C1 Lateral Mass Screw Insertion Research Articles

Nuance in Craniovertebral Junction Surgical Approach for Posterior C1-C2 Harms Stabilization: "Window Transposition" of the External Vertebral Venous Plexus for Bloodless C1 Lateral Mass Screw Insertion: Anatomical Aspects and Technical Notes.

Atlas and axis instrumentation may be necessary in cases of several craniocervical junction pathologies. According to the Harms technique, C1-C2 polyaxial screws are inserted respectively in the C1 lateral masses and in C2 pedicles. C1 lateral mass screw insertion requires the careful subperiosteal dissection of the posterior elements of C1, the identification of the screw entry point by the downward distraction of C2 nerve root, and the cautious sparing of the overlying posterior external vertebral venous plexus (peVVP), whose bleeding, obstructing the surgical field, is sometimes barely controlled by hemostatic agents and swabbing. The authors describe in detail the anatomical aspects of an alternative surgical technique developed for the microsurgical transposition of the C1-C2 interposed external vertebral venous plexus in the case of Harms C1-C2 screw stabilization. The longitudinal median incision of the atlantoaxial membrane, followed by bilateral subperiosteal dissection and microsurgical section respectively at the inferior borders of the C1 laminae and at the superior borders of the C2 laminae, allows, as a "window opening," the symmetrical mediolateral transposition of the peVVP. This procedure provides a faster and cleaner anatomical exposition of the posterior surface of the C1 lateral mass and the C2 isthmus, preventing troublesome intraoperative venous bleeding that hinders C1 lateral mass screw insertion.

Innovative C-Arm-Free Navigation Technique for Posterior Spinal Fixation for Atlantoaxial Subluxation: A Technical Note.

Study design: Technical note. Objectives: To present a novel C-arm-free technique guided by navigation to insert and place a C1 lateral mass screw. Background and Objectives: Atlantoaxial subluxation (AAS) is a relatively common sequelae in patients with rheumatoid arthritis (RA) and upper cervical trauma. If they present with severe symptoms, surgical intervention such as posterior fusion is indicated. The established treatment for AAS is fixation with a C1 lateral mass screw and C2 pedicle screw (modified Goel technique) to achieve bony fusion. However, this technique requires fluoroscopy for C1 screw insertion. To avoid exposing the operating team to radiation, we present here a novel C-arm-free C1 lateral mass screw insertion technique for AAS. Materials and Methods: A 67-year-old man was referred to our hospital with neck pain, quadriparesis, and clumsiness and numbness of both upper and lower limbs. He had undergone C3-6 posterior fusion previously in another hospital. In physical examination, he had severe muscle weakness of bilateral upper limbs and hypoesthesia of all four limbs. He had hyper-reflexia of bilateral lower limbs and pollakiuria. His Japanese orthopedic score was 8 points out of 17. Preoperative radiograms showed AAS with an atlantodental interval (ADI) of 7 mm. MRI indicated retro-odontoid pseudotumor and severe spinal cord compression at the C1-2 level. The patient underwent posterior atlantoaxial fixation under navigation guidance. To prevent epidural bleeding during the insertion and placement of a C1 lateral mass screw, we have here defined a novel screw insertion technique. Results: The surgical time was clocked as 127 min and blood loss was 100 mL. There were no complications per-operatively or in the postoperative period. The patient showed almost full recovery (JOA 16/17) at two months follow-up and a solid bony fusion was noticed in the radiograms at one year follow-up. Conclusions: This novel surgical procedure and C1 lateral mas screw placement technique is a practical and safe method in recent advances of AAS treatment. Procedurally, the technique helps prevent epidural bleeding from the screw entry point and also allows for proper C1 screw insertion under navigation guidance without exposing surgeons and staff to the risk of fluoroscopic radiation.

