C2 Laminar Screws Research Articles

Posterior Atlantoaxial Screw Placement in a Portuguese Population: A Morphometric Analysis Based on Computed Tomography Scan Measurements.

Objective The present study aims to evaluate the screw length and trajectory angles for posterior atlantoaxial fixation in a Portuguese population, through the study of cervical computed tomography (CT) scans. Methods Cervical CT scans of 50 adults were measured according to predefined screw trajectories of C1-C2 transarticular (C1C2TA), C1 lateral mass (C1LM), C2 pedicle (C2P), C2 pars and C2 laminar (C2L) screws. For each of these trajectories, screw length and angles were measured and compared between males and females. Results For the C1C2TA screw trajectory, the mean length, medial, and cranial angles were 34.12 ± 3.19 mm, 6.24° ± 3.06, and 59.25° ± 5.68, respectively, and for the C1LM screw trajectory, they were 27.12 ± 2.15 mm, 15.82° ± 5.07, and 13.53° ± 4.80, respectively. The mean length, medial, and cranial angles for the C2P screw trajectory were 23.44 ± 2.49 mm, 27.40° ± 4.88, and 30.41° ± 7.27, respectively; and for the C2 pars screw trajectory, they were 16.84 ± 2.08 mm, 20.09° ± 6.83, and 47.53° ± 6,97. The mean length, lateral, and cranial angles for the C2L screw trajectory were 29.10 ± 2.48 mm, 49.80° ± 4.71, and 21.56° ± 7.76, respectively. There were no gender differences except for the lengths of the C1C2TA ( p = 0,020) and C2L ( p = 0,001) screws, which were greater in males than in females. Conclusion The present study provides anatomical references for the posterior atlantoaxial fixation in a Portuguese population. These detailed data are essential to aid spine surgeons to achieve safe and effective screw placement.

Fluoroscopic Detection of Ventral Wall Violation during C2 Intralaminar Screw Insertion: A Descriptive Study

Introduction: The C2 (second cervical) laminar screws were considered for rigid fixation of the axis because the use of pars or pedicle screws posed a risk to the vertebral artery with C2. Though considered to be a relatively safe method, ventral spinal canal violations have been reported in laminar screws fixations. Fluoroscopy-based image guidance may increase the accuracy and safety of the technique. Aim: To report the use of fluoroscopy technique in the detection of ventral wall violation during C2 intralaminar screw insertion. Materials and Methods: This descriptive study reports seven dry axis vertebrae from the adult south Indian population for which fluoroscopic analysis was done from January 2013 to December 2013. True lateral views were taken before and after applying a vertical line of barium paint on the ventral surface of the lamina at two points: at the centre of the lamina and close to the facet joints at the face to-laminar junction. Results: In the total seven dry axis vertebrae analysed, the mean ratio of the distance from the spinolaminar junction to the barium line (drawn on the ventral surface of the lamina just next to face to laminar junction) to the distance between the spinolaminar junction and uppermost part of inferior articular facet of C2 vertebrae was 0.465±0.0389 mm. Conclusion: Even though considered a relatively safer technique, laminar cortical violations have been reported in C2 translaminar screw fixations. Fluoroscopy-based imaging guidance can improve the accuracy of C2 translaminar screw insertion, as this technology provides real-time imaging during the process of screw insertion and helps in accurate screw sizing.

Surgical management of os odontoideum: An Algerian center experience.

