MRI-Based Investigation of Skin-Epidural Distance and Posterior Epidural Space Depth: The Role of Demographic and Anthropometric Factors

MRI-Based Investigation of Skin-Epidural Distance and Posterior Epidural Space Depth: The Role of Demographic and Anthropometric Factors | 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 MRI-Based Investigation of Skin-Epidural Distance and Posterior Epidural Space Depth: The Role of Demographic and Anthropometric Factors Mohammad Dehghan-Tazerjani, Masoud Mahmoodi, Amir pasha Amel shahbaz, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6675174/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 17 You are reading this latest preprint version Abstract Background Precise identification of the skin-to-epidural distance (SED) is essential for safe and effective epidural anesthesia. This study aimed to evaluate the SED and posterior epidural space depth (PESD) at lower thoracic and lumbar levels using MRI, and to investigate their associations with demographic and anthropometric factors in an Iranian adult population. Methods In this cross-sectional study, 227 adult patients undergoing lumbar spine MRI were included. SED and PESD were measured at L2–S1 interspaces using MRI, and their correlations with age, sex, height, weight, and BMI were analyzed. Pearson correlation and multivariate linear regression were applied to identify significant predictors. Results The highest mean SED was observed at L3–L4 (57.05 ± 11.77 mm). BMI and weight showed strong positive correlations with SED across all levels. Age demonstrated a significant negative correlation with PESD at several levels. Multivariate analysis confirmed BMI and height as strong predictors of increased SED, while age was a negative predictor of PESD. Male gender was associated with shorter SED values at lower lumbar levels. Conclusions MRI-based assessment of SED and PESD reveals important correlations with BMI, height, and age. These findings support individualized estimation of epidural depth to enhance procedural safety, particularly in patients with varying body composition and age. Epidural anesthesia Body Mass Index (BMI) Dura space Magnetic Resonance Imaging (MRI) Figures Figure 1 Figure 2 Introduction Epidural anesthesia is a well-established technique for managing neuropathic pain, involving the injection of anesthetic agents into the epidural space to block sensory and motor nerve roots in the thoracic, abdominal, pelvic, and lower limb regions. This method is utilized not only for anesthesia during surgical procedures but also for chronic pain management and muscle spasticity, serving as both a primary and adjunctive analgesic strategy. Over the past century, epidural anesthesia has proven effective, offering significant advantages such as adaptability of medication types and administration methods to meet diverse clinical needs [ 1 , 2 ]. In addition to its versatility, epidural anesthesia has occasionally been considered as an alternative to general anesthesia in scenarios requiring reduced airway manipulation or where minimizing systemic effects is beneficial [ 3 ]. While spinal anesthesia is more commonly used in resource-limited settings due to its simplicity and lower cost, epidural anesthesia offers greater flexibility in drug titration and longer duration of analgesia [ 2 , 4 ]. However, technical challenges persist, particularly during needle placement, where anatomical variations and patient characteristics can influence procedural success [ 5 ]. Accurate localization of the epidural space is essential to minimize risks such as Post-Dural Puncture Headache (PDPH), urinary retention, and back pain [ 6 , 7 ]. Several patient-related factors, such as subcutaneous fat thickness, vertebral anatomy, and soft tissue composition, influence both the risk of complications and the depth required to access the epidural space [ 8 , 9 , 10 ]. The skin-to-epidural distance (SED) varies by spinal level and individual anatomy [ 11 ]. Accurate pre-procedural estimation of this depth is crucial for minimizing dural puncture risk and improving the efficiency of needle placement [ 12 ]. A clearer understanding of SED helps in selecting the appropriate needle length and reducing multiple puncture attempts, thereby enhancing procedural safety [ 13 , 14 ]. Anthropometric factors such as age, gender, height, weight, and Body Mass Index (BMI) have been reported to correlate with variations in SED and the depth of the subarachnoid or epidural space [ 15 ]. For instance, Zhao et al. found a significant association between BMI and the cervical-to-thoracic epidural space distance in Chinese adults, with males generally having longer distances [ 16 ]. Hazarika et al. developed a predictive model for SED based on BMI, showing that males have a consistently longer SED than females [ 15 ]. Similarly, Sargin et al. and Eley et al. confirmed correlations between BMI and SED, with Eley et al. emphasizing a stronger association with BMI than with abdominal fat thickness [ 17 , 18 ]. Various modalities such as direct needle measurement, ultrasound, and imaging techniques including Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) have been employed to assess SED [ 19 ]. Among these, MRI offers superior soft tissue resolution, making it a preferred tool for visualizing spinal anatomy and estimating epidural depth [ 20 , 21 ]. Despite its advantages, limited data exist on MRI-based evaluation of SED and the posterior epidural space depth (PESD), particularly within Middle Eastern populations, including Iran. The present study aims to assess the SED and PESD at thoracic and lumbar levels using MRI in a cohort of Iranian adults and explore their associations with demographic and anthropometric characteristics. By identifying reliable predictors of SED and PESD, this study seeks to support safer and more effective epidural interventions tailored to individual anatomical profiles. Methods and Materials Study Design and Setting This was a cross-sectional, observational, and analytical study conducted at Imam Khomeini Hospital Complex in Tehran and Shahid Rahnamoon Hospital in Yazd, Iran, during the year 2023. Participants Adult patients (aged 18–65 years) referred for thoracic and lumbar spine MRI based on clinical indications from their treating physicians were eligible for inclusion. Exclusion criteria were congenital spinal deformities, vertebral fractures, immobility for more than two days prior to MRI, prior thoracolumbar surgery, corticosteroid therapy, history of bariatric surgery, non-Iranian nationality, congenital musculoskeletal disorders, or rheumatologic diseases causing muscle atrophy. Data Collection and Measurements All participants were interviewed to explain the study objectives. Demographic data (age, sex), height, weight, and BMI were recorded. MRI (Magnetic Resonance Imaging) scans of the thoracic and lumbar spine were performed based on physician referrals. Skin-to-epidural distance (SED) and posterior epidural space depth (PESD) were measured using the hospital's Picture Archiving and Communication System (PACS) by an anesthesia resident under the supervision of a radiologist. SED was defined as the distance from the skin to the anterior border of the ligamentum flavum, while PESD was measured from the inner surface of the ligamentum flavum to the posterior border of the dura mater. Variables Independent variables included demographic and anthropometric factors (age, sex, height, weight, BMI). Dependent variables were SED and PESD measured at the L2–L3, L3–L4, L4–L5, and L5–S1 interspaces. Statistical Analysis Sample size was calculated based on the study by Adegboye et al. [ 22 ], assuming a standard deviation of 0.25, power of 90%, and alpha = 0.05, resulting in a required sample of 167 participants. Descriptive statistics (mean, SD, median, range, frequency) were used to summarize the data. Pearson correlation coefficients were calculated to examine relationships between continuous variables. This coefficient ranges from − 1 to + 1, where values closer to ± 1 indicate stronger linear correlation [ 23 ]. A collinearity matrix was used to evaluate potential multicollinearity between independent variables; predictors with |r| > 0.7 were excluded from regression analysis. Subsequently, multivariate linear regression was conducted separately for each vertebral level, estimating regression coefficients with 95% confidence intervals to quantify the influence of predictors on SED and PESD. The regression coefficient reflects the expected change in the dependent variable for each one-unit change in the predictor variable [ 24 ]. All statistical analyses were performed using SPSS v25 and R software v4.3.3 (2024-02-29 ucrt). A p-value < 0.05 was considered statistically significant. Ethical Considerations This study was approved by the Ethics Committee of Tehran University of Medical Sciences (Approval ID: IR.TUMS.IKHC.REC.1403.072). All procedures performed were in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. All participants provided general written consent for use of anonymized data at the time of hospital admission, which was deemed sufficient for this study. Participation was voluntary, and patients were informed of their right to withdraw at any time without affecting their access to care. Results Demographic and Physical Characteristics A total of 227 individuals participated in the study, comprising 135 women (59.5%) and 92 men (40.5%). The mean age of participants was 45.39 years (SD = 14.30). In terms of physical characteristics, the mean weight was recorded at 73.93 kg (SD = 14.07), with participants' weights ranging from 30 to 113 kg. The mean height was 164.15 cm (SD = 9.85), with a median height of 163 cm and a range spanning from 130 to 187 cm. Additionally, the mean BMI was calculated at 27.54 (SD = 4.99), with values ranging from 14 to 44. Distribution of SED and PESD Table 1 presents the SED and PESD measures across different vertebral levels. The SED exhibited the highest mean value at the L3-L4 level (79.5 ± 36.74 mm), while the lowest mean was observed at the L2-L3 level (51.61 ± 10.15 mm). In contrast, the PESD showed a decreasing trend from L2-L3 (5.91 ± 1.79 mm) to L5-S1 (3.34 ± 1.56 mm), indicating a progressively shallower epidural space at lower spinal levels. Regarding gender differences in the means of SED and PESD, there were no statistically significant differences between the two gender groups for SED measurements at the L2-L3 and L3-L4 levels. However, at the L4-L5 and L5-S1 levels, significant differences were observed (p-value < 0.001), indicating that the mean SED was greater in females than in males. In contrast, for PESD measurements, no significant differences were found between genders. These results suggest that gender may significantly affect SED in certain spinal regions, while it does not appear to correlate with PESD. As shown in Figure 1, the SED increased progressively with BMI across all measured spinal levels. The highest SED values were observed in individuals with BMI > 35, particularly at the L4-L5 level, reaching nearly 70 mm, whereas individuals with BMI < 18 exhibited the lowest SED values across all levels. In contrast, the PESD exhibited an inverse trend, with the highest values recorded in the BMI 35 group. The L5-S1 level consistently exhibited the smallest PESD across all BMI groups. These findings hypothesize a positive relationship between BMI and SED and a negative or weak relationship between BMI and PESD, indicating that increased subcutaneous fat raises needle depth requirements while potentially reducing epidural space depth. Correlations of Variables with SED and PESD The Pearson correlation coefficients and p-values for the relationships between age, weight, height, and BMI with both the SED and the PESD at various spinal levels are presented in Table 2. The summary of findings is presented as follows: Skin-Epidural Distance: SED at L2-L3 : A significant positive correlation was found between weight ( r = 0.730, p < 0.001) and BMI ( r = 0.716, p < 0.001) with SED, indicating that as weight and BMI increase, the SED also increases. SED at L3-L4 : There was a strong and significant positive correlation between SED and BMI ( r = 0.723, p < 0.001) as well as weight ( r = 0.676, p < 0.001), whereas other variables showed no significant correlation. SED at L4-L5 : A significant positive correlation was observed between weight ( r = 0.624, p < 0.001) and BMI ( r = 0.740, p < 0.001) with SED. Conversely, a weak negative correlation with height ( r = -0.141, p = 0.035) was noted, suggesting that increased height may be correlated with a decrease in SED. SED at L5-S1 : Significant positive correlations were found for weight ( r = 0.578, p < 0.001) and BMI ( r = 0.687, p < 0.001), indicating that higher weight and BMI are correlated with greater SED. Posterior Epidural Space Depth: PESD at L2-L3 : A significant negative correlation with age ( r = -0.247, p < 0.001) indicates that older age is correlated with a decrease in PESD. PESD at L3-L4 : A significant negative correlation with age ( r = -0.232, p < 0.001) was observed, along with a weak positive correlation with weight ( r = 0.144, p = 0.033). PESD at L4-L5 : There was a significant negative correlation with age ( r = -0.185, p = 0.006) and a weak positive correlation with weight ( r = 0.159, p = 0.018). PESD at L5-S1 : A weak positive correlation with BMI ( r = 0.144, p = 0.033) was noted, while other factors did not show significant correlations. The analysis of Pearson correlation coefficients reveals significant relationships between demographic variables and both the SED and PESD across various spinal levels. Notably, consistent positive correlations between weight and BMI with SED suggest that individuals with higher body