< Previous20 Abstracts and the benefits for widespread adoption. Nevertheless, early data demonstrates a substantial improvement in surgical time and the potential utility of the p-LLIF technique in the ambulatory surgery center by avoiding the need for prone repositioning. Paper 23: Vascular and Visceral Complications Following Prone Transpsoas Lateral Lumbar Interbody Fusion: A Comparative Study to a Historical Survey Study on Standard Lateral Lumbar Interbody Fusion Mohamed A. Soliman, MD, MSc, PhD - Cairo University; Luis Diaz-Aguilar; Rodrigo Amaral; Bryan S. Lee - Department of Neurosurgery, Barrow Neurological Institute; Muhammad Abd-El-Barr; Gene Massey, MD; Craig McMains; David Schwartz; Gurvinder S. Deol; Andrew D. Nguyen, MD, PhD - UCSD Health Sciences; Tyler Smith; Luiz Pimenta, MD, PhD; William Taylor, MD; John Pollina Introduction: Prone transpsoas lateral lumbar interbody fusion (PTP) is a novel modification of standard lateral lumbar interbody fusion (standard-LLIF). To date, no study has compared the vascular or visceral complications between the PTP and standard-LLIF. Aim/Objectives: This study aimed to compare the vascular and visceral complications between the PTP and standard- LLIF. Methods: A retrospective electronic medical records review was conducted across ten centers to compile the patient-, procedural-, and outcomes data related to patients who underwent PTP. Among the data collected from consecutive cases at each site was itemization of intraoperative and postoperative complications. From those, we highlighted the intraoperative vascular and visceral complications in order to compare these outcomes in PTP procedures to the historical results of a published survey (Uribe et al. Eur Spine J 2015;24:S386-96) about vascular and visceral complications following standard-LLIF. Results: The PTP cohort included a total of 364 patients, and the published standard-LLIF study referenced 13,004 patients. In the PTP cohort, there were no (n=0) visceral injuries and one (n=1) vascular (left common iliac vein) injury. There was no significant difference between the PTP group (n=1) and the published standard-LLIF in terms of vascular injuries (n=13) (p=0.3) or visceral injuries (n=11) (p=0.6). Conclusion: There was no significant difference in the incidence of vascular or visceral injuries between this multi-center cohort of PTP procedures versus what was previously published on standard-LLIF. This comparison may be premature given that PTP is a more recently adopted procedure with a significantly lower case volume denominator; however, the safety profile of the early experience has not been concerning, and as PTP case volumes increase, these centers will continue to track and report these important outcomes. Paper 24: Early Clinical Outcomes of Prone Transpsoas Lumbar Interbody Fusion Technique Ian J. Wellington, MD - UConn Health; Christopher Antonacci, MD - UConn Health; Chirag Chaudhary, MD - UConn Health; Ergin Coskun, MD - UConn Health; Mark Cote, DPT, MSCTR - UConn Health; Hardeep Singh, MD - UConn Health; Scott Mallozzi, MD - UConn Health; Isaac Moss, MD, MASc, FRCSC - UConn Health Background: Lateral lumbar interbody fusion (LLIF) provides a minimally invasive option for accessing the intervertebral disk via the retroperitoneal space. While LLIFs are traditionally performed with the patient in a lateral decubitus position, the prone transpsoas (PTP) technique allows surgeons to access both the anterior and posterior columns of the spine without the need for repositioning. As the PTP approach for LLIF is relatively novel, little is known about the complications and early patient reported outcomes associated with this technique. The aim of this study was to investigate the effect of LLIF performed via the PTP approach on sagittal radiographic parameters and patient reported outcome measures (PROMs), as well as the rates of complications associated with this technique. Methods: A retrospective review was performed of 82 consecutive patients who underwent LLIF via a PTP technique. Lumbar lordosis (LL), segmental lordosis (SL), anterior disc height (ADH), and posterior disc height (PDH) were measured on preoperative, initial postoperative, and 3-month postoperative radiographs. PROMs including the Oswestry Disability Index (ODI), the visual analogue scale (VAS) and pain portions of the EQ5D, VAS back and VAS leg pain numeric ratings were collected at the preoperative and subsequent postoperative visits. Length of hospital stay as well as postoperative complications related to the procedure were recorded. Results: Significant improvements were seen at the initial (4.5° ± 8.6, p < 0.001) and 3- month (4.4° ± 7.2, p < 0.001) postoperative periods for LL, as well as SL (6.8° ± 4.8, p < 0.001; 6.7° ± 4.4, p < 0.001), ADH (8.0mm ± 3.6, p < 0.001; CONCURRENT SESSION 4: FREE PAPERS 13–2421 Please Click Here to VIEW Presenter Disclosures 7.4mm ± 3.6, p < 0.001), and PDH (3.3mm ± 2.4, p < 0.001; 3.1mm ± 2.5, p < 0.001). Significant improvements were seen at 3-months postoperatively for ODI (p < 0.001), EQ5D pain (p = 0.016), VAS leg (p < .001), and VAS back (p <.001). The average length of stay was 2.7 ± 4.5 days. The most common complications were ipsilateral thigh pain/numbness (45.1%), ipsilateral hip flexor weakness (39.0%), contralateral thigh pain/numbness (14.6%), urinary retention (7.3%), and ipsilateral thigh numbness (7.3%). Conclusions: While early PROMs and correction of sagittal radiographic parameters show promising results for the PTP approach for LLIF, it is not without risks, the most common of which is ipsilateral thigh numbness and hip flexor weakness. Further investigation is needed to determine the long-term outcomes of this procedure and its associated complications. Paper 25:Long-term Durability of Stand- alone Lateral Lumbar Interbody Fusion Nitin Agarwal - Washington University School of Medicine; Michael D. White, MD - Barrow Neurological Institute; Souvik Roy; Alp Ozpinar; Nima Alan; David O. Okonkwo - University of Pittsburgh; David Hamilton; Adam S. Kanter Introduction: The long-term durability of stand-alone lateral lumbar interbody fusion (LLIF) remains unknown. Objectives: This study evaluates whether early patient reported outcome measures (PROMs) after stand-alone lateral lumbar interbody fusion (LLIF) are sustained on long-term follow-up. Methods: Within a large quaternary care academic institution, 126 consecutive patients who underwent stand-alone LLIF between 2009 and 2017 met inclusion criteria. PROMs included the Oswestry Disability Index (ODI), EuroQOL-5D (EQ-5D), and visual analogue scale (VAS). Durable outcomes were defined as scores showing a significant improvement between preoperative and 6-week scores without demonstrating any significant decline at future time points. A repeated measures analysis was conducted using Generalized Estimating Equations (GEE model) to assess the outcome across different postoperative time points, including 6 weeks, 1 year, 2 years, and 5 years. Results: ODI scores showed durable improvement at 5 years follow-up, with scores improving from 46.9 to 38.5 (p< 0.05). Improvements in EQ-5D showed similar durability up to 5 years, improving from 0.48 to 0.65 (p< 0.05). VAS scores also demonstrated significant improvements postoperatively that were durable at 2 years follow-up, improving from 7.0 to 4.6 (p< 0.0001). Conclusion: Patients undergoing stand-alone LLIF were found to have significant improvements in ODI and EQ-5D at 6 weeks follow-up that remained durable up to 5 years postoperatively. VAS scores were found to be significantly improved at 6 weeks and up to 2 years postoperatively but failed to reach significance at 5 years. These findings demonstrate that patients undergoing stand-alone LLIF show significant improvement in quality of life outcomes after surgery that remain durable at long-term follow-up. Paper 26:Lateral Single Position Anterior- Posterior Lumbar Fusion Outperforms Conventional Anterior-Posterior Lumbar Fusion with Patient Repositioning at 2-year Minimum Follow-Up Aaron J. Buckland, MBBS, FRACS - Melbourne Orthopaedic Group; Brett Braly; Nicholas A. O'Malley, MS - NYU Langone Health, Department of Orthopedic Surgery; Dylan Proctor; Kimberly Ashayeri - NYU Langone Health; Brian Kwon - New England Baptist Hospital; Ivan Cheng - St. David's HealthCare; Themistocles Protopsaltis - NYU Langone Health; J. Alex Thomas Introduction: Previous literature has demonstrated the advantages of Lateral Lumbar Anterior Posterior Single Position Surgery (L-SPS) when compared against traditional Lateral Lumbar Anterior Posterior Surgery (FLIP) with respect to peri-operative outcomes and non-inferiority at 1-year follow-up. Aims/Objectives: The goal of this study is to examine 2-year post-operative outcomes of this novel technique. Methods: This is a multi-center retrospective cohort study. Patients undergoing Anterior-Posterior Fusion, either anterior lumbar interbody fusion (ALIF) and/or lateral lumbar interbody fusion (LLIF) with bilateral percutaneous pedicle screw fixation between the levels of L2 and S1, were grouped as L-SPS. Patients for whom repositioning from either the supine or lateral to prone position for the posterior portion of the procedure, under the same anesthesia, were grouped as FLIP patients. Groups were compared in terms of demographics; intra-operative, peri-operative, and radiographic outcomes; complications; and re-operations up to 2 years follow-up. Metrics were compared using independent samples t-tests and chi-squared analyses with significance set at p< 0.05. Results: The final study cohort consisted of 442 patients (352 L-SPS and 90 FLIP). The L-SPS group demonstrated lower operative time (97.7 min vs. 297.0 min; p< 0.001), radiation dose (36.5 mGy vs. CONCURRENT SESSION 5: YOUNG SURGEON FREE PAPERS22 Abstracts 78.8 mGy; p< 0.001), estimated blood loss (88.8 mL vs. 270.0 mL; p< 0.001), and length of stay (1.91 days vs. 3.61 days; p< 0.001) versus the FLIP group. Further, the L-SPS group demonstrated fewer post-op complications (21.9% vs. 34.4%; p=0.013) and rates of ileus (0.0% vs. 5.6%; p< 0.001). Rates of re-operation were similar at 30-days (1.7% L-SPS vs. 4.4% FLIP, p=0.125), 90-days (5.1% L-SPS vs. 5.6% FLIP, p=0.795) and 2-years (9.7% L-SPS vs. 12.2% FLIP; p=0.441). Rates of radiographic fusion (94.3% L-SPS vs. 97.8% FLIP; p=0.266) and subsidence (6.9% L-SPS vs. 12.2% FLIP; p=0.260) were also similar. Further, no differences were noted in change in Lumbar Lordosis (LL) from Baseline to 1-year (3.5o vs. 2.8o; p=0.466) and post-op to 1-year (-0.18o vs. -0.51o; p=0.777), or in Pelvic Incidence Lumbar Lordosis mismatch (PI-LL) from Baseline to 1-year (-3.5o vs. -3.2o; p=0.835) and from post-op to 1-year (0.71o vs. 0.71o; 0.998). Conclusion: The lateral single position anterior posterior lumbar fusion technique improves safety and operative efficiency while reducing complications peri-operatively when compared against traditional anterior posterior lumbar fusions. Further, the approach demonstrated non-inferiority at 2-year follow-up as reflected in similar incidence of re-operation and radiographic alignment. Paper 27:Implant Size and Position Affects Patient Reported Outcomes After Lateral Lumbar Interbody Fusion Alexander J. Butler, MD - Lenox Hill Hospital; Mohammed Munim; Athan Zavras - Rush University Medical Center; Matthew Colman, MD - Rush University Medical Center; Frank Phillips, MD - Rush University Medical Center Background Context: Lateral lumbar interbody fusion (LLIF) has gained popularity in recent years as a minimally invasive option for arthrodesis, alignment correction, and indirect decompression. The radiographic effects of lateral