< Previous30 Abstracts and oral opioids (oxycodone, titrated to pain scores). IV hydromorphone was included in the multimodal analgesia but only given as rescue medication. Data was collected from patient electronic medical records. Results: Patients in the continuous ESPB group reported an average length of stay (LOS) of 2.3 ± 1.1 days compared to 3.2 ± 1.3 days in the non-ESPB group. Mean oral opioid use was 65.4 ± 54.3mg (Morphine equivalent dose (MED) = 98.1mg ± 81.5mg) in the continuous ESPB cohort compared to 140.4 ± 138.0mg (MED = 210.6 ± 207.0mg) in the non-ESPB group. IV hydromorphone use was 1.9 ± 1.7mg (MED = 5.7 ± 5.1mg) in the ESPB group compared to 3.9 ± 2.9 mg (MED = 11.7 ± 8.7mg) in the non ESPB group. There were no adverse events related to the use of continuous ESPB. Conclusion: Continuous ESPB is associated with a shorter hospital LOS and reduced opioid consumption in subjects undergoing one- and two-level MIS lumbar fusions performed by a single surgeon at a single center. Of note, continuous ESPB was placed by the surgeon, eliminating the need for advanced anesthesia providers. Larger, randomized controlled trials are needed to confirm the results of this case series. References: (1) Yong Qiu, Teng-Jiao Zhang, Zhen Hu Erector Spinae Plane Block for Lumbar Spinal Surgery: A Systematic Review, Journal of Pain Research 2020 (13): 1611–1619. Paper 39:Resolution of Back Pain Following Minimally Invasive Laminectomy Daniel Shinn; Pratyush Shahi; Kyle Morse; Sidhant Dalal; Tejas Subramanian; Sheeraz Qureshi; Sravisht Iyer Introduction: Symptomatic improvement of leg pain as a predominant presenting symptom has been demonstrated following laminectomy; however, resolution of back pain as a predominant presenting symptom remains underreported. Aims/Objectives: Compare clinical outcomes of patients undergoing minimally invasive (MIS) Laminectomy with lower extremity neurologic symptoms with and without a significant component of back pain. Methods: This was a retrospective review of a prospectively maintained database from 2017 to 2020. PROMs including ODI, VAS for back and leg pain, SF-12 PCS and SF-12 MCS, and PROMIS-PF were collected. Patients were divided into two groups: predominant leg pain (pLP) and predominant back pain (pBP). The pLP patients had pre-operative VAS leg>VAS back. The pBP cohort patients had pre-operative VAS back≥VAS leg. Baseline characteristics were summarized using descriptive statistics and compared using Chi-Squared, Fisher’s Exact Test, or two-sample T-Test. Changes in PROMs were compared at the 2-week, 6-week, 12-week, 6-month, 1-year, and 2-year. Achievement of Minimal Clinically Important Difference (MCID) at an early post-operative (2-12 week) and late post-operative (6 month-2 years) timepoint was assessed as well using the following MCID cutoffs: -12.8 for ODI, -1.2 for VAS back, -1.6 for VAS leg, +4.9 for SF12 PCS, +4.6 for SF12 MCS, and +4 for PROMIS. Results: 135 total patients were included, 65 pLP and 70 pBp patients. There were no significant differences in patient demographics, operative level, or follow-up length. The degree of improvement in PROMIS was greater in the pLP cohort from 2-weeks (pLP:4.5±8.3vspBP:-0.2±10.1;p=0.006) to 6-months (pLP:12.4±12.7vspBP:5.1±7.9;p=0.021), but this difference lost significance by 1 and 2-years. There was no difference in the magnitude of change in ODI, SF12 PCS, or SF12 MCS. There was also no significant difference in the MCID achievement rate in any of the PROMs. By the late post-operative timepoint, 64.9% and 62.7% achieved a MCID in ODI (p=0.848), 60.5% and 75.4% in VAS back (p=0.177), 80.3% and 66.7% in VAS leg (p=0.136), 60.4% and 60.8% in SF12 PCS (p=1), 41.5% and 48% in SF12 MCS (p=0.556), 77.1% and 67.3% in PROMIS (p=0.366), for pLP and pBP respectively. The only significant difference in time to MCID achievement was for PROMIS (pLP:3.2±5.8months,pBP: 5.8±7.4months;p=0.004). Conclusions: MCID achievement rate didn’t differ between the cohorts for any PROMs. A significant difference magnitude of PROMIS improvement was noted only from 2-12 weeks, which demonstrated a faster time to PROMIS MCID in the pLP cohort. The ultimate PROMIS MCID achievement rate was not significantly different. Paper 40: Impact of Facet Replacement vs. TLIF in a Prospective Randomized FDA Study on ODI and Post-Operative Opioid Utilization Among Subjects at 24 Months John H. Chi, MD, MPH - Harvard Medical School; Michael Steinmetz; Scott Meyer; Ahmad Nassr - Mayo Clinic; Vikas Patel; Michael W. Groff - Brigham and Women's Hospital, Harvard Medical School; Evalina Burger; William C. Welch, MD, FACS, FICS - University of Pennsylvania, Perelman School of Medicine; Domagoj Coric Introduction: Conservative treatment of pain associated with lumbar spondylolisthesis and stenosis often includes the use of narcotics. Long-term narcotic use, however, is associated with potentially life-threatening side effects and has been shown to negatively affect clinical outcomes following SESSION 12: FREE PAPERS—LIGHTNING ROUND31 Please Click Here to VIEW Presenter Disclosures lumbar spine surgery. Facet arthroplasty represents a possible alternative to current surgical treatment options for patients suffering from lumbar spondylolisthesis and stenosis. The effect of facet replacement arthroplasty versus lumbar fusion on post-operative narcotic use is worthy of assessment. Objective: This study examines the association of post- operative opioid use and clinical outcomes among patients undergoing facet arthroplasty and fusion surgery. Methods: This interim analysis from a randomized, prospective study examined 249 subjects that were randomly assigned (2:1) to either facet arthroplasty with the TOPS System or to TLIF. All subjects underwent decompressive laminectomy via a mid-line incision at one lumbar level. Patient reported outcomes alongside opioid use were assessed through 24 months of