Anterior Transarticular Screw Fixation Research Articles

Anterior Transarticular Crossing Screw Fixation for Atlantoaxial Joint Instability: A Biomechanical Study.

To evaluate the biomechanical stability of anterior transarticular crossing screw (ATCS) and compare it with anterior transarticular screw (ATS) which may provide basic evidence for clinical application. Eight human fresh cadaveric specimens (occiput-C4) were tested with 5 conditions including the intact status, the injury status (type II odontoid fracture), the injury+ATS fixation status (traditional bilateral ATS fixation); the injury+unilateral ATCS fixation status; and the injury+bilateral ATCS fixation status. Specimens were applied to a pure moment of 1.5 Nm in flexion-extension, lateral bending, and axial rotation, respectively. The range of motions (ROMs) and the neutral zones (NZs) of C1 to C2 segment were calculated and compared between 5 status. ATS and ATCS fixations significantly reduced the motions in all directions when compared with the intact and injury statues (p < 0.05). In flexion-extension, the ROMs of ATS, unilateral ATCS, and bilateral ATCS were 4.7° ± 2.5°, 4.1° ± 1.9°, and 3.2° ± 1.2°, respectively. Bilateral ATCS resulted in a significant decrease in ROM in flexion-extension when compared with ATS and unilateral ATCS (p = 0.035 and p = 0.023). In lateral bending and axial rotation, there was no significant difference in ROM between the 3 fixations (p > 0.05). Three fixations resulted in similar NZs in all directions (p > 0.05). ATCS is a biomechanically effective alternative or supplemental method for atlantoaxial instability.

Anterior atlanto-occipital transarticular screw fixation: a biomechanical comparison with posterior fixation techniques.

Atlanto-occipital instability is commonly treated with posterior fixation. However, in patients with congenital or acquired factors, posterior fixation may not be possible. For these situations, a novel anterior atlanto-occipital transarticular screw (AATS) fixation technique has been introduced recently. However, biomechanical study of this technique is lacking. This study was designed to evaluate the biomechanical stability of AATS fixation for the atlanto-occipital joint and compare it with conventional posterior occipitocervical fixation (POCF). Six cadaveric specimens (occiput-C4) were tested in four conditions, including intact, injury, injury + AATS, and injury + POCF states. A pure moment of 1.5 Nm was applied to specimens in flexion, extension, lateral bending, and axial rotation. The range of motion (ROM) and neutral zone (NZ) were calculated and compared from the occiput to C1. The AATS fixation constrained ROMs to 0.4° in flexion (p < 0.001), 0.4° in extension (p < 0.001), 1.0° in lateral bending (p < 0.001), and 0.7° in axial rotation (p < 0.001) when compared with the injury state. In all directions, there was no statistically significant difference observed in ROMs and NZs between AATS fixation and POCF (p > 0.05). This study identified that the novel AATS fixation, as stand-alone anterior fixation, was equivalent to POCF in all directions. The results suggest that anterior transarticular screw fixation is a biomechanically effective salvage technique for posterior atlanto-occipital fixation, and may also serve as supplemental fixation.

Atlantoaxial Anterior Transarticular Screw Fixation: Indications and Surgical Technique.

Posterior atlantoaxial screw fixation is a widely adopted therapeutic option for C1-C2 instability secondary to fractures or dislocation, degenerative diseases, or tumors at this level. Anterior transarticular screw fixation (ATSF) is an effective alternative to the posterior approaches, presenting several advantages despite being scarcely known and rarely chosen.In this chapter, we describe the ATSF step by step, illustrating its variations reported in literature, and we critically analyze the several advantages and contraindications of this technique. Moreover, we provide a list of tips and tricks on the surgical procedure, including critical operating room settings-the result of more than 10years of experience in the field by a senior author.ATSF is a valid strategy for the treatment of different diseases occurring at the level of the atlantoaxial complex that needs consideration. Given the significant learning curve of this strategy, some hints may be essential to begin introducing this technique in the personal armamentarium of a spine surgeon so that they can perform ATSF safely and effectively.

