Comparison of cup placement angles accuracy of total hip arthroplasty using the Augmented Reality hip navigation system in supine and lateral positions

Comparison of cup placement angles accuracy of total hip arthroplasty using the Augmented Reality hip navigation system in supine and lateral positions | 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 Comparison of cup placement angles accuracy of total hip arthroplasty using the Augmented Reality hip navigation system in supine and lateral positions Kohei Motono, Shinya Hayashi, Tomoyuki Kamenaga, Masanori Tsubosaka, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7664849/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 Introduction: We aimed to compare the accuracy of acetabular cup positioning angles between supine and lateral total hip arthroplasty (THA) using an augmented reality hip navigation system (AR Hip) and identify predictive risk factors for cup placement angles in lateral THA. Materials and Methods This study included 139 THA procedures performed using the AR Hip between June 2021 and July 2024 (mean age 66.1 years, 25 males, 114 females). To match the patient backgrounds between the groups, propensity score matching (PSM) was performed using sex, age, height, weight, and Crowe classification as covariates. The absolute error in the difference between the intraoperative navigation records and postoperative measurements using computed tomography data was evaluated between the supine and lateral positions. Additionally, we conducted a multivariate analysis to identify preoperative clinical factors associated with positioning errors ≥ 5° in the lateral position. Results In the supine group after PSM, the average absolute errors were 2.9° for both inclination and anteversion. In the lateral position group, the mean absolute errors were 2.2° and 1.9 °for inclination and anteversion, respectively. No significant difference was observed between the two groups in terms of average absolute error. Additionally, multiple regression analysis revealed that pelvic tilt (odds ratio 0.8; 95% confidence interval 0.69–0.98; p = 0.03) was a predictive factor for inaccuracy of cup placement angle. Conclusions When using the AR Hip, no significant cup positioning accuracy difference was noted between supine and lateral THA. In cases of severe preoperative pelvic posterior tilt, cup positioning accuracy may be adversely affected. Total hip arthroplasty cup positioning augmented reality navigation propensity score matching pelvic tilt Figures Figure 1 Background Accurate cup positioning during total hip arthroplasty (THA) crucially affects hip stability and long-term prognosis. Conventional freehand cup positioning is particularly prone to error in the lateral position, with 27.8% of 834 cases deviating from the safe zone, and only 57% reported accuracy within ± 5° [ 1 ]. Portable navigation systems may overcome these issues; in fact, they have been proven to improve the cup placement angles [ 2 – 3 ]. Portable navigation systems can register the pelvic functional plane (FPP) intraoperatively and have been reported to provide good positioning angles during supine surgery [ 4 ]. Moreover, accelerated and augmented reality navigation systems have demonstrated better results in cup-positioning angles compared to conventional freehand techniques in the supine position [ 5 – 6 ]. Several reports have described the use of a portable navigation system in lateral-position THA. Ozaki et al. reported that, with the augmented reality navigation system (AR Hip; Zimmer Biomet Japan, Tokyo, Japan), the absolute error between the cup placement position displayed on the intraoperative AR Hip and that measured on postoperative computed tomography (CT) was comparable for supine or lateral THA [ 7 ]. Similarly, Oyama et al. found no significant difference in the absolute error of the cup placement angle between the two groups when comparing the use of a portable navigation system in THA performed in the supine or lateral decubitus positions [ 8 ]. Conversely, Naito et al. conducted a study comparing cases in which both registration and THA with a portable navigation system were performed in the lateral position with cases in which registration and THA were performed in the supine and lateral positions, respectively, and reported that the absolute error in cup placement was greater in the former than in the latter [ 9 ]. To date, several comparative studies have been conducted on cup placement using navigation systems in supine and lateral positions; nonetheless, their results remain controversial. Therefore, we aimed to compare the accuracy of acetabular cup positioning between supine and lateral THA using the AR Hip while accounting for differences in patient characteristics through propensity score matching (PSM), which was implemented to ensure greater accuracy of the study findings. Additionally, we evaluated the factors associated with cup malpositioning in the lateral position when the AR Hip was used as a secondary outcome. Patients and Methods Patients In this retrospective cohort study, data were obtained from medical records and radiographic databases at our institution. From an initial cohort of 147 hips treated from June 2021 to July 2024, 8 were excluded based on the exclusion criteria, leaving 92 and 47 hips in the supine and lateral groups, respectively. Overall, 139 hips of 129 patients underwent THA with an AR Hip and a cementless G7 cup. All patients were diagnosed with osteoarthritis (grade 3 or 4 according to the Tönnis classification system) [ 10 ] or avascular necrosis of the femoral head (stages 4, 5, or 6 according to Steinberg staging of avascular necrosis). The demographic characteristics of the patients are summarized in Table 1 and Fig. 1 . Preoperative plan A preoperative CT scan was obtained with a slice thickness of 1 mm from the iliac wing to the femoral condyle to evaluate pelvic orientation and femoral morphology. Data were transferred to three-dimensional (3D) template software (Zed Hip; Lexi, Tokyo, Japan) for preoperative templating, enabling visualization