< Previous40 Abstracts Conclusions: The prevalence of subsidence after LLIF was quite high (37.5%) in our series. However, clinical and radiographic outcomes after subsidence were not unfavorable. Patients with intraoperative endplate injury were likely to show late-onset subsidence; however, fusion rate was not affected. Late-onset subsidence did not seem clinically significant. Paper 54:Minimally Invasive Lumbar Decompression Versus Minimally Invasive Transforaminal Lumbar Interbody Fusion for Treatment of Low-Grade Lumbar Degenerative Spondylolisthesis Patawut Bovonratwet; Andre Samuel; Jung Kee Mok; Avani Vaishnav; Kyle Morse, MD - Hospital for Special Surgery; Junho Song - Hospital for Special Surgery; Michael Steinhaus; Yusef Jordan; Sheeraz Qureshi Introduction: While lumbar degenerative spondylolisthesis is a common condition, optimal surgical treatment remains controversial. Newer minimally invasive (MIS) techniques, which preserve bone, paraspinal musculature, and posterior midline stabilizers, are thought to reduce the risk of iatrogenic instability and may obviate the need for fusion. However, few comparative studies of MIS techniques for low-grade lumbar degenerative spondylolisthesis currently exist. Aims/Objectives: To compare the patient-reported outcome measures (PROMs) following treatment of lumbar degenerative spondylolisthesis using MIS unilateral laminectomy for bilateral decompression (MIS-ULBD) or MIS transforaminal lumbar interbody fusion (MIS-TLIF). Methods: Consecutive patients with low-grade (Meyerding grade I or II) lumbar degenerative spondylolisthesis treated with single-level MIS-ULBD or MIS-TLIF were identified retrospectively from a prospectively collected spine surgery registry from April 2017 to November 2021. Perioperative outcomes, radiographic data, and PROMs were assessed. Results: A total of 188 patients underwent either MIS-ULBD or MIS-TLIF (79 MIS-ULBD and 109 MIS-TLIF). Patients who underwent MIS-ULBD tended to be older, had higher Charlson Comorbidity Index, lower mean percentage back pain, higher percentage of L4-L5 pathology, shorter operative time, lower estimated blood loss, and lower postoperative pain (p< 0.05). In both groups, there were statistically significant improvements at 1 year for five out of the six PROMs studied: Oswestry Disability Index (ODI), visual analog scale (VAS)- back pain, VAS-leg pain, Short Form 12 Physical Component Score (SF12-PCS), and Patient-Reported Outcomes Measurement Information System (PROMIS) (p< 0.05). On multivariate analysis controlling for confounders, there were no associations between procedure type and achieving MCID at 1 year in any of the PROMs studied. Conclusions: The current study suggests that both MIS- ULBD and MIS-TLIF result in significant improvements in pain and physical function for patients with low-grade lumbar degenerative spondylolisthesis. Paper 55:Early Outcomes of Multilevel ACDF with Segmental Plate Fixation Kody Barrett; Robert K. Eastlack; Gregory M. Mundis; Matthew Hatter; Ryan Beyer; Bahar Shahidi; Fernando Rios; Courtney Molzen; James Bruffey; Hani Malone, MD - Scripps Clinic / San Diego Spine Foundation Introduction: Multilevel ACDF constructs with a single contiguous plate have higher rates of pseudoarthrosis, dysphagia, and mechanical failure, compared to single level fusions. Optimal placement of long cervical plates may also present a technical challenge, requiring multiple x-rays and prolonged retraction. The use of low-profile single segment plates in series has been proposed as a means of making anterior fixation more facile, while avoiding the biomechanical limitations of “zero profile” integrated fixation implants. Aims/Objectives: Clinical and radiographic outcome assessment of segmental plate fixation in multilevel ACDF at 1-year. Methods: We prospectively followed patients undergoing multilevel segmental ACDF from 2018 to 2021. Pre and post operative demographic/radiographic characteristics and PROMs were recorded. Fusion was assessed through evaluation of bridging bone and interspinous movement (ISM, < 2mm) on flexion/extension x-rays. Results: 66 patients with one-year follow up were included in the analysis. NDI scores improved from an average of 33.9 (17.9) preop to 17.7 (13.0) at 1 year (p0.16). Four (6.1%) patients experienced a complication; 3 (4.5%) C5 palsy, 1 (1.5%) hematoma. Importantly, no patients required reoperation for pseudoarthrosis or instrumentation failure. Conclusion: Multilevel segmental ACDF is safe and led to significant improvements in NDI, pain, and radiographic SESSION 12: FREE PAPERS—LIGHTNING ROUND41 Please Click Here to VIEW Presenter Disclosures alignment in this cohort. There was an excellent rate of fusion based on bone bridging, but a greater than expected amount interspinous movement (22.4%, >2mm) was observed in asymptomatic patients, suggesting further study may be needed to assess fusion grading in multilevel segmental ACDF. Unlike traditional ACDF, the number of levels treated did not appear to influence rates of pseudoarthrosis in segmental ACDF. Further research is needed to evaluate the potential long term benefit of segmental plating on adjacent segment degeneration. Paper 56:Impact of Age Within Younger