A Clinical Study to Assess the Efficacy of Anterior Transarticular C1-C2 Screw Fixation for Stabilization of AtlantoAxial Instability

Introduction: The upper cervical spine includes the atlas (C1) and Axis (C2). The anatomy of upper twovertebrae is unique from each other. Atlanto-axial articulation is the most unique, mobile segment of spine,which largely depends on ligamentous supports based on integrity of odontoid for its stability. Historically,atlanto-axial subluxation was treated by reduction and fusion of C1-C2 joint. However, High riding vertebralartery precludes the placement of posterior trans-articular screw, which is liable to injury during screwplacement. Socomputed tomography scans can be used to evaluate the risk of “high riding” vertebral arteryduring the management of atlanto-axial subluxation. Hence, anterior trans-articular screw fixation techniqueavoids the course of high riding vertebral artery.Material and Method: Nine patients underwent NCCT cervical spine with 3-D reconstruction and clinicalevaluation of pain was done by recording the VAS score done pre operatively and after surgery.Results: All surgical cohorts underwent anterior C1-C2 fixation with an average follow up for 24 months.All patients were assessed as per fixed protocol of our local hospital guidelines of orthopaedics department.Pain score was clinically evaluated by VAS score before and after surgery yielding 90% excellent result.Conclusion: Anterior Trans-articular C1-C2 screw fixation isa minimally invasive technique with less bloodloss, shorter skins car and faster post-operative recovery. It is an appropriate technique for stabilization ofAtlanto-Axial instabilities.

Design a novel integrated screw for minimally invasive atlantoaxial anterior transarticular screw fixation: a finite element analysis

PurposeTo design a new type of screw for minimally invasive atlantoaxial anterior transarticular screw (AATS) fixation with a diameter that is significantly thicker than that of traditional screws, threaded structures at both ends, and a porous metal structure in the middle. The use of a porous metal structure can effectively promote bone fusion and compensate for the disadvantages of traditional AATSs in terms of insufficient fixation strength and difficulty of bone fusion. The biomechanical stability of this screw was verified through finite element analysis. This instrument may provide a new surgical option for the treatment of atlantoaxial disorders.MethodsAccording to the surgical procedure, the new type of AATS was placed in a three-dimensional atlantoaxial model to determine the setting of relevant parameters such as the diameter, length, and thread to porous metal ratio of the structure. According to the results of measurement, the feasibility and safety of the new AATS were verified, and a representative finite element model of the upper cervical vertebrae was chosen to establish, and the validity of the model was verified. Then, finite element-based biomechanical analysis was performed using three models, i.e., atlantoaxial posterior pedicle screw fixation, traditional atlantoaxial AATS fixation, and atlantoaxial AATS fixation with the new type of screw, and the biomechanical effectiveness of the novel AATS was verified.ResultsBy measuring the atlantoaxial parameters, the atlantoaxial CT data of the representative 30-year-old normal adult male were selected to create a personalized 3D printing AATS screw. In this case, the design parameters of the new screw were determined as follows: diameter, 6 mm; length of the head thread structure, 10 mm; length of the middle porous metal structure, 8 mm (a middle porous structure containing an annular cylinder ); length of the tail thread structure, 8 mm; and total length, 26 mm. Applying the same load conditions to the atlantoaxial complex along different directions in the established finite element models of the three types of atlantoaxial fusion modes, the immediate stability of the new AATS is similar with Atlantoaxial posterior pedicle screw fixation.They are both superior to traditional atlantoaxial anterior screw fixation.The maximum local stress on the screw head in the atlantoaxial anterior surgery was less than those of traditional atlantoaxial anterior surgery.ConclusionsBy measuring relevant atlantoaxial data, we found that screws with a larger diameter can be used in AATS surgery, and the new AATS can make full use of the atlantoaxial lateral mass space and increase the stability of fixation. The finite element analysis and verification revealed that the biomechanical stability of the new AATS was superior to the AATS used in traditional atlantoaxial AATS fixation. The porous metal structure of the new AATS may promote fusion between atlantoaxial joints and allow more effective bone fusion in the minimally invasive anterior approach surgery.

The Anterior Transarticular Fixation of C1/C2 in the Elderly With Dens Fractures.

