Pedicle Screw Misplacement Research Articles

Complications of percutaneous pedicle screw fixation in treating thoracolumbar and lumbar fracture

Percutaneous pedicle screw fixation (PPSF) has been a popular approach for treating thoracolumbar and lumbar fracture, and its relevant complications have been gradually recognized. This study aimed to summarize the complications of PPSF in treating thoracolumbar and lumbar fracture as well as the management and outcomes of the complications.We retrospectively analyzed the patients with thoracolumbar and lumbar fracture who were admitted to our department from February 2011 to February 2015 and underwent posterior PPSF. Information on demographics, medical comorbidities, radiographs, and treatment was obtained from hospital medical records and follow-up records. Main outcome indexes included adverse clinical and radiological outcomes during and after surgery.A total of 781 patients were included in this study. Forty-six patients (5.9%) presented with complications during or after surgery. The complications included intraoperative guide wire breakage, abdominal artery injury, spinal dura mater injury, postoperative pedicle screw misplacement, screw breakage, plug screw falling off, connecting rod loosening, poor reduction, and late infection. Among the 39 cases with postoperative complications, 14 underwent revision surgery, and the remaining patients underwent conservative treatment and presented good outcomes.PPSF is associated with the following complications: guide wire rupture, blood vessel injury, cerebrospinal fluid leakage, screw misplacement, poor reduction, failed internal fixation, and infection. A thorough preoperative evaluation, accurate operation, and timely and correct management of complications are critical to achieving satisfactory surgical outcomes.

Repeat Surgical Interventions Following “Definitive” Instrumentation and Fusion for Idiopathic Scoliosis: 25-Year Update*

Study DesignSingle-institution, retrospective review of prospectively collected data on pediatric patients with adolescent idiopathic scoliosis (AIS) undergoing spinal fusion with a minimum two-year follow-up. ObjectiveTo determine the rate of reoperation in AIS patients undergoing spine fusion from 2008 to 2012. Summary of Background DataRecent trends in the surgical treatment of AIS have included increased use of all–pedicle screw constructs, smaller implants, more posterior-only approaches, and improved correction techniques. MethodsA retrospective review of 467 patients undergoing spinal fusion from 2008 to 2012 was performed. Demographic, clinical, radiographic, and surgical data were collected prospectively on all patients for the index procedure and any reoperations. Data were compared to previously published cohorts of patients from the authors' institution who underwent spinal fusion for AIS between 1988 and 2007. ResultsThe rate of reoperation in this five-year cohort of patients was 9.9%. The most common indications for reoperation were infection (4.5%: 2.4% delayed infections and 2.1% acute infections), symptomatic implants (2.1%), and misplaced pedicle screws (1.7%). When compared to the 2003-2007 cohort, the rate of reoperation for acute infection and malpositioned pedicle screws increased significantly (p = .01 and p = .04), whereas the rate of reoperation for curve progression decreased (p = .01). Reoperations for acute infections and malpositioned pedicle screws also increased significantly (p = .047 and p = .042) compared with the 1988-2002 cohort, whereas the rate of reoperation for pseudarthrosis decreased (p = .002). ConclusionReoperation rates for AIS have not improved with more sophisticated implants and techniques, predominantly because of increased acute infections and malpositioned pedicle screws despite decreasing pseudarthrosis rates and curve progression. Level of EvidenceLevel II.

