Transarticular Screw Placement Research Articles

Atlas Morphometry: A Radiologic- Anatomical Study

Abstract Introduction: Atlas is an atypical cervical vertebra with unique anatomy and related to many vital structures. Any surgical intervention at this level, especially transpedicular and transarticular screw placement, requires in detail assessment of the structure of the atlas. Certain measurements considered surgically important were measured on computerized tomography (CT) scans and compared with corresponding measurements on dry bones. Methodology: The study was carried out in KVG Medical College and Hospital, Sullia, including 100 CT scans of 43 females and 57 males with a mean age of 31.4 years and 40 dried atlas vertebrae available in the Department of Anatomy. Lengths and widths of superior and inferior articular facets were measured on both CT scans and dry bones and compared. Length, width, and heights of lateral masses, along with height below the posterior arch (HBPA), maximum medialization and cranialization angles were assessed on CT scans. The mean, standard deviation, and significance of differences were calculated using an independent t-test. Results: Mean value and standard deviation were calculated for the measured parameters. Superior and inferior facet measurements were compared between CT scan images and dry bones and no significant difference was found. Conclusion: Morphometric measurements of atlas on CT images are useful for planning of screw fixation surgeries, particularly to avoid injury to vital structures. Values of measurements, especially maximum medialization angle, maximum cranialization angle, and HBPA, are in agreement with other studies and are proposed to be included as part of preoperative workup.

Different C2 screw placement techniques with mobilization of the vertebral artery in high-riding vertebral artery cases: Cadaver dissection.

In neurosurgery, posterior approaches intended at the craniovertebral junction are frequently used. The most popular procedures for treating upper cervical instability are C1 lateral mass, C2 pedicle, and C1-C2 transarticular screw stabilization. Due to their proximity to neural structures and the presence of the high-riding vertebral artery (VA), these techniques are complicated. The risk of VA damage can be decreased by mobilizing the VA. Using cadaveric specimens in this study was aimed to demonstrate C2 pedicle and C1-C2 transarticular screw placement with VA mobilization and a novel C2 inferior corpus screw placement technique. In this study, twelve adult cadaveric specimens and two adult dry cadaveric C2 bones were used with the permission and decision of the University Research Ethics Committee. Colored silicone was injected into the arteries and veins of these twelve cadaveric specimens. Then, muscle dissection was performed stepwise, and the C2 vertebrae of the cadavers were revealed with a surgical microscope. Each specimen and entire stages of the dissections were recorded photographically. After cadaver dissections, screw placement was performed with three different techniques. Finally, radiological imaging was done with fluoroscopy. After dissection, the lateral mass of the C2 vertebra was observed, and lateral to it, the transverse process and foramen were detected with the help of a hook. Next, the posterior wall of the VA groove was removed using a 1 mm thin plate Kerrison rongeur until the VA loop could partially be observed the VA. This enables us to find the top of the loop of the VA and mobilize it inferiorly using a dissector. Following this step, the C1-2 transarticular, C2 pedicle, and the novel C2 inferior corpus screw placement can be performed safely by directly visualizing the artery. Due to the nearby neurologic and vascular structures, placing the C2 pedicle and C1-2 transarticular screw is a challenging procedure, especially in high-riding VA cases. However, it is possible to place the C2 pedicle, C1-2 transarticular, and novel C2 inferior corpus screw after the mobilization of the VA. This study aimed to show all of them together on a cadaver for the first time, to understand the anatomy of the C2 vertebra, and to use screw placement techniques to minimize the risk of complications.

Referencing for anterior atlantoaxial trans-articular osteosynthesis: a radiological study and proposal of a decisional algorithm.