Populations on Outcomes Following Cervical Surgery in the Ambulatory Setting Timothy J. Hartman, BS - Rush University Medical Center; James W. Nie, BS - Rush University Medical Center; Hanna Pawlowski, BS - Rush University Medical Center; Michael C. Prabhu, BS - Rush University Medical Center; Nisheka N. Vanjani, BS - Rush University Medical Center; Keith R. MacGregor, BS - Rush University Medical Center; Kern Singh, MD - Rush University Medical Center Introduction: Few studies have investigated the effect of age on postoperative outcomes following cervical spine surgery in the younger population (< 65 years) within an ambulatory surgical setting. Objective: To determine the effect of age within the younger population seen at ambulatory surgical centers on Patient- reported Outcome Measures (PROMs) after cervical spine surgery. Methods: Patients of age < 65 years undergoing single-level anterior cervical discectomy and fusion (ACDF) or cervical disc replacement (CDR) were included. Patients were divided by mean age of initial population (46 years). PROMs included Patient-reported Outcomes Measurement Information System Physical Function (PROMIS-PF), 12-item Short-Form Health Survey Physical Component Summary (SF-12 PCS), Visual Analogue Scale (VAS) neck, VAS arm, and Neck Disability Index (NDI) collected preoperatively and 6-week, 12-week, 6-month, 1-year, and 2-years postoperatively. Results: 138 patients were included, with 66 patients < 46 years. Both cohorts demonstrated improvement from preoperative baseline with regard to all studied PROMs at multiple time points postoperatively (p≤0.042, all). Between groups, the older cohort demonstrated greater mean PROMIS-PF scores preoperatively and at 6 weeks (p≤0.011, both), while VAS arm scores were lower in the older group at 1 year (p=0.002), and NDI scores were lower in the older group at 6 weeks and 1 year (p< 0.027, both). Minimal Clinically Important Difference (MCID) achievement rates were greater in the younger group in PROMIS PF at 2 years (p=0.002), and in the older group in VAS arm score at 1 year (p=0.007). Conclusion: Both cohorts showed significant improvement at multiple postoperative time points for all PROMs. Between groups, the older group reported more favorable physical function, VAS arm, and NDI scores at several time points. However, MCID achievement rates only significantly differed in two PROMs at singular time points. Difference in age in patients < 65 years likely does not significantly affect long- term outcomes after cervical spine surgery. Paper 57: Anterior Vertebral Body Tethering Has Reduced Pain and Improved Function for the First 6 Weeks After Surgery Compared to Fusion Jennifer M. O'Donnell, MD - UCSF; Alex Gornitzky; Hao-Hua Wu; Kira Furie - UCSF; Mohammad Diab - UCSF Introduction: While posterior spinal instrumentation and fusion (PSIF) for severe adolescent idiopathic scoliosis (AIS) is the gold standard, anterior vertebral body tethering (AVBT) is becoming an alternative for select cases. Several studies have compared technical outcomes for these two procedures, but no studies have compared post-operative pain and recovery. Aims and Objectives: We aimed to prospectively compare AVBT and PSIF recovery periods in regards to pain, functional recovery, and patient perception of pain. Methods: In this prospective cohort, we evaluated patients who underwent AVBT or PSIF for AIS for a period of 6 weeks after operation. Pre-operative curve data were obtained from the medical record. Post-operative pain and recovery was evaluated with pain scores, pain confidence scores, PROMIS scores for pain behavior, interference, mobility, functional milestones of opiate use, independence in activities of daily living (ADLs), and sleeping. Results: The cohort included 9 patients who underwent AVBT and 22 who underwent PSIF, with a mean age of 13.7 years, 90% girls, and 77.4% white. The AVBT patients were younger (p=0.03), less skeletally mature (p=0.03), and had fewer instrumented levels (p=0.03). Results were significant SESSION 12: FREE PAPERS—LIGHTNING ROUND42 Abstracts for decreased pain scores at 2- and 6-weeks after operation (p=0.004, and 0.030), decreased PROMIS pain behavior at all time points (p=0.024, 0.049, and 0.001), decreased pain interference at 2- and 6-weeks post-operative (p=0.012 and 0.009), increased PROMIS mobility scores at all time points (p=0.036, 0.038, and 0.018), and faster time to functional milestones of weaning opiates, independence in ADLs, and sleep (p=0.024, 0.049, and 0.001). After 6 weeks, all AVBT patients were independent in ADLs, and after 3 weeks, all AVBT patients were weaned from opiates. Conclusion: In this prospective cohort study, the early recovery period following AVBT for AIS is characterized by less pain, increased mobility, and faster recovery of functional milestones, compared with PSIF. Paper 58:Clinical and Radiographic Results After Proximal Lumbar Anterior Column Realignment in Patients with Adult Spinal Deformity Timothy Y. Wang; Jason Frerich; Khoi D. Than Introduction: Anterior column realignment (ACR) via lateral lumbar interbody fusion is a novel minimally invasive (MIS) technique to restore sagittal alignment in patients with adult spinal deformity (ASD). Compared to traditional 3-column posterior osteotomies, ACR can provide similar degrees of correction, although with less blood loss, and similar if not improved complication rates. ACR can be performed at any lumbar level; however, previous spinal fusions can sometimes limit its application to the upper lumbar spine. As two-thirds of physiologic lordosis is found between L4 and S1, the ideal shape of the fused spine remains unclear. We evaluated radiographic and clinical outcomes in patients with ASD who underwent proximal (L1-L4) ACR for sagittal balance restoration. Aims and Objectives: Assess radiographic and clinical outcomes following lumbar anterior column realignment in the proximal lumbar spine. Methods: A retrospective review was performed of consecutive patients (n = 13) who underwent surgical treatment for ASD at a single tertiary referral center. All patients underwent MIS lateral interbody fusion technique with ACR above the level of L4, placement of either 20 or 30-degree hyper-lordotic cage, and reconstruction with posterior instrumented fusion. Pre- and post-operative radiographic and functional outcomes were reviewed by two independent reviewers. Demographic and surgical complications were recorded, as were visual analogue scale scores for back pain pre- and postoperatively. Results: Patients were 49-82 years of age with an average BMI of 30.3. Mean SVA decreased from 12.5 cm to 6.8 cm (p< 0.001), PI-LL decreased from 31.4° to 10.6° (p< 0.001), and segmental lordosis (SL) increased from 2.2° to 23.2° (p< 0.001). Proximal lumbar lordosis (PLL) increased from 2.5° to 21.8° (p< 0.001), and distal lumbar lordosis (DLL) did not significantly change (p=0.65). Mean lordosis distribution index (LDI) decreased from 51% to 38.0% (p=0.18). Average visual analogue back pain score (VAS) decreased from 7.5 to 2.6 (p=0.002). Mean intra-operative EBL was 880mL, and major complication rate was 7.7%. There were no neurological or vascular injuries. In one patient, a pre-existing spinal cord stimulator was dislodged from the epidural space and not replaced. Mean follow-up was 10.0 months. Conclusion: Proximal lumbar ACR in ASD patients can achieve significant correction of sagittal spinopelvic malignment with low complication rates. Differentially increasing PLL and lowering LDI does not have any obvious negative effects on clinical outcomes around 1-year. Further long-term follow-up is required to address the effect of altered lumbar morphology on the durability of results. Paper 59:Does the Severity of Facet Arthropathy Limit the Sagittal Re-alignment in Circumferential Minimally Invasive Surgical (CMIS) Correction of Adult Spinal Deformity (ASD)? Neel Anand - Cedars Sinai Medical Center; Andrew Chung; Anita Anand - Cedars Sinai Medical Center; Bardia Khandehroo - New York Medical College; Jose Jimenez Almonte; David Gendelberg - of California San Francisco - Orthopaedic Trauma Institute; Babak Khandehroo - Cedars Sinai Medical Center; Sheila Kahwaty - Cedars Sinai Medical Center Introduction: The first stage of circumferential minimally invasive (cMIS) correction of adult spinal deformity (ASD) involves lateral or oblique lumbar interbody fusion (OLIF). Success of this stage is measured by the achievement of indirect decompression and improvement of alignment. Improvement in alignment can be measured by observing increases in both disc space height and segmental lordosis. SESSION 12: FREE PAPERS—LIGHTNING ROUND43 Please Click Here to VIEW Presenter Disclosures Aim/Objectives: We conducted this study to assess if the severity of facet arthropathy limits the radiological improvement after CMIS correction of ASD. Methods: We review our prospectively collected data registry of 294 ASD patients who underwent staged CMIS correction from Jan 2011 to Jun 2021. Inclusion criteria of having ASD (Cobb>20,SVA>50mm,(PI-LL)>10) and 3+ levels fused, identified 161pts. 130 pts who had pre-op lumbar MRI/CT scans to evaluate the facet joints on each lumbar level (L1- S1) were included for this study. Total of 1024 facets were reviewed, and we assigned a preoperative grade (0-3) to the severity of the facet arthropathy using CT/ MRI described by Weishaupt et al. We then assessed the success of the improvement in alignment by evaluating post-op Posterior disc space height and Segmental lordosis. Result: Mean age was 66.6(22-84). Mean follow-up was 69 months(24-132). Total of 512 interbody levels were fused. Total of 1024 facets were graded as: 67 Grade 0, 245 Grade 1, 513 Grade 2 and 199 Grade 3. The radiological evaluation showed that the pre-op posterior disc space height and segmental lordosis improvements were not compromised by the severity of the facets arthropathy and were significantly increased at all lumbar levels(p< 0.05) after LIF surgery. Conclusion: Our study suggests that if the facets are not fused, the success of lateral/oblique interbody fusion in realignment for adult spinal deformity correction is independent of the severity of facet arthropathy posteriorly. Paper 60: Circumferential Minimally-Invasive Adult Spinal Deformity Surgery Provides Incremental Benefit for Increasingly Frail Patients Peter Passias; Peter Tretiakov; Rachel Joujon-Roche; Tyler