follow-up. Results: There were no significant differences in baseline demographics or operative characteristics. At 24 months, only 9.9% of TOPS subjects utilized opioid pain medication compared to 25.3% of subjects at pre-op. This represents a 60.9% decrease at 24 months compared to baseline in the TOPS subjects, while the fusion subjects reported only a 27.0% decrease in the same time period. This difference trended toward significance but did not reach significance. At 24 months the mean ODI score for the TOPS group decreased from 56.9 ± 12.2 at baseline to 9.0 ± 13.6, while the fusion group decreased from 56.4 ± 13.3 at baseline to 21.4 ± 21.6. Meaningful reductions in both opioid use and ODI through the first 6 months are seen in both groups; however, the fusion group reports an increase in opioid use at 12 and 24 months, and this coincides with slightly worsening disability scores. Conclusion: For subjects that undergo facet arthroplasty, the use of narcotics post-operatively decreases more than among fusion patients (61% versus 24% decrease). Moreover, this reduction in medication usage transpires concurrently with a more significant improvement in patients’ daily function— as measured by ODI—among TOPS subjects versus fusion subjects. Paper 41: Hardware Failure Over Ten Years After 574 Levels of Lateral Lumbar Interbody Fusion Deborah Liaw, BS - USF Health Morsani College of Medicine; Elliot Pressman, MD - USF Health Morsani College of Medicine; Molly Monsour, BS - USF Health Morsani College of Medicine; Puya Alikhani, MD - USF Health Morsani College of Medicine Lateral lumbar interbody fusion (LLIF) is one of many techniques used to treat degenerative spine disease. While sometimes used as a standalone, it is often supplemented by posterior instrumentation. LLIF is a useful adjunct due to its ability to improve lordosis, lower subsidence rates, and its minimally invasive nature. Given its different technique and approach, it subjects the spine to different loading forces and stiffness of construct. These may play a role in hardware failure. We sought to measure a large cohort of these patients to find factors that affect the rates of hardware failure (HF). We conducted a retrospective cohort study on all patients who underwent LLIF at a single academic center between 2012 and 2021. HF was defined as any rod fracture, rod dislodgement, or screw pullout. Demographics and operative variables were collected and analyzed. 325 patients, comprising 574 levels, were identified that were operated on by seven neurosurgeons; 10 were included twice as they had two LLIFs at different times. 6 patients were diagnosed with HF. Median time from index surgery to revision for this was 189 days; median follow-up was 776 days. The most common lateral upper instrumented vertebra (UIV) was L2 (108; 33.2%), followed by L3 (103; 31.7%) and L4 (69; 21.2%). The most common total construct UIV was L2 and L3 (97; 29.8% each), followed by L4 (65; 20.0%). There was no difference in demographics between those who developed HF and those who did not. Operatively, increased lateral levels fused in the index surgery (no HF 1.75±0.108 vs. HF 2.67±2.07; p=0.021), increased levels of posterior levels instrumented both in the index surgery (no HF 2.55±0.288 vs. HF 5.33±1.52; p=0.009) and in the total construct (no HF 3.43±0.292 vs. HF 6.83±3.36; p=0.002), increased interbody cages added in the index surgery (no HF 1.91±0.128 vs. HF 3.33±0.666; p=0.003) and in the total construct (no HF 2.29±0.134; HF 3.33±0.666), were all associated with an increased risk of HF. On logistic regression analysis, the variable with the strongest predictive ability of HF was total posterior levels of instrumentation (p=0.006; 95% confidence interval=1.077-1.550). This predicts that each level of posterior instrumentation increases the odds of HF by 1.292. This is to our knowledge the largest SESSION 12: FREE PAPERS—LIGHTNING ROUND32 Abstracts cohort of LLIF patients being analyzed for risk of HF. Our outcomes show that larger spine surgeries both in terms of lateral levels included, and especially posterior levels included, predispose a patient to HF. Paper 42: Biomechanical Comparison of Unilateral and Bilateral Pedicle Screw Fixation After Multilevel Lumbar Lateral Interbody Fusion Utilizing 26 mm Cages James M. Mok, MD, MBA - NorthShore University HealthSystem; Craig Forsthoefel, MD - University of Illinois Chicago; Roberto Leonardo Diaz, PhD - University of Illinois Chicago; Ye Lin, MD - University of Illinois Chicago; Farid Amirouche, PhD - University of Illinois Chicago Introduction: Lumbar Lateral Interbody Fusion (LLIF) utilizing a 26 mm wide cage has been reported as having favorable biomechanical characteristics compared to narrower cages. Objective: In this human cadaveric biomechanical study, we examine the biomechanical stability of unilateral pedicle screw and rod fixation after multilevel LLIF utilizing 26 mm wide cages compared to bilateral fixation. Methods: Eight fresh frozen human cadaveric specimens of L1-L5 were included. Specimens were stripped of soft tissue while preserving the discs and spinal ligaments and attached to a universal testing machine (MTS 30/G). Flexion, extension, and lateral bending were attained by applying a 200 N load at a rate of 2 mm/s. Axial rotation was applied at a rate of 2 deg/s. Three-dimensional specimen range of motion (ROM) was recorded using an optical motion-tracking device. Specimens were tested in 3 conditions: 1) intact, 2) L1-L5 LLIF (4 levels) with unilateral rod, 3) L1-L5 LLIF with bilateral rods. Results: Range-of-motion measurements in flexion/extension, lateral bending, and axial rotation were measured at each segment (L1-L2, L2-L3, L3-L4, L4-L5) and combined. From the intact condition, LLIF with unilateral rod decreased flexion-extension by 77%, lateral bending by 53%, and axial rotation by 26%. In LLIF with bilateral