Anterior trans-articular C1-C2 screw placement can be considered as a surgical alternative in different conditions affecting the atlantoaxial region. While its rigidity is similar to posterior Magerl and Harms techniques, it also provides some surgical advantages. However, the literature lacks papers exhaustively describing indication criteria, surgical steps, and pitfalls. This is a radiological study on 100 healthy subjects. Thin-layer CT scans of the craniovertebral junction were retrieved from the institutional database. The coronal inclination of the C1-C2 joint rim and the depth of the entry point of the screw with respect to the anterior profile of C2 were measured. The antero-posterior and the medio-lateral surgical corridors for the screw placement, and the wideness of the target area on the upper surface of C1 were also measured. The multivariate analysis showed that the coronal inclination of the C1-C2 articular joint rim strongly influences the surface extension of the C1 target area; the depth of the entry point and the C1-C2 articular rim inclination seem to be independent factors in influencing both the medio-lateral and the antero-posterior surgical corridors wideness. A decisional algorithm on whether to perform an anterior or posterior approach to the atlantoaxial region was also proposed. We can conclude that, as much as the C1-C2 articular rim is tending to the horizontal line, and as deeper is the entry point of the screw on the anterior profile of C2, as easier the anterior C1-C2 trans-articular screw placement will result.

Versatility of Anterior Approach for Management of Odontoid Fractures

Background Data: Odontoid fractures comprise about 20 % of all cervical fractures. Odontoid fractures have been classified according to Anderson and D'Alonzo classification system. Anterior and posterior approaches can manage odontoid fractures, and various schools of thought favor both approaches. This article highlights the versatility of the anterior approach to treat varying types of odontoid fractures. Indications for surgical management include the age of the patient more than 55 years, displacement of fracture fragment more than 4 mm, nonunion, and disruption of the transverse atlantal ligament. The odontoid has 55% less trabecular bone than the body of the axis. This trabecular bone is required for callus formation and bone healing; hence, nonunion of type 2 fractures is more common than that of type 3 fractures. Purpose: To present different anterior methods of managing odontoid fractures. Study Design: A case report. Patients and Methods: In the present report, we have deployed three different techniques using the anterior approach for the fixation of the odontoid fracture. Plate and screw fixation is far more effective as the odontoid is a non-weight-bearing structure, and it compresses the fragments for a better union. Results: In all three cases, we found good evidence of radiographic healing of the fracture in the postoperative period with no significant immediate or delayed complications. Neck mobility was limited to some extent with the placement of transarticular screws but was preserved completely in the other two patients. Conclusion: Anterior cervical approaches in odontoid fractures carry safe and promising results in achieving solid fusion, less operative risk to vital structures, and preserving the cervical range of motion. The learning curve is also shallow compared to posterior approaches. (2022ESJ262)

Versatility of Anterior approache for management of Odontoid fractures

Odontoid fractures comprise about 20 % of all cervical fractures. Odontoid fractures have been classified according to Anderson and D’Alonzo classification system. Odontoid fractures can be managed by both anterior and posterior approaches and there are various schools of thought favouring both approaches. This paper attempts to highlight the versatility of the anterior approach to treat varying types of odontoid fractures. Indications for surgical management include age of the patient more than 55 years , displacement of fracture fragment more than 4mm, non union and disruption of transverse atlantal ligament. The odontoid has 55% less trabecular bone than the body of axis. This trabecular bone is required for callus formation and bone healing , hence non-union of type 2 fractures is more common as compared to type 3 fractures. In the present report , we have deployed 3 different techniques using the anterior approach for fixation of odontoid fracture. Plate and screw fixation is far more effective as the odontoid is a non-weight bearing structure, and it compresses the fragments for better union. In all the 3 cases , we found good evidence of radiographic healing of the fracture in the post-op period with no significant immediate or delayed complications. Neck mobility was limited to some extent with placement of transarticular screws ,but was preserved completely in the other two patients. Based on our experience with these cases , we strongly advocate that successful reduction of the fracture with adequate fusion can be achieved by using anterior approaches without restricting neck mobility (plate and screw fixation or odontoid screw fixation) and the same approach can be used to fix the C1 and C2 facet joints in case of irreducible/incompetent transverse ligament injuries.

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.