Williamson; Oscar Krol; Bailey Imbo; Nima Alan; Pierce D. Nunley; Paul Park; Robert K. Eastlack; Gregory Mundis; Dean Chou; Juan Uribe; Neel Anand; Khoi D. Than; Saman Shabani; Breton Line; Christopher Ames; Justin S. Smith; Christopher Shaffrey; Robert Hart; Douglas Burton; Renaud Lafage; Frank Schwab; Shay Bess - Denver International Spine Center, Presbyterian St. Luke’s Medical Center; Praveen Mummaneni; Michael Wang; Adam Kanter; David O. Okonkwo - University of Pittsburgh; Nitin Agarwal - Washington University School of Medicine; Andrew Chan; Richard Fessler; Gregory Brusko; Sumedh Shah; Kai- Ming Fu Introduction: Circumferential minimally-invasive surgery (cMIS) techniques in ASD surgery provide greater incremental benefit to patients with increasing frailty states, though may be limited with increasing deformity status. Objective: To determine differences in 2-year outcomes for ASD patients receiving cMIS surgery over consecutive years based upon frailty and deformity states. Methods: Operative ASD patients ≥18yrs with complete pre- (BL) and 2-year(2Y) postop radiographic/HRQL data were assessed. Baseline, radiographic, and patient-reported data was analyzed via two-way ANOVA and MANOVA assessing interactions between frailty categorization and cMIS vs. Open technique. Propensity score matching (PSM) was used to align cMIS vs. Open groups by BL BMI, C7-S1 SVA, PI-LL, and S1PT. Frailty categorization was calculated per Passias et al. modified ASD frailty index scores and stratified as Not Frail (NF), Frail (F), and Severely Frail (SF). Peri- and post- operative factors were assessed using two-way ANCOVA and MANCOVA analysis while controlling for BL age, CCI, and levels fused. Recovery kinetics were assessed using time- adjusted HRQLs representing changes in Integrated Health State (IHS). Results: 174 ASD patients (62.85±13.93 years, 75.7% female, 29.23±6.64 kg/m2) were included after PSM, split evenly between cMIS and Open. At BL, two-way analysis demonstrated that increasingly frail MIS patients were older, more likely to be female, and have higher CCI than Open patients (all p.05). Peri-operatively, cMIS patients demonstrated reduced EBL and use of cell saver across frailty groups when adjusting for BL age, CCI, and levels fused, less peri-operative complications (p<0.001). Adjusted analysis also revealed that increasingly frail MIS patients were also more likely to demonstrate larger improvement in 1Y and 2Y ODI, SRS-36 Total, EQ5D, SF-36 metrics compared to Open patients (all p<0.05). By post-operative complications, increasingly frail cMIS patients were noted to experience significantly less complications overall (0.581 vs. 0.760, p=0.037), less major intra-operative complications (p= 0.039), and were less likely to need reoperation than their Open counterparts (p=0.043). Conclusion: Circumferential minimally invasive technique may offer acceptable outcomes with diminishment of peri- operative complications and mitigation of catastrophic outcomes in increasingly frail patients who may not be candidates for traditional open techniques. cMIS patients demonstrated lower intraoperative invasiveness, peri- operative complications, postoperative complications, and reoperations. However, further study should investigate the long-term impact of less optimal alignment in this population. SESSION 12: FREE PAPERS—LIGHTNING ROUND44 Abstracts Paper 61: Sacroiliac Joint Fusion Navigation: How Accurate is Pin Placement? Shea Comadoll, MD; Jason Haselhuhn, DO; David Polly, MD; Jonathan Sembrano, MD; Christian Ogilvie, MD; Edward Cheng, MD; Kristen Jones, MD; Christopher Martin, MD Introduction: Percutaneous pin placement is used in a variety of orthopaedic surgery settings, including external fixator application, fracture fixation, and reference frame establishment for navigation. Pin placement is typically uncomplicated; however, patient, surgeon, and anatomic site- specific factors may create additional challenges. For spine and pelvic cases with intraoperative navigation, a standard reference frame is often placed using a percutaneous pin. Ideal placement is in the posterior ilium, which is an oblique surface. Proper pin placement helps to ensure the correct positioning of the sacroiliac joint (SIJ) fusion implants. To date, there is no literature specifically examining the accuracy of pin placement. Aims/Objectives: The purpose of this study was to evaluate the occurrence of ideal percutaneous pin placement into the posterior iliac wing during navigated SIJ fusion surgery. Methods: Following IRB approval, we reviewed the charts and intraoperative CT images of patients who underwent navigated SIJ fusion by the senior author between 10/2013 and 1/2020. A pin placement grading scheme was developed initially and then tested. The definition of ‘ideal’ placement was a concept developed by the authors, and after modification it was deemed acceptable by fellow attending surgeons. This was then used for two rounds of grading. Six attending surgeons completed two rounds of pin placement grading, and statistical analysis was conducted. Results: Of the 90 eligible patients, 73.3% had ‘ideal’ pin placement, 17.8% medial/lateral breach, and 8.9% complete miss. There were no observed complications from pin placement. Male patients were 3.7 times more likely to have ideal placement than females. There was no relationship between BMI or fusion side and ideal placement. Interobserver reliability was rated as 0.72 and 0.69 in the first and second rounds, respectively, defined as ‘substantial agreement.’ The measured intraobserver reliability ranged from 0.74 (substantial agreement) to 0.92 (almost perfect agreement). Conclusions: This study demonstrates that even in the hands of an experienced surgeon, non-ideal pin placement occurs 26.7% of the time. However, engagement of the medial or lateral cortex may make the pin more rigid. Though pin placement does not meet our preconceived ‘ideal’, it is only rarely a true ‘miss’ where it is placed into the sacrum. ‘Ideal’ pin placement was more likely in males and was not associated with BMI or fusion laterality. When placing percutaneous pins, it is important to be aware of factors that can decrease placement accuracy, regardless of location. Paper 62: Shorter Length of Stay and Increased Return to Work with Cervical Disc Arthroplasty Versus Anterior Cervical Discectomy and Fusion Philip Zakko; Alex K. Miller, MD - Beaumont Health; Travis Hamilton; Victor Chang; Daniel Park; Jad Khalil Introduction: Anterior cervical discectomy and fusion (ACDF) and cervical disc arthroplasty (CDA) are established surgical options for the treatment of cervical degenerative disc disease. Current literature does not demonstrate a clear benefit between ACDF or CDA. Aims/Objectives: The primary objective of this study is to compare the outcomes of ACDF and CDA for patients enrolled in the Michigan Spine Surgery Improvement Collaborative (MSSIC) database. Methods: Patients undergoing 1 or 2 level ACDF or CDA surgery were included. A 4:1 propensity score matching analysis was performed between ACDF and CDA, with an exact match performed for number of levels operated on. Univariate comparisons were performed both pre- and post- propensity score matching. Results: 10,991 patients undergoing surgery between 2016 and 2021 were included. After matching, there were 3552 patients in the ACDF group and 888 patients in the CDA group. Demographics yielded significant differences in age (48.8 ± 10.0 years and 46.6 ± 10.8 for ACDF vs. CDA, respectively; p < 0.001). Regarding outcomes, length of surgery in hours was increased in the CDA group (1.7 ± 0.9 CDA vs. 1.5 ± 0.7 ACDF; p < 0.001) while length of stay in days was decreased (1.0 ± 1.0 CDA vs. 1.4 ± 1.8 ACDF; p < 0.001). Patients who underwent CDA were more likely to be discharged home (100% CDA vs. 98% ACDF; p = 0.002) and experience an outpatient surgery (62% CDA vs. 51% ACDF; p < 0.001). There was a higher incidence of postoperative complications in the ACDF group, including urinary retention, readmission, surgical site infection, return to OR, new or worsening radicular findings, cerebrospinal fluid leak, and myelopathy (25% ACDF vs. 21% CDA; p = 0.022). At 1 year postop, more patients were satisfied with their surgery in the CDA group (87% CDA vs. 82% ACDF; p = 0.049). No SESSION 12: FREE PAPERS—LIGHTNING ROUND45 Please Click Here to VIEW Presenter Disclosures significant differences in satisfaction were observed at 90 days or 2 years. No significant differences were observed in PROMIS, EQ-5D, neck pain, and arm pain MCID. Return to work favored CDA at 90 days (78% in CDA vs. 71% in ACDF; p = 0.043) and 2 years (92% in CDA vs. 83% in ACDF; p = 0.049). Conclusion: Patients undergoing CDA were more likely to be discharged home and experience an outpatient procedure, experienced fewer complications, were more satisfied with their surgery at 1 year, and had higher rates of return to work at 90 days and 2 years after surgery. Paper 63: Timing of Nerve Transfer Surgery for C5 Palsy: Does Recovery at 6 Months Predict Final Recovery? Yamaan Saadeh, MD - Unviersity of Michigan; Paul Park; Osama Kashlan; Brandon Smith Introduction: C5 palsy can occur following surgery for cervical spine pathology. The prognosis is generally favorable, and patients can recover useful function. However, a subset of patients do not experience recovery of useful strength. Nerve transfers have shown potential for the treatment of post- operative C5 palsy. Nerve transfers must be completed prior to muscle fibrosis associated with prolonged denervation, 12-18 months after denervation. However, spontaneous recovery from C5 palsy has been reported as occurring greater than 2 years post- operatively. This temporal limitation introduces uncertainty about whether to offer nerve transfer surgery or await the possibility of spontaneous recovery. Our aim was to determine whether failure to recover within 1 year post-operatively predicts failure to recover in the long term, to aid decision making regarding offering nerve transfer surgery. Objectives: To better understand the natural history of recovery from post-operative C5 palsy.To determine whether lack of recovery at a specific time point predicts a poor recovery prognosis from post-operative C5 palsy. To determine a reasonable time point for offering nerve transfer surgery for treatment of post-operative C5 palsy. Methods: We conducted retrospective chart review of 72 patients who underwent