rods, flexion-extension decreased by 83%, lateral bending by 64%, and axial rotation by 34%. Comparing unilateral and bilateral fixation, LLIF with bilateral rods reduced ROM by a further 23% in flexion- extension, 25% in lateral bending, and 11% in axial rotation. The difference was statistically significant in flexion-extension and lateral bending (p< 0.005) Conclusions: Unilateral screw and rod fixation would facilitate single position posterior instrumentation after lateral interbody fusion in the lateral decubitus position. Considerable decreases in ROM were observed after multilevel (4-level) LLIF utilizing 26 mm cages in both the unilateral and bilateral pedicle screws and rods situations. The addition of bilateral fixation provides a 10-25% additional decrease in ROM. These results can inform surgeons of the incremental biomechanical benefit when considering unilateral or bilateral posterior fixation after multilevel LLIF. Paper 43: Biomechanical Comparison of Stability and Anterior Column Load Sharing: Transfacet-Intralaminar Cortical Fixation versus Traditional Pedicle Screw Instrumentation After Lateral Interbody Fusion Robert K. Eastlack; Pierce D. Nunley; Kornelis A. Poelstra, MD PhD - The Robotic Spine Institute of Las Vegas / Nevada Spine Clinic; Iris Wu; Pierre Legay; Aakash Agarwal Introduction: A novel metal-free PEEK cortico-pedicular strap, placed after unique curvilinear drill-hole creation through the lamina-facet complex interface, has been FDA-approved. This strap provides circumferential and compressive cortical fixation of the lamina, pedicle, and facet joints. This fixation method closer approximates the instantaneous axis of rotation relative to other available fixation system. Objective: To characterize the biomechanical differences between transfacet-intralaminar cortical fixation and pedicle screw system (PSS) for stability and anterior column load dynamics in conjunction with lateral interbody fusion (LLIF). Methods: A validated L1-S1 osteoligamentous spinal finite element model simulated L4-L5 LLIF with a PEEK lateral cage (18mm x 40mm, height 8mm, lordosis 12deg) with posterior fixation. Mechanical properties were assigned to physiologic tissues per published literature. Spinal weight and muscle stabilization of a 90kg male was applied through 414N follower load. Group 1 received standard posterior Ti6AL4V PSS with 5.5mm rods, whereas PEEK strap intralaminar fixation was used for Group 2. Each lamina, pedicle, and facet joint was circumferentially fixed using a ratcheting strap creating a compressive force between the facet surfaces at maximum tension of 222N. An intact model was used as the control group. All three models were simulated for flexion, extension, lateral bending (LB), and torsion using a maximum load of 7.5Nm. Outputs recorded were range of motion, neutral zone motion at 0.75Nm (i.e., 10% of maximum load), and anterior column load through the cage. SESSION 12: FREE PAPERS—LIGHTNING ROUND33 Please Click Here to VIEW Presenter Disclosures Results: Both posterior fixation techniques (Groups 1 & 2) provided similar stabilization of L4-L5 with an average of 81% reduction in motion across all planes, compared to intact. Similarly, the neutral zone motion (at 0.75Nm) in all planes decreased to zero in both groups after posterior stabilization. In comparison to the intact spine, anterior column load in group 1 decreased by 66% in extension, increased by 7% in flexion, and decreased by 23-27% in the remaining conditions (standing, torsion, and LB). In contrast, anterior load decreased by only 23% in extension for group 2 and increased 9%- 43% for the remaining conditions (standing, torsion, LB, and flexion). On average, anterior column loading was higher in group 2 compared to group 1 by 130N. Conclusions: Both fixation techniques provided similarly effective reduction in L4-L5 spinal element motion. However, anterior column stress shielding was lower in the transfacet- intralaminar strap fixation method while forces remained below its yield strength. This could translate into more physiologic fusion characteristics for the interbody space via Wolff’s law. Paper 44:A Retrospective Study of Lumbar Circumferential Fusion: Interlaminar Fusion Stabilization versus Pedicle Screw Instrumentation Philip K. Paschal, MS - Hospital for Special Surgery; Daniel Alicea, BS - Albert Einstein College of Medicine; Kevin Tang, BS - Albert Einstein College of Medicine; Celeste Abjornson, PhD - Hospital for Special Surgery; Frank Cammisa, MD - Hospital for Special Surgery Introduction: Lumbar spinal fusion procedures are commonly performed with an anterior column support utilizing an interbody device and posterior supplemental fixation with pedicle screw instrumentation (PSI) and bone grafting. Although PSI techniques have advanced, there are reports of significant morbidities, decreased lordosis, and limit options if revision surgery is required. Interlaminar fusion devices (ILFD) have been shown to provide similar support to PSI with less morbidity. ILFD is a U-shaped device that is fixed to the adjacent spinous processes, with the stabilizing portion lying between the laminae. The implant is designed for one to two level lumbar fusion for patients with degenerative disc disease without significant spondylolisthesis. Objective: The purpose of this study is to compare the clinical outcomes of patients undergoing 1 or 2 level circumferential lumbar fusion supplemented by either ILFD or PSI. Methods: After Institutional Review Board (IRB) approval, a single center, retrospective, matched consecutive series study was performed using data from the electronic medical record. Operative reports were utilized to identify patients who underwent a single-level lateral lumbar interbody fusion (LLIF) supplemented with posterior stabilization with ILFD (Cofix®: Surgalign, San Diego, CA) or PSI. 153 patients were categorized into