Anterior transarticular screw fixation (ATSF) of C1/C2 can be used for the treatment of unstable dens fractures. Here, we evaluated the feasibility of an anterior C1/C2 fixation in elderly patients with unstable dens fractures. Furthermore, we tried to analyze safe entry zones for ATSF surgery. A consecutive cohort of 13 patients with unstable dens fractures were treated with ATSF of C1/C2 between January 2015 and October 2016. If necessary, an additional screw was placed into the odontoid process. The placement was radiographically analyzed using the 3D Arcadis Orbic (Siemens, Erlangen, Germany). Additionally, computed tomography scans of the cervical spine from 50 trauma patients were analyzed to evaluate safe entry zones for anterior odontoid screw fixation and for ATSF. ATSF was performed in 13 cases (7 female, 6 male; mean age 81.80 years). One screw had to be corrected intraoperatively due to initial malplacement. Neurological deficits or an injury of the vertebral artery were not observed. All patients suffered from swallowing difficulties during the postoperative course, without lesions of the esophagus or the trachea. In 4 patients (30.8%), an additional posterior fixation was offered to the patients due to progressive loosening of the screws.The anatomical-radiographic analyzes revealed a significantly shallower angle of trajectory for anterior odontoid screw fixation (24.9° ± 5.85°) than for ATSF (39.1° ± 6.44° (left); 40.5° ± 6.79° (right) P = 0.02). The ATSF of C1/C2 might be a valuable option in the treatment of instable C1/C2 fractures, especially in the elderly or in patients with short necks and/or high body mass index due to the steeper trajectory compared with odontoid screw placement. Yet available screws seem to be of inferior resistance compared with the biomechanical properties of a dorsal fixation. Further studies should focus on screws with better mechanical properties and probably additional cement augmentation. 4.

Anatomic Considerations of Anterior Transarticular Screw Fixation for Atlantoaxial Instability.

Study DesignCadaveric, observational study.PurposeAtlantoaxial instability (AAI) is characterized by excessive movement at the C1–C2 junction between the atlas and axis. An anterior surgical approach to expose the upper cervical spine for internal fixation and bone grafting has been developed to fix AAI. Currently, no anatomic information exists on the anterior transarticular atlantoaxial screw or screw and plate fixation between C1 and C2 in the Indian population. The objective of this study is to assess the anatomic landmarks of C1–C2 vertebrae: entry point, trajectory, screw length, and safety of the procedure.Overview of LiteratureMethods outlined by Magerl and Harms are the optimal approaches among the dorsal techniques. Contraindications for these techniques include aberrant location of vertebral arteries, fractures of C1–C2 posterior structures. In these cases, anterior transarticular fixation is an alternative. Several available screw insertion trajectories have been reported. Biomechanical studies have demonstrated that adequate rigidity of this fixation is comparable with posterior fusion techniques.MethodsDirect measurements using Vernier calipers and a goniometer were recorded from 30 embalmed human cadavers. The primary parameters measured were the minimum and maximum lateral and posterior angulations of the screw in the sagittal and coronal planes, respectively, and optimum screw length, if it was placed accurately.Results The posterior and lateral angles of screw placement in the coronal and sagittal planes ranged from 16° to 30° (mean±standard deviation [SD], 23.93°±3.93°) and 8° to 17° (mean±SD, 13.3°±2.26°), respectively. The optimum screw length was 25–38 mm (mean±SD, 28.76±3.69 mm).ConclusionsIf the screw was inserted without lateral angulation, the spinal canal or cord could be violated. If a longer screw was inserted with greater posterior angulation, the vertebral artery at the posterior or posterolateral aspect of the C1 superior facet could be violated. Thus, 26° and 30° of lateral and posterior angulations, respectively, are the maximum angles permissible to avoid injury of the vertebral artery and violations of the spinal canal or atlanto-occipital joint.

Ošetření zlomeniny zubu čepovce u starších pacientů metodou kompresní osteosyntézy a přední transartikulární stabilizací

Ošetření zlomeniny zubu čepovce u starších pacientů metodou kompresní osteosyntézy a přední transartikulární stabilizací

A Method to Prevent Occipitocervical Joint Violation Using Plain Radiography During Percutaneous Anterior Transarticular Screw Fixation.

