Dural Entrapment by Facet Joint after Unilateral Biportal Endoscopic Lumbar Decompression Surgery: Incidence, Risk Factors, and Biomechanical Considerations

Dural Entrapment by Facet Joint after Unilateral Biportal Endoscopic Lumbar Decompression Surgery: Incidence, Risk Factors, and Biomechanical Considerations | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Dural Entrapment by Facet Joint after Unilateral Biportal Endoscopic Lumbar Decompression Surgery: Incidence, Risk Factors, and Biomechanical Considerations Sang-Woo Lee, JinWoo Jung, Sang-Kyu Son, Dae-Chul Cho, Young San Ko, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7580616/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Objective Dural entrapment by the facet joint is a rare but potentially serious complication following unilateral biportal endoscopic (UBE) lumbar decompression. However, its incidence, risk factors, and biomechanical mechanisms remain unclear. This study aimed to investigate the incidence, clinical characteristics, and predictive factors for dural entrapment following UBE lumbar decompression, with a particular focus on anatomical and biomechanical considerations. Methods This retrospective cohort study included 181 patients (257 spinal segments) who underwent UBE lumbar decompression at a single institution between January 2023 and January 2024. Patients with prior lumbar surgery, deformity, severe instability, or incomplete imaging were excluded. Clinical and radiological parameters, including facet joint gap, facet joint angle, and dural sac-to-canal ratio, were evaluated. Multivariate logistic regression and receiver operating characteristic (ROC) curve analyses were performed to identify independent risk factors and their predictive performance. Results Dural entrapment occurred in 15 of 257 segments (5.8%). Symptomatic entrapment was observed in 2 cases (0.8%), one requiring revision surgery. Multivariate analysis identified degenerative spondylolisthesis (adjusted OR 46.88, p < 0.001), postoperative ipsilateral facet joint gap (adjusted OR 8.02, p = 0.003), and dural sac-to-canal ratio (adjusted OR 3.21, p = 0.031) as independent risk factors. ROC analysis demonstrated good predictive accuracy for the facet joint gap (AUC 0.786) and dural sac-to-canal ratio (AUC 0.705), with excellent performance for the combined model (AUC 0.925). Conclusion Dural entrapment after UBE lumbar decompression, though uncommon, may cause significant morbidity. Anatomical and biomechanical factors, including facet joint gap widening, play a critical role. Careful surgical techniques and targeted preventive strategies are essential to minimize this complication. Unilateral Biportal Endoscopy Lumbar decompression Minimally invasive Facet joint Entrapment Dura mater Figures Figure 1 Figure 2 Figure 3 Figure 4 INTRODUCTION Degenerative lumbar disease is a leading cause of chronic pain, neurological impairment, and reduced quality of life in the aging population. For patients with persistent symptoms refractory to conservative treatment, surgical decompression is often required. In recent decades, the pursuit of safer and less invasive procedures has driven the evolution of minimally invasive spine surgery, with the goals of reducing complications, controlling postoperative pain, and shortening recovery times.[ 1 , 2 ] Among these innovations, unilateral biportal endoscopy (UBE) has emerged as a key technique in the field of spine surgery.[ 3 ] UBE utilizes two small skin portals—one for the endoscope and one for surgical instruments—allowing precise decompression under a magnified view with free bimanual handling.[ 3 – 5 ] This approach preserves important spinal structures while minimizing muscle and ligament damage, resulting in consistently favorable outcomes, shorter hospital stays, and faster recovery compared with conventional open or microscopic techniques.[ 2 , 4 ] Although UBE surgery has many advantages and has been rapidly adopted worldwide, it is not without potential complications. Existing literature has mainly focused on common complications, such as dural tear, nerve root injury, postoperative infection, and epidural hematoma[ 1 , 3 – 6 ]. Still, less attention has been paid to the phenomenon of dural entrapment by the facet joint. This unique complication is distinctly different from a simple dural tear. In dural entrapment, the dural sac is entrapped and impinged in the surgically created facet joint gap, which may cause persistent or recurrent neurological symptoms that severely impair postoperative recovery. Unlike incidental dural tear, which is usually immediately recognizable intraoperatively, dural entrapment appears subtly and gradually appears postoperatively, leaving clinicians with challenges to its delayed or nonspecific clinical symptoms. The literature on dural or nerve root entrapment following conventional or endoscopic lumbar decompression remains sparse, consisting almost entirely of case reports and anecdotal observations.[ 7 , 8 ] Consequently, fundamental questions about its true incidence, underlying mechanisms, and reliable predictors remain unanswered. This knowledge gap is a significant barrier, preventing clinicians from preoperatively identifying patients at high risk or implementing specific intraoperative strategies for prevention. We hypothesized that dural entrapment develops through a multifactorial mechanism. This mechanism is influenced by both patient-specific anatomical predispositions, such as degenerative spondylolisthesis (DS), a relatively enlarged dural sac compared to the spinal canal, or inherent facet joint morphology, and by surgical factors. In particular, the extent of facet joint resection or medial facetectomy performed during decompression may play a critical role. A comprehensive understanding of these factors through rigorous investigation may enable more precise patient selection, optimized surgical planning, and, ultimately, a reduction in postoperative complications. Therefore, the objectives of this study are: (1) to systematically quantify the incidence and define the clinical presentation characteristics of dural entrapment by the facet joint following UBE lumbar decompression surgery; (2) to identify independent anatomical, demographic, and surgical risk factors predictive of this complication using robust statistical methods, including multivariate logistic regression; and (3) to ultimately establish clinical evidence-based recommendations that can guide surgical techniques, enhance preoperative patient counseling, and promote targeted preventive strategies in clinical practice; and (4) to propose practical intraoperative techniques aimed at minimizing the risk of dural entrapment based on biomechanical insights. MATERIALS AND METHODS Patient Selection This retrospective cohort study included patients aged ≥ 18 years who underwent UBE lumbar decompression surgery at our institution between January 2023 and January 2024. Eligible patients had degenerative lumbar disease (spinal stenosis, disc herniation, or lateral recess stenosis) confirmed on preoperative MRI, underwent surgery exclusively via UBE, had complete pre- and postoperative MRI and/or CT imaging, and ≥ 12 months of follow-up. Exclusion criteria were prior lumbar surgery, revision procedures, spinal deformity (Cobb angle ≥ 20°), Meyerding grade II or higher spondylolisthesis, severe instability (≥ 4 mm translation or ≥ 15° angulation on flexion-extension radiographs), infection, trauma, malignancy, inflammatory disease, or incomplete data. Institutional Review Board approval was obtained, and informed consent was waived owing to the retrospective design. Surgical Technique All operations were performed by a senior spine surgeon with experience in more than 5,000 UBE cases. Under general or epidural anesthesia, patients were positioned prone, and two ipsilateral portals (~ 1 cm each) were created for the endoscope and instruments. Continuous saline irrigation was used for visualization. Decompression included removal of hypertrophic ligamentum flavum and osteophytes, with partial medial facetectomy and lateral recess decompression when necessary. Facet joint and posterior ligamentous structures were preserved whenever possible. Meticulous hemostasis and drainage insertion were done at closure. Postoperative management consisted of routine analgesics, 48-hour antibiotics, early mobilization, and discharge typically within one week. Radiological Analysis Two blinded reviewers (a neurosurgeon and a radiologist) independently assessed all imaging, with mean values used for analysis. Measurements were performed using the INFINITT PACS system (INFINITT Healthcare, Seoul, Korea). -Imaging Measurement Protocol: MRI scans were performed using a standardized protocol (1.5T or 3.0T MRI scanner, T1-weighted and T2-weighted axial and sagittal sequences). In cases of uncertainty or significant degenerative facet changes, CT scans were utilized to clarify ambiguous findings or in cases with significant degenerative facet changes. - Definition of Dural Entrapment: Entrapment was strictly defined as ≥ 1 mm indentation of the dural sac into the facet joint gap, distinct from joint effusion or hematoma (Fig. 1 A). Cases with uncertain margins were resolved by consensus or excluded. - Facet Joint Gap and Gap Angle Measurement: Facet joint measurements were obtained at the lateral recess level, immediately below the lower disc margin. The facet joint gap was defined as the length (in mm) of the gap on the medial side of the facet joint. The facet joint gap angle was defined as the angle formed between the perpendicular line to the medial facet line, and the midsagittal line of the vertebral body (Fig. 1 B). - Working Angle Measurement: Working angle was defined as the angle formed between the plane of the resected bone surface and the midsagittal line described above (Fig. 1 C). - Dural Sac/Canal Ratio: Calculated as the cross-sectional dural sac area divided by the bony canal area on axial images (Fig. 1 D). Measurements were taken just below the lower disc margin, averaged from two adjacent normal levels to account