C1 lateral mass screw insertion using cannulated, navigated screws: preliminary results of a novel technique

Purpose The upper cervical spine region is densely populated by neural and vascular structures impeding the approach for fusion surgery. Technological advancement simplify the approach to C1-C2 fusion, thus reduce risks. The current paper purpose is to describe initial experience with a novel technique modification for C1 lateral screw insertion that incorporates cannulated-navigated screw system with intra-operative 3D imaging. Methods A single-center single surgeon database was reviewed to identify all patients who underwent placement of C1 lateral mass screw insertion using the novel technique modification described below, on 2020. This cohort was retrospectively analyzed and compared with a cohort of patients who were operated on by the same surgeon with non-cannulated, navigated screws with intra-operative 3D imaging (O-arm, Medtronic, USA) between 2011 and 2019. Following navigated starting hole and drilling of the C1 lateral mass, a blunt guide-wire is used to palpate the hole and cannulated screw is advanced to the correct position over the wire. After initial purchase, a navigated screw driver is used for final screw depth position. Results Twelve C1 lateral mass screws were inserted in six patients using this novel cannulated-navigated screw placement technique and compared to 24 patients operated using navigated non-cannulated screws. Minimal Estimated Blood Loss (EBL) was recorded in five of six cases undergoing the novel cannulated navigated placement of C1 lateral mass screws. Comparison to non-cannulated cohort demonstrated an EBL of 83CC vs. 354CC (Not significant). Mean surgery time was 97min and 118min for the cannulated-navigated and navigated only procedures (p = 0.03, statistically significant) respectively. In the current cohort, all screws were rated in optimal position and no repositioning procedures were performed. Conclusion The new method presented allows for faster and possibly safer and more accurate C1 lateral mass screw insertion.

Posterior First and Second Cervical Vertebrae Fusion by Screw Fixation Technique using the Modern Pre-fabricated Template Method on Cadaver Samples

Introduction:C1 lateral mass and C2 pedicular screws insertion are used for C1-C2 posterior fusion. Fluoroscopy Guided technique is routinely used for screw placement but it is associated with risk of injury to spinal cord and vertebral artery. 3D printing has developed rapidly in the fields of medicine. It is helpful in improving precise treatment and used for instrumentation in spine. We want to evaluate the accuracy of C1 lateral mass screws and C2 pedicle screws insertion by Pre-Fabricated Template made by three-dimensional (3D) printing.Materials and methods:Five cervical samples were obtained from cadavers. Based on fine-cut CT scan 3D-images reconstructed and the path of the screws designed by special software. A template produced by 3D-printer from 3D images. After printing the templates, they were fixed on the relevant vertebra in the operation room and based on the template path, C1 lateral mass screw and C2 pedicular screws were inserted. Placement of the screws was evaluated using CT scans post-operatively.Results:A total of 14 screws were inserted by above-mentioned method. After evaluation with CT scans none of the screws were entered in the spinal canal. Two screws had vertebral artery canal perforation with less than 50% breach. Violation was judged as noncritical and would probably not have resulted in injury to vertebral artery.Conclusions:The accuracy of C1 lateral mass screw and C2 pedicle screw insertion is acceptable with pre-fabricated template and can provide a useful aid for screw placement.

The Intersection Between Lateral Mass and Inferomedial Edge of the C1 Posterior Arch: A Reference Point for C1 Lateral Mass Screw Insertion

ObjectiveTo determine the ideal Atlas (C1) lateral mass screw placement and trajectory using the intersection between the lateral mass and inferomedial edge of the posterior arch as an easily identifiable and reproducible medial reference point. Selection of an ideal entry point and trajectory of C1 lateral mass screw insertion can help to minimize neurovascular injuries. While various techniques for screw insertion have been proposed in the past, they all require extensive dissection of the C1 lateral mass, which can cause profuse bleeding. MethodsNinety-three 3-dimensional computed tomography reconstructed images of C1 lateral masses in adult patients were utilized to simulate the placement of C1 lateral mass screws via 4 entry points and 2 trajectory angles referencing off of a medial reference point using Vero’s VISI 17 software. The safety during screw insertion simulation, as well as the screw length, were evaluated. ResultsWe found that C1 lateral mass screws could be safely placed bilaterally at 3 mm lateral to the reference point in both 0° and 15° medial screw angulation without violation of the cortex. The 15° medial angulation allowed for longer (18 mm) screws than the 0° angulation. ConclusionWe recommend starting C1 lateral mass screws 3 mm lateral to the intersection between the lateral mass and inferomedial edge of the posterior arch at a 15° medial angulation.