ABSTRACTBackground:Os odontoideum (OO) is a craniovertebral junction malformation of unknown origin. In most times, this lesion is highly unstable demanding surgical management. We present our series of OO surgical management and we discuss clinical, radiological, and management aspects of this pathology via our experience and literature opinions.Methods:This is a retrospective study of patients operated on at our department between May 2014 and May 2021 for OO. All patients were explored with plane X-rays and computed tomography (CT). In some cases, magnetic resonance imaging (MRI) was necessary. Posterior C1–C2 or C1-C3 fixation with polyaxial screws and rod fixation was used. In postoperative, the patient is asked to put Philadelphia collar for 3 months. Hospitalization periods vary between 3 and 7 days. After discharge, all our patients are followed up regularly in consultation. Control radiographs of the occipito cervical region were performed. After 3 months postoperatively, the CT scan is performed on all our patients to assess the quality of fusion. Patient's follow-up ranges from 4 months to 6 years.Results:Fifteen patients were included in this study; nine males (60%) and six females (40%); with mean age of 32.5 years old. Ten patients (67%) presented motor weakness, three patients (20%) with neck pain, one patient (6.5%) with torticollis, and one patient (6.5%) presented vertigo. No notable cervical trauma was present in six patients (40%) and in nine patients (60%), a remote history of traumatism was noted. All cases of our series presented mobile OO. Normal thickness of the C2 pedicle was noted in nine patients (60%). In two patients (13%), there was hypoplasia of one pedicle and in four patients (27%) both pedicles. MRI showed direct signs of spinal cord aggression: simple compression, myelomalacia, strangulation, or hypotrophy. C1 lateral mass screw fixation was performed in all patients; and according to C2 morphology: nine patients underwent C1-C2 pedicular fixation, in one patient, bilateral crossing C2 laminar screws technique, in three patients, we skipped C2 to perform a C1-C3 articular fixation, and in two patients, C1-C2-C3 fixations were performed. All patients improved clinically. In one patient, we noted an infection resulting in bad wound healing this infection was successfully treated with no complications. In the patient with bilateral crossing C2 laminar screws technique, CT control objectified 4 mm exceeding of one screw; the patient was reoperated and the screw was slightly pulled back. No other complications were noted.Conclusion:Congenital origin of OO is always evoked. C1-C2 fixation according to Goel and Harms technique with grafting proved its safety, providing high fixation quality with the acceptable biodynamic outcome. Once treated, the prognostic of OO is in general good, and improvement is observed in most patients with few complications.

2021 Canadian Spine Society Abstracts.

# Abstract 45. Determining clinically important improvement following surgery for degenerative conditions of the spine: analysis of the Canadian Spine Outcomes and Research Network (CSORN) Registry {#article-title-2} There is significant variability in clinically important improvement (CII)

Occipitocervical instrumented fixation utilising patient-specific C2 3D-printed spinal screw trajectory guides in complex paediatric skeletal dysplasia.

Instability of the craniocervical junction in paediatric patients with skeletal dysplasia poses a unique set of challenges including anatomical abnormalities, poor bone quality, skeletal immaturity and associated general anaesthetic risks. Instrumented fixation provides optimal stabilisation and fusion rates. The small vertebrae make the placement of C2 pedicle screws technically demanding with low margins of error between the spinal canal and the vertebral artery. We describe a novel clinical strategy utilising 3D-printed spinal screw trajectory guides (3D-SSTG) for individually planned C2 pedicle and laminar screws. The technique is based on a pre-operative CT scan and does not require intraoperative CT imaging. This reduces the radiation burden to the patient and forgoes the associated time and cost. The time for model generation and sterilisation was < 24h. We describe two patients (3 and 6years old) requiring occipitocervical instrumented fixation for cervical myelopathy secondary to Morquio syndrome with 3D-SSTGs. In the second case, bilateral laminar screw trajectories were also incorporated into the same guide due to the presence of high-riding vertebral arteries. Registration of the postoperative CT to the pre-operative imaging revealed that screws were optimally placed and accurately followed the predefined trajectory. To our knowledge, we present the first clinical report of 3D-printed spinal screw trajectory guides at the craniocervical junction in paediatric patients with skeletal dysplasia. The novel combination of multiple trajectories within the same guide provides the intraoperative flexibility of potential bailout options. Future studies will better define the potential of this technology to optimise personalised non-standard screw trajectories.

Treatment strategy and curative effect analysis of os odontoideum complicated with atlantoaxial joint dislocation