for anatomical variation. Clinical Assessment Visual analogue scale (VAS) scores for back and leg pain and Oswestry Disability Index (ODI) scores were recorded preoperatively and at 1, 3, 6, and 12 months postoperatively. Data from the 12-month follow-up were used for analysis. Statistical Analysis An independent professional statistician conducted all statistical analyses using R software version 4.5.0(R Foundation for Statistical Computing, Vienna, Austria). Continuous variables were analyzed using Student’s t-tests or Mann-Whitney U tests, depending on normality distribution, while categorical variables were analyzed using Chi-square tests or Fisher’s exact tests as appropriate. Logistic regression was performed to determine independent predictors of dural entrapment. Initially, a generalized linear mixed model (GLMM) with a random intercept for each patient was fitted to account for potential clustering from multiple spinal segments within individual patients. However, the GLMM demonstrated negligible between-subject variation (singular fit with near-zero variance), prompting the use of a standard logistic regression model for the final analysis. Adjusted odds ratios (OR) and 95% confidence intervals (CI) were calculated. Statistical significance was established at p < 0.05, with variables exhibiting borderline significance (p < 0.10) highlighted as potential clinically relevant trends. Ethical Considerations This study was approved by the Public Institutional Review Board designated by the Ministry of Health and Welfare (approval number: P01-202506-01-049). Patient consent was waived, and confidentiality was maintained in accordance with the Declaration of Helsinki and institutional policies. RESULTS Patient Demographics and Clinical Characteristics A total of 257 spinal segments from 181 patients were analyzed. Mean age was 64.4 ± 12.7 years, and 128 segments (49.8%) were from female patients. Mean BMI was 26.1 ± 2.0 kg/m². Hypertension was present in 125 patients (69.1%) and diabetes in 61 (33.7%). Smoking status was: never 81 (44.8%), former 60 (33.1%), and current 40 (22.1%). Preoperative VAS scores were high (back 6.76 ± 1.15, leg 7.87 ± 0.64) and ODI averaged 59.3 ± 11.1. At 12 months, both VAS (back 2.69 ± 0.77, leg 2.03 ± 0.47, p<0.001) and ODI (21.1 ± 9.3, p<0.001) improved significantly (Table 1). Incidence of Dural Entrapment and Associated Clinical and Radiological Characteristics Dural entrapment was identified in 15 of 257 segments (5.8%). It occurred more frequently in females (80.0% vs. 47.9%, p=0.018) and tended to affect older patients (69.0 ± 11.6 vs. 64.1 ± 12.7 years, p=0.135). Entrapment was strongly associated with DS (53.3% vs. 2.9%, p<0.001) and instability (20.0% vs. 0.8%, p=0.002). Two cases (13.3%) became symptomatic—one resolved with conservative care, and one required revision surgery (Table 2). Radiological analysis showed significantly greater preoperative ipsilateral facet gaps (2.57 ± 0.46 vs. 2.25 ± 0.52 mm, p=0.017), larger postoperative ipsilateral gaps (3.59 ± 0.65 vs. 2.90 ± 0.64 mm, p=0.001), and steeper ipsilateral gap angles (25.9 ± 6.1° vs. 21.0 ± 9.0°, p=0.009) in the entrapment group. Δ facet gap was greater (1.02 ± 0.30 vs. 0.65 ± 0.44 mm, p<0.001), and dural sac/canal ratio was higher (0.55 ± 0.08 vs. 0.48 ± 0.08, p=0.009). No significant group differences were found regarding disease type, decompression technique, spinal level, or number of segments (all p>0.05) (Table 3). Multivariate Logistic Regression Analysis Multivariate logistic regression analysis identified significant independent risk factors for dural entrapment. DS was the strongest predictor (adjusted OR 46.88, 95% CI 6.46–340.18, p<0.001), followed by postoperative ipsilateral facet joint gap size (adjusted OR 8.02, 95% CI 2.04–31.52, p=0.003), and higher dural sac/canal ratio (adjusted OR 3.21, 95% CI 1.11–9.23, p=0.031) (Table 4). Female sex showed borderline significance with an adjusted OR of 4.88 (95% CI 0.89–26.69, p = 0.068), suggesting a potential trend towards a higher risk in females, although statistical significance was not achieved. Other variables, including instability, Δ facet joint gap, ipsilateral facet joint gap angle, and Δ angle, did not reach statistical significance in multivariate analysis. Receiver operating characteristic (ROC) analysis was conducted to further evaluate the predictive performance of these significant factors (Figure 2). Postoperative ipsilateral facet joint gap showed good predictive capability (AUC = 0.786, 95% CI: 0.670–0.902), with an optimal cutoff value of 3.475 mm (Figure 2A). The dural sac-to-canal ratio demonstrated moderate discriminatory performance (AUC = 0.705, 95% CI: 0.583–0.828), with an optimal cutoff of 0.5015 (Figure 2B). Importantly, the combined multivariate logistic regression model, integrating DS, postoperative ipsilateral facet joint gap, and dural sac-to-canal ratio, exhibited excellent overall predictive accuracy (AUC = 0.925, 95% CI: 0.865–0.984) (Figure 2C), underscoring the robustness and clinical relevance of the identified predictors. DISCUSSION This study systematically analyzed the incidence, clinical characteristics, and predictive risk factors of dural entrapment by the facet joint following UBE lumbar decompression surgery. Although dural entrapment occurred in 15 of 257 segments (5.8%), only 2 cases (0.8%) presented postoperative neurological symptoms. Among the symptomatic cases, one patient improved with conservative management, while the other required revision surgery. While the overall incidence of symptomatic dural entrapment was low, the potential for severe morbidity warrants attention. Early identification of high-risk patients may help prevent such complications. The key findings of our study were as follows: dural entrapment was significantly associated with DS, increased postoperative ipsilateral facet joint gap, and an elevated dural sac-to-canal ratio. Additionally, female sex demonstrated borderline significance, suggesting a possible sex-related predisposition that warrants further research with larger patient cohorts. Our results strongly suggest that anatomical and biomechanical factors play crucial roles in the pathogenesis of dural entrapment. In particular, the significantly increased postoperative facet joint gap observed ipsilaterally is likely due to the geometric characteristics inherent to the UBE surgical approach[4, 9, 10]. Ipsilateral access, characterized by a nearly perpendicular working angle relative to the facet joint orientation, creates a substantially larger facet joint opening compared to contralateral undercutting approaches, thus providing a direct pathway for the dura mater to invaginate[9–11]. This finding aligns well with the geometric principle that when a cylindrical structure is cut at an oblique angle (θ), the cross-sectional area increases according to the formula B = A × sec(θ), where A represents the original cross-sectional area parallel to the base and θ is the angle between the cutting plane and the base (Figure 3A). This concept illustrates how the working trajectory in UBE surgery can significantly enlarge the facet joint opening. Furthermore, the biomechanical relationship between the vector of dural expansion after decompression and the surgically created facet joint gap orientation appears critical[12, 13]. Ipsilaterally, the dural expansion force vector acts nearly perpendicular to the facet joint gap, minimizing vector force loss (F × sinθ, with θ ≈ 90°), thereby efficiently transmitting dural expansion forces directly into the opened facet joint space (Figure 3B). This efficient force transmission significantly increases the risk of dural entrapment on the ipsilateral side, while the oblique angle and smaller resultant gap opening contralaterally decrease the likelihood of contralateral entrapment. In addition, we propose another plausible biomechanical explanation: ipsilateral bone removal reduces local tissue pressure, creating a low-resistance pathway[12–14]. This pressure gradient allows the dural sac to preferentially expand toward the ipsilateral side, which may mechanically limit further displacement or expansion toward the contralateral facet joint. Similar asymmetric dural sac behavior has been described in spinal surgery literature, where unilateral decompression or tissue removal alters dural sac mobility in a predictable direction (Figure 3C). Clinically, the strong association between dural entrapment and DS highlights the importance of thorough preoperative evaluation. Patients with DS often present with altered spinal anatomy, abnormal facet orientation, and inherent spinal instability, all of which predispose them to dural entrapment[15, 16]. Recognizing this anatomical vulnerability allows spine surgeons to take preventive measures through meticulous intraoperative technique adjustments and vigilant postoperative monitoring. The borderline significance of female sex (adjusted OR 4.88, p=0.068) may reflect underlying anatomical or biomechanical differences, such as smaller facet joints, higher joint laxity between males and females[17]. In addition, previous studies have shown DS is more prevalent in females and that females with DS tend to exhibit wider facet joints compared to their male counterparts[16, 18, 19]. Given the associate ion between facet joint morphology and dural entrapment demonstrated in our study, these findings may partially explain the observed sex-related trend. Although statistical significance was not fully reached, the present results raise the possibility of a sex-related predisposition to dural entrapment. Further large-scale and multicenter studies are warranted to confirm this relationship. To date, no definitive preventive measures for dural entrapment have been established in clinical practice. Based on our findings and the discussed theoretical framework, we propose a preventive strategy (Figure 4): temporary sealing of the facet joint gap during surgery using bioabsorbable collagen-bound fibrin sealing materials. These materials are widely used for dural repair in spinal surgery, providing temporary