Prevalence of high-riding vertebral arteries and narrow C2 pedicles among Central-European population: a computed tomography-based study

High-riding vertebral artery (HRVA) and narrow C2 pedicles (C2P) pose a great risk of injuring the vessel during C2 pedicle or transarticular screw placement. Recent meta-analysis revealed a paucity of European studies regarding measurements and prevalence of these anatomical variants. Three hundred eighty-three consecutive cervical spine CT scans with 766 potential screw insertion sites were analyzed independently by two trained observers. C2 internal height (C2InH), C2 isthmus height (C2IsH), and C2P width were measured. Kappa statistics for inter- and intraobserver reliability as well as for inter-software agreement were calculated. HRVA was defined as C2IsH of ≤ 5 mm and/or C2InH of ≤ 2 mm. Narrow C2P was defined as C2P width ≤ 4 mm. STROBE checklist was followed. At least 1 HRVA was found in 25,3% (95% CI 21,1–29,8) of patients (16,7% of potential sites). At least 1 narrow C2P was seen in 36,8% (95% CI 32,1–41,7) of patients (23,8% of potential sites). Among those with HRVA, unilateral HRVA was present in 68,0% (95% CI 58,4–77,0), whereas bilateral HRVA in 32,0% (95% CI 23,0–41,6). No difference in terms of laterality (right or left) was seen neither for HRVA nor narrow C2P. Significant differences were found between females and males for all measurements. Each parameter showed either good or excellent inter- or intraobserver, and inter-software agreement coefficients. HRVA and narrow C2P are common findings in Central-European population and should be appreciated at the planning stage before craniocervical instrumentation. Measurements can be consistently reproduced by various observers at varying intervals using different software.

Anthropometric evaluation for surgical feasibility of C1-C2 transarticular screw stabilization in Indian population.

Study Design:This study was a radiographic observational study for C1–C2 anthropometry.Purpose:The purpose of the study was to understand the anatomic relationship of C1–C2 in view of transarticular screw (TAS) fixation, to overcome the difficulties related with TAS placement, and to minimize the technique-related complications.Materials and Methods:It was an anthropometric observational study with retrospectively obtained anatomical data of randomly selected 116 patients from a single center. The anatomical measurements such as pars width, pars height, screw trajectory, and length were evaluated on the axial, sagittal, and three-dimensional reconstructed cervical CT scan using the radiant DICOM viewer software by the two fellowship trained spine surgeons which were blind to the study group details. The intra- and interobserver reliability with regard to the measured parameters was statistically analyzed.Results:The mean age of male and female was 28 and 29 years. The average BMI was calculated to be 23.5 and 25 for males and females, respectively. The mean right pars width in males was 5.78 ± 0.93 (range: 3.1–6.5 mm), while in female, it was 5.84 ± 0.95 (range: 3.1–6.5). The mean left pars width in males was 5.95 ± 1.13 (range: 3.8–8.1 mm), while in females, it was 5.70 ± 1.18 (range: 3.7–8.1 mm). Right side mean pars height in males was 5.90 ± 1.2 (range: 3.7–9.4 mm), and in females, it was 6.11 ± 1.04 (range: 3.8–9.3 mm). Left-sided mean pars height in males was 6.0 ± 1.1 (range: 3.2–9.4 mm) as compared to females, in which it was 5.77 ± 1.23 (range: 4.1–9.3 mm). The mean lateral angulation angle in males was 9.99° ± 1.70° (8.1°–15°), while in females, it was 10.15° ± 1.73° (8.1°–15°). The mean sagittal angulation in males was 26.33° ± 3.32° (21.0°–32.80°), while in females, it was 27.18 ± 3.05 (21.0°–32.10°). The average screw length in males was 41.74 ± 5.63 (34–54.8 mm), whereas in females, it was 41.35 ± 4.77 (34–54.8 mm).Conclusion:This study provides a morphometric database which is characteristic of the C1–C2 vertebrae in the normal Indian population with regard to the anatomic feasibility of the TAS fixation for various C1–C2 pathologies. The C2 pars width and height measured in the current study can guide the selection of TAS screws in the Indian population. This study could serve in providing the baseline anatomic parameters assessed in the healthy individuals to design and develop customized screws and related implant assembly which might provide wider clinical applicability.