To explore the treatment strategy and clinical efficacy for os odontoideum complicated with atlantoaxial dislocation. The clinical data of 17 patients with os odontoideum complicated with atlantoaxial dislocation surgically treated from January 2006 to January 2015 were retrospectively analyzed, including 7 males and 10 females, aged 17 to 53 (43.1±11.3) years old;course of disease was 3 to 27(10.2±6.9) months. All patients received cranial traction before operation, 12 of 14 patients with reducible dislocation were treated by posterior atlantoaxial fixation and fusion, and 2 patients with atlantooccipital deformity were treated by posterior occipitocervical fixation and fusion;3 patients with irreducible alantoaxial dislocation were treated by transoral approach decompression combined with posterior atlantoaxial fixation and fusion. The operation time, intraoperative blood loss and perioperative complications were recorded. Visual analogue scale (VAS) and Japanese Orthopaedic Association (JOA) score were used to evaluate the change of neck pain and neurological function. Atlantoaxial joint fusion rate was evaluated by CT scan. The operation time of posterior fixation and fusion ranged from 86 to 170 (92.2±27.5) min, and the intraoperative blood loss was 200-350 (250.7±65.2) ml. No vertebral artery injury and spinal cord injury were recorded. Among the patients underwent atlantoaxial fixation and fusion, 1 patient with reducible dislocation fixed by C2 laminar screw lost reduction after primary operation, and received anterior release again and finally occipitocervical fusion. All patients were followed up for 15 to 58 (32.0±12.2) months. VAS score was decreased from preoperative 4.2±0.9 to 1.3±0.7 at final follow up and the JOA score was improved from preoperative 11.2±1.2 to 16.9±0.8 at final follow-up. CT scan confirmed that the atlantoaxial or occipitocervical fusion wasgood, and the fusion time was 5 to 9 (6.7±0.6) months. Surgical treatment of os odontoideum complicated with atlantoaxial dislocation can achieve satisfactory results, improve the patient's neurological function and improve the quality of life, however the surgical options needs to be individualized.

Letter: C2 Pedicle Screws Combined With C1 Laminar Hooks for Reducible Atlantoaxial Dislocation: An Ideal Salvage Technique for C1-C2 Pedicle Screws.

To the Editor: We read the article by Han et al1 with great interest in which the authors describe an innovative option to salvage C1-C2 fusion using laminar hooks instead of pars screws. We take this opportunity to share a similar experience and agree that it is not always possible to place screws in C1 or C2. C1-C2 fusion using C1 lateral mass and C2 pars or pedicle screws is a safe modality for the reduction and fusion of abnormal C1-C2 alignment and instability, including cases of post-traumatic C1-C2 subluxation.2-4 We managed a case of a 4-yr-old child who suffered odontoid tip fracture with rotatory atlantoaxial dislocation (Figure 1) following a fall from a height and presenting with torticollis and quadriparesis. The patient presented to us 2 wk after the fall. A 3-dimensional (3D) computed tomography (CT) reconstruction revealed a thin C2 pars and lamina. Based on CT measurements, a high chance of cortical breach of C2 while placing 3.5-mm pars or pedicle screws was anticipated during preoperative planning. Hence, that laminar screws over C2 could be an option during surgery was kept as an alternative salvaging procedure. The subluxation reduced under traction as soon as bilateral C1-C2 joints were opened and further distracted using dissectors. Then C1-C2 joint surfaces were curetted, and bone chips from iliac crest were inserted. The placement of C2 pedicle, pars, or laminar screws is considered to be more technically demanding than C1 lateral screw placement.5 Often, it is the C2 screw placement that more commonly leads to vascular or neural injury.6 This is particularly true in the case of children in which the small dimension of C2 makes it even more difficult to place screws of diameter 3.5 mm, which is the commonly available size.FIGURE 1.: Preoperative imaging of the patient showing the odontoid fracture and atlantoaxial dislocation A in the sagittal view. In the 3D CT angiogram, the right lateral mass of C1 is not visible B from the posterior view, which is seen subluxated anteriorly in the anterior view C.C1 lateral mass screws were placed according to the technique described by Goel et al.7 Because C2 dimensions were very thin for 3.5-mm screws, laminar hooks were placed bilaterally over C2 and minirods placed between C1 lateral mass screws and C2 laminar hooks. Finally, the C1 and C2 laminae were decorticated and iliac crest graft placed to achieve posterior bony fusion as well. A repeat scan at 3 mo showed good decompression of the craniovertebral junction and cord along with the implant in Situ (Figure 2). The patient's myelopathy has improved and is now mobilized independently. Therefore, in cases in which certain factors preclude the use of C2 pars/pedicle or lamina screws, C2 laminar hooks can be a useful rescue adjunct.FIGURE 2.: Postoperative CT showing a good reduction achieved with restoration of canal space in the sagittal view A. The 3D color rendering on maximum intensity projection B shows the C1 lateral mass screws and C2 laminar hooks in Situ.Funding This study did not receive any funding or financial support. Disclosures The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.

