomechanical stability in axial rotation, flexion/extension, and lateral bending, for a total of 12 analyses. The C1LM-C2TL construct did not achieve significant lateral bending stabilization (p=0.70). All the other analyses showed significant stabilization (p<0.001 for each analysis). Significant heterogeneity was found among the reported stabilities achieved in the analyses (p<0.001; I2>80% for all significant analyses). The C1LM-C2 pars construct achieved significantly less axial rotation stability (average ROM 36.27° [95% CI 34.22°-38.33°]) than the 3 other constructs (p<0.001; C1LM-C2PS average ROM 49.26° [95% CI 47.66°-50.87°], C1-C2TA average ROM 47.63° [95% CI 45.22°-50.04°], and C1LM-C2TL average ROM 53.26° [95% CI 49.91°-56.61°]) and significantly more flexion/extension stability (average ROM 13.45° [95% CI 10.53°-16.37°]) than the 3 other constructs (p<0.001; C1LM-C2PS average ROM 9.02° [95% CI 8.25°-9.80°], C1-C2TA average ROM 7.39° [95% CI 5.60°-9.17°], and C1LM-C2TL average ROM 7.81° [95% CI 6.93°-8.69°]). The C1-C2TA (average ROM 5.49° [95% CI 3.89°-7.09°]) and C1LM-C2 pars (average ROM 4.21° [95% CI 2.19°-6.24°]) constructs achieved significantly more lateral bending stability than the other constructs (p<0.001; C1LM-C2PS average ROM 1.51° [95% CI 1.23°-1.78°]; C1LM-C2TL average ROM -0.07° [95% CI -0.44° to 0.29°]). Meta-analysis of the existing literature showed that all constructs provided significant stabilization in all axes of rotation, except for the C1LM-C2TL construct in lateral bending. There were significant differences in stabilization achieved in each axis of motion by the various screw constructs. These results underline the various strengths and weaknesses in biomechanical stabilization of different screw constructs. There was significant heterogeneity in the data reported across the studies. Standardized spinal motion segment configuration and injury models may provide more consistent and reliable results.

C1 posterior arch screw as an auxiliary anchor in posterior reconstruction for atlantoaxial dislocation associated with type II odontoid fracture: a case report and review of the literature.

AbtractIntroductionAlthough pedicle or lateral mass screws are usually chosen to fix atlantoaxial (C1-C2) instability, there is an increased risk for vertebral artery (VA) injury when used in patients with bone or arterial anomalies or osteoporotic bone. Here we report the C1 posterior arch screw as a new technique for upper cervical fixation.Case descriptionA 90-year-old man complained of upper cervical pain after falling in his house. The initial computed tomography (CT) scan showed C1-C2 posterior dislocation with a type II odontoid fracture. The patient underwent C2 fracture reduction and posterior C1-C2 fixation. On the right side of C1, because lateral mass screw placement could cause injury to the dominant VA considering a risk in oldest-old osteoporotic patients, a posterior arch screw was chosen instead as an auxiliary anchor. An intralaminar screw was placed on the right side of C2 because a high-riding VA was observed. A lateral mass screw and a pars interarticularis screw were placed on the left side of C1 and C2, respectively. Ten months later, the odontoid fracture had healed, with normal anatomical alignment. Although the patient experienced slight weakness when spreading his bilateral fingers, his overall condition was good.Discussion and evaluationWe have presented a novel technique using C1 posterior arch screws for the fixation of a C1-C2 dislocation. Such a screw is an alternative to the C1 lateral mass screw in patients who are at risk for a VA injury because of anomalous bone and arterial structures or poor bone quality.ConclusionsAlthough there have been few comparable studies, and the long-term outcome is unknown, fixation with a posterior arch screw could be a beneficial choice for surgeries involving the upper cervical region.

Treatment of fixed atlantoaxial dislocation and basilar invagination with C1-2 screw and rod reduction and fixation technique

To introduce a novel technique of reducing fixed atlantoaxial dislocation (FAAD) and basilar invagination (BI) with C1-C2 screw and rod system. From January 2009 to December 2011, 26 patients of FAAD and BI were reduced successfully with an insertion of C1 lateral mass and C2 pedicle/pars screw and rod system. The cohort had 17 females and 9 males. And their most common presenting symptoms were extremity muscle weakness, restricted neck movement and paresthesia. All of them achieved effective reduction. Among them, 18 attained complete reduction and 8 partial reduction (over 60% extent of reduction). The mean atlanto-dental interval (ADI) value was 2.1 mm postoperatively versus 8.8 mm preoperatively (t = 21.1, P < 0.01) . All of them had relieved compression of dura and medulla oblongata and cervical cord. All clinical symptoms improved. One case had pulmonary infection while another case delayed healing of incision. Both recovered well after symptomatic treatments. Bony fusion reached 100% during a mean follow-up period of 22 months. The C1-C2 screw and rod system may achieve effective reduction and fixation for FAAD and BI. Capable of preserving atlanto-occipital joints in patients without atlas assimilation, this procedure provide more solid immobilization than occipitocervical fusion in those with atlas assimilation.