An alternative way of C1 screwing: Supralaminar C1 lateral mass screws.

Study Design:This study involves literature review, technical note, and case series.Objectives:The objectives were to analyze indications and contraindications, advantages, and disadvantages for C1 lateral mass screw (LMS) insertion above or partially above the arch, to descript technical features, and to give examples of the practical application of this technique and investigated its safety.Methods:A literature review was carried out in English and Russian in PubMed, Google Scholar, and eLibrary databases. We selected four patients, treated in our clinic, which was carried out partially supralaminar C1 LMS.Results:Only three descriptions of supralaminar C1 LMS were found in the literature. Four adult patients underwent posterior C1–C2 screw fixation with C1 LMS along the superior edge of the C1 arch at our clinic. Partially supralaminar C1 screws were inserted on one of the sides due to the difficulties of using classical techniques. The main reasons for supralaminar screw fixation were narrow C1 lamina, hypertrophied venous plexus, and intraoperative failures of classic techniques application (broken screw trajectory, profuse venous bleeding from the plexus). The average follow-up time for the patients was 2.7 years, no complications were noted, and all had a satisfactory spinal fusion.Conclusions:The proposed types of C1 LMS above or partially above the C1 arch can be useful alternative method of C1 screwing in selected patients. Indications for the use of the supralaminar C1 LMS method can be narrow C1 posterior arch and pedicle, pronounced C1-C2 venous plexus, some V3 segment anomalies at C1 level, small arthritic inferior part of lateral mass, and intraoperative failures of classic techniques application.

Modified C1 lateral mass screw insertion using a threaded K-wire. A technical note

Instrumented fixation of the C1-C2 motion segment is a standard surgical technique to stabilise that spinal segment. Instability at C1-C2 can arise from a number of conditions. Fixation of the C1 lateral mass usually involves dissection and exposure of the C2 nerve root and the posterior wall of the C2 lateral mass which can result in significant bleeding from the venous plexus. Whilst image guidance is increasing in accessibility, there are few public hospitals in Australia that have access to this technology. The authors describe their technique for insertion of a C1 lateral mass screw over a threaded K-wire to avoid extensive dissection of the C2 nerve root, reducing the risk of significant haemorrhage from the epidural venous plexus during the procedure. A retrospective analysis was undertaken on 18 consecutive patients who underwent C1-C2 instrumented fixation using this technique. Indications for C1-C2 instrumented fixation included traumatic injury (10 patients), failure of non-operative management of odontoid fractures (5 patients), pathological fractures of C2 (2 patients) and inflammatory conditions (1 patient). All patients underwent successful C1-C2 stabilisation using this technique. Blood loss did not exceed 400mls in any patient. There were no vertebral artery injuries and no patient experienced a neurological deterioration. The authors propose that their technique for insertion of a C1 lateral mass screw over a threaded K-wire is safe and effective with a low risk of neurological or vertebral artery injury. The technique may be considered as a slight modification of the Harm’s procedure to reduce disturbance of the adjacent venous plexus and thereby reduction in intraoperative bleeding and operative time.