In Reply to the Letter to the Editor Regarding “Development of a Novel 3D Printed Phantom for Teaching Neurosurgical Trainees the Freehand Technique of C2 Laminar Screw Placement”

In Reply to the Letter to the Editor Regarding “Development of a Novel 3D Printed Phantom for Teaching Neurosurgical Trainees the Freehand Technique of C2 Laminar Screw Placement”

Letter to the Editor Regarding: “Development of a Novel 3D-Printed Phantom for Teaching Neurosurgical Trainees the Freehand Technique of C2 Laminar Screw Placement”

Letter to the Editor Regarding: “Development of a Novel 3D-Printed Phantom for Teaching Neurosurgical Trainees the Freehand Technique of C2 Laminar Screw Placement”

Posterior Arch Screw for Type II Odontoid Fracture: An Alternative Procedure

Atlantoaxial fusion procedures may be difficult in situations such as high-riding vertebral artery, a narrow C2 pedicle, and the presence of ponticulus posticus-arcuate foramen. With respect to vertebral artery (VA) anomalies, persistent first intersegmental artery, extracranial origin of the posterior inferior cerebellar artery at the C1-C2 level, and fenestration of the VA are all major risk factors for VA injury in C1-C2 fusion surgeries. To safeguard the VA, we designed the unilateral fusion procedure (all screws lie in the ipsilateral side, either the right side or left side): a unilateral transarticular screw combined with an ipsilateral-side C1 posterior arch screw and a C2 laminar screw (LS), with both C1-C2 screws inserted from opposite side, although the trajectory will be on the same side. In addition to atlantoaxial stabilization with screws and rod, autograft bony fusion was performed on the same side as modified Brook's procedure and augmented with sublaminar tapping. We present a series of 3 cases operated for odontoid fracture with associated high risk for fusion on one side alone. The fact that the chance of VA injury is high in transarticular screw, in lateral mass screw, less in pars screw, and pedicle screw is well known. Alternate screw placement to avoid VA injury would be a posterior arch screw for C1 and laminar screw for C2, which was adopted in our technique. We combined a unilateral transarticular screw and modified Brook's procedure with sublaminar tapping for additional augmentation of fusion. We would like to highlight this C1 posterior arch screw as an alternative procedure for atlantoaxial fusion.

Freehand C2 Laminar Screw Placement: Technical Note and Operative Video.

The placement of C2 laminar screws is a safe and useful method of axis fixation. The freehand method of screw placement was originally described by Wright et al., and requires detailed knowledge of the C2 posterior element anatomy, relationship to vital neurovascular structures, and technical acumen. The current evidence, surgical anatomy and technical details of screw insertion are investigated and highlighted in this manuscript and surgical video.

Development of a Novel 3D Printed Phantom for Teaching Neurosurgical Trainees the Freehand Technique of C2 Laminar Screw Placement

3D printed models have grown in popularity for resident training. Currently there is a paucity of simulators specifically designed for advanced cervical instrumentation. Our institution created a unique simulator for the instruction of freehand placement of C2 laminar screws using a specific 3-dimensional printing technique to replicate the corticocancellous interface. This study was designed to determine the efficacy of the simulator for teaching neurosurgical residents the freehand technique of C2 laminar screw placement. Ten participants with different experience levels participated in the study. The participants were separated into 2 groups based on experience level. Primary outcome assessments were breach rates, screw-screw interaction, and the ability to successfully place 2 screws in 1 model. Participants were graded based on a performance scoring system, and the outcomes of the 2 groups were compared. All participants in the novice group showed improved technical ability on repeated use of the simulator and were able to successfully place bilateral screws by the fourth attempt. Statistical analysis indicated an association between operative experience level and successful bilateral screw placement, implying that the simulator accurately represented an invivo intraoperative scenario. By utilizing our novel 3D printing production method, we have created a unique simulator for the freehand placement of C2 laminar screws. To our knowledge, this is the first report of a study investigating the use of a 3-dimensional printed simulator specifically designed to teach the freehand placement of C2 laminar screws to neurosurgical trainees.