mechanical protection and promoting safe healing[20, 21]. Dural entrapment likely occurs within a 'window of vulnerability'—the period after surgical decompression but before sufficient granulation tissue forms to physiologically stabilize the space[14, 22, 23]. During this time, the dural sac remains in a dynamic state of gradual expansion, increasing the risk of migration into the facet joint gap[14]. A temporary sealant provides a physical barrier during this critical period, minimizing the risk of initial dural entrapment, by which point granulation and fibrous tissue formation would naturally stabilize and occlude this space. Future prospective clinical trials or controlled experimental studies should evaluate this innovative approach to confirm its effectiveness, safety, and feasibility. Several limitations of our study should be acknowledged. First, due to the retrospective design and relatively small number of dural entrapment cases, the statistical power was limited, particularly for subgroup analyses and borderline significant variables such as female sex. In addition, although radiological evaluations were performed independently by two blinded reviewers to minimize measurement bias, minor interpretation differences or measurement variability cannot be completely excluded. Moreover, the short-term follow-up duration of approximately 12 months limits the evaluation of potential late-occurring symptomatic dural entrapment or delayed clinical manifestations. Longer follow-up and prospective cohort designs would strengthen future studies. In conclusion, this study offers novel insights into the pathomechanism and risk factors associated with dural entrapment following UBE lumbar decompression. Although symptomatic cases were uncommon, dural entrapment can lead to persistent neurological symptoms that are difficult to manage once they occur. Our findings highlight the importance of understanding how surgical technique, dural sac dynamics, and anatomical factors interact to influence entrapment risk. Particularly in patients with degenerative spondylolisthesis or specific anatomical predispositions, careful surgical planning may help reduce complications. Further research with larger cohorts is needed to confirm these results and improve patient outcomes in minimally invasive spine surgery. Declarations Funding/Support: None. Conflict of Interest: The authors have nothing to disclose. Author Contribution Conceptualization: SK. S, MK. P; Methodology: SW. L; Formal Analysis: SW. L.; Resources: MK P, SW L.; Data Curation: SW L, JW. J; Writing – Original Draft: SW. L.; Writing – Review & Editing: SW L, MK. P, JW. J, DC. C, YS. K; Visualization: SW. L; Supervision: MK.P; Project Administration: MK. P; All authors reviewed the manuscript. 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Patient’s demographic data No. of Patients 181 Age 63.7 ± 13.2 Sex Male Female 86 (47.5) 95 (52.5) BMI 26.1 ± 2.0 Smoking Never Current Former 81 (44.8) 40 (22.1) 60 (33.1) HTN = Yes 125 (69.1) DM = Yes 61 (33.7) Pre – OP Final follow up p-value VAS_Back 6.8 ± 1.2 2.7 ± 0.8 < 0.001 VAS_Leg 7.9 ± 0.6 2.0 ± 0.5 < 0.001 ODI 59.3 ± 11.1 21.1 ± 9.3 < 0.001 Follow up length (Mo) 12.5 ± 1.3 Values are presented as mean ± standard deviation or number (%) Demographic data are based on the number of patients (N=181) BMI, Body mass index; HTN, Hypertension; DM, Diabetes mellitus; VAS, Visual analog scale; ODI, Oswestry disability index Table 2. Comparison of Clinical characteristics Between Entrapment and Non-entrapment Group Variable Overall Non-entrapment Entrapment p-value No. 257 242 15 Female (%) 128 (49.8) 116 (47.9) 12 (80%) 0.018 Age 64.4 ± 12.7 64.1 ± 12.7 69.0 ± 11.6 0.135 Disease type 0.676 SS (%) 143 (55.6) 133 (55.0) 10 (66.7) HNP (%) 55 (21.4) 52 (21.5) 3 (20.0) LRS (%) 59 (23.0) 57 (23.6) 2 (13.3) OP type 0.876 ULBD 147 (57.2) 139 (57.4) 8 (53.3) Discectomy 48 (18.7) 45 (18.6) 3 (20.0) DL 62 (24.1) 58 (24.0) 4 (26.7) OP side (Right) 37 (14.4) 33 (13.6) 4 (26.7) 0.244 DS (%) 15 (5.8) 7 (2.9) 8 (53.3) <0.001 Instability 5 (1.9) 2 (0.8) 3 (20.0) 0.002 Values are presented as mean ± standard deviation or number (%) SS, Spinal stenosis; HNP, Herniation of nucleus pulposus; LRS, Lateral recess stenosis; ULBD, Unilateral laminectomy bilateral decompression; DL, Decompressive laminotomy; DS, Degenerative spondylolisthesis Table 3. Comparison of Radiological Parameters Between Entrapment and Non-Entrapment Groups Variable Overall Non-entrapment Entrapment p-value Pre facet joint gap (I) 2.26 ± 0.52 2.25 ± 0.52 2.57 ± 0.46 0.017 Pre facet joint gap (C) 2.25 ± 0.54 2.25 ± 0.54 2.13 ± 0.49 0.375 Post facet joint gap (I) 2.94 ± 0.66 2.90 ± 0.64 3.59 ± 0.65 0.001 Post facet joint gap (C) 2.47 ± 0.59 2.47 ± 0.59 2.48 ± 0.66 0.934 Facet gap angle (I) 21.28 ± 8.91 20.99 ± 8.98 25.91 ± 6.11 0.009 Facet gap angle (C) 23.24 ± 8.85 23.06 ± 8.83 26.15 ± 8.95 0.213 Working angle (I) 4.17 ± 6.54 4.16 ± 6.58 4.31 ± 6.07 0.931 Working angle (C) 22.30 ± 5.70 22.22 ± 5.80 23.68 ± 3.24 0.270 Δ angle (I) 17.11 ± 9.20 16.83 ± 9.26 21.60 ± 7.06 0.023 Δ angle (C) 1.59 ± 8.59 1.59 ± 8.64 1.69 ± 8.21 0.974 Dural sac / Canal ratio 0.49 ± 0.08 0.48 ± 0.08 0.55 ± 0.08 0.009 Values are presented as mean ± standard deviation Facet joint gap is measured in millimeters (mm), and angles are expressed in degrees (°) I, Ipsilateral side; C, Contralateral side; Δ angle, Difference between facet gap angle and working angle Table 4. Multivariate Logistic Regression Analysis for Predictors of Dural Entrapment Variable Adjusted OR (95% CI) Adjusted p-value Sex: Female vs Male 4.88 (0.89 - 26.69) 0.068 DS: Yes or No 46.88 (6.46 – 340.18) <0.001 Instability: Yes or No 2.12 (0.09 – 50.76) 0.643 Post facet joint gap (I, per mm increase) 8.02 (2.04 – 31.52) 0.003 Δ Facet joint gap (I, per mm increase) 0.37 (0.06 – 2.46) 0.307 Facet gap angle (I, per degree increase) 1.02 (0.91 – 1.13) 0.757 Δ Angle (I, per degree increase) 1.01 (0.90 – 1.13) 0.851 Dural sac / Canal ratio (Per 0.1 increase) 3.21 (1.11 – 9.23) 0.031 OR, odds ratio; CI, confidence interval; Δ, difference between facet joint gap and working angle for angles, or between pre- and postoperative measurements for facet joint gap.; I, Ipsilateral side; C, Contralateral side Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7580616","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":532290379,"identity":"aa55250e-02bd-4756-a27e-52fb492aa73d","order_by":0,"name":"Sang-Woo Lee","email":"","orcid":"","institution":"Hu hospital","correspondingAuthor":false,"prefix":"","firstName":"Sang-Woo","middleName":"","lastName":"Lee","suffix":""},{"id":532290380,"identity":"c04a5949-58c5-4685-816c-ac22bf97d8f0","order_by":1,"name":"JinWoo Jung","email":"","orcid":"","institution":"Hu 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23:26:09","extension":"html","order_by":32,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":98074,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7580616/v1/cdcfc719a6e686e1053a6f75.html"},{"id":94047804,"identity":"f6c199bf-9e33-405c-92b2-141d7b96937b","added_by":"auto","created_at":"2025-10-21 23:18:08","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":20431884,"visible":true,"origin":"","legend":"\u003cp\u003eRadiological definitions and measurement methods for dural entrapment.\u003cbr\u003e\nA, Dural entrapment was defined as ≥1 mm indentation of the dural sac into the facet joint gap on axial imaging.\u003cbr\u003e\nB, Measurement of facet joint gap (medial side) and facet joint gap angle, defined as the angle between the facet orientation and midsagittal reference line.\u003cbr\u003e\nC, Measurement of ipsilateral and contralateral working angles, determined by the relationship between the surgical bone removal trajectory and the midsagittal line.\u003cbr\u003e\nD, Dural sac-to-canal ratio was calculated by dividing the dural sac area by the bony canal area on axial images.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7580616/v1/9753a1d0d5e17b79c165f2ad.png"},{"id":94047796,"identity":"e6b3e17d-8e51-48f6-bfdf-107529af7619","added_by":"auto","created_at":"2025-10-21 23:18:08","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":102752,"visible":true,"origin":"","legend":"\u003cp\u003eReceiver operating characteristic (ROC) curves for predicting dural entrapment.\u003cbr\u003e\nA, ROC curve for postoperative ipsilateral facet joint gap (AUC = 0.786, cutoff = 3.475 mm).\u003cbr\u003e\nB, ROC curve for dural sac-to-canal ratio (AUC = 0.705, cutoff = 0.5015).\u003cbr\u003e\nC, ROC curve for the combined multivariate logistic regression model incorporating significant independent predictors (AUC = 0.925), demonstrating excellent discriminatory performance.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7580616/v1/820e3e6574dcfa8cee89309f.png"},{"id":94047798,"identity":"eb447a1f-7158-4c49-b3e0-78376c871e7a","added_by":"auto","created_at":"2025-10-21 23:18:08","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":3833467,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic illustrations of biomechanical mechanisms contributing to dural sac displacement toward the ipsilateral facet joint gap.\u003cbr\u003e\nA, A conceptual geometric model using a cylinder to demonstrate how the sectional area changes depending on the cutting angle. The cutting angle (θ) is defined as the angle between the cutting plane and the base of the cylinder. When the cylinder is cut parallel to its base (θ = 0°), the cross-sectional area is minimal (circular). In contrast, an oblique cut (θ ＞0°) produces a larger elliptical area, illustrating how the working trajectory angle can influence the opening size in real anatomical structures. \u003cbr\u003e\n B, Vector analysis of dural sac expansion forces. The ipsilateral facet joint gap receives more direct force transmission due to a nearly perpendicular angle, while the contralateral side shows reduced force transmission.\u003cbr\u003e\nC, Ipsilateral bone removal creates a localized low-pressure zone, resulting in preferential dural sac expansion and displacement toward the ipsilateral facet joint gap.