Thoracic Pedicle Screw Research Articles

Posterior Cervicothoracic Stabilization Using Tapered Rods

Background Data: The cervicothoracic spine is a junction area with complex biomechanics. A variety of disorders affect this region, rendering it unstable. Numerous posterior constructs have been evaluated. The clinical efficacy of a screwrodsystem utilizing tapered (dual-diameter) rods in cervicodorsal stabilization is still not evident. Purpose: Our aim is to evaluate the clinical efficacy of dual diameter rods (5.5– 3.5mm taper), connecting 3.5-mm cervical lateral mass screws/pedicle screws and 5.5-mm thoracic pedicle screws used to instrument across the cervicothoracic junction for a variety of pathologies. Study Design: A retrospective descriptive clinical case study. Patients and Methods: The authors retrospectively reviewed their archive between February 2011 and February 2015, and ten patients who were operated upon due to cervicothoracic junction pathologies were included. All patients underwent surgical treatment by posterior instrumentation utilizing tapered rods. The cases were periodically followed up. Results: There were six men and four women included in the study, with a mean age of 40 years (range 21–62 years). There were five cases of trauma, two cases of tuberculosis and three cases of spine metastasis. Seven patients experienced marked improvement of their preoperative weakness according to Frankel grades of paraplegia. All patients showed stable cervicodorsal junction with fusion after one year. Three patients suffered postoperative wound infection. Conclusion: Tapered rods are an excellent and a viable option to connect screws to stabilize cervicothoracic junction. (2015ESJ089)

Assessment of Medial Malpositioning during Thoracic Pedicle Screws Placement with a Contemporary Intraoperative Neurophysiological Monitoring Method

Introduction Thoracic pedicle screws placement remains being a challenge despite modern technologies available. To assess neural integrity during these surgeries, intraoperative neurophysiological monitoring (IOM) is indicated. Motor-evoked potentials (MEP) and somatosensory-evoked potentials (SSEP) give valuable information regarding spinal cord function, and pedicle screws stimulation could evaluate medial malpositioning. However, the accuracy of thoracic pedicle screws stimulation is still controversial, using single-pulse stimulation, recording from intercostal and abdominal muscles, and with high false-positive rate. Objective This article aims to demonstrate the superiority of a recently validated IOM method by Blair Calancie, and share our experience with it. Material and Methods Prospective collected and reviewed study since March to October 2014. During T1–T12 level surgeries, we stimulated medial wall of pedicle track before screw placement with a ball-tipped probe using pulse-train stimulation, and recording from lower limbs muscles. MEP and SSEP were performed, and a postoperative computed tomography (CT) scans in all the cases. Results In 21 patients, 240 thoracic pedicle screws were analyzed. In 36 screws of them (17.6%), a medial pedicle breach was informed, and 19 of 36 were redirected correctly more lateral; 8 of 36 pedicles were skipped; and 7 of 36 screws were placed regardless IOM warning criteria (3.4%), with a CT scan confirming medial misplacement > 2 mm. Fluoroscopy and manual pedicle palpation evinced a medial breach in 3 of 36 and 1 of 36 trajectories, respectively, but after pedicle track stimulation was done and informed. We did not observe any MEP or SSEP change during all these screws. Fortunately, no patients developed a new neurological deficit. CSF leak was not reported in this series. Our sensitivity with this method was 93.9%, specificity 97.6%, positive predictive value 86.1%, and negative predictive value was 99.0%. Conclusion Pulse-train stimulation of pedicle track before screw placement has huge superiority over traditional IOM techniques, avoiding spinal cord encroachment and new neurological deficit. This IOM method is highly accurate during thoracic pedicle screws placement.

A Case-Controlled Study Evaluating the Effect of Cone Beam CT (O-Arm) Imaging and Navigation on Pedicle Screw Placement in Adult Spinal Surgery

