The transepicondylar axis or the posterior condylar axis: Which is the best reference for femoral component rotation in robotic-assisted total knee arthroplasty?

The transepicondylar axis or the posterior condylar axis: Which is the best reference for femoral component rotation in robotic-assisted total knee arthroplasty? | 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 The transepicondylar axis or the posterior condylar axis: Which is the best reference for femoral component rotation in robotic-assisted total knee arthroplasty? Qing-Da WEI, Hao-Ming AN, Yun-Hao TANG, Ming-Feng LI, Rui LI, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6737486/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Objective For robotic-assisted total knee arthroplasty (TKA), accurate identification of landmarks may have a direct impact on the displayed value for femoral component rotation. The aim of this study was to determine the effects of landmark identification by different surgeons on the consistency of the displayed values of the TEA (the angle between the transepicondylar axis and the femoral component axis) and PCA (the angle between the posterior condylar axis and the femoral component axis). Methods The anatomical data of 56 patients who underwent robotic-assisted TKA at our institution and whose landmarks (the transepicondylar axis and the posterior condylar axis) were identified by the two surgeons using the MAKO TKA system . After the data were standardized, the TEA value when the PCA was adjusted to 0° was recorded as α , and the PCA value when the TEA was adjusted to 0° was recorded as β . The measured value was α 1 β 1 for Surgeon-1 and α 2 β 2 for Surgeon-2. The values of α and β are defined as positive for external rotation and negative for internal rotation. Results The ICC consistency test of α was 0.761, and that of β was 0.943. Our data revealed that 26.8% of the ∆ α ( α 1 - α 2 ) values were > 2°, 42.9% were within 1°, 5.4% of the ∆ β ( β 1 - β 2 ) values were > 2°, and 80.4% were within 1°. Conclusion The posterior condylar axis was significantly more consistently identified than the transepicondylar axis was during robotic-assisted TKA by different surgeons. To avoid inappropriate femoral component rotation due to inaccurate identification, the surgeon should check the position of the landmarks, especially in patients who have anatomical abnormalities. Level of Evidence Level III, diagnostic study. Robotic-assisted Surgery Total knee arthroplasty Femoral component rotation Landmark Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Surgical robots are efficient tools that have changed the total knee arthroplasty (TKA) process owing to their use in preoperative planning and during surgery [ 1 – 3 ]. However, an issue prone to be overlooked is that the osteotomy plan displayed by the robot is dependent on the landmark identified by engineer (product specialist). The different landmark identification may affect the surgeon's judgment of the osteotomy parameters. Robotic precision for coronal alignment restoration has been confirmed in several studies [ 4 , 5 ]. However, few studies [ 6 ] have focused on femoral component rotation in robotic-assisted TKA, which may affect knee biomechanics [ 7 ]. In robotic-assisted TKA, the transepicondylar axis (a line connecting the medial epicondylar sulcus with the most prominent point of the lateral epicondylar sulcus [ 8 ]) and the posterior condylar axis (a line connecting the posterior aspect of the medial and lateral femoral condyles [ 9 ]) are commonly used to determine the degree of rotation of the femoral component. Which parameter is more suitable as a reference line in robotic-assisted TKA remains to be investigated. Some studies have confirmed that the transepicondylar axis is more difficult to identify [ 10 – 12 ], and some researchers believe that the posterior condylar axis is more stable [ 13 , 14 ]; Our study of robotic-assisted TKA osteotomy parameters also confirmed that the coefficient of variation for the transepicondylar axis is greater than that of the posterior condylar axis [ 15 ], which suggests that the identification of the landmark location have a direct effect on the osteotomy parameters. However, the magnitude of impact on the judgment of femoral component rotation remains unknown. Therefore, the aim of this study was to determine the effects of landmark