C1 lateral mass screw placement in occipitalization with atlantoaxial dislocation and basilar invagination: a report of 146 cases.

Retrospective study of 146 patients with the diagnosis of occipitalization, atlantoaxial dislocation (AAD) and basilar invagination, using a novel surgical treatment strategy. To introduce a novel fixation and reduction technique. 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. 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. 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. 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.

C2 nerve dysfunction associated with C1 lateral mass screw fixation.

The C1 lateral mass screw technique is widely used for atlantoaxial fixation. However, C2 nerve dysfunction may occur as a complication of this procedure, compromising the quality of life of affected patients. This is a review of the topic of C2 nerve dysfunction associated with C1 lateral mass screw fixation and related research developments. The C2 nerve root is located in the space bordered superiorly by the posterior arch of C1 , inferiorly by the C2 lamina, anteriorly by the lateral atlantoaxial joint capsule, and posteriorly by the anterior edge of the ligamentum flavum. Some surgeons suggest cutting the C2 nerve root during C1 lateral mass screw placement, whereas others prefer to preserve it. The incidence, clinical manifestations, causes, management, and prevention of C2 nerve dysfunction associated with C(1) lateral mass screw fixation are reviewed. Sacrifice of the C2 nerve root carries a high risk of postoperative numbness, whereas postoperative nerve dysfunction can occur when it has been preserved. Many surgeons have been working hard on minimizing the risk of postoperative C2 nerve dysfunction associated with C1 lateral mass screw fixation.

A Simple Preoperative Evaluation to Avoid Postoperative C2 Nerve Dysfunction Related With C1 Lateral Mass Screw

A Simple Preoperative Evaluation to Avoid Postoperative C2 Nerve Dysfunction Related With C1 Lateral Mass Screw

Pseudo-anévrysme géant différé provoqué par la mise en place d’une vis dans la masse latérale de C1

We report the case of a patient who suffered iatrogenic vertebral artery injury (VAI) during a cervical spine posterior fixation procedure. The patient suffered massive bleeding and hemorrhagic shock at the time of screws placement in C1 lateral mass and C2 pedicle. The postoperative MRI and CT angiography showed a pseudoaneurysm 7.0 centimeter in diameter in the cervical spine. The iatrogenic VAI during posterior screw fixation is extremely rare. But, it can cause catastrophic consequences. We discuss the causes for the iatrogenic VAI and review the preventative measures and suitable management to avoid iatrogenic complications.

Commentary on: "Vertebral Artery Anomalies at the Craniovertebral Junction: A Case Report and Review of the Literature".

The authors report a case of an unstable C1 fracture with magnetic resonance imaging demonstrating rupture of the transverse ligament. Posterior vertebral artery anomaly in the form of a right persistent first intersegmental artery was identified preoperatively in the region of the right posterior C1–C2 lateral mass interval. The surgical plan was altered to avoid the anomalous vertebral artery and the patient was successfully managed with an uncomplicated occiput to C3 instrumentation and fusion procedure. The literature review includes a discussion of the work by Uchino et al who have reported a persistent first intersegmental artery in up to 3.2% of normal subjects and an overall prevalence of craniovertebral junction vertebral artery anomalies of 5%.1 This article is an important addition to the existing literature as it highlights the relatively high prevalence of vertebral artery anomalies at the craniovertebral junction. The case described involves an aberrant vertebral artery with an anomalous course located posteriorly between the C1 and C2 lateral masses. This particular vertebral artery anomaly poses great risk to the conventional placement of C1 lateral mass screws through previously described techniques involving the exposure of the C1 lateral mass or placement of the screw through the C1 posterior ring. The anomaly was identified preoperatively by computed tomography angiography in this case, and intraoperative vertebral artery injury was avoided. The utility of the use of routine of preoperative imaging studies to demonstrate the course of the bilateral vertebral arteries before any planned exposure of the craniocervical junction is clearly implied in this case report. The significance of this case report and review of the literature lies in the identification of the increased risk of complication involving vertebral artery injury through a routine posterior cervical spine surgical exposure. Much of the existing literature involving vertebral artery injury in cervical spinal surgery has focused on injuries incurred with anterior cervical spinal surgical procedures. Tortuous anterior course of the vertebral artery in the subaxial cervical spine has been well described by Curylo et al in approximately 5.5% of subjects.2 Multiple reports of injury to the vertebral artery during anterior cervical decompression surgery exist in the literature.3 Five studies reported rates of 0.10 to 1.96%, depending on the type of anterior cervical spine procedure.3 There remains, however, a paucity of literature with respect to vertebral artery injury incurred with a posterior cervical surgical exposure. Molinari et al recently reported vertebral artery injury in two cases involving a persistent first intersegmental artery in the region of C1–C2. Both injuries were incurred with routine posterior exposure of the C1–C2 anatomy. A review of the existing literature demonstrates few publications on this topic.3 The authors should be applauded for this work, which raises a greater sense of awareness as to the increased potential for vertebral artery injury during posterior cervical spine exposure in the region of the craniocervical junction. Their work underscores the need for thorough preoperative evaluation of the course of the vertebral artery before performing operative procedures on the cervical spine.