and simulation of the acetabular cup position and allowing accurate determination of the optimal cup size, orientation, and placement in 3D. The target cup inclination and anteversion were typically set at 40° and 20° with respect to the FPP, respectively [ 11 ]. Registration In the supine position, two anatomical bony landmarks were registered: the left and right anterior superior iliac spines. The navigation system automatically determined the gravity vector using the gyro sensor of a smartphone [ 6 ]. Threaded pins were inserted parallel to the iliac crest, and a QR code marker plate was mounted on them. The cup inclination and anteversion angles were calculated and displayed on a smartphone screen using real-time image analysis from the smartphone camera [ 5 ]. During THA performed in the lateral position, the flip technique was applied, which involves registering landmarks in the supine position before repositioning the patient laterally [ 12 ]. All procedures were performed by a single experienced orthopedic surgeon. Postoperative evaluation One week after surgery, CT from the iliac to the femoral condyle was performed, and the data were transferred to the zed hip. The cup inclination and anteversion, positioned relative to the FFP, were measured. The primary endpoint of this study was the absolute difference between the intraoperatively recorded cup angles and those measured on postoperative CT, as assessed by the zed hip, in both the supine and lateral positions. As a secondary endpoint, preoperative clinical factors associated with poor cup positioning in the lateral position group were investigated. Statistics All data are expressed as mean ± standard deviation unless otherwise indicated. The 92 and 47 hips operated on in the supine and lateral positions, respectively, were divided into two groups. To adjust for potential confounding factors, PSM was performed between supine and lateral positions. Four baseline variables (sex, age, height, weight, and Crowe classification) were included in the propensity score model. A 1:1 matched cohort (cases:controls) was created using the nearest neighbor method without replacement by applying a caliper width = 0.2 of the standard deviation of the logit of the propensity score, as recommended by Rosenbaum and Rubin [ 13 ]. The two groups were balanced with respect to these background characteristics, resulting in 52 patients in each group for the final analysis. The demographic data after PSM are presented in Table 2. Differences in cup angles between intraoperative and postoperative CT measurements were analyzed using a paired t-test. The outliers in accurate acetabular cup placement were defined as an absolute difference in inclination or anteversion ≥ 5° [ 14 – 16 ]. To identify predictors of outliers of postoperative cup position abnormalities in THA in the lateral position using the AR Hip, outliers and nonoutliers were compared using Fisher's exact test for the degree of progression of osteoarthritis (Crowe classification) and the unpaired t-test for continuous variables. Additionally, a multiple regression analysis examined the association between age, body mass index (BMI), pelvic tilt, and cup placement outliers. The database was analyzed using EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan), and a p-value < 0.05 was considered statistically significant. Ethics This study complied with the Declaration of Helsinki, and the research protocol was approved by the Ethics Committee of No.1220. Informed consent was obtained from all participants. Results Primary outcomes In the supine group, the mean intraoperative inclination and anteversion relative to the FPP were 39.2 ± 2.9° (range, 29.9–43.2°) and 19.7 ± 3.1° (range, 11.2–24°), respectively. The mean postoperative CT-based inclination and anteversion were 39.7 ± 3.4° (range, 31.3–45.9°) and 19.7 ± 4.3° (range, 10–26.9°), respectively. The mean absolute errors between intraoperatively measured angles and the target angles, as determined by postoperative CT, were 2.9 ± 1.8° (range, 0.1–7.4°) and 2.9 ± 3.2° (range, 0.1–13.6°) for inclination and anteversion, respectively. In the lateral group, the mean intraoperative inclination and anteversion relative to the FPP were 39.2 ± 2.1° (range, 35.3–42.9°) and 21.2 ± 3.9° (range, 14.5–31.3°), respectively. The mean postoperative CT-based inclination and anteversion were 41.4 ± 3.7° (range, 36.9–56.4°) and 20.5 ± 3.3° (range, 14.5–27.8°), respectively. The mean absolute errors in the intraoperatively measured angles relative to the target angles, as determined by postoperative CT, were 2.6 ± 3.4° (range, 0–16.2°) and 2.0 ± 1.5° (range, 0–6.5°) for inclination and anteversion, respectively. No statistically significant differences were noted in the mean absolute errors for either inclination ( p = 0.117) or anteversion ( p = 0.595) between the supine and lateral groups. The results are summarized in Table 3. Secondary outcomes Logistic regression analysis revealed that a greater posterior pelvic tilt was significantly associated with an increased likelihood of cup positioning outliers (odds ratio: 0.82, 95% confidence interval: 0.69–0.98, p = 0.03) in the lateral position. The details are summarized in Table 4. No significant differences were observed between the outliers and age or BMI. Furthermore, Fisher’s exact test demonstrated no significant association between outlier occurrence and the Crowe classification ( p = 0.59) in the lateral position. Discussion This study examined the reproducibility of cup placement in THA using an AR hip system and demonstrated, for the first time, that there was no significant difference in cup placement between the supine and lateral positions after adjusting for confounders using PSM. Additionally, pelvic tilt was a risk factor for poor cup placement when THA was performed with the AR Hip in the lateral position. According to Naito et al., when a portable navigation system was used for registration in the lateral position and surgery was performed in the same position, the absolute error values were 3.9 ± 2.2° and 4.8 ± 3.5° for