weight and BMI tend to have greater distances from the skin to the epidural space, which may affect the efficacy of epidural anesthesia. Conversely, significant negative correlations between age and PESD indicate that as individuals’ age, the PESD decreases, likely due to age-related anatomical changes such as disc degeneration. Additionally, a weak negative correlation between height and SED at the L4-L5 level suggests that taller individuals may experience slightly reduced distances to the epidural space. Variables Collinearity To prevent issues related to collinearity in the linear regression model, a thorough examination of variable relationships was conducted. It was found that weight had a high correlation with BMI (0.77), indicating a significant overlap in the information they provide (Figure 2). To avoid potential multicollinearity problems, weight was excluded from the model. This decision ensures the reliability and clarity of the regression analysis, allowing for more accurate interpretations of the remaining variables. Regression Model The linear regression analysis examined the associations between ten dependent variables and four predictors: age, sex (male), height, and BMI (Table 3). For the SED outcomes, significant associations were observed, indicating that certain predictors may intensify the measurements. In the SED at L2-L3 model, height was positively associated with a regression coefficient of 1.25 (95% CI = [1.09, 1.44]), suggesting that greater height may lead to increased SED. Similarly, BMI showed a strong association with a coefficient of 4.78 (95% CI = [3.97, 5.76]), indicating that higher BMI is significantly related to larger SED values. In the SED at L3-L4 model, age had a coefficient of 0.90 (95% CI = [0.83, 0.98]), highlighting as older age was negatively associated with SED. Conversely, both height (Coefficient = 1.19, 95% CI = [1.01, 1.41]) and BMI (Coefficient = 6.56, 95% CI = [5.23, 8.24]) were positively associated, reinforcing the notion that taller individuals and those with higher BMI tend to exhibit greater SED values. The SED at the L4-L5 level further illustrated these dynamics, with age exhibiting a negative association (Coefficient = 0.88, 95% CI = [0.80, 0.97]) and male sex also showing a significant negative association (Coefficient = 0.03, 95% CI = [0.00, 0.42]), suggesting that being male is associated with lower SED. Height (Coefficient = 1.28, 95% CI = [1.04, 1.56]) and BMI (Coefficient = 9.73, 95% CI = [7.45, 12.72]) demonstrated significant positive associations as well, indicating that these factors intensify SED values. In the SED at L5-S1 model, age continued to show a protective association (Coefficient = 0.90, 95% CI = [0.81, 1.00]), while male had a notably strong negative association, further emphasizing the trend of lower SED in elder males. Height (Coefficient = 1.49, 95% CI = [1.20, 1.85]) and BMI (Coefficient = 8.05, 95% CI = [6.04, 10.72]) were both significantly associated, reinforcing the notion that these predictors lead to increased SED. Finally, in the SED mean model, which is the mean of all above SED measurements, age (Coefficient = 0.92, 95% CI = [0.85, 0.99]) and male sex (Coefficient = 0.01, 95% CI = [0.00, 0.23]) highlighted their protective roles, while, height (Coefficient = 1.30, 95% CI = [1.11, 1.52]), and BMI (Coefficient = 7.04, 95% CI = [5.71, 8.69]) demonstrated significant positive associations. For the PESD outcomes, age was consistently associated with a protective effect across several models, with a coefficient of 0.97 in the PESD at L2-L3 (95% CI = [0.96, 0.99]) and PESD at L3-L4 (95% CI = [0.95, 0.99]) models, indicating that older individuals may exhibit smaller PESD. Height also showed a positive association in the PESD at L2-L3 model (Coefficient = 1.04, 95% CI = [1.00, 1.08]), suggesting that taller individuals may have deeper PESD. In the PESD at L4-L5 model, age maintained a protective association, while BMI was positively associated (Coefficient = 1.05, 95% CI = [1.00, 1.10]), indicating that higher BMI can lead to deeper PESD. The PESD at L5-S1 model reinforced this finding with BMI (Coefficient = 1.05, 95% CI = [1.00, 1.10]) positively associated, while in the PESD mean model, age had a coefficient of 0.98 (95% CI = [0.97, 0.99]), further underscoring its negative association. These findings underscore the significant associations between the predictors and both SED and PESD measurements. BMI consistently demonstrates strong positive associations, indicating it as a major factor influencing these measurements, while age exhibits a protective effect in several contexts, suggesting that older age may be linked to smaller SED and PESD values. Discussion In this study, we aimed to determine the distance from the skin to the dura mater and the depth of the posterior epidural space in Iranian adult patients undergoing MRI, while also examining the relationship with BMI, sex, height, weight, and age. A total of 227 participants were included, with a mean age of approximately 45 years, and a major portion being female. Our findings indicated that the greatest distance from the skin to the dura was observed at the L4-L5 level, which aligns with previous literature suggesting that lumbar regions typically exhibit greater anatomical distances due to the presence of surrounding adipose tissue. Additionally, the maximum PESD was recorded at the L3-L4 level, reinforcing the notion that this region is crucial for epidural interventions. In the context of the correlation between demographic and physical factors with SED and PESD, weight and BMI showed a strong positive correlation with the SED across various spinal levels. This suggests that individuals with higher body weight and BMI may have greater distances, which is particularly relevant for anesthetic practices, as it could influence the effectiveness of epidural anesthesia. Conversely, a weak negative correlation was noted between height and the SED at the L4-L5 level, indicating that taller individuals may experience slightly less distance. Significant but weak negative correlations were found between age and PESD at various levels, suggesting that as patients get older, the PESD tends to decrease. This finding aligns with another study that reported a weak inverse correlation between age and gracilis muscle mass; however, it does not directly address changes in the epidural space depth (25). Furthermore, a weak positive correlation was observed between weight and PESD at certain levels, suggesting that increased BMI may also affect the depth of the epidural space. The results of the linear regression models reveal significant associations between various predictors and both SED and PESD measurements. Height and BMI emerged as strong positive predictors of SED, indicating that taller individuals and those with higher BMI are likely to exhibit increased SED values. Supporting this, a study found a direct relationship between BMI and epidural space depth during lumbar transforaminal epidural steroid injections, where higher BMI correlated with greater needle depth. This aligns with the assertion that elevated BMI increases SED (10). As well as, Hazarika et al. (15) found that the distance to the subarachnoid space correlated with BMI in Indian population, while Eley et al. (18) demonstrated that both subcutaneous fat and BMI significantly correlated with SED. Similarly, Sargin et al. (17) concluded that BMI and body weight significantly influenced the skin-to-subarachnoid space distance, with age and gender showing minimal impact. While no studies explicitly link height to SED, research on gracilis muscle mass suggests that height may indirectly influence anatomical dimensions relevant to SED, although direct evidence remains absent (25). Conversely, age was identified as a negative predictor, particularly at the L4-L5 level, where older age correlated with lower SED. This finding suggests that age-related anatomical changes may contribute to variations in epidural space dimensions. However, another study explicitly found no predictive value of age on foraminal epidural depth, highlighting the complexity of these relationships (10). It is important to note that female gender was also a positive predictor of larger SED, particularly at the L4-L5 and L5-S1 levels, highlighting potential gender differences in anatomical characteristics that warrant further investigation. Eley et al.'s study (18) demonstrated an association between increased SED and being female. However, since this study focused specifically on pregnant women, we should exercise caution in generalizing our results to that population. Brummett et al. initially identified sex as a predictor of epidural depth; however, this association became insignificant when BMI was included in the model (10). Our findings also contrast with those of Zhao et al. (16), who reported greater distances in males within the cervical and upper thoracic regions among Chinese adults. Additionally, a study highlights sex-specific differences in body proportions within a Mexican population, which may partially account for anatomical variations that influence SED (26). Recognizing gender as a factor influencing SED can provide valuable insights for practitioners, as males generally exhibit a smaller distance from the skin to the epidural space. In the context of PESD, although a weak positive association was observed between BMI and PESD—reinforcing the notion that increased body mass can contribute to greater depth of the posterior epidural space—age emerged as a significant negative predictor of PESD. In all models developed based on PESD measurements, age negatively affected the depth of the posterior epidural space, indicating that older individuals tend to have a shallower epidural space. This trend emphasizes age-related changes in spinal anatomy, which could lead to variations in the depth of the posterior epidural space. The provided studies do not directly address age-related reductions in PESD; however, a study found no significant correlation between age and posterior epidural space width in adults (27). Additionally, a CT-based anatomical analysis observed age-related structural changes, such as reduced soft tissue volume in certain spinal regions, which could theoretically influence PESD (28). This study concentrated on the infraorbital cheek rather than the lumbar spine, highlighting the need for further research specifically targeting geriatric populations to validate these observations. Overall, these findings underscore the complex interplay between demographic and anthropometric factors in determining SED and PESD measurements. Understanding these associations is crucial for optimizing clinical practices, particularly in procedures involving the epidural space. Our study provides valuable insights into the anatomical relationships influencing epidural procedures in Iranian adults, emphasizing the importance of considering factors such as sex, age, weight, height, and BMI. These insights highlight the necessity for personalized approaches in anesthetic practice, as variations in body composition and age can significantly affect the success of epidural interventions. Additionally, the findings suggest that anatomical considerations should account for specific vertebral levels and age-related differences. Future research should continue to explore these relationships across diverse populations to enhance the safety and efficacy of epidural interventions, ultimately leading to improved clinical outcomes. Strengths and Limitations This study's strengths include its focus on a specific Iranian population, contributing valuable data on anatomical relationships relevant to epidural procedures. Future studies should involve larger sample sizes and further investigations, particularly focusing on patients with higher BMI, to enhance the accuracy of determining the SED using MRI. However, limitations were present; the study excluded non-Iranian patients and individuals with pathological conditions affecting spinal measurements, which may limit the generalizability of the findings. Additionally, weight restrictions for MRI limited participant inclusion, though this was addressed by setting criteria for weight and BMI. Future research should aim to include a more diverse population and explore the implications of various spinal pathologies on measurement outcomes. Conclusion This MRI-based study confirms that BMI and height are strong positive predictors of skin-to-epidural distance (SED), while age is a significant negative predictor of posterior epidural space depth (PESD). Additionally, male sex was associated with smaller SED values in lower lumbar levels. These findings support the importance of individualized pre-procedural planning in neuraxial anesthesia, particularly in populations with varying body habitus and age. Recognizing the influence of these variables can improve the precision and safety of epidural procedures. Further research across diverse populations and spinal levels is warranted to expand our understanding and optimize anesthetic strategies globally. Abbreviations BMI Body Mass Index MRI Magnetic Resonance Imaging PESD Posterior Epidural Space Depth SED Skin-to-Epidural Distance PDPH Post-Dural Puncture Headache PACS Picture Archiving and Communication System SD Standard Deviation CI Confidence Interval Declarations Potential Conflicts of Interest The authors declare that there are no known competing interests that could affect this work. Funding This research received no external funding. Conflicts of Interest The authors declare no conflicts of interest. Ethical Approval and Consent to Participate This study was approved by the Ethics Committee of Tehran University of Medical Sciences (Approval ID: IR.TUMS.IKHC.REC.1403.072). All procedures performed were in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Consent for Publication Not applicable. Author Contributions Mohammad Dehghan-Tazerjani : Conceptualization, supervision, methodology, writing, review & editing. Babak Eslami : Project administration, writing – original draft. Masoud Mahmoodi : Data collection, interpretation of results. Amir Pasha Amel Shahbaz: Statistical analysis Alireza Montaseri, Ebrahim Espahbodi, Laya Amoozadeh, Merhrshad Namazi, Ehsan Ziaeii : Patient recruitment, data acquisition, and critical revision of the manuscript. All authors reviewed and approved the final version of the manuscript. Data Availability The datasets generated and analyzed during the current study are available from the corresponding author upon reasonable request. References Chou R, Gordon DB, Leon-Casasola OA de, Rosenberg JM, Bickler S, Brennan T, et al. Management of Postoperative Pain: A Clinical Practice Guideline From the American Pain Society, the American Society of Regional Anesthesia and Pain Medicine, and the American Society of Anesthesiologists’ Committee on Regional Anesthesia, Executive Committee, and Administrative Council. J Pain. 2016 Feb 1;17(2):131–57. Hermanns H, Bos EME, van Zuylen ML, Hollmann MW, Stevens MF. The Options for Neuraxial Drug Administration. CNS Drugs. 