implant size and position on these effects are an area of active exploration; the clinical outcomes of these effects have been described to a lesser extent. Aims/Objectives: To investigate the effects implant size and position achieved during LLIF on PROMs. Methods: This study retrospectively reviewed patients who underwent LLIF with one of two senior surgeons between 2013 and 2019 for spondylolisthesis, severe degenerative disc disease, and/or foraminal stenosis with a minimum of 1 year follow-up. Radiographs were reviewed from the preoperative and 6-week postoperative time points to measure operative segment disc height as well as anterior vs. posterior cage placement. Radiographic parameters were compared between groups using preoperative, 6 weeks postoperative, and final postoperative radiographs. Parameters included were lumbar lordosis (LL), Pelvic Tilt (PT), Sacral Slope (SS), Pelvic Incidence (PI), PI-LL mismatch, disc height, and subsidence. Patient- reported outcome metrics (PROMs) were also compared between groups at preoperative, 6 weeks, 3 months, 6 months, and final postoperative time points. Results: 72 patients who underwent LLIF at 104 levels were included in the analysis. The average age was 57.85 ± 10.24 years, and average follow up was 22.28 ± 10.78 months. The LLIF cage was placed posteriorly in 66 levels and anteriorly in 38. Anterior cage placement led to a greater increase in LL (6.96±11.32 vs. -1.58±11.03 vs, p< 0.001) and greater correction of PI-LL mismatch (-6.94±15.07 vs. 1.83±12.78, p=0.003) at 6 weeks post-operatively. Disc space distraction 5mm. From preoperative to 6-week postoperative time points, >5 mm distraction led to a greater increase in LL (5.85±9.98 vs. -1.29±12.13, p=0.002) and greater correction of PI-LL mismatch (-6.94±15.07 vs. 1.83±12.78: p=0.003, -5.84±13.59 vs. 1.52±14.08: p=0.012). The differences between these groups were maintained at final follow-up. At 6 months postoperatively, the >5mm distraction group had significantly less back (4.39±2.21 vs. 2.79±1.53) and leg pain (3.51±3.01 vs. 1.98±1.90, p=0.044), as well as less leg pain at final follow-up (3.73±3.13 vs. 1.98±2.52, p=0.009). Conclusions: Anterior positioning and distraction >5mm had a greater effect on LL and PI-LL mismatch. Implant position alone did not affect PROMs post-operatively. Patients with disc space distraction of >5mm were characterized by less back and leg pain post-operatively. CONCURRENT SESSION 5: YOUNG SURGEON FREE PAPERS23 Please Click Here to VIEW Presenter Disclosures Paper 28: High-level Evidence of Posterior Minimally Invasive Scoliosis Surgery Versus the Standard Posterior Approach for the Management of Adolescent Idiopathic Scoliosis Honghao Yang - Department of Orthopedic Surgery, Beijing Chao-Yang Hospital, Capital Medical University; Xiangyuan Jia - Department of Orthopedic Surgery, Beijing Chao-Yang Hospital, Capital Medical University; Yong Hai - Department of Orthopedic Surgery, Beijing Chao-Yang Hospital, Capital Medical University Introduction: Surgical management of adolescent idiopathic scoliosis (AIS) can be performed using standard posterior spinal fusion (PSF) or with a posterior minimally invasive approach. Minimally invasive scoliosis surgery (MISS) has several theoretical advantages, such as less tissue dissection, less blood loss, and earlier recovery. However, the difference in safety and effectiveness between MISS and PSF still needs to be clarified. Objectives: This meta-analysis aimed to compare the outcomes of MISS and standard PSF for the management of AIS. Methods: A comprehensive literature search of PubMed, EMBASE, MEDLINE, and Cochrane Library without time restriction was performed to identify relevant studies. MISS and PSF were compared in terms of radiographic parameters, estimated blood loss (EBL), blood transfusion rate, operative time (ORT), length of hospital stay (LOS), overall Scoliosis Research Society-22 (SRS-22) score, postoperative pain, and complication rate. Results: A total of seven studies comprising 767 patients (329 MISS and 438 PSF) with AIS were included. MISS and PSF yielded comparable deformity correction at the last follow-up. There were no significant differences in the overall SRS-22 scores or complication rates between the groups. Nevertheless, greater restoration of thoracic kyphosis (WMD, 2.98; 95% CI 0.58 to 5.37, P = 0.015), less EBL (WMD, −218.76; 95% CI −256.41 to −181.11, P < 0.001), a lower blood transfusion rate (RR, 0.31; 95% CI 0.20 to 0.48, P < 0.001), a shorter LOS (WMD, −1.48; 95% CI −2.48 to −0.48, P = 0.004), less postoperative pain (WMD, 0.57; 95% CI 0.16 to 0.98, P=0.006), and a longer ORT (WMD, 84.85; 95% CI 33.30 to 136.40, P = 0.001) were observed in the MISS group. Conclusion: Despite its inherent technical challenges, MISS is a feasible and effective alternative to standard PSF for AIS patients with moderate and flexible curves. MISS was associated with adequate deformity correction, better restoration of sagittal alignment, less EBL, fewer transfusions, shorter LOS, and better pain management compared to PSF. Further research is required to determine the detailed indications for the MISS procedure. Paper 29: Comparing 12-month Quality of Life, Work Status, and Disability Outcomes Between Decompression & Dynamic Sagittal Tether Stabilization vs. Transforaminal Lumbar Interbody Fusion for the Management of Lumbar Degenerative Spondylolisthesis. Interim Results of an FDA IDE Study Hania Shahzad, MBBS - Wexner Medical Center; Elizabeth Yu, MD - The Ohio State University Wexner Medical Center; Nazihah Bhatti, BS - Wexner Medical Center; Rick Sasso; Serena Hu, MD - Stanford University; Eugene Carragee, MD; Hyun Bae; 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; 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; 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; 