Thoracic Pedicle Screw Research Articles

A novel computer-assisted drill guide template for thoracic pedicle screw placement: a cadaveric study

The objective of this study was to develop a novel, patient-specific, navigational template for thoracic pedicle screw placement. Twenty thoracic cadaver specimens were randomly divided into two groups of 10: the navigational template group and the free-hand group. A volumetric CT scan was performed on each thoracic vertebra, and a three-dimensional reconstruction model was generated. A drill template was designed with a surface that was the inverse of the posterior vertebral surface. Each drill template and its corresponding vertebra were manufactured using a rapid prototyping technique and tested for violation. Two hundred and forty screws were implanted into the thoracic spines and the positions of the screws were evaluated. Two hundred and forty thoracic screws were inserted using either the navigational template method or the free-hand method. The accuracy rate and incidence of risk for setting thoracic pedicle screws differed statistically between the two methods (P < 0.05): The navigational template method had a higher accuracy rate and a lower incidence of risk than the free-hand method. Moreover, the free-hand method had a significant learning curve, whereas a learning curve for the navigational template method was not obvious. We have developed a novel, patient-specific, navigational template for thoracic pedicle screw placement with good applicability and high accuracy.

Combined endovascular and neurosurgical approach to the removal of an intraaortic pedicle screw

Iatrogenic aortic injuries are a potentially devastating complication of spine surgery. In instrumented cases, injuries may occur in the perioperative period due to iatrogenic vessel injury, or they may occur years later as prominent implants erode or penetrate major vessels. The authors present a case of a 71-year-old man in whom a thoracic pedicle screw was found perforating the thoracic aorta during routine follow-up 6 months after surgery. Due to the risk of future complications, the screw was removed while simultaneously delivering an endovascular aortic stent to gain vascular control. Surgical considerations and potential technical limitations are discussed.

A novel cost-effective computer-assisted imaging technology for accurate placement of thoracic pedicle screws

Use of computer-assisted spine surgery (CASS) technologies, such as navigation systems, to improve the accuracy of pedicle screw (PS) placement is increasingly popular. Despite of their benefits, previous CASS systems are too expensive to be ubiquitously employed, and more affordable and portable systems are desirable. The aim of this study was to introduce a novel and affordable computer-assisted technique that 3-dimensionally visualizes anatomical features of the pedicles and assists in PS insertion. The authors have termed this the 3D-visual guidance technique for inserting pedicle screws (3D-VG TIPS). The 3D-VG technique for placing PSs requires only a consumer-class computer with an inexpensive 3D DICOM viewer; other special equipment is unnecessary. Preoperative CT data of the spine were collected for each patient using the 3D-VG TIPS. In this technique, the anatomical axis of each pedicle can be analyzed by volume-rendered 3D models, as with existing navigation systems, and both the ideal entry point and the trajectory of each PS can be visualized on the surface of 3D-rendered images. Intraoperative guidance slides are made from these images and displayed on a TV monitor in the operating room. The surgeon can insert PSs according to these guidance slides. The authors enrolled 30 patients with adolescent idiopathic scoliosis (AIS) who underwent posterior fusion with segmental screw fixation for validation of this technique. The novel technique allowed surgeons, from office or home, to evaluate the precise anatomy of each pedicle and the risks of screw misplacement, and to perform 3D preoperative planning for screw placement on their own computer. Looking at both 3D guidance images on a TV monitor and the bony structures of the posterior elements in each patient in the operating theater, surgeons were able to determine the best entry point for each PS with ease and confidence. Using the current technique, the screw malposition rate was 4.5% in the thoracic region in corrective surgery for AIS. The authors found that 3D-VG TIPS worked on a consumer-class computer and easily visualized the ideal entry point and trajectory of PSs in any operating theater without costly special equipment. This new technique is suitable for preoperative planning and intraoperative guidance when performing reconstructive surgery with PSs.

