Patient preoperative positioning for THA affects postoperative acetabular cup angle and leg length discrepancy - a prospective case series

Patient preoperative positioning for THA affects postoperative acetabular cup angle and leg length discrepancy - a prospective case series | 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 Patient preoperative positioning for THA affects postoperative acetabular cup angle and leg length discrepancy - a prospective case series Petr Fulin, David Pokorny, Dariusz Grzelecki, David Jonas, David Jahoda, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6347220/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background Proper orientation of the acetabular cup in total hip arthroplasty (THA) is essential to reduce dislocation risk, improve range of motion, and enhance implant longevity. Misalignment can lead to complications such as impingement, wear, and aseptic loosening. Patient positioning on the operating table is a critical yet often overlooked factor influencing pelvic tilt and cup placement accuracy during THA. This study evaluates the impact of preoperative patient positioning on acetabular component placement and explores whether surgeon experience affects cup placement precision. Methods In this prospective case series, 135 patients undergoing non-navigated THA in the supine position at a single tertiary center were included. Preoperative photographs captured pelvic inclination, which was compared to postoperative cup orientation measured on radiographs. Patients were divided into three groups based on surgeon experience ( 15 years). Statistical analyses assessed relationships among patient positioning, cup orientation, leg length discrepancy, and surgeon experience. Results Greater pelvic inclination measured before sterile draping was significantly associated with a smaller acetabular cup angle (Pearson’s R = -0.72, p 15 years of experience demonstrated less variability in cup orientation and leg length discrepancy than those with fewer years of experience (p < 0.001). Despite variations in pelvic positioning, the overall postoperative cup angle was consistent across groups. Conclusion Preoperative patient positioning significantly impacts acetabular cup orientation, with more experienced surgeons better able to compensate for these deviations. Positioning protocols and surgeon training on pelvic orientation may enhance THA outcomes, particularly for early-career surgeons. Acetabular cup orientation Preoperative patient positioning Surgeon experience Leg length discrepancy Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Proper orientation of the acetabular component is critical in total hip arthroplasty (THA) to preserve the patient’s range of motion and reduce the risk of dislocation [ 1 ]. Misalignment of the acetabular cup can lead to impingement [ 2 ], increased wear [ 3 ], and edge loading [ 4 ], which can in turn result in osteolysis and aseptic loosening [ 5 ]. Traditionally, cup positioning has been guided by the "safe zone" concept introduced by Lewinnek et al. in 1978, derived from an analysis of 300 THAs [ 6 ]. This study suggested an optimal positioning range of 30° to 50° inclination and 5° to 25° anteversion, with cups outside this zone exhibiting a fourfold increase in dislocation risk [ 6 ]. However, recent studies question the predictive accuracy of Lewinnek’s safe zone, particularly as it does not account for functional spine-pelvis-hip motion, which can influence postoperative outcomes [ 7 – 10 ]. Nevertheless, this standard remains widely used in preoperative planning [ 1 ] and these target angles are even endorsed by implant manufacturers and integrated into surgical guides for accurate positioning [ 11 ]. Patient positioning on the operating table is widely recognized as a key factor for ensuring stable pelvis orientation during surgery [ 12 – 14 ]. Ideally, if the pelvis maintains the same tilt, obliquity, and rotation relative to the operating table as it will postoperatively, this would optimize cup placement accuracy [ 11 ]. However, radiographic comparisons between intraoperative and postoperative positioning have not confirmed this assumption [ 15 ]. In practice, the surgeon is often unable to follow the sagittal plane of the body or the position of the patient’s pelvis due to the patient’s sterile draping. The surgeon orients the implantation of the acetabular component according to the edge of the operating table (Fig. 1 A), which sets the resulting inclination of the acetabular component [ 16 ]. In doing so, the patient is very often positioned on the edge of the operating table for better access to the hip joint with tilted pelvis. This can lead to inaccurate implantation of the acetabular component and also to incorrect determination of the length of the lower limbs within the patient’s malposition on the operating table (Fig. 2 ). Although the importance of proper cup positioning and the factors influencing it are well acknowledged and extensively discussed in the literature [ 1 , 17 , 18 ], the specific impact of patient positioning on the operating table during preoperative preparation on the accuracy of acetabular cup placement in non-navigated THA has not been objectively proven or quantified. Despite its presumed significance, no studies have systematically investigated this relationship and we do not know the extent to which patient positioning influences acetabular cup placement accuracy. The objective of this study was to photographically record and measure pelvic inclination angles on the operating table in the supine position during preoperative preparation, comparing these to radiographic inclination angles on postoperative anteroposterior radiographs. Our study aimed to address the following questions: (1) What is the relationship between preoperative patient positioning, acetabular cup orientation, and leg length discrepancy (LLD)? (2) Is there a difference in cup placement accuracy between experienced and early-career surgeons? We hypothesized that patient positioning on the operating table would influence postoperative cup positioning, but that experienced surgeons would be better able to compensate for this effect. Methods This prospective, multi-surgeon, consecutive case series from a single tertiary centre had ethical approval. The study was conducted according to the Helsinki Declaration of 2008 and all patients gave informed consent. We included a total of 135 patients indicated for total hip arthroplasty implantation (Table 1 ). Only patients with a diagnosis of osteoarthritis or osteoarthritis on the basis of rheumatoid arthritis were included in the study. Only patients with a maximum variation in hip length difference of less than 1cm (LLD \(\:\le\:\) 1cm) were included. The number of women in the cohort was 69 and the number of men was 66. The mean age at the time of surgery was 68.7 years (range 45–78 years). Patients were classified into 3 groups according to the experience of the surgeon. The first group of 45 THAs consisted of patients operated on by early carrier surgeon (less than 5 years of clinical experience). In the second group (45 THAs), the length of clinical experience of the surgeon was 5–15 years, while the third group (45 THAs) consists of surgeon with more than 15 years of experience. Table 1 Patient demographics and surgical details Total Surgeon experience 15 years Mean age, yrs (SD) 68.7 (10.6) 69,1 (9,8) 68,8 (11,3) 68,2 (10,7) Mean height, m (SD) 1.75 (0.1) 1,75 (0,1) 1,76 (0,1) 1,74 (0,2) Mean weight, kg (SD) 80.8 (13.3) 79,1 (10,1) 80,5 (14,2) 82,8 (15,6) Mean BMI, kg/m 2 (SD) 26.4 (3.2) 26,1 (3,0) 26,6 (3,4) 26,5 (3,2) Gender, n (%) Male 66 (48,9%) 23 (51,1%) 22 (48,9%) 21 (46,7%) Female 69 (51,1%) 22 (48,9%) 23 (51,1%) 24 (53,3%) Side, n (%) Left 65 (48%) 21 (46,7%) 21 (46,7%) 22 (48,9%) Right 70 (52%) 24 (53,3%) 24 (53,3%) 23 (51,1%) All surgeries were performed as non-navigated THA with preoperative planning based on standard supine anteroposterior radiographs. An optimal cup inclination in preoperative planning was based on reccomendation of the producer, 45° degrees to the sagital plane of the body. All cases were positioned in the supine position and as close as possible to the edge of the table with the aim of operated pelvis in neutral position. For each patient, we identified anterior superior iliac spines (ASIS) by palpation and marked them bilaterally with a marker before surgery after the patient was positioned. After positioning the patient on the operating table, we performed preoperative photodocumentation of the patient’s position. Photodocumentation was performed each time from the mounted camera (camera Nikon D3100 Sigma DC) fixed 2 metres over the center of the operating table. The focal length was adjusted to minimize image distortion, and distortion evaluation using a chess calibration image indicated an error of less than 0.3° in pelvic inclination. We have assured that in addition to the patient’s position, we may identify the edge of the operating table. From the photodocumentation, we then measured the angle between the edge of the operating table and the junction of the two ASIS using impage processing sofware ImageJ, version 1.52 (NIH, MD, USA). An anterolateral approach in the supine position was performed in all procedures. Allofit cup and Avenir stem (Zimmer Biomet, Warsaw, IN, USA) were implanted to all patient. The acetabular component anteversion was placed taking into consideration, the orientation of the transverse acetabular ligament (TAL), the version of the femoral component and the combined anteversion value as femoral preparation proceeded that of the acetabulum. The acetabular component inclination was positioned freehand using a recommendation provided by a mechanical guide set by the manufacturer at an inclination/anteversion of 45°/15°. However, the final alignment was determined by the surgeon and not strictly dictated by the guide. For all cases, it was recomended that the intra-operative inclination was 45° (i.e. guide parallel to the edge of the surgery table). Postoperatively, we performed a radiograph of the entire pelvis in supine position and determined the angle of inclination of the acetabular component with respect to the transverse axis of the pelvis (relative to the perpendicular to the sagittal axis of the body) (Fig. 1 A,B). We further evaluated the pelvic inclination using method described in Lewinnek et al, 1978 [ 6 ] and difference in length of legs by measuring the difference in height of the lesser trochanters on the anteroposterior postoperative radiograph between the operated and the non-operated sides as described in Hardwick-Morris, 2022 (Fig. 1 C). Data Analysis We performed a sample size calculation a priori, based upon previously published data on reported cup intraoperative inclinations [ 11 , 15 ], resulting in a minimum cohort size of 41 patients per group ( \(\:\alpha\:\) = 0.05, \(\:1=\beta\:\) = 0.95, difference of 5° in cup inclination). All data were tested for normality using the Shapiro-Wilk test. The distribution of each variable was assessed to determine the suitability of parametric tests for further analysis. Pearson’s correlation coefficient was calculated to evaluate the relationships between pelvic inclinations, cup inclination, and LLD with normal distribution, while Spearman’s rank correlation was applied for variables not meeting the assumption of normality. Differences between groups were analyzed using independent samples t-tests for normally distributed data and the Mann-Whitney U test for data that did not meet the criteria for normality. For comparisons involving more than two groups, one-way ANOVA with post-hoc Tukey’s test was performed on normally distributed data, and the Kruskal-Wallis test was used for non-normally distributed data with Wilcoxon rank sum test. Homogeneity of variance was assessed using Levene’s test to compare the variations in cup inclination and LLD among the groups. Statistical significance was set at \(\:p\) < 0.05 for all analyses, and effect sizes were calculated to supplement the interpretation of significant findings. All analysis were performed in R, version 4.1.2 (R Foundation for Statistical Computing, Vienna, Austria) Results A larger pelvic inclination on the operating table ( \(\:\beta\:\) ) was associated with a smaller acetabular cup angle ( \(\:\varTheta\:\) ), with a strong negative correlation (Pearson’s R = -0.72, 95% CI [0.62, 0.79], p < 0.001). Notably, the achieved cup inclination tended to exceed the theoretical (45°- \(\:\beta\:\) ) angle targeted during implantation (Fig. 2 , Fig. 3 ). Pelvic position on the surgical table ( \(\:\beta\:\) ) had a significant effect on leg length discrepancy (LLD), showing a moderate positive correlation (Spearman’s R = 0.42, 95% CI [0.27, 0.55], p < 0.001). Greater pelvic inclination during surgery was associated with leg elongation on the operated side (Fig. 4 A). Despite deviations in pelvic positioning during surgery, all surgeons — regardless of experience level — achieved an average postoperative cup angle close to the targeted 45°, as measured on postoperative radiographs (Table 2 ). Differences in average cup inclination across surgeons with varying experience levels were negligible (ANOVA, F(2, 132) = 0.37, p = 0.690, 95% CI [0.00, 1.00]). However, more experienced surgeons achieved significantly lower variance in cup placement around the target angle (Fig. 3 B), as indicated by Levene’s test for homogeneity of variance (p < 0.001, F(2, 132) = 8.71). Additionally, surgeons with greater experience achieved significantly lower discrepancies in leg length (Kruskal-Wallis H(2) = 18.7, p < 0.001), as illustrated in Fig. 4 B. Table 2 Summary of measured values (mean and standard deviation) grouped by surgeon’s experience. (β) pelvic inclination measured during patient preparation, (Θ) cup inclination measured postoperatively, (LLD) leg length discrepancy measured posoperatively. Statistical significance p between measured values in different groups obtained from Kruskal-Wallis test (β and LLD) and ANOVA test (Θ). Surgeon experience β (SD) [°] Θ (SD) [°] LLD (SD) [mm] cohort (n = 135) 5.7 (3.6) 45.1 (7.2) 4.1 (3.4) 15 years (n = 45) 5.9(3.3) 44.4 (5.2) 2.7 (3.2) p 0.884 0.690 p < 0.001 Discussion The optimal position of the acetabular component in primary total hip arthroplasties is a crucial factor influencing functional outcomes and implant longevity [ 10 , 19 ]. Although it is generally understood that patient positioning on the surgical table in the supine position can influence the postoperative orientation of the acetabular component, this study provides the objective evidence quantifying its significant impact. While earlier research has primarily addressed intraoperative changes in pelvic position [ 15 , 20 ], this study underscores the importance of preoperative patient positioning. Initial pelvic inclination significantly affects postoperative cup positioning (Fig. 3 A). Surgeons seem able to anticipate this deviation and adjust cup alignment during surgery, deviating from the strict 45° orientation relative to the operating table. This deliberate “misalignment” leads to more accurate postoperative cup positioning (Table 2 ). Grammatopoulos et al. (2018) reported an average cup inclination of 41° with a standard deviation of 6° in the