the tilt and anterior tilt angles, respectively. Conversely, when registration was performed in the supine position followed by surgery in the lateral decubitus position, the absolute error values were 2.9 ± 2.7° and 3.2 ± 3.5° for the inclination and anterior tilt angles, respectively, indicating that registration in the supine position yielded better results. This is because, when using a portable navigation system, the operating table and body axis serve as reference points, and accuracy is considered lower in the lateral position than in the supine position [ 9 ]. Nevertheless, AR hip is utilized in the supine position, and cup placement along the FPP remains feasible even in the lateral position by changing position from supine to lateral using the flip technique [ 7 , 12 ]. The AR Hip enables quantification and visualization of acetabular cup angles via an attached iPhone, which provides substantial visual information and leads to superior error avoidance. Therefore, even with a patient background arranged by PSM, cup placement position accuracy could be demonstrated as comparable between lateral and supine approaches. Furthermore, multiple logistic regression analysis of the risk factors for poor cup placement when THA was performed in the lateral position using the AR Hip revealed that pelvic tilt was a risk factor. Conversely, age and BMI were not identified as risk factors. Fujita et al. reported that the AR Hip achieved a better cup placement position in THA performed in the supine position, even in patients with a high BMI, compared with the HIP alignment and AR navigation systems [ 17 ]. Additionally, previous studies have demonstrated no significant differences in implant placement error between patients with high and low BMI, even in the supine position, indicating that the AR Hip can be effectively used regardless of BMI in the supine or lateral position. Notably, variations in pelvic tilt significantly affect acetabular anteversion [ 18 ]. Moreover, posterior pelvic tilt has a negative effect on cup placement, even in CT-based and portable navigation [ 19 – 20 ]. We previously reported that preoperative posterior pelvic tilt is significantly associated with intraoperative pelvic rotation and tilt movements [ 21 ], which may have caused errors in cup placement, even [ 22 ] with THA using the AR Hip. This study has some limitations. First, the study design was retrospective, which carries inherent limitations. Second, it was limited to Japanese subjects, with few patients exhibiting a high BMI. Conclusions When the AR navigation system was used in THA, cup placement accuracy was achieved to the same degree in both the supine and lateral positions. However, caution is required, as errors may occur in cup placement, even when using AR Hip in cases of severe preoperative pelvic posterior tilt. Declarations Author Contribution Conceptualization: Shinya Hayashi, Tomoyuki Matsumoto; Methodology: Tomoyuki Kamenaga, Masanori Tsubosaka; Formal analysis and investigation: Yuichi Kuroda, Nakano Naoki; Writing - original draft preparation: Kohei Motono; Writing - review and editing: Shinya Hayashi; Supervision: Ryosuke Kuroda Acknowledgement The authors thank Editage, a division of Cactus Communications, for assistance in the preparation of this manuscript. References Minoda YK, Kim T (2006) Mitsunari Acetabular Component Orientation in 834 Total Hip Arthroplasties Using a Manual Technique. Clin Orthop Relat Res 445:186–191 Wasterlain AS, Buza JA 3rd, Thakkar SC, Schwarzkopf R, Vigdorchik J (2017) Navigation and Robotics in Total Hip Arthroplasty. JBJS Rev. ;5(3) Takada R, Jinno T, Miyatake K, Hirao M, Yoshii T, Okawa A (2020) Portable imageless navigation system and surgeon's estimate for accurate evaluation of acetabular cup orientation during total hip arthroplasty in supine position. Eur J Orthop Surg Traumatol 30(4):707–712 Okamoto M, Kawasaki M, Okura T, Ochiai S, Yokoi H (2021) Comparison of accuracy of cup position using portable navigation versus alignment guide in total hip arthroplasty in supine position. Hip Int 31(4):492–499 Ogawa H, Hasegawa S, Tsukada S, Matsubara M (2018) A Pilot Study of Augmented Reality Technology Applied to the Acetabular Cup Placement During Total Hip Arthroplasty. J Arthroplasty 33(6):1833–1837 Ogawa H, Kurosaka K, Sato A, Hirasawa N, Matsubara M, Tsukada S (2020) Does An Augmented Reality-based Portable Navigation System Improve the Accuracy of Acetabular Component Orientation During THA? A Randomized Controlled Trial. Clin Orthop Relat Res 478(5):935–943 Ozaki Y, Yamamoto T, Kimura S, Kasai T, Niki R, Niki H (2024) Accuracy of Cup Placement Angle, Leg Lengthening, and Offset Measurement Using an AR-Based Portable Navigation System: Validation in Supine and Lateral Decubitus Positions for Total Hip Arthroplasty. Med (Kaunas). ;60(10) Ohyama Y, Sugama R, Kim Y, Ohta Y, Minoda Y, Nakamura H (2023) A new accelerometer-based portable navigation system provides high accuracy of acetabular cup placement in total hip arthroplasty in both the lateral decubitus and supine positions. Arch Orthop Trauma Surg 143(7):4473–4480 Naito Y, Hasegawa M, Tone S, Wakabayashi H, Sudo A (2023) Registration in the supine position improve the accuracy of cup placement in total hip arthroplasty using a portable navigation system. Sci Rep 13(1):20222 Kovalenko B, Bremjit P, Fernando N (2018) Classifications in Brief: Tonnis Classification of Hip Osteoarthritis. Clin Orthop Relat Res 476(8):1680–1684 Miki H, Yamanashi W, Nishii T, Sato Y, Yoshikawa H, Sugano N (2007) Anatomic hip range of motion after implantation during total hip arthroplasty as measured by a navigation system. J Arthroplasty 22(7):946–952 Carcangiu A, D'Arrigo C, Topa D, Alonzo R, Speranza A, De Sanctis S et al (2011) Reliability of cup position in navigated THA in the lateral decubitus position using the 'flip technique'. Hip Int 21(6):700–705 Rosenbaum PRRD (1985) Constructing a control group using multivariate matched sampling methods that incorporate the propensity score. Biometrika. ;70 Hayashi S, Hashimoto S, Kuroda Y, Nakano N, Matsumoto