Development of a non-invasive augmented reality-based navigation system for total hip arthroplasty in the supine position

Development of a non-invasive augmented reality-based navigation system for total hip arthroplasty in the supine position | 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 Development of a non-invasive augmented reality-based navigation system for total hip arthroplasty in the supine position Ryohei Takada, Naoto Watanabe, Kazumasa Miyatake, Naohiko Sugita, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4173945/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 A new non-invasive augmented reality (AR)-based portable navigation system was developed for accurate cup positioning during total hip arthroplasty (THA) in the supine position. This study aimed to clarify whether the navigation system supports cup positioning more accurately than a conventional goniometer during surgery. The navigation system may provide more accurate cup alignment than the conventional goniometer. Methods Sixty patients who underwent THA in the supine position were enrolled. The navigation system was used for 30 patients (navigation group), and a conventional goniometer was used for 30 patients (control group) to measure radiographic cup inclination and anteversion during surgery. The primary outcome was the absolute value of the difference in cup alignment measured during surgery and by postoperative radiography. Results The new non-invasive AR-based navigation system showed superior cup positioning accuracy compared to a conventional goniometer. An assessment of the primary outcome showed no significant difference in the radiographic cup inclination in the navigation and control groups (2.9° vs. 3.2°; mean difference, 0.3°; 95% confidence interval, -1.4–0.9; p = 0.67); however, the positioning in the navigation group was significantly more accurate than that in the control group in terms of radiographic anteversion (3.4° vs. 5.4°; mean difference, 2.0°; 95% confidence interval, 0.4–3.8; p = 0.017). Conclusions A new non-invasive AR-based portable navigation system resulted in more accurate cup positioning than the conventional goniometer. Because it is non-invasive, this system should be used for THA in the supine position. Augmented reality Navigation system Total hip arthroplasty Cup alignment Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1. Background The orientation of the acetabular cup during total hip arthroplasty (THA) is critical for the prevention of postoperative dislocation, accelerated wear and loosening, reduced range of motion, and patient dissatisfaction [ 1 , 2 ]. Various computer-assisted devices have been developed worldwide to achieve ideal cup positions, such as computed tomography-based navigation and other image-free navigation systems, including portable navigation systems [ 3 , 4 ]. New portable navigation systems using smartphone technology have recently been developed [ 5 ]. Smartphones with cameras and augmented reality (AR) technology allowing for high-quality pictures can be used to enhance cup positioning accuracy at a lower cost than other navigation systems. Several concerns regarding these navigation systems have been reported [ 6 – 9 ]. During most navigation system procedures, fixation pins must be inserted in the pelvic crest to trace pelvic movement during surgery; this prolongs surgical time and is invasive [ 10 ]. Moreover, it increases the risk of complications [ 6 ]. Other limitations include patient and surgeon X-ray exposure, high costs, and complicated procedures that prolong surgical time [ 11 ]. A novel, portable, non-invasive, cost-effective, time-saving, and accurate navigation system for cup alignment during THA must be developed. During this study, the accuracy of a new non-invasive AR-based portable navigation system for cup positioning was investigated. The results were compared to those achieved with a conventional goniometer. The study’s research question is 1) Does a new portable navigation system give more accurate cup positioning compared to a conventional goniometer? The hypothesis was that the navigation system would provide more accurate cup alignment than the conventional goniometer. 2. Methods 2.1. Patients This study is a consecutive case series. The navigation system started to be used in March 2022, for all supine position THAs. The navigation group comprised 30 patients who underwent THA with the navigation system. The control group comprised 30 consecutive patients who underwent THA with a conventional goniometer. The conventional goniometer measured radiographic cup inclination and anteversion after cup insertion (Fig. 1 ). Patient background and surgical characteristics (age, sex, side, body mass index [BMI], diagnosis, surgical time, and intraoperative blood loss) were recorded (Table 1 ). All surgeries were performed using a modified Watson–Jones anterolateral approach and Trident II acetabular cups (Stryker, Mahwah, NJ, USA). No additional screws were used for cup fixation. An Accolade II stem or Exeter stem was used for all patients. All surgeries were performed under general anesthesia. Three surgeons performed all the surgeries (R.T., N.W., and K.M.). Femoral preparation was performed first when the Exeter stem was used because final femoral anteversion can be adjusted. Subsequently, cup preparation was performed. Cup insertion was performed in a flat, supine position. Femoral preparation was performed in the extended hip position. Radiographic cup inclination was aimed for 40 degrees and radiographic cup anteversion for 10–30 degrees. Radiographic cup anteversion was defined intraoperatively considering femoral and stem anteversion. No other assistive devices—including X-ray imaging and fluoroscopy—were used intraoperatively. Informed consent was obtained from all patients before surgery. This study was performed at a single university hospital following the principles of the Declaration of Helsinki. Approval was obtained from the institutional research ethics committee. Table 1 Background and surgical characteristics Variable Navigation (n = 30) Control (n = 30) p-value Age (years) 67.5 ± 10.7 64.4 ± 10.4 0.29 Sex (female/male) 27/3 25/5 0.52 Side (right/left) 14/16 10/20 0.29 Body mass index (kg/m 2 ) 22.9 ± 2.8 23.9 ± 3.8 0.23 Diagnosis 1.00 Osteoarthritis 28 28 Osteonecrosis 2 2 Operative time (min) 84.5 ± 20.6 86.5 ± 27.6 0.79 Intraoperative blood loss (mL) 251.9 ± 98.5 249.7 ± 190.3 0.66 Values are presented as mean ± standard deviation. 