Pedicle Screw Placement Research Articles

Evaluation of the nutrient foramen as a suitable landmark in spinal surgery

BACKGROUND CONTEXTThe posterior cervical approach is a very popular surgical procedure. Because of the slope-shaped laminae, a suitable landmark for laminectomy, laminoplasty, and pedicle screw placement does not exist. PURPOSEWe investigated the association between the nutrient foramen and spinal canal, and the safety of bone gutter placement using nutrient foramina for safe and effective spinal surgery. STUDY DESIGNObservational SETTINGUniversity Hospital PATIENT SAMPLESTwo hundred and sixty-six consecutive patients treated for cervical pathologies in our university hospital between January 2005 and December 2019. OUTCOME MEASURESWe identified the location of nutrient foramina and their anatomical association with the spinal canal using preoperative three-dimensional CT scanning. METHODSWe studied the distance between each foramen and the spinal canal, and the angle of the nutrient foramen at each vertebral level. RESULTSThe nutrient foramina were always located outside the spinal canal, with an average distance of +3.06±1.74 mm. The lower the spinal level, the closer the nutrient foramen to the spinal canal. CONCLUSIONSThe nutrient foramen can be considered a reliable landmark when using the posterior cervical approach.

Accuracy of Robot-Assisted Percutaneous Pedicle Screw Placement under Regional Anesthesia: A Retrospective Cohort Study.

Background Robot-assisted pedicle screw placement is usually performed under general anesthesia to keep the body still. The aim of this study was to compare the accuracy of the robot-assisted technique under regional anesthesia with that of conventional fluoroscopy-guided percutaneous pedicle screw placement under general anesthesia in minimally invasive lumbar fusion surgery. Methods This study recruited patients who underwent robot-assisted percutaneous endoscopic lumbar interbody fusion (PELIF) or fluoroscopy-guided minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) between December 2017 and February 2020 at a single center. Based on the method of percutaneous pedicle screw placement used, patients were divided into the robot-assisted under regional anesthesia (group RE-RO) and fluoroscopy-guided under general anesthesia (group GE-FLU) groups. The primary outcome measures were screw accuracy and the incidence of facet joint violation (FJV). Secondary outcome measures included X-ray and visual analogue scale (VAS) scores which were used to evaluate the degree of the postoperative pain at 4 hours and on postoperative days 1, 2, and 3. Intraoperative adverse events were also recorded. Results Eighteen patients were included in group RE-RO, and 23 patients were included in group GE-FLU. The percentages of clinically acceptable screws (Gertzbein and Robbins grades A and B) were 94.4% and 91.5%, respectively. There was no significant difference in the percentages of clinically acceptable screws (p=0.44) or overall Gertzbein and Robbins screw accuracy grades (p=0.35). Only the top screws were included in the analysis of FJVs. The percentages of FJV (Babu grades 1, 2, and 3) were 5.6% and 28.3%, respectively. This difference was statistically significant (p=0.01). Overall, the FJV grades in group RE-RO were significantly better than those in group GE-FLU (p=0.009). The mean fluoroscopy time for each screw in group RE-RO was significantly shorter than that in group GE-FLU (group RE-RO: 5.4 ± 1.9 seconds and group GE-FLU: 6.8 ± 2.0 seconds; p=0.03). The postoperative pain between the RE-RO and GE-FLU groups was not statistically significant. The intraoperative adverse events included 1 case of registration failure and 1 case of guide-wire dislodgment in group RE-RO, as well as 2 cases of screw misplacement in group GE-FLU. No complications related to anesthesia were observed. Conclusion Robot-assisted pedicle screw placement under regional anesthesia can be performed effectively and safely. The accuracy is comparable to the conventional technique. Moreover, this technique has the advantage of fewer FJVs and a lower radiation time.