Atlantoaxial fixation using C1 posterior arch screws: feasibility study, morphometric data, and biomechanical analysis.

OBJECTIVEC1-2 is a highly mobile complex that presents unique surgical challenges to achieving biomechanical rigidity and fusion. Posterior wiring methods have been largely replaced with segmental constructs using the C1 lateral mass, C1 pedicle, C2 pars, and C2 pedicle. Modifications to reduce surgical morbidity led to the development of C2 laminar screws. The C1 posterior arch has been utilized mostly as a salvage technique, but recent data indicate that this method provides significant rigidity in flexion-extension and axial rotation. The authors performed biomechanical testing of a C1 posterior arch screw (PAS)/C2 pars screw construct, collected morphometric data from a population of 150 CT scans, and performed a feasibility study of a freehand C1 PAS technique in 45 cadaveric specimens.METHODSCervical spine CT scans from 150 patients were analyzed to determine the average C1 posterior tubercle thickness and size of C1 posterior arches. Eight cadavers were used to compare biomechanical stability of intact specimens, C1 lateral mass/C2 pars screw, and C1 PAS/C2 pars screw constructs. Paired comparisons were made using repeated-measures ANOVA and Holm-Sidak tests. Forty-five cadaveric specimens were used to demonstrate the feasibility and safety of the C1 PAS freehand technique.RESULTSMorphometric data showed the average craniocaudal thickness of the C1 posterior tubercle was 12.3 ± 1.94 mm. Eight percent (12/150) of cases showed thin posterior tubercles or midline defects. Average posterior arch thickness was 6.1 ± 1.1 mm and right and left average posterior arch length was 28.7 mm ± 2.53 mm and 28.9 ± 2.29 mm, respectively. Biomechanical testing demonstrated C1 lateral mass/C2 pars and C1 PAS/C2 pars constructs significantly reduced motion in flexion-extension and axial rotation compared with intact specimens (p < 0.05). The C1 lateral mass/C2 pars screw construct provided significant rigidity in lateral bending (p < 0.05). There was no statistically significant difference between the two constructs in flexion-extension, lateral bending, or axial rotation. Of the C1 posterior arches, 91.3% were successfully cannulated using a freehand technique with a low incidence of cortical breach (4.4%).CONCLUSIONSThis biomechanical analysis indicates equivalent stability of the C1 PAS/C2 pars screw construct compared with a traditional C1 lateral mass/C2 pars screw construct. Both provide significant rigidity in flexion-extension and axial rotation. Feasibility testing in 45 cadaveric specimens indicates a high degree of accuracy with low incidence of cortical breach. These findings are supported by a separate radiographic morphometric analysis.

Novel unilateral C1 double screw and ipsilateral C2 pedicle screw placement combined with contralateral laminar screw-rod fixation for atlantoaxial instability.

To investigate the anatomical and biomechanical feasibility of the unilateral C1 double screw [pedicle screw (PS) + lateral mass screw (LMS)] and ipsilateral C2 PS combined with contralateral C2 laminar screw (LS)-rod fixation for atlantoaxial instability by comparison with traditional posterior fixation methods. Fifteen sets of complete dry bony specimens of atlas were used for morphometric analysis. The working length, width and thickness of the C1 PSs and LMSs were manually measured. Ten fresh-frozen cervical spines (C0-C7) were used to complete the range of motion (ROM) testing in their intact condition, under destabilization and after stabilization by the following procedures: unilateral C1-C2 PS rod fixation (Group A), bilateral C1-C2 PS rod fixation (Group B), and unilateral C1 double screw and ipsilateral C2 PS combined with contralateral C2 LS rod fixation (Group C). The working thickness of the C1 PS was ≤ 3.5mm in only one (1/15 = 6.7%) specimen. The other parameters were > 3.5mm in all specimens. In the ROM test, all fixation groups showed significantly reduced flexibility in all directions compared with both the intact and destabilization groups. Further, Groups B and C showed better stability in all directions than Group A. However, no significant differences were observed between Groups B and C. The C1 unilateral lateral mass could mostly contain two screws(PS + LMS) with diameters ≤ 3.5mm. The novel technique of unilateral C1 double screw and ipsilateral C2 PS combined with contralateral C2 LS rod fixation provided better stability than unilateral PS rod fixation and similar as bilateral PS rod fixation. Therefore, it is a feasible salvage method that provides a new insight into atlantoaxial instability. These slides can be retrieved under Electronic Supplementary Material.