T, Ishida K et al (2021) Accuracy of cup position following robot-assisted total hip arthroplasty may be associated with surgical approach and pelvic tilt. Sci Rep 11(1):7578 Kanawade V, Dorr LD, Banks SA, Zhang Z, Wan Z (2015) Precision of robotic guided instrumentation for acetabular component positioning. J Arthroplasty 30(3):392–397 Kajino Y, Kabata T, Maeda T, Iwai S, Kuroda K, Tsuchiya H (2012) Does degree of the pelvic deformity affect the accuracy of computed tomography-based hip navigation? J Arthroplasty 27(9):1651–1657 Fujita M, Hayashi S, Kuroda Y, Nakano N, Maeda T, Matsushita T et al (2023) Accuracy comparison of cup positioning during total hip arthroplasty using Hip Align and AR-Hip in the supine position. Arch Orthop Trauma Surg 143(12):7229–7235 Buckland AJ, Vigdorchik J, Schwab FJ, Errico TJ, Lafage R, Ames C et al (2015) Acetabular Anteversion Changes Due to Spinal Deformity Correction: Bridging the Gap Between Hip and Spine Surgeons. J Bone Joint Surg Am 97(23):1913–1920 Hasegawa M, Naito Y, Tone S, Wakabayashi H, Sudo A (2021) Accuracy of acetabular cup insertion in an anterolateral supine approach using an accelerometer-based portable navigation system. J Artif Organs 24(1):82–89 Yamada K, Endo H, Tetsunaga T, Miyake T, Sanki T, Ozaki T (2018) Accuracy of Cup Positioning With the Computed Tomography-Based Two-dimensional to Three-Dimensional Matched Navigation System: A Prospective, Randomized Controlled Study. J Arthroplasty 33(1):136–143 Kamenaga T, Hayashi S, Hashimoto S, Takayama K, Fujishiro T, Hiranaka T et al (2020) Intraoperative pelvic movement is associated with the body mass index in patients undergoing total hip arthroplasty in the supine position. J Orthop Sci 25(3):446–451 Tetsunaga T, Yamada K, Tetsunaga T, Sanki T, Kawamura Y, Ozaki T (2020) An accelerometer-based navigation system provides acetabular cup orientation accuracy comparable to that of computed tomography-based navigation during total hip arthroplasty in the supine position. J Orthop Surg Res 15(1):147 Tables Tables 1 to 4 are available in the Supplementary Files section Additional Declarations No competing interests reported. Supplementary Files table1.jpg Table 1. Patient demographic data table2.jpg Table 2. Patient demographic data after propensity score matching table3.jpg Table 3. Comparison of cup angles between the supine and lateral groups table4.jpg Table 4. Results of multiple logistic regression analysis for preoperative factors associated with inaccurate cup positioning in lateral position THA using the AR navigation system. 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. 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15:09:10","extension":"jpg","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":100233,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTable 1. \u003c/strong\u003ePatient demographic data\u003c/p\u003e","description":"","filename":"table1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7664849/v1/e504698e735b56d561b2d209.jpg"},{"id":93245483,"identity":"0abf5b85-0765-4a61-914d-d4b4ecf1a370","added_by":"auto","created_at":"2025-10-10 15:09:09","extension":"jpg","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":87804,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTable 2. \u003c/strong\u003ePatient demographic data after propensity score matching\u003c/p\u003e","description":"","filename":"table2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7664849/v1/1cb7e3d22ea12d7e8acd005d.jpg"},{"id":93246688,"identity":"4836cc09-1d7d-4c21-bcf9-b7c2ebc5faee","added_by":"auto","created_at":"2025-10-10 15:17:10","extension":"jpg","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":114685,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTable 3. \u003c/strong\u003eComparison of cup angles between the supine and lateral groups\u003c/p\u003e","description":"","filename":"table3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7664849/v1/14456a020752493488368f7d.jpg"},{"id":93244052,"identity":"68b960bf-dc91-4f69-aaad-73ee26fbe9da","added_by":"auto","created_at":"2025-10-10 15:01:10","extension":"jpg","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":73638,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTable 4. \u003c/strong\u003eResults of multiple logistic regression analysis for preoperative factors associated with inaccurate cup positioning in lateral position THA using the AR navigation system.\u003c/p\u003e","description":"","filename":"table4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7664849/v1/0cdbf5b57cd3787ae7a232aa.jpg"}],"financialInterests":"No competing interests reported.","formattedTitle":"Comparison of cup placement angles accuracy of total hip arthroplasty using the Augmented Reality hip navigation system in supine and lateral positions","fulltext":[{"header":"Background","content":"\u003cp\u003eAccurate cup positioning during total hip arthroplasty (THA) crucially affects hip stability and long-term prognosis. Conventional freehand cup positioning is particularly prone to error in the lateral position, with 27.8% of 834 cases deviating from the safe zone, and only 57% reported accuracy within \u0026plusmn;\u0026thinsp;5\u0026deg; [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Portable navigation systems may overcome these issues; in fact, they have been proven to improve the cup placement angles [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Portable navigation systems can register the pelvic functional plane (FPP) intraoperatively and have been reported to provide good positioning angles during supine surgery [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Moreover, accelerated and augmented reality navigation systems have demonstrated better results in cup-positioning angles compared to conventional freehand techniques in the supine position [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Several reports have described the use of a portable navigation system in lateral-position THA. Ozaki et al. reported that, with the augmented reality navigation system (AR Hip; Zimmer Biomet Japan, Tokyo, Japan), the