Late Complication of Surgically Treated Atlantoaxial Instability: Occipital Bone Erosion Induced by Protruded Fixed Titanium Rod: A Case Report

ObjectivePolyaxial screw-rod fixation of C1-C2 is a relatively new technique to treat atlantoaxial instability, and there have been few reports in the literature outlining all possible complications. The purpose of this case report is to present the occurrence and management of occipital bone erosion induced by the protruded rostral part of a posterior atlantoaxial screw-rod construct causing headache. Clinical FeaturesA 70-year-old Asian man with rheumatoid arthritis initially presented to our institution with atlantoaxial instability causing progressive quadraparesis and neck pain. Intervention and OutcomePosterior atlantoaxial instrumented fixation using C1 lateral mass screws in conjunction with C2 pedicle screws was performed to stabilize these segments. Postoperatively, the patient regained the ability to independently walk and had no radiographic evidence of instrumentation hardware failure and excellent sagittal alignment. However, despite a well-stabilized fusion, the patient began to complain of headache during neck extension. Follow-up imaging studies revealed left occipital bone erosion induced by a protruded titanium rod fixed with setscrews. During revision surgery, the rod protrusion was modified and the headaches diminished. ConclusionThis case demonstrates that occipital bone erosion after posterior atlantoaxial fixation causing headache may occur. The principal cause of bone erosion in this case was rod protrusion. Although posterior atlantoaxial fixation using the screw-rod system was selected to manage atlantoaxial instability because it has less complications than other procedures, surgeons should pay attention that the length of the rod protrusion should not exceed 2 mm.

Giant delayed pseudo-aneurysm following screw placement in C1 lateral mass

We report the case of a patient who suffered iatrogenic vertebral artery injury (VAI) during a cervical spine posterior fixation procedure. The patient suffered massive bleeding and hemorrhagic shock at the time of screws placement in C1 lateral mass and C2 pedicle. The postoperative MRI and CT angiography showed a pseudoaneurysm 7.0 cm in diameter in the cervical spine. The iatrogenic VAI during posterior screw fixation is extremely rare. But, it can cause catastrophic consequences. We discuss the causes for the iatrogenic VAI and review the preventative measures and suitable management to avoid iatrogenic complications.

Ideal screw entry point and optimal trajectory for anterior C1 lateral mass screw: an anatomical study

To explore the ideal screw entry point and optimal trajectory for anterior C1 lateral mass screw internal fixation, and provide an anatomical basis for the technique of anterior C1 lateral mass screw placement. A radiographic analysis of the anatomy of the C1 lateral mass using Computed tomography, CT scan was performed in cervical spine of 56 healthy Chinese adults (28 males, 28 females; mean age, 36.5 years; age range, 18-55 years), by using the Mimics software to reconstruct the 3-D morphology of C1 lateral mass and measuring the inside, middle and outside effective height of the C1 lateral mass in front and back. Measuring the C1 lateral mass safe width with different extraversion angles range from 0° to 30° with a uniform interval of 5°, to find out the ideal extraversion angle. Measuring the range of sagittal angle, to find out the ideal sagittal angle. The inside (H1), middle (H3) and outside (H5) effective height of the C1 lateral mass in front is 6.67 mm, 12.09 mm, and 17.51 mm, the inside (H2), middle (H4) and outside(H6) effective height of the C1 lateral mass in back is 8.17 mm, 13.20 mm, and 18.22 mm. When the extraversion angle choose 0°, 5°, 10°, 15°, 20°, 25°, 30°, and δ, the relative results of safe width (SW) of lateral mass were 4.73 mm, 5.36 mm, 5.90 mm, 6.33 mm, 6.44 mm, 5.70 mm, 4.38 mm, 6.95 mm averagely. The mean distance along the atlas anterior surface between the anterior tubercle and the screw entry point was 12.80 mm, the mean distance from the inferior border of the lateral mass to the screw entry point was 6.87 mm. The range of sagittal angle is 24.22° (-17.74°∼6.48°) . The ideal extraversion angle was 21.14°. The mean distance along the atlas anterior surface between the anterior tubercle and the screw entry point was 12.80 mm. The mean distance from the inferior border of the lateral mass to the screw entry point was 6.87 mm. The ideal sagittal angle is -5.63°. These measurements may facilitate anterior C1 lateral mass screw fixation decreasing the risk of injury to the spinal cord, vertebral artery, and internal carotid artery theoretically. Delineating the individual anatomy in each case with CT scan before surgery is recommended.