Axis vertebral dimensions for safe screw placement: A CT normative data analysis

IntroductionMorphometric evaluation of the pedicle and isthmus of second cervical vertebra (C2) (Axis) is extremely vital before contemplating any surgical stabilization involving the Craniovertebral region, in view of its proximity to the vertebral artery and the cervical nerve root. The dimensions of pedicles and isthmuses in C2 vary between individuals and there is paucity of data in the Indian population. This study strives to measure the average pedicle and isthmus dimensions in a sample of population, which would enable selection of screws with safest diameters to be used in C2; thereby avoiding injury to adjacent neurovascular structures. Materials and methodsOne Hundred patients in the age group between 18 and 70 years who underwent CT scan of head and neck region were included in the study. The aim of this study was to assess the anatomic suitability of transarticular and pedicle screw placement in Axis vertebrae of Indian population and determine the maximum safe diameter for screw placement. The following parameters were measured in millimeters: Pedicle width, Pedicle angle, Internal height and Isthmic height. ResultsThe Mean maximum diameter of potential pedicle screw was 4.99 ± 1.1 mm for the right side with the left side being slightly wider at 5.20 ± 1.16 mm. Twenty eight (28%; 56 out of 200 pedicles) had a measurement < 4.5 mm. The internal height in sagittal images representing the pedicle height was found to be 4.79 ± 0.96 mm on the right side and 4.75 ± 1.04 mm on the left side. Sixty five (65) out of 200 pedicles (32.5%) had measurements < 4.5 mm in sagittal plane. The Mean maximum diameter of potential Transarticular screw (outer diameter of isthmus) was 5.05 ± 0.78 mm for the right side and 5.18 ± 0.84 mm on the left side. DiscussionIsthmic height < 4.5 mm could potentially violate the vertebral foramen when a 3.5 mm screw is used. In our study 22.5% isthmuses were narrow (<4.5 mm). The mean maximum safe diameter for a potential transarticular screw in the present study was 5.11 mm. Though our patients had smaller isthmus dimensions compared with literature, 77.5% of C2 could take a 4 mm transarticular screw quite comfortably considering the 0.5 mm margin on either side. In the present study, 28% of pedicles were found to be inappropriately sized (<4.5 mm) to accommodate the standard 3.5 mm screw. The mean maximum diameter of a potential pedicle screw in our study was 5.09 mm; and in 72% of patients a 4 mm screw could be placed with confidence. Though our patients on an average can accommodate a 4 mm screw comfortably, we suggest a protocol of obtaining CT measurements of C2 prior to operative intervention for identifying those individuals at risk of neurovascular injury; 22.5% for transarticular screw and 28% for pedicle screw.

The C2 "Parsicle" Screw: Introduction of a Novel Posterior Surgical Technique For Upper Cervical Fixation.

The instrumentation of C2 is technically challenging given the anatomic complexity of the upper cervical spine. Although the placement of C2 pedicle screws may be safer than transarticular screw placement, the inconsistent location of the transverse foramen and vertebral artery precludes placement of such screws in up to 26% of patients. In cases where vertebral artery anatomy prevents the safe placement of a pedicle screw, a pars screw is an excellent alternative. However, pars screws must stop short of the vertebral foramen, limiting the typical length of these screws to only 14-18 mm. The associated purchase and rigidity are compromised compared with the pedicle screw. A modified C2 fixation technique was developed by our group which we have named the C2 "parsicle" screw reflecting the hybrid nature of the screw incorporating aspects of pars and pedicle screw fixation.

Can the position of the vertebral artery be predicted on a lateral view X-ray of the craniovertebral junction? A radiological anatomy study.