supine position [ 15 ]. Our findings are comparable (Table 2 ), although the absolute achieved cup inclination in our study is slightly lower, likely due to different target zones (40° in Grammatopoulos et al. versus 45° in this study). Additionally, leg length discrepancy (LLD) in our findings, which ranges from − 2 to 18 mm with a mean of 4.1 mm, aligns with previous reports [ 21 ]. Accurate acetabular cup placement is essential not only to prevent dislocation but also to reduce wear. Daniel et al. (2016) found an increase in contact pressure when the cup inclination was above 50°, which applies across different head diameters. Higher contact pressure can increase wear, leading to an elevated risk of implant fatigue fracture [ 22 ]. Experienced surgeons demonstrate greater consistency in both LLD and acetabular inclination (Figs. 3 B, 4 B), with a lower mismatch in leg length than less experienced surgeons (Table 2 ). Variability in less experienced surgeons may stem from concerns about restoration instability. Overall, a tendency toward elongation on the operated side may result from a higher operated joint position relative to the ipsilateral joint, potentially due to patient malpositioning, as indicated by the average positive angle \(\:\beta\:\) in Fig. 2 . In this study, we chose the supine position as it was proposed that the supine position yields more accurate cup placements than the lateral position [ 13 , 14 ]. It has been shown that during THA via a posterolateral approach, the pelvis tends to roll anteriorly during cup insertion, creating a difference between the target and radiographic cup inclinations [ 15 , 19 , 20 ]. Our study design employs a straightforward data collection method that requires minimal additional patient preparation before surgery. Spinopelvic relationships were not directly analyzed, and the final implant position in the standing posture may be more clinically relevant than its position in the supine position [ 18 ]. Additionally, different methodologies for measuring inclination and anteversion may yield varying values, as noted by Murray et al. (1993) [ 23 ]. However, since the study aims to compare THA outcomes between groups and the measurement of cup inclination from anteroposterior radiographs was applied consistently throughout, the assessment method may affect the absolute values of cup inclination and LLD but is unlikely to alter the study’s overall conclusions. Our study did not explicitly account for pelvic rotation and tilt during acetabular cup implantation [ 19 ]. Accurately measuring pelvic tilt during preoperative positioning would require a more complex setup [ 24 ]. Since the cup face is oblique, pelvic tilt can influence the inclination angle. As the pelvis and cup tilt around the medial-lateral axis, the superior radiographic landmark used to measure inclination may shift medially with posterior tilt or laterally with anterior tilt, resulting in variations in the measured acetabular inclination [ 25 ]. Another potential source of variation is the detection of the ASIS using skin markers, which may be affected by skin movement artifacts. These factors contribute to the variability observed in patient data (Figs. 3 and 4 ). The study by Hardwick-Morris et al. (2022) demonstrated that functional leg-length discrepancy may not be accurately estimated from anteroposterior radiographs, as it is also influenced by hip and knee contractures as well as altered spinal mechanics. Therefore, the LLD measured in this study does not represent true leg-length discrepancy but rather the specific contribution of cup positioning during THA to the overall discrepancy. Computer-guided surgery presents an alternative to freehand techniques. Although CT-based navigation is highly accurate, its high cost, invasiveness, and longer operation times have limited its adoption in the clinical practice [ 26 ]. Other options, such as alignment guides, goniometers, and intraoperative radiography, are also available [ 11 , 14 , 18 , 27 , 28 ]. However, even intraoperative fluoroscopic control does not necessarily improve final positioning or limb length accuracy. Bingham et al. reported similar results in X-ray-guided (mean cup inclination of 39.4° with a 1.1 mm LLD) and control groups (mean inclination of 39.9° with a 0.8 mm LLD) [ 29 ]. Ogawa et al. (2018) found no significant difference in radiographic inclination between augmented reality and conventional goniometer techniques but noted more precise anteversion with augmented reality [ 26 ]. Conclusion Although the impact of patient positioning on cup placement accuracy is generally acknowledged, no previous prospective study has specifically examined the link between preoperative patient positioning and acetabular cup orientation. Our findings reveal that most patients are positioned with a medial rotation of the pelvis on the operated side, which significantly affects postoperative acetabular inclination and limb length discrepancy. Additionally, our study demonstrates that increased surgical experience reduces errors related to patient positioning. These results underscore the clinical importance of carefully controlling pelvic alignment prior to sterile draping. By ensuring optimal preoperative pelvic positioning, surgeons can minimize the risk of inaccurate cup placement and unequal limb lengths—key factors that impact implant success. Preoperative assessment of pelvic position is a straightforward procedure that can improve THA accuracy and may reduce the likelihood of revision surgeries related to improper cup positioning. Declarations Ethics approval and consent to participate The study was approved by Ethics committee of the University Hospital Motol and 2nd Faculty of Medicine, Charles University in Prague with reference number EK-673/24. Consent for publication Not applicable Availability of data and materials The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request. Competing interests The authors declare that they have no competing interests Funding Charles University - Cooperatio – Surgical disciplines Authors' contributions PF is responsible for design, data acquisition and analysis and interpretation of data, writing manuscript. DP is responsible for data acquisition and analysis and interpretation of data. DG is responsible for language correction and manuscript review. DJ is responsible for responsible for data acquisition, data analysis. DJ is responsible for analysis and interpretation of data and manuscript review. MD is responsible for analysis and interpretation of data, statistical analysis, figure creation and manuscript writing. Acknowledgments Not applicable References Seagrave K, Troelsen A, Malchau H, Husted H, Gromov K. Acetabular cup position and risk of dislocation in primary total hip arthroplasty: A systematic review of the literature. Acta Orthop. 2016;88:1–8. https://doi.org/10.1080/17453674.2016.1251255 . Ramkumar PN, Pang M, Vigdorchik JM, Chen AF, Iorio R, Lange JK. Patient-Specific Safe Zones for Acetabular Component Positioning in Total Hip Arthroplasty: Mathematically Accounting for Spinopelvic Biomechanics. J Arthroplast. 2023;38:1779–86. https://doi.org/10.1016/j.arth.2023.03.025 . Daniel M, Rijavec B, Dolinar D, Pokorný D, Iglič A, Kralj-Iglič V. 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Patient positioning during the radiographic procedure affects the radiological signs of acetabular retroversion - A systematic review. J Clin Imaging Sci. 2023;13:34. https://doi.org/10.25259/JCIS_82_2023 . Ogawa H, Hasegawa S, Tsukada S, Matsubara M. A Pilot Study of Augmented Reality Technology Applied to the Acetabular Cup Placement During Total Hip Arthroplasty. J Arthroplast. 