Letter to the Editor Regarding “Traumatic Brain Injury–Related Pediatric Mortality and Morbidity in Low- and Middle-Income Countries: A Systematic Review”

Cervical pedicle screws (CPS) in the subaxial cervical spine (C3-C6) are faced with high incidence of perforating the lateral pedicular cortex endangering the vertebral artery (VA). The present study analyzes the pedicle width (PW) from C3 to C6 and defines the relation of VA with regard to pedicle and transverse foramen (TF) to determine the safety margin in cases of lateral pedicular breach.Computed tomography angiograms of 500 patients were retrospectively studied to identify the pedicle width (PW), VA area, TF area, and the lateral pedicle to vertebral artery distance (LPVA). Occupancy ratio (OR; the percentage area of transverse foramen occupied by VA) and safety margin (SM; permissible displacement of VA in TF), along with LPVA were considered to be protective parameters against VA injury if lateral pedicle breach happens.PW was 4.7 mm at C3, 4.83 mm at C4, 5.26 mm at C5 and 5.41 mm at C6. Mean LPVA at different levels was between 0.97 mm and 1.15 mm, OR was around 20% at all levels, and mean SM was between 2.34 mm and 2.92 at various levels. Sex differences were statistically significant for PW but not for LPVA, SM, or OR.This study gives us an idea about the various parameters in placement of cervical pedicle screw in subaxial cervical spine and the probable reasons there are few vertebral artery injuries despite high incidence of cervical pedicle breach. LPVA, safety margin, and OR may explain why even very significant CPS misplacement does not lead to vascular injury or neurologic deficit.

O-Arm Assisted Cervicothoracic Spine Pedicle Screw Placement Accuracy Is Higher Than C-Arm Fluoroscopy

We compared the accuracy of C-arm fluoroscopy versus O-arm-assisted pedicle screw (PS) placement in the cervicothoracic spinal junction (CTSJ). Patients who underwent PS placement in the CTSJ (C7-T4) at our hospital were included in this study. Of 37 patients who underwent PS placement in the CTSJ, 20 underwent intraoperative C-arm fluoroscopy-assisted surgery (C Group) and 17 underwent intraoperative O-arm-assisted surgery (O Group). In total, 159 PSs were placed-73 in the C Group and 86 in the O Group. The accuracy of PS placement was compared between the C Group and O Group using the classification proposed by Gertzbein and Robbins to analyze pedicle violation. PS accuracy was higher in the O Group than C Group; PS placement evaluated as grade A, representing no perforation, was 95.3% (82/86) for the O Group, whereas it was 78.1% (57/73) for the C Group. There was a clear statistically significant difference in accuracy of PS placement between the groups (P= 0.0013). O-arm-assisted surgery improved the accuracy of PS placement in the CTSJ.

Clinical Outcomes of Robotic Versus Freehand Pedicle Screw Placement After One-to Three-Level Lumbar Fusion.

Retrospective cohort study. The purpose of this study is to compare patient-reported outcome measures (PROMs) for patients undergoing one-to three-level lumbar fusion using robotically assisted vs freehand pedicle screw placement. Patients who underwent either robotically assisted or freehand pedicle screw placement for one-to three-level lumbar fusion surgery from January 1, 2014 to August 31, 2020 at a single academic institution were identified. Propensity score matching was performed based on demographic variables. Clinical and surgical outcomes were compared between groups. Recovery Ratios (RR) and the proportion of patients achieving the minimally clinically important difference (%MCID) were calculated for Oswestry Disability Index, PCS-12, MCS-12, VAS Back, and VAS Leg at 1 year. Surgical outcomes included complication and revision rates. A total of 262 patients were included in the study (85 robotic and 177 freehand). No significant differences were found in ΔPROM scores, RR, or MCID between patients who underwent robotically assisted vs freehand screw placement. The rates of revision (1.70% freehand vs 1.18% robotic, P = 1.000) and complications (.57% freehand vs 1.18% robotic, P = .546) were not found to be statically different between the 2 groups. Controlling for demographic factors, procedure type (robotic vs freehand) did not emerge as a significant predictor of ΔPROM scores on multivariate linear regression analysis. Robotically assisted pedicle screw placement did not result in significantly improved clinical or surgical outcomes compared to conventional freehand screw placement for patients undergoing one-to three-level lumbar fusion.

Initial Intraoperative Experience with Robotic-Assisted Pedicle Screw Placement with Cirq® Robotic Alignment: An Evaluation of the First 70 Screws.