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: Degenerative Spondylolisthesis (DS) is commonly treated with decompression and fusion. The complications and risks associated with instrumented fusion have warranted surgeons to simply decompress patients, which often results in postoperative instability. The dynamic sagittal tether stabilization (DST) is a new stabilization option that maintains motion in patients in whom stabilization in addition to decompression is desirable. Aims/Objectives: We aim to compare 12-month health outcomes in patients undergoing standard decompression and transforaminal lumbar interbody fusion (TLIF) vs. decompression and DST. Methods: Propensity score-selected IDE study subjects with 12-month follow-up were included in this analysis. Study records were queried for health-related quality of life (HRQoL), work status, return to work (RTW), return to activities of daily living (ADLs), and change in disability (Oswestry Disability Index; ODI) pre-operatively and at 12-months. Outcomes were compared with PS-adjusted 95% confidence interval (CI) to assess statistical significance (SS) or CONCURRENT SESSION 5: YOUNG SURGEON FREE PAPERS24 Abstracts non-significance (NS) for HRQoL and ODI and student’s t-test for RTW/ADL outcomes. Results: 225 patients (98TLIF/127D+DST) had 12-month follow-up. Mean age, BMI, and CCI of TLIF/DST were 64.1/65.8yrs; 30.0/28.1kg/m2, and 2.4/2.3. Mean baseline SF-12 physical and mental components of TLIF/DST patients were 27.7±7.0/27.2±0.7 and 48.2±12.9/46.6±12.7 (both NS). At 12 months, the mean physical and mental components for TLIF/DST groups were 44.3±12.6/46.4±11.2 and 54.5±8.5/54.1±9.6 (both NS). Preoperatively, 43%/49% of TLIF/DST subjects were working (p=0.14) and 11%/7% of DST subjects were not working due to spinal condition (NWSC) (p=0.13). At 12 months, 34%/44% of TLIF/DST subjects were working (p=0.08) and 10%/2% of TLIF/DST were NWSC (p< 0.01). The proportion of DST NWSC was significantly lower at 12 months compared to baseline (p=0.02). RTW time for DST/TLIF subjects was 5.4±6.6/11.8±9.6 weeks (p< 0.01) and return to ADL time was 5.5±6.5/10.0±9.5 weeks (p< 0.01). Changes in disability at 12 months from baseline were -38.7±18.2 for the DST group and -33.4±19.1 for the TLIF group with effect sizes of -2.1 and -1.7, respectively (NS). Conclusions: DST and TLIF-treated patients demonstrated similar, significant reductions in disability and improvement in HRQoL at a 12-month follow-up. Significantly faster RTW and ADL were observed for DST compared to TLIF patients. Our results show that dynamic sagittal tether stabilization represents a promising alternative to lumbar fusion for symptomatic DS with comparable health outcomes to the current standard surgical technique. Paper 30:Are 2-year Reoperation Rates Different for Circumferential Minimally Invasive Surgery (cMIS) vs. Open ASD Surgery? A Propensity Matched Cohort Study Using a Prospective ASD Database Saman Shabani, MD - Medical College of Wisconsin; Andrew K. Chan, MD - Columbia University/NewYork-Presbyterian; Nitin Agarwal; Vivian Le, MPH - UCSF; Alexander A. Aabedi; Paul Park; Juan Uribe; Jay Turner; Robert K. Eastlack; Richard Fessler; Khoi D. Than; Kai-Ming Fu; Michael Y. Wang, MD, FACS; Adam S. Kanter; David O. Okonkwo - University of Pittsburgh; Pierce D. Nunley; Neel Anand; Gregory M. Mundis; Peter Passias; Shay Bess - Denver International Spine Center, Presbyterian St. Luke’s Medical Center; Christopher Shaffrey; Dean Chou; Praveen Mummaneni Introduction: As surgical techniques for deformity correction evolve towards minimizing tissue trauma, further clarity is warranted to define differences in complication profiles between cMIS and open surgeries. We sought to compare cMIS and open surgery reoperation rates and etiologies. Aims/Objectives: To assess whether in adult spinal deformity (ASD) surgeries, the risk factors between cMIS vs. open techniques will differ. Methods: This is a retrospective analysis of prospective ASD database. 85 patients with cMIS for ASD with 2-year follow- up (2YFU) were identified and propensity matched to 85 patients in open cohort. Propensity matching was performed based on pre-operative PT, PI-LL, BMI, and SVA. Patient demographic variables, reoperation rate, and complications contributing to reoperation were compared with uni- and multi-variate analysis at any time in each cohort. PROMS at 2YFU were compared in the reoperated cohorts. Results: Total of 33 reoperations in the open cohort vs. 17 in cMIS were identified. The reoperation rate was significantly higher in the open cohort at 39% (33/85) compared to 20% (17/85) in the cMIS cohort (P= 0.012). The re-operation rate in open cohort related to mechanical failure was 52% (17/33) compared to 35% (6/17) in cMIS cohort (P= 0.43). No significant difference was found in rates of specific etiologies contributing to complications in the cMIS vs. open reoperation cohorts under uni- and multivariate analysis. The change in spinopelvic parameters among the two reoperation cohorts at 2YFU were statistically not significant (ΔCVA, ΔSVA, ΔPI-LL, ΔPT, ΔLL CA, ΔTL CA). Under univariate analysis, the following PROMS were similar: ODI, NRS Leg and Back Pain, EQ5D, EQ5D-VAS, SF-36 PCS, SF-36 MCS. However, SRS-22 in open cohort was significantly higher at 2YFU (3.55 ± 0.73 open vs. 3.10 ± 0.56 MIS, p = 0.029). CONCURRENT SESSION 5: YOUNG SURGEON FREE PAPERS25 Please Click Here to VIEW Presenter Disclosures Conclusion: Findings in our ongoing study show that cMIS procedures were associated with a significantly lower reoperation rate compared to open surgical approaches. Open cohort was associated with higher mechanical failure rate. PROMS and the change in spinopelvic parameters were similar at 2YFU in both reoperated cohorts (except for SRS-22 favored open cohort). Paper 31: Comparing Long-Term