2.2. Non-invasive AR-Based Navigation This AR-based navigation system comprises a smartphone application, marker probe, smartphone fixation device, and cup holder (Fig. 2 ). This system has been studied and developed by the Engineering Department of Tokyo University. Pharmaceutical approval in Japan was obtained in March 2022. Since then, this system has been commercially available only in Japan. The marker probe, fixation device, and cup holder were used after sterilization. The smartphone was placed in a sterilized plastic bag. The smartphone application uses gyro and acceleration sensors to measure smartphone orientation and gravity vector. The application also uses AR technology to measure marker position, orientation, and probe tip position by capturing marker patterns. The marker pattern and the offset from the marker center to the probe tip are preliminarily programmed and used for the measurement. Before surgery, the smartphone is placed into the sterilized plastic bag. Before cup insertion, the smartphone is attached to the fixation device, which is rigidly clamped to the cup holder. The application procedure involves three steps: cup registration (step 1), anterior superior iliac spine (ASIS) registration (step 2), and target hunting (step 3). During step 1, the cup axis relative to the smartphone is measured by placing the flat aspect of the marker probe body along the cup rim and then measuring the marker probe (Fig. 3 ). In this case, the relative unit vector \({\text{V}}_{\text{c}\text{u}\text{p}}\) of the cup axis from the smartphone can be measured as the Y-axis of the marker transformation matrix \({\text{M}}_{\text{m}\text{a}\text{r}\text{k}\text{e}\text{r}}\) (Fig. 4 a). During step 2, the position of the left and right ASIS—palpable through the skin and soft tissue—is provided to the application by measuring the tip of the marker probe. Let \(\text{O}\) be the world coordinate system, \({\text{M}}_{\text{c}\text{a}\text{m}}\) the transformation matrix from \(\text{O}\) to the camera, \({\text{M}}_{\text{m}\text{a}\text{r}\text{k}\text{e}\text{r}}\) the transformation matrix from camera to marker center, and \({\text{P}}_{\text{o}\text{f}\text{f}\text{s}\text{e}\text{t}}\) the offset from the marker center to the probe tip (Fig. 4 b). The probe tip position \(\text{P}\) can be calculated using the following equation. $$\text{P}={\text{M}}_{\text{c}\text{a}\text{m}}*{\text{M}}_{\text{m}\text{a}\text{r}\text{k}\text{e}\text{r}}*{\text{P}}_{\text{o}\text{f}\text{f}\text{s}\text{e}\text{t}}$$ \({\text{M}}_{\text{c}\text{a}\text{m}}\) is calculated using position-tracking technology that can correct the smartphone’s location using visual information obtained from its camera, even if the smartphone is moved. \({\text{M}}_{\text{m}\text{a}\text{r}\text{k}\text{e}\text{r}}\) is calculated using AR technology that detects the relative position and orientation from the camera to the marker based on the marker pattern from the camera image. The functional pelvic plane (FPP) defines cup inclination and anteversion [ 12 ] and is calculated from the left and right ASIS positions and gravity vector; it is then displayed using AR technology (Figs. 5 , 6 ). Finally, during step 3, the smartphone attached to the cup holder shows the surgeon’s real-time cup alignment (Fig. 7 ). The application calculates and shows real-time cup alignment using two factors: the real-time cup axis—calculated from the relative cup axis achieved during step 1—and real-time smartphone orientation, and the FPP achieved during step 2. The cup alignment value is correct provided that the pelvis does not move during step 3. Surgeons can adjust the cup by checking the real-time cup alignment. They can also verify the final cup alignment by attaching a smartphone to the cup holder. Step 2 can be repeated if the pelvis moves during step 3. 2.3. Outcomes The primary outcome was the absolute value of the difference between the cup alignment—measured intraoperatively—and the postoperative cup alignment (absolute estimate error). Radiographic definitions were used for the intra- and postoperative measurements [ 13 ]. In the navigation group, radiographic inclination and anteversion were measured using a navigation system after cup fixation. In the control group, alignment values were measured using a conventional goniometer after cup fixation. Postoperative radiographic cup inclination and anteversion on the first anteroposterior postoperative radiograph were manually measured by the first author (R.T.) using the iRad-OT system (INFOCOM Corp., Tokyo, Japan). To evaluate inter-observer reliability, the radiographic inclination and anteversion of 20 randomly selected patients were measured by a second observer (N.W.) using the iRad-OT system. To determine intra-observer reliability, the first author measured 30 patients 2 months after the first measurement. An absolute value of more than 10° was considered an outlier. The number of outliers was estimated for both groups. 2.4. Statistical and Power Analyses Welch’s t -test and chi-square tests were used to compare all navigation and control groups’ factors. Intra- and inter-observer reliability for the postoperative cup alignment measurements were analyzed using intra-class correlation coefficients. Statistical significance was defined as a two-sided p < 0.05. A statistical power analysis showed that 30 patients in each group would be sufficient to detect a 2.0° difference in the absolute estimate error between groups, with a power of 80% and a type I error rate of 5%. For the sample size calculation, based on the results of other studies, a standard deviation of 3.0° was used for the absolute target error [,14]. All statistical analyses were performed using G*Power, Version 3.1.9.2 (Düsseldorf University, Düsseldorf, Germany) and JMP for Mac, version 13.0.0 (SAS Institute, Cary, NC, USA). 3. Results The mean absolute estimate errors of cup inclination in the navigation and control groups were 2.9° (standard deviation [SD], ± 2.8°) and 3.1° (SD, ± 1.7°), respectively (p = 0.67). Conversely, those of cup anteversion were 3.4° (SD, ± 3.0°) and 5.4° (SD, ± 3.6°), respectively (p = 0.018) (Table 2 ). No outliers were found in the navigation group, while two were found in the control group (p = 0.52) (Fig. 8 ). Cup alignment data of both groups are shown in Table 3 and the related scattergram is shown in Fig. 9 . There were no significant differences between groups regarding patient background characteristics (Table 1 ). The intra-class correlation coefficients showed that intra- and inter-observer reliability for cup inclination and anteversion—measured using the iRad-OT system—was good to excellent (0.90 and 0.79, and 0.91 and 0.73, respectively). Table 2 Absolute target error Navigation (n = 30) Control (n = 30) Difference (95% CI) p-value Radiographic inclination (°) 2.9 ± 2.8 3.2 ± 1.7 0.3 (-0.9–1.4) 0.67 Radiographic anteversion (°) 3.4 ± 3.0 5.4 ± 3.6 2.0 (0.4–3.8) 0.018 Values are presented as mean ± standard deviation. CI, confidence interval Table 3 Cup alignment Navigation (n = 30) Control (n = 30) Difference (95% CI) p-value Radiographic inclination (°) 40.1 ± 3.9 38.6 ± 3.5 1.5 (-0.3–3.5) 0.1 Radiographic anteversion (°) 19.6 ± 4.4 19.7 ± 3.7 0.01 (-2.1–2.1) 0.99 4. Discussion This new non-invasive AR-based navigation system enabled surgeons to achieve better cup orientation accuracy compared with the conventional goniometer. Furthermore, this system is simple and time efficient. The greatest advantage of this navigation system is that it is not invasive. Although AR technology has already been used in other navigation systems, this is the first portable navigation system that does not require an invasive procedure [ 5 ]. Theoretically, cup alignment accuracy could be reduced if the pelvis moves during the ASIS registration step. However, each step was completed within 1 minute, substantially aiding pelvic position maintenance throughout all procedures. There was no significant between-group difference regarding cup inclination because, in both groups, it was measured by referencing both ASIS locations. In contrast, cup anteversion was not measured using bone landmarks (Fig. 1 ); therefore, there was a significant between-group difference in cup anteversion accuracy. Some authors have reported the cup positioning accuracy provided by other portable navigation systems [ 5 , 15 – 17 ]. Ogawa et al. reported the absolute error of the AR navigation system; their absolute values of radiographic inclination and anteversion were 1.9 and 2.8 degrees, respectively. Although their accuracy is superior to that of this study, this study’s system warrants recommendation because it is non-invasive [ 5 ]. However, this navigation system can be used only for THA in the supine position. Therefore, a new non-invasive navigation system for THA in the lateral position should be developed. This study had several limitations. First, it was a single-center study. Second, the accuracy of this system was not directly compared with that of other navigation systems. The influence of this navigation system on important factors—including cup position, offset, and leg length—was not evaluated. Therefore, it cannot be completely concluded that our system is superior to others. However, because of its non-invasiveness, this system is worth using. Further studies should clarify whether this navigation system is superior to others. Third, the relatively small sample size prevented an evaluation of how patient characteristics (especially BMI, height, and osteoarthritis grade) influence this system’s accuracy. Fourth, the supine position during surgery was used as FPP; however, pelvic tilt during general anesthesia may differ from that of during awake state. Moreover, this system assumes no pelvic deformity/asymmetry; otherwise, this system would provide a wrong cup alignment value. CT-based navigation and robotic systems may overcome these issues [ 18 ]. Although no critical errors were found in the navigation group of this study, further research should evaluate the difference of the accuracy due to pelvic tilt and the influence of pelvic deformity and asymmetry. Fifth, a modified Watson–Johnes approach was used in this study; it is unclear whether this navigation system is useful if other approaches are used. 5. Conclusions This new non-invasive AR-based navigation system showed superior cup positioning accuracy compared to a conventional goniometer. Because it is non-invasive, this system should be used to increase cup positioning accuracy during THA in the supine position. Abbreviations AR Augmented reality ASIS Anterior superior iliac spine BMI Body mass index FPP Functional pelvic plane THA Total hip arthroplasty Declarations Ethics approval and consent to participate: This study was performed at a single university hospital following the principles of the Declaration of Helsinki. Approval was obtained from the institutional research ethics committee. Informed consent was obtained from all patients before surgery. Consent for publication: Not applicable. Availability of data and materials: All data generated or analysed during this study are included in this published article . Competing interests: Theauthors declare that they have no competing interests. Funding: This project received technical support from Xel-ha Medical CO., LTD. Authors’ contributions : RT designed the study, performed data collection, analysis, and interpretation, and drafted the manuscript. KM, WN, and NS contributed to study design and data interpretation. WN contributed to the statistical processing of matching. KM contributed to data collection and interpretation. TY and HK contributed to restructuring the article. All the authors approved the final manuscript as submitted and have agreed to be responsible for all aspects of this work. Acknowledgements: Not applicable. Authors’ information: Not applicable. References D’Lima DD, Urquhart AG, Buehler KO, Walker RH, Colwell CW. The effect of the orientation of the acetabular and femoral components on the range of motion of the hip at different head-neck ratios. J Bone Joint Surg Am. 2000;82:315–21. 10.2106/00004623-200003000-00003 . Patil S, Bergula A, Chen PC, Colwell CW, D’Lima DD. 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Is a portable accelerometer-based navigation system useful in total hip arthroplasty? A systematic review and meta-analysis. Orthop Traumatol Surg Res. 2021;107:102742. 10.1016/j.otsr.2020.08.014 . Coulomb R, Cascales V, Haignere V, Bauzou F, Kouyoumdjian P. Does acetabular robotic-assisted total hip arthroplasty with femoral navigation improve clinical outcomes at 1-year post-operative? A case-matched propensity score study comparing 98 robotic-assisted versus 98 manual implantation hip arthroplasties. Orthop Traumatol Surg Res. 2023;109:103477. 10.1016/j.otsr.2022.103477 . Epub 2022 Nov 11. 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. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4173945","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":284766010,"identity":"342d1425-706d-400d-ba60-199b620b9227","order_by":0,"name":"Ryohei Takada","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA6UlEQVRIiWNgGAWjYFACNgYGHjCDh/EBAwMzmGmATwMPXAsbD7PBAVK1sEnAtOAF9uzHEj+8qWGQM5/fe6z6Y441A3/7AYbiAny28KQdlpxzjMFY5hhf2o2D29IZJM4kMBjPwOuw9AZpHjaGxBlsPGZALYcZGG4wMBjz4NPC/7z5N88/iJYCkBZ5glok0o5J87ZBtDCAtBgQ1HLjWZrl3D4JYwm2HGOJs9vSeQzPJDbg9Qt7f5rxjTffbOQkmM8YfqjcZi0nd/zwMWN8IQYFEghrGRgY24wJ60ADzI9J1jIKRsEoGAXDGQAAWRtC7AUQAZ4AAAAASUVORK5CYII=","orcid":"","institution":"Tokyo Medical and Dental University","correspondingAuthor":true,"prefix":"","firstName":"Ryohei","middleName":"","lastName":"Takada","suffix":""},{"id":284766011,"identity":"4698e3dc-2024-4aef-b11f-c20b46b24bda","order_by":1,"name":"Naoto Watanabe","email":"","orcid":"","institution":"Tokyo Medical and Dental University","correspondingAuthor":false,"prefix":"","firstName":"Naoto","middleName":"","lastName":"Watanabe","suffix":""},{"id":284766012,"identity":"76ae405d-14c3-4ef4-bcdd-49997597b948","order_by":2,"name":"Kazumasa Miyatake","email":"","orcid":"","institution":"Tokyo Medical and Dental University","correspondingAuthor":false,"prefix":"","firstName":"Kazumasa","middleName":"","lastName":"Miyatake","suffix":""},{"id":284766013,"identity":"c3a8d854-05e9-4ade-85e6-092293307487","order_by":3,"name":"Naohiko Sugita","email":"","orcid":"","institution":"The University of Tokyo","correspondingAuthor":false,"prefix":"","firstName":"Naohiko","middleName":"","lastName":"Sugita","suffix":""},{"id":284766014,"identity":"d6939b81-daeb-4a96-b116-68aaa47040da","order_by":4,"name":"Toshitaka Yoshii","email":"","orcid":"","institution":"Tokyo Medical and Dental