T96. Neuromonitoring adolescent idiopathic scoliosis with pulse train technique

The placement of thoracic pedicle screw is technically difficult, and the medial mal position can result in a feared risk for the spinal cord. The effectiveness of detecting mal-positioning of pedicle screws varies widely in the literature, specially at thoracic levels, but in 2014, Calancie et al. described a technique with high accuracy in preventing that in adult patients. We prospectively studied the usefulness of the technique in adolescents with idiopathic scoliosis. We studied 51 adolescent patients (41 female), mean age of 14.8 y (11–18 y) diagnosed with idiopathic scoliosis, submitted to scoliosis correction with the free-hand technique for thoracic pedicle screw placement under total intravenous anesthesia (TIVA) and intraoperative neuromonitoring (IONM) with our standard protocol updated with the multi-train stimulation technique (MTST). MTST parameters consists of a repetitive train of electric pulses applied in the track and in the implanted pedicle screw. The warning criteria was a muscle MEP recorded in lower limb muscles with stimulus below 12 mA for the track and 25 mA for the screw. Intraoperative fluoroscopy was used to check screw position if the warning criteria was achieved and after the placement of all screws if there were no alarms. The final decision of the surgeon to a given alarm considered anatomical features, the threshold and the fluoroscopy images. We studied 210 tracks/screws from T2 to L1 in the first 13 cases and 390 from T2 to T10 in the remaining 38. Track/screw threshold was below the limit 49 times (8.2%), with higher incidence for T5 and T9 (10 times each), and for T7 and T8 (8 times each). Tracks/screws were redirected successfully in 33 cases and due to their persistent lower thresholds, withdrawn in 8, all of them from the apex of the scoliosis concavity. In the remaining 8 cases the surgeon decided to let the implant in the original position considering the imaged and the screw thresholds close to the limit. In 24 cases (47%) the warning criteria were not achieved neither for track or screw, and the images agreed with the IONM findings. In 3 cases the thresholds for the screws were below 4 mA and a complete loss of TcMEP in lower limb immediately followed the screw placement. In two cases the screws were removed immediately, and the patients have transitory motor deficit, but in one case the surgeon took a long time to remove the implants and the patient become paraplegic. MTST takes no more than 10 s for each screw. The technique showed a good relationship with medial mal-positioning of the track/screw. It was not time consuming and the surgeons felt confident with the warning criteria, reducing also the X-ray exposition. Very low thresholds can even suggest spinal cord lesion demanding the cross checking with TcMEP. The technique showed to be safe and trustful for younger patients (adolescents) with idiopathic scoliosis and should be considered a standard of care for thoracic pedicle screw placement.

F170. Usefulness of t-EMG of the pedicle hole after withdrawal of lumbar pedicle screws

t-EMG of the pedicle hole before the placement of lumbar pedicle screws, and later stimulation of the screw is an established neurophysiologic method to avoid lumbar pedicle screw malposition. Occasionally it is necessary to remove some of the instrumentation in a later surgery, which made us wonder if it is necessary to stimulate the trajectories of the screws once they have been removed, before the re-instrumentation of those levels. We have studied 12 patients with previous surgeries for the correction of vertebral deformities, in which a posterior surgery for the removal of part of the instrumentation was performed. In this second surgery, screws were stimulated before their removal, and their pedicle trajectories were performed afterwards. We have considered of risk t-EMG values below 10 mA 62 screws were removed, all lumbar. In the first surgery t-EMG values were all normal, both the trajectory and the screw. None of the patients presented neurological symptoms. A CT scan was performed before the second surgery, and 16 of the 62 screws to be removed had a certain degree of medial-caudal displacement. During the surgery for their removal, t-EMG of the screws was performed, being normal in all cases, and after the withdrawal of the screws, their trajectories were also stimulated. A 48% of the screws’ trajectories had t-EMG values under 10 mA. None of the removed screws was repositioned, regardless of their t-EMG value. In an off-line analysis of the results, 14 out of the 16 malpositioned screws (87%) had a low t-EMG value of the pedicle hole after their removal. And 16 out of the 46 well-positioned screws (34%) presented a low t-EMG value of the pedicle hole after their removal. Even though the usefulness of the t-EMG of the pedicle track before the screw placement has been proven to avoid lumbar pedicle screw malposition, it seems that the stimulation of the pedicle track once a screw has been removed does not have the same implication, at least with the current threshold values. We need more cases to be able to establish t-EMG of the pedicle trajectories of the removed screws as a useful tool to decide the replacement of a screw using the same trajectory.