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7580616/v1/e55f0d3804f8bad18f8a41b7.png"},{"id":94047810,"identity":"bf12b100-29f5-45ec-b1ba-0b0d27a0bfb0","added_by":"auto","created_at":"2025-10-21 23:18:09","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":615846,"visible":true,"origin":"","legend":"\u003cp\u003eIntraoperative image\u003c/p\u003e\n\u003cp\u003eIntraoperative endoscopic image showing temporary sealing of the ipsilateral facet joint gap using a bioabsorbable collagen-bound fibrin sealing material (white arrows).\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7580616/v1/25531041e2fa123f4614ef87.jpg"},{"id":102264920,"identity":"7ea243a5-d9a3-4bf2-ac1b-e0ff1cab8f21","added_by":"auto","created_at":"2026-02-10 02:10:29","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":24267776,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7580616/v1/3ac1dbf8-b327-4e6d-af18-7f36c26b2a0f.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Dural Entrapment by Facet Joint after Unilateral Biportal Endoscopic Lumbar Decompression Surgery: Incidence, Risk Factors, and Biomechanical Considerations","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eDegenerative lumbar disease is a leading cause of chronic pain, neurological impairment, and reduced quality of life in the aging population. For patients with persistent symptoms refractory to conservative treatment, surgical decompression is often required. In recent decades, the pursuit of safer and less invasive procedures has driven the evolution of minimally invasive spine surgery, with the goals of reducing complications, controlling postoperative pain, and shortening recovery times.[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e] Among these innovations, unilateral biportal endoscopy (UBE) has emerged as a key technique in the field of spine surgery.[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] UBE utilizes two small skin portals\u0026mdash;one for the endoscope and one for surgical instruments\u0026mdash;allowing precise decompression under a magnified view with free bimanual handling.[\u003cspan additionalcitationids=\"CR4\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] This approach preserves important spinal structures while minimizing muscle and ligament damage, resulting in consistently favorable outcomes, shorter hospital stays, and faster recovery compared with conventional open or microscopic techniques.[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/p\u003e\u003cp\u003eAlthough UBE surgery has many advantages and has been rapidly adopted worldwide, it is not without potential complications. Existing literature has mainly focused on common complications, such as dural tear, nerve root injury, postoperative infection, and epidural hematoma[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan additionalcitationids=\"CR4 CR5\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Still, less attention has been paid to the phenomenon of dural entrapment by the facet joint. This unique complication is distinctly different from a simple dural tear. In dural entrapment, the dural sac is entrapped and impinged in the surgically created facet joint gap, which may cause persistent or recurrent neurological symptoms that severely impair postoperative recovery. Unlike incidental dural tear, which is usually immediately recognizable intraoperatively, dural entrapment appears subtly and gradually appears postoperatively, leaving clinicians with challenges to its delayed or nonspecific clinical symptoms.\u003c/p\u003e\u003cp\u003eThe literature on dural or nerve root entrapment following conventional or endoscopic lumbar decompression remains sparse, consisting almost entirely of case reports and anecdotal observations.[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] Consequently, fundamental questions about its true incidence, underlying mechanisms, and reliable predictors remain unanswered. This knowledge gap is a significant barrier, preventing clinicians from preoperatively identifying patients at high risk or implementing specific intraoperative strategies for prevention.\u003c/p\u003e\u003cp\u003eWe hypothesized that dural entrapment develops through a multifactorial mechanism. This mechanism is influenced by both patient-specific anatomical predispositions, such as degenerative spondylolisthesis (DS), a relatively enlarged dural sac compared to the spinal canal, or inherent facet joint morphology, and by surgical factors. In particular, the extent of facet joint resection or medial facetectomy performed during decompression may play a critical role. A comprehensive understanding of these factors through rigorous investigation may enable more precise patient selection, optimized surgical planning, and, ultimately, a reduction in postoperative complications.\u003c/p\u003e\u003cp\u003eTherefore, the objectives of this study are: (1) to systematically quantify the incidence and define the clinical presentation characteristics of dural entrapment by the facet joint following UBE lumbar decompression surgery; (2) to identify independent anatomical, demographic, and surgical risk factors predictive of this complication using robust statistical methods, including multivariate logistic regression; and (3) to ultimately establish clinical evidence-based recommendations that can guide surgical techniques, enhance preoperative patient counseling, and promote targeted preventive strategies in clinical practice; and (4) to propose practical intraoperative techniques aimed at minimizing the risk of dural entrapment based on biomechanical insights.\u003c/p\u003e"},{"header":"MATERIALS AND METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003ePatient Selection\u003c/h2\u003e\u003cp\u003eThis retrospective cohort study included patients aged\u0026thinsp;\u0026ge;\u0026thinsp;18 years who underwent UBE lumbar decompression surgery at our institution between January 2023 and January 2024. Eligible patients had degenerative lumbar disease (spinal stenosis, disc herniation, or lateral recess stenosis) confirmed on preoperative MRI, underwent surgery exclusively via UBE, had complete pre- and postoperative MRI and/or CT imaging, and \u0026ge;\u0026thinsp;12 months of follow-up. Exclusion criteria were prior lumbar surgery, revision procedures, spinal deformity (Cobb angle\u0026thinsp;\u0026ge;\u0026thinsp;20\u0026deg;), Meyerding grade II or higher spondylolisthesis, severe instability (\u0026ge;\u0026thinsp;4 mm translation or \u0026ge;\u0026thinsp;15\u0026deg; angulation on flexion-extension radiographs), infection, trauma, malignancy, inflammatory disease, or incomplete data. Institutional Review Board approval was obtained, and informed consent was waived owing to the retrospective design.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eSurgical Technique\u003c/h3\u003e\n\u003cp\u003eAll operations were performed by a senior spine surgeon with experience in more than 5,000 UBE cases. Under general or epidural anesthesia, patients were positioned prone, and two ipsilateral portals (~\u0026thinsp;1 cm each) were created for the endoscope and instruments. Continuous saline irrigation was used for visualization. Decompression included removal of hypertrophic ligamentum flavum and osteophytes, with partial medial facetectomy and lateral recess decompression when necessary. Facet joint and posterior ligamentous structures were preserved whenever possible. Meticulous hemostasis and drainage insertion were done at closure. Postoperative management consisted of routine analgesics, 48-hour antibiotics, early mobilization, and discharge typically within one week.\u003c/p\u003e\n\u003ch3\u003eRadiological Analysis\u003c/h3\u003e\n\u003cp\u003eTwo blinded reviewers (a neurosurgeon and a radiologist) independently assessed all imaging, with mean values used for analysis. Measurements were performed using the INFINITT PACS system (INFINITT Healthcare, Seoul, Korea).\u003c/p\u003e\u003cp\u003e-Imaging Measurement Protocol:\u003c/p\u003e\u003cp\u003eMRI scans were performed using a standardized protocol (1.5T or 3.0T MRI scanner, T1-weighted and T2-weighted axial and sagittal sequences). In cases of uncertainty or significant degenerative facet changes, CT scans were utilized to clarify ambiguous findings or in cases with significant degenerative facet changes.\u003c/p\u003e\u003cp\u003e- Definition of Dural Entrapment:\u003c/p\u003e\u003cp\u003eEntrapment was strictly defined as \u0026ge;\u0026thinsp;1 mm indentation of the dural sac into the facet joint gap, distinct from joint effusion or hematoma (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA). Cases with uncertain margins were resolved by consensus or excluded.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e- Facet Joint Gap and Gap Angle Measurement:\u003c/p\u003e\u003cp\u003eFacet joint measurements were obtained at the lateral recess level, immediately below the lower disc margin. The facet joint gap was defined as the length (in mm) of the gap on the medial side of the facet joint. The facet joint gap angle was defined as the angle formed between the perpendicular line to the medial facet line, and the midsagittal line of the vertebral body (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB).\u003c/p\u003e\u003cp\u003e- Working Angle Measurement:\u003c/p\u003e\u003cp\u003eWorking angle was defined as the angle formed between the plane of the resected bone surface and the midsagittal line described above (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC).\u003c/p\u003e\u003cp\u003e- Dural Sac/Canal Ratio:\u003c/p\u003e\u003cp\u003eCalculated as the cross-sectional dural sac area divided by the bony canal area on axial images (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eD). Measurements were taken just below the lower disc margin, averaged from two adjacent normal levels to account for anatomical variation.\u003c/p\u003e\n\u003ch3\u003eClinical Assessment\u003c/h3\u003e\n\u003cp\u003eVisual analogue scale (VAS) scores for back and leg pain and Oswestry Disability Index (ODI) scores were recorded preoperatively and at 1, 3, 6, and 12 months postoperatively. Data from the 12-month follow-up were used for analysis.