Posterior Cervical Fixation Research Articles

Surgical Technique for Cervical Pedicle Screw Insertion using O-Arm

Introduction Posterior cervical fixation using lateral mass screw and cervical pedicle screw (CPS) is getting available for various disorders such as trauma and degenerative disease and so on. The purpose is to report our detail surgical technique for CPS insertion using O-Arm, about cannulated CPS particularly. Material and Methods Consecutive one hundred twenty patients underwent posterior cervical fixation using CPSs since January 2007. Preoperatively we made further evaluation of the each patient's radiological condition including collateral circulation using MRI and MR angiography and CT angiography. We evaluated local instability with dynamic cervical radiography at each. During making pilot hole of CPS, usually we have felt resistant strong force which cervical back muscles and subcutaneous tissues have produced. So if we made short midline skin incision in particular, CPS underwent through the bilateral another skin incision which we made at the paramedian area. Using O-arm, CPSs were inserted slowly and intermittently taking care not to produce axial rotation or sagittal bending of the cervical spine, which related to the screw malposition including VA injury. And recently we used to use the cannulated screw. Results We inserted 668 CPS and classified their position with Neo's classification using postoperative CT scan, grade 0 (635 screws, 95.0%), grade 1 (27 screws, 4.0%), grade 2 (6 screws, 0.9%), grade 3 (0 screws). No neurovascular complications associated with surgery were encountered. Conclusion We believe what is the most important for safe CPS insertion is preoperative detail further evaluation including the indication of CPS. We think our procedure and techniques for CPS insertion are useful and safe.

A Case Report of Rod Migration into Cerebellum through Foramen Magnum after Lateral Mass Fixation

Introduction There are many methods of posterior cervical fixation for various indications and each with its own early & late known complications. Among the late complications, Screw or rod pullout, screw or plate breakage, and screw loosening are common. We are reporting here, connecting rod migration into posterior cranial fossa, a rare complication after lateral mass fixation. Case Report: A 55 year old male patient was operated with lateral mass fixation after posterior cervical decompression for ossification of posterior longitudinal ligament (OPLL). Patient had symptomatic recovery without any complication postoperatively. One and half years later the patient started complaining of sudden onset giddiness followed by loss of consciousness a few hours later. Ct scan showed lateral mass screws construct with migration of left sided connecting rod into the right cerebellum through foramen magnum. Patient was operated for rod removal but he never regained consciousness and was lost on eighth postoperative day. Autopsy confirmed damage to right cerebellum due to rod migration. Conclusion Clinician should be aware that superior rod migration is a rare but potentially disastrous complication. Regular follow up with radiological evaluation should be done to look for implant loosening, migration and non-union even in asymptomatic patients. The implant should be subsequently removed after it has served its purpose.

Endoscopic Endonasal Approach to the Odontoid Pathologies

Surgical anterior decompression represents the treatment of choice for symptomatic irreducible ventral craniovertebral junction (CVJ) compression. With the refinement of the endoscopic techniques, the endonasal route has been proposed as alternative to the classic transoral approach to CVJ. Some reports assess the effectiveness and safety of endoscopic endonasal approaches to CVJ pathologies. From July 2011 to February 2014, 12 patients with symptomatic nonreducible ventral spinal cord compression underwent purely 3-dimensional endoscopic endonasal odontoidectomy in our department. The surgical technique is described. A good brainstem-medullary decompression was achieved in all patients. In 10 of 12 patients the endotracheal tube was removed just after the procedure with good recovery of the respiratory function. We report no cases of velopharyngeal insufficiency. In 5 of 12 patients the preservation of C1 anterior was achieved, without the need for posterior cervical fixation. Endoscopic endonasal odontoidectomy has proven to be safe and effective in selected patients. Soft and hard palate preservation dramatically reduces the risk of postoperative velopharyngeal insufficiency. Moreover, the endonasal endoscopic approach provides a direct access to the dens. Three-dimensional high-definition endoscope, laser, and ultrasound bony curettes revealed to be useful tools for this approach that, however, remains a demanding one.