2022 Aug;36(8):877–96. Uppal V, Sondekoppam RV, Landau R, El-Boghdadly K, Narouze S, Kalagara HKP. Neuraxial anaesthesia and peripheral nerve blocks during the COVID-19 pandemic: a literature review and practice recommendations. Anaesthesia. 2020 Oct;75(10):1350–63. Gogarten W, Van Aken H. A century of regional analgesia in obstetrics. Anesth Analg. 2000 Oct;91(4):773–5. Shaikh F, Voicu L, Tole S, To T, Doria AS, Sung L, et al. The risk of traumatic lumbar punctures in children with acute lymphoblastic leukaemia. Eur J Cancer Oxf Engl 1990. 2014 May;50(8):1482–9. Rastogi S, Bhandari R, Sharma V, Pandey T. Neurological complications following spinal anaesthesia in a patient with congenital absence of lumbar vertebra. Indian J Anaesth. 2014;58(4):484–6. Tandale SR, Kelkar KV, Abhade SR, Gadre VN. Diagnostic Dilemma of Severe Excruciating Low Backache in Pediatric Patient Following Spinal Anesthesia. Med J Dr Patil Vidyapeeth. 2018 Oct;11(5):456. Unic-Stojanovic D, Babic S, Jovic M. Benefits, risks and complications of perioperative use of epidural anesthesia. Med Arch Sarajevo Bosnia Herzeg. 2012;66(5):340–3. Kang XH, Bao FP, Xiong XX, Li M, Jin TT, Shao J, et al. Major complications of epidural anesthesia: a prospective study of 5083 cases at a single hospital. Acta Anaesthesiol Scand. 2014 Aug;58(7):858–66. Brummett CM, Williams BS, Hurley RW, Erdek MA. A prospective, observational study of the relationship between body mass index and depth of the epidural space during lumbar transforaminal epidural steroid injection. Reg Anesth Pain Med. 2009;34(2):100–5. Garcia-Pereira F. Epidural anesthesia and analgesia in small animal practice: An update. Vet J Lond Engl 1997. 2018 Dec;242:24–32. Ravi KK, Kaul TK, Kathuria S, Gupta S, Khurana S. Distance from Skin to Epidural Space: Correlation with Body Mass Index (BMI). J Anaesthesiol Clin Pharmacol. 2011 Jan;27(1):39–42. Nayate AP, Nasrallah IM, Schmitt JE, Mohan S. Using Body Mass Index to Predict Needle Length in Fluoroscopy-Guided Lumbar Punctures. AJNR Am J Neuroradiol. 2016 Mar;37(3):572–8. Wenk M, Weiss C, Möllmann M, Pöpping DM. Procedural complications of spinal anaesthesia in the obese patient. Anesthesiol Res Pract. 2012;2012:165267. Hazarika R, Choudhury D, Nath S, Parua S. Estimation of Skin to Subarachnoid Space Depth: An Observational Study. J Clin Diagn Res JCDR. 2016 Oct;10(10):UC06–9. Zhao Q, Huang K, An J, Fang Q, Wen H, Qian X, et al. The distance from skin to cervical and high thoracic epidural space on chinese adults as read from MRI. Pain Physician. 2014;17(2):163–8. Sargin M, Hanedan B, Aydoğan E, Akin F, Özmen S. Evaluation of factors that affect skin to subarachnoid space distance. J Health Sci. 2017;7(1):23–6. Eley VA, Chin A, Sekar R, Donovan T, Krepska A, Lawrence M, et al. Increasing body mass index and abdominal subcutaneous fat thickness are associated with increased skin-to-epidural space distance in pregnant women. Int J Obstet Anesth. 2019 May;38:59–65. Franklin AD, Lorinc AN, Shotwell MS, Greene EB, Wushensky CA. Evaluation of the skin to epidural and subarachnoid space distance in young children using magnetic resonance imaging. Reg Anesth Pain Med. 2015;40(3):245–8. Zhuge W, Ben-Galim P, Hipp JA, Reitman CA. Efficacy of MRI for assessment of spinal trauma: correlation with intraoperative findings. J Spinal Disord Tech. 2015 May;28(4):147–51. Parizel PM, van der Zijden T, Gaudino S, Spaepen M, Voormolen MHJ, Venstermans C, et al. Trauma of the spine and spinal cord: imaging strategies. Eur Spine J Off Publ Eur Spine Soc Eur Spinal Deform Soc Eur Sect Cerv Spine Res Soc. 2010 Mar;19 Suppl 1(Suppl 1):S8-17. Adegboye MB, Bolaji BO, Ibraheem GH. The Correlation Between Body Mass Index On The Length From Skin To Lumbar Epidural Space In Nigerian Adults. J West Afr Coll Surg. 2017;7(1):113–27. Mansouritorghabeh H, Bagherimoghaddam A, Eslami S, Raouf-Rahmati A, Hamer DH, Kiani B, et al. Spatial epidemiology of COVID-19 infection through the first outbreak in the city of Mashhad, Iran. Spat Inf Res. 2022 Jun 28;30(5):585–95. MohammadEbrahimi S, Kiani B, Rahmatinejad Z, Baral S, Hashtarkhani S, Dehghan-Tezerjani M, et al. Geospatial epidemiology of hospitalized patients with a positive influenza assay: A nationwide study in Iran, 2016–2018. PLOS ONE. 2022 Dec 13;17(12):e0278900. Oranges CM, Tremp M, Wang W, Madduri S, DI Summa PG, Wettstein R, et al. Patient Height, Weight, BMI and Age as Predictors of Gracilis Muscle Free-Flap Mass in Lower Extremity Reconstruction. Vivo Athens Greece. 2018;32(3):591–5. Datta Banik S. Association of early menarche with elevated BMI, lower body height and relative leg length among 14- to 16-year-old post-menarcheal girls from a Maya community in Yucatan, Mexico. Anthropol Rev. 2022 Mar 18;85(1):85–100. Jiang M, Shao H, Li Q. Analysis of Anatomy and Age-related Changes in Infraorbital Cheek Using Computed Tomography. Aesthetic Plast Surg. 2024 Aug;48(16):3061–7. Gupta A, Gupta A, Singh F, Mandhyan R. Correlation of skin epidural distance and posterior epidural space depth with age, weight, height, BMI, abdominal girth and position of the patient: A prospective randomised study. Indian J Clin Anaesth. 2021 Sep 28;8(3):361–6. Tables Table 1. Total distribution and gender differences in Skin-Epidural Distance (SED) and the Posterior Epidural Space Depth (PESD) across vertebral column. SED Total (Mean ± SD) Female (Mean ± SD) Male (Mean ± SD) p-value * SEDL2-L3 51.61 ± 10.15 51.26 ± 10.34 52.12 ± 9.91 0.537 SEDL3-L4 57.05 ± 11.77 57.62 ± 12.53 56.20 ± 10.43 0.373 SEDL4-L5 62.75 ± 14.63 65.70 ± 15.49 58.40 ± 12.07 <0.001 SEDL5-S1 62.22 ± 14.81 65.81 ± 15.17 56.95 ± 12.59 <0.001 PESD Total (Mean ± SD) Female (Mean ± SD) Male (Mean ± SD) p-value * PESDL2-L3 5.91 ± 1.79 5.90 ± 1.75 5.93 ± 1.86 0.901 PESDL3-L4 5.92 ± 1.79 5.89 ± 1.81 5.97 ± 1.76 0.734 PESDL4-L5 4.93 ± 1.76 4.95 ± 1.87 4.90 ± 1.60 0.839 PESDL5-S1 3.34 ± 1.56 3.39 ± 1.56 3.26 ± 1.57 0.555 * Independent t-test applied for comparison between the genders. SED: Skin-Epidural Distance, PESD: Posterior Epidural Space Depth, L: Lumbar, S: Sacrum. Table 2. Correlation analysis of demographic variables with Skin-Epidural Distance (SED) and Posterior Epidural Space Depth (PESD) across vertebral levels. SED Age Weight Height BMI SEDL2-L3 Correlation 0.075 0.730 0.024 0.716 p-value 0.263 0.000 0.718 0.000 SEDL3-L4 Correlation -0.050 0.676 0.010 0.723 p-value 0.465 0.000 0.881 0.000 SEDL4-L5 Correlation -0.029 0.624 -0.141 0.740 p-value 0.671 0.000 0.035 0.000 SEDL5-S1 Correlation -0.037 0.578 -0.122 0.687 p-value 0.578 0.000 0.067 0.000 PESD Age Weight Height BMI PESDL2-L3 Correlation -0.247 0.122 0.088 -0.004 p-value 0.000 0.068 0.190 0.948 PESDL3-L4 Correlation -0.232 0.144 0.028 0.053 p-value 0.000 0.033 0.675 0.430 PESDL4-L5 Correlation -0.185 0.159 -0.021 0.119 p-value 0.006 0.018 0.752 0.077 PESDL5-S1 Correlation 0.074 0.119 0.015 0.144 p-value 0.272 0.078 0.830 0.033 SED: Skin-Epidural Distance, PESD: Posterior Epidural Space Depth, BMI: Body Index Mass, L: Lumbar, S: Sacrum. Table 3. Multivariate linear regression model of Skin-Epidural Distance (SED) and Posterior Epidural Space Depth (PESD) across different vertebral levels based on explanatory factors. Variable Parameter Coefficient SE 95% CI p-value SEDL2-L3 Age 1.00 0.03 [0.94, 1.07] 0.986 Sex [Male]* 1.79 2.37 [0.13, 24.32] 0.662 Height 1.25 0.09 [1.09, 1.44] 0.002 BMI 4.78 0.45 [3.97, 5.76] < .001 SEDL3-L4 Age 0.90 0.04 [0.83, 0.98] 0.010 Sex [Male] 0.41 0.67 [0.02, 10.05] 0.585 Height 1.19 0.10 [1.01, 1.41] 0.042 BMI 6.56 0.76 [5.23, 8.24] < .001 SEDL4-L5 Age 0.88 0.04 [0.80, 0.97] 0.008 Sex [Male] 0.03 0.04 [0.00, 0.42] < .001 Height 1.28 0.13 [1.04, 1.56] 0.017 BMI 9.73 1.32 [7.45, 12.72] < .001 SEDL5-S1 Age 0.90 0.05 [0.81, 1.00] 0.040 Sex [Male] 0.01 0.01 [0.00, 0.10] < .001 Height 1.49 0.16 [1.20, 1.85] < .001 BMI 8.05 1.17 [6.04, 10.72] < .001 SED mean Age 0.92 0.03 [0.85, 0.99] 0.025 Sex [Male] 0.01 0.02 [0.00, 0.23] 0.003 Height 1.30 0.10 [1.11, 1.52] 0.001 BMI 7.04 0.75 [5.71, 8.69] < .001 Variable Parameter Coefficient SE 95% CI p-value PESDL2-L3 Age 0.97 0.01 [0.96, 0.99] 0.005 Sex [Male]* 0.56 0.20 [0.28, 1.15] 0.112 Height 1.04 0.02 [1.00, 1.08] 0.032 BMI 1.01 0.03 [0.96, 1.07] 0.571 PESDL3-L4 Age 0.97 0.01 [0.95, 0.99] 0.001 Sex [Male] 0.82 0.30 [0.41, 1.68] 0.593 Height 1.02 0.02 [0.98, 1.06] 0.330 BMI 1.03 0.03 [0.98, 1.09] 0.202 PESDL4-L5 Age 0.97 0.01 [0.96, 0.99] 0.004 Sex [Male] 0.75 0.27 [0.37, 1.52] 0.426 Height 1.02 0.02 [0.98, 1.06] 0.327 BMI 1.05 0.03 [1.00, 1.10] 0.049 PESDL5-S1 Age 1.01 0.01 [0.99, 1.02] 0.439 Sex [Male] 0.84 0.27 [0.45, 1.59] 0.597 Height 1.01 0.02 [0.97, 1.04] 0.661 BMI 1.05 0.02 [1.00, 1.10] 0.035 PESD mean Age 0.98 0.01 [0.97, 0.99] 0.005 Sex [Male] 0.74 0.19 [0.44, 1.23] 0.243 Height 1.02 0.01 [0.99, 1.05] 0.122 BMI 1.04 0.02 [1.00, 1.08] 0.051 * Sex was treated as a dichotomous variable, with females as the reference category. SE: Standard Error, CI: Confidence Interval, BMI: Body Index Mass. Additional Declarations No competing interests reported. Supplementary Files SupplementaryFile1DataCollectionForm.docx Cite Share Download PDF Status: Under Revision Version 1 posted Editorial decision: Revision requested 18 May, 2026 Reviews received at journal 12 May, 2026 Reviews received at journal 11 May, 2026 Reviews received at journal 08 May, 2026 Reviewers agreed at journal 07 May, 2026 Reviewers agreed at journal 07 May, 2026 Reviews received at journal 05 May, 2026 Reviewers agreed at journal 05 May, 2026 Reviewers agreed at journal 05 May, 2026 Reviews received at journal 23 Jun, 2025 Reviewers agreed at journal 19 Jun, 2025 Reviewers agreed at journal 18 Jun, 2025 Reviewers invited by journal 11 Jun, 2025 Editor invited by journal 20 May, 2025 Editor assigned by journal 20 May, 2025 Submission checks completed at journal 19 May, 2025 First submitted to journal 19 May, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-6675174","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":470049190,"identity":"a0067e9c-1ccc-40a3-8c6e-6566ad2cffea","order_by":0,"name":"Mohammad Dehghan-Tazerjani","email":"","orcid":"","institution":"Imam Khomeini Hospital Complex, Tehran University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Mohammad","middleName":"","lastName":"Dehghan-Tazerjani","suffix":""},{"id":470049191,"identity":"f0bc973c-9411-4035-bb1f-7084ca4bf66b","order_by":1,"name":"Masoud Mahmoodi","email":"","orcid":"","institution":"Imam Khomeini Hospital Complex, Tehran University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Masoud","middleName":"","lastName":"Mahmoodi","suffix":""},{"id":470049192,"identity":"50318c39-890c-46f9-9a53-1f0ff4a25a2c","order_by":2,"name":"Amir pasha Amel shahbaz","email":"","orcid":"","institution":"Shahid Sadoughi University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Amir","middleName":"pasha Amel","lastName":"shahbaz","suffix":""},{"id":470049193,"identity":"96cf0939-e897-491d-8c89-49d0e76947d4","order_by":3,"name":"Alireza Montaseri","email":"","orcid":"","institution":"Imam Khomeini Hospital Complex, Tehran University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Alireza","middleName":"","lastName":"Montaseri","suffix":""},{"id":470049194,"identity":"03fb38f1-32a6-4a88-9f17-ea0080645c39","order_by":4,"name":"Ebrahim Espahbodi","email":"","orcid":"","institution":"Imam Khomeini Hospital Complex, Tehran University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Ebrahim","middleName":"","lastName":"Espahbodi","suffix":""},{"id":470049195,"identity":"90530b98-0f5b-4364-9b78-f451f3506153","order_by":5,"name":"Laya Amoozadeh","email":"","orcid":"","institution":"Imam Khomeini Hospital Complex, Tehran University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Laya","middleName":"","lastName":"Amoozadeh","suffix":""},{"id":470049196,"identity":"93ed7040-a648-4c1b-9af8-22e7cd0b1238","order_by":6,"name":"Mehrshad Namazi","email":"","orcid":"","institution":"AJA University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Mehrshad","middleName":"","lastName":"Namazi","suffix":""},{"id":470049197,"identity":"779f8d01-a021-4fd4-835c-a5a327b79c81","order_by":7,"name":"Ehsan Ziaeii","email":"","orcid":"","institution":"Shahid Sadoughi University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Ehsan","middleName":"","lastName":"Ziaeii","suffix":""},{"id":470049198,"identity":"99b35713-2430-4016-bfbd-fcb7710e8f54","order_by":8,"name":"Babak Eslami","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+0lEQVRIiWNgGAWjYBACAwYeBsYGIIMPxEuoABLMzA3EaWEDazkD0sJIihbGNjCJX4s5+9mDH2cw2NizsR9+uuHhvNpo/naglh8V23BqsezJS5bcwJCW2MaTZnYjcdvx3BmHGRsYe87cxu2wAzkGkg8YDiewMSSAtBzLbQBqYWZsw6Pl/Bvjnw8Y/tuz8T//diNxzrHc+QS13MgxAzrsAGObRA7Qloaa3A2EtFjOeJdmOcMgObFN4k3ZjYRjB3I3ArUcxOcXc/7cwzd7Kuzs+fnTt938UVOXO+/84YMPflTg1gJ1Hpx1GEweIKAeBdSRongUjIJRMApGCAAApB9eu9B/45oAAAAASUVORK5CYII=","orcid":"","institution":"Imam Khomeini Hospital Complex, Tehran University of Medical Sciences","correspondingAuthor":true,"prefix":"","firstName":"Babak","middleName":"","lastName":"Eslami","suffix":""}],"badges":[],"createdAt":"2025-05-15 19:08:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6675174/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6675174/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":84817304,"identity":"136c66c4-a5a9-42d0-8813-be6e8e98ed5c","added_by":"auto","created_at":"2025-06-17 15:48:56","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":62565,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between Body Mass Index (BMI) and the Skin-Epidural Distance (SED) and Posterior Epidural Space Depth (PESD) across different vertebral levels.