Morphologic evaluation of the thoracic vertebrae for safe free-hand pedicle screw placement in adolescent idiopathic scoliosis: a CT-based anatomical study

To evaluate the morphologic characteristics of the thoracic pedicle with regard to safe free-hand thoracic pedicle screw placement, based on multi-planar reconstruction CT images. Thirty adolescent idiopathic scoliosis (AIS) patients who had undergone posterior corrective surgery for major thoracic curve were included in this study. Reconstructed CT axial images at each thoracic vertebra were used to measure: (1) the shortest distance from an entry point to the ventral cortex of the lamina (critical distance), and (2) the distance from the entry point to the tangent of the spinal canal at the medial wall of the pedicle (safe distance). The critical length was defined as the distance between the critical distance and the safe distance. The distance from the entry point to the medial wall breach site (breach distance) was measured on post-operative CT images. The mean critical distance was 9.3 ± 1.1 mm. The critical distance of vertebrae from different levels was relatively constant, between 8.1 and 10.1 mm. The mean safe distance was 15.2 ± 1.3 mm. The safe distance of vertebrae from different levels was also relatively constant, between 14.5 and 16 mm. The mean critical length was 5.9 ± 1.0 mm. The critical length of vertebrae between T3 and T12 was relatively constant, ranging from 5 to 6.5 mm. The mean breach distance was 12.3 ± 1.3 mm and the each breach always recognized between the critical distance and the safe distance. The risk of pedicle medial wall perforation increases as the pedicle probe advances beyond the critical distance of 8-10 mm from the entry point, while it decreases entering into the safe distance at 14.5-16 mm. These parameters were relatively constant even in the most rotated vertebrae at T9 or those with the narrowest pedicle at T7 or T4.

Computed tomographic evaluation of thoracic pedicle screw placement in idiopathic scoliosis

This retrospective observational study aimed to determine the accuracy of the placement of transpedicular thoracic screws used in idiopathic scoliosis and to evaluate the position and safety of the implants using postoperative computed tomography. Twenty-nine patients who underwent surgery for scoliosis between May 2003 and November 2005 were included in this study. The mean spinal curvature was 67°, and all of the patients had thoracic screws or hooks implanted. The positioning of 78 pedicle screws was evaluated using computed tomography after the free-handed technique was performed. The mean spinal curvature after surgery was 29°. Seventy-six percent of the screws were fully contained within the pedicle. Twenty-one screws breached the pedicle by between 2 and 4 mm (three medially and 18 laterally). Two screws were broken. A neurological deficit was identified in one case after surgery, but the deficit was reversed after the removal of the screws. This screw had a medial breach of greater than 4 mm. Most screws were inserted between the cortical vertebrae. Misplaced screws were most commonly inserted with a lateral cortical perforation.

A Novel Method of Screw Placement for Extremely Small Thoracic Pedicles in Scoliosis

A retrospective clinical study. To introduce a novel method of pedicle screw placement for extremely small thoracic pedicles in scoliosis and evaluate the safety and accuracy of the method. Few studies have provided technical guidelines for screw placement in patients with extremely small thoracic pedicles in scoliosis. In a severely rotated scoliotic spine, thoracic pedicle screw placement is challenging, and particularly more so for extremely small pedicles with a diameter less than 2 mm. The authors introduced a novel method of screw placement for these small pedicles: "medial margin targeting method."The C-arm fluoroscope is rotated until a true PA image of the rotated vertebral body is acquired and both pedicle shadows are symmetrically visualized en face. In extremely small pedicles, pedicle shadows appear as long, slender ellipses or lines. An imaginary pedicle outline is presumed with the elliptical or linear shadows being the medial margin of the pedicle. The entry point of a screw can be made at the 10-o'clock or 2-o'clock position on the presumed pedicle outline, and the screw can be safely inserted targeting the presumed medial margin with caution not to penetrate the medial cortex using the guidance of a true PA image. This is a kind of extrapedicular screw placement method.The safety and accuracy of this method were evaluated in 97 patients with scoliosis who had undergone posterior correction and instrumentation using postoperative computed tomography scans. A total of 1634 pedicle screws were inserted into thoracic pedicles, 128 of them (7.8%) being extremely small pedicles with a diameter less than 2 mm. Among 128 extremely small thoracic pedicles with a diameter less than 2 mm, one screw (0.8%) violated the medial cortex and 22 screws (17.6%) violated the anterior cortex of the vertebral body. No screws violated the lateral cortex of the pedicle-rib unit. There were no complications associated with screw misplacement. In scoliosis patients with extremely small thoracic pedicles, our pedicle screw placement method targeting the presumed medial margin in a true PA C-arm image allows easy application with accuracy and safety, which would not possible by any other method described so far.