Introduction Intraoperative CT and navigation systems (NAV) may provide an opportunity to improve precision and accuracy of pedicle screw placement, and in so doing, improve patient outcomes. Our study aimed to examine the efficacy and safety of NAV for pedicle screw placement in elective and emergent adult spinal surgery cases. We currently use this technology for surgery in all primary diagnoses of the adult spine including trauma, degenerative, deformity, revision surgery, and tumor. We sought to examine the efficacy and safety of NAV for pedicle screw placement in this broad range of surgical spinal cases. Materials and Methods All patients who underwent pedicle screw fixation with O-arm imaging and StealthStation navigation between January 2008 and December 2012 were analyzed. Patients were matched with historic case controls (non-NAV). Diagnosis, number, timing, and degree of screw malposition were recorded. Any screw with pedicle breach greater than 0 mm was recorded as misplaced. All patients had a minimum follow-up of 1 year. Quantitative statistical analysis compared screw placement between NAV and non-NAV cases. Results A total of 253 patients met the inclusion criteria by primary diagnosis in the NAV group. Diagnosis categories were not significantly different between groups (trauma 20%, oncology 12%, inflammatory arthropathy 2%, scoliotic deformity 23%, spondylolisthesis 25%, degenerative 13%, and miscellaneous other diagnoses 5%, p = 0.269). Mean number of screws placed was 11.4 in the NAV group and 10.8 in the non-NAV group ( p = 0.299) with misplaced screws in 78 patients (31%) in the NAV group and 105 (42.2%) in the non-NAV group ( p < 0.009). Intraoperative screw revision rates were equivalent between groups (21 in the NAV group and 20 in the non-NAV group, p = 1); however, the number of screws revised during the same admission was significantly different (2 in the NAV group and 9 in the non-NAV group, p < 0.004). Likewise, late postoperative surgical revision rates were significantly different with six patients requiring readmission for screw revision within 1 year in the non-NAV group compared with none in the NAV cohort ( p < 0.008). All categories of primary diagnosis demonstrated reduction ( p < 0.05) in the rate of screw malposition. Screw revision rates for individual diagnoses, however, intraoperatively or early postoperatively were not different between groups with the exception of major adult deformity ( p < 0.002). Thoracic trauma pedicle screws ( p < 0.005) and pedicle screws for deformity ( p < 0.001) were most likely to be malpositioned. Traumatic cervical screws were most likely to require subsequent admission and screw revision. Rates of adverse events were not significantly different between groups. Reoperation for instrumentation failure was significantly different (0 cases in the NAV group and 7 in the non-NAV cohort, p < 0.008). Conclusion Intraoperative 3D imaging with navigation provides an equally safe and more accurate and precise tool for pedicle screw placement than traditional techniques in adult spine surgery. Our data demonstrated a difference in the need for revision screw placement, particularly noted for deformity procedures. Considering the serious consequences of deviant screw position, the use of this technology provides a promising tool to increase patient safety and accuracy for hardware placement.

Freehand Thoracic Pedicle Screw Placement Techniques: A Comprehensive Review of Safety and Efficacy

Introduction Freehand techniques for thoracic pedicle screw placement have gained popularity as they reduce intraoperative radiation exposure and overall operative time. The goal of this work is to present our technique as well as systematically and comprehensively review the published literature on this topic. Material and Methods A PubMed search from 2001 to 2014 was performed, focusing on clinical studies that describe technical aspects of freehand thoracic pedicle screw placement. Cadaveric studies were excluded. Results The search yielded 15 studies and, of those, only 5 described technical aspects of thoracic screw placement. Definitive entry points were represented in four studies, and in one study entry point varied by a thoracic level. There were no definitive guidelines for sagittal or an axial trajectory with an exception of a one study in which sagittal trajectory was based on suboptimally visualized endplate. In our technique, we identified a uniform entry point for each thoracic level that is 3 mm caudal to the junction of the transverse process and the lateral margin of the superior articulating process. The sagittal trajectory is orthogonal to the dorsal curvature of the corresponding spine. Conclusion Freehand thoracic pedicle screw placement is safe and effective based on published reports in the literature. Few studies, however, detail the technique and provide meaningful instructions for trainees. We are hopeful that precise parameters that rely on less variability in entry point and trajectories will facilitate trainee education.

Effectiveness and Safety of Convex Derotation in Thoracic Adolescent Idiopathic Scoliosis

Introduction Concave derotation is the traditional correction maneuver in adolescent idiopathic scoliosis surgery. However, the positioning of thoracic pedicle screws at the concave side of the curve can be quite challenging, because of the small pedicle size and the wide variation in its morphological characteristics, due to the vertebral dystrophy observed in scoliotic patients. Then, to reduce risks of neural damages and ensure the same strength of derotation maneuver, a convex derotation through an all-level pedicle screws convex instrumentation can be performed. We report perioperative and 1-year results in a consecutive series of patients treated by convex derotation through an all-level pedicle screws convex instrumentation. Materials and Methods From January 2013 to January 2014, we surgically treated 24 consecutive patients (18 female patients and 6 male patients, mean age 13 years) affected by thoracic adolescent idiopathic scoliosis (Lenke Type 1, 19 patients, and Lenke Type 2, 5 patients). Mean preoperative Cobb angle was 56 ± 6 degrees in Lenke Type 1 group and 51 ± 4 degrees plus 32 ± 3 degrees in Lenke Type 2 group. We performed a posterior access only in patients using polyaxial pedicle screws at each level on the convex side and two sublaminar acrylic loops (universal clamps) at the upper instrumented vertebra, to reduce the stiffness of the construct. Derotation maneuver was performed on the convex prebent rod. In all cases, motor-evoked potential monitoring was used. Mean follow-up time was 15 months. Results The average percentage of coronal correction was 76 ± 5% (mean postoperative Cobb angle 15 ± 4 degrees), with no neurological complications. Regarding the postoperative kyphosis, we observed a slight decrease in mean values compared with preoperative measurements (mean reduction of thoracic kyphosis 5 ± 2 degrees). At 1-year follow-up, no changes in coronal or sagittal plane were observed. The mean operative time was 210 ± 30 minutes, with a mean blood loss of approximately 500 ± 100 mL. Using the free-hand technique, the mean time of pedicle screws positioning in the thoracic area on the convex side was approximately 2 ± 1 minutes from T6 to T12 and approximately 4 ± 1 minutes from T3 to T5. Whenever included in the area of arthrodesis, T2 was usually instrumented with the universal clamps. Instead, T1 has never been included in the arthrodesis area. Conclusion This case-series study shows the effectiveness and safety of convex derotation in Lenke Type 1 and 2 scoliosis. The coronal correction obtained with this technique is comparable to that obtained with the traditional concave derotation. Other advantages are short operative time, low intraoperative blood loss, and, mostly, a reduced risk of neurological complications.