Safety and Accuracy of Anatomic and Lateral Fluoroscopic-Guided Placement of C2 Pars/Pedicle Screws and C1 Lateral Mass Screws, and Freehand Placement of C2 Laminar Screws

To evaluate the safety and accuracy of anatomic- and lateral fluoroscopic-guided placement of C2 pars/pedicle, C1 lateral mass screws, and freehand placement of C2 laminar screws. All the patients who underwent posterior cervical/occipitocervical fixation that involved the placement of C1/C2 screws during a 5-year period (2011-2015) at our institute were included in this study. C1/C2 screws were placed in a total of 94 patients during this period. A total of 97 C1 lateral mass, 49 C2 pars, 24 C2 pedicle, and 82 C2 laminar screws were placed in these patients. C1 lateral mass screws and C2 pars/pedicle screws were placed under anatomic and lateral fluoroscopic guidance. C2 laminar screws were placed by a freehand technique. The mean length (range) of various C2 screws was 16.4 ± 2.6 mm (12-22 mm) for pars screws, 18.8 ± 2.7 mm (14-24 mm) for pedicle screws, and 25.6 ± 3.4 mm (18-32 mm) for laminar screws. Postoperative CT imaging done in all patients before discharge revealed malposition of 2 laminar screws with breach of the inner cortex. The position of the remaining C1/C2 screws was perfect. The superior and medial angulation of the pars screws and superior angulation of the pedicle screws as measured in postoperative CT images were found to significantly deviate from the angles described in the literature. There was no mortality, vertebral artery injury, or neurologic injury related to C1/C2 screw placement in this series. Anatomic and lateral fluoroscopic-guided placement of C2 pars/pedicle screws and C1 lateral mass screws and freehand placement of C2 laminar screws is extremely safe.

Occipito - C2 laminar screws fixation for treatment of chronic C1-2 instability

Introduction: Anomalies of the craniovertebral junction (CVJ) include a wide range of conditions, such as C1-2 chronic instability. Surgery is generally indicated in the context of neurological deficits, although the best surgical option to be chosen is controversy. Method: A 12-year-old girl with severe neurological deficits due to a chronic fixed C1-2 subluxation underwent to an occipito-C2 laminar screws fusion and posterior decompression, with significant neurological improvement after three months follow-up. Discussion: Treatment of cranio-cervical junction anomalies is challenging. An extensive knowledge of all the fixation techniques available for occipito-C1-2 fusion is needed due to frequent anatomical variations, to achieve good surgical results.

C1-2 Fixation Approach for Patients With Vascular Irregularities: A Case Report.

In posterior spinal fusion (PSF), the vertebral artery is most vulnerable to injury at C1-2. C2 pedicle screws are often placed into the dorsomedial isthmus of C2. Alternative techniques include C2 laminar screws and wiring techniques. A 67-year-old male underwent PSF for persistent severe intractable neck pain and degeneration at C1-2. The patient had an enlarged left vertebral artery with midline migration into the C2 body. This pattern was within one standard deviation of normal; however, it rendered typical placement of a C2 pedicle screw unsafe. As a salvage, a C2 laminar screw was placed on the left to avoid risk of vertebral artery injury. The operation and recovery were without complication. C2 laminar screws can be viable alternatives to C2 pedicle screws in cases of midline vertebral artery migration or other vascular anomalies preventing normal safe placement of C2 pedicle screws.

Biomechanical study of novel unilateral C1 posterior arch screws and C2 laminar screws combined with an ipsilateral crossed C1-C2 pedicle screw-rod fixation for atlantoaxial instability.