Upper Cervical Spine Infection. Complication of Hypopharyngeal Injury

Background: We describe a rare case of Candida albicans retropharyngeal infection with upper cervical spondylodiscitis associated with epidural abscess triggered by ingestion of a chicken bone. Case Description: A 63-year-old woman presented with posterior neck and bilateral shoulders pain three weeks after choking on a 2-centimeter chicken bone. Magnetic resonance imaging (MRI) revealed spondylodiscitis and epidural abscess with significant spinal cord compression at C2 and C3 levels. A Barium swallow showed a focal disruption of the posterior wall of the esophagus. A posterior upper cervical fixation (C2-C5) was initially performed. One week later an anterior decompressive procedure was carried out followed by iliac crest bony fusion, and repair of the esophageal defect. Intra-operative cultures showed heavy growth of Candida albicans. After a transitory post-operative neurologic worsening, and after six weeks of appropriate antifungal therapy, the patient achieved a full clinical and radiologic recovery. Conclusion: Prompt surgical debridement, fusion and stabilization combined with adequate antimicrobial agents are necessary to guarantee a good outcome and reverse the neurological deficits.

Surgical Intervention for Instability of the Craniovertebral Junction.

Surgical approaches for stabilizing the craniovertebral junction (CVJ) are classified as either anterior or posterior approaches. Among the anterior approaches, the established method is anterior odontoid screw fixation. Posterior approaches are classified as either atlanto-axial fixation or occipito-cervical (O-C) fixation. Spinal instrumentation using anchor screws and rods has become a popular method for posterior cervical fixation. Because this method achieves greater stability and higher success rates for fusion without the risk of sublaminar wiring, it has become a substitute for previous methods that used bone grafting and wiring. Several types of anchor screws are available, including C1/2 transarticular, C1 lateral mass, C2 pedicle, and translaminar screws. Appropriate anchor screws should be selected according to characteristics such as technical feasibility, safety, and strength. With these stronger anchor screws, shorter fixation has become possible. The present review discusses the current status of surgical interventions for stabilizing the CVJ.

Hybrid lateral mass screw sublaminar wire construct: A salvage technique for posterior cervical fixation in pediatric spine surgery

We present a novel salvage technique for pediatric subaxial cervical spine fusion in which lateral mass screw fixation was not possible due to anatomic constraints. The case presentation details a 4-year-old patient with C5–C6 flexion/distraction injury with bilateral jumped facets. Posterior cervical fixation was attempted; however, lateral mass fracture occurred during placement of screws. Using a wire-screw construct, an attempt was made to provide stable fixation. The patient was followed post-operatively for assessment of outcomes. After the patient had progressive kyphosis following initial closed reduction and external orthosis, internal reduction with fusion/fixation was performed. Lateral mass fracture occurred during placement of lateral mass screws. After placement of a sub-laminar wire-lateral mass screw construct, intra-operative evaluation determined stability. Post-operatively, the procedure resulted in stable fixation with evidence of bony fusion on follow-up. Pediatric subaxial cervical spine instrumentation provides rigid fixation however is technically difficult due to anatomic and instrumentation related constraints. In the presented patient, the wire-screw construct resulted in stable fixation and bony fusion on follow-up. A modified sublaminar wire-lateral mass screw construct is an example of a salvage technique that provides immediate stability in the event of instrumentation related lateral mass fracture.