Background:The most feared complication while inserting C2 screws is vertebral artery injury. This article proposes predicting the position of the vertebral artery on a true lateral X-ray of the axis vertebra from the background information acquired from the computed tomography (CT) scan utilizing fluoroscopy.Methods:Spiral CT scans of 33 C2 vertebrae were performed utilizing a 16-slice CT scanner lateral X-rays of C2 were then obtained before and after painting the vertebral artery grooves with barium. The space available for transarticular and C2 pedicle screw insertion above the vertebral artery groove in the isthmus was then calculated as a ratio for both X-rays and CT scans.Results:There was no statistically significant difference between the (mean) ratios calculated by CT scan and X-rays regarding the space available for transarticular and C2 pedicle screw insertion (left side: 0.3894 vs 0.3897; right side: 0.3892 vs 0.3925; P > 0.05). The Kappa test revealed that CT scan and X-ray findings were in agreement in majority of the bones (left side: n = 24, 72.7%, right side: n = 22, 73.3%; P < 0.05).Conclusion:A thorough understanding of a true lateral view X-ray based on background information extracted from three dimensional CT scans helps predict the highest point of the vertebral artery groove. This proves useful for placement of C2 transarticular and pedicle screws during regular “open” and “minimally invasive” spine surgery.

Posterior atlantoaxial fusion using a C2 transverse foramen-penetrating screw: A technical note.

Background:Although recent development of screw instrumentation techniques for rigid fixation of the atlantoaxial joint has increased surgical options, patients in whom screws of any type cannot be safely placed are sometimes encountered. We present a unique surgical technique for C1-2 transarticular screw placement utilizing a novel trajectory.Methods:A 35-year-old male with a history of Down's syndrome and cognitive dysfunction with hyperkinesis spontaneously developed rapid onset of tetraparesis and gait disturbance. Radiographs of the cervical spine revealed atlantoaxial subluxation (AAS) that could not be reduced. Computed tomography (CT) of the head showed multiple subacute cerebral infarctions in the territory of the right vertebral artery (VA). Three-dimensional CT angiography of the craniovertebral junction additionally confirmed right VA occlusion at the C2/3 level, a left C2 origin of the posterior inferior cerebellar artery, and hypoplasia of the bilateral C2 pedicles/C2 lamina. Because traditional screw-placement was not feasible, we performed a unique atlantoaxial fusion utilizing a C2 transverse foramen-penetrating screw with iliac bone grafting performed under neuronavigation.Results:The postoperative course was uneventful, and the patient regained the ability to ambulate, returning to his previous level of function. The CT of the cervical spine 12 months postoperatively showed rigid bony C1-C2 fusion, without recurrence of stroke.Conclusion:We introduced a novel C1-C2 transarticular screw-placement technique in which the trajectory went through the ipsilateral VA foramen due to already extent VA occlusion.

A novel computed method to reconstruct the bilateral digital interarticular channel of atlas and its use on the anterior upper cervical screw fixation.

Purpose. To investigate a novel computed method to reconstruct the bilateral digital interarticular channel of atlas and its potential use on the anterior upper cervical screw fixation.Methods. We have used the reverse engineering software (image-processing software and computer-aided design software) to create the approximate and optimal digital interarticular channel of atlas for 60 participants. Angles of channels, diameters of inscribed circles, long and short axes of ellipses were measured and recorded, and gender-specific analysis was also performed.Results. The channels provided sufficient space for one or two screws, and the parameters of channels are described. While the channels of females were smaller than that of males, no significant difference of angles between males and females were observed.Conclusion. Our study demonstrates the radiological features of approximate digital interarticular channels, optimal digital interarticular channels of atlas, and provides the reference trajectory of anterior transarticular screws and anterior occiput-to-axis screws. Additionally, we provide a protocol that can help make a pre-operative plan for accurate placement of anterior transarticular screws and anterior occiput-to-axis screws.