Additive-manufactured patient-specific titanium templates for thoracic pedicle screw placement: novel design with reduced contact area.

Image-based navigational patient-specific templates (PSTs) for pedicle screw (PS) placement have been described. With recent advances in three-dimensional computer-aided designs and additive manufacturing technology, various PST designs have been reported, although the template designs were not optimized. We have developed a novel PST design that reduces the contact area without sacrificing stability. It avoids susceptibility to intervening soft tissue, template geometric inaccuracy, and difficulty during template fitting. Fourteen candidate locations on the posterior aspect of the vertebra were evaluated. Among them, locations that had high reproducibility on computed tomography (CT) images and facilitated accurate PS placement were selected for the final PST design. An additive manufacturing machine (EOSINT M270) fabricated the PSTs using commercially pure titanium powder. For the clinical study, 36 scoliosis patients and 4 patients with ossification of the posterior longitudinal ligament (OPLL) were treated with thoracic PSs using our newly developed PSTs. We intraoperatively and postoperatively evaluated the accuracy of the PS hole created by the PST. Based on the segmentation reproducibility and stability analyses, we selected seven small, round contact points for our PST: bilateral superior and inferior points on the transverse process base, bilateral inferior points on the laminar, and a superior point on the spinous process. Clinically, the success rates of PS placement using this PST design were 98.6% (414/420) for scoliosis patients and 100% (46/46) for OPLL patients. This study provides a useful design concept for the development and introduction of patient-specific navigational templates for placing PSs.

Biomechanical Determination of Distal Level for Fusions across the Cervicothoracic Junction.

Study Design In vitro testing. Objective To determine whether long cervical and cervicothoracic fusions increase the intradiscal pressure at the adjacent caudal disk and to determine which thoracic end vertebra causes the least increase in the adjacent-level intradiscal pressure. Methods A bending moment was applied to six cadaveric cervicothoracic spine specimens with intact rib cages. Intradiscal pressures were recorded from C7–T1 to T9–10 before and after simulated fusion by anterior cervical plating and posterior thoracic pedicle screw constructs. The changes in the intradiscal pressure from baseline were calculated and compared. Results No significant differences where found when the changes of the juxtafusion intradiscal pressure at each level were compared for the flexion, extension, and left and right bending simulations. However, combining the pressures for all directions of bending at each level demonstrated a decrease in the pressures at the T2–T3 level. Exploratory analysis comparing changes in the pressure at T2–T3 to other levels showed a significant decrease in the pressures at this level (p = 0.005). Conclusions Based on the combined intradiscal pressures alone it may be advantageous to end long constructs spanning the cervicothoracic junction at the T2 level if there are no other mitigating factors.

Pedicle Screw Placement in the Thoracolumbar Spine Using a Novel, Simple, Safe, and Effective Guide-Pin : A Computerized Tomography Analysis.

ObjectiveTo improve pedicle screw placement accuracy with minimal radiation and low cost, we developed specially designed K-wire with a marker. To evaluate the accuracy of thoracolumbar pedicle screws placed using the novel guide-pin and portable X-rays.MethodsObservational cohort study with computerized tomography (CT) analysis of in vivo and in vitro pedicle screw placement. Postoperative CT scans of 183 titanium pedicle screws (85 lumbar and 98 thoracic from T1 to L5) placed into 2 cadavers and 18 patients were assessed. A specially designed guide-pin with a marker was inserted into the pedicle to identify the correct starting point (2 mm lateral to the center of the pedicle) and aiming point (center of the pedicle isthmus) in posteroanterior and lateral X-rays. After radiographically confirming the exact starting and aiming points desired, a gearshift was inserted into the pedicle from the starting point into the vertebral body through the center of pedicle isthmus.ResultsNinety-nine percent (181/183) of screws were contained within the pedicle (total 183 pedicle screws : 98 thoracic pedicle screws and 85 lumbar screws). Only two of 183 (1.0%) thoracic pedicle screws demonstrated breach (1 lateral in a patient and 1 medial in a cadaver specimen). None of the pedicle breaches were associated with neurologic or other clinical sequelae.ConclusionA simple, specially designed guide-pin with portable X-rays can provide correct starting and aiming points and allows for accurate pedicle screw placement without preoperative CT scan and intraoperative fluoroscopic assistance.