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6675174/v1/b3ca11248c21cb5a2cc2add2.png"},{"id":84817301,"identity":"3b5d1a17-3a99-43ea-9a2d-034268a35e09","added_by":"auto","created_at":"2025-06-17 15:48:56","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":26139,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation matrix of demographic and physical variables: This matrix highlights strong correlations between variables.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6675174/v1/7742edeb7a9be5747226c61d.png"},{"id":84819913,"identity":"462111bb-e9a6-4909-bf20-b0b2e1b9cbe2","added_by":"auto","created_at":"2025-06-17 16:05:03","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1035958,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6675174/v1/8d7f34b2-eae5-46a4-b327-35c08eea0917.pdf"},{"id":84818986,"identity":"74d279c9-8bf8-4217-97cd-d0b9b0f74ed7","added_by":"auto","created_at":"2025-06-17 15:56:56","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":27895,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryFile1DataCollectionForm.docx","url":"https://assets-eu.researchsquare.com/files/rs-6675174/v1/82e5e406aba448673183e9ba.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"MRI-Based Investigation of Skin-Epidural Distance and Posterior Epidural Space Depth: The Role of Demographic and Anthropometric Factors","fulltext":[{"header":"Introduction","content":"\u003cp\u003eEpidural anesthesia is a well-established technique for managing neuropathic pain, involving the injection of anesthetic agents into the epidural space to block sensory and motor nerve roots in the thoracic, abdominal, pelvic, and lower limb regions. This method is utilized not only for anesthesia during surgical procedures but also for chronic pain management and muscle spasticity, serving as both a primary and adjunctive analgesic strategy. Over the past century, epidural anesthesia has proven effective, offering significant advantages such as adaptability of medication types and administration methods to meet diverse clinical needs [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. In addition to its versatility, epidural anesthesia has occasionally been considered as an alternative to general anesthesia in scenarios requiring reduced airway manipulation or where minimizing systemic effects is beneficial [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eWhile spinal anesthesia is more commonly used in resource-limited settings due to its simplicity and lower cost, epidural anesthesia offers greater flexibility in drug titration and longer duration of analgesia [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. However, technical challenges persist, particularly during needle placement, where anatomical variations and patient characteristics can influence procedural success [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Accurate localization of the epidural space is essential to minimize risks such as Post-Dural Puncture Headache (PDPH), urinary retention, and back pain [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSeveral patient-related factors, such as subcutaneous fat thickness, vertebral anatomy, and soft tissue composition, influence both the risk of complications and the depth required to access the epidural space [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The skin-to-epidural distance (SED) varies by spinal level and individual anatomy [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Accurate pre-procedural estimation of this depth is crucial for minimizing dural puncture risk and improving the efficiency of needle placement [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. A clearer understanding of SED helps in selecting the appropriate needle length and reducing multiple puncture attempts, thereby enhancing procedural safety [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAnthropometric factors such as age, gender, height, weight, and Body Mass Index (BMI) have been reported to correlate with variations in SED and the depth of the subarachnoid or epidural space [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. For instance, Zhao et al. found a significant association between BMI and the cervical-to-thoracic epidural space distance in Chinese adults, with males generally having longer distances [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Hazarika et al. developed a predictive model for SED based on BMI, showing that males have a consistently longer SED than females [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Similarly, Sargin et al. and Eley et al. confirmed correlations between BMI and SED, with Eley et al. emphasizing a stronger association with BMI than with abdominal fat thickness [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eVarious modalities such as direct needle measurement, ultrasound, and imaging techniques including Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) have been employed to assess SED [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Among these, MRI offers superior soft tissue resolution, making it a preferred tool for visualizing spinal anatomy and estimating epidural depth [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Despite its advantages, limited data exist on MRI-based evaluation of SED and the posterior epidural space depth (PESD), particularly within Middle Eastern populations, including Iran.\u003c/p\u003e \u003cp\u003eThe present study aims to assess the SED and PESD at thoracic and lumbar levels using MRI in a cohort of Iranian adults and explore their associations with demographic and anthropometric characteristics. By identifying reliable predictors of SED and PESD, this study seeks to support safer and more effective epidural interventions tailored to individual anatomical profiles.\u003c/p\u003e"},{"header":"Methods and Materials","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy Design and Setting\u003c/h2\u003e \u003cp\u003eThis was a cross-sectional, observational, and analytical study conducted at Imam Khomeini Hospital Complex in Tehran and Shahid Rahnamoon Hospital in Yazd, Iran, during the year 2023.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eParticipants\u003c/h3\u003e\n\u003cp\u003eAdult patients (aged 18\u0026ndash;65 years) referred for thoracic and lumbar spine MRI based on clinical indications from their treating physicians were eligible for inclusion. Exclusion criteria were congenital spinal deformities, vertebral fractures, immobility for more than two days prior to MRI, prior thoracolumbar surgery, corticosteroid therapy, history of bariatric surgery, non-Iranian nationality, congenital musculoskeletal disorders, or rheumatologic diseases causing muscle atrophy.\u003c/p\u003e\n\u003ch3\u003eData Collection and Measurements\u003c/h3\u003e\n\u003cp\u003eAll participants were interviewed to explain the study objectives. Demographic data (age, sex), height, weight, and BMI were recorded. MRI (Magnetic Resonance Imaging) scans of the thoracic and lumbar spine were performed based on physician referrals. Skin-to-epidural distance (SED) and posterior epidural space depth (PESD) were measured using the hospital's Picture Archiving and Communication System (PACS) by an anesthesia resident under the supervision of a radiologist. SED was defined as the distance from the skin to the anterior border of the ligamentum flavum, while PESD was measured from the inner surface of the ligamentum flavum to the posterior border of the dura mater.\u003c/p\u003e\n\u003ch3\u003eVariables\u003c/h3\u003e\n\u003cp\u003eIndependent variables included demographic and anthropometric factors (age, sex, height, weight, BMI). Dependent variables were SED and PESD measured at the L2\u0026ndash;L3, L3\u0026ndash;L4, L4\u0026ndash;L5, and L5\u0026ndash;S1 interspaces.\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eStatistical Analysis\u003c/h2\u003e \u003cp\u003eSample size was calculated based on the study by Adegboye et al. [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], assuming a standard deviation of 0.25, power of 90%, and alpha\u0026thinsp;=\u0026thinsp;0.05, resulting in a required sample of 167 participants. Descriptive statistics (mean, SD, median, range, frequency) were used to summarize the data. Pearson correlation coefficients were calculated to examine relationships between continuous variables. This coefficient ranges from \u0026minus;\u0026thinsp;1 to +\u0026thinsp;1, where values closer to \u0026plusmn;\u0026thinsp;1 indicate stronger linear correlation [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eA collinearity matrix was used to evaluate potential multicollinearity between independent variables; predictors with |r| \u0026gt; 0.7 were excluded from regression analysis. Subsequently, multivariate linear regression was conducted separately for each vertebral level, estimating regression coefficients with 95% confidence intervals to quantify the influence of predictors on SED and PESD. The regression coefficient reflects the expected change in the dependent variable for each one-unit change in the predictor variable [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAll statistical analyses were performed using SPSS v25 and R software v4.3.3 (2024-02-29 ucrt). A p-value\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eEthical Considerations\u003c/h2\u003e \u003cp\u003e This study was approved by the Ethics Committee of Tehran University of Medical Sciences (Approval ID: IR.TUMS.IKHC.REC.1403.072). All procedures performed were in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. All participants provided general written consent for use of anonymized data at the time of hospital admission, which was deemed sufficient for this study. Participation was voluntary, and patients were informed of their right to withdraw at any time without affecting their access to care.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eDemographic and Physical Characteristics\u003c/p\u003e\n\u003cp\u003eA total of 227 individuals participated in the study, comprising 135 women (59.5%) and 92 men (40.5%). The mean age of participants was 45.39 years (SD = 14.30). In terms of physical characteristics, the mean weight was recorded at 73.93 kg (SD = 14.07), with participants\u0026apos; weights ranging from 30 to 113 kg. The mean height was 164.15 cm (SD = 9.85), with a median height of 163 cm and a range spanning from 130 to 187 cm. Additionally, the mean BMI was calculated at 27.54 (SD = 4.99), with values ranging from 14 to 44.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDistribution of SED and PESD\u003c/p\u003e\n\u003cp\u003eTable 1 presents the SED and PESD measures across different vertebral levels. The SED exhibited the highest mean value at the L3-L4 level (79.5 \u0026plusmn; 36.74 mm), while the lowest mean was observed at the L2-L3 level (51.61 \u0026plusmn; 10.15 mm). In contrast, the PESD showed a decreasing trend from L2-L3 (5.91 \u0026plusmn; 1.79 mm) to L5-S1 (3.34 \u0026plusmn; 1.56 mm), indicating a progressively shallower epidural space at lower spinal levels.\u003c/p\u003e\n\u003cp\u003eRegarding gender differences in the means of SED and PESD, there were no statistically significant differences between the two gender groups for SED measurements at the L2-L3 and L3-L4 levels. However, at the L4-L5 and L5-S1 levels, significant differences were observed (p-value \u0026lt; 0.001), indicating that the mean SED was greater in females than in males. In contrast, for PESD measurements, no significant differences were found between genders. These results suggest that gender may significantly affect SED in certain spinal regions, while it does not appear to correlate with PESD.\u003c/p\u003e\n\u003cp\u003eAs shown in Figure 1, the SED increased progressively with BMI across all measured spinal levels. The highest SED values were observed in individuals with BMI \u0026gt; 35, particularly at the L4-L5 level, reaching nearly 70 mm, whereas individuals with BMI \u0026lt; 18 exhibited the lowest SED values across all levels. In contrast, the PESD exhibited an inverse trend, with the highest values recorded in the BMI \u0026lt; 18 category, particularly at L3-L4 (~7 mm). As BMI increased, PESD values showed a general decline, with the lowest measurements in the BMI \u0026gt; 35 group. The L5-S1 level consistently exhibited the smallest PESD across all BMI groups.\u003c/p\u003e\n\u003cp\u003eThese findings hypothesize a positive relationship between BMI and SED and a negative or weak relationship between BMI and PESD, indicating that increased subcutaneous fat raises needle depth requirements while potentially reducing epidural space depth.