A prospective study of anterior transarticular screw (ATS) fixation patients. To develop a method to determine screw tip position through plain radiography after percutaneous ATS fixation to prevent occipitocervical joint (OCJ) violation. No studies using plain radiography to prevent OCJ violation during percutaneous ATS fixation have been performed. In total, 34 subjects (with 68 screws) who had undergone percutaneous ATS fixation were enrolled. To evaluate the screw tip location in relation to the C1 lateral mass (LM), the screw tip positions were graded 1, 2, or 3 on anteroposterior (AP) radiographs, and I, II, or III on lateral radiographs. OCJ violation was analyzed by postoperative computed tomography (CT). Screws with tips located lower (tip I) in the LM did not result in OCJ violation. Only one tip in the tip 3 position showed OCJ perforation, and this screw was also located in tip III. Screw perforation rates of tip 1-tip II, tip 1-tip III, and tip 2-tip III were the highest (100%), followed by tip 2-tip II (10.5%) and tip3-tip III (10%). This study provides insights into OCJ violation during percutaneous ATS fixation. According to AP radiography, a percutaneous ATS with the screw tip located in the lateral part of the LM resulted in a lower rate of OCJ perforation, whereas screws located in the medial LM resulted in the highest rate of perforation. Percutaneous ATS with the screw tip located in the neutral part of the LM should ensure that the screw tip is below the upper part of the LM, preventing OCJ violation. These findings may help surgeons assess screw positioning both during and after the operation. 3.

Biomechanical study of the atlantoaxial joint after artificial atlanto-odontoid joint arthroplasty

ObjectiveTo investigate the stability and three-dimensional movements of the atlantoaxial joint after artificial atlanto-odontoid joint (AAOJ) arthroplasty by comparing with a conventional method. MethodsAfter anterior decompression, 24 human cadaveric spinal specimens of C0-C3 were randomly divided into two groups: Group A receiving artificial AAOJ arthroplasty; Group B experiencing anterior transarticular screw (ATAS) fixation. Two groups underwent flexibility test in intact and instrumented states. Rotational angle of the C0-C3 segments was measured to study the immediate stability and function of anterior decompression with AAOJ arthroplasty compared with the intact state and ATAS fixation. ResultsCompared with the intact state, anterior decompression with AAOJ arthroplasty resulted in a significant decrease in the range of motion (ROM) and neutral zone (NZ) during flexion, extension and lateral bending (P<0.05); however, with regard to axial rotation, there was no significant difference in ROM and NZ (P>0.05). Compared with anterior decompression with ATAS fixation, anterior decompression with AAOJ arthroplasty during flexion, extension and lateral bending, significant difference was found in ROM and NZ (P>0.05); however, as for axial rotation, there was a significant increase in ROM and NZ (P<0.05). ConclusionThe self-designed AAOJ has an excellent biomechanical performance, which can restore excellent instant stability and preserve the movement of the atlanto-axialjoint.

Morphometric Characteristics of C1-C2 Vertebrae to Perform Anterior Transarticular Crossing Screw Fixation.

In unique clinical situations where C1-C2 posterior fixation is not available or has previously failed, an anterior transarticular screw (ATAS) may be a viable alternative. However, there are no previous reports that investigate possible screw angles, screw entry points, and screw length based on computed tomography (CT) multiplanar reconstruction images in Turkish patients. The aim of this study was to determine the morphometric characteristics C1-C2 vertebrae in order to perform anterior transarticular crossing screw fixation. Patients who underwent a complete CT scan of the cervical spine for causes other than an investigation of cervical spine malformation or congenital anomaly between the years 2013 and 2015 were included in this study. The anterior transarticular C1-C2 screw angles, screw entry point, and screw length were measured on coronal and sagittal CT multiplanar reconstruction images. Twenty-five male and 14 female patients were included in the study. The mean maximum screw angle for ATAS was found to be 41.18°±4.49°. The minimum and maximum screw lengths were 27.46±3.39 mm and 28.46±3.60 mm, respectively. Preoperatively, performing a calculation of the possible screw angles, screw entry point, and screw length based on CT multiplanar reconstruction images for ATAS is a safe and applicable method. In cases in which ATAS fixation across the atlantoaxial joint procedure should be performed without performing a measurement, a screw angle not more than 41.18°±4.49° on the coronal plane does not damage the vertebral artery. Furthermore, using screws shorter than 28.46±3.60 mm doesn"t purchase the atlantoaxial joint.

Feasibility and trajectory study of anterior transarticular crossing screw placement for atlantoaxial joint instability: a cadaveric study and description of a novel technique.