Pullout strength of thoracic pedicle screws improved with cortical bone ratio: a cadaveric study

The application of pedicle screw constructs for the osteoporotic vertebrae remains a serious clinical challenge for spinal surgeons and has been intensely studied recently. However, the exact role of the pedicular cortical bone composition and the screw-bone gap on the screw fixation failure has yet to be quantitatively documented. The current study aims to address this gap in our knowledge and elucidate possible relationships. Twelve fresh-frozen human cadaveric thoracic spine vertebrae (T9-T12) were harvested from six human cadavers (five males; one female; 63.5±17years). A three-dimensional reconstruction of the individual vertebrae was firstly rendered from computed tomography (CT) scan images to allow calculation of the cortical bone ratio. Specimens were then subdivided into three groups: Intact, 1-mm screw-bone gap, and 2-mm screw-bone gap. The gap groups were subjected to a standard cyclic fatigue-loading protocol. The pullout strength of the pedicle screws for all specimens were then determined. The pullout strength of the 1-mm and 2-mm groups were significantly reduced when compared with the intact group. A moderate to excellent positive correlation was identified between the cortical bone area ratio and pullout strength for all groups (r>0.55). A cortical shell ratio of 0.73 or higher was also found to be a safe cut-off index for screw fixation failure, even with an observable 1-mm screw-bone gap. The current in vitro cadaveric spine study identified a significant correlation between cortical bone area ratio and the thoracic pedicle screw pullout strength. The presented results also demonstrate that the fatigue-loading-induced screw-bone gap of 1-mm was sufficient to cause a significant decrease in the pullout strength. However, a cortical bone area ratio of 0.73 or higher in this group was able to preserve most of the screw-bone interfacial strength, and subsequently may prevent a complete implant failure.

Biomechanical study of the funnel technique applied in thoracic pedicle screw replacement.

Funnel technique is a method used for the insertion of screw into thoracic pedicle. To evaluate the biomechanical characteristics of thoracic pedicle screw placement using the Funnel technique, trying to provide biomechanical basis for clinical application of this technology. 14 functional spinal units (T6 to T10) were selected from thoracic spine specimens of 14 fresh adult cadavers, and randomly divided into two groups, including Funnel technique group (n = 7) and Magerl technique group (n = 7). The displacement-stiffness and pull-out strength in all kinds of position were tested and compared. Two fixed groups were significantly higher than that of the intact state (P < 0.05) in the spinal central axial direction, compression, anterior flexion, posterior bending, lateral bending, axial torsion, but there were no significant differences between two fixed groups (P > 0.05). The mean pull-out strength in Funnel technique group (789.09 ± 27.33) was lower than that in Magerl technique group (P < 0.05). The Funnel technique for the insertion point of posterior bone is a safe and accurate technique for pedicle screw placement. It exhibited no effects on the stiffness of spinal column, but decreased the pull-out strength of pedicle screw. Therefore, the funnel technique in the thoracic spine affords an alternative for the standard screw placement.

Freehand thoracic pedicle screw technique using a uniform entry point and sagittal trajectory for all levels: preliminary clinical experience.

Experience with freehand thoracic pedicle screw placement is well described in the literature. Published techniques rely on various starting points and trajectories for each level or segment of the thoracic spine. Furthermore, few studies provide specific guidance on sagittal and axial trajectories. The goal of this study was to propose a uniform entry point and sagittal trajectory for all thoracic levels during freehand pedicle screw placement and determine the accuracy of this technique. The authors retrospectively reviewed postoperative CT scans of 33 consecutive patients who underwent open, freehand thoracic pedicle-screw fixation using a uniform entry point and sagittal trajectory for all levels. The same entry point for each level was defined as a point 3 mm caudal to the junction of the transverse process and the lateral margin of the superior articulating process, and the sagittal trajectory was always orthogonal to the dorsal curvature of the spine at that level. The medial angulation (axial trajectory) was approximately 30° at T-1 and T-2, and 20° from T-3 to T-12. Breach was defined as greater than 25% of the screw diameter residing outside of the pedicle or vertebral body. A total of 219 thoracic pedicle screws were placed with a 96% accuracy rate. There were no medial breaches and 9 minor lateral breaches (4.1%). None of the screws had to be repositioned postoperatively, and there were no neurovascular complications associated with the breaches. It is feasible to place freehand thoracic pedicle screws using a uniform entry point and sagittal trajectory for all levels. The entry point does not have to be adjusted for each level as reported in existing studies, although this technique was not tested in severe scoliotic spines. While other techniques are effective and widely used, this particular method provides more specific parameters and may be easier to learn, teach, and adopt.