2018;33:1833–7. https://doi.org/10.1016/j.arth.2018.01.067 . Rutherford M, O’Connor JD, Hill JC, Beverland DE, Lennon AB, Dunne NJ. Patient positioning and cup orientation during total hip arthroplasty: Assessment of current UK practice. HIP Int. 2019;29:89–95. https://doi.org/10.1177/1120700018760818 . Cruz J, Gonçalves SB, Neves MC, Silva HP, Silva MT. Intraoperative Angle Measurement of Anatomical Structures: A Systematic Review. Sensors. 2024;24:1613. https://doi.org/10.3390/s24051613 . Bingham JS, Spangehl MJ, Hines JT, Taunton MJ, Schwartz AJ. Does Intraoperative Fluoroscopy Improve Limb-Length Discrepancy and Acetabular Component Positioning During Direct Anterior Total Hip Arthroplasty? J Arthroplast. 2018;33:2927–31. https://doi.org/10.1016/j.arth.2018.05.004 . Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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-6347220","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":445815160,"identity":"b0cd56c3-0135-4757-ae53-6a466fb476d6","order_by":0,"name":"Petr Fulin","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2ElEQVRIiWNgGAWjYLCCCgYLHgb2BiDLwIIY9cwMDGcYJHgYeA6AtEgQr4WBQSIBxCNCizl7/7EPB9skZMwln1/d8KNAgoG/vTsBrxbLnsPMM4BaeCxn55Td7AE6TOLM2Q14tRjcSGZm/gjUYnA7J+0GD1CLgUQuAS33HzMzgGwxuHkm7eYforTcYIZqucF+7DZRtlj2JBszHDgH1HImh+22jIEED0G/mLMffMxwoMzG3uD48Wc33/yxkeNv7yXgMASTB8zmwascTQv7A4KqR8EoGAWjYGQCAI4SRIuAm6PHAAAAAElFTkSuQmCC","orcid":"","institution":"1st Orthopedic Clinic, First Faculty of Medicine, Charles University, University Hospital Motol","correspondingAuthor":true,"prefix":"","firstName":"Petr","middleName":"","lastName":"Fulin","suffix":""},{"id":445815161,"identity":"e4c72a25-97a7-4577-8de5-aa756da32d97","order_by":1,"name":"David Pokorny","email":"","orcid":"","institution":"1st Orthopedic Clinic, First Faculty of Medicine, Charles University, University Hospital Motol","correspondingAuthor":false,"prefix":"","firstName":"David","middleName":"","lastName":"Pokorny","suffix":""},{"id":445815162,"identity":"6fff22b3-f99a-489c-aed4-1cd1158b1d9f","order_by":2,"name":"Dariusz Grzelecki","email":"","orcid":"","institution":"Department of Orthopedics and Rheumoorthopedics, Centre of Postgraduate Medical Education, Prof. Adam Gruca Orthopedic and Trauma Teaching Hospital","correspondingAuthor":false,"prefix":"","firstName":"Dariusz","middleName":"","lastName":"Grzelecki","suffix":""},{"id":445815163,"identity":"1487151d-c76f-48d0-aee3-96f17fe5e47e","order_by":3,"name":"David Jonas","email":"","orcid":"","institution":"1st Orthopedic Clinic, First Faculty of Medicine, Charles University, University Hospital Motol","correspondingAuthor":false,"prefix":"","firstName":"David","middleName":"","lastName":"Jonas","suffix":""},{"id":445815166,"identity":"1b00d96b-dccc-4032-9f59-7bea0c4be43c","order_by":4,"name":"David Jahoda","email":"","orcid":"","institution":"1st Orthopedic Clinic, First Faculty of Medicine, Charles University, University Hospital Motol","correspondingAuthor":false,"prefix":"","firstName":"David","middleName":"","lastName":"Jahoda","suffix":""},{"id":445815167,"identity":"5a3a1e4b-2fd6-4741-a671-9a9329e5227d","order_by":5,"name":"Matej Daniel","email":"","orcid":"","institution":"Department of Mechanics, Biomechanics and Mechatronics, Faculty of Mechanical Engineering, Czech Technical University","correspondingAuthor":false,"prefix":"","firstName":"Matej","middleName":"","lastName":"Daniel","suffix":""}],"badges":[],"createdAt":"2025-03-31 18:23:14","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6347220/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6347220/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":82145300,"identity":"5eb46d6c-30dd-4352-9d05-c40be1350eb7","added_by":"auto","created_at":"2025-05-07 06:52:25","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":204198,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Schematic view of patient positioning on surgical table and implantation using edge of surgical table as guide. (B) Measurement of pelvic inclination β . (C) Measurement of cup inclination Θ and leg length discrepancy (LLD).\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6347220/v1/162eede364eea99aab835738.png"},{"id":82145290,"identity":"afb22c21-fb0c-4cbb-87a4-81c5a16a5a77","added_by":"auto","created_at":"2025-05-07 06:52:25","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":92628,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic representation of the mechanism by which cup inclination set to external frame during surgery \u003cem\u003eα\u003c/em\u003e and pelvic inclination \u003cem\u003eβ\u003c/em\u003e affect the cup inclination \u003cem\u003eθ\u003c/em\u003e.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6347220/v1/35b88a8089dbffdf43cdd3a8.png"},{"id":82145291,"identity":"8bb560ab-af6e-46e7-b110-cda59353b9d2","added_by":"auto","created_at":"2025-05-07 06:52:25","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":45148,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Pelvic inclination during surgery β and its impact on acetabular cup inclination Θ. The solid line represents the linear fit, with shaded regions indicating the 95% confidence intervals. The dashed line illustrates the theoretical dependency (45°- β), assuming an optimal acetabular cup inclination of 45° achieved during surgery as depicted on Fig. 2. (B) Boxplots showing acetabular cup inclination, categorized by the surgeon’s experience level. The shape of individual points represents the level of surgeon experience in both graphs.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6347220/v1/20046d393ce87ad396000d0a.png"},{"id":82147318,"identity":"4e59aa61-1c6e-4011-9934-3e23e4be4eb2","added_by":"auto","created_at":"2025-05-07 07:00:25","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":40466,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Relationship between postoperative leg length discrepancy (LLD), measured from radiographs, and pelvic inclination during surgery (β). The solid line represents the linear fit, with shaded regions indicating the 95% confidence intervals. (B) Boxplots showing the distribution of measured LLD values, categorized by surgeon experience level. Statistically significant differences between groups obtained from Kruskal-Wallis test are indicated as follows: p \u0026lt; 0.05, ** p \u0026lt; 0.001. The shape of individual points represents the level of surgeon experience in both graphs.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6347220/v1/fcd374f79874f52b9148d89d.png"},{"id":82391149,"identity":"099cb6e7-e7c8-48f8-b643-27fcd2573e11","added_by":"auto","created_at":"2025-05-09 18:16:33","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":962592,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6347220/v1/0896b486-10a0-42ab-ace4-129a2b65cd4b.