identification by different surgeons on the consistency of the displayed values of the TEA (the angle between the transepicondylar axis and the femoral component axis) and PCA (the angle between the posterior condylar axis and the femoral component axis). Material and Methods In accordance with the Declaration of Helsinki, scientific and ethical committees of our institution approved this study (2024KY074-KS001). We reviewed the distal femoral model data stored in the MAKO TKA system ( Stryker, USA ) in our institute. All this cases were performed TKA with MAKO system between June 2021 and March 2024. The exclusion criteria for this study were (1) severe flexion contracture deformities (> 15°); (2) severe varus or valgus deformities (> 15°); Cases which modeling data was missing in the MAKO TKA system were not included. Ultimately, 56 patients with unilateral primary knee osteoarthritis were included in the study. Informed written consent has been obtained from all participants. Landmark Identification In the 3D model of the distal femur reconstructed by MAKO TKA system , the bony landmark points were marked by two experienced surgeons following previously published studies, and then each reference axis was determined. The surgical transepicondylar axis [ 8 ] is the line between the most prominent point of the lateral epicondyle (Fig. 1 . A ) and the sulcus of the medial epicondyle (Fig. 1 . B ). The posterior condylar axis [ 9 ] is the line connecting the lowest points of the medial (Fig. 1 . C ) and lateral posterior condyles (Fig. 1 . D ) of the femur. All landmarks were identified twice repeatedly and then averaged. Experimental Procedure All operations were performed on the MAKO TKA system , and the TEA (the angle between the transepicondylar axis and the femoral component axis) and PCA (the angle between the posterior condylar axis and the femoral component axis) values were displayed on the preoperative planning interface. All of the operations were performed after the surgery, only using the patient's anatomical model, without interfering with the surgery. First, the transepicondylar axis was selected as the first landmark, and, using the landmark selection interface, surgeon-1 marked the medial and lateral epicondyles to obtain the respective TEA and PCA values while keeping the default values of other landmarks. Since the robot system automatically adjusts the position of the femoral component according to the landmark, thereby affecting the angles [ 16 ], the data were standardized: the TEA value when the PCA was adjusted to 0° was recorded as α . The procedure was repeated for Surgeon-2. The measured value was α 1 for Surgeon-1 and α 2 for Surgeon-2. The posterior condylar axis was selected as the second landmark, and, using the landmark selection interface, surgeon-1 marked the medial and lateral posterior femoral condyles to obtain the respective TEA and PCA values while keeping the default values of other landmarks. Since the robot system automatically adjusts the position of the femoral component according to the landmark, thereby affecting the angles, the data were standardized: the PCA value when the TEA was adjusted to 0° was recorded as β . Surgeon-2 repeated the procedure. The measured value was β 1 for Surgeon-1 and β 2 for Surgeon-2 (Fig. 2 ). To minimize bias, Surgeon-1 and Surgeon-2 operated with mutual blinding. In addition, to circumvent the interference of the previous location, after each operation, return to the landmark selection interface, and the selected points were changed to random landmarks. The values of α and β are defined as positive for external rotation and negative for internal rotation. Statistical analysis Patient characteristics were subjected to statistical analysis, and a p value < 0.05 indicated statistical significance. We performed t tests to compare continuous variables and the chi-square test or Fisher’s exact probability test to compare categorical variables. We performed an ICC consistency test to compare the landmark identified by each surgeon and used scatter plots and bar graphs to depict the differences between the landmarks selected by different surgeons. Statistical analyses were performed using SPSS (v27.0), and the figures were drawn with GraphPad Prism, version 9.5 for Windows (GraphPad software). Results The characteristics of the patients are shown in Table 1 . Table 1 Characteristics