In unique clinical situations where C1-C2 anterior transarticular screw (ATS) fixation is not available or has failed, an anterior transarticular crossing screw (ATCS) with transcorporal pathway of the screws inside the contralateral promontory of C2 may enhance the stabilization and achieve atlantoaxial arthrodesis. The present study was to describe a novel technique of ATCS fixation for atlantoaxial joint instability and its applied anatomy, and compared it with ATS fixation method. Direct measurements using digital calipers and a goniometer were conducted on 30 pairs of dried human C1 and C2 vertebrae. The ATS and ATCS with screws (Φ 4.0mm) were performed on 11 fresh cervical spine specimens. The screw lengths in the C1 and C2, and screw entry angles of the ATS and ATCS were measured, respectively. Cadaver specimens were dissected to observe the incidence of violation to the important structures surrounding the ATS andATCS fixation technique. There was enough osseous space for ATCS placement. The lateral and incline angle of the ATCS was 36.2° and 28.7°, respectively. Screw purchase in C2 of the ATCS (25.6mm) was greater than that of the ATS (11.4mm). The ATCS C1 purchase (14.8mm) was similar to the ATS C1 purchase (14.9mm). No violation to the vertebral artery groove, the spinal canal or the atlanto-occipital joint was observed after the ATCS placement. Anterior transarticular crossing screw is a feasible and viable option for atlantoaxial fixation in selected cases. This technique achieved remarkable longer screw purchase and could enhance the atlantoaxial stability.

Atlantoaxial anterior transarticular screw fixation: a case series and reappraisal of the technique

Background contextAtlantoaxial instability is commonly treated with C1–C2 fixation performed via posterior approaches. Although anterior transarticular screw (ATS) fixation, performed with a classic retropharyngeal approach, was described more than 10 years ago, the published literature still lacks a comprehensive analysis of the procedure and a real case series. PurposeWe report a series of patients treated with atlantoaxial ATS, describing the surgical procedure in detail and discussing advantages and disadvantages of the technique. Study designThe study design includes case series and technical report. MethodsWe prospectively enrolled 15 patients affected by atlantoaxial instability secondary to trauma, degenerative diseases, or inflammatory diseases. Anterior transarticular screw fixation was performed with anteroposterior open-mouth and lateral intraoperative radiographs. All patients were evaluated radiologically at follow-up to identify bone fusion. ResultsAnterior transarticular screw was performed successfully in 14 patients without complications. The procedure was aborted in a case of vertebral invagination, and one case required revision surgery owing to C2 articular bone fracture. Solid C1–C2 fusion was achieved in all cases (at 10- to 21-week follow-up) except in an elderly patient affected by severe osteoporosis. No complications occurred. ConclusionsAlthough the procedure is still not widely known, ATS allows the effective and safe treatment of C1–C2 instability even in patients with systemic comorbidities. It offers several advantages over posterior approaches.

Anterior transarticular screw fixation as a conventional operation for rigid stabilization.

Background:Anterior transarticular screw (ATS) fixation is a useful surgical option for atlantoaxial (AA) stabilization. This report presents a revised ATS method for AA fusion.Methods:A 79-year-old male presented with AA instability attributed both to an old odontoid fracture and severe degeneration of the lateral atlantoaxial joints (LAAJs). ATS fixation was performed through the conventional anterior cervical approach. The longest screw trajectories were planned preoperatively using multiplanar reconstruction computed tomography (CT) scans, with entry points of the screws situated at the midpoint on the inferior border of the axial body. The surgical exposure was limited to opening at the entry points alone. Our retractor of choice was the Cusco speculum; it sufficiently secured space for utilizing the required instruments for screw placement while offering sufficient protection of soft tissues. Cannulated full-threaded bicortical screws stabilized the LAAJs. Screw insertion required a significant amount of coronal angulation up to the superior articular process of the atlas under open-mouth and lateral fluoroscopy image guidance. After ATS fixation, bone grafting was performed between the posterior laminae of the axis and the atlas through a conventional posterior approach.Results:Bony fusion between the atlas and the axis was confirmed radiographically. Arthrodesis of the LAAJs occurred despite no bone grafting.Conclusions:Rigid fixation of the LAAJs was obtained by our ATS technique, indicating that it is an alternative method for AA fixation when posterior rigid internal fixation is not applicable.