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Patient preoperative positioning for THA affects postoperative acetabular cup angle and leg length discrepancy - a prospective case series","fulltext":[{"header":"Introduction","content":"\u003cp\u003eProper orientation of the acetabular component is critical in total hip arthroplasty (THA) to preserve the patient\u0026rsquo;s range of motion and reduce the risk of dislocation [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Misalignment of the acetabular cup can lead to impingement [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], increased wear [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], and edge loading [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], which can in turn result in osteolysis and aseptic loosening [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTraditionally, cup positioning has been guided by the \"safe zone\" concept introduced by Lewinnek et al. in 1978, derived from an analysis of 300 THAs [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. This study suggested an optimal positioning range of 30\u0026deg; to 50\u0026deg; inclination and 5\u0026deg; to 25\u0026deg; anteversion, with cups outside this zone exhibiting a fourfold increase in dislocation risk [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. However, recent studies question the predictive accuracy of Lewinnek\u0026rsquo;s safe zone, particularly as it does not account for functional spine-pelvis-hip motion, which can influence postoperative outcomes [\u003cspan additionalcitationids=\"CR8 CR9\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Nevertheless, this standard remains widely used in preoperative planning [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] and these target angles are even endorsed by implant manufacturers and integrated into surgical guides for accurate positioning [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePatient positioning on the operating table is widely recognized as a key factor for ensuring stable pelvis orientation during surgery [\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Ideally, if the pelvis maintains the same tilt, obliquity, and rotation relative to the operating table as it will postoperatively, this would optimize cup placement accuracy [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. However, radiographic comparisons between intraoperative and postoperative positioning have not confirmed this assumption [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn practice, the surgeon is often unable to follow the sagittal plane of the body or the position of the patient\u0026rsquo;s pelvis due to the patient\u0026rsquo;s sterile draping. The surgeon orients the implantation of the acetabular component according to the edge of the operating table (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA), which sets the resulting inclination of the acetabular component [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. In doing so, the patient is very often positioned on the edge of the operating table for better access to the hip joint with tilted pelvis. This can lead to inaccurate implantation of the acetabular component and also to incorrect determination of the length of the lower limbs within the patient\u0026rsquo;s malposition on the operating table (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Although the importance of proper cup positioning and the factors influencing it are well acknowledged and extensively discussed in the literature [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], the specific impact of patient positioning on the operating table during preoperative preparation on the accuracy of acetabular cup placement in non-navigated THA has not been objectively proven or quantified. Despite its presumed significance, no studies have systematically investigated this relationship and we do not know the extent to which patient positioning influences acetabular cup placement accuracy.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe objective of this study was to photographically record and measure pelvic inclination angles on the operating table in the supine position during preoperative preparation, comparing these to radiographic inclination angles on postoperative anteroposterior radiographs. Our study aimed to address the following questions: (1) What is the relationship between preoperative patient positioning, acetabular cup orientation, and leg length discrepancy (LLD)? (2) Is there a difference in cup placement accuracy between experienced and early-career surgeons? We hypothesized that patient positioning on the operating table would influence postoperative cup positioning, but that experienced surgeons would be better able to compensate for this effect.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e This prospective, multi-surgeon, consecutive case series from a single tertiary centre had ethical approval. The study was conducted according to the Helsinki Declaration of 2008 and all patients gave informed consent.\u003c/p\u003e \u003cp\u003eWe included a total of 135 patients indicated for total hip arthroplasty implantation (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Only patients with a diagnosis of osteoarthritis or osteoarthritis on the basis of rheumatoid arthritis were included in the study. Only patients with a maximum variation in hip length difference of less than 1cm (LLD\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\le\\:\\)\u003c/span\u003e\u003c/span\u003e1cm) were included. The number of women in the cohort was 69 and the number of men was 66. The mean age at the time of surgery was 68.7 years (range 45\u0026ndash;78 years). Patients were classified into 3 groups according to the experience of the surgeon. The first group of 45 THAs consisted of patients operated on by early carrier surgeon (less than 5 years of clinical experience). In the second group (45 THAs), the length of clinical experience of the surgeon was 5\u0026ndash;15 years, while the third group (45 THAs) consists of surgeon with more than 15 years of experience.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePatient demographics and surgical details\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTotal\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSurgeon\u003c/p\u003e \u003cp\u003eexperience\u0026thinsp;\u0026lt;\u0026thinsp;5 years\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSurgeon experience 5\u0026ndash;15 years\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSurgeon experience\u0026thinsp;\u0026gt;\u0026thinsp;15 years\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMean age, yrs (SD)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e68.7 (10.6)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e69,1 (9,8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e68,8 (11,3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e68,2 (10,7)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMean height, m (SD)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.75 (0.1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1,75 (0,1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1,76 (0,1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1,74 (0,2)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMean weight, kg (SD)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e80.8 (13.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e79,1 (10,1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e80,5 (14,2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e82,8 (15,6)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMean BMI, kg/m\u003csup\u003e2\u003c/sup\u003e (SD)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e26.4 (3.