Thoracic pedicle classification determined by inner cortical width of pedicles on computed tomography images: its clinical significance for posterior vertebral column resection to treat rigid and severe spinal deformities-a retrospective review of cases.

BackgroundPosterior vertebral column resection (PVCR) is an effective alternative for treating rigid and severe spinal deformities. Accurate placement of pedicle screws, especially apically, is crucial. As morphologic evaluations of thoracic pedicles have not provided objective criteria, we propose a thoracic pedicle classification for treating rigid and severe spinal deformities.MethodsA consecutive series of 56 patients with severe and rigid spinal deformities who underwent PVCR at a single institution were reviewed retrospectively. Altogether, 1098 screws were inserted into thoracic pedicles at T2-T12. Based on the inner cortical width of the thoracic pedicles, the patients were divided into four groups: group 1 (0–1.0 mm), group 2 (1.1–2.0 mm), group 3 (2.1–3.0 mm), group 4 (≥3.1 mm). The proportion of screws accurately inserted in thoracic pedicles for each group was calculated. Statistical analysis was also performed regarding types of thoracic pedicles classified by Lenke et al. (SPINE 35:1836-1842, 2010) using a morphological method.ResultsThere were statistically significant differences in the rates of screws inserted in thoracic pedicles between the groups (P < 0.008) except groups 3 and 4 (P > 0.008), which were then combined. The accuracies for the three new groups were 35.05%, 65.34%, and 88.32%, respectively, with statistically significant differences between the groups (P < 0.017). Rates of screws inserted in thoracic pedicles classified by Lenke et al. (SPINE 35:1836-1842, 2010) were 82.31%, 83.40%, 80.00%, and 30.28% for types A, B, C, and D, respectively. There was no statistically significant difference (P > 0.008) between these types except between type D and the other three types (P < 0.008).ConclusionsThe inner cortical width of thoracic pedicles is the sole factor crucial for accurate placement of thoracic pedicle screws. We propose a computed tomography-based classification of the pedicle’s inner cortical width: type I thoracic pedicle: absent channel, inner cortical width of 0–1 mm; type II: presence of a channel of which type IIa has an inner cortical width of 1.1–2.0 mm and type IIb a width of ≥2.1 mm. The proposed classification can help surgeons predict whether screws can be inserted into the thoracic pedicle, thus guiding instrumentation when PVCR is performed.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2474-15-278) contains supplementary material, which is available to authorized users.

Effects of rod reduction on pedicle screw fixation strength in the setting of Ponte osteotomies

Background contextThe use of a rod reduction device can have deleterious consequences on pedicle screw pullout strength (POS) in the thoracic spine. However, posterior-only osteotomies in the thoracic spine are often performed to improve flexibility of the spine and offset forces of deformity correction maneuvers. PurposeTo investigate the effect on pedicle screw POS caused by the rod reduction technique in the presence of facet osteotomies in the thoracic spine. Study design/settingThe study is a biomechanical study using human cadaveric spine specimens. MethodsThoracic Ponte osteotomies were performed on 3 thoracic levels in 15 cadaveric specimens. The right rod was contoured with a 5-mm residual gap at the middle level and was reduced using a rod reduction device. On the left side (paired control), a rod with no mismatch was placed. Biomechanical testing was performed with tensile load to failure “in line” with the screw axis and POS measured in Newtons (N). ResultsAfter rod reduction, thoracic pedicle screw POS was significantly decreased (40%) compared with the control (419±426 N vs. 708±462 N, p=.002) and remained statistically significant after adjusting for bone mineral density (BMD) (p=.05). Eleven (73%) of the pedicle screws had visible pullout/failure during the reduction attempt and occurred irrespective of BMD. ConclusionsDespite thoracic Ponte osteotomies and increased flexibility of the spinal segments, the rod reduction device still significantly decreased pedicle screw POS, typically resulting in outright failure of the screw-bone interface. Therefore, rod reduction technique of any kind should be performed with caution as it frequently results in suboptimal pedicle screw fixation.