Percutaneous anterior occiput-to-axis screw fixation: technique aspects and case series

Background contextPosterior occipitocervical fusion techniques have been previously described; however, traditional open anterior approaches are plagued by exposure difficulty. A minimally invasive percutaneous anterior occipitocervical fixation approach avoids this difficult exposure procedure. PurposeThis article describes a novel technique of percutaneous anterior occiput-to-axis screw fixation and its clinical outcomes. Study designTechnique report. MethodsAnteroposterior, lateral and open-mouth views, and computed tomography scans are preoperatively obtained to appraise the feasibility of surgery. We extend our experience of using percutaneous anterior transarticular screw fixation to occiput-to-axis screw fixation. This procedure was performed on six patients. ResultsThe operation was successfully performed on all patients without technical difficulties, and no vertebral artery, nerve injury or soft tissue (such as esophageal) complications occurred. All six patients followed up 10 to 39 months (averaged 20.5 months). Bone union was achieved in five patients, and the one patient lacking bone union was stable at final follow-up. The syringomyelia of four patients is almost complete reduction. No screw loosening or breakage has occurred. ConclusionsWith the correct puncture point, angle of insertion, and use of the appropriate tools, we suggest that percutaneous anterior occiput-to-axis fixation technique is a feasible, safe, and minimally invasive procedure.

Anterior atlantoaxial transarticular screw fixation for treatment of atlantoaxial instability

Objective To analyze clinical outcome of anterior atlantoaxial transarticular screw fixation in treatment of atlantoaxial instability.Methods Thirty-two patients with atlantoaxial instability treated between March 2004 and June 2009 were enrolled in the study.The patients consisted of 21 males and 11 females,at age of 22-64 years (mean 49 years).Atlantoaxial instability was attributed to old odontoid fracture in 10 patients,free odontoid malformation in 16,transverse ligament rupture in two,and rheumatoid arthritis in four.Anterior atlantoaxial transarticular screw fixation under monitoring of cortical somatosensory evoked potential (CSEP) was performed for all patients.Operation time,intraoperative blood loss,and complications were recorded.Japanese Orthopedic Association (JOA) scoring system was used to evaluate neurologic function preoperatively and at one year postoperatively.Results Operation lasted for average 98 minutes and intraoperative blood loss averaged 110 ml.Injuries on esophagus,nerve and vertebral arteries as well as leakage of cerebrospinal fluid were not observed in operation.All patients received a follow-up of 12-31 months.JOA score was increased from preoperative 9.8 points to 15.8 points at one year postoperatively,with improvement rate of 83％.Bone fusion and satisfactory internal fgxation were achieved in all patients.Hypoglossal nerve injury symptom was found in two patients postoperatively and was recovered two months later.Conclusion Anterior atlantoaxial transarticular screw fixation is an effective treatment for atlantoaxial instability. Key words: Spinal injuries; Atlanto-axial joint; Fracture fixation, internal; Anterior approach

Comparison of the anatomic risk for vertebral artery injury associated with percutaneous atlantoaxial anterior and posterior transarticular screws

As a minimally invasive spine surgery, percutaneous atlantoaxial fixation techniques using anterior transarticular screw (ATS) and posterior transarticular screw (PTS) have promising clinical results. However, transarticular screw fixation is technically demanding and carries a potential risk of iatrogenic vertebral artery (VA) injury. There were no available data comparing the anatomic risk of VA injury associated with these screws. To evaluate the trajectories of percutaneous atlantoaxial ATS and PTS through three-dimensional (3D) computerized tomography. To compare the anatomic risk of VA injury between percutaneous ATS andPTS. Sixty patients ranged in age from 19 to 75 years (mean, 45.08 years) and included 35 men and 25 women. Image measurement of C2 isthmus height and C2 isthmus width and the distance between the medial-most superior articular facet to the medial-most edge of the VA groove of the C2 (D). Sixty consecutive patients (in total) with lower cervical lesions were evaluated through 3D images reconstructed by a rapid 3D system. The maximum possible diameters of the percutaneous atlantoaxial ATS and PTS trajectories were compared and examined. Mean, range, and standard deviations for each type of screw, for left and right trajectories, and for men and women were calculated from 120 percutaneous atlantoaxial ATS and PTS measurements through SPSS. The maximum mean diameter differed significantly between the trajectories of 120 percutaneous atlantoaxial ATS and PTS. For screw trajectories ≤3.5 mm in diameter, 19.2% of the PTS trajectories were judged as risky, whereas all the anterior ones were judged as safe. From an anatomic perspective, percutaneous ATS fixation poses less anatomic risk of VA injury than percutaneous PTS fixation. As an alternative surgical therapy for atlantoaxial subluxation, percutaneous ATS fixation may play a more important role in the future.