Deformity Correction and Other Outcomes Between Single Level Circumferential XLIF and MI- TLIF: A Retrospective Review With 5-Year Minimum Follow Up Stephen Saela; Daniel Coban; Stuart Changoor; Neil Patel; Kumar Sinha; Ki Hwang; Michael Faloon; Arash Emami Introduction: Extreme Lateral Interbody Fusion with percutaneous pedicle screw fixation (circumferential XLIF) and minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) are commonly used minimally invasive approaches to the lumbar spine. Unlike MI-TLIF, traditional XLIF is unable to access the L5-S1 disc space due to the presence of the iliac crest. Studies that have compared these two techniques typically do not account for this limitation and often do not stratify by the number of levels being operated on or assess for long-term outcomes (>5 years). Objectives: To compare the clinical and radiological outcomes of single level circumferential XLIF and MI-TLIF exclusively at the L4-L5 disc space. Methods: A retrospective review was performed to identify all patients between 2008 and 2015 who underwent circumferential XLIF or MI-TLIF with a minimum follow up of 5 years. Demographic data and complication-related data, including rate of complications requiring return to the OR (RTO), were recorded. Radiographic outcomes were assessed using graft subsidence, as well as final anterior and posterior disc height (ADH and PDH). Patient functional outcome scores, which included the Oswestry Disability Index (ODI) and Visual Analogue Scale (VAS), were recorded and compared between cohorts. Standard binominal and categorical comparative analyses were performed. Results: A total of 108 patients were included for analysis (MI-TLIF: 75, circumferential XLIF: 33). Mean age (MI-TLIF: 53.5, XLIF: 53.9), body mass index (BMI) (MI-TLIF: 32.3, XLIF: 31.4), and length of follow up (MI-TLIF: 90 months, XLIF: 103 months) were similar between cohorts. Overall RTO rate was found to be statistically similar between groups at 16.0 % (95% CI, 9.24–26.07) in the MI-TLIF group and 6.1% (95% CI, 0.68–20.60) in the XLIF group. Final ADH (MI-TLIF: 9.03±1.10 mm, XLIF: 12.3±2.60 mm, p< 0.0001) and final PDH (MI- TLIF: 9.97±1.96 mm, XLIF: 7.12±2.2 mm, p< 0.0001) varied significantly between the two cohorts, but average DH (MI- TLIF: 9.50±1.59 mm, XLIF: 9.71±2.41 mm, p=0.593) showed no significant differences. Change in ODI and VAS scores at final follow up were similar between MI-TLIF and XLIF groups (p=0.629 for ODI and p=0.322 for VAS). Conclusions: This long-term comparative study demonstrates similar clinical and radiological outcomes between single level MI-TLIF and circumferential XLIF at the L4-L5 level. As expected, MI-TLIF had greater improvement in PDH and XLIF had greater improvement in ADH. However, average disc height was found to be similar between groups, further indicating that choosing one’s approach based on the specific anatomy of the patient may enhance outcomes. Paper 32: A Powerful Tool to Create Lordosis, Anterior Column Release Can Come with Its Own Complications — A Case Series Elliot Pressman, MD - USF Health Morsani College of Medicine; Mohammad Noureldine, MD - University of South Florida, Department of Neurosurgery and Brain Repair; Puya Alikhani, MD - USF Health Morsani College of Medicine Introduction: Lateral lumbar interbody fusions are one modality used to treat lumbar degenerative spine disease. One of the benefits of this approach is the ability to improve segmental lordosis. Anterior column release (ACR) was developed as an adjunct in the lateral lumbar approach to improve even further the technique’s ability to increase lordosis. ACR, however, requires a wider exposure anteriorly exposing the retroperitoneal space to greater risk of injury, including important arteries, bowel, and nerves in the lumbosacral plexus. Further, it typically requires longer times of retraction, a known risk factor for nerve stretch and injury. Additionally, ACR can increase lordosis beyond what is physiologic, exposing the patient to hyperphysiologic lordosis. This increases the biomechanical forces that hardware is exposed to and may increase the rates of hardware failure and proximal junctional kyphosis. We sought to analyze a large cohort of patients undergoing ACR to see the potential dangers associated with this approach. Methods: We conducted a retrospective cohort study on all patients who underwent ACR as part of a lateral lumbar fusion at a single academic center between 2016 and 2018. This included ACRs performed by four surgeons at our facility. Demographic data and operative variables CONCURRENT SESSION 5: YOUNG SURGEON FREE PAPERS26 Abstracts Results: 27 patients, comprising 28 ACRs, were identified. All patients had an ACR at L3-L4; one patient had an additional level of release at L2-L3. Median patient age was 64, there were 14 males and 13 females, and median BMI was 31. 20 patients (74%) were current tobacco smokers at the time of surgery. Of these 27 patients, 11 (41%) had complications related to surgical approach: nine (33%) had persistent postoperative thigh paresthesias, one had an arterial injury during ACR, and one had abdominal wall paresis. In terms of hardware and construct stability, nine patients (33%) developed proximal junctional kyphosis (a median of 377 days from surgery), four patients (15%) were found to have rod fractures in follow-up, and one patient (4%) had screw loosening. At the end of follow-up, median ODI was 10 (SE 0.61) from a median preoperative ODI of 60 (SE 1.2), though this includes patients who also required revisions from the above. Conclusion: ACR is an adjunct to anterior or lateral approaches to the lumbar spine. Even in spine surgeons experienced in lateral lumbar spine surgery, ACR is associated with a high risk of approach-related complications and hardware complications. Paper 33: The Anatomical