The diagnosis and management for the combination fractures of atlas and axis

Objective To investigate the treatment strategies and clinical effect of the combination fractures of atlas and axis. Methods Data of 56 cases with combination fractures of the atlas and axis treated from July 2006 to March 2014 were retrospectively analyzed. There were 36 males and 20 females with mean age of 38.6 years old (range, 21 to 63 years old). Dickman Atlantoaxial compound fracture classification: C1-II type dens fracture 21 cases, C1 fracture-atlantoaxial stability fracture 8 cases; C1 fracture-III type dens fracture 9 cases; C1 fracture-Hangman fracture 18 cases. 8 cases of C1-atlantoaxial stability fracture, 2 cases of C1-III type dens fracture and 7 cases of C1-Hangman fracture had conservative treatment and the other 39 cases were taken surgery. There were 13 patients who suffered from nerve injury such as limbs numbness, movement and the reflecting barrier before surgery: 2 Frankel B, 4 Frankel C, and 7 Frankel D. The mean preoperative JOA score was 8.6 ranging from 5.5 to 12.8. Results All patients were followed-up for a mean period of 32 months (range, 6-58 months). All the operated segments of atlas and axis showed stability and X ray showed fusion achieved within six months (average 4.5 months). Postoperative pain, upper limb numbness and neck pain were improved. 13 cases who had neurological symptoms before surgery achieved an average of 1-2 degrees of Frankel grade recovery after 6 months. The average JOA scores 6 months after operation were 14.1 ranging from 11.5 to 15.8 and the rate of improvement was 82.7% ranging from 71.5% to 95.3%. At the latest follow-up, 39 cases with surgical treatment had no complications such as fracture fixation, spinal cord injury, vertebral artery injury and cerebrospinal fluid leakage; 1 case occurred wound infection which healed after a month by debridement and dressing. Conclusion C1 fracture-III type dens fracture and stable axis fracture and stable Hangman stability fracture should be undertaken with conservative treatment. C1 fracture-II type dens fracture with atlantoodontoid interval >5 mm and unstable Hangman fracture should be treated with posterior cervical pedicle screw fixation. Occipitocervical fixation could be taken with the atlas anatomical abnormalities, severe comminuted fractures and atlas pedicle screw fixation loosening. Key words: Cervical atlas; Axis; Fractures, bone; Fracture fixation, internal

Safety and Efficacy of Reconstruction of Complex Cervical Spine Pathology Using Pedicle Screws Inserted with Stealth Navigation and 3D Image-Guided (O-Arm) Technology.

Retrospective analysis. To determine safety and efficacy of cervical pedicle screw placement using O-Arm and Stealth Navigation in patients with cervicothoracic spinal deformities and revision subaxial cervical pathology. Cervical pedicle screws are biomechanically advantageous to other posterior cervical fixation techniques; however, their use is limited by concerns for neurovascular injury. Few clinical reports exist on their placement safety and efficacy using modern navigation systems. Adults who had cervical pedicle screws inserted using O-Arm and Stealth Navigation between November 2007 and January 2014 and with a minimum 1-year follow-up were retrospectively studied. Screw insertion safety, surgical complications, need for reoperation, and clinical outcomes [Neck Disability Index, EQ-5D, numeric pain rating scales] were evaluated. 21 patients (female-10; male-11; average age 63 yr [32-83 yr]) met inclusion criteria. Average follow-up was 29.8 months (12-81.6 mo). Reconstruction of C2 and the subaxial cervical spine included 8 primary operations for cervicothoracic kyphosis and 13 revision operations. 121 pedicle screws were placed (C2: 4, C3: 20, C4: 22, C5: 23, C6: 18, C7: 34) using Stealth Navigation. The average number of screws placed per case was 6 (1-12). Greater than 99% of screws were placed safely without neurovascular injury. 1 screw (0.8%) was noted postoperatively to critically breach the medial wall and was associated with an acute C5 nerve root palsy. 2 patients required revisions for postoperative iatrogenic foraminal stenosis and associated C8 radiculopathies. No vascular complications due to aberrant screw placement occurred. There were significant improvements (P < 0.05) in EQ-5D utility scores and neck and arm pain. Neck Disability Index scores decreased on average by 10 points (P = 0.12). Placement of cervical pedicle screws using O-Arm/Stealth Navigation in this series was a safe and effective method for posterior stabilization in cervicothoracic deformity and revision operations of the subaxial cervical spine. 4.