Spinal navigation for minimally invasive thoracic and lumbosacral spine fixation: implications for radiation exposure, operative time, and accuracy of pedicle screw placement.

Navigation is emerging as a useful adjunct in percutaneous, minimally invasive spinal surgery (MIS). The aim of this study was to compare C-Arm navigated, O-Arm navigated and conventional 2D-fluoroscopy assisted MIS thoracic and lumbosacral spine fixation techniques in terms of operating time, radiation exposure and accuracy of pedicle screw (PS) placement. Retrospective observational study of 152 consecutive adults who underwent MIS fixations for spinal instability: 96 2D-fluoroscopy assisted, 39 3D-C-Arm navigated and 27 using O-Arm navigated. O-Arm navigation significantly reduced PS misplacement (1.23%, p) compared to 3D-C-Arm navigation (7.29%, p = 0.0082) and 2D-fluoro guided placement (5.16%, p = 0379). 3D-C-Arm navigation was associated with lower procedural radiation exposure of the patient (0.4mSv) than O-Arm navigation (3.24mSv) or 2D-fluoro guidance (1.5mSv). Operative time was comparable between three modalities. O-Arm navigation provides greater accuracy of percutaneous instrumentation placement with an acceptable procedural radiation dose delivered to the patients and comparable operative times. These slides can be retrieved under Electronic Supplementary material.

Postoperative Assessment of Pedicle Screws and Management of Breaches: A Survey among Canadian Spine Surgeons and a New Scoring System.

Study DesignThis study was designed as a survey amongst Canadian spine surgeon to determine a scoring system to standardize pedicle screw placement assessment.PurposeThis study aimed to obtain and analyze the opinions of spine surgeons regarding the assessment of pedicle screw accuracy, with the goal of establishing clinical guidelines for interventions for malpositioned pedicle screws.Overview of LiteratureAccurate placement of pedicle screws is challenging, and misalignment can lead to various complications. To date, there is no recognized gold standard for assessing pedicle screw placement accuracy. The literature is lacking studies attempting to standardize pedicle screw placement accuracy assessment.MethodsA survey of the clinical methods and imaging criteria that are used for assessing pedicle screw placement accuracy was designed and sent to orthopedic and neurosurgery spine surgeons from the Canadian Spine Society for their anonymous participation.ResultsThirty-five surgeons completed the questionnaire. The most commonly used modalities for assessing pedicle screw position postoperatively were plain X-rays (97%) and computed tomography (CT, 97%). In both symptomatic and asymptomatic patients, the most and least worrisome breaches were medial and anterior breaches, respectively. The majority of surgeons tended not to re-operate on asymptomatic breaches. More than 60% of surgeons would re-operate on patients with new-onset pain and a ≤4-mm medial or inferior breach in both thoracic and lumbar regions. If a patient experienced sensory loss and a breach on CT, in either the thoracic or lumbar levels, 90% and 70% of the surgeons would re-operate for a medial breach and an inferior breach, respectively.ConclusionsPostoperative clinical presentation and imaging findings are crucial for interpreting aberrant pedicle screw placement. This study presents a preliminary scoring system for standardizing the classification of pedicle screws.

Sagittal orientation and uniform entry for thoracic pedicle screw placement with free-hand technique: A retrospective study on 382 pedicle screws

BackgroundOne of the most important factors in obtaining a successful outcome in spinal surgery is appropriate placement of the pedicle screw. A number of different techniques are used to achieve successful pedicle screw placement. The free-hand technique has the advantage of no requirement for radiation exposure, but its success is highly dependent on surgeon experience. Here, we describe our entry point and perioperative sagittal orientation method, and evaluate postoperative sagittal alignment of pedicle screws with the free-hand pedicle screw placement technique. Materials and methodsEighty-two patients undergoing spinal surgery between 2015 and 2016 were included in this study. Pedicle screw placement was evaluated retrospectively on postoperative anterior-posterior (A-P) and lateral load-bearing radiographs of the entire spinal column. The vertebral body was divided into five areas in the lateral plane. Sagittal orientation of the pedicle screws on lateral radiographs was evaluated by two spine surgeons with 3 years of experience and one radiologist experienced in musculoskeletal radiology, with each observer evaluating the image twice according to a 1-month interval. ResultsA total of 382 pedicle screws were evaluated. There was no statistically significant difference between the first and second measurements, performed by individual observers, and there was good concordance among the three observers. ConclusionsUse of a uniform entry point at all levels may increase the effectiveness of the free-hand technique and decrease the pedicle screw misplacement rate. Our technique may standardize the free-hand technique, which does not require radiation exposure, and make it more practical to apply uniformly.