\u003c/p\u003e\n\u003cp\u003eCorrelations of Variables with SED and PESD\u003c/p\u003e\n\u003cp\u003eThe Pearson correlation coefficients and p-values for the relationships between age, weight, height, and BMI with both the SED and the PESD at various spinal levels are presented in Table 2.\u0026nbsp;The summary of findings is presented as follows:\u003c/p\u003e\n\u003cp\u003eSkin-Epidural Distance:\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eSED at L2-L3\u003c/em\u003e: A significant positive correlation was found between weight (\u003cem\u003er\u003c/em\u003e = 0.730, p \u0026lt; 0.001) and BMI (\u003cem\u003er\u003c/em\u003e = 0.716, p \u0026lt; 0.001) with SED, indicating that as weight and BMI increase, the SED also increases. \u003cem\u003eSED at L3-L4\u003c/em\u003e: There was a strong and significant positive correlation between SED and BMI (\u003cem\u003er\u003c/em\u003e = 0.723, p \u0026lt; 0.001) as well as weight (\u003cem\u003er\u003c/em\u003e = 0.676, p \u0026lt; 0.001), whereas other variables showed no significant correlation. \u003cem\u003eSED at L4-L5\u003c/em\u003e: A significant positive correlation was observed between weight (\u003cem\u003er\u0026nbsp;\u003c/em\u003e= 0.624, p \u0026lt; 0.001) and BMI (\u003cem\u003er\u003c/em\u003e = 0.740, p \u0026lt; 0.001) with SED. Conversely, a weak negative correlation with height (\u003cem\u003er\u003c/em\u003e = -0.141, p = 0.035) was noted, suggesting that increased height may be correlated with a decrease in SED. \u003cem\u003eSED at L5-S1\u003c/em\u003e: Significant positive correlations were found for weight (\u003cem\u003er\u003c/em\u003e = 0.578, p \u0026lt; 0.001) and BMI (\u003cem\u003er\u003c/em\u003e = 0.687, p \u0026lt; 0.001), indicating that higher weight and BMI are correlated with greater SED.\u003c/p\u003e\n\u003cp\u003ePosterior Epidural Space Depth:\u003c/p\u003e\n\u003cp\u003e\u003cem\u003ePESD at L2-L3\u003c/em\u003e: A significant negative correlation with age (\u003cem\u003er\u003c/em\u003e = -0.247, p \u0026lt; 0.001) indicates that older age is correlated with a decrease in PESD. \u003cem\u003ePESD at L3-L4\u003c/em\u003e: A significant negative correlation with age (\u003cem\u003er\u003c/em\u003e = -0.232, p \u0026lt; 0.001) was observed, along with a weak positive correlation with weight (\u003cem\u003er\u003c/em\u003e = 0.144, p = 0.033). \u003cem\u003ePESD at L4-L5\u003c/em\u003e: There was a significant negative correlation with age (\u003cem\u003er\u003c/em\u003e = -0.185, p = 0.006) and a weak positive correlation with weight (\u003cem\u003er\u003c/em\u003e = 0.159, p = 0.018). \u003cem\u003ePESD at L5-S1\u003c/em\u003e: A weak positive correlation with BMI (\u003cem\u003er\u003c/em\u003e = 0.144, p = 0.033) was noted, while other factors did not show significant correlations.\u003c/p\u003e\n\u003cp\u003eThe analysis of Pearson correlation coefficients reveals significant relationships between demographic variables and both the SED and PESD across various spinal levels. Notably, consistent positive correlations between weight and BMI with SED suggest that individuals with higher body weight and BMI tend to have greater distances from the skin to the epidural space, which may affect the efficacy of epidural anesthesia. Conversely, significant negative correlations between age and PESD indicate that as individuals\u0026rsquo; age, the PESD decreases, likely due to age-related anatomical changes such as disc degeneration. Additionally, a weak negative correlation between height and SED at the L4-L5 level suggests that taller individuals may experience slightly reduced distances to the epidural space.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eVariables Collinearity\u003c/p\u003e\n\u003cp\u003eTo prevent issues related to collinearity in the linear regression model, a thorough examination of variable relationships was conducted. It was found that weight had a high correlation with BMI (0.77), indicating a significant overlap in the information they provide (Figure 2). To avoid potential multicollinearity problems, weight was excluded from the model. This decision ensures the reliability and clarity of the regression analysis, allowing for more accurate interpretations of the remaining variables.\u003c/p\u003e\n\u003cp\u003eRegression Model\u003c/p\u003e\n\u003cp\u003eThe linear regression analysis examined the associations between ten dependent variables and four predictors: age, sex (male), height, and BMI (Table 3). For the SED outcomes, significant associations were observed, indicating that certain predictors may intensify the measurements. In the SED at L2-L3 model, height was positively associated with a regression coefficient of 1.25 (95% CI = [1.09, 1.44]), suggesting that greater height may lead to increased SED. Similarly, BMI showed a strong association with a coefficient of 4.78 (95% CI = [3.97, 5.76]), indicating that higher BMI is significantly related to larger SED values.\u003c/p\u003e\n\u003cp\u003eIn the SED at L3-L4 model, age had a coefficient of 0.90 (95% CI = [0.83, 0.98]), highlighting as older age was negatively associated with SED. Conversely, both height (Coefficient = 1.19, 95% CI = [1.01, 1.41]) and BMI (Coefficient = 6.56, 95% CI = [5.23, 8.24]) were positively associated, reinforcing the notion that taller individuals and those with higher BMI tend to exhibit greater SED values.\u003c/p\u003e\n\u003cp\u003eThe SED at the L4-L5 level further illustrated these dynamics, with age exhibiting a negative association (Coefficient = 0.88, 95% CI = [0.80, 0.97]) and male sex also showing a significant negative association (Coefficient = 0.03, 95% CI = [0.00, 0.42]), suggesting that being male is associated with lower SED. Height (Coefficient = 1.28, 95% CI = [1.04, 1.56]) and BMI (Coefficient = 9.73, 95% CI = [7.45, 12.72]) demonstrated significant positive associations as well, indicating that these factors intensify SED values.\u003c/p\u003e\n\u003cp\u003eIn the SED at L5-S1 model, age continued to show a protective association (Coefficient = 0.90, 95% CI = [0.81, 1.00]), while male had a notably strong negative association, further emphasizing the trend of lower SED in elder males. Height (Coefficient = 1.49, 95% CI = [1.20, 1.85]) and BMI (Coefficient = 8.05, 95% CI = [6.04, 10.72]) were both significantly associated, reinforcing the notion that these predictors lead to increased SED. Finally, in the SED mean model, which is the mean of all above SED measurements, age (Coefficient = 0.92, 95% CI = [0.85, 0.99]) and male sex (Coefficient = 0.01, 95% CI = [0.00, 0.23]) highlighted their protective roles, while, height (Coefficient = 1.30, 95% CI = [1.11, 1.52]), and BMI (Coefficient = 7.04, 95% CI = [5.71, 8.69]) demonstrated significant positive associations.\u003c/p\u003e\n\u003cp\u003eFor the PESD outcomes, age was consistently associated with a protective effect across several models, with a coefficient of 0.97 in the PESD at L2-L3 (95% CI = [0.96, 0.99]) and PESD at L3-L4 (95% CI = [0.95, 0.99]) models, indicating that older individuals may exhibit smaller PESD. Height also showed a positive association in the PESD at L2-L3 model (Coefficient = 1.04, 95% CI = [1.00, 1.08]), suggesting that taller individuals may have deeper PESD.\u003c/p\u003e\n\u003cp\u003eIn the PESD at L4-L5 model, age maintained a protective association, while BMI was positively associated (Coefficient = 1.05, 95% CI = [1.00, 1.10]), indicating that higher BMI can lead to deeper PESD. The PESD at L5-S1 model reinforced this finding with BMI (Coefficient = 1.05, 95% CI = [1.00, 1.10]) positively associated, while in the PESD mean model, age had a coefficient of 0.98 (95% CI = [0.97, 0.99]), further underscoring its negative association.\u003c/p\u003e\n\u003cp\u003eThese findings underscore the significant associations between the predictors and both SED and PESD measurements. BMI consistently demonstrates strong positive associations, indicating it as a major factor influencing these measurements, while age exhibits a protective effect in several contexts, suggesting that older age may be linked to smaller SED and PESD values.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this study, we aimed to determine the distance from the skin to the dura mater and the depth of the posterior epidural space in Iranian adult patients undergoing MRI, while also examining the relationship with BMI, sex, height, weight, and age. A total of 227 participants were included, with a mean age of approximately 45 years, and a major portion being female. Our findings indicated that the greatest distance from the skin to the dura was observed at the L4-L5 level, which aligns with previous literature suggesting that lumbar regions typically exhibit greater anatomical distances due to the presence of surrounding adipose tissue. Additionally, the maximum PESD was recorded at the L3-L4 level, reinforcing the notion that this region is crucial for epidural interventions.\u003c/p\u003e \u003cp\u003eIn the context of the correlation between demographic and physical factors with SED and PESD, weight and BMI showed a strong positive correlation with the SED across various spinal levels. This suggests that individuals with higher body weight and BMI may have greater distances, which is particularly relevant for anesthetic practices, as it could influence the effectiveness of epidural anesthesia. Conversely, a weak negative correlation was noted between height and the SED at the L4-L5 level, indicating that taller individuals may experience slightly less distance. Significant but weak negative correlations were found between age and PESD at various levels, suggesting that as patients get older, the PESD tends to decrease. This finding aligns with another study that reported a weak inverse correlation between age and gracilis muscle mass; however, it does not directly address changes in the epidural space depth (25). Furthermore, a weak positive correlation was observed between weight and PESD at certain levels, suggesting that increased BMI may also affect the depth of the epidural space.\u003c/p\u003e \u003cp\u003eThe results of the linear regression models reveal significant associations between various predictors and both SED and PESD measurements. Height and BMI emerged as strong positive predictors of SED, indicating that taller individuals and those with higher BMI are likely to exhibit increased SED values. Supporting this, a study found a direct relationship between BMI and epidural space depth during lumbar transforaminal epidural steroid injections, where higher BMI correlated with greater needle depth. This aligns with the assertion that elevated BMI increases SED (10). As well as, Hazarika et al. (15) found that the distance to the subarachnoid space correlated with BMI in Indian population, while Eley et al. (18) demonstrated that both subcutaneous fat and BMI significantly correlated with SED. Similarly, Sargin et al. (17) concluded that BMI and body weight significantly influenced the skin-to-subarachnoid space distance, with age and gender showing minimal impact.\u003c/p\u003e \u003cp\u003eWhile no studies explicitly link height to SED, research on gracilis muscle mass suggests that height may indirectly influence anatomical dimensions relevant to SED, although direct evidence remains absent (25).\u003c/p\u003e \u003cp\u003eConversely, age was identified as a negative predictor, particularly at the L4-L5 level, where older age correlated with lower SED. This finding suggests that age-related anatomical changes may contribute to variations in epidural space dimensions. However, another study explicitly found no predictive value of age on foraminal epidural depth, highlighting the complexity of these relationships (10).\u003c/p\u003e \u003cp\u003eIt is important to note that female gender was also a positive predictor of larger SED, particularly at the L4-L5 and L5-S1 levels, highlighting potential gender differences in anatomical characteristics that warrant further investigation. Eley et al.'s study (18) demonstrated an association between increased SED and being female. However, since this study focused specifically on pregnant women, we should exercise caution in generalizing our results to that population. Brummett et al. initially identified sex as a predictor of epidural depth; however, this association became insignificant when BMI was included in the model (10). Our findings also contrast with those of Zhao et al. (16), who reported greater distances in males within the cervical and upper thoracic regions among Chinese adults. Additionally, a study highlights sex-specific differences in body proportions within a Mexican population, which may partially account for anatomical variations that influence SED (26). Recognizing gender as a factor influencing SED can provide valuable insights for practitioners, as males generally exhibit a smaller distance from the skin to the epidural space.\u003c/p\u003e \u003cp\u003eIn the context of PESD, although a weak positive association was observed between BMI and PESD\u0026mdash;reinforcing the notion that increased body mass can contribute to greater depth of the posterior epidural space\u0026mdash;age emerged as a significant negative predictor of PESD. In all models developed based on PESD measurements, age negatively affected the depth of the posterior epidural space, indicating that older individuals tend to have a shallower epidural space. This trend emphasizes age-related changes in spinal anatomy, which could lead to variations in the depth of the posterior epidural space. The provided studies do not directly address age-related reductions in PESD; however, a study found no significant correlation between age and posterior epidural space width in adults (27). Additionally, a CT-based anatomical analysis observed age-related structural changes, such as reduced soft tissue volume in certain spinal regions, which could theoretically influence PESD (28). This study concentrated on the infraorbital cheek rather than the lumbar spine, highlighting the need for further research specifically targeting geriatric populations to validate these observations.