Positioning of Retroperitoneal Organs in Single-position Prone Lateral Lumbar Surgery Yusuke Dodo - Hospital for Special Surgery; Ichiro Okano; Neil Kelly; Henryk Haffer; Maximillian Muellner; Erika Chiapparelli; Jennifer Shue; Darren Lebl, MD, MBA - Hospital for Special Surgery; Frank Cammisa, MD - Hospital for Special Surgery; Federico Girardi, MD - Hospital for Special Surgery; Alexander Hughes; Gbolabo Sokunbi, MD - Hospital for Special Surgery; Andrew Sama Background: Lateral lumbar interbody fusion (LLIF) is often performed in combination with posterior lumbar instrumentation, which requires patient repositioning during the procedure. There are reports that performing LLIF in a prone, single position with posterior fixation may result in a shorter operative time by eliminating patient repositioning. It is also hypothesized that the LLIF procedure can be done safely in the prone position due to the abdominal content in the prone position reflecting anteriorly with gravity. However, no study has investigated the safety of this single position procedure by demonstrating the abdominal organ positioning in the prone position. Objectives: To investigate the positioning of abdominal organs in the prone position and evaluate the safety of single position prone lateral lumbar interbody fusion. Methods: A total of 94 adult patients undergoing lumbar fusion surgery were retrospectively reviewed. The anatomical positioning of the abdominal organs was evaluated by CT in the supine and prone position. The center of the intervertebral body was defined as a reference location and horizontal base line (HBL) was drawn through the center of the intervertebral body. The distances from the HBL to the abdominal organs including aorta, inferior vena cava (IVC), ascending and descending colons, and bilateral kidneys were measured for the lumbar spine. An “at risk” position was defined as less than 10mm anteriorly from the HBL. Results: Compared to supine preoperative CTs, the IVC and bilateral kidneys at the L2-L3 level as well as the IVC and bilateral colons at the L3-L4 had a statistically significant ventral shift with prone positioning. The proportions of risk positions for the aorta, IVC, ascending colon, descending colon, right kidney, and left kidney were 0%, 0%, 29.6%, 48.3%, 88.6%, and 56.8 % at the L2-L3 level and 0%, 1.1%, 51.6%, 52.1%, 65.4%, and 63.6 % at the L3-L4 level, respectively. For the L4-L5 level, the proportions of risk position of aorta, IVC, ascending colon, and descending colon were 0%, 1.1%, 53.8%, and 53.2%, respectively. Females had significantly smaller distances for most measurements compared to males. Conclusions: Our results indicate that the kidneys at the L2- L3 level and the ascending and descending colon at the L3-L4 level shifted ventrally with prone positioning. However, the amount of shift was not large enough to avoid risk positioning, and a substantial proportion of patients had organs within the cage insertion corridor. Careful preoperative planning is warranted when considering prone, single-position LLIF. CONCURRENT SESSION 5: YOUNG SURGEON FREE PAPERS27 Please Click Here to VIEW Presenter Disclosures Paper 34:VR Simulation Module for Spinal Instrumentation Demonstrates Improved Procedural Confidence and Performance Dose Response in Neurosurgical Trainees: Pilot Study Nicholas M. Laskay, MD - University of Alabama at Birmingham Hospital; Matthew Parr; James Mooney; S. Harrison Farber, MD - Barrow Neurological Institute; Ryan Ehredt; Chinami Michaels; Juan Uribe; Jake Godzik Introduction: Technological advancements are the drivers of modern-day spine care. With the growing pressure to deliver faster and better care, surgical-assist technology is needed to harness computing power and enable the surgeon to improve outcomes. With the advent of virtual reality (VR), we now have the opportunity to utilize this low-cost, accessible technology to deliver higher-quality education through simulated operative techniques. This technology has the ability to aid in preoperative planning and education for the next generation of academic spine surgeons. Objectives: Evaluate feasibility of implementing a 2-month surgical training curriculum for neurosurgical trainees and quantify impact on procedural confidence and performance metrics. Methods: VR simulation module was developed with a high-quality replication of the operating room, with procedural capabilities involving placement of pedicle screw instrumentation into an anatomically realistic model of the lumbar spine. Oculus 2 headsets were distributed to neurosurgical residents at a single institution over a 2-month period using a randomized, intervention-control design with crossover as part of a pilot study. Trainees were asked to participate in a pre-post exposure survey design evaluating (procedural confidence). Intraprocedural performance metrics were tracked including instrumentation accuracy (accuracy rate, extent of error) and surgical time. Results: Data from a single institution survey of neurosurgical trainees (N=6) indicated a neutral to mild initial comfort level with spinal anatomy and moderate to significant discomfort with placement of pedicle screws. Post-exposure survey results following 3 month VR training demonstrates an improvement in comfort with the placement of pedicle screws in the lumbar spine. Overall screw accuracy defined as breach rate improved over each session for 50% (3/6) of the residents. However, if breach occurred, the average breach amount (in millimeters) decreased in 100% of the residents over successive simulation sessions. 