The morphological relationship between lumbosacral transitional vertebrae and lumbosacral pedicle asymmetry.

Introduction The clinical significance of lumbosacral transitional vertebrae (LSTV) has been reported. However, the association between LSTV and lumbosacral pedicle anatomical anomaly has not been investigated. We hypothesized that LSTV might be associated with lumbosacral anatomical anomaly. The purpose of this study was to examine the morphological association between LSTV and lumbosacral pedicle asymmetry (PA) using computed tomography (CT). Methods A retrospective review of CT images of 347 lumbosacral degenerative disease patients was performed. We divided the subjects into two groups: the normal and LSTV groups. LSTV was classified based on Castellvi's classification. PA was defined as a difference of more than 20° between the right and left angles of the pedicle. Results Seventy out of 347 lumbosacral degenerative disease patients (20.17%) were diagnosed with LSTV. In the normal group, only a 0.54% incidence of PA was seen; however, with respect to the LSTV group, a 9.29% incidence of PA was seen. A significant difference in PA incidence was observed between the groups (p < 0.001). Type IIIa and Type IV in the LSTV group showed a statistically significant PA incidence rate (p = 0.004 and p = 0.039, respectively). Conclusions Our study demonstrated that there was a significant difference in the incidence of PA between LSTV subjects and normal subjects. Moreover, the incidence of PA was significantly higher in LSTV subjects with severe anomaly. These results suggested that lumbosacral spine anomaly might have a close relationship with the incidence of PA and lumbosacral nerve root asymmetry. Therefore, morphological evaluation of the pedicle is important for preoperative surgical management, especially in cases using pedicle screws. This information could lower the incidence of pedicle screw malposition when pedicle screws are inserted at the lumbosacral spine.

Epidemiology and Clinical Management of Traumatic Spine Injuries at a Major Government Hospital in Cambodia.

Study DesignCross sectional study.PurposeTo characterize the pattern of injury, describe the current clinical management, and determine the outcomes in traumatic spine injury (TSI) patients presenting to a major government hospital in Phnom Penh, Cambodia.Overview of LiteratureThere is a paucity of literature on epidemiology or current clinical practices for TSIs in Cambodia. The findings from this study can thus serve as a valuable resource for future progress in treating TSIs in low-income countries.MethodsThis study was a cross-sectional study of TSI patients admitted to Preah Kossamak Hospital in Phnom Penh, Cambodia. Demographics, cause of spinal injury, spinal level of injury, surgical procedures and techniques, complications, and American Spinal Injury Association (ASIA) grades were recorded and analyzed.ResultsEighty patients were admitted with TSI between October 2013 and June 2014. Falls from heights were the most common cause of TSI, followed by road traffic accidents. 78% of the admitted patients underwent at least one surgical procedure. Without intraoperative imaging, 4 patients (6%) had wrong level surgery, and 1 patient (2%) had misplacement of pedicle screws. Sacral decubitus ulcers were the most common non-surgically related complication. Antibiotics were administered to >90% of patients. There were no in-hospital mortalities. Of the 60 spinal cord injury (SCI) patients, 32% (19/60) showed improvement in their ASIA grade at the time of discharge, and 52% (31/60) showed no change. At follow-up, 32% (19/60) of SCI patients reported improvement, and 8% (5/60) reported no change. However, 36 SCI patients (60%) were lost to follow-up.ConclusionsDespite technological limitations, outcomes of TSI patients in Cambodia appear favorable with evidence of clinical improvement and low mortality.