\u003c/p\u003e \u003cp\u003eOverall, these findings underscore the complex interplay between demographic and anthropometric factors in determining SED and PESD measurements. Understanding these associations is crucial for optimizing clinical practices, particularly in procedures involving the epidural space. Our study provides valuable insights into the anatomical relationships influencing epidural procedures in Iranian adults, emphasizing the importance of considering factors such as sex, age, weight, height, and BMI. These insights highlight the necessity for personalized approaches in anesthetic practice, as variations in body composition and age can significantly affect the success of epidural interventions. Additionally, the findings suggest that anatomical considerations should account for specific vertebral levels and age-related differences. Future research should continue to explore these relationships across diverse populations to enhance the safety and efficacy of epidural interventions, ultimately leading to improved clinical outcomes.\u003c/p\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eStrengths and Limitations\u003c/h2\u003e \u003cp\u003eThis study's strengths include its focus on a specific Iranian population, contributing valuable data on anatomical relationships relevant to epidural procedures. Future studies should involve larger sample sizes and further investigations, particularly focusing on patients with higher BMI, to enhance the accuracy of determining the SED using MRI. However, limitations were present; the study excluded non-Iranian patients and individuals with pathological conditions affecting spinal measurements, which may limit the generalizability of the findings. Additionally, weight restrictions for MRI limited participant inclusion, though this was addressed by setting criteria for weight and BMI. Future research should aim to include a more diverse population and explore the implications of various spinal pathologies on measurement outcomes.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis MRI-based study confirms that BMI and height are strong positive predictors of skin-to-epidural distance (SED), while age is a significant negative predictor of posterior epidural space depth (PESD). Additionally, male sex was associated with smaller SED values in lower lumbar levels. These findings support the importance of individualized pre-procedural planning in neuraxial anesthesia, particularly in populations with varying body habitus and age. Recognizing the influence of these variables can improve the precision and safety of epidural procedures. Further research across diverse populations and spinal levels is warranted to expand our understanding and optimize anesthetic strategies globally.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eBMI\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eBody Mass Index\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eMRI\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eMagnetic Resonance Imaging\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePESD\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ePosterior Epidural Space Depth\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eSED\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eSkin-to-Epidural Distance\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePDPH\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ePost-Dural Puncture Headache\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePACS\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ePicture Archiving and Communication System\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eSD\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eStandard Deviation\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eCI\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eConfidence Interval\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003ePotential Conflicts of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that there are no known competing interests that could affect this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research received no external funding.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflicts of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval and Consent to Participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was approved by the Ethics Committee of Tehran University of Medical Sciences (Approval ID: IR.TUMS.IKHC.REC.1403.072). All procedures performed were in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for Publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMohammad Dehghan-Tazerjani\u003c/strong\u003e: Conceptualization, supervision, methodology, writing, review \u0026amp; editing.\u003cbr\u003e\u003cstrong\u003eBabak Eslami\u003c/strong\u003e: Project administration, writing \u0026ndash; original draft.\u003cbr\u003e\u003cstrong\u003eMasoud Mahmoodi\u003c/strong\u003e: Data collection, interpretation of results.\u003cbr\u003e\u003cstrong\u003eAmir Pasha Amel Shahbaz:\u0026nbsp;\u003c/strong\u003eStatistical analysis\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAlireza Montaseri, Ebrahim Espahbodi, Laya Amoozadeh, Merhrshad Namazi, Ehsan Ziaeii\u003c/strong\u003e: Patient recruitment, data acquisition, and critical revision of the manuscript.\u003cbr\u003e\u0026nbsp;All authors reviewed and approved the final version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated and analyzed during the current study are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eChou R, Gordon DB, Leon-Casasola OA de, Rosenberg JM, Bickler S, Brennan T, et al. Management of Postoperative Pain: A Clinical Practice Guideline From the American Pain Society, the American Society of Regional Anesthesia and Pain Medicine, and the American Society of Anesthesiologists\u0026rsquo; Committee on Regional Anesthesia, Executive Committee, and Administrative Council. J Pain. 2016 Feb 1;17(2):131\u0026ndash;57. \u003c/li\u003e\n\u003cli\u003eHermanns H, Bos EME, van Zuylen ML, Hollmann MW, Stevens MF. The Options for Neuraxial Drug Administration. CNS Drugs. 2022 Aug;36(8):877\u0026ndash;96. \u003c/li\u003e\n\u003cli\u003eUppal V, Sondekoppam RV, Landau R, El-Boghdadly K, Narouze S, Kalagara HKP. Neuraxial anaesthesia and peripheral nerve blocks during the COVID-19 pandemic: a literature review and practice recommendations. Anaesthesia. 2020 Oct;75(10):1350\u0026ndash;63. \u003c/li\u003e\n\u003cli\u003eGogarten W, Van Aken H. A century of regional analgesia in obstetrics. Anesth Analg. 2000 Oct;91(4):773\u0026ndash;5. \u003c/li\u003e\n\u003cli\u003eShaikh F, Voicu L, Tole S, To T, Doria AS, Sung L, et al. The risk of traumatic lumbar punctures in children with acute lymphoblastic leukaemia. Eur J Cancer Oxf Engl 1990. 2014 May;50(8):1482\u0026ndash;9. \u003c/li\u003e\n\u003cli\u003eRastogi S, Bhandari R, Sharma V, Pandey T. Neurological complications following spinal anaesthesia in a patient with congenital absence of lumbar vertebra. Indian J Anaesth. 2014;58(4):484\u0026ndash;6. \u003c/li\u003e\n\u003cli\u003eTandale SR, Kelkar KV, Abhade SR, Gadre VN. Diagnostic Dilemma of Severe Excruciating Low Backache in Pediatric Patient Following Spinal Anesthesia. Med J Dr Patil Vidyapeeth. 2018 Oct;11(5):456. \u003c/li\u003e\n\u003cli\u003eUnic-Stojanovic D, Babic S, Jovic M. Benefits, risks and complications of perioperative use of epidural anesthesia. Med Arch Sarajevo Bosnia Herzeg. 2012;66(5):340\u0026ndash;3. \u003c/li\u003e\n\u003cli\u003eKang XH, Bao FP, Xiong XX, Li M, Jin TT, Shao J, et al. Major complications of epidural anesthesia: a prospective study of 5083 cases at a single hospital. Acta Anaesthesiol Scand. 2014 Aug;58(7):858\u0026ndash;66. \u003c/li\u003e\n\u003cli\u003eBrummett CM, Williams BS, Hurley RW, Erdek MA. A prospective, observational study of the relationship between body mass index and depth of the epidural space during lumbar transforaminal epidural steroid injection. Reg Anesth Pain Med. 2009;34(2):100\u0026ndash;5. \u003c/li\u003e\n\u003cli\u003eGarcia-Pereira F. Epidural anesthesia and analgesia in small animal practice: An update. Vet J Lond Engl 1997. 2018 Dec;242:24\u0026ndash;32. \u003c/li\u003e\n\u003cli\u003eRavi KK, Kaul TK, Kathuria S, Gupta S, Khurana S. Distance from Skin to Epidural Space: Correlation with Body Mass Index (BMI). J Anaesthesiol Clin Pharmacol. 2011 Jan;27(1):39\u0026ndash;42. \u003c/li\u003e\n\u003cli\u003eNayate AP, Nasrallah IM, Schmitt JE, Mohan S. Using Body Mass Index to Predict Needle Length in Fluoroscopy-Guided Lumbar Punctures. AJNR Am J Neuroradiol. 2016 Mar;37(3):572\u0026ndash;8. \u003c/li\u003e\n\u003cli\u003eWenk M, Weiss C, M\u0026ouml;llmann M, P\u0026ouml;pping DM. Procedural complications of spinal anaesthesia in the obese patient. Anesthesiol Res Pract. 2012;2012:165267. \u003c/li\u003e\n\u003cli\u003eHazarika R, Choudhury D, Nath S, Parua S. Estimation of Skin to Subarachnoid Space Depth: An Observational Study. J Clin Diagn Res JCDR. 2016 Oct;10(10):UC06\u0026ndash;9. \u003c/li\u003e\n\u003cli\u003eZhao Q, Huang K, An J, Fang Q, Wen H, Qian X, et al. The distance from skin to cervical and high thoracic epidural space on chinese adults as read from MRI. Pain Physician. 2014;17(2):163\u0026ndash;8. \u003c/li\u003e\n\u003cli\u003eSargin M, Hanedan B, Aydoğan E, Akin F, \u0026Ouml;zmen S. Evaluation of factors that affect skin to subarachnoid space distance. J Health Sci. 2017;7(1):23\u0026ndash;6. \u003c/li\u003e\n\u003cli\u003eEley VA, Chin A, Sekar R, Donovan T, Krepska A, Lawrence M, et al. Increasing body mass index and abdominal subcutaneous fat thickness are associated with increased skin-to-epidural space distance in pregnant women. Int J Obstet Anesth. 2019 May;38:59\u0026ndash;65. \u003c/li\u003e\n\u003cli\u003eFranklin AD, Lorinc AN, Shotwell MS, Greene EB, Wushensky CA. Evaluation of the skin to epidural and subarachnoid space distance in young children using magnetic resonance imaging. Reg Anesth Pain Med. 2015;40(3):245\u0026ndash;8. \u003c/li\u003e\n\u003cli\u003eZhuge W, Ben-Galim P, Hipp JA, Reitman CA. Efficacy of MRI for assessment of spinal trauma: correlation with intraoperative findings. J Spinal Disord Tech. 2015 May;28(4):147\u0026ndash;51. \u003c/li\u003e\n\u003cli\u003eParizel PM, van der Zijden T, Gaudino S, Spaepen M, Voormolen MHJ, Venstermans C, et al. Trauma of the spine and spinal cord: imaging strategies. Eur Spine J Off Publ Eur Spine Soc Eur Spinal Deform Soc Eur Sect Cerv Spine Res Soc. 2010 Mar;19 Suppl 1(Suppl 1):S8-17. \u003c/li\u003e\n\u003cli\u003eAdegboye MB, Bolaji BO, Ibraheem GH. The Correlation Between Body Mass Index On The Length From Skin To Lumbar Epidural Space In Nigerian Adults. J West Afr Coll Surg. 2017;7(1):113\u0026ndash;27. \u003c/li\u003e\n\u003cli\u003eMansouritorghabeh H, Bagherimoghaddam A, Eslami S, Raouf-Rahmati A, Hamer DH, Kiani B, et al. Spatial epidemiology of COVID-19 infection through the first outbreak in the city of Mashhad, Iran. Spat Inf Res. 2022 Jun 28;30(5):585\u0026ndash;95. \u003c/li\u003e\n\u003cli\u003eMohammadEbrahimi S, Kiani B, Rahmatinejad Z, Baral S, Hashtarkhani S, Dehghan-Tezerjani M, et al. Geospatial epidemiology of hospitalized patients with a positive influenza assay: A nationwide study in Iran, 2016\u0026ndash;2018. PLOS ONE. 2022 Dec 13;17(12):e0278900. \u003c/li\u003e\n\u003cli\u003eOranges CM, Tremp M, Wang W, Madduri S, DI Summa PG, Wettstein R, et al. Patient Height, Weight, BMI and Age as Predictors of Gracilis Muscle Free-Flap Mass in Lower Extremity Reconstruction. Vivo Athens Greece. 2018;32(3):591\u0026ndash;5. \u003c/li\u003e\n\u003cli\u003eDatta Banik S. Association of early menarche with elevated BMI, lower body height and relative leg length among 14- to 16-year-old post-menarcheal girls from a Maya community in Yucatan, Mexico. Anthropol Rev. 2022 Mar 18;85(1):85\u0026ndash;100. \u003c/li\u003e\n\u003cli\u003eJiang M, Shao H, Li Q. Analysis of Anatomy and Age-related Changes in Infraorbital Cheek Using Computed Tomography. Aesthetic Plast Surg. 2024 Aug;48(16):3061\u0026ndash;7. \u003c/li\u003e\n\u003cli\u003eGupta A, Gupta A, Singh F, Mandhyan R. Correlation of skin epidural distance and posterior epidural space depth with age, weight, height, BMI, abdominal girth and position of the patient: A prospective randomised study. Indian J Clin Anaesth. 2021 Sep 28;8(3):361\u0026ndash;6. \u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTable\u0026nbsp;1. Total distribution and gender differences in Skin-Epidural Distance (SED) and the Posterior Epidural Space Depth\u0026nbsp;(PESD) across vertebral column.\u003c/p\u003e\n\u003cdiv align=\"Left\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"594\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSED\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTotal (Mean \u0026plusmn; SD)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 144px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFemale\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e(Mean \u0026plusmn; SD)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMale\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e(Mean \u0026plusmn; SD)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ep-value\u003csup\u003e*\u003c/sup\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003eSEDL2-L3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e51.61 \u0026plusmn; 10.