Accuracy of Image-Guided Pedicle Screw Placement Using Intraoperative Computed Tomography-Based Navigation With Automated Referencing. Part II

Image-guided spinal instrumentation may reduce complications in spinal instrumentation. To assess accuracy, time efficiency, and staff radiation exposure during thoracolumbar screw instrumentation guided by intraoperative computed tomography (iCT)-based neuronavigation (iCT-N). In 55 patients treated for idiopathic and degenerative deformities, 826 screws were inserted in the thoracic (T2-T12; n = 243) and lumbosacral (L1-S1; n = 545) spine, as well as ilium (n = 38) guided by iCT-N. Up to 17 segments were instrumented following a single automated registration sequence with the dynamic reference arc (DRA) uniformly attached to L5. Accuracy of iCT-N was assessed by calculating angular deviations between individual navigated tool trajectories and final implant positions. Final screw positions were also graded according to established classification systems. Clinical and radiological outcome was assessed at 12 to 14 months. Additional intraoperative fluoroscopy was unnecessary, eliminating staff radiation exposure. Unisegmental K-wire insertion required 4.6 ± 2.9 minutes. Of the thoracic pedicle screws 98.4% were assigned grades I to III according to the Heary classification, with 1.6% grade IV placement. In the lumbar spine, 94.4% of screws were completely contained (Gertzbein classification grade 0), 4.6% displayed minor pedicle breaches <2 mm (grade 1), and 1% of lumbar screws deviated by >2 to <4 mm (grade 2). The accuracy of iCT-N progressively deteriorates with increasing distance from the DRA, but allows safe instrumentation of up to 12 segments. iCT-N using automated referencing allows for safe, highly accurate multilevel instrumentation of the entire thoracolumbosacral spine and ilium, rendering additional intraoperative imaging dispensable. In addition, automated registration is time-efficient and significantly reduces the need for re-registration in multilevel surgery.

Accuracy of Image-Guided Pedicle Screw Placement Using Intraoperative Computed Tomography-Based Navigation With Automated Referencing, Part I: Cervicothoracic Spine

Image-guided spinal instrumentation reduces the incidence of implant misplacement. To assess the accuracy of intraoperative computed tomography (iCT)-based neuronavigation (iCT-N). In 35 patients (age range, 18-87 years), a total of 248 pedicle screws were placed in the cervical (C1-C7) and upper and midthoracic (T1-T8) spine. An automated iCT registration sequence was used for multisegmental instrumentation, with the reference frame fixed to either a Mayfield head clamp and/or the most distal spinous process within the instrumentation. Pediculation was performed with navigated drill guides or Jamshidi cannulas. The angular deviation between navigated tool trajectory and final implant positions (evaluated on postinstrumentation iCT or postoperative CT scans) was calculated to assess the accuracy of iCT-N. Final screw positions were also graded according to established classification systems. Mean follow-up was 16.7 months. Clinically significant screw misplacement or iCT-N failure mandating conversion to conventional technique did not occur. A total of 71.4% of patients self-rated their outcome as excellent or good at 12 months; 99.3% of cervical screws were compliant with Neo classification grades 0 and 1 (grade 2, 0.7%), and neurovascular injury did not occur. In addition, 97.8% of thoracic pedicle screws were assigned grades I to III of the Heary classification, with 2.2% grade IV placement. Accuracy of iCT-N progressively deteriorated with increasing distance from the spinal reference clamp but allowed safe instrumentation of up to 10 segments. Image-guided spinal instrumentation using iCT-N with automated referencing allows safe, highly accurate multilevel instrumentation of the cervical and upper and midthoracic spine. In addition, iCT-N significantly reduces the need for reregistration in multilevel surgery.