Modélisation par éléments finis de l’ostéosynthèse rachidienne cervicale postérieure

Background contextDespite largely, used in the past, biomechanical test, to investigate the fixation techniques of subaxial cervical spine, information is lacking about the internal structural response to external loading. It is not yet clear which technique represents the best choice and whether stabilization devices can be efficient and beneficial for three-column injuries (TCI). HypothesisThe different posterior cervical fixation techniques (pedicle screw PS, lateral mass screw LS, and transarticular screw TS) have respective indications. Materials and methodsA detailed, geometrically accurate, nonlinear C3–C7 finite element model FEM had been successfully developed and validated. Then three FEMs were reconstructed from different fixation techniques after C4–C6 TCI. A compressive preload of 74N combined with a pure moment of 1.8 Nm in flexion, extension, left–right lateral bending, and left–right axial rotation was applied to the FEMs. ResultsThe ROM results showed that there were obvious significant differences when comparing the different fixation techniques. PS and TS techniques can provide better immediate stabilization, compared to LS technique. The stress results showed that the variability of von Mises stress in the TS fixation device was minimum and LS fixation device was maximum. Furthermore, the screws inserted by TS technique had high stress concentration at the middle part of the screws. Screw inserted by PS and LS techniques had higher stress concentration at the actual cap–rod–screw interface. ConclusionsThe research considers that spinal surgeon should first consider using the TS technique to treat cervical TCI. If PS technique is used, we should eventually prolong the need for external bracing in order to reduce the higher risk of fracture on fixation devices. If LS technique is used, we should add anterior cervical operation for acquire a better immediate stabilization.

Finite element analysis of posterior cervical fixation

Background contextDespite largely, used in the past, biomechanical test, to investigate the fixation techniques of subaxial cervical spine, information is lacking about the internal structural response to external loading. It is not yet clear which technique represents the best choice and whether stabilization devices can be efficient and beneficial for three-column injuries (TCI). HypothesisThe different posterior cervical fixation techniques (pedicle screw PS, lateral mass screw LS, and transarticular screw TS) have respective indications. Materials and methodsA detailed, geometrically accurate, nonlinear C3–C7 finite element model (FEM) had been successfully developed and validated. Then three FEMs were reconstructed from different fixation techniques after C4–C6 TCI. A compressive preload of 74N combined with a pure moment of 1.8 Nm in flexion, extension, left–right lateral bending, and left–right axial rotation was applied to the FEMs. ResultsThe ROM results showed that there were obvious significant differences when comparing the different fixation techniques. PS and TS techniques can provide better immediate stabilization, compared to LS technique. The stress results showed that the variability of von Mises stress in the TS fixation device was minimum and LS fixation device was maximum. Furthermore, the screws inserted by TS technique had high stress concentration at the middle part of the screws. Screw inserted by PS and LS techniques had higher stress concentration at the actual cap–rod–screw interface. ConclusionsThe research considers that spinal surgeon should first consider using the TS technique to treat cervical TCI. If PS technique is used, we should eventually prolong the need for external bracing in order to reduce the higher risk of fracture on fixation devices. If LS technique is used, we should add anterior cervical operation for acquire a better immediate stabilization.

Pedicle Screws Can be 4 Times Stronger Than Lateral Mass Screws for Insertion in the Midcervical Spine

A biomechanical study. To compare, in cervical vertebrae (C3-C6), the pullout strengths of pedicle screws and lateral mass screws after both types of screw had been subjected to a period of cyclic loading in 2 planes. In posterior subaxial cervical fixation systems, screws are usually inserted into the lateral mass. As an alternative to lateral mass fixation, pedicle screw fixation became popular in the 1990s and was first used for lower cervical spine trauma cases. However, it is controversial as to whether lateral mass screw fixation in the upper-middle cervical spine offers as much biomechanical security as compared with pedicle screw fixation. For each of the 32 vertebrae, 1 side was randomly chosen to receive a pedicle screw and the other side a lateral mass screw. The pedicle or lateral mass screws inserted into the first 16 vertebrae were cyclically loaded to simulate torsion and the remaining 16 vertebrae were cyclically loaded to simulate flexion/extension of the spine. At the end of the cyclic loading each screw was pulled out along its long axis. For the torsion group, the mean pullout strength of the pedicle screws was nearly 4 times greater than the mean pullout strength of the lateral mass screws (cf 762 N with 191 N). In contrast, the mean pullout strength of the pedicle screws in the flexion/extension group was only twice the mean pullout strength of the lateral mass screws (cf 571 N with 289 N). Not forgetting the potential risks of inserting pedicle screws in cervical vertebrae, pedicle screws are a better biomechanical choice than lateral mass screws for cervical fixation at the levels C3 through to C6.