Clinically significant pedicle screw malposition is an underestimated cause of radiculopathy

Clinically significant pedicle screw malposition is an underestimated cause of radiculopathy

Malpositioned Pedicle Screw Compressed Thoracic Aorta of a Patient With Adolescent Idiopathic Scoliosis: Case Report and Literature Review

Background: Aortic injuries because of pedicle screw placement are quite rare, consequently management strategies to avoid vascular complications are lacking. Intraoperative or postoperative images to reveal the accuracy of screw placement in scoliotic misalignment with freehanded placed pedicle screws is therefore essential. Case Report: A 13-year-old girl with adolescent idiopathic scoliosis (AIS) was presented at the outpatient clinic of the authors department. Operative correction of the scoliotic misalignment including dorsal pedicle screw and rod placement with fusion from T3 to L4 was performed. Computed tomography scan after surgery showed left T9 screw malposition, accompanied by lateral compression of thoracic aorta. No clinical manifestations of aortic stenosis were noted. To avoid severe vascular complications, the thoracic screw was removed with the help of a specialized team of vascular as well as thoracic surgeons through extrapleural thoracotomy. After the removal of the malpositioned screw, the correction maneuvres were applied without the left T9 screw. No posttraumatic aortic aneurysm and other wall injury were identified after the revision surgery. The patient was discharged after 20 days of inpatient stay without the use external immobilization. The girl was in a good clinical condition after the 1-year follow-up visit without vascular or neurological complications. Conclusions: Malpositioned pedicle screws after dorsal correction in patients with adolescent idiopathic scoliosis might be challenging. Aortic injuries because of malpositioned screws are rare; nevertheless, the presence might be a life-threatening condition despite a clinical asymptomatic patient. As a consequence, the authors recommend to perform routine postoperative computed tomography scans combined with angiography in the case of significant lateral screw positioning.

Minimally Invasive Cervical Pedicle Screw Fixation by a Posterolateral Approach for Acute Cervical Injury.

This is a retrospective case series. To avoid lateral misplacement of midcervical pedicle screws, T.T., one of our authors, developed a method for minimally invasive cervical pedicle screw (MICEPS) fixation by a posterolateral approach. We reviewed our initial experience with this fixation for trauma cases. Excellent clinical results with cervical screws have been reported for trauma cases. Although cervical pedicle screw fixation can be an essential part of reconstruction in spinal disorders, there is also a risk for injury to the vertebral artery. This study included 56 consecutive patients who received surgery for cervical fractures. We inserted a total of 203 cervical pedicle screws. Nineteen patients were treated by conventional methods. Thirty-seven patients were treated by MICEPS fixation. According to the MICEPS fixation, 12 patients were treated by unilateral fusion, 25 patients by bilateral fusion. All pedicle screws were inserted using spinal navigation system in the both groups. The average surgical time was 217 minutes with the conventional pedicle screw fixation and 165 minutes with the MICEPS fixation (P=0.0014). The average intraoperative bleeding was 560 mL in the conventional fixation and 140 mL in the MICEPS fixation (P<0.0001). Clinically significant screw deviation was significantly lower in the MICEPS fixation group than in the conventional cervical pedicle screw group (P=0.0039). There was not any deep wound infection in both groups. This intramuscular approach allows for horizontal pedicle screw insertion. This technique is probably useful for reducing intraoperative bleeding. In this study, incidence of screw perforation was significantly lower in the MICEPS fixation group than in the conventional cervical pedicle screw group. In particular, neither of the misplaced screws was laterally deviated in the MICEPS group.

Pedicle Screw Safety: How Much Anterior Breach Is Safe?: A Cadaveric and CT-Based Study.