Endovascular aortic injury repair after thoracic pedicle screw placement

Our objective was to describe the management and prevention of thoracic aortic injuries caused by a malposition of pedicle screws in corrective surgery of major spine deformities. Positioning pedicle screws in thoracic vertebras by posterior approach exposes to the risk of injury of the elements placed ahead of the thoracic spine, as the descending thoracic aorta. This complication can result in a cataclysmic bleeding, needing urgent vascular care, but it can also be totally asymptomatic, resulting in the long run in a pseudoaneurysm, justifying the systematic removal of the hardware. We report the case of a 76-year-old woman who underwent spinal correction surgery for thoraco-lumbar degenerative kypho-scoliosis. Immediately after the surgery, a thoracic aortic injury caused by the left T7 pedicle screw was diagnosed. The patient underwent a two-step surgery. The first step was realized by vascular surgeons and aimed to secure the aortic wall by short endovascular aortic grafting. During the second step, spine surgeons removed the responsible screw by posterior approach. The patient was discharged in a rehabilitation center 7 days after the second surgery. When such a complication occurs, a co-management by vascular and spine surgeons is necessary to avoid major complications. Endovascular management of this kind of vascular injuries permits to avoid an open surgery that have a great rate of morbi-mortality in frail patients. Nowadays, technologies exist to prevent this kind of event and may improve the security when positioning pedicle screws.

Influence of Prone Positioning on Potential Risk of Aorta Injury From Pedicle Screw Misplacement in Adolescent Idiopathic Scoliosis Patients

A prospective magnetic resonance imaging (MRI) study. The aim of this study was to quantitatively analyze the potential risks of aorta injury from thoracic pedicle screw (TPS) misplacement in right thoracic adolescent idiopathic scoliosis (RT-AIS) patients who are in the prone position. The aorta injuries are rare during posterior spinal surgery, but they can result in catastrophic complications when they do occur. However, we are aware of no prior studies that have used MRI images obtained with patients in the prone position for the purpose of systematically evaluating the potential risks of aorta injury due to TPS misplacement. This prospective study included 38 RT-AIS patients who underwent MRI scans in the prone position. We evaluated on the MRI images the aorta position relative to the scoliotic spine, and simulated placement of a left TPS with a lateral deviation different from the medium trajectory using Surgimap Spine imaging software. The maximum error of lateral direction was set to 10, 20, or 30 degrees (3 scenarios), and the length of the TPS was set at 30, 35, or 40 mm (3 scenarios). Sensitivity analysis was performed by variable direction errors and TPS lengths. The potential risk of aorta impingement was defined as the virtual TPS crossing the aorta. The percentages of potential risk of aorta impingement were calculated at each level in 9 scenarios. In the RT-AIS patients, the aorta shifted gradually from the left side of the vertebrae at midthoracic levels to a more anterior position at the lower thoracic levels, and was close to the vertebral body at T5-T6 and far away from the left cortex of vertebrae at T12. In 9 scenarios, with the increment of the lengths or/and direction errors of the simulated TPS, the risks of aorta impingement were consistently elevated at all the levels. The simulated 40 mm TPS at T5, T6, and T11 posed a higher potential risk of aorta injury (66%-74%) with a 30-degree lateral direction error. Prone positioning may increase the potential risk of aorta injury in RT-AIS patients, particularly at T5-T6 and T11 even if a left TPS just barely touches the anteriolateral or lateral cortex of the vertebrae. Laterally misplaced TPSs should be removed at these high aorta-at-risk levels.

Positioning thoracic pedicle screw entry point using a new landmark: a study based on 3-dimensional computed tomographic scan.

A novel method to identify the entry point. To quantify the position of thoracic pedicle screw entry points on the lamina at various segments of the thoracic vertebrae in normal subjects and patients with adolescent idiopathic scoliosis and propose a new technique to select entry points using a new landmark. Thoracic pedicle screws have been widely used in thoracic surgery, and the placement of pedicle screws has been studied extensively. However, there are only qualitative studies on selecting the entry point, and no study has quantified the position of entry points. A retrospective study using 3-dimensional computed tomographic reconstruction techniques were used to study the morphology of thoracic vertebrae in 110 adolescents (56 cases of adolescent idiopathic scoliosis and 54 normal subjects). A quantitative area was used to select the entry point. Thoracic pedicle screw entry point was determined using the new landmark as reference and thoracic pedicle screws were placed in 21 patients. Postoperative computed tomographic scanning was performed to assess the safety and effectiveness of this entry point selection technique. We determined that the accuracy of pedicle screw placing after positioning entry point using the quantitative area was significantly superior to that after positioning entry point using the traditional method (P < 0.05). The new technique quantifies the position of each thoracic pedicle screw entry point and it is convenient, easy to operate, and has relatively high accuracy of screw placement. This positioning technique can provide safe and accurate clinical guidance for selecting thoracic pedicle screw entry point.