50% (3/6) of residents felt that VR simulation could potentially shorten the length of neurosurgery training, while 100% (6/6) of the residents felt that VR simulation could be a useful adjunct to clinical neurosurgical experience. Conclusion: Pilot study data at a single institution demonstrate the feasibility of a 2-month VR simulation- based training curriculum for neurosurgical trainees. Trainees reported improved procedural confidence and demonstrated a dose response to training simulations, with improved performance metrics over successive simulation sessions. This represents the first study to evaluate multiple iterative VR-based training sessions in surgical trainees. Further multi- institutional studies are necessary to evaluate value of VR simulated as adjunct to the current clinical training paradigm. Paper 35: The Safety and Efficacy of Erector Spinae Plane Blocks in Minimally Invasive Spine Surgery: Modulation of Pain Scores, Opioid Requirements, and Adverse Events Josha Woodward, MD, MCR - Rush University Medical Center, Department of Neurological Surgery; Samuel Meza, MD - Rush University Medical Center, Department of Neurological Surgery; Daniel I. Wolfson, MD - Rush University Medical Center, Department of Neurological Surgery; Ryan M. Kelly, MD - Rush University Medical Center, Department of Neurological Surgery; Mena Kerolus, MD - Rush University Medical Center, Department of Neurological Surgery; Mitchell Bosman, MD - Rush University Medical Center, Department of Anesthesia and Perioperative Medicine; Asokumar Buvanendran, MD - Rush University Medical Center, Department of Anesthesia and Perioperative Medicine; Andrew Platt, MD MS - Rush University Medical Center, Department of Neurological Surgery; Ricardo Fontes, MD, PhD - Rush University Medical Center, Department of Neurological Surgery; Harel Deutsch, MD - Rush University Medical Center, Department of Neurological Surgery; Richard Fessler; Neal Mehta, MD - Rush University Medical Center, Department of Anesthesia and Perioperative Medicine; John O'Toole, MD - Rush University Medical Center, Department of Neurological Surgery Introduction: Pain management regimens in minimally invasive spinal surgery (MISS) aim to complement surgery by reducing opioid requirements and inpatient length of stay (LOS). Previously, enhanced recovery after surgery (ERAS) pain pathways have been shown to reduce postoperative opioid requirements and LOS. Here, we investigate the effect of preoperative erector spinae plane block (ESPB) in addition to an ERAS protocol in MISS. Aim: To evaluate and compare the efficacy and safety of ESPB on pain scores, opioid requirements, and LOS. CONCURRENT SESSION 5: YOUNG SURGEON FREE PAPERS28 Abstracts Study Design: A retrospective cohort study of 333 patients undergoing single-level MIS transforaminal lumbar interbody fusion (TLIF) was performed between 4/2015 and 4/2021. All patients were divided among a Pre-ERAS (n=210), ERAS (n=85), or ESPB (n=38) cohort. Adult patients with no prior history of lumbar surgery were included. Morphine equivalent units (MUE) were calculated for determination of oral, intravenous, and total opioid requirements. Results: 333 patients were included for analysis. Baseline demographics were comparable among cohorts except for mean age between the Pre-ERAS and ESPB cohort (65.8±2.1 vs. 60.2±0.9 years, p=0.04). Daily mean postoperative pain scores were comparable among cohorts on POD 1 and 3. A significant increase on POD 2 was noted in the ESPB cohort, likely correlated with resolution of the regional pain blockage (Pre-ERAS 4.7±0.1, ERAS 5.2±0.2, EPSB 5.8±0.2, p0.05). A similar trend was noted on POD 3 with a significant reduction in total opioid requirements favoring the ESPB cohort (p0.05). No technical or clinical adverse events related to ESPB were observed. Conclusion: The present study demonstrates a substantial reduction in opioid requirements with comparable pain scores related to integration of ESPB with an ERAS pain management pathway following MIS TLIF. Although further study is necessary to understand nuanced differences, taken together these promising findings suggest ESPB is a high-efficacy and safe adjuvant to MISS. Paper 36:Impact of Pandemic-induced Staff Shortages and Utilization of Immediate Use Surgical Sterilization on Surgical Site Infection After Spine Surgery Sharath Kumar Anand, MD - UPMC; Nima Alan; Adam S. Kanter Introduction: The COVID-19 pandemic has placed an inordinate stress on the health care system. With the rise of Delta and Omicron variants, widespread changes in the labor market have particularly affected the health care industry, resulting in staff shortages not only among the well- publicized physicians and nurses, but also in supporting staff such as central sterile processing technicians. Consequently, necessary measures have been adopted to mitigate the staff shortage impact on sterilization deficiencies. Specifically, an increased frequency in utilization of immediate use surgical sterilization (IUSS) techniques (‘flashing’) to sanitize the instruments was employed as opposed to the standard autoclaving of instruments the night prior. Hereby, we study the temporal correlation between rise in IUSS and surgical site infection (SSI) in spine surgery. Methods: This is a study of consecutive neurosurgical spine cases that took place in a tertiary academic center in the United States between January and December 2021. The procedures were identified using CPT code. SSI was defined as those surgical cases that required revision in the operating room with positive wound culture, hence sterile wound dehiscence as well as non-operative or aseptic wound complications were excluded. The correlation between IUSS and SSI was determined in univariate logistic regression. P< 0.05 was considered statistically significant. Results: A total of 1,619 spine operations took place at our institution during the 12-month study period. IUSS was utilized in 158 of the total cases (9.7%). The rate of IUSS use within our hospital rapidly rose from 2.7% in January 2021 to 20% in July, concurrent with spread of Delta