\u003c/p\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003eStatistical Analysis\u003c/h2\u003e\u003cp\u003eAn independent professional statistician conducted all statistical analyses using R software version 4.5.0(R Foundation for Statistical Computing, Vienna, Austria). Continuous variables were analyzed using Student\u0026rsquo;s t-tests or Mann-Whitney U tests, depending on normality distribution, while categorical variables were analyzed using Chi-square tests or Fisher\u0026rsquo;s exact tests as appropriate.\u003c/p\u003e\u003cp\u003eLogistic regression was performed to determine independent predictors of dural entrapment. Initially, a generalized linear mixed model (GLMM) with a random intercept for each patient was fitted to account for potential clustering from multiple spinal segments within individual patients. However, the GLMM demonstrated negligible between-subject variation (singular fit with near-zero variance), prompting the use of a standard logistic regression model for the final analysis. Adjusted odds ratios (OR) and 95% confidence intervals (CI) were calculated. Statistical significance was established at p\u0026thinsp;\u0026lt;\u0026thinsp;0.05, with variables exhibiting borderline significance (p\u0026thinsp;\u0026lt;\u0026thinsp;0.10) highlighted as potential clinically relevant trends.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003eEthical Considerations\u003c/h2\u003e\u003cp\u003eThis study was approved by the Public Institutional Review Board designated by the Ministry of Health and Welfare (approval number: P01-202506-01-049). Patient consent was waived, and confidentiality was maintained in accordance with the Declaration of Helsinki and institutional policies.\u003c/p\u003e\u003c/div\u003e"},{"header":"RESULTS","content":"\u003cp\u003e\u003cem\u003ePatient Demographics and Clinical Characteristics\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eA total of 257 spinal segments from 181 patients were analyzed. Mean age was 64.4 \u0026plusmn; 12.7 years, and 128 segments (49.8%) were from female patients. Mean BMI was 26.1 \u0026plusmn; 2.0 kg/m\u0026sup2;. Hypertension was present in 125 patients (69.1%) and diabetes in 61 (33.7%). Smoking status was: never 81 (44.8%), former 60 (33.1%), and current 40 (22.1%).\u003cbr\u003e\u0026nbsp;Preoperative VAS scores were high (back 6.76 \u0026plusmn; 1.15, leg 7.87 \u0026plusmn; 0.64) and ODI averaged 59.3 \u0026plusmn; 11.1. At 12 months, both VAS (back 2.69 \u0026plusmn; 0.77, leg 2.03 \u0026plusmn; 0.47, p\u0026lt;0.001) and ODI (21.1 \u0026plusmn; 9.3, p\u0026lt;0.001) improved significantly (Table 1).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIncidence of Dural Entrapment and Associated Clinical and Radiological Characteristics\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eDural entrapment was identified in 15 of 257 segments (5.8%). It occurred more frequently in females (80.0% vs. 47.9%, p=0.018) and tended to affect older patients (69.0 \u0026plusmn; 11.6 vs. 64.1 \u0026plusmn; 12.7 years, p=0.135). Entrapment was strongly associated with DS (53.3% vs. 2.9%, p\u0026lt;0.001) and instability (20.0% vs. 0.8%, p=0.002). Two cases (13.3%) became symptomatic\u0026mdash;one resolved with conservative care, and one required revision surgery (Table 2).\u003c/p\u003e\n\u003cp\u003eRadiological analysis showed significantly greater preoperative ipsilateral facet gaps (2.57 \u0026plusmn; 0.46 vs. 2.25 \u0026plusmn; 0.52 mm, p=0.017), larger postoperative ipsilateral gaps (3.59 \u0026plusmn; 0.65 vs. 2.90 \u0026plusmn; 0.64 mm, p=0.001), and steeper ipsilateral gap angles (25.9 \u0026plusmn; 6.1\u0026deg; vs. 21.0 \u0026plusmn; 9.0\u0026deg;, p=0.009) in the entrapment group. \u0026Delta; facet gap was greater (1.02 \u0026plusmn; 0.30 vs. 0.65 \u0026plusmn; 0.44 mm, p\u0026lt;0.001), and dural sac/canal ratio was higher (0.55 \u0026plusmn; 0.08 vs. 0.48 \u0026plusmn; 0.08, p=0.009). No significant group differences were found regarding disease type, decompression technique, spinal level, or number of segments (all p\u0026gt;0.05) (Table 3).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eMultivariate Logistic Regression Analysis\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eMultivariate logistic regression analysis identified significant independent risk factors for dural entrapment. DS was the strongest predictor (adjusted OR 46.88, 95% CI 6.46\u0026ndash;340.18, p\u0026lt;0.001), followed by postoperative ipsilateral facet joint gap size (adjusted OR 8.02, 95% CI 2.04\u0026ndash;31.52, p=0.003), and higher dural sac/canal ratio (adjusted OR 3.21, 95% CI 1.11\u0026ndash;9.23, p=0.031) (Table 4). Female sex showed borderline significance with an adjusted OR of 4.88 (95% CI 0.89\u0026ndash;26.69, p = 0.068), suggesting a potential trend towards a higher risk in females, although statistical significance was not achieved. Other variables, including instability, \u0026Delta; facet joint gap, ipsilateral facet joint gap angle, and \u0026Delta; angle, did not reach statistical significance in multivariate analysis.\u003c/p\u003e\n\u003cp\u003eReceiver operating characteristic (ROC) analysis was conducted to further evaluate the predictive performance of these significant factors (Figure 2). Postoperative ipsilateral facet joint gap showed good predictive capability (AUC = 0.786, 95% CI: 0.670\u0026ndash;0.902), with an optimal cutoff value of 3.475 mm (Figure 2A). The dural sac-to-canal ratio demonstrated moderate discriminatory performance (AUC = 0.705, 95% CI: 0.583\u0026ndash;0.828), with an optimal cutoff of 0.5015 (Figure 2B). Importantly, the combined multivariate logistic regression model, integrating DS, postoperative ipsilateral facet joint gap, and dural sac-to-canal ratio, exhibited excellent overall predictive accuracy (AUC = 0.925, 95% CI: 0.865\u0026ndash;0.984) (Figure 2C), underscoring the robustness and clinical relevance of the identified predictors.\u003c/p\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eThis study systematically analyzed the incidence, clinical characteristics, and predictive risk factors of dural entrapment by the facet joint following UBE lumbar decompression surgery. Although dural entrapment occurred in 15 of 257 segments (5.8%), only 2 cases (0.8%) presented postoperative neurological symptoms. Among the symptomatic cases, one patient improved with conservative management, while the other required revision surgery. While the overall incidence of symptomatic dural entrapment was low, the potential for severe morbidity warrants attention. Early identification of high-risk patients may help prevent such complications.\u003c/p\u003e\n\u003cp\u003eThe key findings of our study were as follows: dural entrapment was significantly associated with DS, increased postoperative ipsilateral facet joint gap, and an elevated dural sac-to-canal ratio. Additionally, female sex demonstrated borderline significance, suggesting a possible sex-related predisposition that warrants further research with larger patient cohorts.\u003c/p\u003e\n\u003cp\u003eOur results strongly suggest that anatomical and biomechanical factors play crucial roles in the pathogenesis of dural entrapment. In particular, the significantly increased postoperative facet joint gap observed ipsilaterally is likely due to the geometric characteristics inherent to the UBE surgical approach[4, 9, 10]. Ipsilateral access, characterized by a nearly perpendicular working angle relative to the facet joint orientation, creates a substantially larger facet joint opening compared to contralateral undercutting approaches, thus providing a direct pathway for the dura mater to invaginate[9\u0026ndash;11]. This finding aligns well with the geometric principle that when a cylindrical structure is cut at an oblique angle (\u0026theta;), the cross-sectional area increases according to the formula B = A \u0026times; sec(\u0026theta;), where A represents the original cross-sectional area parallel to the base and \u0026theta; is the angle between the cutting plane and the base (Figure 3A). This concept illustrates how the working trajectory in UBE surgery can significantly enlarge the facet joint opening.\u003c/p\u003e\n\u003cp\u003eFurthermore, the biomechanical relationship between the vector of dural expansion after decompression and the surgically created facet joint gap orientation appears critical[12, 13]. Ipsilaterally, the dural expansion force vector acts nearly perpendicular to the facet joint gap, minimizing vector force loss (F \u0026times; sin\u0026theta;, with \u0026theta; \u0026asymp; 90\u0026deg;), thereby efficiently transmitting dural expansion forces directly into the opened facet joint space (Figure 3B). This efficient force transmission significantly increases the risk of dural entrapment on the ipsilateral side, while the oblique angle and smaller resultant gap opening contralaterally decrease the likelihood of contralateral entrapment.\u003c/p\u003e\n\u003cp\u003eIn addition, we propose another plausible biomechanical explanation: ipsilateral bone removal reduces local tissue pressure, creating a low-resistance pathway[12\u0026ndash;14]. This pressure gradient allows the dural sac to preferentially expand toward the ipsilateral side, which may mechanically limit further displacement or expansion toward the contralateral facet joint. Similar asymmetric dural sac behavior has been described in spinal surgery literature, where unilateral decompression or tissue removal alters dural sac mobility in a predictable direction (Figure 3C).\u003c/p\u003e\n\u003cp\u003eClinically, the strong association between dural entrapment and DS highlights the importance of thorough preoperative evaluation. Patients with DS often present with altered spinal anatomy, abnormal facet orientation, and inherent spinal instability, all of which predispose them to dural entrapment[15, 16]. Recognizing this anatomical vulnerability allows spine surgeons to take preventive measures through meticulous intraoperative technique adjustments and vigilant postoperative monitoring.