Recording triggered EMG thresholds from axillary chest wall electrodes: a new refined technique for accurate upper thoracic (T2–T6) pedicle screw placement

This study was aimed at evaluating the sensitivity and safety of a new technique to record triggered EMG thresholds from axillary chest wall electrodes when inserting pedicle screws in the upper thoracic spine (T2-T6). A total of 248 (36.6%) of a total of 677 thoracic screws were placed at the T2-T6 levels in 92 patients with adolescent idiopathic scoliosis. A single electrode placed at the axillary midline was able to record potentials during surgery from all T2-T6 myotomes at each side. Eleven screws were removed during surgery because of malposition according to intraoperative fluoroscopic views. Screw position was evaluated after surgery in the remaining 237 screws using a CT scan. Malposition was detected in 35 pedicle screws (14.7%). Pedicle medial cortex was breached in 24 (10.1%). Six screws (2.5%) were located inside the spinal canal. Mean EMG threshold was 24.44 ± 11.30 mA in well-positioned screws, 17.98 ± 8.24 mA (p < 0.01) in screws violating the pedicle medial cortex, and 10.38 ± 3.33 mA (p < 0.005) in screws located inside the spinal canal. Below a threshold of 12 mA, 33.4% of the screws (10/30) were malpositioned. Furthermore, 36% of the pedicle screws with t-EMG stimulation thresholds within the range 6-12 mA were malpositioned. In conclusion, assessment of upper thoracic pedicle screw placement by recording tEMG at a single axillary electrode was highly reliable. Thresholds below 12 mA should alert surgeons to suspect screw malposition. This technique simplifies tEMG potential recording to facilitate safe placement of pedicle screws at upper thoracic levels.

Learning Retention of Thoracic Pedicle Screw Placement Using a High-Resolution Augmented Reality Simulator With Haptic Feedback

We evaluated the use of a part-task simulator with 3D and haptic feedback as a training tool for a common neurosurgical procedure--placement of thoracic pedicle screws. To evaluate the learning retention of thoracic pedicle screw placement on a high-performance augmented reality and haptic technology workstation. Fifty-one fellows and residents performed thoracic pedicle screw placement on the simulator. The virtual screws were drilled into a virtual patient's thoracic spine derived from a computed tomography data set of a real patient. With a 12.5% failure rate, a 2-proportion z test yielded P = .08. For performance accuracy, an aggregate Euclidean distance deviation from entry landmark on the pedicle and a similar deviation from the target landmark in the vertebral body yielded P = .04 from a 2-sample t test in which the rejected null hypothesis assumes no improvement in performance accuracy from the practice to the test sessions, and the alternative hypothesis assumes an improvement. The performance accuracy on the simulator was comparable to the accuracy reported in literature on recent retrospective evaluation of such placements. The failure rates indicated a minor drop from practice to test sessions, and also indicated a trend (P = .08) toward learning retention resulting in improvement from practice to test sessions. The performance accuracy showed a 15% mean score improvement and more than a 50% reduction in standard deviation from practice to test. It showed evidence (P = .04) of performance accuracy improvement from practice to test session.

Aortic Abutment After Direct Vertebral Rotation

Retrospective case series. To report the occurrence of pedicle screw plow after individual-level direct vertebral rotation (DVR) that resulted in critical screw proximity to the aorta, from three institutions over a four-year period (2004-2008). Thoracic pedicle screws are generally accepted as safe implants that possess sufficient strength to correct the coronal, sagittal, and now transverse plane deformities associated with scoliosis. Structural failure of the bone resulting in translation of the screw in the transverse plane, defined as plow, can occur with individual-level DVR. We performed a retrospective review of all pediatric patients who underwent posterior spinal fusion with pedicle screws for neuromuscular and idiopathic scoliosis and underwent postoperative computed tomographic scan. We identified all patients who required a secondary procedure for implant removal because of malposition of the screw. Six patients with lateral screw direction after a DVR maneuver required screw removal because of proximity to the aorta. All patients had intraoperative confirmation of adequate screw placement before introducing the rod and performing derotation. CONCLUSIONS.: The biologic limitations of vertebrae are approached as we strive to achieve further correction of the spine. Surgeons' experience and methods to assess proper screw placement may give a false sense of adequate final implant position after DVR. Vigilance to ensure proper pedicle screw position can avoid potential iatrogenic catastrophes.