University","correspondingAuthor":false,"prefix":"","firstName":"Toshitaka","middleName":"","lastName":"Yoshii","suffix":""},{"id":284766015,"identity":"67d9f4a9-624a-4100-8092-4f5abb72ba96","order_by":5,"name":"Hideyuki Koga","email":"","orcid":"","institution":"Tokyo Medical and Dental University","correspondingAuthor":false,"prefix":"","firstName":"Hideyuki","middleName":"","lastName":"Koga","suffix":""}],"badges":[],"createdAt":"2024-03-27 06:46:17","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4173945/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4173945/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":53878528,"identity":"15aba7c9-3ae1-416a-be52-54d6f2afbd17","added_by":"auto","created_at":"2024-04-01 17:00:08","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":518093,"visible":true,"origin":"","legend":"\u003cp\u003eRadiographic inclination and anteversion of the control group measured using a conventional goniometer\u003c/p\u003e\n\u003cp\u003e(a) The radiographic inclination angle is defined as the angle between the face of the acetabular cup and the transverse axis (a line between the anterior superior iliac spines). (B) Radiographic anteversion is defined as the angle between the acetabular and coronal planes (a surface perpendicular to the direction of gravity).\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-4173945/v1/102488a9438987ea1ad73afb.png"},{"id":53878519,"identity":"34e0d86a-466f-4d56-bf5b-1d0e20c3ae6a","added_by":"auto","created_at":"2024-04-01 17:00:04","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":792428,"visible":true,"origin":"","legend":"\u003cp\u003eMarker probe and smartphone with a fixation device\u003c/p\u003e\n\u003cp\u003eThe smartphone is contained within a sterile plastic bag.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-4173945/v1/9cfa50cc432f0c8a11ad5a86.png"},{"id":53878526,"identity":"f9a39bae-00da-4e15-a8c7-8a752afed784","added_by":"auto","created_at":"2024-04-01 17:00:07","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1064643,"visible":true,"origin":"","legend":"\u003cp\u003eCup registration procedure – Step 1\u003c/p\u003e\n\u003cp\u003e(a) To achieve a relative axis between the smartphone and the cup rim, the marker probe is placed along the rim for a few seconds. (b) Smartphone screen when the cup rim plane is registered. The marker pattern is highlighted when the smartphone recognizes the marker.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-4173945/v1/a7ce93f8f376a668ca997e1b.png"},{"id":53878521,"identity":"8f2d0246-837e-46e9-a00e-4168ca8addc9","added_by":"auto","created_at":"2024-04-01 17:00:05","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":164650,"visible":true,"origin":"","legend":"\u003cp\u003eOverview of Methodology Steps 1 and 2\u003c/p\u003e\n\u003cp\u003e(a) Method used to calculate the cup axis relative to the smartphone. (b) Method used to calculate the probe tip position in the world coordinate system.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-4173945/v1/4013a6f748b08cd332e1aef3.png"},{"id":53878527,"identity":"57b0e3e2-2868-45d5-b7d0-5e4cad68d462","added_by":"auto","created_at":"2024-04-01 17:00:08","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":958623,"visible":true,"origin":"","legend":"\u003cp\u003eAnterior superior iliac spine (ASIS) registration procedure – Step 2\u003c/p\u003e\n\u003cp\u003e(a) ASIS registration is performed just before the cup is placed on the acetabulum. (b) Smartphone screenshot when ASIS registration is finished. The smartphone can recognize the functional pelvic plane (FPP) (orange line) using the geographical information of the left and right ASISs. The sagittal vector of the FPP (dotted line) is defined as perpendicular to the gravitational vector (red line).\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-4173945/v1/29d146eba6286560ba0934a5.png"},{"id":53878522,"identity":"3203866c-0edf-49f2-abd4-37cb1f55c64b","added_by":"auto","created_at":"2024-04-01 17:00:05","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":844015,"visible":true,"origin":"","legend":"\u003cp\u003eIntraoperative procedure of Step 2\u003c/p\u003e\n\u003cp\u003eSurgeon pointing to the right anterior superior iliac spine (ASIS) with the marker probe; the smartphone recognizes the marker pattern which is illuminated on the smartphone screen. The cup figure achieved in Step 1 is also illuminated at the bottom of the screen.\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-4173945/v1/e8db9a58cf4480aadcbdd85b.png"},{"id":53878516,"identity":"8eea584e-ca54-42ff-abeb-42969ed501c0","added_by":"auto","created_at":"2024-04-01 17:00:01","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":884979,"visible":true,"origin":"","legend":"\u003cp\u003eTarget hunting procedure of Step 3\u003c/p\u003e\n\u003cp\u003e(a) The cup alignment shown on the smartphone changes in real-time as the surgeon moves the cup holder. (b) Smartphone screenshot during step 3. The cup alignment is theoretically correct unless the pelvis moves during the procedure.\u003c/p\u003e","description":"","filename":"Figure7.png","url":"https://assets-eu.researchsquare.com/files/rs-4173945/v1/2ad7e83bbca3ad11132cafac.png"},{"id":53878520,"identity":"d6f81b55-68f8-4d7a-9d98-10ef46251616","added_by":"auto","created_at":"2024-04-01 17:00:05","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":68960,"visible":true,"origin":"","legend":"\u003cp\u003eScatter diagram of the target error\u003c/p\u003e\n\u003cp\u003eThe case with a positive target error indicates that the postoperative angle is larger than the target angle. The square box reflects the defined outlier line (absolute target error ≥10°). The filled marker represents the outlier.\u003c/p\u003e","description":"","filename":"Figure8.png","url":"https://assets-eu.researchsquare.com/files/rs-4173945/v1/72ac1afabacd1ef9f22c12d0.png"},{"id":53878518,"identity":"1d47c520-c03e-4403-8ff6-43ad47dd321f","added_by":"auto","created_at":"2024-04-01 17:00:03","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":58400,"visible":true,"origin":"","legend":"\u003cp\u003eScatter diagram of the radiographic inclination and anteversion\u003c/p\u003e\n\u003cp\u003eThe radiographic inclination and anteversion of the navigation and control groups are shown.\u003c/p\u003e","description":"","filename":"Figure9.png","url":"https://assets-eu.researchsquare.com/files/rs-4173945/v1/e6dca9945d04db515e8b98f6.png"},{"id":53879663,"identity":"6f37a0cb-a293-4e56-bd20-2992962ee3e2","added_by":"auto","created_at":"2024-04-01 17:16:16","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6973867,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4173945/v1/c9667dbd-e786-4f73-af0e-b8a1243df257.