\u003c/p\u003e\n\u003cp\u003eThe borderline significance of female sex (adjusted OR 4.88, p=0.068) may reflect underlying anatomical or biomechanical differences, such as smaller facet joints, higher joint laxity between males and females[17]. In addition, previous studies have shown DS is more prevalent in females and that females with DS tend to exhibit wider facet joints compared to their male counterparts[16, 18, 19]. Given the associate\u0026nbsp;ion between facet joint morphology and dural entrapment demonstrated in our study, these findings may partially explain the observed sex-related trend. Although statistical significance was not fully reached, the present results raise the possibility of a sex-related predisposition to dural entrapment. Further large-scale and multicenter studies are warranted to confirm this relationship.\u003c/p\u003e\n\u003cp\u003eTo date, no definitive preventive measures for dural entrapment have been established in clinical practice. Based on our findings and the discussed theoretical framework, we propose a preventive strategy (Figure 4): temporary sealing of the facet joint gap during surgery using bioabsorbable collagen-bound fibrin sealing materials. These materials are widely used for dural repair in spinal surgery, providing temporary mechanical protection and promoting safe healing[20, 21]. Dural entrapment likely occurs within a \u0026apos;window of vulnerability\u0026apos;\u0026mdash;the period after surgical decompression but before sufficient granulation tissue forms to physiologically stabilize the space[14, 22, 23]. During this time, the dural sac remains in a dynamic state of gradual expansion, increasing the risk of migration into the facet joint gap[14]. A temporary sealant provides a physical barrier during this critical period, minimizing the risk of initial dural entrapment, by which point granulation and fibrous tissue formation would naturally stabilize and occlude this space. Future prospective clinical trials or controlled experimental studies should evaluate this innovative approach to confirm its effectiveness, safety, and feasibility.\u003c/p\u003e\n\u003cp\u003eSeveral limitations of our study should be acknowledged. First, due to the retrospective design and relatively small number of dural entrapment cases, the statistical power was limited, particularly for subgroup analyses and borderline significant variables such as female sex. In addition, although radiological evaluations were performed independently by two blinded reviewers to minimize measurement bias, minor interpretation differences or measurement variability cannot be completely excluded. Moreover, the short-term follow-up duration of approximately 12 months limits the evaluation of potential late-occurring symptomatic dural entrapment or delayed clinical manifestations. Longer follow-up and prospective cohort designs would strengthen future studies.\u003c/p\u003e\n\u003cp\u003eIn conclusion, this study offers novel insights into the pathomechanism and risk factors associated with dural entrapment following UBE lumbar decompression. Although symptomatic cases were uncommon, dural entrapment can lead to persistent neurological symptoms that are difficult to manage once they occur. Our findings highlight the importance of understanding how surgical technique, dural sac dynamics, and anatomical factors interact to influence entrapment risk. Particularly in patients with degenerative spondylolisthesis or specific anatomical predispositions, careful surgical planning may help reduce complications. Further research with larger cohorts is needed to confirm these results and improve patient outcomes in minimally invasive spine surgery.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003e\u003cstrong\u003eFunding/Support:\u0026nbsp;\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eNone.\u003c/p\u003e\u003cp\u003e\u003ch2\u003eConflict of Interest:\u003c/h2\u003e\u003cp\u003eThe authors have nothing to disclose.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConceptualization: SK. S, MK. P; Methodology: SW. L; Formal Analysis: SW. L.; Resources: MK P, SW L.; Data Curation: SW L, JW. J; Writing \u0026ndash; Original Draft: SW. L.; Writing \u0026ndash; Review \u0026amp; Editing: SW L, MK. P, JW. J, DC. C, YS. K; Visualization: SW. L; Supervision: MK.P; Project Administration: MK. P; All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThis research was supported by Kyungpook National University Research Fund. 2025\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eWang B, He P, Liu X, Wu Z, Xu B (2023) Complications of Unilateral Biportal Endoscopic Spinal Surgery for Lumbar Spinal Stenosis: A Systematic Review of the Literature and Meta‐analysis of Single‐arm Studies. Orthop Surg 15:3\u0026ndash;15\u003c/li\u003e\n\u003cli\u003eWu K, Yun Z, Suvithayasiri S, Liang Y, Setiawan DR, Kotheeranurak V, Jitpakdee K, Giordan E, Liu Q, Kim J-S (2024) Evolving Paradigms in Spinal Surgery: A Systematic Review of the Learning Curves in Minimally Invasive Spine Techniques. Neurospine 21:1251\u0026ndash;1275\u003c/li\u003e\n\u003cli\u003eXu J, Wang D, Liu J, Zhu C, Bao J, Gao W, Zhang W, Pan H (2022) Learning Curve and Complications of Unilateral Biportal Endoscopy: Cumulative Sum and Risk-Adjusted Cumulative Sum Analysis. Neurospine 19:792\u0026ndash;804\u003c/li\u003e\n\u003cli\u003ePao J-L, Lin S-M, Chen W-C, Chang C-H (2020) Unilateral biportal endoscopic decompression for degenerative lumbar canal stenosis. J Spine Surg 6:438\u0026ndash;446\u003c/li\u003e\n\u003cli\u003eHwa Eum J, Hwa Heo D, Son SK, Park CK (2016) Percutaneous biportal endoscopic decompression for lumbar spinal stenosis: a technical note and preliminary clinical results. J Neurosurg Spine 24:602\u0026ndash;607\u003c/li\u003e\n\u003cli\u003eLee HG, Kang MS, Kim SY, Cho KC, Na YC, Cho JM, Jin BH (2021) Dural Injury in Unilateral Biportal Endoscopic Spinal Surgery. Glob Spine J 11:845\u0026ndash;851\u003c/li\u003e\n\u003cli\u003ePark SH, Lee JH, Chough CK (2023) Nerve Root Herniation With Entrapment After Endoscopic Spine Decompression. J Minim Invasive Spine Surg Tech 8:219\u0026ndash;223\u003c/li\u003e\n\u003cli\u003ePopadic B, Scheichel F, Themesl M, Decristoforo I, Sherif C, Marhold F (2021) Nerve root herniation with entrapment in the facet joint gap after lumbar decompression surgery: a case presentation. BMC Musculoskelet Disord 22:736\u003c/li\u003e\n\u003cli\u003eLee DH, Park CK, Jang J-W, Lee D-G (2025) Safety and Utility of Bilateral-contralateral Decompression for Adjacent Segment Stenosis After Lumbar Interbody Fusion Using Unilateral Biportal Endoscopy. Clin Spine Surg. https://doi.org/10.1097/BSD.0000000000001777\u003c/li\u003e\n\u003cli\u003eLi W, Han J, Xin Q, Liu Q, Feng C, Liu Y, Zhang D (2023) Finite element mechanical analysis of ipsilateral approach and contralateral approach in unilateral bilateral endoscopic spine surgery. J Orthop Surg 18:979\u003c/li\u003e\n\u003cli\u003ePark S-R, Choi S-R, Kim N-H, et al (2025) Biportal Endoscopic Decompression with Maximized Facet Joint Preservation for Central to Extraforaminal Lumbar Stenosis. J Clin Med 14:2725\u003c/li\u003e\n\u003cli\u003eHermansen E, Austevoll IM, Hellum C, et al (2020) Comparable increases in dural sac area after three different posterior decompression techniques for lumbar spinal stenosis: radiological results from a randomized controlled trial in the NORDSTEN study. Eur Spine J 29:2254\u0026ndash;2261\u003c/li\u003e\n\u003cli\u003eChung S-W, Kang M-S, Shin Y-H, Baek O-K, Lee S-H (2014) Postoperative Expansion of Dural Sac Cross-Sectional Area after Unilateral Laminotomy for Bilateral Decompression: Correlation with Clinical Symptoms. Korean J Spine 11:227\u003c/li\u003e\n\u003cli\u003eOba H, Takahashi J, Futatsugi T, Mogami Y, Shibata S, Ohji Y, Tanikawa H (2013) Study of dural sac cross-sectional area in early and late phases after lumbar decompression surgery. Spine J 13:1088\u0026ndash;1094\u003c/li\u003e\n\u003cli\u003eRai RR, Shah Y, Shah S, Palliyil NS, Dalvie S (2019) A Radiological Study of the Association of Facet Joint Tropism and Facet Angulation With Degenerative Spondylolisthesis. Neurospine 16:742\u0026ndash;747\u003c/li\u003e\n\u003cli\u003eBall JR, Gallo MC, Kebaish K, et al (2024) National Trends in Lumbar Degenerative Spondylolisthesis With Stenosis Treated With Fusion Versus Decompression. Neurospine 21:1068\u0026ndash;1077\u003c/li\u003e\n\u003cli\u003eMizukoshi R, Yagi M, Yamada Y, Yokoyama Y, Yamada M, Watanabe K, Nakamura M, Nagura T, Jinzaki M (2024) Gender differences in spinal mobility during postural changes: a detailed analysis using upright CT. Sci Rep 14:9154\u003c/li\u003e\n\u003cli\u003eHe L-C, Wang Y-XJ, Gong J-S, Griffith JF, Zeng X-J, Kwok AW, Leung JC, Kwok T, Ahuja AT, Leung PC (2014) Prevalence and risk factors of lumbar spondylolisthesis in elderly Chinese men and women. Eur Radiol 24:441\u0026ndash;448\u003c/li\u003e\n\u003cli\u003eWang YXJ, K\u0026aacute;pl\u0026aacute;r Z, Deng M, Leung JCS (2017) Lumbar degenerative spondylolisthesis epidemiology: A systematic review with a focus on gender-specific and age-specific prevalence. J Orthop Transl 11:39\u0026ndash;52\u003c/li\u003e\n\u003cli\u003eCarretta A, Epskamp M, Ledermann L, Staartjes VE, Neidert MC, Regli L, Stienen MN (2022) Collagen-bound fibrin sealant (TachoSil\u0026reg;) for dural closure in cranial surgery: single-centre comparative cohort study and systematic review of the literature. Neurosurg Rev 45:3779\u0026ndash;3788\u003c/li\u003e\n\u003cli\u003eKinaci A, Moayeri N, Van Der Zwan A, Van Doormaal TPC (2019) Effectiveness of Sealants in Prevention of Cerebrospinal Fluid Leakage after Spine Surgery: A Systematic Review. World Neurosurg 127:567-575.e1\u003c/li\u003e\n\u003cli\u003eKohlhauser M, Mayrhofer M, Kamolz L-P, Smolle C (2024) An Update on Molecular Mechanisms of Scarring\u0026mdash;A Narrative Review. Int J Mol Sci 25:11579\u003c/li\u003e\n\u003cli\u003eLewik G, Lewik G, M\u0026uuml;ller LS, Von Glinski A, Schulte TL, Lange T (2024) Postoperative Epidural Fibrosis: Challenges and Opportunities - A Review. Spine Surg Relat Res 8:133\u0026ndash;142\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTable 1. Patient\u0026rsquo;s demographic data\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eNo. of Patients\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 140px;\"\u003e\n \u003cp\u003e181\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAge\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 140px;\"\u003e\n \u003cp\u003e63.7\u0026nbsp;\u0026plusmn; 13.