Suboccipital neuralgia after C1 pedicle screw insertion: do we neglect atlantooccipital joint violation? - Case report and literature review

BackgroundOccipital neuralgia is one of the postoperative complications of C1 lateral mass screw insertion, which was deemed to be related with the C2 nerve root dysfunction.Case presentationA 52-year-old female patient presented with gradually progressive numbness and weakness in her extremities for 6 months. X-ray and computed tomography (CT) scan revealed obvious anterior atlantoaxial dislocation (ADD), which was reducible on extensive view. Atlantoaxial pedicle screw fixation and bone graft was performed. Immediately after the operation, the neurological symptom significantly improved. The patient complained of restricted cervical rotation and suboccipital neuralgia which was exacerbated by rotation with an intensity of 7 on a visual analog scale (VAS) ranging from 0 to 10 at postoperative day 5. While a satisfactory reduction was detected in the postoperative CT, violation of the left atlantooccipital joint was observed in the left C1 screw. Nimesulide (daily dosage of 0.2 g) and bracing were recommended immediately. At the 2 month follow-up, both the neurological improvement and reduction were maintained. The VAS of suboccipital neuralgia is 3 and decreased to 1 at 6 months postoperative. Bony fusion of the left atlantooccipital joint was confirmed by CT scan at 6 months postoperative. The patient complained that the suboccipital neuralgia was tolerable without the assistance of braces or medications for pain. At the 18 month follow-up, only stiffness of head flexion and rotation was observed without suboccipital neuralgia.ConclusionSuboccipital neuralgia after atlantooccipital joint violation of C1 pedicle screw placement most likely results from C1 nerve root irritation. As the corresponding dermatome differs from the distributing region and aggravated factor of C2 nerve root dysfunction, neuralgia due to C1 irritation was only localized at suboccipital region and exacerbated by rotation.

Feasibility of atlantal lateral mass and axoid pedicle screw insertion in children younger than 6 years

Objective To analyze the feasibility of C1 lateral mass (C1LM) and C2 pedicle (C2P) screw insertion in atlantoaxial fixation surgeries for children younger than 6 years. Methods The computed tomography images of 250 patients (age 2-6 years) were randomly collected and studied. The inner diameter and length for each C1LM and C2P were measured in axial view. Height was measured in sagittal view. Screw choice was considered feasible when a sample maintained an additional 0.5 mm bone cortex at the transverse diameter, length, and height at the same time. Analyses with the Student t test were performed for age, sex, and laterality. The screw choice was evaluated with a feasibility percentage. Results The length and transverse diameter of the whole C1LM in children aged 2-6 years were (21.12±2.94) mm and (7.35±1.41) mm, respectively. The overall C2P length, transverse diameter and height were (19.77±2.92), (5.30±1.02), and (5.39±0.85) mm, respectively. The feasibilities of 3.5 mm diameter screw insertion for atlantoaxial vertebrae at different ages, genders, and side children were above 88.00%, and up to 92.12% or more in children older than 3. Conclusion The use of a 3.5-mm lateral mass and pedicle screw in 2- to 6-year-old children was feasible in the majority of cases. Age, sex, and laterality should all be considered when choosing screw sizes in pediatric upper cervical surgeries. Key words: Atlantoaxial; C1 Lateral Mass; C2 Pedicle; Tomographic Study

C1 lateral mass screw insertion from the caudal–dorsal to the cranial–ventral direction as an alternate method for C1 fixation: A quantitative anatomical and morphometric evaluation

ObjectC1 lateral mass screw has been widely used for fixation of the upper cervical spine. However, traditional fixation methods are not without complication. Morphometric measurement of an alternative approach is conducted. MethodsThree-dimensional CT scans of the cervical spine obtained in 100 adults were evaluated, and key measurements were determined for screw entry points, trajectories, and screw lengths for placement of a C1 screw via this alternate approach. Additional measures were included to account for relevant anatomic variation, including the size of the dangerous lateral zone of the C1 entry point and depth of the atlantooccipital joint surface. Twenty dried atlantal specimens were evaluated to determine corresponding ex vivo measurements. ResultsThe mean maximum angle of medialization was 20.8°±2.8° (right) and 21.1°±2.8° (left), as measured in the axial CT images. Sagittal CT images show the mean maximum superior angulation was 24.7°±4.3° (right) and 24°±4.0° (left), and the mean minimum superior angulation was 13.6°±4.4° (right) and 13.6°±3.9° (left). The mean screw length within the lateral mass was 21.2±1.9mm (right) and 21.3±2.0mm (left). Given an additional 10–15mm needed for rod adaptation, an ideal screw length of 30–35mm was determined. ConclusionThe C1 insertion caudally from the C2 nerve root may become an alternate method. Preoperative consideration of the ideal screw insertion point, trajectory, and length are vital for safe and effective surgical intervention.