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Development of a non-invasive augmented reality-based navigation system for total hip arthroplasty in the supine position","fulltext":[{"header":"1. Background","content":"\u003cp\u003eThe orientation of the acetabular cup during total hip arthroplasty (THA) is critical for the prevention of postoperative dislocation, accelerated wear and loosening, reduced range of motion, and patient dissatisfaction [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Various computer-assisted devices have been developed worldwide to achieve ideal cup positions, such as computed tomography-based navigation and other image-free navigation systems, including portable navigation systems [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. New portable navigation systems using smartphone technology have recently been developed [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Smartphones with cameras and augmented reality (AR) technology allowing for high-quality pictures can be used to enhance cup positioning accuracy at a lower cost than other navigation systems.\u003c/p\u003e \u003cp\u003eSeveral concerns regarding these navigation systems have been reported [\u003cspan additionalcitationids=\"CR7 CR8\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. During most navigation system procedures, fixation pins must be inserted in the pelvic crest to trace pelvic movement during surgery; this prolongs surgical time and is invasive [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Moreover, it increases the risk of complications [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Other limitations include patient and surgeon X-ray exposure, high costs, and complicated procedures that prolong surgical time [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eA novel, portable, non-invasive, cost-effective, time-saving, and accurate navigation system for cup alignment during THA must be developed. During this study, the accuracy of a new non-invasive AR-based portable navigation system for cup positioning was investigated. The results were compared to those achieved with a conventional goniometer. The study\u0026rsquo;s research question is 1) Does a new portable navigation system give more accurate cup positioning compared to a conventional goniometer? The hypothesis was that the navigation system would provide more accurate cup alignment than the conventional goniometer.\u003c/p\u003e"},{"header":"2. Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Patients\u003c/h2\u003e \u003cp\u003eThis study is a consecutive case series. The navigation system started to be used in March 2022, for all supine position THAs. The navigation group comprised 30 patients who underwent THA with the navigation system. The control group comprised 30 consecutive patients who underwent THA with a conventional goniometer. The conventional goniometer measured radiographic cup inclination and anteversion after cup insertion (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Patient background and surgical characteristics (age, sex, side, body mass index [BMI], diagnosis, surgical time, and intraoperative blood loss) were recorded (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). All surgeries were performed using a modified Watson\u0026ndash;Jones anterolateral approach and Trident II acetabular cups (Stryker, Mahwah, NJ, USA). No additional screws were used for cup fixation. An Accolade II stem or Exeter stem was used for all patients. All surgeries were performed under general anesthesia. Three surgeons performed all the surgeries (R.T., N.W., and K.M.). Femoral preparation was performed first when the Exeter stem was used because final femoral anteversion can be adjusted. Subsequently, cup preparation was performed. Cup insertion was performed in a flat, supine position. Femoral preparation was performed in the extended hip position. Radiographic cup inclination was aimed for 40 degrees and radiographic cup anteversion for 10\u0026ndash;30 degrees. Radiographic cup anteversion was defined intraoperatively considering femoral and stem anteversion. No other assistive devices\u0026mdash;including X-ray imaging and fluoroscopy\u0026mdash;were used intraoperatively. Informed consent was obtained from all patients before surgery. This study was performed at a single university hospital following the principles of the Declaration of Helsinki. Approval was obtained from the institutional research ethics committee.\u003c/p\u003e \u003cp\u003e \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\u003eBackground and surgical characteristics\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=\"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=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNavigation (n\u0026thinsp;=\u0026thinsp;30)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eControl (n\u0026thinsp;=\u0026thinsp;30)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ep-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge (years)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e67.5\u0026thinsp;\u0026plusmn;\u0026thinsp;10.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e64.4\u0026thinsp;\u0026plusmn;\u0026thinsp;10.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.29\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSex (female/male)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e27/3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e25/5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.52\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSide (right/left)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e14/16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10/20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.29\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBody mass index (kg/m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e22.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e23.9\u0026thinsp;\u0026plusmn;\u0026thinsp;3.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.23\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDiagnosis\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.00\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOsteoarthritis\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOsteonecrosis\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOperative time (min)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e84.5\u0026thinsp;\u0026plusmn;\u0026thinsp;20.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e86.5\u0026thinsp;\u0026plusmn;\u0026thinsp;27.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.79\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIntraoperative blood loss (mL)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e251.9\u0026thinsp;\u0026plusmn;\u0026thinsp;98.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e249.7\u0026thinsp;\u0026plusmn;\u0026thinsp;190.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.66\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\u003eValues are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Non-invasive AR-Based Navigation\u003c/h2\u003e \u003cp\u003eThis AR-based navigation system comprises a smartphone application, marker probe, smartphone fixation device, and cup holder (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This system has been studied and developed by the Engineering Department of Tokyo University. Pharmaceutical approval in Japan was obtained in March 2022. Since then, this system has been commercially available only in Japan. The marker probe, fixation device, and cup holder were used after sterilization. The smartphone was placed in a sterilized plastic bag. The smartphone application uses gyro and acceleration sensors to measure smartphone orientation and gravity vector. The application also uses AR technology to measure marker position, orientation, and probe tip position by capturing marker patterns. The marker pattern and the offset from the marker center to the probe tip are preliminarily programmed and used for the measurement.