absolute error between the cup placement position displayed on the intraoperative AR Hip and that measured on postoperative computed tomography (CT) was comparable for supine or lateral THA [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Similarly, Oyama et al. found no significant difference in the absolute error of the cup placement angle between the two groups when comparing the use of a portable navigation system in THA performed in the supine or lateral decubitus positions [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Conversely, Naito et al. conducted a study comparing cases in which both registration and THA with a portable navigation system were performed in the lateral position with cases in which registration and THA were performed in the supine and lateral positions, respectively, and reported that the absolute error in cup placement was greater in the former than in the latter [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. To date, several comparative studies have been conducted on cup placement using navigation systems in supine and lateral positions; nonetheless, their results remain controversial. Therefore, we aimed to compare the accuracy of acetabular cup positioning between supine and lateral THA using the AR Hip while accounting for differences in patient characteristics through propensity score matching (PSM), which was implemented to ensure greater accuracy of the study findings. Additionally, we evaluated the factors associated with cup malpositioning in the lateral position when the AR Hip was used as a secondary outcome.\u003c/p\u003e"},{"header":"Patients and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003ePatients\u003c/h2\u003e\u003cp\u003eIn this retrospective cohort study, data were obtained from medical records and radiographic databases at our institution. From an initial cohort of 147 hips treated from June 2021 to July 2024, 8 were excluded based on the exclusion criteria, leaving 92 and 47 hips in the supine and lateral groups, respectively. Overall, 139 hips of 129 patients underwent THA with an AR Hip and a cementless G7 cup. All patients were diagnosed with osteoarthritis (grade 3 or 4 according to the T\u0026ouml;nnis classification system) [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] or avascular necrosis of the femoral head (stages 4, 5, or 6 according to Steinberg staging of avascular necrosis). The demographic characteristics of the patients are summarized in Table\u0026nbsp;1 and Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003ePreoperative plan\u003c/h3\u003e\n\u003cp\u003eA preoperative CT scan was obtained with a slice thickness of 1 mm from the iliac wing to the femoral condyle to evaluate pelvic orientation and femoral morphology. Data were transferred to three-dimensional (3D) template software (Zed Hip; Lexi, Tokyo, Japan) for preoperative templating, enabling visualization and simulation of the acetabular cup position and allowing accurate determination of the optimal cup size, orientation, and placement in 3D.\u003c/p\u003e\u003cp\u003eThe target cup inclination and anteversion were typically set at 40\u0026deg; and 20\u0026deg; with respect to the FPP, respectively [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e\n\u003ch3\u003eRegistration\u003c/h3\u003e\n\u003cp\u003eIn the supine position, two anatomical bony landmarks were registered: the left and right anterior superior iliac spines. The navigation system automatically determined the gravity vector using the gyro sensor of a smartphone [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Threaded pins were inserted parallel to the iliac crest, and a QR code marker plate was mounted on them. The cup inclination and anteversion angles were calculated and displayed on a smartphone screen using real-time image analysis from the smartphone camera [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. During THA performed in the lateral position, the flip technique was applied, which involves registering landmarks in the supine position before repositioning the patient laterally [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. All procedures were performed by a single experienced orthopedic surgeon.\u003c/p\u003e\n\u003ch3\u003ePostoperative evaluation\u003c/h3\u003e\n\u003cp\u003eOne week after surgery, CT from the iliac to the femoral condyle was performed, and the data were transferred to the zed hip. The cup inclination and anteversion, positioned relative to the FFP, were measured.\u003c/p\u003e\u003cp\u003eThe primary endpoint of this study was the absolute difference between the intraoperatively recorded cup angles and those measured on postoperative CT, as assessed by the zed hip, in both the supine and lateral positions.\u003c/p\u003e\u003cp\u003eAs a secondary endpoint, preoperative clinical factors associated with poor cup positioning in the lateral position group were investigated.\u003c/p\u003e\n\u003ch3\u003eStatistics\u003c/h3\u003e\n\u003cp\u003eAll data are expressed as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation unless otherwise indicated. The 92 and 47 hips operated on in the supine and lateral positions, respectively, were divided into two groups. To adjust for potential confounding factors, PSM was performed between supine and lateral positions. Four baseline variables (sex, age, height, weight, and Crowe classification) were included in the propensity score model. A 1:1 matched cohort (cases:controls) was created using the nearest neighbor method without replacement by applying a caliper width\u0026thinsp;=\u0026thinsp;0.2 of the standard deviation of the logit of the propensity score, as recommended by Rosenbaum and Rubin [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The two groups were balanced with respect to these background characteristics, resulting in 52 patients in each group for the final analysis. The demographic data after PSM are presented in Table\u0026nbsp;2. Differences in cup angles between intraoperative and postoperative CT measurements were analyzed using a paired t-test. The outliers in