The Safe Placement of Upper and Middle Thoracic Pedicle Screws in Pediatric Deformity

A retrospective clinical study to discuss the diameter of pedicle screw used in upper and middle thoracic vertebrae of pediatric patients with spinal deformity. To determine the diameter of pedicle screw that can be accommodated in upper and middle thoracic vertebra fixation in the correction of pediatric spinal deformity. Internal pedicle screw fixation has been widely used in the treatment of pediatric spinal disorders, but the screw size is still a focus of debates in the application of internal pedicle screw placement in pediatric patients. From March 2004 to March 2008, 32 pediatric patients (aged from 6 to 12 y, mean age 9.2 y) with idiopathic and congenital kyphoscoliosis were treated with surgical correction of the deformity through posterior approach pedicle screw placement. Before operation, thin-slice computed tomography (CT) (1.0 mm) scan along the direction of the pedicle axis was done to scan the operative vertebra segments of all the patients. The transverse pedicle diameter was measured at the same time. When inserting thoracic pedicle screws, after having confirmed that the screw tract was completely contained within the pedicle walls, the surgeons gradually increased the pedicle screw diameter based on the transverse pedicle diameter measured before operation, and carefully sensed the differences in palpation accordingly, so as to determine the appropriate diameter of screws inserted. The position of screws was reevaluated by postoperative CT scan. The stability of internal pedicle screw fixation and neurologic functions of the patients were assessed in the follow-up. In this study, a total of 206 screws were placed into upper and middle thoracic pedicles (T1 to T8) of pediatric patients. Of them, the numbers of screws placed in pedicles T1 through T8 were 12, 36, 26, 22, 25, 23, 30, and 32, respectively. No screw was misplaced. The diameter of inserted pedicle screws ranged from 4.5 to 5.5 mm, 140.2%±19.2% that of the preoperative CT scan measurement of pedicles. The length of pedicle screws inserted varied from 30 to 40 mm. No postoperative neurologic deficit or vascular injury occurred. The period of follow-up was from 16 months to 36 months (22.7 mo on average). No loosening, deformation, breakage, or removal of inserted pedicle screws was reported in the follow-up. It is safe and feasible to use internal pedicle screw fixation to treat pediatric patients with upper and middle thoracic deformity in the process of screw placement, a pedicle screw with a larger diameter can be accommodated in upper and middle thoracic pedicles, if the axis of pedicle screw is confirmed within the pedicle walls. The most appropriate diameter of the screws can be determined concurrently by the palpation of the surgeon when placing the screw and referring to the pedicle screw diameter measured by CT before operation.

Triggered electromyography for placement of thoracic pedicle screws: is it reliable?

Reliable electromyography (EMG) thresholds for detecting medial breaches in the thoracic spine are lacking, and there is a paucity of reports evaluating this modality in patients with adolescent idiopathic scoliosis (AIS). This retrospective analysis evaluates the ability of triggered EMG to detect medial breaches with thoracic pedicle screws in patients with AIS. We reviewed 50 patients (937 pedicle screws) undergoing posterior spinal fusion (PSF) with intraoperative EMG testing. Postoperative CT scans were used for breach identification, and EMG values were analyzed. There were 47 medial breaches noted with a mean threshold stimulus of 10.2mA (milliamperes). Only 8/47 breaches stimulated at 2-6mA. Thirteen of the forty-seven screws tested at an EMG value ≤6mA and/or a decrease of ≥65% compared with intraosseously placed screws. The sensitivity and positive predictive value for EMG was 0.28 and 0.21. A subanalysis of T10-T12 screws identified six of seven medial breaches. Using guidelines from the current literature, EMG does not appear to be reliable in detecting medial breaches from T2 to T9 but may have some utility from T10 to T12.