C1 lateral mass screw insertion caudally from C2 nerve root - An alternate method for insertion of C1 screws: A technical note and preliminary clinical results.

C1 lateral mass screw was widely used for fixation of the upper cervical spine. However, massive bleeding from the C1-2 venous plexus is sometimes encountered. In this study, we proposed an alternate method for C1 lateral mass screw insertion, which involves insertion of the screws caudally from the C2 nerve root to reduce bleeding from C1-2 venous plexus. Seven patients with atlantoaxial lesions were included in this study. The mean age at surgery was 65.9 (34-82) years. The mean follow-up period was 23.1 (12-38) months. All patients underwent atlantoaxial fusion with C1 lateral mass screws, which were inserted caudally from the C2 nerve root. All screws were inserted using O-arm based navigation system. Operative time, blood loss, C2 nerve root injury and perioperative complications were investigated. The accuracy of C1 screws and bone union were evaluated using postoperative computed tomography. A total of 13 C1 lateral mass screws were inserted using this method. The mean operative time was 224 (144-305) min. The mean blood loss was 209 (100-357) g. One perioperative complication was observed, which was recurrent laryngeal nerve palsy. There were no vertebral artery or spinal cord injuries. No case of massive bleeding from the C1-2 venous plexus was observed. One patient complained of postoperative occipital neuralgia, which disappeared in 2 weeks. No malposition of C1 lateral mass screws was observed on postoperative computed tomography. Bone union was observed in all patients. The C1 lateral mass screw insertion caudally from the C2 nerve root may become an alternate method for insertion of C1 screws.

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

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

Vertebral artery anomalies at the craniovertebral junction in the US population.

Retrospective review. To evaluate the prevalence of anatomical variations of the vertebral artery at the craniovertebral junction and the posterior arch of the atlas in the US population. Recent studies from Asia have reported a 5% to 10% prevalence of a persistent first intersegmental vertebral artery and 1% to 2% prevalence of a fenestrated artery. These anomalous vertebral artery courses lie directly over the starting point for atlas lateral mass screw insertion. The relatively high reported prevalence of these anomalies suggests that routine preoperative computed tomographic angiogram be considered prior to upper cervical fixation. We have not observed this anomaly as commonly as reported. The authors analyzed the records of 975 patients from a level I trauma center and adjacent university hospital who underwent computed tomographic angiography to evaluate the incidence of anomalous variations in the third segment of the vertebral artery. These results were compared with similar studies performed in Korea and Japan. The mean age of the patients was 52.9 years. The ethnic distribution of the patients was as follows: 69.3% of the patients were Caucasian, 11% Asian, 10.8% African American, and 6% Hispanic. The prevalence of a persistent intersegmental artery was 0.01% (1/975); a fenestrated vertebral artery was 0.01% (1/975); and origin of a posterior inferior cerebellar artery was 0.4% (4/975). The incidence of these anomalies was significantly lower than those previously published from Korea and Japan. Vertebral artery course anomalies in the upper cervical spine were rare (0.42%) in our patient population. This finding contrasts with recent published reports from Asia, citing as high as a 10% rate of vertebral artery presence over the starting point for C1 lateral mass screw insertion. On the basis of the infrequent occurrence of this anomaly, we do not recommend routine computed tomographic angiography when planning upper cervical instrumentation. N/A

Subarachnoid Hemorrhage and Acute Hydrocephalus as a Complication of C1 Lateral Mass Screws