two groups: ILFD (n = 80) or PSI (n = 73). Results: The average age of ILFD and PSI groups was 56.4 +/- 8.4 years and 58.8 +/- 11.4 years, respectively. Compared to the ILFD group, the PSI group had more patients who received two-level surgery (57.5% in PSI versus 35% in ILFD). Those who received ILFD had significantly less mean EBL (ILFD: 209.3 ± 122.2 cc, PSI: 329.5 ± 244.6 cc; p < 0.001) and mean procedure time (ILFD: 195.8 ± 84.6 minutes, PSI: 256.6 ± 96.6 minutes; p < 0.001). There were no statistical differences in fusion rate at 6- and 12 months (or ILFD: 83.8% and 88.8%; PSI: 79.5% and 87.7%). Segmental and global lordosis were statistically similar between groups. Kaplan Meier Survivability curve based on reoperation rates favored ILFD to PSI. Those who received ILFD were less likely than those who received PSI to use narcotics at 6 months (ILFD: 20%, PSI: 49.3%; p < 0.001) and 12 months (ILFD: 8.8%, PSI: 30.1%; p < 0.001). Conclusions: ILFD is a minimally invasive option for circumferential fusion that is safe and durable. Compared to PSI, it provides similar restoration of lordosis and fusion stability, and offers greater options for revision and less narcotic use. Paper 45: The Efficiency and Accuracy of the Robotic Assistance in Pedicle Screw Placement Peter Boucas; Adam Strigenz, BA - Northwell Health; Shaya Shahsavarani; Rohit Verma Introduction/Aims/Objective: There is a growing interest in robotic-assisted spine surgery as new technologies emerge. This study characterizes the utility of robotic systems with navigation in assisting with pedicle screw placement by examining the accuracy and efficiency of screws placed by robotic assistance compared with conventional techniques. Further, this study evaluates how accuracy and efficiency changed over time to illustrate the learning curve of robotic systems. Methods: One surgeon’s data from 80 cases using the Mazor X robot was reviewed retrospectively. Registration times, average screw placement times, and operative times were recorded. Intraoperative CTs post-screw insertion were obtained for each patient. 3 orthopedic spine surgeons SESSION 12: FREE PAPERS—LIGHTNING ROUND34 Abstracts independently graded screw accuracy using the Gertzbein- Robbins grading scale. Grades A and B were considered clinically acceptable. Grades C, D, and E were considered failures. Screw insertion times were compared with documented averages in literature for freehand techniques. Screw accuracy was evaluated similarly. A two-tailed t-test was used to compare registration time, average screw placement time, and accuracy between the first 40 cases and second 40 cases. Results: Average registration time and screw placement time for the 80 cases overall with the Mazor X system were 18.52 minutes and 8.27 minutes respectively. 97% of screws placed with robotic assistance were deemed clinically accurate. Registration times were 17.10 min and 19.88 minutes in the first 40 and second 40 cases respectively (p=0.52). Screw insertion times were 10.34 and 6.20 minutes per screw in first 40 and second 40 cases respectively (p< 0.01). There was a significant decrease in the average time required for screw placement (p< 0.01) between these two groups. There was no significance in clinical accuracy and registration times between both groups. Conclusion: Pedicle screws placed with robotic assistance were associated with high precision overall. Screw placement times were significantly reduced from the first 40 cases to the second 40, owing to the learning curve of working with robotics in surgery. Registration times, reflective of equipment setup, did not differ between groups. We attribute this to knowledgeable support staff, another component that cannot be overlooked. When compared with navigated non- robotic pedicle screw insertion times reported in literature – 7.8 min/screw – our data demonstrates that using robotics may present the benefit of navigation and optimal implant positioning without sacrificing operative time. This evidence suggests that with greater use of the robot, placement times will quicken while accuracy remains excellent, making this an efficient alternative to freehand techniques. Paper 46:Objective and Subjective Validations of a Novel Spinal Guidance System for Pedicle Screw Placement Using Augmented Reality and Artificial Intelligence G. Bryan Cornwall, PhD, MBA, PEng - Surgalign; Cristian J. Luciano, PhD - Surgalign; Selvon St. Clair, MD, PhD - Orthopaedic Institute of Ohio; Hani Malone, MD - Scripps Clinic; Michal Trzmiel, MS - Surgalign; Kateryna Parfeniuk, MS - Surgalign; Kris Siemionow, MD, PhD - University of Illinois Introduction: Spinal navigation addresses some challenges associated with posterior spinal instrumentation, including minimizing pedicle screw misplacement, decreasing radiation exposure, and improving procedural efficiency. Augmented reality (AR) and Artificial Intelligence (AI) are emerging technologies that can benefit current navigation systems. Aims/Objectives: To evaluate a novel spine guidance system that performs anatomical segmentation, registration, presurgical planning, and intraoperative guidance using a combination of AR and AI by (1) objectively assess the 3D placement precision of navigated pedicle screws, and (2) subjectively validate the system usability in a clinical setting. Outcome Measures: Orthopedic stereotaxic guidance systems are required to meet a regulatory placement precision established by the US FDA consisting of a mean translational error < 3 mm and a mean trajectory deviation < 3°. The System Usability Scale (SUS) is a reliable industry standard tool, consisting of subjective questions with a 5-point Likert scale from strongly agree to strongly disagree. A SUS score above 68 is considered average. Methods: Eighty lumbosacral pedicle screws were placed by 4 spine surgeons in 8 cadavers using AR/AI navigation. Intraoperative CTs were