Background: Robot-guided spine surgery is based on a preoperatively planned trajectory that is reproduced in the operating room by the robotic device. This study presents our initial experience with thoracolumbar pedicle screw placement using Brainlab’s Cirq® surgeon-controlled robotic arm (BrainLab, Munich, Germany). Methods: All patients who underwent robotic-assisted implantation of pedicle screws in the thoracolumbar spine were included in the study. Our workflow, consisting of preoperative imagining, screw planning, intraoperative imaging with automatic registration, fusion of the preoperative and intraoperative imaging with a review of the preplanned screw trajectories, robotic-assisted insertion of K-wires, followed by a fluoroscopy-assisted insertion of pedicle screws and control iCT scan, is described. Results: A total of 12 patients (5 male and 7 females, mean age 67.4 years) underwent 13 surgeries using the Cirq® Robotic Alignment Module for thoracolumbar pedicle screw implantation. Spondylodiscitis, metastases, osteoporotic fracture, and spinal canal stenosis were detected. A total of 70 screws were implanted. The mean time per screw was 08:27 ± 06:54 min. The mean time per screw for the first 7 surgeries (first 36 screws) was 16:03 ± 09:32 min and for the latter 6 surgeries (34 screws) the mean time per screw was 04:35 ± 02:11 min (p < 0.05). Mean entry point deviation was 1.9 ± 1.23 mm, mean deviation from the tip of the screw was 2.61 ± 1.6 mm and mean angular deviation was 3.5° ± 2°. For screw-placement accuracy we used the CT-based Gertzbein and Robbins System (GRS). Of the total screws, 65 screws were GRS A screws (92.85%), one screw was a GRS B screw, and two further screws were grade C. Two screws were D screws (2.85%) and underwent intraoperative revision. There were no perioperative deficits. Conclusion: Brainlab’s Cirq® Robotic Alignment surgeon-controlled robotic arm is a safe and beneficial method for accurate thoracolumbar pedicle screw placement with high accuracy.

Efficacy and safety for combination of t-EMG with O-arm assisted pedicle screw placement in neurofibromatosis type I scoliosis surgery

BackgroundDue to the characteristics of neurofibromatosis type I (NF-1) scoliosis, the precise placement of pedicle screws still remains to be a challenge. Triggered screw electromyography (t-EMG) has been proved to exhibit high sensitivity to identify mal-positioned pedicle screws, but no previous study assessed the combination of t-EMG with O-arm-assisted pedicle screw placement in NF-1 scoliosis surgery.ObjectiveTo evaluate efficacy and safety for combination of t-EMG with O-arm-assisted pedicle screw placement in NF-1 scoliosis surgery.Materials and methodsFrom March 2018 to April 2020, sixty-five NF-1 scoliosis patients underwent t-EMG and O-arm-assisted pedicle screw fixation were retrospectively reviewed. The channel classification system was applied to classify the pedicle morphology based on pedicle width measurement by preoperative computed tomography scans. The minimal t-EMG threshold for screw path inspection was used as 8 mA, and operative screw redirection was also recorded. All pedicle screws were verified using a second intraoperative O-arm scan. The correlation between demographic and clinical data with amplitude of t-EMG were also analyzed.ResultsA total of 652 pedicle screws (T10-S1) in 65 patients were analyzed. The incidence of an absent pedicle (channel classification type C or D morphology) was 150 (23%). Overall, abnormal t-EMG threshold was identified in 26 patients with 48 screws (7.4%), while 16 out of the 48 screws were classified as G0, 14 out of the 48 screws were classified as G1, and 18 out of the 48 screws were classified as G2. The screw redirection rate was 2.8% (18/652). It showed that t-EMG stimulation detected 3 unacceptable mal-positioned screws in 2 patients (G2) which were missed by O-arm scan. No screw-related neurological or vascular complications were observed.ConclusionsCombination of t-EMG with O-arm-assisted pedicle screw placement was demonstrated to be a safe and effective method in NF-1 scoliosis surgery. The t-EMG could contribute to detecting the rupture of the medial wall which might be missed by O-arm scan. Combination of t-EMG with O-arm could be recommended for routine use of screw insertion in NF-1 scoliosis surgery.