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 144px;\"\u003e\n \u003cp\u003e51.26 \u0026plusmn; 10.34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003e52.12 \u0026plusmn; 9.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003e0.537\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003eSEDL3-L4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e57.05 \u0026plusmn; 11.77\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 144px;\"\u003e\n \u003cp\u003e57.62 \u0026plusmn; 12.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003e56.20 \u0026plusmn; 10.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003e0.373\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003eSEDL4-L5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e62.75 \u0026plusmn; 14.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 144px;\"\u003e\n \u003cp\u003e65.70 \u0026plusmn; 15.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003e58.40 \u0026plusmn; 12.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003eSEDL5-S1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e62.22 \u0026plusmn; 14.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 144px;\"\u003e\n \u003cp\u003e65.81 \u0026plusmn; 15.17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003e56.95 \u0026plusmn; 12.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePESD\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTotal (Mean \u0026plusmn; SD)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 144px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFemale\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e(Mean \u0026plusmn; SD)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMale\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e(Mean \u0026plusmn; SD)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ep-value\u003csup\u003e*\u003c/sup\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003ePESDL2-L3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e5.91 \u0026plusmn; 1.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 144px;\"\u003e\n \u003cp\u003e5.90 \u0026plusmn; 1.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003e5.93 \u0026plusmn; 1.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003e0.901\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003ePESDL3-L4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e5.92 \u0026plusmn; 1.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 144px;\"\u003e\n \u003cp\u003e5.89 \u0026plusmn; 1.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003e5.97 \u0026plusmn; 1.76\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003e0.734\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003ePESDL4-L5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e4.93 \u0026plusmn; 1.76\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 144px;\"\u003e\n \u003cp\u003e4.95 \u0026plusmn; 1.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003e4.90 \u0026plusmn; 1.60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003e0.839\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003ePESDL5-S1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e3.34 \u0026plusmn; 1.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 144px;\"\u003e\n \u003cp\u003e3.39 \u0026plusmn; 1.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003e3.26 \u0026plusmn; 1.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003e0.555\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" valign=\"top\" style=\"width: 594px;\"\u003e\n \u003cp\u003e\u003csup\u003e*\u003c/sup\u003eIndependent t-test applied for comparison between the genders.\u0026nbsp;\u003c/p\u003e\n \u003cp\u003eSED: Skin-Epidural Distance, PESD: Posterior Epidural Space Depth,\u0026nbsp;L: Lumbar, S: Sacrum.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cspan dir=\"LTR\"\u003e\u0026nbsp;\u003c/span\u003eTable\u0026nbsp;2. Correlation analysis of demographic variables with Skin-Epidural Distance (SED) and Posterior Epidural Space Depth (PESD) across vertebral levels.\u003c/p\u003e\n\u003cdiv align=\"Left\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"462\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 98px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSED\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAge\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eWeight\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eHeight\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eBMI\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 98px;\"\u003e\n \u003cp\u003eSEDL2-L3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003eCorrelation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.075\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.730\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.024\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.716\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003ep-value\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.263\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.718\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.000\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 98px;\"\u003e\n \u003cp\u003eSEDL3-L4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003eCorrelation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e-0.050\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.676\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.010\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.723\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003ep-value\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.465\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.881\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.000\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 98px;\"\u003e\n \u003cp\u003eSEDL4-L5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003eCorrelation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e-0.029\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.624\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e-0.141\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.740\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003ep-value\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.671\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.035\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.000\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 98px;\"\u003e\n \u003cp\u003eSEDL5-S1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003eCorrelation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e-0.037\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.578\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e-0.122\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.687\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003ep-value\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.578\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.067\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.000\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 98px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePESD\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAge\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eWeight\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eHeight\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eBMI\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 98px;\"\u003e\n \u003cp\u003ePESDL2-L3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003eCorrelation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e-0.247\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.122\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.088\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e-0.004\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003ep-value\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.068\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.190\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.948\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 98px;\"\u003e\n \u003cp\u003ePESDL3-L4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003eCorrelation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e-0.232\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.144\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.028\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.053\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003ep-value\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.033\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.675\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.430\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 98px;\"\u003e\n \u003cp\u003ePESDL4-L5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003eCorrelation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e-0.185\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.159\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e-0.021\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.119\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003ep-value\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.006\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.018\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.752\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.077\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 98px;\"\u003e\n \u003cp\u003ePESDL5-S1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003eCorrelation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.074\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.119\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.015\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.144\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003ep-value\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.272\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 72px;\"\u003e\n \u003cp\u003e0.078\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.830\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.033\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"6\" valign=\"top\" style=\"width: 462px;\"\u003e\n \u003cp\u003eSED: Skin-Epidural Distance, PESD: Posterior Epidural Space Depth, BMI: Body Index Mass, L: Lumbar, S: Sacrum.\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u0026nbsp;Table 3. Multivariate linear regression model of Skin-Epidural Distance (SED) and Posterior Epidural Space Depth (PESD) across different vertebral levels based on explanatory factors.\u003c/p\u003e\n\u003cdiv align=\"Left\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eVariable\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eParameter \u0026nbsp;\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCoefficient\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSE\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e95% CI\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\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 rowspan=\"4\" style=\"width: 108px;\"\u003e\n \u003cp\u003eSEDL2-L3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eAge\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.94, 1.07]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.986\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eSex [Male]*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e1.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e2.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.13, 24.32]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.662\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eHeight\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e1.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[1.09, 1.44]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.002\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eBMI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e4.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[3.97, 5.76]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u0026lt; .001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"4\" style=\"width: 108px;\"\u003e\n \u003cp\u003eSEDL3-L4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eAge\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.83, 0.98]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.010\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eSex [Male]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.02, 10.05]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.585\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eHeight\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e1.19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[1.01, 1.41]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.042\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eBMI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e6.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.76\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[5.23, 8.24]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u0026lt; .001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"4\" style=\"width: 108px;\"\u003e\n \u003cp\u003eSEDL4-L5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eAge\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.80, 0.97]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.008\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eSex [Male]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.00, 0.42]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u0026lt; .001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eHeight\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e1.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[1.04, 1.56]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\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: 114px;\"\u003e\n \u003cp\u003eBMI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e9.73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e1.