surgery for degenerative stenosis complicated by C5 palsy. Strength was recorded preoperatively, at discharge, two weeks, three months, six months, twelve months, and twenty-four months postoperatively. Multivariable logistic regression models were used to identify independent demographic and clinical risk factors for failure of recovery. Results: At 6 month follow up, 12 patients (15.8%) had not recovered useful deltoid or biceps function with 2/5 strength or less. At 1 year follow up, only 3 of these 12 patients recovered useful strength. No patient with 0/5 or 1/5 strength at 6 months recovered useful strength at 12 months. Conclusion: The majority of patients with C5 palsy recover useful strength in their C5 myotome within 12 months of onset. For patients at 6-months post-operatively without recovery of useful strength, offering nerve transfer surgery for reconstruction of C5 myotome would be reasonable for patient with 0/5 or 1/5 strength. Paper 64:Incidence of Major Complications in Lateral Lumbar Interbody Fusion (LLIF) Performed via the Prone Transpsoas (PTP) Technique: A Survey of the Complete Early Experience Luiz Pimenta, MD, PhD; William Taylor, MD; Kelli Howell - ATEC Spine; PTP Surgeon Council Introduction: A modification of the LLIF approach wherein lateral transpsoas access is achieved with the patient in the prone position was first presented in 2019, and was launched as a proceduralized technique known as PTP in 2020. Early reports focused on feasibility, perioperative clinical outcomes and efficiencies, and immediate postoperative alignment. Perioperative complications were reported as occurred in these small studies, and were consistent with reports of similar complications in the historical LLIF literature. However, the novelty of prone positioning has raised question about the potential for different rates of known but uncommon lateral-approach complications such as visceral, vascular, and neurologic injury. The current study sought to identify the incidence of select major complications from the early PTP experience to-date. Methods: A survey was created to query whether any patient in a surgeon’s PTP experience had suffered a major vascular (great vessel), visceral (bowel/kidney), or persistent (>6 mo) neurologic injury -- major complications that have a high probability of recall. The survey was sent to all US surgeons who performed PTP from its launch in June 2020 to July 1, 2022, as identified through a commercial operational database. Through the same database, the number of procedures performed in that timeframe by each surgeon SESSION 12: FREE PAPERS—LIGHTNING ROUND46 Abstracts was confirmed. No surgeons were excluded from receiving the survey based on case volumes (any surgeon having completed at least a single PTP procedure was included), and the case data represented each surgeon’s entire consecutive PTP series. Multiple reminders were issued to solicit survey responses. If a positive response was received, the respondent was sent a follow-up survey to query the details of that case. Results: A total of 243 surgeons were identified as having received the survey (after some attrition due to email blocking/bouncing). Responses were received from 119, a response rate of 49% of surgeons, and making up the majority of the total procedures known to have been performed. Among the 2,539 procedures completed by respondents, there were 2 vascular injuries (0.08%; CI: 0.01-0.28%), 4 bowel injuries (0.16%; CI: 0.04-0.40%), and 8 persistent neurologic injuries (0.32%; CI: 0.01-0.62%). Details of each incident are pending responses to the follow-up survey. Conclusion: The early PTP experience does not demonstrate a significantly higher rate of major vascular, visceral, or persistent neurologic injury than what has been reported in the literature for lateral decubitus LLIF. PTP is a safe procedure; the risk of any major complication is under 1%. Paper 65: Clinical Outcomes of the Prone Transpsoas Lateral Lumbar Interbody Fusion for Degenerative Lumbar Spine Disease: A Multicentre Study Mohamed A. Soliman, MD, MSc, PhD - Cairo University; Luis Diaz-Aguilar; Asham Khan; Jose San Miguel; 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: The prone transpsoas lateral lumbar interbody fusion (PTP) is a novel technique for degenerative lumbar spine disease. However, there is a paucity of the literature on the clinical outcomes of this procedure, with all the published being of a small sample size. Aims/Objectives: This study aimed to report the intraoperative and postoperative clinical outcomes of PTP in the largest study to date. Methods: A retrospective electronic medical records review was conducted in ten centers for patients who underwent PTP. We collected the intraoperative data (operative time, estimated blood loss [EBL], intraoperative complications [anterior longitudinal ligament (ALL) rupture, cage subsidence, vascular and visceral injuries), postoperative complications, the patient-reported outcome measures (PROMS) such as back pain visual analogue scale (VAS), and hospital stay. Results: A total of 350 patients were included in the study. There was a significant improvement in the mean VAS by 4.4±6.7 (p< 0.001). 