Is Intraoperative CT of Posterior Cervical Spine Instrumentation Cost-effective and Does It Reduce Complications?

Symptomatic multilevel cervical myelopathy is often addressed using posterior decompression using two-dimensional fluoroscopy. Intraoperative three-dimensional fluoroscopy provides more accurate information on the position of instrumentation to prevent screw-related complications. We documented the incidence of hardware-related complications and evaluate cost-effectiveness when using intraoperative three-dimensional fluoroscopy (ISO-C CT) in posterior cervical spine surgery. Records from 87 patients who underwent posterior cervical decompression and instrumented fusion for multilevel cervical spondylosis with myelopathy were retrospectively reviewed. Patients in whom a lateral mass, pars, or pedicle screw was removed or revised based on intraoperative ISO-C CT was recorded. Cost analysis was performed using 2008 Medicare reimbursements and was compared against cost estimates for ISO-C CT. Seven patients (8%) had screws changed based on the results of the three-dimensional fluoroscopy: 0.5% of lateral mass screws, 3.1% of thoracic pedicle screws, and 15% of C2 pars screws. No patients who had evaluation of hardware with the ISO-C CT required a return to surgery for complications secondary to hardware failure, malposition, or cutout. Cost savings are achieved if use of intraoperative ISO-C CT prevents eight patients from requiring a return to the operating room. If every malpositioned screw has the potential to be symptomatic, then 240 patients must have screws placed to be cost-effective. ISO-C CT can safely replace postoperative CT as the standard of care in patients undergoing posterior cervical spinal fusion. Level III, economic and decision analyses. See Guidelines for Authors for a complete description of levels of evidence.

P31-21 Recording triggered EMG thresholds from axillary chest wall electrodes. A new refined technique for accuracy of upper thoracic pedicle screw placement

P31-21 Recording triggered EMG thresholds from axillary chest wall electrodes. A new refined technique for accuracy of upper thoracic pedicle screw placement

The effect of spinal instrumentation on kinematics at the cervicothoracic junction: emphasis on soft-tissue response in an in vitro human cadaveric model

Thoracic pedicle screw instrumentation is often indicated in the treatment of trauma, deformity, degenerative disease, and oncological processes. Although classic teaching for cervical spine constructs is to bridge the cervicothoracic junction (CTJ) when instrumenting in the lower cervical region, the indications for extending thoracic constructs into the cervical spine remain unclear. The goal of this study was to determine the role of ligamentous and facet capsule (FC) structures at the CTJ as they relate to stability above thoracic pedicle screw constructs. A 6-degree-of-freedom spine simulator was used to test multidirectional range of motion (ROM) in 8 human cadaveric specimens at the C7–T1 segment. Flexion-extension, lateral bending, and axial rotation at the CTJ were tested in the intact condition, followed by T1–6 pedicle screw fixation to create a long lever arm inferior to the C7–T1 level. Multidirectional flexibility testing of the T1–6 pedicle screw construct was then sequentially performed after sectioning the C7–T1 supraspinous ligament/interspinous ligament (SSL/ISL) complex, followed by unilateral and bilateral FC disruption at C7–T1. Finally, each specimen was reconstructed using C5–T6 instrumented fixation and ROM testing at the CTJ performed as previously described. Whereas the application of a long-segment thoracic construct stopping at T-1 did not significantly increase flexion-extension peak total ROM at the supra-adjacent level, sectioning the SSL/ISL significantly increased flexibility at C7–T1, producing 35% more motion than in the intact condition (p < 0.05). Subsequent FC sectioning had little additional effect on ROM in flexion-extension. Surprisingly, the application of thoracic instrumentation had a stabilizing effect on the supra-adjacent C7–T1 segment in axial rotation, leading to a decrease in peak total ROM to 83% of the intact condition (p < 0.05). This is presumably due to interaction between the T-1 screw heads and titanium rods with the C7–T1 facet joints, thereby limiting axial rotation. Incremental destabilization served only to restore peak total ROM near the intact condition for this loading mode. In lateral bending, the application of thoracic instrumentation stopping at T-1, as well as SSL/ISL and FC disruption, demonstrated trends toward increased supraadjacent ROM; however, these trends did not reach statistical significance (p > 0.05). When stopping thoracic constructs at T-1, care should be taken to preserve the SSL/ISL complex to avoid destabilization of the supra-adjacent CTJ, which may manifest clinically as proximal-junction kyphosis. In an analogous fashion, if a T-1 laminectomy is required for neural decompression or surgical access, consideration should be given to extending instrumentation into the cervical spine. Facet capsule disruption, as might be encountered during T-1 pedicle screw placement, may not be an acutely destabilizing event, due to the interaction of the C7–T1 facet joints with T-1 instrumentation.