of the patients (n = 56) Characteristic Value Age(yrs) 67.69 ± 5.27 (55–79) BMI(kg/m2) 26.40 ± 2.54 (19.14–31.05) Sex (n, % ) Men 19 (33.9%) Women 37 (66.1%) Side (n,% ) Left 26 (46.4%) Right 30 (53.6%) Preoperative HKA(°) 8.01 ± 7.47 (-15.8-26.1) Preoperative LDFA(°) 88.22 ± 4.12 (74.8–100.0) Preoperative MPTA(°) 84.90 ± 3.72 (75.2–95.9) Quantitative data are presented as means ± SDs, with the range in brackets; categorical data are presented as numbers, with the corresponding percentages in brackets; BMI, body mass index; HKA, hip-knee angle, positive for varus, negative for valgus; LDFA, lateral distal femoral angle; MPTA, medial proximal tibial angle. The values of α and β measured by the two surgeons are detailed in Fig. 3 . The above data conformed to a normal distribution after the Kolmogorov-Smirlov test (p > 0.05). The ICC consistency test revealed that both the TEA landmark location ( α ) and the PCA landmark location ( β ) were consistent across different surgeons (P 2°, 42.9% were within 1°, 5.4% of the ∆ β ( β 1 - β 2 ) values were > 2°, and 80.4% were within 1° (Fig. 4 ), indicating that the posterior condylar axis seems to have better consistency. Table 2 ICC consistency test between two surgeons N = 56 Surgeon-1 Surgeon-2 ICC ( P-Value ) α value 2.28 ± 3.06° 2.36 ± 3.40° 0.761 (< 0.001) β value 2.19 ± 2.82° 2.22 ± 3.29° 0.943 (0.000) α value, the angle between the transepicondylar axis and the femoral component axis when the angle between the posterior condylar axis and the femoral component axis was adjusted to 0°; β value, the angle between the posterior condylar axis and the femoral component axis when the angle between the transepicondylar axis and the femoral component axis was adjusted to 0°; Define the values of α and β as positive for external rotation and negative for internal rotation; Quantitative data are presented as means ± SDs Discussion This is the first study to quantitatively evaluate the differences in femoral component rotation due to landmarks identified by different surgeons directly on the MAKO TKA system . Our data revealed that the ICC of the TEA (0.761) was smaller than the ICC of the PCA (0.943), and 26.8% of patients had an observer difference > 2° for the TEA, whereas 5.4% of patients had an observer difference > 2° for the PCA, which may have caused problems with surgical planning. Our data revealed that the posterior condylar axis was significantly more consistently identified than the transepicondylar axis was (the ICCs of α and β were 0.761 and 0.943, respectively). Jerosch [ 17 ] reported that the range of anatomical points chosen by each surgeon during the operation varied by 22.3 mm on the medial epicondyle and 13.8 mm on the lateral epicondyle; even experienced surgeons experience difficulty in identifying its location [ 18 ] which was in line with our results. Morover, our results indicated that, in 26.8% of patients, the observer difference was > 2° for the TEA and up to 12°, which may significantly affect the degree of femoral component rotation. Numerous studies have shown that incorrect rotation of the femoral component is associated with many complications, including patellofemoral maltracking [ 19 ], anterior knee pain [ 20 ], stiffness [ 21 ], flexion instability [ 22 ], abnormal torsional stress on the tibial component leading to wear or loosening [ 23 ], and cam post impingement in a posterior-stabilized knee [ 24 ]. Therefore, the difference caused by landmark selection warrants attention considering the significant observer difference for the TEA. Although the transepicondylar axis is considered the most accurate landmark for locating the flexion axis of the knee [ 9 ], such a large variation can cause confusion for doctors during surgery. On the other hand, based on our data, the observer difference was within 1° for the PCA in 80.4% of patients, thus the posterior condylar line seems to be a more informative landmark under robotic-assisted TKA. In general, the posterior condylar axis + 3° is usually used to determine the external rotation of the femoral component during surgery [ 9 ]. However, ethnic groups also have an effect on the angle between the posterior condylar line and transepicondylar axis [ 25 ], so 3° is not accurate for all patients. Besides, in the robotic-assisted TKA, how much PCA is appropriate remains to be further studied. Therefore the experience of