2.8% had ALL rupture, 1.2% had cage subsidence, 0.4% had a vascular injury, and none had visceral injuries. The mean operative time was 229.9±144 minutes, the mean EBL was 134.3±210.2 mL, and the mean hospital stay was 2.6±2.2. In regard to postoperative complications, there was 8.9% new sensory symptoms, 6% transient hip flexor weakness, 1.4% wound infection, 1.4% cage subsidence, 0.6% psoas hematoma, 0.3% ureteric injury, 0.3% small bowel obstruction/ischemia, and 1.6% 90-days readmission. Conclusion: Multicenter consecutive case series show that PTP is well tolerated and has satisfactory clinical outcomes. Paper 66:Complications Associated with Single Position Prone Lateral Lumbar Interbody Fusion: a Systematic Review and Meta-analysis S. Harrison Farber, MD - Barrow Neurological Institute; Bayron Valenzuela Cecchi; Luke O'Neill; James Zhou - Barrow Neurological Institute; Joseph Didomenico - Barrow Neurological Institute; Nima Alan; Laura Snyder; Jay Turner; Juan Uribe Introduction: Lateral lumbar interbody fusion (LLIF) is a workhorse surgical approach for lumbar arthrodesis. There is now emerging interest in performing single position surgery in which both LLIF and pedicle screw fixation are performed in the prone position. To date, most studies of prone LLIF are of poor quality and without long-term follow up; and as such, the complication profile related to this novel approach is not well known. The objective of this study was to perform a meta- analysis to understand the safety profile of prone LLIF. Methods: A systematic review of the literature and a meta- analysis were conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. All studies reporting prone LLIF were assessed for inclusion. Studies not reporting complication rates were excluded. SESSION 12: FREE PAPERS—LIGHTNING ROUND47 Please Click Here to VIEW Presenter Disclosures Results: A total of 10 studies met inclusion criteria and were included in the analysis. Overall, 286 patients were treated with prone LLIF across these studies with an average of 1.3 (0.2) levels per patient. There were 18 reported intra- operative complications including cage subsidence (3.8%), rupture of the anterior longitudinal ligament (ALL) (2.3%), cage repositioning (2.1%), aborted prone interbody placement (0.82%), and durotomy (0.6%). There were no reported major vascular or peritoneal injuries. A total of 68 post-operative complications occurred. These included thigh/groin sensory symptoms (13.3%), hip flexor weakness (17.8%), wound infection (1.9%), psoas hematoma (1.3%), motor neural injury (1.2%), and revision surgery (3.8%). Conclusion: Single position LLIF in the prone position appears to be a safe surgical approach with a low complication profile. Longer term follow up and prospective studies are needed in order to better characterize long-term complication rates related to this approach. Paper 67:Minimally Invasive Lateral Lumbar Interbody Fusion for Clinical Adjacent Segment Pathology — A Comparative Study with Conventional Posterior Lumbar Interbody Fusion Hyung-Youl Park - Eunpyeong Saint Mary's Hospital, The Catholic University of Korea; Soo-Bin 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 St. Mary's Hospital, The Catholic University of Korea; 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 Introduction: Minimally invasive techniques have been increasingly applied for spinal surgery. No report has compared lateral lumbar interbody fusion (LLIF) with conventional posterior lumbar interbody fusion (PLIF) for clinical adjacent segment pathology (ASP). The purpose of this study was to evaluate the clinical and radiological efficacies of minimally invasive LLIF for clinical ASP. Material and Methods: Forty patients undergoing LLIF with posterior fusion (hybrid surgery) were compared with 40 patients undergoing conventional PLIF (posterior surgery). The radiological outcomes including indirect decompression in hybrid surgery group, and clinical outcomes such as the Oswestry Disability Index (ODI) and visual analog scale (VAS) were assessed. Post-operative major complications and re- operations were also compared between the two groups. Results: Correction of coronal Cobb’s angle and segmental lordosis in the hybrid surgery were significantly greater post- operatively (2.8° vs. 0.9°, p=0.012; 7.4° vs. 2.5°, p=0.009) and at the last follow-up (2.4° vs. 0.5°, p=0.026; 4.8° vs. 0.8°, p=0.016) compared with posterior surgery. Regarding indirect decompression of the LLIF, significant increases in thecal sac (83.4 vs. 113.8 mm2) and foraminal height (17.8 vs. 20.9 mm) were noted on post-operative MRI. Although post-operative back VAS (4.1 vs. 5.6, p=0.011) and ODI (48.9 vs. 59.6%, p=0.007) were significantly better in hybrid surgery, clinical outcomes at the last follow-up were similar. Moreover, intra- operative endplate fractures developed in 17.7% and lower leg symptoms occurred in 30.0% of patients undergoing hybrid surgery. Conclusion: Hybrid surgery for clinical ASP has advantages of segmental coronal and sagittal correction, and indirect decompression compared with conventional posterior surgery. However, LLIF related complications such as endplate fracture and lower leg symptoms also developed. LLIF should be performed considering