Comparative In Vitro Biomechanical Analysis of a Novel Posterior Cervical Fixation Technique Versus Conventional Posterior-based Constructs

Comparative in vitro, cadaveric biomechanical study. To compare the kinematic response of a new posterior cervical midline surgical technique versus that of conventional fixation techniques. A new method was designed using alternating bilateral intralaminar screws connected with a single midline rod. This technique provides the theoretical benefits of less operative dissection and reduced implant cost, but the acute flexibility properties remain unknown. Using an in vitro cadaveric model, the study objective was to define the operative level(s) changes in multidirectional flexibility after posterior destabilization/reconstruction from C3 to C6. A 6 degree of freedom spine stimulator was used to test flexibility in 7 human cadaveric specimens. Flexion-extension, lateral bending, and axial rotation were tested in the intact condition, followed by destabilization by a simulated posterior column injury from C3 to C6. Specimens were then reconstructed from C3 to C6 and tested in the following sequence: sublaminar hook rod (SH), lateral mass screw rod (LMR), midline laminectomy from C3 to C6 with LMR (MLR), and midline posterior fixation from C3 to C6 (SMF). Range of motion (ROM) and neutral zone were quantified and analyzed. Significant increases in ROM and neutral zone at C3 to C6 were found under all loading conditions for the destabilized condition and intact spine versus all other treatments (P<0.05). The conventional treatments: SH, LMR, and MLR resulted in significantly less ROM than the proposed SMF in flexion-extension and lateral bending (P<0.05). Axial rotation provided similar results; however, no differences were observed between the SH and SMF (P>0.05). Notably, LMR and MLR provided significantly more stability than SH in axial rotation (P<0.05). Data produced suggest that the new, midline rod fixation approach provides less biomechanical stability than conventional posterior cervical reconstruction techniques. In addition, the high incidence of laminar fracture during screw placement and close proximity of the screw trajectory and polyaxial heads to the dura suggest a practical limitation as well.

Posterior stabilization of cervical spine injuries using the Roy-Camille plates: a long-term follow-up

Posterior cervical spine fixation has undergone tremendous advancement in recent years. The purpose of this study is to present our experience with the Roy-Camille instrumentation for posterior cervical stabilization after injury in a long-term follow-up. From 1985 to 1995, 76 patients with a lower cervical spine traumatic lesion were treated in a single institution by posterior plate stabilization using the Roy-Camille plates (R-C plates). Fifty-four men and 22 women with a mean age of 43.2years were involved. In 59 patients the injuries were due to a road traffic accident, in 14 cases the fall from a high was responsible, while in two cases the injuries were due to sport activities. There were four bilateral dislocations, nine unilateral dislocations, 56 fracture dislocations, five fracture separations of a lateral mass and two burst fractures. Neurological lesions were present in 65 patients (9 ASIA A, 16 ASIA B, 22 ASIA C, 18 ASIA D and 11 ASIA E). All patients had minimum follow-up of 7years. Fifty-nine patients were followed up for a mean period of 21years (14-27years). Stability was obtained in all but two cases. Reoperation was done in two cases: in one for the correction of the lost reduction and in a second for the reinsertion of a screw irritating a nerve root. No case in the ASIA A group showed neurological improvement, a fact observed in the other groups. The R-C plates were used in the last quarter of the last century. This technique showed good short-time results, and we have shown good results in a long-term follow-up as well. The literature referred to this technique was favorable, as far as the biomechanical behavior and also clinical application concern. The question about this plating system abundance still remains unanswered.

Osteocondroma de la columna cervical provocando tortícolis y hemiparesia

Osteochondromas are slow-growing benign bone tumors that are located frequently in the long bones. Approximately 1-4% of them occur in the spine. Solitary spinal osteochondromas may produce a wide variety of symptoms depending on their location and relationship to associated structures. We report a case of a 74-year old woman who was admitted to our hospital with complaints of progressive left hemibody weakness and cervicalgia. Neurological examination disclosed mild left-sided hemiparesis and left torticollis. Computed tomography and magnetic resonance imaging of the cervical spine revealed an expansive lesion affecting the left C3-C4 facet joint. The patient underwent a posterior C3 and C4 hemilaminectomy, complete excision of the lesion and instrumented posterior cervical fixation. Histological examination confirmed the diagnosis of osteochondroma. After surgery her symptoms improved progressively with no neurological sequels.