accurate acetabular cup placement were defined as an absolute difference in inclination or anteversion\u0026thinsp;\u0026ge;\u0026thinsp;5\u0026deg; [\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. To identify predictors of outliers of postoperative cup position abnormalities in THA in the lateral position using the AR Hip, outliers and nonoutliers were compared using Fisher's exact test for the degree of progression of osteoarthritis (Crowe classification) and the unpaired t-test for continuous variables. Additionally, a multiple regression analysis examined the association between age, body mass index (BMI), pelvic tilt, and cup placement outliers. The database was analyzed using EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan), and a p-value\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003eEthics\u003c/h2\u003e\u003cp\u003e This study complied with the Declaration of Helsinki, and the research protocol was approved by the Ethics Committee of No.1220. Informed consent was obtained from all participants.\u003c/p\u003e\u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003ePrimary outcomes\u003c/h2\u003e\u003cp\u003eIn the supine group, the mean intraoperative inclination and anteversion relative to the FPP were 39.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.9\u0026deg; (range, 29.9\u0026ndash;43.2\u0026deg;) and 19.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u0026deg; (range, 11.2\u0026ndash;24\u0026deg;), respectively. The mean postoperative CT-based inclination and anteversion were 39.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4\u0026deg; (range, 31.3\u0026ndash;45.9\u0026deg;) and 19.7\u0026thinsp;\u0026plusmn;\u0026thinsp;4.3\u0026deg; (range, 10\u0026ndash;26.9\u0026deg;), respectively. The mean absolute errors between intraoperatively measured angles and the target angles, as determined by postoperative CT, were 2.9\u0026thinsp;\u0026plusmn;\u0026thinsp;1.8\u0026deg; (range, 0.1\u0026ndash;7.4\u0026deg;) and 2.9\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2\u0026deg; (range, 0.1\u0026ndash;13.6\u0026deg;) for inclination and anteversion, respectively.\u003c/p\u003e\u003cp\u003eIn the lateral group, the mean intraoperative inclination and anteversion relative to the FPP were 39.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.1\u0026deg; (range, 35.3\u0026ndash;42.9\u0026deg;) and 21.2\u0026thinsp;\u0026plusmn;\u0026thinsp;3.9\u0026deg; (range, 14.5\u0026ndash;31.3\u0026deg;), respectively. The mean postoperative CT-based inclination and anteversion were 41.4\u0026thinsp;\u0026plusmn;\u0026thinsp;3.7\u0026deg; (range, 36.9\u0026ndash;56.4\u0026deg;) and 20.5\u0026thinsp;\u0026plusmn;\u0026thinsp;3.3\u0026deg; (range, 14.5\u0026ndash;27.8\u0026deg;), respectively. The mean absolute errors in the intraoperatively measured angles relative to the target angles, as determined by postoperative CT, were 2.6\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4\u0026deg; (range, 0\u0026ndash;16.2\u0026deg;) and 2.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5\u0026deg; (range, 0\u0026ndash;6.5\u0026deg;) for inclination and anteversion, respectively.\u003c/p\u003e\u003cp\u003eNo statistically significant differences were noted in the mean absolute errors for either inclination (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.117) or anteversion (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.595) between the supine and lateral groups. The results are summarized in Table\u0026nbsp;3.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003eSecondary outcomes\u003c/h2\u003e\u003cp\u003eLogistic regression analysis revealed that a greater posterior pelvic tilt was significantly associated with an increased likelihood of cup positioning outliers (odds ratio: 0.82, 95% confidence interval: 0.69\u0026ndash;0.98, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.03) in the lateral position. The details are summarized in Table\u0026nbsp;4. No significant differences were observed between the outliers and age or BMI. Furthermore, Fisher\u0026rsquo;s exact test demonstrated no significant association between outlier occurrence and the Crowe classification (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.59) in the lateral position.\u003c/p\u003e\u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis study examined the reproducibility of cup placement in THA using an AR hip system and demonstrated, for the first time, that there was no significant difference in cup placement between the supine and lateral positions after adjusting for confounders using PSM. Additionally, pelvic tilt was a risk factor for poor cup placement when THA was performed with the AR Hip in the lateral position.\u003c/p\u003e\u003cp\u003eAccording to Naito et al., when a portable navigation system was used for registration in the lateral position and surgery was performed in the same position, the absolute error values were 3.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.2\u0026deg; and 4.8\u0026thinsp;\u0026plusmn;\u0026thinsp;3.5\u0026deg; for the tilt and anterior tilt angles, respectively. Conversely, when registration was performed in the supine position followed by surgery in the lateral decubitus position, the absolute error values were 2.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.7\u0026deg; and 3.2\u0026thinsp;\u0026plusmn;\u0026thinsp;3.5\u0026deg; for the inclination and anterior tilt angles, respectively, indicating that registration in the supine position yielded better results. This is because, when using a portable navigation system, the operating table and body axis serve as reference points, and accuracy is considered lower in the lateral position than in the supine position [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Nevertheless, AR hip is utilized in the supine position, and cup placement along the FPP remains feasible even in the lateral position by changing position from supine to lateral using the flip technique [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. The AR Hip enables quantification and visualization of acetabular cup angles via an attached iPhone, which provides substantial visual information and leads to superior error avoidance. Therefore, even with a patient background arranged by PSM, cup placement position accuracy could be demonstrated as comparable between lateral and supine approaches.