Structures at risk from pedicle screws in the proximal thoracic spine: computed tomography evaluation

Background context Pedicle screw placement in the proximal thoracic spine may result in unwanted bicortical breach. An understanding of the potential structures at risk is paramount to safe screw placement. Purpose To assess the anatomic location of structures at risk with the placement of bicortical pedicle screw fixation in the proximal thoracic spine. Study design Retrospective radiographic review. Patient sample Twenty patients with dedicated computed tomography (CT) scans of the thoracic spine. Outcome measures Radiographic parameters on CT. Methods and materials Computed tomography was performed on 20 patients and analyzed from T1 to T4 for proximity of major structures at risk with breach of the anterior vertebral body cortex from pedicle screw placement. Descriptive statistics, analyses of variance and post hoc paired t tests were used to analyze screw position relative to the esophagus, trachea, aortic arch, carotid, and vertebral arteries. Results One hundred sixty potential anterior cortical violation positions were analyzed. Left-sided pedicle screws posed a significantly higher risk (p<.05) to the esophagus at T1–T3; in particular, the left T2 screw was significantly closer (p<.05). Right-sided pedicle screws posed a significantly higher risk to the trachea at T2–T4 (p<.05). The right T3 and T4 screws posed the greatest risk to the trachea and right main bronchus, respectively (p<.05). The carotid and vertebral arteries were not at risk for injury. The aortic arch was present at T4 in 70% of patients and was not at risk. Conclusions Careful preoperative evaluation with CT is warranted to determine anatomic structures at risk when placing proximal thoracic pedicle screws. Left-sided screws pose the greatest risk to the esophagus; right-sided screws pose the greatest risk to the trachea. The carotid and vertebral arteries, along with the aortic arch are at minimal risk for injury.

Thoracic pedicle screw insertion in Asian cadaveric specimen: does radiological pedicle profile affect outcome?

Pedicle screw instrumentation has superior biomechanical as well as clinical outcome. Thoracic pedicles show great variation in different population groups, particularly in Asians who have been shown to have smaller pedicle dimensions. Although plain radiographs are widely performed prior to spine surgery, no studies have been done so far to investigate whether the thoracic pedicle profile on plain radiographs affect thoracic pedicle screw insertion. Therefore, this is a cadaveric study aimed to determine the relationship between plain radiographic thoracic pedicle profile in Asians and the outcome of pedicle screw insertion in the thoracic spine. A pre-insertion radiograph with an enlargement reference scale was performed and surgeons were blinded to the plain radiographic morphometry of the thoracic pedicles. From the pre-insertion radiograph, the normalized pedicle width and height (which controls for any magnification error) as well as the pedicle width:body width (PWBW) and pedicle width:pedicle height (PWPH) ratio was derived. 240 pedicle screws were inserted in ten Asian cadavers from T1 to T12 using the funnel technique. 5.0 mm screws were used from T1 to T6 while 6.0 mm screws were used from T7 to T12. Perforations were detected by direct visualization via wide laminectomies after pedicle screw insertion. The outcome of thoracic pedicle screw insertion was correlated with the radiological profile using independent t-test. Pearson correlation coefficient was used to investigate the correlation between the ratios and the normalised pedicle width and height. The narrowest pedicle width is from T3 to T6 determined from normalized measurement of the pedicle width. T5 pedicle width is the smallest measuring 4.1 ± 1.3 mm. The overall perforation rate is 10.4% (25 perforations). There is only one significant perforation. There were twice as many lateral and inferior perforations compared to the medial perforations. 48% of the perforations occurred at T1, T2 and T3. Pedicles <4.0 mm in width and upper thoracic pedicles are risk factors for pedicle perforation. The normalised pedicle width has a high degree of linear correlation with PWBW and a normalised pedicle width of 4.0 mm correlated with a PWBW ratio of 0.3. Plain radiographic thoracic pedicle morphometry has an influence on the outcome of thoracic pedicle screw insertion in Asian cadavers. Pedicle width <4.0 mm is associated with higher risk of pedicle perforation. This critical value corresponds to a PWBW ratio of 0.3. Identification of such pedicle profile warrants full evaluation of the morphometry of the thoracic pedicles and possibly extra-pedicular techniques should be employed to avert the risk of critical pedicle perforation.