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBefore surgery, the smartphone is placed into the sterilized plastic bag. Before cup insertion, the smartphone is attached to the fixation device, which is rigidly clamped to the cup holder. The application procedure involves three steps: cup registration (step 1), anterior superior iliac spine (ASIS) registration (step 2), and target hunting (step 3). During step 1, the cup axis relative to the smartphone is measured by placing the flat aspect of the marker probe body along the cup rim and then measuring the marker probe (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). In this case, the relative unit vector \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\text{V}}_{\\text{c}\\text{u}\\text{p}}\\)\u003c/span\u003e\u003c/span\u003e of the cup axis from the smartphone can be measured as the Y-axis of the marker transformation matrix \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\text{M}}_{\\text{m}\\text{a}\\text{r}\\text{k}\\text{e}\\text{r}}\\)\u003c/span\u003e\u003c/span\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). During step 2, the position of the left and right ASIS\u0026mdash;palpable through the skin and soft tissue\u0026mdash;is provided to the application by measuring the tip of the marker probe. Let \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\text{O}\\)\u003c/span\u003e\u003c/span\u003e be the world coordinate system, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\text{M}}_{\\text{c}\\text{a}\\text{m}}\\)\u003c/span\u003e\u003c/span\u003e the transformation matrix from \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\text{O}\\)\u003c/span\u003e\u003c/span\u003e to the camera, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\text{M}}_{\\text{m}\\text{a}\\text{r}\\text{k}\\text{e}\\text{r}}\\)\u003c/span\u003e\u003c/span\u003e the transformation matrix from camera to marker center, and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\text{P}}_{\\text{o}\\text{f}\\text{f}\\text{s}\\text{e}\\text{t}}\\)\u003c/span\u003e\u003c/span\u003e the offset from the marker center to the probe tip (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). The probe tip position \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\text{P}\\)\u003c/span\u003e\u003c/span\u003e can be calculated using the following equation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv id=\"Equa\" class=\"Equation\"\u003e \u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\text{P}={\\text{M}}_{\\text{c}\\text{a}\\text{m}}*{\\text{M}}_{\\text{m}\\text{a}\\text{r}\\text{k}\\text{e}\\text{r}}*{\\text{P}}_{\\text{o}\\text{f}\\text{f}\\text{s}\\text{e}\\text{t}}$$\u003c/div\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\({\\text{M}}_{\\text{c}\\text{a}\\text{m}}\\)\u003c/span\u003e \u003c/span\u003e is calculated using position-tracking technology that can correct the smartphone\u0026rsquo;s location using visual information obtained from its camera, even if the smartphone is moved. \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\text{M}}_{\\text{m}\\text{a}\\text{r}\\text{k}\\text{e}\\text{r}}\\)\u003c/span\u003e\u003c/span\u003e is calculated using AR technology that detects the relative position and orientation from the camera to the marker based on the marker pattern from the camera image. The functional pelvic plane (FPP) defines cup inclination and anteversion [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] and is calculated from the left and right ASIS positions and gravity vector; it is then displayed using AR technology (Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Finally, during step 3, the smartphone attached to the cup holder shows the surgeon\u0026rsquo;s real-time cup alignment (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). The application calculates and shows real-time cup alignment using two factors: the real-time cup axis\u0026mdash;calculated from the relative cup axis achieved during step 1\u0026mdash;and real-time smartphone orientation, and the FPP achieved during step 2. The cup alignment value is correct provided that the pelvis does not move during step 3. Surgeons can adjust the cup by checking the real-time cup alignment. They can also verify the final cup alignment by attaching a smartphone to the cup holder. Step 2 can be repeated if the pelvis moves during step 3.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Outcomes\u003c/h2\u003e \u003cp\u003eThe primary outcome was the absolute value of the difference between the cup alignment\u0026mdash;measured intraoperatively\u0026mdash;and the postoperative cup alignment (absolute estimate error). Radiographic definitions were used for the intra- and postoperative measurements [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. In the navigation group, radiographic inclination and anteversion were measured using a navigation system after cup fixation. In the control group, alignment values were measured using a conventional goniometer after cup fixation. Postoperative radiographic cup inclination and anteversion on the first anteroposterior postoperative radiograph were manually measured by the first author (R.T.) using the iRad-OT system (INFOCOM Corp., Tokyo, Japan). To evaluate inter-observer reliability, the radiographic inclination and anteversion of 20 randomly selected patients were measured by a second observer (N.W.) using the iRad-OT system. To determine intra-observer reliability, the first author measured 30 patients 2 months after the first measurement. An absolute value of more than 10\u0026deg; was considered an outlier. The number of outliers was estimated for both groups.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Statistical and Power Analyses\u003c/h2\u003e \u003cp\u003eWelch\u0026rsquo;s \u003cem\u003et\u003c/em\u003e-test and chi-square tests were used to compare all navigation and control groups\u0026rsquo; factors. Intra- and inter-observer reliability for the postoperative cup alignment measurements were analyzed using intra-class correlation coefficients. Statistical significance was defined as a two-sided p\u0026thinsp;\u0026lt;\u0026thinsp;0.05. A statistical power analysis showed that 30 patients in each group would be sufficient to detect a 2.0\u0026deg; difference in the absolute estimate error between groups, with a power of 80% and a type I error rate of 5%. For the sample size calculation, based on the results of other studies, a standard deviation of 3.0\u0026deg; was used for the absolute target error [,14]. All statistical analyses were performed using G*Power, Version 3.1.9.2 (D\u0026uuml;sseldorf University, D\u0026uuml;sseldorf, Germany) and JMP for Mac, version 13.0.0 (SAS Institute, Cary, NC, USA).