Clinical retrospective chart review and basic science study. To determine the safety limits of an anterior/anterorolateral misplaced pedicle screw on computed tomography (CT) scan in spinal deformity. Although the limits of medial breaches (<4 mm) are known, the safe limits for anterior/anterolateral breaches in spine deformity are not yet defined. The present study had two parts. In part I, postoperative CT scans of 165 patients operated on for spine deformity were reviewed for screw misplacement (2800 screws). The amount of anterior/anterolateral breach was measured. Protrusions were also evaluated for proximity to vital structures. All scans were reviewed by musculoskeletal radiologist. In part II, eight cadavers were instrumented with 6 × 30 and 6 × 40 mm bilaterally from T1-S1. Screws were randomly inserted under navigation guidance either "IN" or "OUT-anterior/lateral." CT scan was performed, followed by gross dissection to determine screw position. Part I: 116(4.2%) screws were misplaced anterior/anterolaterally. Thirty-one (26.7%) were adjacent to vital structures. Fisher exact test showed 4 mm or less breach has significantly lower likelihood of impingement (P < 0.001). Screws adjacent/impinging the aorta protruded an average 5.7 ± 0.6 mm, whereas screws not involving the aorta breached an average 3.9 ± 0.2 mm, (P < 0.001). Part II: 285 screws were inserted. On CT scan, 125 were misplaced anterior/anterolaterally. On gross dissection, 89 were visibly misplaced; 23 were covered entirely by soft tissue but were palpable; and 13 were contained in bone. All 23 screws did not endanger any structures and protruded less than 4 mm on CT scan. Anterior/anterolateral breaches of 4 mm or less on CT poses no significant risk of impingement and therefore can be considered safe. 3.

Management of major vascular injury during pedicle screw instrumentation of thoracolumbar spine

ObjectivesVascular injury is a rare complication of spinal instrumentation. Presentation can vary from immediate hemorrhage to pseudoaneurysm formation. In the literature, surgical approach to repair has varied based on anatomy, acuity of diagnosis, infection, and available technology. In this manuscript, we aim to describe our institutional experience with vascular injuries in thoraco-lumbar spine surgery. Patients and methodsWe report our institutional experience of three cases of vascular injury secondary to pedicle screw misplacement and their management, as well as a review of the literature. ResultsThe first case had a history of previous instrumentation and presented with back pain and fever. The patient was taken for instrumentation exploration via a posterior approach. Aortic violation was discovered at T6 intraoperatively during instrumentation removal and the patient underwent emergent endovascular repair. The second case presented with chronic back pain after multiple prior posterior fusions and CT angiogram showing screw perforation on the aorta at T10. The patient underwent elective endovascular repair with synchronous removal of the instrumentation. The third case presented with radicular leg pain 6 months after L4-S1 posterior lumbar interbody fusion, with CT scan demonstrating the left S1 screw abutting the L5 nerve root and common iliac vein. The patient underwent elective instrumentation revision with intraoperative venography. ConclusionMajor vascular injury is a known complication of spinal surgery, especially if it involves instrumentation with pedicle screws. Treatment approach has evolved with the advancement of endovascular technology; however, open surgery remains an option when anatomy or infection is prohibitive. In the elective setting, preoperative planning with attention to surgical approach, positioning, and contingencies, should occur in a multidisciplinary fashion. Repair with an aortic stent-graft cuff may minimize unnecessary coverage of the descending thoracic aorta and intercostal arteries.

Delayed Dural Leak Following Posterior Spinal Fusion for Idiopathic Scoliosis Using All Posterior Pedicle Screw Technique.