PP209 Analysis Of The Efficacy And Safety Of Robotic Spinal Surgery

IntroductionRobotic surgery (RS) can offer benefits compared to freehand surgery (FS) in the treatment of patients with spinal diseases. The aim of this study was to assess efficacy and safety of RS versus FS in spinal fusion. The outcomes considered were accuracy in the placement of pedicle screws, surgical times, hospital stay, exposure to radiation, and complications.MethodsA systematic review and meta-analysis were performed by researchers at the Instituto de Salud Carlos III (ISCIII). Studies published until June 2019 in the English, Spanish, or French languages were retrieved. The data analyses and risk of bias assessments were undertaken using RevMan 5.3.ResultsEight randomized controlled trials including 610 patients (RS: 308, FS: 302) were found. The mean age of the patients ranged from 56 to 68 years in the FS group and from 55 to 68 years in the RS group. The percentage of women included ranged from 46 to 73 percent undergoing FS and from 33 to 70 percent undergoing RS. The main diagnosis was degenerative spine disease. The number of screws implanted ranged from 22 to 584 for FS and 23 to 532 for RS. The robots used were the SpineAssist and Renaissance Guidance System (Mazor Robotics, Ltd) and the TiRobot® Orthopaedic Robotic System (Beijing Tinavi Medical Technologies Co., Ltd). Pedicle screw placement within the safety zone (Grades A and B on the Gertzbein and Robbins scale) ranged from 93 to 100 percent in FS and from 85 to 100 percent in RS (relative risk 1.0, 95% confidence interval [CI] 0.99–1.03; p = 0.36) (I2=75%; p = 0.0005). Regarding intervention time, the meta-analysis showed a mean difference (MD) of 15.2 minutes (95% CI 5.35–25.05; p = 0.002) (I2 = 0%; p = 0.39) in favor of FS. The MD in hospital stay was 0.36 days (95% CI -1.03–0.31; p = 0.30) (I2 = 62%; p = 0.07), which was not statistically significant. Contradictory results were found for fluoroscopy time, although RS was associated with a lower radiation dose than FS (p &lt; 0.05). In relation to safety, studies only reported on rates of surgical revision, which ranged from 0 to 2 after FS and from 0 to 10 after RS. The risk or bias was unclear in most studies.ConclusionsWe found no conclusive results suggesting benefits for spinal fusion using RS compared with FS. Further research with adequate selection of patients, type of robot, and comparator is needed.

3D printed templates improve the accuracy and safety of pedicle screw placement in the treatment of pediatric congenital scoliosis

BackgroundThree-dimensional (3-D) printed guidance templates are being increasingly used in spine surgery. The purpose of this study was to determine if 3D printed navigation templates can improve the accuracy of pedicle screw placement and decrease the complication rate compared to freehand screw placement in the treatment of children with congenital scoliosis.MethodsThe records of pediatric patients with congenital scoliosis treated at our hospital from January 2017 to January 2019 were retrospectively reviewed. Patients were divided into those where a 3D printed guidance templated was used and those in which the freehand method was used for pedicle screw placement. The accuracy rate of pedicle screw placement, surgical outcomes, and complications were compared between groups.ResultsA total of 67 children with congenital scoliosis were included (43 males and 24 females; mean age of 4.13 ± 2.66 years; range, 2–15 years). There were 34 children in the template-assisted group and 33 in the freehand group. The excellent accuracy rate of pedicle screw placement was significantly higher in the template-assisted group (96.10% vs. 88.64%, P = 0.007). The main Cobb angle and kyphosis angle were similar between the 2 groups preoperatively and postoperatively (all, P > 0.05), and in both groups both angles were significantly decreased after surgery as compared to the preoperative values (all, P < 0.001). The degree of change of the Cobb angle of the main curve and kyphosis angle were not significantly different between the 2 groups. There were no postoperative complications in the template group and 4 in the freehand group (0% vs. 12.12%; P = 0.009). All 4 patients with complications required revision surgery.

Intraoperative 3D imaging with cone-beam computed tomography leads to revision of pedicle screws in dorsal instrumentation: a retrospective analysis