obtained before and after screw placement. The comparison between the 3D positions and orientations of the virtual and real pedicle screws was performed by automatically registering both volumetric datasets and manually defining the real screw placement. For screw placement precision testing, mean, standard deviation, and upper bound limit (UBL) of the 99% confidence interval are reported. The Human Factors usability study was conducted with 16 surgeons, presented with identical 10-item questionnaire. Video was recorded and analyzed afterwards to ensure repeatability in a clinical setting. Results: For the 80 pedicle screws, the mean positional error was 2.31±1.01 mm, with a 99% UBL of 2.60 mm. The mean angular error was 1.45±0.72°, with a 99% UBL of 1.66°. The Human Factor study reported a SUS score of 87 (grade A) assessing the system usability as above average. Surgeons found the system intuitive and were very satisfied with the visualization of the 3D anatomy under various lighting conditions. There were no reported instances of disorientation and dizziness with this system, commonly experienced in VR/ AR systems using head-mounted displays due to vergence- accommodation conflict. SESSION 12: FREE PAPERS—LIGHTNING ROUND35 Please Click Here to VIEW Presenter Disclosures Conclusions: This objective validation demonstrated the system is safe and effective, fully complying with FDA regulatory requirements. The subjective validation showed the system is easy to use, provides consistent and accurate information, without the typical motion sickness issues of other AR/VR systems. Paper 47:Minimally Invasive Percutaneous Screw Placement in Thoracic and Lumbar Spine with Optical Skin Marker Based Augmented Reality Navigation: Results from a Prospective Study Pietro Scarone, Dr - Neurocenter of Southern Switzerland; Caterina Mollica - Neurosurgical Service, Neurocenter of Southern Switzerland, Lugano, Switzerland; Sebastian Lippross; Anindita Chatterjea - Philips; Inge Jenniskens; Andreas Seekamp Background: Use of superior quality 3D intra-operative imaging, non-invasive dynamic patient monitoring and camera based Augmented Reality Navigation (ARN), providing real time visual feedback of instrument location, without relying on fluoroscopy, can assist with improving accuracy of pedicle screw placements in MISS, without increasing staff and patient radiation dose. Utility of ARN has already been demonstrated for open procedures, but no data are available on MIS procedures. Purpose of the study: A prospective, multi-center clinical study was designed using non-invasive skin markers for motion tracking and video camera based optical navigation cameras integrated into the flat detector of a robotic C-arm, with intraoperative 2D/3D imaging capabilities. Aim of the study was to determine the accuracy of percutaneous pedicle screw fixation. In addition, time to insert a screw in optimum position and staff and radiation dose were measured. Materials and Methods: 211 percutaneous pedicle screws (126 in lumbar, 69 in thoracic, and 16 in sacral regions) were inserted in 39 adult patients between levels T2 and S1. A disposable Jamshidi needle with on shaft optical markers was guided to the desired location in the vertebral body using Augmented Reality. Screw position was rated on an intra- operatively obtained 3D verification scan by 3 independent reviewers, as per the Gertzbein grading. Operator dose was measured using personal dosimeters worn over the lead apron at the chest level, while the patient dose was recorded in mGy-cm2 and then converted into effective doses. Results: Overall, 98.1% screws had accurate placement (92.9% grade 0 (no breach), 5.2% grade 1 (4 mm breach). Six screws (2.7%) were intraoperatively revised. Median time per screw was 6 minutes and 25 sec (± 3.3 min). The radiation dose received by the patient was 11.94 mSv, and this included the dose required for planning and verification scans as well as for fluoroscopy during cage placements, decompressions, biopsies, and cement augmentations. The staff radiation dose was on an average 40.3µSv. Conclusions: Skin marker tracking based augmented reality optical navigation allows for highly accurate pedicle screw placements in a percutaneous setting, without compromising on efficiency and radiation dose. This study could form the basis for future studies that do a head-to-head comparison of this technology with traditional infra-red camera-based systems that rely on bone anchored reference arrays. Paper 48:Location Variance of the Great Vessels During Positioning Changes While Undergoing DLIF Aaron Joiner - Jack Hughston Memorial Orthopaedic Surgery Residency; Gilberto Gomez - Hughston Clinic; Sohrab Vatsia Hughston Clinic; Tyler Ellett - Edward Via College of Osteopathic Medicine; Douglas Pahl - Hughston Clinic Introduction: Minimally invasive direct lateral interbody fusion (DLIF) has recently gained traction as a technique for lumbar spinal fusion; however, it is not without its risks – namely, neurovascular insult and injury. There is a paucity of evidence exploring the anatomic profile of vascular injury during DLIF according to operative positioning. Aims/Objectives: The purpose of this study is to assess and characterize the clinical and radiographic changes in distance from the lumbar interbody discs to the major abdominal vessels with DLIF surgical positioning. Methods: Unenhanced magnetic resonance imaging (MRI) of the lumbar spine was performed in a series of 10 skeletally mature patients with imaging in the supine, right (RLD), and left (LLD) lateral decubitus positions with a standardized bump. Positional changes in the aorta, inferior vena cava (IVC), right (RCIA) and left (LCIA) common iliac arteries, right (RCIV) and left (LCIV) common iliac veins, and right (RIIA) and left (LIIA) internal iliac arteries were quantified according to mean distance changes across all three