advantages and approach related complications for the clinical ASP. Paper 68:Comparison of Pressure on the Soft Tissue Using 2 Different Lateral Retractors: Sweeping in Muscular Plane vs. Traditional Tubular Dilation. Burak M. Ozgur; Sunil Jeswani - UC San Diego Health Introduction: One of the concerns of the LLIF approach is the reports of postoperative incidence of thigh pain, weakness, and paresthesias. The design and goal of the lateral retractor, therefore, would be to minimize the disturbance to the psoas muscle fibers as well and the lumbosacral plexus. The sequential muscle plane lateral retractor has blades that begin in the plane parallel to the psoas muscle fibers, thus more anatomic and then open in a sweeping fashion to thereby reducing force on soft tissues. Objective: The purpose of this cadaver study is to compare the force/pressure on the soft tissues using the Sweeping in Muscular Plane (SMP) vs. Traditional Tubular Dilation (TTD). Methods: Two senior spine surgeons performed the access and dilation on sixteen levels between L2-L5 on both the left and right sides of four whole-torso cadaver specimen. Each level was randomized to either Sweeping (n=8) or Traditional (n=8). A Codman ICP Express pressure transducer, used to measure intra cranial pressure (mmHg) in neurosurgery, SESSION 12: FREE PAPERS—LIGHTNING ROUND48 Abstracts SESSION 12: FREE PAPERS—LIGHTNING ROUND was inserted into the posterior aspect of the Psoas muscle 5mm from K-wire. Maximum pressure was measured as the magnitude of the highest pressure reached after a motion event, and equilibrium pressure was the magnitude at which it settled. Visual assessments were performed via digital photography, and dilation site assessed for deformation caused by excess pressure. Results: Five different motion events: Dilation, Retractor Installation, Shim Installation, Blade Opening, and Blade Tilt were assessed for maximum measured pressure and equilibrium pressure. There was a significant difference between the SMP group and TTD group in equilibrium pressure for the Blade Opening event (3.63mmHg vs. 26.6mmHg) (p< 0.034), and the Blade Tilt event (3.50mmHg vs. 37.3mmHg) (p< 0.003). In addition, the difference between SMP and TTD groups in maximum pressure for the Blade Opening event was also statistically significant (4.38mmHg vs. 43.8mmHg) (p< 0.013). Conclusion: There was a significant difference in the magnitude of maximum psoas pressure between the SMP group vs. the TTD group for the blade opening action (p-value = 0.013). The difference in the magnitude of equilibrium pressure on the psoas between SMP group vs. TTD group for Retractor installation and Blade opening actions were also significant (p-value = 0.056 and 0.013 respectively). Paper 69: Risk Factors Analysis for Inferior Clinical Outcome and Recurrence After Full- endoscopic Interlaminar Discectomy (FEID) for Lumbar Disc Herniation; A Prospective Observational Study Jung-woo Hur - Eunpyeong St. Mary's Hospital, The Catholic University of Korea Introduction: Full endoscopic interlaminar discectomy (FEID) for lumbar disc herniation (LDH) has become popular in recent years. However, the major concerns for the beginners are inadequate neural decompression and early recurrence. Previous studies have proven the efficacy, but few have discussed the possible risk factors of poor outcome and recurrence. Aim/Objectives: The objective of this study is to determine the possible risk factors for inferior clinical outcome and early recurrence of FEID for LDH in minimum 12 month follow-up. Methods: This study is a prospective observational study from a single surgeon’s experience as a beginner in endoscopic spinal surgery. From May 2019 to July 2020, FEID was performed in consecutive 72 patients for LDH. The operated level was L5-S1 in 41, L4-L5 in 29 and L3-L4 in 2 patients. Mean operation time was 66.4 minutes and mean hospital stay after the operation was 2.1 days. Results: The follow-up period was at least 12 month. The visual analog scale (VAS) for back and leg pain, and Owestry disability index (ODI) showed significant improvement after operation. Excellent or good outcome by the modified MacNab’s criteria was observed in 88.8% (64/72) of patients. Disc migration, late surgery, previous spine operation, recurrent herniation and urinary/bowel dysfunction were associated with poor outcome. 8 patients were diagnosed with recurrent disc herniation (11.1%, 8/72) during follow-up period. Recurrence was more common in younger age, higher body mass index (BMI) and early operation. Broad-based (MSU classification 3) discs without calcification or spinal stenosis were also possible risk factors for recurrence. Small durotomy was occurred in 7 patients and no visible cerebrospinal fluid (CSF) leakage was detected after fibrin sealant patch repair. Conclusion: FEID is a safe and effective alternative to conventional microscopic techniques for LDH, even for a beginner in endoscopic spine surgery. We concluded that disc migration, late surgery, previous spine operation, recurrent herniation, and urinary/bowel dysfunction were possibly associated with unsatisfactory surgical outcomes. Recurrence was more common in younger age, higher BMI, and early operation.Next >