BackgroundCorrect positioning of pedicle screws can be challenging. Intraoperative imaging may be helpful. The purpose of this study was to evaluate the use of intraoperative 3D imaging with a cone-beam CT. The hypotheses were that intraoperative 3D imaging (1) will lead to an intraoperative revision of pedicle screws and (2) may diminish the rate of perforated screws on postoperative imaging.MethodsTotally, 351 patients (age 60.9 ± 20.3 a (15–96); m/f 203/148) underwent dorsal instrumentation with intraoperative 3D imaging with 2215 pedicle screws at a trauma center level one. This study first evaluates intraoperative imaging. After this, 501 screws in 73 patients (age 62.5 ± 19.7 a; m/f 47/26) of this collective were included in the study group (SG) and their postoperative computed tomography was evaluated with regard to screw position. Then, 500 screws in 82 patients (age 64.8 ± 14.4 a; m/f 51/31) as control group (CG), who received the screws with conventional 2D fluoroscopy but without 3D imaging, were evaluated with regard to screw position.ResultsDuring the placement of the 2215 pedicle screws, 158 (7.0%) intraoperative revisions occurred as a result of 3D imaging. Postoperative computed tomography of the SG showed 445 (88.8%) screws without relevant perforation (type A + B), of which 410 (81.8%) could be classified as type A and 35 (7.0%) could be classified as type B. Fifty-six (11.2%) screws in SG showed relevant perforation (type C–E). In contrast, 384 (76.8%) screws in the CG were without relevant perforation (type A + B), of which 282 (56.4%) could be classified as type A and 102 (20.4%) as type B. One hundred and sixteen (23.2%) screws in the CG showed relevant perforation (type C–E).ConclusionThis study shows that correct placement of pedicle screws in spine surgery with conventional 2D fluoroscopy is challenging. Misplacement of screws cannot always be prevented. Intraoperative 3D imaging with a CBCT can be helpful to detect and revise misplaced pedicle screws intraoperatively. The use of intraoperative 3D imaging will probably minimize the number of revision procedures due to perforating pedicle screws.

Robotic-Assisted Trajectory Into Kambin's Triangle During Percutaneous Transforaminal Lumbar Interbody Fusion-Initial Case Series Investigating Safety and Efficacy.

Minimally invasive spine surgery (MISS) has the potential to further advance with the use of robot-assisted (RA) techniques. While RA pedicle screw placement has been extensively investigated, there is a lack of literature on the use of the robot for other tasks, such as accessing Kambin's triangle in percutaneous lumbar interbody fusion (percLIF). To characterize the surgical feasibility and preliminary outcomes of an initial case series of 10 patients receiving percLIF with RA cage placement via Kambin's triangle. We performed a single-center, retrospective review of patients undergoing RA percLIF using robot-guided trajectory to access Kambin's triangle for cage placement. Patients undergoing RA percLIF were eligible for enrollment. Baseline health and demographic information in addition to peri- and postoperative data was collected. The dimensions of each patient's Kambin's triangle were measured. Ten patients and 11 levels with spondylolisthesis were retrospectively reviewed. All patients successfully underwent the planned procedure without perioperative complications. Four patients underwent their procedure with awake anesthesia. The average dimension of Kambin's triangle was 66.3 m2. With the exception of 1 patient who stayed in the hospital for 7 d, the average length of stay was 1.2 d, with 2 patients discharged the day of surgery. No patients suffered postoperative motor or sensory deficits. Spinopelvic parameters and anterior and posterior disc heights were improved with surgery. As MISS continues to evolve, further exploration of robot-guided surgical practice, such as our technique, will lead to creative solutions to challenging anatomical variation and overall improved patient care.

Accuracy of ‘O arm’ guided pedicle screw placement in osteoporotic spine with the ‘precious pedicle’

IntroductionOsteoporosis is a global burden with the prevelance ranging from 15 to 20% in women and 4–7% in men across the globe. This is the age group which most commonly presents in spine clinic with pathologies requiring pedicle screw fixation. Pedicle screw fixation in osteoporotic spine is a challenge pertaining to the poor bone quality leading to various complication like screw backout, loosening and pedicle breach. With the advent of O arm and navigation, it is now possible to place pedicle screw with reported accuracy of 96%. Here, in this one of a kind study, we study the accuracy of O arm guided pedicle screw insertion in osteoporotic spine. Materials and methodThis is a retrospective study of patients operated between July 2020 to December 2020 for pedicle screw fixation at a tertiary care center by a single senior spine surgeon using O arm (O2) Navigation. All patients, over the age of 55 years having osteoporosis; defined by Singh’s index; who were operated for lumbar pedicle screw fixation were included in the study. All patients under the age of 55 or having Singh’s index of more than 3 were excluded. ResultsAll the patients operated at a tertiary care center by a single senior spine surgeon was considered in our study. Of 67 patients operated between July 2020 to December 2020 using O arm navigation, 32 patients fit into our criteria. Total 172 pedicle screws were inserted in osteoporotic spine. One of the patients had one pedicle breach in our group intra operatively which needed reinsertion of screw. ConclusionO arm guided pedicle screw placement is a novel technique which seems to be the most accurate technique till date. With an accuracy of 99.5% in osteoporotic spine, this should be the method of choice when using pedicle screws, whenever available.

Augmented Reality (AR) in Orthopedics: Current Applications and Future Directions.