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[7.45, 12.72]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u0026lt; .001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"4\" style=\"width: 108px;\"\u003e\n \u003cp\u003eSEDL5-S1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eAge\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.81, 1.00]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.040\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eSex [Male]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.00, 0.10]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u0026lt; .001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eHeight\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e1.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[1.20, 1.85]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u0026lt; .001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eBMI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e8.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e1.17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[6.04, 10.72]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u0026lt; .001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"4\" style=\"width: 108px;\"\u003e\n \u003cp\u003eSED mean\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eAge\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.85, 0.99]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.025\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eSex [Male]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.00, 0.23]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\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: 114px;\"\u003e\n \u003cp\u003eHeight\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e1.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[1.11, 1.52]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\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: 114px;\"\u003e\n \u003cp\u003eBMI\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e7.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[5.71, 8.69]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u0026lt; .001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eVariable\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eParameter \u0026nbsp;\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCoefficient\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSE\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e95% CI\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\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 rowspan=\"4\" style=\"width: 108px;\"\u003e\n \u003cp\u003ePESDL2-L3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eAge\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.97\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.96, 0.99]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.005\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eSex [Male]*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.28, 1.15]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.112\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eHeight\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e1.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[1.00, 1.08]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.032\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eBMI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e1.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.96, 1.07]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.571\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"4\" style=\"width: 108px;\"\u003e\n \u003cp\u003ePESDL3-L4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eAge\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.97\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.95, 0.99]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\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: 114px;\"\u003e\n \u003cp\u003eSex [Male]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.41, 1.68]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.593\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eHeight\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e1.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.98, 1.06]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.330\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eBMI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e1.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.98, 1.09]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.202\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"4\" style=\"width: 108px;\"\u003e\n \u003cp\u003ePESDL4-L5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eAge\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.97\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.96, 0.99]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.004\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eSex [Male]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.37, 1.52]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.426\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eHeight\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e1.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.98, 1.06]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.327\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eBMI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e1.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[1.00, 1.10]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.049\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"4\" style=\"width: 108px;\"\u003e\n \u003cp\u003ePESDL5-S1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eAge\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e1.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.99, 1.02]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.439\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eSex [Male]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.45, 1.59]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.597\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eHeight\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e1.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.97, 1.04]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.661\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eBMI\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e1.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[1.00, 1.10]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.035\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"4\" style=\"width: 108px;\"\u003e\n \u003cp\u003ePESD mean\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eAge\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.97, 0.99]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.005\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eSex [Male]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.44, 1.23]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.243\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eHeight\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e1.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[0.99, 1.05]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.122\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003eBMI\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e1.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003e[1.00, 1.08]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.051\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"6\" valign=\"top\" style=\"width: 533px;\"\u003e\n \u003cp\u003e*\u0026nbsp;Sex was treated as a dichotomous variable, with females as the reference category.\u003c/p\u003e\n \u003cp\u003eSE: Standard Error, CI: Confidence Interval, BMI: Body Index Mass.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"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":"bmc-medical-imaging","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmim","sideBox":"Learn more about [BMC Medical Imaging](http://bmcmedimaging.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/bmim/default.aspx","title":"BMC Medical Imaging","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Epidural anesthesia, Body Mass Index (BMI), Dura space, Magnetic Resonance Imaging (MRI)","lastPublishedDoi":"10.21203/rs.3.rs-6675174/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6675174/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground\u003c/strong\u003e\u003cbr\u003e\nPrecise identification of the skin-to-epidural distance (SED) is essential for safe and effective epidural anesthesia. This study aimed to evaluate the SED and posterior epidural space depth (PESD) at lower thoracic and lumbar levels using MRI, and to investigate their associations with demographic and anthropometric factors in an Iranian adult population.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods\u003c/strong\u003e\u003cbr\u003e\nIn this cross-sectional study, 227 adult patients undergoing lumbar spine MRI were included. SED and PESD were measured at L2–S1 interspaces using MRI, and their correlations with age, sex, height, weight, and BMI were analyzed. Pearson correlation and multivariate linear regression were applied to identify significant predictors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults\u003c/strong\u003e\u003cbr\u003e\nThe highest mean SED was observed at L3–L4 (57.05 ± 11.77 mm). BMI and weight showed strong positive correlations with SED across all levels. Age demonstrated a significant negative correlation with PESD at several levels. Multivariate analysis confirmed BMI and height as strong predictors of increased SED, while age was a negative predictor of PESD. Male gender was associated with shorter SED values at lower lumbar levels.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions\u003c/strong\u003e\u003cbr\u003e\nMRI-based assessment of SED and PESD reveals important correlations with BMI, height, and age. These findings support individualized estimation of epidural depth to enhance procedural safety, particularly in patients with varying body composition and age.\u003c/p\u003e","manuscriptTitle":"MRI-Based Investigation of Skin-Epidural Distance and Posterior Epidural Space Depth: The Role of Demographic and Anthropometric Factors","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-17 15:48:51","doi":"10.21203/rs.3.rs-6675174/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-05-18T06:14:48+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-12T10:51:06+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-12T03:47:00+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-08T19:23:06+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"321211521155826751102978767557726721271","date":"2026-05-07T20:48:41+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"132190306645273123810163731842235106305","date":"2026-05-07T08:57:30+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-05T13:26:13+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"132865043642770510825808854965976054981","date":"2026-05-05T12:31:04+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"126721612149048988084082475978376012016","date":"2026-05-05T09:32:03+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-23T19:33:25+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"243834160636545517866177642926465355937","date":"2025-06-20T03:41:03+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"178679218913452392840325899210170474566","date":"2025-06-18T19:06:25+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-06-11T19:29:24+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-05-20T10:53:47+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-05-20T10:43:47+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-05-19T18:05:22+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Medical Imaging","date":"2025-05-19T18:04:16+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-medical-imaging","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmim","sideBox":"Learn more about [BMC Medical Imaging](http://bmcmedimaging.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/bmim/default.aspx","title":"BMC Medical Imaging","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"535c374f-58c5-46c9-857d-b8e24cf7c1dc","owner":[],"postedDate":"June 17th, 2025","published":true,"recentEditorialEvents":[{"type":"decision","content":"Revision requested","date":"2026-05-18T06:14:48+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-12T10:51:06+00:00","index":94,"fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-12T03:47:00+00:00","index":93,"fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-08T19:23:06+00:00","index":92,"fulltext":""},{"type":"reviewerAgreed","content":"321211521155826751102978767557726721271","date":"2026-05-07T20:48:41+00:00","index":91,"fulltext":""},{"type":"reviewerAgreed","content":"132190306645273123810163731842235106305","date":"2026-05-07T08:57:30+00:00","index":88,"fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-05T13:26:13+00:00","index":87,"fulltext":""},{"type":"reviewerAgreed","content":"132865043642770510825808854965976054981","date":"2026-05-05T12:31:04+00:00","index":86,"fulltext":""},{"type":"reviewerAgreed","content":"126721612149048988084082475978376012016","date":"2026-05-05T09:32:03+00:00","index":85,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"in-revision","subjectAreas":[],"tags":[],"updatedAt":"2026-05-18T06:24:37+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-17 15:48:51","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6675174","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6675174","identity":"rs-6675174","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}