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSex\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 140px;\"\u003e\n \u003cp\u003eMale\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003eFemale\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 140px;\"\u003e\n \u003cp\u003e86 (47.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e95 (52.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eBMI\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 140px;\"\u003e\n \u003cp\u003e26.1\u0026nbsp;\u0026plusmn; 2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSmoking\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 140px;\"\u003e\n \u003cp\u003eNever\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003eCurrent\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003eFormer\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 140px;\"\u003e\n \u003cp\u003e81 (44.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e40 (22.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e60 (33.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eHTN = Yes\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 140px;\"\u003e\n \u003cp\u003e125 (69.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eDM = Yes\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 140px;\"\u003e\n \u003cp\u003e61 (33.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 140px;\"\u003e\n \u003cp\u003ePre \u0026ndash; OP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003eFinal follow up\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003ep-value\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eVAS_Back\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 140px;\"\u003e\n \u003cp\u003e6.8\u0026nbsp;\u0026plusmn; 1.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e2.7 \u0026plusmn; 0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u0026lt; 0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eVAS_Leg\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 140px;\"\u003e\n \u003cp\u003e7.9 \u0026plusmn; 0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e2.0 \u0026plusmn; 0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u0026lt; 0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eODI\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 140px;\"\u003e\n \u003cp\u003e59.3 \u0026plusmn; 11.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e21.1 \u0026plusmn; 9.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u0026lt; 0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFollow up length (Mo)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 140px;\"\u003e\n \u003cp\u003e12.5\u0026nbsp;\u0026plusmn; 1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eValues are presented as mean\u0026nbsp;\u0026plusmn; standard deviation or number (%)\u003c/p\u003e\n\u003cp\u003eDemographic data are based on the number of patients (N=181)\u003c/p\u003e\n\u003cp\u003eBMI, Body mass index; HTN, Hypertension; DM, Diabetes mellitus; VAS, Visual analog scale; ODI, Oswestry disability index\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 2. Comparison of Clinical characteristics Between Entrapment and Non-entrapment Group\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eVariable\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eOverall\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eNon-entrapment\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eEntrapment\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ep-value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eNo.\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e257\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e242\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFemale (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e128 (49.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e116 (47.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e12 (80%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e0.018\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAge\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e64.4\u0026nbsp;\u0026plusmn; 12.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e64.1 \u0026plusmn; 12.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e69.0 \u0026plusmn; 11.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e0.135\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eDisease type\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e0.676\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cul\u003e\n \u003cli\u003e\u003cstrong\u003eSS (%)\u003c/strong\u003e\u003c/li\u003e\n \u003c/ul\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e143 (55.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e133 (55.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e10 (66.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cul\u003e\n \u003cli\u003e\u003cstrong\u003eHNP (%)\u003c/strong\u003e\u003c/li\u003e\n \u003c/ul\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e55 (21.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e52 (21.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e3 (20.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cul\u003e\n \u003cli\u003e\u003cstrong\u003eLRS (%)\u003c/strong\u003e\u003c/li\u003e\n \u003c/ul\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e59 (23.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e57 (23.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e2 (13.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eOP type\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e0.876\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cul\u003e\n \u003cli\u003e\u003cstrong\u003eULBD\u003c/strong\u003e\u003c/li\u003e\n \u003c/ul\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e147 (57.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e139 (57.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e8 (53.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cul\u003e\n \u003cli\u003e\u003cstrong\u003eDiscectomy\u003c/strong\u003e\u003c/li\u003e\n \u003c/ul\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e48 (18.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e45 (18.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e3 (20.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cul\u003e\n \u003cli\u003e\u003cstrong\u003eDL\u003c/strong\u003e\u003c/li\u003e\n \u003c/ul\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e62 (24.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e58 (24.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e4 (26.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eOP side (Right)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e37 (14.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e33 (13.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e4 (26.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e0.244\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eDS (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e15 (5.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e7 (2.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e8 (53.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eInstability\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e5 (1.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e2 (0.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e3 (20.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e0.002\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eValues are presented as mean\u0026nbsp;\u0026plusmn; standard deviation or number (%)\u003c/p\u003e\n\u003cp\u003eSS, Spinal stenosis; HNP, Herniation of nucleus pulposus; LRS, Lateral recess stenosis; ULBD, Unilateral laminectomy bilateral decompression; DL, Decompressive laminotomy; DS, Degenerative spondylolisthesis\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 3. Comparison of Radiological Parameters Between Entrapment and Non-Entrapment Groups\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eVariable\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eOverall\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eNon-entrapment\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eEntrapment\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 91px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ep-value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePre facet joint gap (I)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e2.26 \u0026plusmn; 0.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e2.25 \u0026plusmn; 0.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e2.57 \u0026plusmn; 0.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 91px;\"\u003e\n \u003cp\u003e0.017\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePre facet joint gap (C)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e2.25 \u0026plusmn; 0.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e2.25 \u0026plusmn; 0.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e2.13 \u0026plusmn; 0.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 91px;\"\u003e\n \u003cp\u003e0.375\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePost facet joint gap (I)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e2.94 \u0026plusmn; 0.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e2.90 \u0026plusmn; 0.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e3.59 \u0026plusmn; 0.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 91px;\"\u003e\n \u003cp\u003e0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePost facet joint gap (C)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e2.47 \u0026plusmn; 0.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e2.47 \u0026plusmn; 0.