Imaging technologies (X-ray, CT, MRI, and ultrasound) have revolutionized orthopedic surgery, allowing for the more efficient diagnosis, monitoring, and treatment of musculoskeletal aliments. The current review investigates recent literature surrounding the impact of augmented reality (AR) imaging technologies on orthopedic surgery. In particular, it investigates the impact that AR technologies may have on provider cognitive burden, operative times, occupational radiation exposure, and surgical precision and outcomes. Many AR technologies have been shown to lower provider cognitive burden and reduce operative time and radiation exposure while improving surgical precision in pre-clinical cadaveric and sawbones models. So far, only a few platforms focusing on pedicle screw placement have been approved by the FDA. These technologies have been implemented clinically with mixed results when compared to traditional free-hand approaches. It remains to be seen if current AR technologies can deliver upon their multitude of promises, and the ability to do so seems contingent upon continued technological progress. Additionally, the impact of these platforms will likely be highly conditional on clinical indication and provider type. It remains unclear if AR will be broadly accepted and utilized or if it will be reserved for niche indications where it adds significant value. One thing is clear, orthopedics' high utilization of pre- and intra-operative imaging, combined with the relative ease of tracking rigid structures like bone as compared to soft tissues, has made it the clear beachhead market for AR technologies in medicine.

Optimizing Lumbar Pedicle Screw Trajectory Utilizing a 3D-Printed Drill Guide to Ensure Placement of Pedicle Screws Into Higher Density Bone May Improve Pedicle Screw Pullout Resistance

Lower preoperative Hounsfield Unit (HU) values of vertebral body are associated with pedicle screw (PS) loosening after implantation with traditional trans-pedicular trajectory. However, the relationship between trajectory HU value and PS fixation quality remains unknown. This study aimed to investigate if 3-dimensionally (3D)-printed guider directed accurate implantationof pedicle screw could increase the anti-pulling properties of screws. 3D models of cadaveric spines were reconstructed by using computed tomography image and PS trajectories were designed for both sides of vertebra. The designed trajectories were divided into high HU group and low HU group. PS implantation with 3D-printed screw guide can be in complementary shape with target vertebra. Throughout 3D finite element analysis and biomechanical tests, the pull-out strength of screws in high or low trajectoryHU groups were compared. The HU value was 132 ± 13 (mean ± standard deviation) in low HU group and 189 ± 17 in high HU group. The distance between planned trajectories and actual trajectories was 1.69 ± 0.4 mm. Biomechanical tests showed that in the high trajectory HU group the pull-out strength of screws was 750.41 ± 80.65 N; compared with 655.83 ± 74.31 N in the low trajectory HU group, the difference was statistically significant. When simulated with the finite element method, the pull-out strength of low HU trajectory pedicle screws was lower than that of high HU trajectory pedicle screws. Preoperative computer-assisted trajectory design using a 3D-printed screw guide may direct more accurate implantation with optimal implantation trajectory, and may provide a new way to improve pedicle screw fixation.

Effects of rocuronium dosage on intraoperative neurophysiological monitoring in patients undergoing spinal surgery.

What is known and objectiveIntraoperative neurophysiological monitoring (IONM) has been widely used in clinical practice. Therefore, the influence of neuromuscular blockers essential for spinal anaesthesia on IONM is worthy of our attention, but no randomized study has evaluated the dose‐response effect. This study investigated the effects of different doses of rocuronium bromide on the intraoperative monitoring of motor evoked potentials (MEPs).MethodsWe conducted a randomized, double‐blind trial to assess the effects of three rocuronium bromide doses (6.0, 9.0, 12 μg·kg−1·min−1) combined with intravenous infusion of propofol 6–8 mg·kg−1·h−1 and remifentanil 10 μg·kg−1·h−1 on the amplitudes of somatosensory evoked potentials (SEPs) and MEPs at the time of the baseline recording (T1), before pedicle screw placement (T2) and before spinal canal decompression (T3). Secondary outcomes included measurement of neuromuscular function, the occurrence of unexpected intraoperative body movement and recovery of spontaneous breathing.Results and discussionA total of 123 patients were enrolled, and 120 patients were ultimately analysed. No differences were observed in the amplitude of SEPs among the three groups (p > 0.05). The MEP amplitude differences at T1, T2 and T3 in all limbs did not differ in patients receiving rocuronium at 6.0 μg·kg−1·min−1 and 9.0 μg·kg−1·min−1 (p > 0.05). However, when rocuronium was administered at 12.0 μg·kg−1·min−1, MEP amplitudes at the time point T3 were significantly attenuated compared with the time points T1 and T2 in both right upper limb and left lower limb (p = 0.002, p = 0.025, respectively). In patients treated with rocuronium 6.0 μg·kg−1·min−1, the incidence of unexpected body movement was significantly higher (p = 0.026), and the train‐of‐four count (TOF count) showed a significant increase at T2 and T3 (p < 0.001) compared to other doses.What is new and conclusionRocuronium bromide at a rate of 9.0 μg·kg−1·min−1 provided suitable and adequate muscle relaxation without inhibiting IONM; thus, this dose is recommended for spinal surgery.