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26,1 (3,0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e26,6 (3,4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e26,5 (3,2)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003eGender, n (%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e66 (48,9%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e23 (51,1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e22 (48,9%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e21 (46,7%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFemale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e69 (51,1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e22 (48,9%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e23 (51,1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e24 (53,3%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003eSide, n (%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLeft\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e65 (48%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e21 (46,7%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e21 (46,7%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e22 (48,9%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRight\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e70 (52%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e24 (53,3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e24 (53,3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e23 (51,1%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAll surgeries were performed as non-navigated THA with preoperative planning based on standard supine anteroposterior radiographs. An optimal cup inclination in preoperative planning was based on reccomendation of the producer, 45\u0026deg; degrees to the sagital plane of the body. All cases were positioned in the supine position and as close as possible to the edge of the table with the aim of operated pelvis in neutral position.\u003c/p\u003e \u003cp\u003eFor each patient, we identified anterior superior iliac spines (ASIS) by palpation and marked them bilaterally with a marker before surgery after the patient was positioned. After positioning the patient on the operating table, we performed preoperative photodocumentation of the patient\u0026rsquo;s position. Photodocumentation was performed each time from the mounted camera (camera Nikon D3100 Sigma DC) fixed 2 metres over the center of the operating table. The focal length was adjusted to minimize image distortion, and distortion evaluation using a chess calibration image indicated an error of less than 0.3\u0026deg; in pelvic inclination. We have assured that in addition to the patient\u0026rsquo;s position, we may identify the edge of the operating table. From the photodocumentation, we then measured the angle between the edge of the operating table and the junction of the two ASIS using impage processing sofware ImageJ, version 1.52 (NIH, MD, USA).\u003c/p\u003e \u003cp\u003eAn anterolateral approach in the supine position was performed in all procedures. Allofit cup and Avenir stem (Zimmer Biomet, Warsaw, IN, USA) were implanted to all patient. The acetabular component anteversion was placed taking into consideration, the orientation of the transverse acetabular ligament (TAL), the version of the femoral component and the combined anteversion value as femoral preparation proceeded that of the acetabulum. The acetabular component inclination was positioned freehand using a recommendation provided by a mechanical guide set by the manufacturer at an inclination/anteversion of 45\u0026deg;/15\u0026deg;. However, the final alignment was determined by the surgeon and not strictly dictated by the guide. For all cases, it was recomended that the intra-operative inclination was 45\u0026deg; (i.e. guide parallel to the edge of the surgery table).\u003c/p\u003e \u003cp\u003ePostoperatively, we performed a radiograph of the entire pelvis in supine position and determined the angle of inclination of the acetabular component with respect to the transverse axis of the pelvis (relative to the perpendicular to the sagittal axis of the body) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA,B). We further evaluated the pelvic inclination using method described in Lewinnek et al, 1978 [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] and difference in length of legs by measuring the difference in height of the lesser trochanters on the anteroposterior postoperative radiograph between the operated and the non-operated sides as described in Hardwick-Morris, 2022 (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC).\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eData Analysis\u003c/h2\u003e \u003cp\u003eWe performed a sample size calculation a priori, based upon previously published data on reported cup intraoperative inclinations [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], resulting in a minimum cohort size of 41 patients per group (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\alpha\\:\\)\u003c/span\u003e\u003c/span\u003e = 0.05, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:1=\\beta\\:\\)\u003c/span\u003e\u003c/span\u003e = 0.95, difference of 5\u0026deg; in cup inclination). All data were tested for normality using the Shapiro-Wilk test. The distribution of each variable was assessed to determine the suitability of parametric tests for further analysis. Pearson\u0026rsquo;s correlation coefficient was calculated to evaluate the relationships between pelvic inclinations, cup inclination, and LLD with normal distribution, while Spearman\u0026rsquo;s rank correlation was applied for variables not meeting the assumption of normality.\u003c/p\u003e \u003cp\u003eDifferences between groups were analyzed using independent samples t-tests for normally distributed data and the Mann-Whitney U test for data that did not meet the criteria for normality. For comparisons involving more than two groups, one-way ANOVA with post-hoc Tukey\u0026rsquo;s test was performed on normally distributed data, and the Kruskal-Wallis test was used for non-normally distributed data with Wilcoxon rank sum test. Homogeneity of variance was assessed using Levene\u0026rsquo;s test to compare the variations in cup inclination and LLD among the groups. Statistical significance was set at \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:p\\)\u003c/span\u003e\u003c/span\u003e \u0026lt; 0.05 for all analyses, and effect sizes were calculated to supplement the interpretation of significant findings. All analysis were performed in R, version 4.1.2 (R Foundation for Statistical Computing, Vienna, Austria)\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eA larger pelvic inclination on the operating table (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\beta\\:\\)\u003c/span\u003e\u003c/span\u003e) was associated with a smaller acetabular cup angle (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varTheta\\:\\)\u003c/span\u003e\u003c/span\u003e), with a strong negative correlation (Pearson\u0026rsquo;s R = -0.72, 95% CI [0.62, 0.79], p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Notably, the achieved cup inclination tended to exceed the theoretical (45\u0026deg;-\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\beta\\:\\)\u003c/span\u003e\u003c/span\u003e) angle targeted during implantation (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Pelvic position on the surgical table (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\beta\\:\\)\u003c/span\u003e\u003c/span\u003e) had a significant effect on leg length discrepancy (LLD), showing a moderate positive correlation (Spearman\u0026rsquo;s R\u0026thinsp;=\u0026thinsp;0.42, 95% CI [0.27, 0.55], p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Greater pelvic inclination during surgery was associated with leg elongation on the operated side (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDespite deviations in pelvic positioning during surgery, all surgeons \u0026mdash; regardless of experience level \u0026mdash; achieved an average postoperative cup angle close to the targeted 45\u0026deg;, as measured on postoperative radiographs (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Differences in average cup inclination across surgeons with varying experience levels were negligible (ANOVA, F(2, 132)\u0026thinsp;=\u0026thinsp;0.37, p\u0026thinsp;=\u0026thinsp;0.690, 95% CI [0.00, 1.00]). However, more experienced surgeons achieved significantly lower variance in cup placement around the target angle (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB), as indicated by Levene\u0026rsquo;s test for homogeneity of variance (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, F(2, 132)\u0026thinsp;=\u0026thinsp;8.71). Additionally, surgeons with greater experience achieved significantly lower discrepancies in leg length (Kruskal-Wallis H(2)\u0026thinsp;=\u0026thinsp;18.7, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSummary of measured values (mean and standard deviation) grouped by surgeon\u0026rsquo;s experience. (β) pelvic inclination measured during patient preparation, (Θ) cup inclination measured postoperatively, (LLD) leg length discrepancy measured posoperatively. Statistical significance p between measured values in different groups obtained from Kruskal-Wallis test (β and LLD) and ANOVA test (Θ).