Atlantoaxial fusion assisted by 3D fluoroscopy-based navigation

C1–2 fusion is indicated in atlantoaxial instabilities. C1–2 transarticular screws described by Magerl and Seemann [1] are an effective option for durable fusion. Vertebral artery injuries may occur in 4 % of patients undergoing transarticular screw placement. One of the causes of vertebral artery injuries might be the abnormal trajectory of the artery in the pars of C2, whereby the artery might cross the path of the transarticular screw trajectory. Preoperative CT scan is a suitable method to assess VA trajectory. In case of contraindication for transarticular screws, the alternative would be to use the lateral mass of C1 at that level and the pars of C2 for the construct. To optimise and facilitate screw placement, 3D fluoroscopy-based navigation has been used.

Deviation Analysis of C1–C2 Transarticular Screw Placement Assisted by a Novel Rapid Prototyping Drill Template

Cadaveric study. The aim of this study was to develop and validate the accuracy of a novel navigational template for C1-C2 transarticular screw (C1C2TAS) placement in cadaveric specimens. Currently, C1C2TASs are primarily positioned using a free-hand technique or under fluoroscopic guidance. Screw placement is challenging owing to the small size of the C2 isthmus, which places technical demands on the surgeon. Screw insertion carries a potential risk of neurovascular injury, magnifying the importance of using a precise technique for screw insertion. Computed tomography (CT) scans with 0.625-mm wide cuts were obtained from the 32 cadaveric cervical specimens. The CT data were imported into a computer navigation system. We developed 32 three-dimensional drill templates, which were created by computer modeling using a rapid prototyping technique based on the CT data. We constructed drill templates using a custom trajectory for each level and side based on specimen anatomy. The drill templates were used to guide establishment of a pilot hole for screw placement. The entry point and angular direction of the intended screw positions and inserted screw positions were measured by comparing postoperative and preoperative images after the coordinate axes were synchronized. The average displacement of the entry point of the left and right C1C2TAS in the x-, y-, and z-axis was 0.13±0.90 mm, 0.50±1.50 mm, and -0.22±0.71 mm on the left, and 0.21±1.03 mm, 0.46±1.55 mm, and -0.29±0.58 mm on the right. There was no statistically significant difference in entry point and direction between the intended and actual screw trajectory. The small deviations seen are likely due to human error in the form of small variations in the surgical technique and use of software to design the prototype. This technology improves the safety profile of this fixation technique and should be further studied in clinical applications.

Deviation factors of posterior atlantoaxial transarticular screw placement assisted by rapid prototyping drill templates

Objective To validate the safety and accuracy of a rapid prototyping drill template (RPDT) for posterior atlantoaxial transarticular screw placement and analyze factors for screw deviation.Methods Twelve normal cadaveric cervical spines were examined using 64 slice CT with 1-mm thick scan and data in Dicom format were recorded.After data was processed using software Mimics 10.01 for three-dimensional (3-D) model reconstruction,computer-assisted design of optimum trajactory for atlantoaxial transarticular screw placement was worked out and made into a drill template,where the surface was created as the inverse of axial posterior surface.The drill template was materialized in a rapid prototyping machine and used to place the screws.After surgery,the position of posterior atlantoaxial transarticular screw was evaluated by X-ray and CT scan.Screw entry point,angle and orientation of the optimal and actual trajactory were determined after fitting the position of the pre-operative and post-operative specimen in computer software and the redefining the 3-D coordinate axis.Results Twenty-four screws were implanted with no cortex perforation.Depth of the optimum save screw trajectory for atlantoaxial transarticular fixation was (37.34 ± 2.31) mm on the left side and (37.11 ± 2.21) mm on the right side.Introversion angles of the optimum save screw trajectory was 0° in both sides,but the actual angle was (0.15 ±0.58)°on the left side and (0.11 ±0.46)°on the right side.Elevation angle of the optimum save screw trajectory was (49.35 ± 1.62) °on the left side and (48.83 ± 1.83) ° on the right side,but the actual angle was (49.29 ± 1.68) °and (49.10 ± 1.45) °respectively.Average displacement of screw entry point in the x,y and z axis was respective (0.21 ±0.65) mm,(0.69 ± 1.48) mm and (0.39 ±0.11) mm on the right side,while (0.19 ± 0.66) mm,(0.53 ± 1.45) mm and (0.38 ± 0.13) mm on the left side.There were no statistically significant differences in deviation levels of entry point and orientation between the optimum and actual screw trajectory (P ＞ 0.05).Conclusions Causes for deviation in RPDT-assisted placement of atlantoaxial transarticular screw are mainly intrinsic factors of the hardware and software and human factors in the operation.RPDT is easy in operation and has individualized design,which greatly improves the accuracy of screw placement and reduces screw deviation.RPDT can be widely used in clinical practice. Key words: Spinal injuries; Cervical vertebrae; Transarticular screws