3D-CTA multi-plane measurements and clinical study on anterior C1-C2 transarticular screw fixation

Objective To investigate screw path safety and clinical efficacy assessment of anterior C1-C2 transarticular screw fixation.Methods 21 cases of traumatic atlantoaxial instability were treated by anterior C1-C2 transarticular screw fixation and followed up,After operation,X-ray and CTA are examed.With the application of 3D-CTA and the AW three-dimensional measurement software,the measurement of the angle of the screw placement and the distance between the screw and the vertebral artery as well as spinal canal at different plane is accessible and used for statistical analysis.Results All the cases with the placement of the cancellous bone screw of which the length is froml9 to 30 mm and diameter is 3.5 mm with the lateral angulation to the sagittal plane ranged from 9 ° to 22 °and the posterior angulation to the coronal plane from 12° to 29° had no trauma on vertebral artery and cervical cord during their cervical operations;20 cases were followed up for about 5 months to 9 years with an average of 20 months.Screw position after operation review showed well with no loosening or breakage and Atlantoaxial synostosis rate was 95％.The clinical symptoms were improved to different levels and patients recovered well.The minimum distance between the screw and the vertebral artery is located inside the plane of transverse foramen of atlas with an average of 5.71 mm(2.2-10.2 mm).The minimum distance between the screw and the spinal canal is located outside the plane of transverse foramen of atlas with an average of 7.36 mm(3.8-13.2 mm).Conclusion Our Research have indicated that anterior C1-C2 transarticular screw fixation is safe and effective. Key words: Atlantoaxial; Anterior path; Transarticular screw fixation; Angiography; Vertebral artery

Microendoscopic Anterior Approach for Irreducible Atlantoaxial Dislocation

Surgical techniques and preliminary results. To describe and evaluate the safety and efficacy of a new minimal invasive technique for the irreducible atlantoaxial dislocation (IADD). Endoscope has been widely used in minimal invasive spinal surgery. However, there are no clinical reports regarding anterior approach for IADD in the literature. Ten consecutive patients with IADD were treated by anterior release with microendoscopic aide and subsequently reduction, anterior transarticular screw fixation and morselized autologous bone grafts. There were 3 cases of odontoid dysplasia, 4, chronic odontoid fracture, 1, odontoid absence, 1 fasilar impression, and 1 malunion of odontoid fracture. According to Symon and Lavender's classification of disability, 6 cases were moderate disability, 3 severe nonbedbound, and 1 severe bedridden. The procedure was performed by the same surgeon (Yong-Long Chi). The new technique was performed successfully in all cases. All the patients underwent transarticular screw fixation and anterior morselized autograft fusion. The average operation time was 120 min (range, 90 to 150 min) and the mean estimated blood loss was 150 mL (range, 100 to 250 mL). Postoperative radiographs demonstrated that 9 cases restored anatomic position and 1 had partial reduction. According to the postoperative computed tomography all the screws were appropriately placed. Follow-up after surgery, longest is 16 months and minimal 8 months with a mean of 12 months, neurologic status was improved in all patients. There was no loss of fixation and solid fusion was achieved in all cases. Surgical technique of microendoscopic anterior release, reduction, fixation, and fusion is safe and reliable minimally invasive for treating IADD.

Percutaneous anterior transarticular screw fixation for atlantoaxial instability

We reviewed the outcome of a retrospective case series of eight patients with atlantoaxial instability who had been treated by percutaneous anterior transarticular screw fixation and grafting under image-intensifier guidance between December 2005 and June 2008. The mean follow-up was 19 months (8 to 27). All eight patients had a solid C1-2 fusion. There were no breakages or displacement of screws. All the patients with pre-operative neck pain had immediate relief from their symptoms or considerable improvement. There were no major complications. Our preliminary clinical results suggest that percutaneous anterior transarticulation screw fixation is technically feasible, safe, useful and minimally invasive when using the appropriate instruments allied to intra-operative image intensification, and by selecting the correct puncture point, angle and depth of insertion.