\u003c/p\u003e\u003cp\u003eFurthermore, multiple logistic regression analysis of the risk factors for poor cup placement when THA was performed in the lateral position using the AR Hip revealed that pelvic tilt was a risk factor. Conversely, age and BMI were not identified as risk factors. Fujita et al. reported that the AR Hip achieved a better cup placement position in THA performed in the supine position, even in patients with a high BMI, compared with the HIP alignment and AR navigation systems [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Additionally, previous studies have demonstrated no significant differences in implant placement error between patients with high and low BMI, even in the supine position, indicating that the AR Hip can be effectively used regardless of BMI in the supine or lateral position. Notably, variations in pelvic tilt significantly affect acetabular anteversion [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Moreover, posterior pelvic tilt has a negative effect on cup placement, even in CT-based and portable navigation [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. We previously reported that preoperative posterior pelvic tilt is significantly associated with intraoperative pelvic rotation and tilt movements [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], which may have caused errors in cup placement, even [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] with THA using the AR Hip.\u003c/p\u003e\u003cp\u003eThis study has some limitations. First, the study design was retrospective, which carries inherent limitations. Second, it was limited to Japanese subjects, with few patients exhibiting a high BMI.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eWhen the AR navigation system was used in THA, cup placement accuracy was achieved to the same degree in both the supine and lateral positions. However, caution is required, as errors may occur in cup placement, even when using AR Hip in cases of severe preoperative pelvic posterior tilt.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConceptualization: Shinya Hayashi, Tomoyuki Matsumoto; Methodology: Tomoyuki Kamenaga, Masanori Tsubosaka; Formal analysis and investigation: Yuichi Kuroda, Nakano Naoki; Writing - original draft preparation: Kohei Motono; Writing - review and editing: Shinya Hayashi; Supervision: Ryosuke Kuroda\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors thank Editage, a division of Cactus Communications, for assistance in the preparation of this manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMinoda YK, Kim T (2006) Mitsunari Acetabular Component Orientation in 834 Total Hip Arthroplasties Using a Manual Technique. Clin Orthop Relat Res 445:186\u0026ndash;191\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWasterlain AS, Buza JA 3rd, Thakkar SC, Schwarzkopf R, Vigdorchik J (2017) Navigation and Robotics in Total Hip Arthroplasty. JBJS Rev. ;5(3)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTakada R, Jinno T, Miyatake K, Hirao M, Yoshii T, Okawa A (2020) Portable imageless navigation system and surgeon's estimate for accurate evaluation of acetabular cup orientation during total hip arthroplasty in supine position. Eur J Orthop Surg Traumatol 30(4):707\u0026ndash;712\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOkamoto M, Kawasaki M, Okura T, Ochiai S, Yokoi H (2021) Comparison of accuracy of cup position using portable navigation versus alignment guide in total hip arthroplasty in supine position. Hip Int 31(4):492\u0026ndash;499\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOgawa H, Hasegawa S, Tsukada S, Matsubara M (2018) A Pilot Study of Augmented Reality Technology Applied to the Acetabular Cup Placement During Total Hip Arthroplasty. J Arthroplasty 33(6):1833\u0026ndash;1837\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOgawa H, Kurosaka K, Sato A, Hirasawa N, Matsubara M, Tsukada S (2020) Does An Augmented Reality-based Portable Navigation System Improve the Accuracy of Acetabular Component Orientation During THA? A Randomized Controlled Trial. Clin Orthop Relat Res 478(5):935\u0026ndash;943\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOzaki Y, Yamamoto T, Kimura S, Kasai T, Niki R, Niki H (2024) Accuracy of Cup Placement Angle, Leg Lengthening, and Offset Measurement Using an AR-Based Portable Navigation System: Validation in Supine and Lateral Decubitus Positions for Total Hip Arthroplasty. Med (Kaunas). ;60(10)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOhyama Y, Sugama R, Kim Y, Ohta Y, Minoda Y, Nakamura H (2023) A new accelerometer-based portable navigation system provides high accuracy of acetabular cup placement in total hip arthroplasty in both the lateral decubitus and supine positions. Arch Orthop Trauma Surg 143(7):4473\u0026ndash;4480\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eNaito Y, Hasegawa M, Tone S, Wakabayashi H, Sudo A (2023) Registration in the supine position improve the accuracy of cup placement in total hip arthroplasty using a portable navigation system. Sci Rep 13(1):20222\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKovalenko B, Bremjit P, Fernando N (2018) Classifications in Brief: Tonnis Classification of Hip Osteoarthritis. Clin Orthop Relat Res 476(8):1680\u0026ndash;1684\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMiki H, Yamanashi W, Nishii T, Sato Y, Yoshikawa H, Sugano N (2007) Anatomic hip range of motion after implantation during total hip arthroplasty as measured by a navigation system. J Arthroplasty 22(7):946\u0026ndash;952\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCarcangiu A, D'Arrigo C, Topa D, Alonzo R, Speranza A, De Sanctis S et al (2011) Reliability of cup position in navigated THA in the lateral decubitus position using the 'flip