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSurgeon experience\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eβ\u003c/em\u003e (SD) [\u0026deg;]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eΘ\u003c/em\u003e (SD) [\u0026deg;]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLLD (SD) [mm]\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ecohort (n\u0026thinsp;=\u0026thinsp;135)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.7 (3.6)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e45.1 (7.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.1 (3.4)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;5 years (n\u0026thinsp;=\u0026thinsp;45)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.6 (3.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e45.2 (8.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5.5 (3.3)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u0026ndash;10 years (n\u0026thinsp;=\u0026thinsp;45)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.4 (3.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e45.7 (7.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.1 (3.3)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u0026gt;\u0026thinsp;15 years (n\u0026thinsp;=\u0026thinsp;45)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.9(3.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e44.4 (5.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.7 (3.2)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003ep\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.884\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.690\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe optimal position of the acetabular component in primary total hip arthroplasties is a crucial factor influencing functional outcomes and implant longevity [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Although it is generally understood that patient positioning on the surgical table in the supine position can influence the postoperative orientation of the acetabular component, this study provides the objective evidence quantifying its significant impact.\u003c/p\u003e \u003cp\u003eWhile earlier research has primarily addressed intraoperative changes in pelvic position [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], this study underscores the importance of preoperative patient positioning. Initial pelvic inclination significantly affects postoperative cup positioning (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). Surgeons seem able to anticipate this deviation and adjust cup alignment during surgery, deviating from the strict 45\u0026deg; orientation relative to the operating table. This deliberate \u0026ldquo;misalignment\u0026rdquo; leads to more accurate postoperative cup positioning (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Grammatopoulos et al. (2018) reported an average cup inclination of 41\u0026deg; with a standard deviation of 6\u0026deg; in the supine position [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Our findings are comparable (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), although the absolute achieved cup inclination in our study is slightly lower, likely due to different target zones (40\u0026deg; in Grammatopoulos et al. versus 45\u0026deg; in this study). Additionally, leg length discrepancy (LLD) in our findings, which ranges from \u0026minus;\u0026thinsp;2 to 18 mm with a mean of 4.1 mm, aligns with previous reports [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Accurate acetabular cup placement is essential not only to prevent dislocation but also to reduce wear. Daniel et al. (2016) found an increase in contact pressure when the cup inclination was above 50\u0026deg;, which applies across different head diameters. Higher contact pressure can increase wear, leading to an elevated risk of implant fatigue fracture [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eExperienced surgeons demonstrate greater consistency in both LLD and acetabular inclination (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB), with a lower mismatch in leg length than less experienced surgeons (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Variability in less experienced surgeons may stem from concerns about restoration instability. Overall, a tendency toward elongation on the operated side may result from a higher operated joint position relative to the ipsilateral joint, potentially due to patient malpositioning, as indicated by the average positive angle \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\beta\\:\\)\u003c/span\u003e\u003c/span\u003e in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eIn this study, we chose the supine position as it was proposed that the supine position yields more accurate cup placements than the lateral position [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. It has been shown that during THA via a posterolateral approach, the pelvis tends to roll anteriorly during cup insertion, creating a difference between the target and radiographic cup inclinations [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOur study design employs a straightforward data collection method that requires minimal additional patient preparation before surgery. Spinopelvic relationships were not directly analyzed, and the final implant position in the standing posture may be more clinically relevant than its position in the supine position [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Additionally, different methodologies for measuring inclination and anteversion may yield varying values, as noted by Murray et al. (1993) [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. However, since the study aims to compare THA outcomes between groups and the measurement of cup inclination from anteroposterior radiographs was applied consistently throughout, the assessment method may affect the absolute values of cup inclination and LLD but is unlikely to alter the study\u0026rsquo;s overall conclusions.