Case report. To present a previously unreported complication of subarachnoid hemorrhage and hydrocephalus after C1 lateral mass screw insertion. To inform spine specialists of this potential postoperative complication. Damage to the carotid artery, vertebral artery, hypoglossal nerve and dural tears are all recognized complications. Acute hydrocephalus as a result of subarachnoid hemorrhage is not previously reported. A 63-year-old female with a traumatic C1 ring and C2 peg fracture underwent C1-C2 fixation. During insertion of the C1 lateral mass screws there was significant hemorrhage from the C1-C2 venous plexus. Three days postoperatively, she developed headache, confusion, and became drowsy. Computed tomographic scan of the brain revealed hydrocephalus and intraventricular blood that was managed with an external ventricular drain. The case of acute hydrocephalus due to intraventricular hemorrhage from C1 lateral mass screw placement has not previously been reported. Surgeons performing the procedure should consider the diagnosis if patients display signs of raised intracranial pressure postoperatively. N/A.

Routine sectioning of the C2 nerve root and ganglion for C1 lateral mass screw placement in children: surgical and functional outcomes

Adult studies have shown that sectioning the C2 nerve root and ganglion may facilitate placement of C1 lateral mass screws and lead to decreased operative time and blood loss. We report the functional outcomes and complications following routine sectioning of the C2 nerve root and ganglion, which have not been reported in pediatric patients. Fifteen consecutive pediatric patients underwent C1 lateral mass screw insertion and bilateral C2 nerve root and ganglion sectioning. Clinical and radiographic assessments were performed at follow-up. Numbness in the C2 distribution and/or occipital neuralgia, operative times, estimated blood loss (EBL), length of stay (LOS), and complications were recorded. Average follow-up time was 35.7months. Overall mean operative time was 250.5min, LOS was 8.46days, and EBL was 337cc. When considering only atlantoaxial fusions, mean operative time was 180.7min and EBL was 97.1cc. There were no intraoperative complications, and no patient reported new onset occipital neuralgia or numbness in the C2 distribution that would interfere with daily living. Of the patients, 93% achieved Lenke fusion grade A; one achieved Lenke fusion grade B. Routine C2 nerve root sectioning and ganglionectomy enhanced surgical exposure of the C1 lateral mass and C1-2 facet joint, potentially maximizing fusion rate and minimizing intraoperative complications. This technique may yield favorable operative times, EBL, and LOS in children undergoing C1 lateral mass screw insertion without negatively affecting functional outcome.

C1 Lateral Mass Screw Insertion With Protection of C1-C2 Venous Sinus

This is a technical note and review of the literature. We propose to describe a revised surgical technique of C1 lateral mass screw insertion with protection of C1-C2 venous sinus surrounding the C2 nerve root. During C1 lateral mass screw insertion and in posterior C1-C2 fixation, iatrogenic injury of C1-C2 venous sinus results in bleeding, which is troublesome. Appropriate management of the venous sinus in this region is critical to successful surgery in this complex anatomic region. We reviewed 48 patients who underwent posterior C1-C2 fixation at our institution between September 2001 and October 2008. Twenty-four atlas screws were inserted by the originally described C1 lateral mass screw technique (group A), and 28 through a revised posterior arch and lateral mass screw technique (C1 transpedicular screw) (group B). The final group of 44 atlas screws was placed with our newly revised technique (group C). Bleeding of venous sinus was encountered in 3 group A, 2 group B, and 1 group C atlas screw insertions. The incidence rate was 12.50% (A), 7.14% (B), and 2.27% (C). Statistical comparison showed no significant difference between the groups. All the cases were followed for a mean period of 28.1 month. Four patients in group A complained of postoperative numbness in occipitocervical region. No patients in group B or group C voiced this complaint. A high fusion rate was found in all 3 groups with no signs of implant failure. Bleeding of C1-C2 venous sinus is vigorous and frustrating. The revised technique we describe provides theoretical and practical protection of venous sinus. In addition, the firm bony purchase of screws afforded by this technique contributes to achieving stabilization of the upper cervical spine and a high fusion rate.