operative positions. Results: When operative positioning was changed from supine to RLD, the aorta moved right to 6.5 mm at the L1-L2 intervertebral space (p< 0.001). The IVC moved right to 2.9 SESSION 12: FREE PAPERS—LIGHTNING ROUND36 Abstracts cm at L1-L2 (p<.001), the RCIA moved right to 2.0 cm at L5- S1 (p< 0.001), the LCIA moved right to 1.7 cm at L5-S1 (p< 0.001), the RCIV moved right to 1.2 cm at L5-S1 (p=0.03), the LCIV moved right to 7.0 mm at L4-L5 (p< 0.001), and the RIIA moved right to 3.6 cm at L5-S1 (p< 0.001). When operative positioning was changed from supine to LLD, the aorta moved left to 1.2 cm at L1-L2 (p< 0.001). The IVC moved left to 1.8 cm at L4-L5 (p< 0.001), the RCIA moved left to 3.8 cm at L5-S1 (p< 0.001), the LCIA moved left to 1.0 cm at L4-L5 (p=0.04), the RCIV moved left to 2 mm at L4-L5 (p=0.03), the LCIV moved left to 3.6 cm at L5-S1 (p< 0.001), the RIIA moved left to 3.4 cm at L5-S1 (p< 0.001), and the LIIA moved left to 1.9 cm at L5-S1 (p< 0.001). Conclusion: This study reinforces the notion that DLIF enables indirect lumbar decompression while preserving key vascular structures. RLD positioning affords the greatest risk to the aorta at L1-L2 and the LCIV at L4-L5, while in the LLD position, increased risk to the RCIV manifests at L4-L5. Collectively, LLD positioning may present safer anatomic access for the DLIF surgical window. Paper 49:Do the 5-Year Outcomes for Minimally Invasive and Open Transforaminal Lumbar Interbody Fusion for Grade 1 Degenerative Lumbar Spondylolisthesis Differ? Andrew K. Chan, MD; Erica Bisson; Mohamad Bydon; Steven Glassman, MD; Kevin Foley; Christopher Shaffrey; Eric Potts; Mark Shaffrey; Domagoj Coric; John Knightly; Paul Park; Michael Y. Wang, MD, FACS; Kai-Ming Fu; Jonathan Slotkin; Anthony Asher; Michael Virk; Giorgos Michalopoulos; Jian Guan; Nitin Agarwal; Dean Chou; Regis W. Haid, MD; Praveen Mummaneni Introduction: Minimally invasive transforaminal lumbar interbody fusion (MIS TLIF) has been applied to degenerative lumbar spondylolisthesis and is associated with expedited recovery, reduced operative blood loss, and shorter lengths of hospitalization compared to traditional, open TLIF. However, the impact of MIS TLIF on long-term patient-reported outcomes (PROs) is less clear. Aims/Objectives: To compare MIS TLIF to traditional, open TLIF for grade 1 degenerative lumbar spondylolisthesis 5 years postoperatively. Methods: We utilized the prospective Quality Outcomes Database registry and retrospectively queried patients with grade 1 degenerative lumbar spondylolisthesis who underwent single-segment surgery with MIS or open TLIF methods. Surgeries were classified as MIS TLIF if percutaneous screw placement was utilized and the interbody was placed via a tubular retractor in the Wiltse plane. Outcomes were compared 5 years postoperatively (5Y). The primary outcome was ODI. The secondary outcomes included NRS Back Pain (NRS-BP), NRS Leg Pain (NRS-LP), EQ-5D, NASS Satisfaction, and cumulative reoperation rate. Multivariable models were constructed to assess the impact of MIS TLIF on PROs, adjusting for variables reaching p< 0.20 on univariate analyses. Results: 297 patients were included: 72 MIS TLIF (24.2%) and 225 open TLIF (75.8%). 5Y follow-up was similar (MIS TLIF: 86.1% vs. open TLIF: 75.6%, p=0.06). Patients did not differ significantly at baseline for ODI, NRS-BP, NRS-LP, and EQ-5D (p>0.05). Perioperatively, MIS TLIF was associated with less blood loss (108.8±85.6 vs. 299.6±242.2 ml, p0.001, all comparisons). In adjusted analyses, MIS TLIF—compared to open TLIF—was associated with similar 5Y ODI, ODI change, ODI MCID achievement, NRS-BP, NRS-BP change, NRS-LP, NRS-LP change, EQ-5D, EQ-5D change, and NASS satisfaction (adjusted p>0.05). The reoperation rates did not differ significantly (MIS TLIF: 6.9% vs. open TLIF: 11.1%, p=0.31). Conclusions: For symptomatic, single-level grade 1 degenerative lumbar spondylolisthesis, MIS TLIF was associated with decreased blood loss but no difference in 5-year outcomes for disability, back pain, leg pain, quality of life, and satisfaction. There was no difference in cumulative reoperation rate between MIS and open TLIF. These results suggest that in appropriately selected patients, either procedure may be employed depending on patient and surgeon preferences. SESSION 12: FREE PAPERS—LIGHTNING ROUND37 Please Click Here to VIEW Presenter Disclosures Paper 50: Decompression and Dynamic Sagittal Tether for Degenerative Spondylolisthesis: 24-month Pain, Disability and Reoperation Outcomes in 222 Patients from an FDA IDE Study Hyun Bae; Rick Sasso; Serena Hu, MD - Stanford University; Eugene Carragee, MD; Mick Perez-Cruet, MD, MS - Oakland University; William Beaumont, Department of Neurosurgery, Michigan Head and Spine Institute; Alan T Villavicencio, MD ; Tim Yoon, MD, PhD - Emory University; Kee D Kim, MD; William F. Lavelle, MD; Jeffrey L Gum, MD; Ravi S. Bains, MD; Calvin C. Kuo, MD; Harvinder S. Sandhu, MD, MBA; Michael P. Stauff, MD - UMass Memorial Medical Center; Michael Y. Wang, MD, FACS; Dennis G. Crandall, MD; Sigurd H. Berven, MD; Harel Deutsch, MD; Jeffrey S. Fischgrund, MD - Beaumont Hospital, Royal Oak; Wilson Z. Ray, MD ; Matthew Mermer, MD; Khalid Sethi, MD; Adam L. Shimer, MD; Reginald J. Davis, MD; Elizabeth Yu, MD - The Ohio State University Wexner Medical Center; Jens R. Chapman, MD; Andrew P. White, MD - BIDMC, Harvard Medical School; Richard D. Guyer, MD; Louis C. Fielding, MS - Empirica Spine; Todd F. Alamin, MD; William C. Welch, MD, FACS, FICS - University of Pennsylvania, Perelman School of Medicine Introduction: Symptomatic degenerative spondylolisthesis (DS) is most commonly treated with decompression and fusion (D+F) to address both the compressive neurologic symptoms as well as the underlying instability; however, fusion is costly, invasive, and associated with adjacent segment degeneration (ASD). Direct