\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cp\u003eThe mean absolute estimate errors of cup inclination in the navigation and control groups were 2.9\u0026deg; (standard deviation [SD], \u0026plusmn;\u0026thinsp;2.8\u0026deg;) and 3.1\u0026deg; (SD, \u0026plusmn;\u0026thinsp;1.7\u0026deg;), respectively (p\u0026thinsp;=\u0026thinsp;0.67). Conversely, those of cup anteversion were 3.4\u0026deg; (SD, \u0026plusmn;\u0026thinsp;3.0\u0026deg;) and 5.4\u0026deg; (SD, \u0026plusmn;\u0026thinsp;3.6\u0026deg;), respectively (p\u0026thinsp;=\u0026thinsp;0.018) (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). No outliers were found in the navigation group, while two were found in the control group (p\u0026thinsp;=\u0026thinsp;0.52) (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). Cup alignment data of both groups are shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and the related scattergram is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. There were no significant differences between groups regarding patient background characteristics (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The intra-class correlation coefficients showed that intra- and inter-observer reliability for cup inclination and anteversion\u0026mdash;measured using the iRad-OT system\u0026mdash;was good to excellent (0.90 and 0.79, and 0.91 and 0.73, respectively).\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\u003eAbsolute target error\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=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" 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=\"char\" char=\".\" 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\u003eNavigation\u003c/p\u003e \u003cp\u003e(n\u0026thinsp;=\u0026thinsp;30)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eControl\u003c/p\u003e \u003cp\u003e(n\u0026thinsp;=\u0026thinsp;30)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDifference\u003c/p\u003e \u003cp\u003e(95% CI)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ep-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRadiographic inclination (\u0026deg;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e2.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e3.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.3 (-0.9\u0026ndash;1.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.67\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRadiographic anteversion (\u0026deg;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e3.4\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e5.4\u0026thinsp;\u0026plusmn;\u0026thinsp;3.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.0 (0.4\u0026ndash;3.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.018\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\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eValues are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation.\u003c/p\u003e \u003cp\u003eCI, confidence interval\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCup alignment\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=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026minus;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" 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\u003eNavigation\u003c/p\u003e \u003cp\u003e(n\u0026thinsp;=\u0026thinsp;30)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eControl\u003c/p\u003e \u003cp\u003e(n\u0026thinsp;=\u0026thinsp;30)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDifference\u003c/p\u003e \u003cp\u003e(95% CI)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ep-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRadiographic inclination (\u0026deg;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e40.1\u0026thinsp;\u0026plusmn;\u0026thinsp;3.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e38.6\u0026thinsp;\u0026plusmn;\u0026thinsp;3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c4\"\u003e \u003cp\u003e1.5 (-0.3\u0026ndash;3.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRadiographic anteversion (\u0026deg;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e19.6\u0026thinsp;\u0026plusmn;\u0026thinsp;4.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e19.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c4\"\u003e \u003cp\u003e0.01 (-2.1\u0026ndash;2.1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.99\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":"4. Discussion","content":"\u003cp\u003eThis new non-invasive AR-based navigation system enabled surgeons to achieve better cup orientation accuracy compared with the conventional goniometer. Furthermore, this system is simple and time efficient.\u003c/p\u003e \u003cp\u003eThe greatest advantage of this navigation system is that it is not invasive. Although AR technology has already been used in other navigation systems, this is the first portable navigation system that does not require an invasive procedure [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Theoretically, cup alignment accuracy could be reduced if the pelvis moves during the ASIS registration step. However, each step was completed within 1 minute, substantially aiding pelvic position maintenance throughout all procedures.\u003c/p\u003e \u003cp\u003eThere was no significant between-group difference regarding cup inclination because, in both groups, it was measured by referencing both ASIS locations. In contrast, cup anteversion was not measured using bone landmarks (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e); therefore, there was a significant between-group difference in cup anteversion accuracy.\u003c/p\u003e \u003cp\u003eSome authors have reported the cup positioning accuracy provided by other portable navigation systems [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Ogawa et al. reported the absolute error of the AR navigation system; their absolute values of radiographic inclination and anteversion were 1.9 and 2.8 degrees, respectively. Although their accuracy is superior to that of this study, this study\u0026rsquo;s system warrants recommendation because it is non-invasive [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. However, this navigation system can be used only for THA in the supine position. Therefore, a new non-invasive navigation system for THA in the lateral position should be developed. This study had several limitations. First, it was a single-center study. Second, the accuracy of this system was not directly compared with that of other navigation systems. The influence of this navigation system on important factors\u0026mdash;including cup position, offset, and leg length\u0026mdash;was not evaluated. Therefore, it cannot be completely concluded that our system is superior to others. However, because of its non-invasiveness, this system is worth using. Further studies should clarify whether this navigation system is superior to others. Third, the relatively small sample size prevented an evaluation of how patient characteristics (especially BMI, height, and osteoarthritis grade) influence this system\u0026rsquo;s accuracy. Fourth, the supine position during surgery was used as FPP; however, pelvic tilt during general anesthesia may differ from that of during awake state. Moreover, this system assumes no pelvic deformity/asymmetry; otherwise, this system would provide a wrong cup alignment value. CT-based navigation and robotic systems may overcome these issues [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Although no critical errors were found in the navigation group of this study, further research should evaluate the difference of the accuracy due to pelvic tilt and the influence of pelvic deformity and asymmetry. Fifth, a modified Watson\u0026ndash;Johnes approach was used in this study; it is unclear whether this navigation system is useful if other approaches are used.