Novel Approach for the Efficient Use of a Full-Scale, 3-Dimensional Model for Cervical Posterior Fixation

Case report of a patient with atlantoaxial subluxation who underwent posterior cervical fixation. To describe a novel approach for the efficient use of a full-scale, 3-dimensional model for preoperative planning and surgery. Instrumented fusion of the cervical spine with screws and rods is indicated for atlantoaxial subluxation. Fatal complications, such as vertebral artery and spinal cord injuries, may occur during screw insertion. Making appropriate connecting rods, after screw insertion, is often time consuming. Therefore, precise preoperative planning and careful intraoperative procedures are required. A 73-year-old male with atlantoaxial subluxation presented with progressive quadriplegia and gait disturbance. Surgery involving a C1 laminectomy and posterior cervical fixation was planned; and a 3D model, allowing visualization of the vertebral artery, was developed. Bilateral C1 and C4 lateral mass screws and C2 pars screws were experimentally inserted into the model. Rods with appropriate curvature were created to obtain rigid screw fixation, and were used during the surgery. Moreover, radiography and computed tomographic images of the instrumented model were analyzed to ensure the proper orientation of the screws. During surgery, screw insertion was performed, under fluoroscopic guidance, and compared with the 3D model and its preoperative radiographs. According to the preoperative analysis of the model-computed tomographic images, the direction of the C1 lateral mass screws was changed laterally, and the lengths of the C2 pars screws were shortened to avoid complications. The sterile, prebent rods could be elegantly adapted to the screws without additional bending. The postoperative course was uneventful, and postoperative computed tomographic images showed proper screw positioning. Three-dimensional models that allow (1) visualization of the vertebral artery, (2) evaluation of radiological images after screw insertion, and (3) the use of prebent rods during surgery contribute to the safety of the cervical posterior fixation. N/A.

Spinous process plate fixation for cervical spinal fusion after spinal trauma: two case reports

Spinous process plate fixation for cervical spinal fusion after spinal trauma: two case reports

Lateral Mass Screw Fixation in the Cervical Spine: A Systematic Review

The use of lateral mass screw fixation (LMSF) with plates or rods in the subaxial cervical spine has become the standard method of posterior cervical fixation & stabilization for a variety of cervical indications including spondylosis, trauma, deformity, inflammatory disease, revision surgery and tumor. As the technologies utilized for LMSF are derivative of technologies developed for long bone and thoracolumbar fixation, none of the LMSF systems currently on the market have been subject to the rigors of an IDE pivotal study and thus none of these systems have “on-label” FDA approval for usage in the subaxial posterior cervical spine.

Giant anterior cervical osteophyte leading to Dysphagia.

Large anterior cervical osteophytes can occur in degeneration of the cervical spine or in diffuse idiopathic skeletal hyperostosis(DISH). Large osteophytes can produce otolaryngological symptoms such as dysphagia, dysphonia, and foreign body sensation. We describe a DISH patient with giant anterior cervical osteophyte causing chronic dysphagia and dysphonia. A 56-year-old man presented with increasing dysphagia, dysphonia, neck pain and neck stiffness. Physical examination of the neck showed a non-tender and hard mass on the left side at the level of C4-5. Radiography showed extensive ossification of anterior longitudinal ligament along the left anterolateral aspect of vertebral bodies from C2 to T1. The ossification was espe cially prominent at the level of C4-5 and linear breakage was noted at same level. Esophagogram revealed a filling defect along the pharynx and lateral displacement of the esophagus. Giant anterior cervical osteophyte was removed through the leftsided anterolateral cervical approach to the spine. Anterior cervical interbody fusion at C4-5 was followed by posterior cervical fixation using lateral mass screws from C3 to C6. After surgery, dysphagia and dysphonia improved immediately. One year later, cervical CT showed bone fusion at C4-5 bodies and no recurrence of osteophyte. DISH is a common cause of anterior cervical osteophyte leading to progressive dysphagia. Keeping this clinical entity in the differential diagnosis is important in patients with progressive neck stiffness, dysphagia or dysphonia. And surgical treatment of symptomatic anterior cervical osteophyte due to DISH should be considered with a solid fusion procedure preventing postoperative instability or osteophyte progress.