0.4% incidence of return to OR due to screw malposition in a large prospective adolescent idiopathic scoliosis database.

In contrast to infection and curve progression, return to OR for implant malposition is potentially within the surgeon's control. With increasing surgeon familiarity with freehand/fluoroscopic pedicle screw placement, rates of return to OR due to malposition may have decreased over time. We sought to document the incidence and risk factors for return to OR due to screw malposition in a large cohort of patients with idiopathic scoliosis. AIS patients enrolled in a multicenter prospective registry with minimum 2-year follow-up undergoing PSF between 2003 and 2017 were included. Surgeries with the use of intraoperative CT-guided navigation were excluded. Return to OR due to screw malposition over time was tabulated. Lenke class, age at surgery, year of surgery, height, weight, surgeon and site were evaluated. 2435 patients underwent PSF with non-navigated open pedicle screw instrumentation. Mean age was 14.6years, mean thoracic curve magnitude was 53°, and mean lumbar was 40°. Patients did not routinely undergo intraoperative or postoperative CT evaluation. There were 10 returns to OR for screw malposition at a mean of 0.83years postoperatively (range 0.1-3.4years), for an overall incidence of 0.4%. Of the 14 screws, 10 were thoracic, 7 were left-sided. No association was found between screw malposition and curve size, enrolling site, surgeon, BMI, Lenke class, or age. Five patients had radiculopathy which improved after screw revision. Return to OR for screw malposition changed from 2003 to 2017 (1-0.2%) but this did not reach statistical significance. Although the incidence of asymptomatic malpositioned screws is unknown, the rate of return to the OR for implant malposition overall in this registry was 1 in 250 patients. Recent data suggest the rate has decreased to 1 in 500 patients. Further work may determine whether enabling technologies can reduce the rate, ideally to a "never event".

Usefulness of Preoperative Planning by Three-Dimensional Planning Software for Pedicle Screw Placement in Thoracolumbar Surgeries: Misplacement Rate and Associated Risk Factors.

Introduction A number of imaging technologies have been developed to reduce the risk of pedicle screw (PS) misplacement. For example, preoperative three-dimensional (3D) planning can reportedly enhance implant placement accuracy in some orthopedic surgeries. However, no study has investigated the effect of preoperative 3D planning on PS placement without intraoperative 3D navigation. Thus, in this study, we aim to examine the accuracy of PS placement and identify the risk factors for PS misplacement in thoracolumbar surgeries performed using preoperative 3D planning software with intraoperative fluoroscopic guidance in a retrospective study. Methods In total, 25 consecutive patients (197 PSs) underwent thoracic or lumbar spinal fusion surgeries using preoperative 3D planning with intraoperative fluoroscopic guidance. PS misplacement was graded based on the degree of perforation (Grade 0, no perforation; Grade 1, <2 mm; Grade 2, 2-4 mm; Grade 3, >4 mm) observed in postoperative computed tomography (CT). Deviations between planned and actual PSs were evaluated by matching preoperative and postoperative CT volume images for each vertebra. Results The overall PS misplacement rate was 6.6% (Grade 1: 4.0%, Grade 2: 1.5%, Grade 3: 1.0%). The median linear deviations of PS entry points between planned and actual locations were determined to be 3.3 mm and 3.3 mm for the horizontal and vertical axes, respectively. The median angular deviations of the PS axis were 6.2° and 4.5° for the transverse and sagittal planes, respectively. Multivariate analysis revealed that horizontal deviation of the PS entry point was the sole factor associated with Grade ≥1 PS misplacement (odds ratio=2.47, p<0.001). Conclusions Preoperative 3D planning software without intraoperative 3D navigation was able to achieve a relatively low PS misplacement ratio among the reported ratio of conventional techniques without navigation. Surgeons should carefully ensure that the entry point is consistent with preoperative planning, especially in the mediolateral direction to avoid misplacement in this method.