Neuronavigation in minimally invasive spine surgery

Parallel advancements in image guidance technology and minimal access techniques continue to push the frontiers of minimally invasive spine surgery (MISS). While traditional intraoperative imaging remains widely used, newer platforms, such as 3D-fluoroscopy, cone-beam CT, and intraoperative CT/MRI, have enabled safer, more accurate instrumentation placement with less radiation exposure to the surgeon. The goal of this work is to provide a review of the current uses of advanced image guidance in MISS. The authors searched PubMed for relevant articles concerning MISS, with particular attention to the use of image-guidance platforms. Pertinent studies published in English were further compiled and characterized into relevant analyses of MISS of the cervical, thoracic, and lumbosacral regions. Fifty-two studies were included for review. These describe the use of the iso-C system for 3D navigation during C1-2 transarticular screw placement, the use of endoscopic techniques in the cervical spine, and the role of navigation guidance at the occipital-cervical junction. The authors discuss the evolving literature concerning neuronavigation during pedicle screw placement in the thoracic and lumbar spine in the setting of infection, trauma, and deformity surgery and review the use of image guidance in transsacral approaches. Refinements in image-guidance technologies and minimal access techniques have converged on spinal pathology, affording patients the ability to undergo safe, accurate operations without the associated morbidities of conventional approaches. While percutaneous transpedicular screw placement is among the most common procedures to benefit from navigation, other areas of spine surgery can benefit from advances in neuronavigation and further growth in the field of image-guided MISS is anticipated.

A Comparison C1–C2 Transarticular Screw Placement After Self-Education and Mentored Education of Orthopaedic Residents

Prospective randomized trial. This study will provide preliminary data on whether residents can be "self-taught" and to what extent a lecture, demonstration, and coaching can improve skills and knowledge. Practice-based learning is an essential competency in Accreditation Council for graduate Medical Education-accredited residencies. Little has been done to demonstrate whether residents can be self-taught or benefit from mentoring in understanding and performing difficult surgical tasks. A written test was given to orthopedic residents on C1-C2 transarticular screw placement. They were then provided reading on C1-C2 transarticular screw placement. Residents were then divided into a "self-directed learning" group and a "mentored learning" group. All residents then performed the technique on models, with the "mentored" group receiving a lecture and coaching from the mentor. The models were analyzed for technique errors and the previous test was administered again as a posttest. The test and screw placement were repeated 4 months later. Residents without mentoring had an average improvement of 4.5 points, those with mentoring had average improvement of 8.6 points (P=0.0068). The screw placement technique error rate for the nonmentored group (n=8) was 2.55, and for the mentored group (n=9) was 1.47 (P=0.004). Sixteen residents completed the delayed test, 7 from the nonmentored groups and 8 from the mentored group. Nine residents were able to repeat the screw placement technique 4 months after the initial test and screw placement, 3 nonentored, and 6 mentored. Although there were some trends toward the mentored group having better retention, neither knowledge nor skill was statistically different. This preliminary trial seems to indicate that residents provided a lecture and guided technical instruction will obtain knowledge and perform procedures better than those that do not. Conclusions based upon Post Graduate year, motivation, and interest in spine surgery could not be made.