decompression and stabilization with a Dynamic Sagittal Tether (D+DST) is proposed as a less invasive alternative. Aims/Objectives: Compare perioperative and patient- reported outcomes (PROs) as well as reoperation rates for D+DST vs D+F through 24mo. Methods: Outcomes from propensity score (PS)-selected patients from the ongoing IDE study (NCT03115983) are reported, including VAS leg/hip and back pain, disability (ODI), and reoperations. Statistical significance (SS) was assessed using a 95% confidence interval of the PS-adjusted difference (PSA-95%CI) between groups. PROs were censored for reoperated patients. Results: Results are summarized in the table below. There were no significant differences in baseline demographic of clinical parameters. Surgery time, estimated blood loss, and facility stay were all significantly lower for the D+DST group. Both groups demonstrated significant improvements in VAS leg/hip pain, back pain, and ODI; and low reoperation rates at 24-months with no significant differences between groups. ODI was significantly lower in the D+DST group at 6-weeks, and significantly more patients in the D+DST group had achieved 15-point ODI improvement at 6-weeks and 3-months. MeasureD+DSTD+FPSA-95%CI N12597 Age (years)65.8±7.764.1±9.0-2.05,2.20 BMI (kg/m2)28.1±4.730.0±5.5-1.10,1.35 Preop VAS- leg/hip pain79.5±12.380.0±15.1-3.2,4.0 Preop VAS- back pain67.4±23.969.7±22.8-6.0,6.1 Preop ODI52.6±11.952.5±14.0-3.3,3.4 Surgery time (min)112.0±32.1187.3±75.9-85.3,-54.9 (SS) Est. blood loss (ml)52.2±53.3240.4±231.4-227.1,-138.9 (SS) Facility stay (nights)0.64±1.452.94±1.62-2.7,-1.9 (SS) 24-mo ΔVAS- leg/hi-58.0±27.5-57.3±29.7-7.4,9.7 24-mo ΔVAS- back-48.3±30.0-42.0±31.7-12.4,6.0 24-mo ΔODI-40.0±18.6-32.8±18.8-9.6,1.5 24-mo ΔODI <-1591.2%82.5%-6.3%,11.7% 24-mo Reoperations6.5%7.5%-5.2%,5.3% Conclusions: In these interim results, available subjects at 24-months achieved equivalent improvements in pain and disability as well as reoperation rates in both the D+DST and D+F groups, while the D+DST group had significantly lower operative time and blood loss and shorter hospital stay. The D+DST group had significantly lower disability 6-weeks postoperatively, indicating faster recovery. D+DST may offer a less-invasive alternative with faster recovery to D+F for patients with DS. Further analyses should assess the FDA primary composite endpoint, effects of the two treatments on adjacent segments, and longer-term follow-up. SESSION 12: FREE PAPERS—LIGHTNING ROUND38 Abstracts Paper 51: Evaluating the Incidence of Subsequent Surgical Decompression Following Minimally Invasive Approaches to Treat Symptomatic Lumbar Spinal Stenosis: A Retrospective Database Review Hania Shahzad, MBBS; Nasir Hussain; Nazihah Bhatti, BS; Ryan Souza; Vwaire Orhurhu; Mahmoud Abdel-Rasoul; Tristan Weaver, MD; Safdar Khan, MD, FAAOS Introduction: Surgical decompression is the definitive treatment for the management of symptomatic lumbar spinal stenosis (LSS); however, in poor surgical candidates, it is associated with significant morbidity. In such patients, minimally invasive approaches to treating symptomatic LSS are gaining popularity. There still exists the potential for failure of therapy, thereby necessitating subsequent surgical decompression. This study aims to elucidate the incidence and characteristics of patients who require subsequent surgical decompression after minimally invasive approaches to treat symptomatic LSS. Methods: The PearlDiver-Mariner database of national all- payer claims was used to identify patients who underwent minimally invasive procedures for symptomatic LSS, including minimally invasive lumbar decompression (MILD) or interspinous process device (IPD) placement, and progressed to subsequent surgical decompression within five years. The primary outcome was the overall within five years following the minimally invasive approach. Secondary outcomes included the demographic and comorbid factors associated with an increased odds of requiring subsequent surgery using univariable and multivariable regression analysis. Results: A total of 5,278 patients who underwent a minimally invasive procedure were included in the analysis, of which 3,222 (61.04%) underwent MILD, 1,959 (37.12%) underwent IPD placement, and 97 (1.84%) had claims for both the procedures. Across all minimally invasive interventions, the incidence of subsequent surgical decompression within five years was 6.56% (346 of 5,278 patients). Among these, 56.06% (194 patients) had claims for surgical decompression that occurred within the first year after the initial minimally invasive procedure. Multivariate regression analysis revealed that male gender and a prior history of surgical decompression are associated with a significantly greater odds ratio (OR) [95% confidence interval (CI)] of requiring subsequent surgical decompression by 1.42 times ([1.14, 1.77], P=0.002) and 2.10 times ([1.39, 3.17], P< 0.01), respectively. In contrast, age 65 years and above, a diagnosis of obesity, and a Charlson Comorbidity Index (CCI) score of 3 or greater were associated with a significantly reduced OR [95% CI] of progressing to surgical decompression by 0.64 times ([0.50, 0.81], P< 0.001), 0.62 times ([0.48, 0.81], P< 0.001), and 0.71 times ([0.56, 0.91], P=0.007), respectively. Conclusion: The results highlight that minimally invasive options can be beneficial in managing symptomatic LSS in patients who are poor surgical candidates on a case- by-case basis. Since a subset of patients may still require subsequent surgical decompression, potential patients should be counseled on the possibility of requiring additional surgery even after the utilization of these minimally invasive approaches. Paper 52: Biomechanical Analysis of Expandable Interbody Cage Stiffness, Force Exertion, and Subsidence in the Setting of Spondylolisthesis Junho Song - Hospital for Special Surgery; Austen Katz, MD - Department of Orthopaedic Surgery, North Shore University Hospital-Long Island Jewish Medical Center; Thomas Dowling; David Nuckley; Valerie S. Coldren - Stryker Spine; Josh Rubin; Liam Barnes - Stryker Spine; Jeff Silber, MD - Department of Orthopaedic Surgery, North Shore University Hospital-Long Island Jewish Medical Center; David Essig, MD - Department of Orthopaedic Surgery, North Shore University Hospital-Long Island Jewish Medical Center; Sheeraz Qureshi; Sohrab Virk, MD - Department of Orthopaedic Surgery, North Shore University Hospital-Long Island Jewish Medical Center Introduction: Expandable lumbar interbody fusion cage has been shown to be efficacious in treating symptomatic degenerative spondylolisthesis. However, no prior study has evaluated how the presence and severity of spondylolisthesis may influence the biomechanical properties of expandable interbody cages. Aims/Objectives: To evaluate the impact of spondylolisthesis on expansion stiffness, force exertion, and subsidence associated with expandable interbody cages. Methods: Based on the assumption of a 40 mm anteroposterior vertebral body length, two bone foams (superior and inferior) were loaded with 0%, 35%, and 50% anteroposterior offsets to simulate varying degrees of spondylolisthesis. Increase in spondylolisthesis grade was associated with greater implant contact with the cortical rim. The expansion stiffness, output force-to-input torque ratio, and subsidence depth at a constant input torque (1 Nm) were measured and compared among the varying spondylolisthesis grades. For all measurements, five experimental trials were performed at each spondylolisthesis grade. SESSION 12: FREE PAPERS—LIGHTNING ROUND39 Please Click Here to VIEW Presenter Disclosures Results: The mean expansion stiffness throughout 100-200 N output force range increased linearly with higher grades of spondylolisthesis (103.6±11.8 N/m at 0% offset, 109.4±18.6 N/m at 35% offset, 125.3±22.1 N/m at 50% offset). At all three spondylolisthesis grades, the force exerted onto vertebral bodies was significantly correlated to the input torque to expand the implant. The force-to-torque ratio decreased linearly with greater degrees of spondylolisthesis (186.0 N/Nm at 0% offset, 160.6 N/Nm at 35% offset, 136.5 N/Nm at 50% offset). At a constant 1 Nm input torque, the depth of subsidence decreased linearly with higher spondylolisthesis grade (2.3±0.5 mm at 0% offset, 1.5±0.3 mm at 35% offset, and 0.7±0.4 mm at 50% offset). Conclusions: The current study demonstrates that the presence of spondylolisthesis significantly influences the biomechanics of expandable interbody cages. Higher spondylolisthesis grade is associated with greater expansion stiffness. The force exerted onto vertebral bodies is correlated to the torque applied to expand the implant, and the force- to-torque ratio decreases with higher spondylolisthesis grade. This suggests that in patients with more severe spondylolisthesis, more torque may be required to achieve the equivalent output force. Finally, at a given input torque, the subsidence depth decreases linearly with higher spondylolisthesis grade. This is likely due to the greater implant contact with the cortical rim, equating to the strongest aspect of the vertebral body in vivo. This study allows for a better understanding of how the biomechanics and subsidence risk associated with expandable interbody cages may change based on the presence and severity of spondylolisthesis. Paper 53: Clinical and Radiographic Outcomes of Late-onset Cage Subsidence After Minimally Invasive Lateral Lumbar Interbody Fusion Sang-Il Kim - Seoul Saint Mary's Hospital, The Catholic University of Korea; Yoon-Hoon Kim - Seoul Saint Mary's Hospital, The Catholic University of Korea; Hyung-Youl Park - Eunpyeong Saint Mary's Hospital, The Catholic University of Korea; Hoonseok Sung - Seoul Saint Mary's Hospital, The Catholic University of Korea; Hyungchul Park - Seoul Saint Mary's Hospital, The Catholic University of Korea Introduction: Lateral lumbar interbody fusion (LLIF) can restore disc height and perform indirect decompression of neural elements. However, cage subsidence may lead to clinical problems, including loss of disc height correction, altered spinal alignment, recurrent pain, and vertebral body fracture. The factors leading to subsidence after LLIF are poorly understood. Aims: The purpose of this study was to evaluate clinical and radiographic outcomes according to the subsidence in a case series with LLIF. Methods: A retrospective review of consecutive patients who underwent LLIF between 2012 and 2017 was performed. Patients with a follow-up period less than 1-year were excluded. Subsidence was defined as cage sinking of more than 2 mm from the bony endplate compared to the immediate postoperative status. The timing of cage subsidence was investigated. Clinical (using VAS and ODI) and radiographic outcomes (sagittal parameters) were investigated. The relationships between cage subsidence, and intraoperative endplate injury (IOEI) and fusion rate were analyzed. Results: One hundred sixty-six patients were eligible for this study. They underwent LLIF at a total of 331 levels, and their mean follow-up period was 54.5±23.3 months. Subsidence rate per level was 37.5% (124/331). In patients with IOEI, subsidence occurred more frequently compared to those without IOEI (48.5% vs. 34.6%, p=0.034). VAS and ODI at the final follow-up were not different between patients with or without the subsidence. Although a segmental sagittal angle was smaller in the level with subsidence, lumbar lordosis was not different between patients with or without the subsidence at the final follow-up. Fusion rate at postoperative 1-year was not different. Reoperation was not needed except one patient with coronal split vertebral body fracture followed by IOEI and progressive subsidence. SESSION 12: FREE PAPERS—LIGHTNING ROUNDNext >