femoral rotation in manual TKA may not be applicable to robotic-assisted TKA, and we recommend the use of double landmarks cross-checking. Surgeons who choose the transepicondylar axis may think that the transepicondylar axis is closer to the flexion axis of the knee [ 8 ], whereas the posterior condylar line is based on 3–4° internally rotated in relation to the transepicondylar axis [ 9 ]. However, this anatomical-based definition does not seem important in robotic ligament balancing workflow, and we may need a more stable metric to evaluate the parameter boundaries for each surgery. It seems that the posterior condylar line is more competent to this criterion. However, it does not mean that the transepicondylar axis should be out of history, but rather that when the transepicondylar axis is chosen as a reference, more attention should be paid to the accuracy of landmark identification, especially when it is too far out of line compared to experience. We analyzed cases with excessive differences in landmark location and selected three typical samples (Fig. 5 ). Two representative anatomically abnormal types of the medial and lateral condyles were included in the following typical patients: first, the lateral condylar prominence was so flat that the depression point was not recognizable, and second, two prominences were present in the medial condylar. Surgeons who choose different anatomical points will experience a difference of more than 2°. Thus, surgeons should focus more intently on landmark location during the second preoperative examination. There are several limitations in our study. First, only two surgeons were compared, and differences may vary from surgeon to surgeon; however, the tendency for the TEA to have a greater dispersion is clear. Second, only the MAKO TKA system was used, and results may vary among other robots. Last, the sample size was small, so large-sample studies are needed in the future. Conclusion The posterior condylar axis was significantly more consistently identified than the transepicondylar axis was during robotic-assisted TKA by different surgeons. To avoid inappropriate femoral component rotation due to inaccurate identification, the surgeon should check the position of the landmarks, especially in patients with anatomical abnormalities. Abbreviations TKA, total knee arthroplasty; TEA, the angle between the transepicondylar axis and the femoral component axis; PCA, the angle between the posterior condylar axis and the femoral component axis; ICC, the intraclass correlation coefficient. Declarations Ethics approval and consent to participate Ethical approval for this study was obtained from IEC, the Fourth Medical Center of PLA General Hospital (2024KY074-KS001). Consent for publication Not applicable Availability of data and materials The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request. Competing Interests The authors received no financial or material support for the research, authorship, and publication of this article. Funding This study was supported by the Beijing Science and Technology Plan "AI+ Health Collaborative Innovation Cultivation" project (No. Z221100003522014). Author Contribution This study was conducted under the guidance of R.L. and W.C. The article was written by Q.-D.W. The statistical analysis was performed by Q.-D.W. and H.-M.A. The clinical assessment was done by W.G. and W.S. All authors read and approved the final manuscript. References Liow MH, Xia Z, Wong MK, Tay KJ, Yeo SJ, Chin PL. Robot-assisted total knee arthroplasty accurately restores the joint line and mechanical axis. A prospective randomised study. J Arthroplasty. 2014;29(12):2373-7. Hampp EL, Chughtai M, Scholl LY, Sodhi N, Bhowmik-Stoker M, Jacofsky DJ, et al. Robotic-Arm Assisted Total Knee Arthroplasty Demonstrated Greater Accuracy and Precision to Plan Compared with Manual Techniques. J Knee Surg. 2019;32(3):239-50. Song EK, Seon JK, Yim JH, Netravali NA, Bargar WL. Robotic-assisted TKA reduces postoperative alignment outliers and improves gap balance compared to conventional TKA. Clin Orthop Relat Res. 2013;471(1):118-26. Oussedik S, Abdel MP, Victor J, Pagnano MW, Haddad FS. Alignment in total knee arthroplasty. Bone Joint J. 2020;102-b(3):276-9. Mehliß V, Strauch Leira M, Serrano Olaizola A, Scior W, Graichen H. Proven accuracy for a new dynamic gap measurement in navigated TKA. Knee Surg Sports Traumatol Arthrosc. 