3D ultrasound navigation system for screw insertion in posterior spine surgery: a phantom study.

Posterior spinal fusion surgery is required to correct severe idiopathic scoliosis. The surgery involves insertion of screws which requires high accuracy to prevent neurologic damage to the spinal cord. Although conventional CT navigation can reduce this risk, 3D-ultrasound-based navigation could achieve this without added ionizing radiation and usage of expensive and bulky equipment. This study aimed to evaluate the accuracy of a 3D ultrasound navigation system for posterior spine surgery. A custom 3D ultrasound (3DUS) with model-to-surface registration algorithm was developed and integrated into a 3D navigation environment. A CT scan of an adolescent spine (T3-T11) was segmented and 3D printed for experiments. A probe with reflective markers was placed in vertebral pedicles 684 times in varying levels, positions in the capture space and orientation of vertebra, and the entrypoint and trajectory accuracies were measured. Among 684 probe placements in vertebral levels T3 to T11 in the phantom spine, 95.5% were within 1mm and 5° of accuracy, with an average accuracy of 0.4 ± 0.4mm and 2.1 ± 0.9°, requiring 8.8s to process. Accuracies were statistically significantly affected by vertebral orientation and position in the capture volume, though this was still within the targeted accuracies of 1mm and 5°. This preliminary ultrasound-based navigation system is accurate and fast enough for guiding placement of pedicle screws into the spine in posterior fusion surgery. The current results are limited to phantom spines, and future study in animal or human cadavers is needed to investigate soft tissue effects on registration accuracy.

P.169 Reduced radiation CT imaging for augmented reality spinal surgery applications

Background: There is growing evidence for the use of augmented reality (AR) in pedicle screw placement in spinal surgery to increase surgical accuracy, improve clinical outcomes and reduce the radiation exposure required for intraoperative navigation. Auto-segmentation is the cornerstone of AR applications because it correlates patient-specific anatomy to structures segmented from preoperative computed tomography (pCT) images. These AR techniques allow for a reduction in the radiation dose required to acquire CT images while maintaining accurate segmentation. Methods: In this study, we methodically increase the noise that is introduced into CT images to determine the image quality threshold that is required for auto-segmentation on pCT. We then enhance the images with denoising algorithms to evaluate the effect on the segmentation. Results: The pCT radiation dose is decreased to below the current lowest clinical threshold and the resulting images still produce segmentations that are appropriate for input into AR applications. The application of denoising algorithms to the images resulted in increased artifacts and decreased bone density. Conclusions: The CT image quality that is required for successful AR auto-segmentation is lower than that which is currently employed in spine surgery. Future research is required to identify the specific, clinically relevant radiation dose thresholds.

P.174 Accuracy of pedicle screw placement with X-ray versus O-arm image-guided navigation

Background: Image-guided navigation is routinely used in spine surgery to improve placement of pedicle screws. However, most reports have relied on two-dimensional X-ray evaluation to determine accuracy of screw positioning. In this study, computed tomography (CT) and O-arm imaging enabled a detailed three-dimensional comparison of screw placement. The objective was to compare the accuracy of pedicle screw placement with intraoperative X-ray versus O-arm image-guided navigation. Methods: This was a retrospective analysis of image-guided pedicle screw placement in patients who underwent spinal instrumentation. Post-operative CT and O-arm imaging allowed grading of screw accuracy based on pedicle breaches. Clinical outcomes included patient and operative factors. Results: Pedicle screws were placed in 208 patients (1116 screws). Three-dimensional O-arm guidance was utilized for 126 patients, while the remainder underwent two-dimensional X-ray imaging and post-operative CT assessment. O-arm navigation was associated with improved pedicle screw accuracy: pedicle breaches were more likely to be low grade (odds ratio 2.84, p=0.001) and less likely to be medium grade (odds ratio 0.35, p=0.007) or high grade (odds ratio 0.31, p=0.025). Conclusions: This study provided a detailed comparison of surgical accuracy with X-ray versus O-arm guidance. Navigation with O-arm imaging is associated with benefits in spinal instrumentation, without impacting operative risks for patients.