C1 lateral mass screw-induced occipital neuralgia: a report of two cases

C1-2 polyaxial screw-rod fixation is a relatively new technique. While recognizing the potential for inadvertent vertebral artery injury, there have been few reports in the literature outlining all the possible complications. Aim of this study is to review all cases of C1 lateral mass screws insertion with emphasis on the evaluation of potential structures at risk during the procedure. We retrospectively reviewed all patients in our unit who had C1 lateral mass screw insertion over a 2-year period. The C1 lateral mass screw was inserted as part of an atlantoaxial stabilization or incorporated into a modular occiput/subaxial construct. Outcome measures included clinical and radiological parameters. Clinical indicators included age, gender, neurologic status, surgical indication and the number of levels stabilized. Intraoperative complications including blood loss, vertebral artery injury or dural tears were recorded. Postoperative pain distribution and neurological deficit were recorded. Radiological indicators included postoperative plain radiographs to assess sagittal alignment and to check for screw malposition or construct failure. A total of 18 lateral mass screws were implanted in 9 patients. There were three male and six female patients who had C1 lateral mass screw insertion in this unit. Two patients had atlantoaxial stabilization for C2 fracture. There were four patients with rheumatoid arthritis whose C1 lateral mass screws were inserted as part of an occipitocervical or subaxial cervical stabilization. There was no vertebral artery injury, no cerebrospinal fluid leak and minimal blood loss in all patients. Three patients developed postoperative occipital neuralgia. This neuralgia was transient, in one of the patients having settled at 6-week follow-up. In the other two patients the neuralgia was unresolved at time of latest follow-up but was adequately controlled with appropriate pain management. Postoperatively no patient had radiographic evidence of construct failure and all demonstrated excellent sagittal alignment. It has been reported that the absence of threads on the upper portion of the long shank screw may protect against neural irritation. However, insertion of the C1 lateral mass screw necessitates careful caudal retraction of the C2 dorsal root ganglion. The insertion point for the C1 lateral mass screw is at the junction of the C1 posterior arch and the midpoint of the posterior inferior part of the C1 lateral mass. Two patients in our series suffered occipital neuralgia post-insertion of C1 lateral mass screws. This highlights the potential for damage to the C2 nerve root during C1 lateral mass screw placement.

USE OF AXIAL AND SUBAXIAL TRANSLAMINAR SCREW FIXATION IN THE MANAGEMENT OF UPPER CERVICAL SPINAL INSTABILITY IN A SERIES OF 7 CHILDREN

The management of upper cervical spinal instability in children continues to represent a technical challenge. Traditionally, a number of wiring techniques followed by halo orthosis have been applied; however, they have been associated with a high rate of nonunion and poor tolerance for the halo. Alternatively, C1-C2 transarticular screws and C2 pars/pedicle screws allow more rigid fixation, but they are technically demanding and associated with vertebral artery injuries. Recently, C2 translaminar screws have been added to the armamentarium of the pediatric spine surgeon as a technically simple and biomechanically efficient method of fixation. However, subaxial translaminar screws have not been described in the pediatric population. We describe our experience with axial and subaxial translaminar screws in 7 pediatric patients. Seven pediatric patients with the diagnosis of upper cervical spinal instability required surgical fixation (age, 19 months-14 years; sex, 4 boys and 3 girls; follow-up, 4-21 months; etiology, trauma [3 patients], os odontoideum/os terminale [2 patients], hypoplastic dens [2 patients]). All patients underwent axial and/or subaxial translaminar screw insertion. Iliac crest bone graft was used for fusion in 4 patients; bone morphogenic protein and cancellous morselized allograft was used for fusion in 3 patients. A rigid cervical collar was applied for 12 weeks postoperatively in all cases. No intraoperative image guidance was used for insertion of the translaminar screws. All patients had a postoperative computed tomographic scan. Two patients underwent placement of bilateral crossing C2 translaminar screws. Two patients had subaxial translaminar screw placement at C3 and the upper thoracic spine, respectively. Hybrid constructs (a C2 translaminar screw combined with a C2 pars screw) were incorporated in 3 patients. No patients were found to have a breach of the ventral laminar cortex. All patients achieved solid fusion. One patient had a perioperative complication: prolonged dysphagia probably related to C1 lateral mass screw insertion rather than C2 translaminar screw placement. To our knowledge, this report represents the only series of pediatric patients treated with axial and subaxial translaminar screws. This series shows that axial and subaxial translaminar screw fixation is a viable option for upper cervical spinal fusion in children. The technique is safe and results in adequate fixation with high fusion rates and minimal complications.