variant. This was followed by temporary decline in September (7%), followed by another increase to 10% in October, concurrent with Omicron rise. Surgical site infection followed a similar bimodal distribution with first peak in July (4%) and second in October (5%). There were 38 surgical site infections in total, including 7 (4.4%) in the IUSS group and 31 (2.1%) in the non- IUSS group. We observed a statistically significant correlation between IUSS and SSI, with odds ratio 1.9953 (95% CI = 1.0278 – 3.8735). Conclusion: We observed an increase in IUSS utilization concurrent with the rise of virulent COVID-19 variants (Delta and Omicron) and a correlation with SSI in patients following spine surgery. CONCURRENT SESSION 5: YOUNG SURGEON FREE PAPERS29 Please Click Here to VIEW Presenter Disclosures Paper 37: A Single Center, Randomized Control Trial of IV Versus Oral Acetaminophen Perioperative to Instrumented Lumbar Fusion Gregory K. Paschal, MS - Hospital for Special Surgery; Fedan Avrumova, BS - Hospital for Special Surgery; Philip K. Paschal, MS - Hospital for Special Surgery; Ellen Soffin, MD PhD - Hospital for Special Surgery; Joseph Nguyen, MPH - Hospital for Special Surgery; Russel C. Huang, MD - Hospital for Special Surgery; Matthew Cunningham, MD PhD - Hospital for Special Surgery; Federico Girardi, MD - Hospital for Special Surgery; Frank Cammisa, MD - Hospital for Special Surgery; Darren Lebl, MD, MBA - Hospital for Special Surgery; Celeste Abjornson, PhD - Hospital for Special Surgery Introduction: Opioid analgesics are commonly utilized to manage post-operative pain following spinal surgery. Such medications are associated with side effects that often contribute to morbidity and prolonged hospitalization. In an effort to reduce opioid consumption, alternatives such as intravenous acetaminophen (IV), although having a relatively high cost initially, have shown value. Evaluating patient outcomes may address questions about the cost-effectiveness of this promising opioid alternative. Objective: The main objective of the study is to prospectively evaluate clinical outcomes following spinal fusion for two different pain management regimens: 1) oral administration of acetaminophen (PO) with supplemental pain medications as needed, and 2) intravenous administration of acetaminophen (IV) with supplemental pain medications as needed. We hypothesize that IV will reduce length of hospital stay, analgesic morphine equivalent consumption, and pain levels, and will do so more effectively than PO. Methods: In this prospective, single center, randomized control trial, patients were screened to meet the inclusion/ exclusion criteria. Patients with prior surgery or fracture at the index level(s), significantly elevated surgical risk, a history of drug abuse, and/or inability to take orally administered acetaminophen were excluded from this study. Enrolled patients were randomized into either IV or PO groups. Preoperative baseline surveys were collected. The first dose was administered within 3 hours prior to surgery. 7 postoperative doses were given every 6 hours. Patients had access to supplemental opioid analgesics as needed. Analgesic consumption and visual analog pain scale (VAS) scores were recorded daily until discharge. Patients were followed at 6 week and 6 month post-operatively and administered questionnaires. Pain medication usage was recorded. Results: Daily morphine equivalent (MME) consumption was statistically significantly lower for the IV group than the PO group (p = 0.001) from post-operative to final administration of acetaminophen dosage. Post regimen average daily MME was also statistically significantly lower for IV group than PO group (p = 0.002). Average length of stay was similar between groups. The IV group showed greater reduction in VAS and ODI between baseline and discharge. ODI was also statistically lower than baseline in both groups out to 6 months. Conclusion: In addition to an overall reduction in opioid use, patient surveys indicate an improvement of pain management with the use of IV acetaminophen. Our findings suggest that IV acetaminophen is a safe and effective alternative to opioid use. The decrease in risk of side effects makes IV acetaminophen a promising alternative to opioid use, even despite the added cost. Paper 38: Surgeon-placed Erector Spine Paravertebral Block and Continuous Bupivacaine Infusion for Pain Control After Lumbar fusion Michael Verdon, DO, FACOS - Wright State University - Boonshoft School of Medicine Introduction: Pain management following spinal fusion is an important part of patient recovery. Poor pain control is associated with a number of suboptimal outcomes, including opioid dependence. Regional anesthesia techniques are a promising field; however, they often require advanced anesthesiology providers. Recently, single shot erector spinae plane block (ESPB) has demonstrated short-term pain relief following spinal fusion. (1) It is hypothesized that continuous catheter infusion could provide extended analgesia. Objective: The purpose of this study was to evaluate the efficacy of surgeon-placed ESPB continuous bupivacaine infusion for patients undergoing lumbar fusion by a single surgeon in a single institution. Methods: Patients undergoing surgery were retrospectively identified and chosen consecutively for both ESPB and non- ESPB patients. Twenty patients undergoing one- and two- level MIS lumbar fusion received surgeon-placed continuous ESPB with 1-3 days of bupivacaine infusion. ESPB was placed using both fluoroscopic guidance and bony landmarks. Outcomes for these patients were compared to 20 patients undergoing one- and two-level MIS lumbar fusion who did not receive continuous ESPB. Both groups received standardized, multimodal analgesia including IV-acetaminophen, ketorolac, SESSION 12: FREE PAPERS—LIGHTNING ROUNDNext >