Percutaneous Lumbar and Thoracic Pedicle Screws

Retrospective case study. Percutaneous pedicle screw (PPS) techniques do not allow direct visualization and may lead to erroneous screw placement. A technique utilizing only fluoroscopy is described. Verification of its accuracy and morphometric validation are presented. Minimally invasive spine surgical techniques, particularly PPS placement, have been growing in popularity. The purported benefits of minimally invasive spine surgical stated may be even more advantageous in the trauma setting. Jamshidi needles were docked in the typical starting position verified with posterior-anterior image. Jamshidi needle (20 mm) was advanced ensuring that the tip remained lateral to the medial pedicle wall. A Kirschner (K-wire) was placed through the needle. Once all the K-wires were placed, a lateral image was taken confirming the correct trajectory and that the wire passed the posterior vertebral body wall. Patients with PPS fixation were retrospectively studied with postoperative computed tomography to verify screw accuracy. Screw grade was assessed as grade I when completely within the pedicle, II <2 mm, III 2-4 mm, and IV >4 mm outside the pedicle. Morphometrically, 40 thoracic and lumbar computed tomography scans of patients (<40 y) without spine fractures were reviewed. The pedicle length was defined as the distance from the dorsal cortical margin to the posterior vertebral body in the pedicle's midaxis. A total of 172 screws were placed. Eighteen percent were found to have cortical breach, but only 2.9% were found to have >grade II breach. The morphometric study demonstrated the pedicle length to range from 14.4 to 22.1 mm. The shortest was in the upper thoracic and the longest at L1-L2. The morphometric study demonstrates if a K-wire is placed 20 mm into the bone and remains lateral to the medial pedicle wall and the tip just engages the vertebral body, the screw trajectory is safe particularly in the lower thoracic and upper lumbar spine. A smaller distance may be utilized in the upper thoracic. Breach rates are similar to other reports using other techniques; none were clinically significant. The advantage of this technique is the use of only PA fluoroscopy for placing all the wires percutaneously.

Comparative Accuracy of Cervical Pedicle Screws Placement using Funnel Technique and Topographic Landmarks Surgical Technique

Introduction The aim of the study is to evaluate accuracy of cervical pedicle screws placement using funnel technique and topographic landmarks surgical technique. Materials and Methods Ten fresh frozen cervical spines (C3-C7) were used (100 pedicles, 20 pedicles per level). The average specimen age was 62.5 years (range, 51-75 years); pedicle width, sagittal angle, and transverse angle were measured on preoperative axial computed tomography (1 mm slices) for every pedicle. All the specimens were randomly divided into two groups. The pedicles (C3-C7) of experimental group were instrumented with 3.5 mm screws with the funnel technique and the control group with the topographic landmarks surgical technique. No intraoperative φλuoroscopy or radiographic control was used during any part of the entire procedure. Critical perforations (documented contact of a screw with, or an injury to, a spinal cord, nerve root, or vertebral artery) and noncritical perforations (a perforation with no critical contact) were recorded. Results In five pedicles (5%), the procedure was aborted because of a small or nonexistent pedicle medullary canal. In Group I (funnel technique), 82% of screws were placed in the pedicle correctly, seven pedicles (18%) had noncritical breaches, and two pedicles (4%) had critical perforations. In Group II (topographic landmarks surgical technique), 62.2% of screws were placed in the pedicle correctly, whereas 11 pedicles (24.4%) had noncritical perforations and 6 pedicles (13.3%) had critical perforations. Statistically significant differences were demonstrated between the two groups ( p&lt;0.05). Conclusion Funnel technique can enhance accuracy and further improving the safety of transpedicular screw placement comparing with topographic landmarks surgical technique. Disclosure of Interest None declared References Abumi K, Itoh H, Taneichi H, Kaneda K. Transpedicular screw fixation for traumatic lesions of the middle and lower cervical spine: description of the techniques and preliminary report. J Spinal Disord 1994;7(1):19–28 Yingsakmonkol W, Karaikovic E, Gaines RW. The accuracy of pedicle screw placement in the thoracic spine using the “Funnel Technique”: part 1. A cadaveric study. J Spinal Disord Tech 2002;15(6):445–449 Abumi K, Shono Y, Ito M, Taneichi H, Kotani Y, Kaneda K. Complications of pedicle screw fixation in reconstructive surgery of the cervical spine. Spine 2000;25(8):962–969 Yukawa Y, Kato F, Ito K, et al. Placement and complications of cervical pedicle screws in 144 cervical trauma patients using pedicle axis view techniques by fluoroscope. Eur Spine J 2009;18(9):1293–1299 Karaikovic EE, Yingsakmongkol W, Gaines RW Jr. Accuracy of cervical pedicle screw placement using the funnel technique. Spine 2001;26(22):2456–2462 Chan CY, Kwan MK, Saw LB. Safety of thoracic pedicle screw application using the funnel technique in Asians: a cadaveric evaluation. Eur Spine J 2010;19(1):78–84 Ludwig SC, Kowalski JM, Edwards CC II, Heller JG. Cervical pedicle screws: comparative accuracy of two insertion techniques. Spine 2000;25(20):2675–2681