\u003c/p\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eThis new non-invasive AR-based navigation system showed superior cup positioning accuracy compared to a conventional goniometer. Because it is non-invasive, this system should be used to increase cup positioning accuracy during THA in the supine position.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eAR\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Augmented reality\u003c/p\u003e\n\u003cp\u003eASIS\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Anterior superior iliac spine\u003c/p\u003e\n\u003cp\u003eBMI\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Body mass index\u003c/p\u003e\n\u003cp\u003eFPP\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Functional pelvic plane\u003c/p\u003e\n\u003cp\u003eTHA\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Total hip arthroplasty\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate:\u0026nbsp;\u003c/strong\u003eThis study was performed at a single university hospital following the principles of the Declaration of Helsinki. Approval was obtained from the institutional research ethics committee.\u0026nbsp;Informed consent was obtained from all patients before surgery.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication:\u0026nbsp;\u003c/strong\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials:\u0026nbsp;\u003c/strong\u003eAll data generated or analysed during this study are included in this published article\u003cstrong\u003e.\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests:\u0026nbsp;\u003c/strong\u003eTheauthors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u0026nbsp;\u003c/strong\u003eThis project received technical support from Xel-ha Medical CO., LTD.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; contributions\u003c/strong\u003e\u003cstrong\u003e:\u003c/strong\u003e RT designed the study, performed data collection, analysis, and interpretation, and drafted the manuscript. KM, WN, and NS contributed to study design and data interpretation. WN contributed to the statistical processing of matching. KM contributed to data collection and interpretation. TY and HK contributed to restructuring the article.\u0026nbsp;All the authors approved the final manuscript as submitted and have agreed to be responsible for all aspects of this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements:\u0026nbsp;\u003c/strong\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; information:\u0026nbsp;\u003c/strong\u003eNot applicable.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eD\u0026rsquo;Lima DD, Urquhart AG, Buehler KO, Walker RH, Colwell CW. The effect of the orientation of the acetabular and femoral components on the range of motion of the hip at different head-neck ratios. 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Does acetabular robotic-assisted total hip arthroplasty with femoral navigation improve clinical outcomes at 1-year post-operative? A case-matched propensity score study comparing 98 robotic-assisted versus 98 manual implantation hip arthroplasties. Orthop Traumatol Surg Res. 2023;109:103477. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.otsr.2022.103477\u003c/span\u003e\u003cspan address=\"10.1016/j.otsr.2022.103477\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. Epub 2022 Nov 11.\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":"Augmented reality, Navigation system, Total hip arthroplasty, Cup alignment","lastPublishedDoi":"10.21203/rs.3.rs-4173945/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4173945/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eA new non-invasive augmented reality (AR)-based portable navigation system was developed for accurate cup positioning during total hip arthroplasty (THA) in the supine position. This study aimed to clarify whether the navigation system supports cup positioning more accurately than a conventional goniometer during surgery. The navigation system may provide more accurate cup alignment than the conventional goniometer.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eSixty patients who underwent THA in the supine position were enrolled. The navigation system was used for 30 patients (navigation group), and a conventional goniometer was used for 30 patients (control group) to measure radiographic cup inclination and anteversion during surgery. The primary outcome was the absolute value of the difference in cup alignment measured during surgery and by postoperative radiography.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eThe new non-invasive AR-based navigation system showed superior cup positioning accuracy compared to a conventional goniometer. An assessment of the primary outcome showed no significant difference in the radiographic cup inclination in the navigation and control groups (2.9\u0026deg; vs. 3.2\u0026deg;; mean difference, 0.3\u0026deg;; 95% confidence interval, -1.4\u0026ndash;0.9; p\u0026thinsp;=\u0026thinsp;0.67); however, the positioning in the navigation group was significantly more accurate than that in the control group in terms of radiographic anteversion (3.4\u0026deg; vs. 5.4\u0026deg;; mean difference, 2.0\u0026deg;; 95% confidence interval, 0.4\u0026ndash;3.8; p\u0026thinsp;=\u0026thinsp;0.017).\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eA new non-invasive AR-based portable navigation system resulted in more accurate cup positioning than the conventional goniometer. Because it is non-invasive, this system should be used for THA in the supine position.\u003c/p\u003e","manuscriptTitle":"Development of a non-invasive augmented reality-based navigation system for total hip arthroplasty in the supine position","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-01 16:59:40","doi":"10.21203/rs.3.rs-4173945/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":"088f01d7-bacc-4bf8-960c-e1ef76ecb930","owner":[],"postedDate":"April 1st, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-04-01T16:59:57+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-01 16:59:40","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4173945","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4173945","identity":"rs-4173945","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}