Current surgical methods to treat atlantoaxial instability pose potential risks to the surrounding blood vessels and nerves of operative approach. Therefore, more secure and highly effective methods are expected. This study sought to assess the biomechanical efficacy of a novel unilateral double screw-rod fixation system by comparing with traditional and emerging fixation methods in cadaveric models. Ligamentous cervical spines (C0-C7) from ten fresh cadaveric specimens were used to complete range of motion (ROM) test in their intact condition (control group), destabilization, and stabilization after different fixations, including unilateral C1-C2 pedicle screws (PS) with a screw-rod system (Group A), bilateral C1-C2 PS with screw-rod systems (Group B), unilateral C1 posterior arch screws (PAS) and C2 laminar screws (LS) combined with an ipsilateral paralleled C1-C2 PS-rod (Group C), and unilateral C1 PAS and C2 LS combined with an ipsilateral crossed C1-C2 PS-rod (Group D). After that, pullout strength test was performed between PS and PAS using ten isolated atlas vertebras. All fixation groups reduced flexibility in all directions compared with both control group and destabilization group. Furthermore, comparisons among different fixation groups showed that bilateral C1-C2 PS-rod (Group B), unilateral C1 PAS+C2 LS combined with an ipsilateral paralleled C1-C2 PS-rod (Group C) and unilateral C1 PAS+C2 LS combined with an ipsilateral crossed C1-C2 PS-rod (Group D) could provide a better stability, respectively, in all directions than unilateral C1-C2 PS-rod (Group A). However, no statistical significance was observed among Groups B, C, and D. Data from pullout strength test showed that both C1 PS (585±53N) and PAS (463±49N) could provide high fixed strength, although PS was better (P=0.009). The surgical technique of unilateral C1 PAS+C2 LS combined with a ipsilateral crossed C1-C2 PS-rod fixation could provide a better stability than the traditional unilateral PS-rod fixation and a same stability as bilateral PS-rod fixation, but with less risk of neurovascular injury. Therefore, this new technique may provide novel insight for an alternative of atlantoaxial instability treatment.

Atlantoaxial Stabilization Using C1 and C2 Laminar Screw Fixation.

We describe the use of a C1 laminar screw in combination with a C2 laminar screw as a salvage technique to treat two patients, one with persistent first intersegmental artery and the other with vertebral artery occlusion after cervical spine fracture. The combined use of C1 and C2 laminar screws allows for good fixation of the atlantoaxial joint with a lower risk of vertebral artery injury; therefore, it can be an alternative surgical procedure for patients with congenital or traumatic anomalous vertebral artery.

Accurate and Simple Screw Insertion Procedure With Patient-Specific Screw Guide Templates for Posterior C1-C2 Fixation.

Prospective clinical trial of the screw insertion method for posterior C1-C2 fixation utilizing the patient-specific screw guide template technique. To evaluate the efficacy of this method for insertion of C1 lateral mass screws (LMS), C2 pedicle screws (PS), and C2 laminar screws (LS). Posterior C1LMS and C2PS fixation, also known as the Goel-Harms method, can achieve immediate rigid fixation and high fusion rate, but the screw insertion carries the risk of injury to neuronal and vascular structures. Dissection of venous plexus and C2 nerve root to confirm the insertion point of the C1LMS may also cause problems. We have developed an intraoperative screw guiding method using patient-specific laminar templates. Preoperative bone images of computed tomography (CT) were analyzed using three-dimensional (3D)/multiplanar imaging software to plan the trajectories of the screws. Plastic templates with screw guiding structures were created for each lamina using 3D design and printing technology. Three types of templates were made for precise multistep guidance, and all templates were specially designed to fit and lock on the lamina during the procedure. Surgery was performed using this patient-specific screw guide template system, and placement of the screws was postoperatively evaluated using CT. Twelve patients with C1-C2 instability were treated with a total of 48 screws (24 C1LMS, 20 C2PS, 4 C2LS). Intraoperatively, each template was found to exactly fit and lock on the lamina and screw insertion was completed successfully without dissection of the venous plexus and C2 nerve root. Postoperative CT showed no cortical violation by the screws, and mean deviation of the screws from the planned trajectories was 0.70 ± 0.42 mm. The multistep, patient-specific screw guide template system is useful for intraoperative screw navigation in posterior C1-C2 fixation. This simple and economical method can improve the accuracy of screw insertion, and reduce operation time and radiation exposure of posterior C1-C2 fixation surgery. 3.