Neuromonitoring with pulse-train stimulation for implantation of thoracic pedicle screws: a blinded and randomized clinical study. Part 2. The role of feedback

The authors have reported in Part 1 of this study on a novel neuromonitoring test for the prevention of medial malpositioning of thoracic pedicle screws. In the present paper they examine the impact of providing the results of the test as intraoperative feedback to the surgical team. This is the second part of a 2-part report of a prospective, blinded and randomized neuromonitoring study designed to lower the incidence of medially malpositioned thoracic pedicle screws. Details of the neuromonitoring technique and data supporting the alarm criteria used are contained in the companion article (Part 1). For the majority of pedicle screw placements, intraoperative test results were withheld from the study team (that is, the team members were blinded to the test results). However, for a limited number of pedicle sites the authors provided one of 2 forms of testing feedback to the surgical team: 1) "break the blind" feedback, if testing suggested that screw placement would result in direct contact between screw and the dura mater; and 2) "planned" feedback, beginning during the later stages of the study and provided for 50% of pedicle sites. Feedback gave the surgeon the opportunity to adjust the trajectory that the screw would ultimately take within the pedicle. The final screw position relative to the pedicle's medial wall for all sites in which feedback was withheld from the surgical team was compared with the screw position for those sites in which either form of feedback ("break the blind" or "planned") was provided to and acted upon by the surgical team. Of the 820 pedicle tracks tested among the 71 surgical cases included in this study, a total of 684 were operated upon without any form of feedback. Planned feedback was provided for an additional 107 pedicle tracks, of which 15 triggered an intraoperative alarm (evoked electromyogram response in leg muscles to stimulus intensity ≤ 10 mA) leading to a warning to the surgical team of a medially biased pedicle track. Finally, the blind was broken 29 times, in each case when testing revealed a particularly low threshold (≤ 4 mA) for evoked responses in leg muscles when stimulating along the pedicle track with the ball-tipped probe. As detailed in the companion paper to this one, there were 32 screws with threads lying at least 2 mm medial to the pedicle wall. In all 32 instances (100%), either these screws were in the "no feedback" category (n = 29) or they were in a feedback category but the surgeon elected to not revise the pedicle-track trajectory. Two patients returned to the operating room for revision of screw placements because the screws were encroaching upon the central canal; the pedicle tracks for these screws had been in the "no feedback" category. This is the first blinded and randomized study to prove that implementing a novel neuromonitoring strategy during placement of thoracic pedicle screws can significantly reduce the incidence of clinically relevant thoracic pedicle screw medial malpositioning.

Neuromonitoring with pulse-train stimulation for implantation of thoracic pedicle screws: a blinded and randomized clinical study. Part 1. Methods and alarm criteria

Reports of the accuracy of existing neuromonitoring methods for detecting or preventing medial malpositioning of thoracic pedicle screws have varied widely in their claimed effectiveness. The object of this study was to develop, test, and validate a novel neuromonitoring method for preventing medial malpositioning of pedicle screws in the thoracic spine during surgery. This is a prospective, blinded and randomized study using a novel combination of input (4-pulse stimulus trains delivered within the pedicle track) and output (evoked electromyography from leg muscles) to detect pedicle track trajectories that-once implanted with a screw-would cause that screw to breach the pedicle's medial wall and encroach upon the spinal canal. For comparison, the authors also used screw stimulation as an input and evoked electromyogram from intercostal and abdominal muscles as output measures. Intraoperative electrophysiological findings were compared with postoperative CT scans by multiple reviewers blinded to patient identity or intraoperative findings. Data were collected from 71 patients, in whom 802 screws were implanted between the T-1 and L-1 vertebral levels. A total of 32 screws ended up with screw threads encroaching on the spinal canal by at least 2 mm. Pulse-train stimulation within the pedicle track using a ball-tipped probe and electromyography from lower limb muscles correctly predicted all 32 (100%) of these medially malpositioned screws. The combination of pedicle track stimulation and electromyogram response from leg muscles proved to be far more effective in predicting these medially malpositioned screws than was direct screw stimulation and any of the target muscles (intercostal, abdominal, or lower limb muscles) we monitored. Based on receiver operating characteristic analysis, the combination of 10-mA (lower alarm) and 15-mA stimulation intensities proved most effective for detection of pedicle tracks that ultimately gave rise to medially malpositioned screws. Additional results pertaining to the impact of feedback of these test results on surgical decision making are provided in the companion report. This novel neuromonitoring approach accurately predicts medially malpositioned thoracic screws. The approach could be readily implemented within any surgical program that is already using contemporary neuromonitoring methods that include transcranial stimulation for monitoring motor evoked potentials.