The Study on Comparison of 3 Techniques for Transarticular Screw Placement in the Lower Cervical Spine

Prospective comparative study. To compare 3 techniques for transarticular screw placement in the lower cervical spine. The transarticular screw is found to have satisfactory biomechanical stability. According to current studies, there are several techniques for the placement of transarticular screws in the lower cervical spine. Although several techniques are available for transarticular screw implantation in the lower cervical spine, only a few studies in the literature have been carried out to compare these techniques. The techniques of transarticular screw placement used by Takayasu (group A), Dalcanto (group B), and Klekamp (group C) were applied in 24 cervical specimens. The facet fractures, the encroachment of the cervical anterior branches of nerve roots and vertebral arteries and the failure of the screws to go through the facets were observed and analyzed. One hundred ninety-two transarticular screws were implanted on both sides in 24 cervical cadavers, 64 for each group. There were 25 splits of inferior facets in group B, 2 splits in group C, and none in group A. Thirty-six screws encroached the vertebral arteries in group A, none in groups B and C. Forty anterior branches of lower cervical nerve roots were involved in group A, 5 in group B, and 3 in group C. Although all screws went through facets in the study except for 5 in group A, there were no significant differences between each group (χ(AB)2 = 3.33, P > 0.05; χ(AC)2 = 3.33, P > 0.05). There is a high risk of injury to the anterior branch of the cervical nerve roots and vertebral artery if the screws were too long, and the Takayasu technique was used. However, the rate of facet splitting is high if the Dalcanto technique was applied. Klekamp's technique is recommended.

Computed tomography–based determination of a safe trajectory for placement of transarticular facet screws in the subaxial cervical spine

Placement of transarticular facet screws is one option for stabilization of the subaxial cervical spine. Small clinical series and biomechanical data support their role as a substitute for other posterior stabilization techniques; however, the application of transarticular facet screws in the subaxial cervical spine has not been widely adopted, possibly because of surgeon unfamiliarity with the trajectory. In this study, the authors' objective is to define insertion points and angles of safe trajectory for transarticular facet screw placement in the subaxial cervical spine. Thirty fine-cut CT scans of cervical spines were reconstructed in the multiplanar mode and evaluated for safe transarticular screw placement in the subaxial cervical spine (C2-3, C3-4, C4-5, C5-6, C6-7). As in placement of lateral mass screws, the vertebral artery and exiting nerve root were bypassed posterolaterally. The entry point was set 1 mm medial and 1 mm caudal to the center of the lateral mass. From this entry point, the sagittal angulation was set to traverse the facet joint plane approximately perpendicularly. For the axial angulation, the exit point was set posterolaterally to the transverse process. After ideal insertion angles and screw lengths were identified, the trajectory was simulated on CT scans of 20 different cervical spines to confirm safe screw placement. The mean optimal mediolateral insertion angles (± SD) were as follows: 23° ± 5° at C2-3; 24° ± 4° at C3-4; 25° ± 5° at C4-5; 25° ± 4° at C5-6; and 33° ± 6° at C6-7. The mean sagittal insertion angles measured to the sagittal projection of the facet joint space were as follows: 77° ± 10° at C2-3; 77° ± 10° at C3-4; 80° ± 11° at C4-5; 81°± 8° at C5-6; and 100° ± 11° at C6-7. The mean trajectory lengths were 15 ± 2 mm at C2-3; 14 ± 1 mm at C3-4; 15 ± 1 mm at C4-5; 16 ± 2 mm at C5-6; and 23 ± 4 mm at C6-7. Simulation of these insertion angles on 20 different cervical spine CTs yielded a safe trajectory in 85%-95% of spines for C2-3, C3-4, C4-5, C5-6, and C6-7. The calculated optimal insertion angles and lengths for each level may guide the safe placement of subaxial cervical transfacet screws.