Descending Aortic Injury by a Thoracic Pedicle Screw During Posterior Reconstructive Surgery

Case report. To describe an iatrogenic aortic injury by pedicle screw instrumentation during posterior reconstructive surgery of spinal deformity. Iatrogenic major vascular injuries during anterior instrumentation procedures have been reported by several authors, but there have been few reports regarding iatrogenic major vascular injuries during posterior instrumentation procedures. A 57-year-old woman with thoracolumbar kyphosis due to osteoporotic T12 vertebral fracture underwent posterior correction and fusion (T10-L2), using segmental pedicle screw construct concomitant with T12 pedicle subtraction osteotomy. Postoperative routine plain radiographs and computed tomography myelography demonstrated a misplaced left T10 pedicle screw, which was in contact with the posteromedial aspect of the thoracic aorta, and suspected penetration of the aortic wall. The patient underwent removal of the pedicle screw, and repair of the penetrated aortic wall through a simultaneous anterior-posterior approach. The patient tolerated the procedure well without neurologic sequelae, and was discharged several days after removal of a left tube thoracostomy. Plain radiographs demonstrated solid fusion at the osteotomy site and no loosening of hardware. Preoperative neurologic symptoms improved completely at 18-months follow-up. Use of pedicle screw instrumentation has the potential to cause major vascular injury during posterior spinal surgery, and measures to prevent this complication must be taken. Timely diagnosis and treatment are essential to prevent both early and delayed complications and death.

Pedicle screw placement in the thoracic spine: a randomized comparison study of computer-assisted navigation and conventional techniques

Objective To evaluate the accuracy of computer-assisted pedicle screw installation and its clinical benefit as compared with conventional pedicle screw installation techniques. Methods Total 176 thoracic pedicle screws placed in 42 thoracic fracture patients were involved in the study randomly, 20 patients under conventional fluoroscopic control (84 screws) and 22 patients had screw insertion under three dimensional (3D) computer-assisted navigation (92 screws). The 2 groups were compared for accuracy of screw placement, time for screw insertion by postoperative thin-cut CT scans and statistical analysis by χ 2 test. The cortical perforations were then graded by 2-mm increments: Grade I (good, no cortical perforation), Grade II (screw outside the pedicle <2 mm), Grade III (screw outside the pedicle >2 mm). Results In computer assisted group, 88 (95.65%) were Grade I (good), 4 (4.35%) were Grade II (<2mm), no Grade III (>2 mm) violations. In conventional group, there were 14 cortical violations (16.67%), 70 (83.33%) were Grade I (good), 11 (13.1%) were Grade II (<2 mm), and 3 (3.57%) were Grade III (>2 mm) violations ( P<0.001). The number (19.57%) of upper thoracic pedicle screws (T 1-T 4) inserted under 3D computer-assisted navigation was significantly higher than that (3.57%) by conventional fluoroscopic control ( P <0.001). Average screw insertion time in conventional group was (4.56 ±1.03) min and (2.54 ± 0.63) min in computer assisted group ( P<0.001). In the conventional group, one patient had pleura injury and one had a minor dura violation. Conclusions This study provides further evidence that 3D computer-assisted navigation placement of pedicle screws can increase accuracy, reduce surgical time, and be performed safely and effectively at all levels of the thoracic spine, particularly upper thoracic spine.