Computed tomography-guided C2 pedicle screw placement for treatment of unstable hangman fractures.

Case series and description of technique. The purpose of this study was to evaluate the feasibility and accuracy of inserting pedicle screws in unstable Hangman fracture cases by using intraoperative CT (O-arm) based navigation. Hangman fracture, also known as traumatic spondylolisthesis of the C2, is defined as a fracture involving the lamina, articular facets, pedicles, or pars of the axis vertebra. Opinions vary regarding the optimal treatment of unstable Hangman fractures. Some authors have recommended the use of rigid orthosis, whereas others have recommended surgical stabilization. The peculiar anatomy of the upper cervical spine is highly variable, and the presence of surrounding neurovascular structures makes pedicle screw fixation even more technically challenging. The advent of intraoperative 3-dimensional navigation systems permits safe and accurate instrumentation of the cervical spine. Ten patients with unstable Hangman fracture, with age ranging from 17 years to 81 years, were operated under O-arm-based navigation, and screw position was confirmed with intraoperative computed tomographic scan. A total of 52 screws were inserted under O-arm guidance: 20 in C2 pedicle, 20 in C3 lateral mass, and rest in C4 lateral mass. Screw misplacement was seen in only 1 C2 pedicle screw (1 of 20, 5%). No new-onset neurological deficit developed in any of the patients. Follow-up ranged from 3 months to 21 months. Bony fusion was achieved in all. Full rotation was preserved at C1-C2 joint. All the patients (50%) with neurological deficits before surgery improved after surgery. This series demonstrates that C2 pedicle screws can be put with precision under O-arm-guided navigation, and intraoperative computed tomographic scan can confirm position of screws. Patients can be operated and mobilized early with negligible risk of screw misplacement, with preservation of motion at the C1-C2 joint. 4.

Function-preserving Reduction and Fixation of Unstable Jefferson Fractures Using a C1 Posterior Limited Construct

This is a retrospective, clinical, and radiologic study of posterior reduction and fusion of the C1 arch in the treatment of unstable Jefferson fractures. The aim of the study was to describe a new motion-preserving surgical technique in the treatment of unstable Jefferson fracture. The management of unstable Jefferson fractures remains controversial. The majority of C1 fractures can be effectively treated nonoperatively with external immobilization unless there is an injury to the transverse atlantal ligament (TAL). Conservative treatment usually involves immobilization for a long time in Halo vest, whereas surgical intervention generally involves C1-C2 fusion, eliminating the range of motion of the upper cervical spine. We propose a novel method for the treatment of unstable Jefferson fractures without restricting the range of motion. A retrospective review of 12 patients with unstable C1 fractures between April 2008 and October 2011 was performed. They were treated by inserting bilateral posterior C1 pedicle screws or lateral mass screws interconnected by a transversal rod to achieve internal fixation. There were 8 men and 4 women, with an average age of 35.6 years (range, 20-60 y). Presenting symptoms included neck pain, stiffness, and decreased range of motion but none had neurological injury. Seven patients had bilateral posterior arch fractures associated with unilateral anterior arch fractures (posterior 3/4 Jefferson fracture, Landells type II), and 5 had unilateral anterior and posterior arch fractures (half-ring Jefferson fracture, Landells type II). Seven patients had intact TAL, and 5 patients had fractures and avulsion of the attachment of TAL (Dickman type II). A total of 24 screws were inserted. Five cases had screws placed in the lateral mass: 3 because of posterior arch breakage, and 2 because the height of the posterior arch at the entry point was <4 mm. The remaining 7 cases had pedicle screw fixation. One patient had venous plexus injury during exposure of lower margin of the posterior arch; however, successful hemostasis was achieved with Gelfoam. Postoperative x-ray and computed tomography scan showed partial breach of the transverse foramen caused by a screw in 1 case, and breach of the inner cortex of the pedicle caused by screw displacement in 1 case; however, no spinal cord injury or vertebral artery injury was found. The remaining screws were in good position. Patients were followed up for 6-40 months (average, 22 mo). All cases had recovery of range of motion of the cervical spine to the preinjury level by 3-6 months after surgery, with resolution of pain. At 6 months follow-up, plain radiographs and computed tomography scans revealed satisfactory cervical alignment, no implant failure, and satisfactory bony fusion of the fractures; no C1-C2 instability was observed on the flexion-extension radiographs. C1 posterior limited construct is a valid technique and a feasible method for treating unstable Jefferson fractures, which allows preservation of the function of the craniocervical junction, without significant morbidity.