Clinical evaluation of guiding apparatus assisted individual posterior cervical pedicle screw fixation

Objective To evaluate the clinical effects of guiding apparatus assisted individual posterior cervical pedicle screw fixation technique. Methods The study enrolled 24 patients treated with posterior cervical decompressive single open-door laminoplasty and transpedicular screw-rod fixation from January 2008 to December 2010.The point of screw penetration and screw path direction were confirmed by measuring the transverse nail angle (TNA) and sagittal nail angle (SNA) of nail channel on the pre-operative CT plain scan of cervical pedicle and sagittal two-dimensional imaging of transpedicular axis.According to the results of CT measurement,individual cervical pedicle screw was implanted with the assistance of self-made guiding apparatus and then fixed after decompression.Transverse screw angle ( TSA ) and sagittal screw angle ( SSA ) were determined on the CT scan of cervical pedicle and sagittal two-dimensional imaging of transpedicular axis one week postoperatively in order to analyze the accuracy of placement of pedicle screws.Periodical anteroposterior and lateral X-ray radiographs of cervical vertebra were taken postoperatively to detect the stabilization of internal fixation. Results A total of 223 pedicle screws were inserted successfully into the C3 ～ C7,of which 220 crews were inserted accurately but three had slight inclination according to the postoperative CT,with placement accuracy of 98.7％.The comparison between inclination angle of inserted screws and that of preoperative transpedicular axis showed insignificant statistical difference ( P ＞ 0.05 ).All the patients were followed up for 6-34 months ( mean,18.5 months),which showed no neurovascular complications related to screws perforation out of pedicle cortex or no screw loosening,prolapse or breakage. Conclusion Posterior cervical pedicle screw insertionperformed according to the individual CT measurement is easy and safe and has a high accuracy rate under the assistance of self-made guiding apparatus. Key words: Cervical vertebrae; Fracture fixation, internal; Guiding apparatus

The feasibility of laminar screw placement in the subaxial spine: analysis using 215 three-dimensional computed tomography scans and simulation software

There have been several reports describing the usage of subaxial cervical laminar screws. However, the anatomic feasibility of placing such screws has not been thoroughly evaluated yet. To determine the feasibility of the laminar screw placement in the subaxial cervical spine using a large number of computed tomography (CT) scans and three-dimensional screw trajectory software. Three-dimensional simulation study of screw placement. Computed tomography scans of 215 consecutive patients were examined, for a total of 430 screws at each level of the subaxial cervical spine. Successful screw placement without laminar cortical breach, facet joint violation, and collision between two screws in the same level. We simulated the placement of 4.0-mm subaxial (C3-C7) cervical laminar screws. Unilateral and bilateral screw placement was simulated, and their success rates were evaluated at each level of the subaxial cervical spine. This study was not supported by any financial sources. One of the authors received royalties for a posterior cervical fixation system, which is not the topic of this article and is not used or mentioned in this article. The success rate of unilateral screw placement was the highest at C7 (91.4%), followed by C6 (31.9%), C3 (30.2%), C4 (6.3%), and C5 (4.0%). It was significantly higher (p<.001) in men than in women at C6 and C7 but not at the other levels. The success rate of bilateral screw placement was the highest at C7 (68.8%), followed by C3 (13.5%), C6 (8.8%), C4 (1.9%), and C5 (0.9%). It was significantly higher in men (83.5%) than in women (52.0%) at C7 (p<.001) but not at the other levels. The relatively high success rate at C7, particularly of unilateral placement, suggests that laminar screw placement can be a sound alternative method for fixation at this level. However, careful preoperative CT scan evaluation and patient selection are required, particularly for bilateral fixation in women. At C3 and C6, unilateral screw placement can be considered in approximately 30% of patients after careful selection using preoperative CT scans. At C4 and C5, neither unilateral nor bilateral screw fixation is recommended for most patients.