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e2.48 \u0026plusmn; 0.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 91px;\"\u003e\n \u003cp\u003e0.934\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFacet gap angle (I)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e21.28 \u0026plusmn; 8.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e20.99 \u0026plusmn; 8.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e25.91 \u0026plusmn; 6.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 91px;\"\u003e\n \u003cp\u003e0.009\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFacet gap angle (C)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e23.24 \u0026plusmn; 8.85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e23.06 \u0026plusmn; 8.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e26.15 \u0026plusmn; 8.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 91px;\"\u003e\n \u003cp\u003e0.213\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eWorking angle (I)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e4.17 \u0026plusmn; 6.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e4.16 \u0026plusmn; 6.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e4.31 \u0026plusmn; 6.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 91px;\"\u003e\n \u003cp\u003e0.931\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eWorking angle (C)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e22.30 \u0026plusmn; 5.70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e22.22 \u0026plusmn; 5.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e23.68 \u0026plusmn; 3.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 91px;\"\u003e\n \u003cp\u003e0.270\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026Delta; angle (I)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e17.11 \u0026plusmn; 9.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e16.83 \u0026plusmn; 9.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e21.60 \u0026plusmn; 7.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 91px;\"\u003e\n \u003cp\u003e0.023\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026Delta; angle (C)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e1.59 \u0026plusmn; 8.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e1.59 \u0026plusmn; 8.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e1.69 \u0026plusmn; 8.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 91px;\"\u003e\n \u003cp\u003e0.974\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eDural sac / Canal ratio\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e0.49 \u0026plusmn; 0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e0.48 \u0026plusmn; 0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e0.55 \u0026plusmn; 0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 91px;\"\u003e\n \u003cp\u003e0.009\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eValues are presented as mean\u0026nbsp;\u0026plusmn; standard deviation\u003c/p\u003e\n\u003cp\u003eFacet joint gap is measured in millimeters (mm), and angles are expressed in degrees (\u0026deg;)\u003c/p\u003e\n\u003cp\u003eI, Ipsilateral side; C, Contralateral side; \u0026Delta; angle, Difference between facet gap angle and working angle\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 4. Multivariate Logistic Regression Analysis for Predictors of Dural Entrapment\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 283px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eVariable\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 170px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAdjusted OR (95% CI)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 148px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAdjusted p-value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 283px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSex: Female vs Male\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 170px;\"\u003e\n \u003cp\u003e4.88 (0.89 - 26.69)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 148px;\"\u003e\n \u003cp\u003e0.068\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 283px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eDS: Yes or No\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 170px;\"\u003e\n \u003cp\u003e46.88 (6.46 \u0026ndash; 340.18)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 148px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 283px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eInstability: Yes or No\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 170px;\"\u003e\n \u003cp\u003e2.12 (0.09 \u0026ndash; 50.76)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 148px;\"\u003e\n \u003cp\u003e0.643\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 283px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePost facet joint gap (I, per mm increase)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 170px;\"\u003e\n \u003cp\u003e8.02 (2.04 \u0026ndash; 31.52)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 148px;\"\u003e\n \u003cp\u003e0.003\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 283px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026Delta; Facet joint gap (I, per mm increase)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 170px;\"\u003e\n \u003cp\u003e0.37 (0.06 \u0026ndash; 2.46)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 148px;\"\u003e\n \u003cp\u003e0.307\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 283px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFacet gap angle (I, per degree increase)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 170px;\"\u003e\n \u003cp\u003e1.02 (0.91 \u0026ndash; 1.13)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 148px;\"\u003e\n \u003cp\u003e0.757\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 283px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026Delta; Angle (I, per degree increase)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 170px;\"\u003e\n \u003cp\u003e1.01 (0.90 \u0026ndash; 1.13)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 148px;\"\u003e\n \u003cp\u003e0.851\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 283px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eDural sac / Canal ratio (Per 0.1 increase)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 170px;\"\u003e\n \u003cp\u003e3.21 (1.11 \u0026ndash; 9.23)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 148px;\"\u003e\n \u003cp\u003e0.031\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eOR, odds ratio; CI, confidence interval; \u0026Delta;, difference between facet joint gap and working angle for angles, or between pre- and postoperative measurements for facet joint gap.; I, Ipsilateral side; C, Contralateral side\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Unilateral Biportal Endoscopy, Lumbar decompression, Minimally invasive, Facet joint, Entrapment, Dura mater","lastPublishedDoi":"10.21203/rs.3.rs-7580616/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7580616/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eObjective\u003c/h2\u003e\u003cp\u003eDural entrapment by the facet joint is a rare but potentially serious complication following unilateral biportal endoscopic (UBE) lumbar decompression. However, its incidence, risk factors, and biomechanical mechanisms remain unclear. This study aimed to investigate the incidence, clinical characteristics, and predictive factors for dural entrapment following UBE lumbar decompression, with a particular focus on anatomical and biomechanical considerations.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e\u003cp\u003eThis retrospective cohort study included 181 patients (257 spinal segments) who underwent UBE lumbar decompression at a single institution between January 2023 and January 2024. Patients with prior lumbar surgery, deformity, severe instability, or incomplete imaging were excluded. Clinical and radiological parameters, including facet joint gap, facet joint angle, and dural sac-to-canal ratio, were evaluated. Multivariate logistic regression and receiver operating characteristic (ROC) curve analyses were performed to identify independent risk factors and their predictive performance.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003eDural entrapment occurred in 15 of 257 segments (5.8%). Symptomatic entrapment was observed in 2 cases (0.8%), one requiring revision surgery. Multivariate analysis identified degenerative spondylolisthesis (adjusted OR 46.88, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), postoperative ipsilateral facet joint gap (adjusted OR 8.02, p\u0026thinsp;=\u0026thinsp;0.003), and dural sac-to-canal ratio (adjusted OR 3.21, p\u0026thinsp;=\u0026thinsp;0.031) as independent risk factors. ROC analysis demonstrated good predictive accuracy for the facet joint gap (AUC 0.786) and dural sac-to-canal ratio (AUC 0.705), with excellent performance for the combined model (AUC 0.925).\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e\u003cp\u003eDural entrapment after UBE lumbar decompression, though uncommon, may cause significant morbidity. Anatomical and biomechanical factors, including facet joint gap widening, play a critical role. Careful surgical techniques and targeted preventive strategies are essential to minimize this complication.\u003c/p\u003e","manuscriptTitle":"Dural Entrapment by Facet Joint after Unilateral Biportal Endoscopic Lumbar Decompression Surgery: Incidence, Risk Factors, and Biomechanical Considerations","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-21 23:18:03","doi":"10.21203/rs.3.rs-7580616/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e6b1bfa8-dd5a-40b0-be2e-938b73352b89","owner":[],"postedDate":"October 21st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-02-10T02:09:31+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-21 23:18:03","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7580616","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7580616","identity":"rs-7580616","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}