technique'. Hip Int 21(6):700\u0026ndash;705\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRosenbaum PRRD (1985) Constructing a control group using multivariate matched sampling methods that incorporate the propensity score. Biometrika. ;70\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHayashi S, Hashimoto S, Kuroda Y, Nakano N, Matsumoto T, Ishida K et al (2021) Accuracy of cup position following robot-assisted total hip arthroplasty may be associated with surgical approach and pelvic tilt. Sci Rep 11(1):7578\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKanawade V, Dorr LD, Banks SA, Zhang Z, Wan Z (2015) Precision of robotic guided instrumentation for acetabular component positioning. J Arthroplasty 30(3):392\u0026ndash;397\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKajino Y, Kabata T, Maeda T, Iwai S, Kuroda K, Tsuchiya H (2012) Does degree of the pelvic deformity affect the accuracy of computed tomography-based hip navigation? J Arthroplasty 27(9):1651\u0026ndash;1657\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFujita M, Hayashi S, Kuroda Y, Nakano N, Maeda T, Matsushita T et al (2023) Accuracy comparison of cup positioning during total hip arthroplasty using Hip Align and AR-Hip in the supine position. Arch Orthop Trauma Surg 143(12):7229\u0026ndash;7235\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBuckland AJ, Vigdorchik J, Schwab FJ, Errico TJ, Lafage R, Ames C et al (2015) Acetabular Anteversion Changes Due to Spinal Deformity Correction: Bridging the Gap Between Hip and Spine Surgeons. J Bone Joint Surg Am 97(23):1913\u0026ndash;1920\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHasegawa M, Naito Y, Tone S, Wakabayashi H, Sudo A (2021) Accuracy of acetabular cup insertion in an anterolateral supine approach using an accelerometer-based portable navigation system. J Artif Organs 24(1):82\u0026ndash;89\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eYamada K, Endo H, Tetsunaga T, Miyake T, Sanki T, Ozaki T (2018) Accuracy of Cup Positioning With the Computed Tomography-Based Two-dimensional to Three-Dimensional Matched Navigation System: A Prospective, Randomized Controlled Study. J Arthroplasty 33(1):136\u0026ndash;143\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKamenaga T, Hayashi S, Hashimoto S, Takayama K, Fujishiro T, Hiranaka T et al (2020) Intraoperative pelvic movement is associated with the body mass index in patients undergoing total hip arthroplasty in the supine position. J Orthop Sci 25(3):446\u0026ndash;451\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTetsunaga T, Yamada K, Tetsunaga T, Sanki T, Kawamura Y, Ozaki T (2020) An accelerometer-based navigation system provides acetabular cup orientation accuracy comparable to that of computed tomography-based navigation during total hip arthroplasty in the supine position. J Orthop Surg Res 15(1):147\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTables 1 to 4 are available in the Supplementary Files section\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Total hip arthroplasty, cup positioning, augmented reality navigation, propensity score matching, pelvic tilt","lastPublishedDoi":"10.21203/rs.3.rs-7664849/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7664849/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eIntroduction:\u003c/h2\u003e\u003cp\u003eWe aimed to compare the accuracy of acetabular cup positioning angles between supine and lateral total hip arthroplasty (THA) using an augmented reality hip navigation system (AR Hip) and identify predictive risk factors for cup placement angles in lateral THA.\u003c/p\u003e\u003ch2\u003eMaterials and Methods\u003c/h2\u003e\u003cp\u003eThis study included 139 THA procedures performed using the AR Hip between June 2021 and July 2024 (mean age 66.1 years, 25 males, 114 females). To match the patient backgrounds between the groups, propensity score matching (PSM) was performed using sex, age, height, weight, and Crowe classification as covariates. The absolute error in the difference between the intraoperative navigation records and postoperative measurements using computed tomography data was evaluated between the supine and lateral positions. Additionally, we conducted a multivariate analysis to identify preoperative clinical factors associated with positioning errors\u0026thinsp;\u0026ge;\u0026thinsp;5\u0026deg; in the lateral position.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003eIn the supine group after PSM, the average absolute errors were 2.9\u0026deg; for both inclination and anteversion. In the lateral position group, the mean absolute errors were 2.2\u0026deg; and 1.9 \u0026deg;for inclination and anteversion, respectively. No significant difference was observed between the two groups in terms of average absolute error. Additionally, multiple regression analysis revealed that pelvic tilt (odds ratio 0.8; 95% confidence interval 0.69\u0026ndash;0.98; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.03) was a predictive factor for inaccuracy of cup placement angle.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e\u003cp\u003eWhen using the AR Hip, no significant cup positioning accuracy difference was noted between supine and lateral THA. In cases of severe preoperative pelvic posterior tilt, cup positioning accuracy may be adversely affected.\u003c/p\u003e","manuscriptTitle":"Comparison of cup placement angles accuracy of total hip arthroplasty using the Augmented Reality hip navigation system in supine and lateral positions","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-10 15:01:05","doi":"10.21203/rs.3.rs-7664849/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":"54469c9b-77dd-49f4-b530-65e1125364c3","owner":[],"postedDate":"October 10th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-10-27T17:23:24+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-10 15:01:05","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7664849","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7664849","identity":"rs-7664849","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}