In pediatric patients, pedicle screws are malpositioned 5% to 15% of the time. Complications associated with malpositioned screws are infrequently reported in the literature. We present a series of adolescent idiopathic scoliosis (AIS) patients who presented in a delayed manner with positional headache and chronic dural leak adjacent to the pedicle screw tract. Scoliosis databases at 2 centers were reviewed, and cases of delayed positional headaches following posterior spinal fusion for AIS were identified. Demographic and clinical data were collected. Of 322 patients, 4 patients presented with positional headaches at a mean of 12.8 weeks following posterior spinal fusion surgery for AIS, with an interval time to diagnosis of 5 months. Computed tomographic myelogram demonstrated severe pedicle screw malposition in 1 patient, and minimal malposition in 3 patients (<2 mm violation). The patients had delayed presentation with positional headaches secondary to dural leak. All patients successfully underwent revision surgery with repair of the dural leak. At the time of latest follow-up, all patients are asymptomatic. Pedicle screw malposition can result in dural leaks. Patients may present in a delayed manner with positional headaches and an acquired Chiari malformation. Clinical suspicion should prompt imaging of the brain or cervical spine followed by computed tomographic myelogram to determine site of leak. This is a rare complication from pedicle screw malposition. Level IV-case series.

Free hand technique lumbar spine pedicle screw placement in Indian population

There are different pedicle screws entry point techniques are used for the lumbar pedicle screws placement. This study reported using confluence of pars, mamillary process, midpoint of transverse process, on lateral border of face joint as entry point of lumbar pedicle screws with free hand technique and the accuracy of this technique. Materials and Methods: A prospective study was done from may 2015 to November 2017 in our hospital using free hand technique lumbar pedicle screw placement includes 50 patients 270 screws. The diagnosis includes degenerative spine, trauma, and spondylolithesis. cortical breach by misplaced pedicle screw was determined by review of computed tomography. Results: Among the total 270 lumbar free hand placed pedicle screws, 10 screws with lateral breach, 1 screw inferior breach, 2 medial breach without significant neurological involvement with two cases of radicular pain which subsides over period of time without any revision. Conclusion: Free hand pedicle screw placement based on external landmark using confluence of pars, mamillary process, midpoint of transverse process, on lateral border of face joint as entry point of lumbar pedicle screws with free hand technique and the accuracy of this technique showed acceptable safety and accuracy and avoidance of radiation exposure.

P323 Value of pulse-train stimulation of the pedicle tracks for the detection of thoracic screws malposition in scoliosis surgery

Introduction Despite the improvement in the detection of misplaced thoracic pedicle screws in the last years, there is still a percentage of malpositioned thoracic screws that are not detected by conventional neurophysiological monitoring techniques. Methods We have set a neurophysiological protocol during the scoliosis surgery: simple and pulse-train stimulation at the pedicle track and over the screws. We have included the level L1 because the spinal cord typically extends caudally through that level. We assume a malposition in pedicle holes with thresholds below 9 mA at the simple stimulation and below 15 mA at the pulse-train stimulation. In cases with borderline stimulation thresholds, final placement of the screw was decided by the surgeon. Results Of 436 monitored screws, the surgeon modified 15 pedicle tracks due to low threshold intraoperatively. After the surgery, none of the patients showed neurological symptoms. In the CT-scan, 5 of all analyzed screws showed mediocaudal malposition and the rest of screws were well placed. Conclusion Pulse-train stimulation of the pedicle tracks and of the screws allow us to increase the sensibility for the detection of malpositioned thoracic screws. The stimulation of the pedicle track is a valuable tool to increase the safety and decrease the possibility of complications associated with the thoracic screws malpositioning.

Novel synthetic vertebrae provide realistic haptics for pedicle screw placement.

During vertebral surgery, misplaced pedicle screws can harm vital neural and vascular structures. Haptic distinction between cortical and cancellous bone structures is therefore essential for correct screw placement. This tactile experience during pedicle screw placement can be obtained by training on human or animal specimens even if expensive or ethically questionable. In this study, novel synthetic vertebrae were evaluated within a hybrid simulator to provide realistic haptics for the training of spine surgeries. Synthetic vertebrae were custommade of calcium powder-based composites imitating both, cancellous and cortical bone. The mechanical properties of synthetic surrogates were validated for pedicle screw placement and cement augmentation and were compared with those obtained from human vertebrae and insertion torques were analyzed. In human vertebrae pedicle screw torque measurements resulted in mean torque slopes of 82±33Nm/m. Calcium carbonate-based materials achieved lower torques than the human bone whereas calcium phosphate-based bone surrogates showed comparable results. A further differentiation of the calcium phosphate-based vertebrae revealed, that synthetic vertebrae with lower amounts of blowing agent, achieved suitable torques (83 ± 28Nm/m) in comparison to the human reference (p = 0.39). Cement application and subsequent fluoroscopy images confirmed, that the cancellous core of the synthetic vertebrae enabled cement augmentation. In conclusion, our findings suggest, that the artificial bone samples mimic the properties of human bone during pedicle screw placement and cement augmentation and are therefore suitable as synthetic vertebrae in a hybrid surgical simulator.