The Feasibility of Microscope-Assisted “Free-Hand” C1 Lateral Mass Screw Insertion Without Fluoroscopy

Retrospective study. To determine if C1 lateral mass screws could be safely inserted without the use of fluoroscopy. Standard surgical technique for C1 lateral mass screw placement uses intraoperative fluoroscopy. However, intraoperative fluoroscopy is time consuming, cumbersome, and exposes both the patient and surgical team to radiation. Radiographic analysis and chart review. Surgical technique was analyzed in 3 components: feasibility to complete the screw insertion without intraoperative fluoroscopic guidance; occurrence of any intraoperative, perioperative complications; and radiologic assessment of screw positions on roentgenogram. Forty-six C1 lateral mass screws were inserted in 24 consecutive patients who underwent posterior cervical fusion. There were 19 female and 5 male. The mean age was 63 +/- 18 years at the time of surgery. All C1 lateral mass screws were inserted unicortically using a microscope-assisted "free-hand" technique. The average intraoperative blood loss in C1-C2 fusion was 123 +/- 50 mL. The mean operative time for each C1-C2 fusion was 133 +/- 30 minutes. Satisfactory positions of C1 screws were noted in intraoperative and postoperative radiograph examinations. There was no mortality or wound infection. There was no cortical breach along the screw path palpated intraoperatively. No vertebral artery injury or cerebral spinal fluid leakage during the screw insertion was observed. However, one patient with a prior posterior cervical operation had a dural tear during the exposure, another had new occipital neuralgia, and a third patient had a symptomatic occipitocervical joint violation by a C1 screw, which was diagnosed only on computed tomography scans. The symptoms resolved after the C1 screws were removed. Microscope-assisted "free-hand" C1 lateral mass screws insertion is a feasible and reproducible technique. which offers an alternative method of screw insertion without cumbersome and potentially harmful fluoroscopy.

P105. Posterior atlantoaxial stabilization: a new alternative to C1-2 transarticular screws

Abstract Purpose of study: Develop new techniques to improve safety and success of C1–C2 fusion procedures. Methods used: A standard posterior C1–C2 exposure is performed. Cross-table lateral fluoroscopy is used to guide and confirm screw trajectories. The C2 pedicle screw entry point is identified and drilled with angles 15 degrees medially and 25 degrees cephalad for pedicle cannulation. Drill depth is stopped short of the C2 transverse foramen. The C1 lateral mass screw insertion point is located beneath the posterior arch of C1 in the midposition of the lateral mass just above the C2 root. The drill is then angled 10 degrees medial to lateral and cephalad toward the anterior tubercle of C1 on lateral fluoroscopy. The C1–C2 joint is then decorticated and packed with local bone fragments. Posterior rods are contoured and connected to polyaxial screw heads, and a cross-connector is applied. of findings: This technique has been used in five cases of atlantoaxial instability at our institution during the past year. There have been no C2 nerve root or vertebral artery injuries. No construct failures have been observed during the current follow-up. Relationship between findings and existing knowledge: C1 lateral mass and C2 pedicle screw fixation offers an alternative means of atlantoaxial fusion. The technique is less demanding than C1–C2 transarticular screw placement and reduces the risk of vertebral artery injury. The linked construct is stable in flexion, extension and rotation. Laminectomy or fracture of the posterior elements does not preclude this fixation technique. We think this procedure will replace the C1–C2 transarticular screw procedure. Overall significance of findings: This new technology has the potential to supplant previous C1–C2 procedures with improved safety and success. Disclosures: Device or drug: pedicle screws. Status: approved. Conflict of interest: No conflicts.