\u003c/p\u003e \u003cp\u003eOur study did not explicitly account for pelvic rotation and tilt during acetabular cup implantation [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Accurately measuring pelvic tilt during preoperative positioning would require a more complex setup [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Since the cup face is oblique, pelvic tilt can influence the inclination angle. As the pelvis and cup tilt around the medial-lateral axis, the superior radiographic landmark used to measure inclination may shift medially with posterior tilt or laterally with anterior tilt, resulting in variations in the measured acetabular inclination [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Another potential source of variation is the detection of the ASIS using skin markers, which may be affected by skin movement artifacts. These factors contribute to the variability observed in patient data (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe study by Hardwick-Morris et al. (2022) demonstrated that functional leg-length discrepancy may not be accurately estimated from anteroposterior radiographs, as it is also influenced by hip and knee contractures as well as altered spinal mechanics. Therefore, the LLD measured in this study does not represent true leg-length discrepancy but rather the specific contribution of cup positioning during THA to the overall discrepancy.\u003c/p\u003e \u003cp\u003eComputer-guided surgery presents an alternative to freehand techniques. Although CT-based navigation is highly accurate, its high cost, invasiveness, and longer operation times have limited its adoption in the clinical practice [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Other options, such as alignment guides, goniometers, and intraoperative radiography, are also available [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. However, even intraoperative fluoroscopic control does not necessarily improve final positioning or limb length accuracy. Bingham et al. reported similar results in X-ray-guided (mean cup inclination of 39.4\u0026deg; with a 1.1 mm LLD) and control groups (mean inclination of 39.9\u0026deg; with a 0.8 mm LLD) [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Ogawa et al. (2018) found no significant difference in radiographic inclination between augmented reality and conventional goniometer techniques but noted more precise anteversion with augmented reality [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eAlthough the impact of patient positioning on cup placement accuracy is generally acknowledged, no previous prospective study has specifically examined the link between preoperative patient positioning and acetabular cup orientation. Our findings reveal that most patients are positioned with a medial rotation of the pelvis on the operated side, which significantly affects postoperative acetabular inclination and limb length discrepancy. Additionally, our study demonstrates that increased surgical experience reduces errors related to patient positioning. These results underscore the clinical importance of carefully controlling pelvic alignment prior to sterile draping. By ensuring optimal preoperative pelvic positioning, surgeons can minimize the risk of inaccurate cup placement and unequal limb lengths\u0026mdash;key factors that impact implant success. Preoperative assessment of pelvic position is a straightforward procedure that can improve THA accuracy and may reduce the likelihood of revision surgeries related to improper cup positioning.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study was approved by Ethics committee of the University Hospital Motol and 2nd Faculty of Medicine, Charles University in Prague with reference number EK-673/24.\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\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCharles University - Cooperatio \u0026ndash; Surgical disciplines\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePF is\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eresponsible for design, data acquisition and analysis and interpretation of data, writing manuscript. DP is responsible for data acquisition and analysis and interpretation of data. DG is responsible for language correction and manuscript review. DJ is responsible for responsible for data acquisition, data analysis. DJ is responsible for analysis and interpretation of data and manuscript review. MD is responsible for analysis and interpretation of data, statistical analysis, figure creation and manuscript writing.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eSeagrave K, Troelsen A, Malchau H, Husted H, Gromov K. Acetabular cup position and risk of dislocation in primary total hip arthroplasty: A systematic review of the literature. 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Does Intraoperative Fluoroscopy Improve Limb-Length Discrepancy and Acetabular Component Positioning During Direct Anterior Total Hip Arthroplasty? J Arthroplast. 2018;33:2927\u0026ndash;31. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.arth.2018.05.004\u003c/span\u003e\u003cspan address=\"10.1016/j.arth.2018.05.004\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Acetabular cup orientation, Preoperative patient positioning, Surgeon experience, Leg length discrepancy","lastPublishedDoi":"10.21203/rs.3.rs-6347220/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6347220/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eProper orientation of the acetabular cup in total hip arthroplasty (THA) is essential to reduce dislocation risk, improve range of motion, and enhance implant longevity. Misalignment can lead to complications such as impingement, wear, and aseptic loosening. Patient positioning on the operating table is a critical yet often overlooked factor influencing pelvic tilt and cup placement accuracy during THA. This study evaluates the impact of preoperative patient positioning on acetabular component placement and explores whether surgeon experience affects cup placement precision.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eIn this prospective case series, 135 patients undergoing non-navigated THA in the supine position at a single tertiary center were included. Preoperative photographs captured pelvic inclination, which was compared to postoperative cup orientation measured on radiographs. Patients were divided into three groups based on surgeon experience (\u0026lt;\u0026thinsp;5 years, 5\u0026ndash;15 years, \u0026gt;\u0026thinsp;15 years). Statistical analyses assessed relationships among patient positioning, cup orientation, leg length discrepancy, and surgeon experience.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eGreater pelvic inclination measured before sterile draping was significantly associated with a smaller acetabular cup angle (Pearson\u0026rsquo;s R = -0.72, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Surgeons with \u0026gt;\u0026thinsp;15 years of experience demonstrated less variability in cup orientation and leg length discrepancy than those with fewer years of experience (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Despite variations in pelvic positioning, the overall postoperative cup angle was consistent across groups.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003ePreoperative patient positioning significantly impacts acetabular cup orientation, with more experienced surgeons better able to compensate for these deviations. Positioning protocols and surgeon training on pelvic orientation may enhance THA outcomes, particularly for early-career surgeons.\u003c/p\u003e","manuscriptTitle":"Patient preoperative positioning for THA affects postoperative acetabular cup angle and leg length discrepancy - a prospective case series","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-07 06:52:20","doi":"10.21203/rs.3.rs-6347220/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"85f77587-bdc3-4bda-8a18-1097280a2ebc","owner":[],"postedDate":"May 7th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-07-06T21:23:13+00:00","versionOfRecord":[],"versionCreatedAt":"2025-05-07 06:52:20","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6347220","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6347220","identity":"rs-6347220","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}