Minimally invasive cervical pedicle screw fixation via the posterolateral approach for metastatic cervical spinal tumors.

Background To avoid lateral misplacement of midcervical pedicle screws, we developed a method for Minimally Invasive Cervical Pedicle Screw (MICEPS) fixation via a posterolateral approach. This intramuscular approach allows for horizontal pedicle screw insertion and reduced intraoperative bleeding. We reviewed our initial experience with MICEPS fixation for patients with cervical metastases. Methods This study included 18 consecutive patients who received cervical spinal surgery for metastatic tumor. We treated 12 patients with conventional cervical pedicle screw fixation, and 6 patients with the MICEPS fixation technique. Average follow-up was 14 months (range 3 to 34). We inserted 117 pedicle screws using the navigation system. Average fusion area was 4.9 vertebrae (range 3 to 8). Alpha-angles between a line perpendicular to the posterior cortex of the vertebral body and the screw trajectory in the transverse plane were also measured. Results The average surgical time was 250 min (range 151 to 420 min) with the conventional pedicle screw fixation and 234 min (range 154 to 300 min) with the MICEPS fixation. The average total blood loss was 780 mL (range, 180-1430 mL) in the conventional pedicle screw fixation group and 180 mL (range, 70-400 mL) in the MICEPS fixation group. At the level of midcervical (C3-5), average alpha-angles was 52 degrees (range 43 to 62) in MICEPS fixation group, and 39 degrees (range 19 to 55) in conventional cervical pedicle screw group. Conclusions The MICEPS fixation technique uses an intramuscular approach, which is minimally invasive and reduces intraoperative bleeding. Intramuscular approach allows for horizontal pedicle screw insertion, and reduced critical screw deviation.

Incidence and risk factors for the misplacement of pedicle screws in scoliosis surgery assisted by O-arm navigation—analysis of a large series of one thousand, one hundred and forty five screws

To assess the accuracy of O-arm-navigation-based pedicle screw placement in scoliosis surgery and identify the potential risk factors for the misplacement of pedicle screws. One hundred forty four scoliosis patients treated with O-arm-navigation-based pedicle screw instrumentation were enrolled, and 1145 pedicle screws implanted in the apical region of the curves were retrospectively reviewed for accuracy according to post-operative CT images. The potential risk factors and independent predictive factor(s) for the misplaced screws were identified statistically. The overall malpositioning rate of pedicle screw was 9.8%; 54.5% of which were misplaced laterally. Univariate and multivariate logistic regression analysis of clinical and surgical treatment variables indicated that patients with congenital scoliosis (CS) [OR: 1.489 (95% CI: 1.002-2.213; P = 0.035)] and neurofibromatosis type I (NF-1) [OR: 1.785 (95% CI: 1267-2.045; P = 0.026)], middle-thoracic spine [OR: 1.661 (95% CI: 1.107-2.481; P = 0.021)], the concave pedicles [OR: 1.527 (95% CI: 1.020-2.285; P = 0.019)], and the segments three levels away from the tracker [OR: 3.522 (95% CI: 2.357-5.263; P = 0.001)] were independently associated with pedicle screw misplacement. O-arm-assisted navigation does improve the accuracy and safety of pedicle screw placement in scoliosis surgery. However, unavoidable screw malpositioning remained, which occurred significantly more often in patients with CS and NF-1, in middle-thoracic spine, in the concave pedicles, and in the segments three levels away from the tracker.