2019;27(4):1189-95. Elkins JM, Jennings JM, Johnson RM, Brady AC, Parisi TJ, Dennis DA. Component Rotation in Well-Functioning, Gap Balanced Total Knee Arthroplasty Without Navigation. J Arthroplasty. 2023;38(6s):S204-s8. Kia M, Wright TM, Cross MB, Mayman DJ, Pearle AD, Sculco PK, et al. Femoral Component External Rotation Affects Knee Biomechanics: A Computational Model of Posterior-stabilized TKA. Clin Orthop Relat Res. 2018;476(1):113-23. Churchill DL, Incavo SJ, Johnson CC, Beynnon BD. The transepicondylar axis approximates the optimal flexion axis of the knee. Clin Orthop Relat Res. 1998(356):111-8. Olcott CW, Scott RD. A comparison of 4 intraoperative methods to determine femoral component rotation during total knee arthroplasty. J Arthroplasty. 2000;15(1):22-6. Arima J, Whiteside LA, McCarthy DS, White SE. Femoral rotational alignment, based on the anteroposterior axis, in total knee arthroplasty in a valgus knee. A technical note. J Bone Joint Surg Am. 1995;77(9):1331-4. Katz MA, Beck TD, Silber JS, Seldes RM, Lotke PA. Determining femoral rotational alignment in total knee arthroplasty: reliability of techniques. J Arthroplasty. 2001;16(3):301-5. Berger RA, Rubash HE, Seel MJ, Thompson WH, Crossett LS. Determining the rotational alignment of the femoral component in total knee arthroplasty using the epicondylar axis. Clin Orthop Relat Res. 1993(286):40-7. Jang ES, Connors-Ehlert R, LiArno S, Geller JA, Cooper HJ, Shah RP. Accuracy of Reference Axes for Femoral Component Rotation in Total Knee Arthroplasty: Computed Tomography-Based Study of 2,128 Femora. J Bone Joint Surg Am. 2019;101(23):e125. Conti MS, Kleeblad LJ, Jones CW, Pearle AD, Sculco PK. Distal Femoral Rotation is not Associated With Preoperative Proximal Tibial Varus Angle in Patients With Isolated Medial Compartment Osteoarthritis. J Arthroplasty. 2019;34(2):281-5. Wei QD, An HM, Gu W, Sun W, Li R, Chai W. Characteristics of Resection Parameters in Robot-Assisted Total Knee Arthroplasty With the Ligament Balancing Workflow. Orthop Surg. 2025;17(3):841-7. No A. MAKO Surgical Corp. MAKO TKA Surgical Guide. 2016 [Available from: https://www.strykermeded.com/media/2223/mako-tka-surgical-guide.pdf. Jerosch J, Peuker E, Philipps B, Filler T. Interindividual reproducibility in perioperative rotational alignment of femoral components in knee prosthetic surgery using the transepicondylar axis. Knee Surg Sports Traumatol Arthrosc. 2002;10(3):194-7. Franceschini V, Nodzo SR, Gonzalez Della Valle A. Femoral Component Rotation in Total Knee Arthroplasty: A Comparison Between Transepicondylar Axis and Posterior Condylar Line Referencing. J Arthroplasty. 2016;31(12):2917-21. Akagi M, Oh M, Nonaka T, Tsujimoto H, Asano T, Hamanishi C. An anteroposterior axis of the tibia for total knee arthroplasty. Clin Orthop Relat Res. 2004(420):213-9. Barrack RL, Schrader T, Bertot AJ, Wolfe MW, Myers L. Component rotation and anterior knee pain after total knee arthroplasty. Clin Orthop Relat Res. 2001(392):46-55. Boldt JG, Stiehl JB, Hodler J, Zanetti M, Munzinger U. Femoral component rotation and arthrofibrosis following mobile-bearing total knee arthroplasty. Int Orthop. 2006;30(5):420-5. Romero J, Stähelin T, Binkert C, Pfirrmann C, Hodler J, Kessler O. The clinical consequences of flexion gap asymmetry in total knee arthroplasty. J Arthroplasty. 2007;22(2):235-40. Puloski SK, McCalden RW, MacDonald SJ, Rorabeck CH, Bourne RB. Tibial post wear in posterior stabilized total knee arthroplasty. An unrecognized source of polyethylene debris. J Bone Joint Surg Am. 2001;83(3):390-7. Poilvache PL, Insall JN, Scuderi GR, Font-Rodriguez DE. Rotational landmarks and sizing of the distal femur in total knee arthroplasty. Clin Orthop Relat Res. 1996(331):35-46. Murgier J, Chantalat É, Li K, Chiron P, Telmon N, Huang W, et al. Distal femoral torsion: Differences between caucasians and asians. A multicentre computed tomography study of 515 distal femurs. Orthop Traumatol Surg Res. 2018;104(7):997-1001. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6737486","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":466365529,"identity":"1cf2d371-277d-4402-945c-b94009f12df8","order_by":0,"name":"Qing-Da WEI","email":"","orcid":"","institution":"the Fourth Medical Center of PLA General Hospital","correspondingAuthor":false,"prefix":"","firstName":"Qing-Da","middleName":"","lastName":"WEI","suffix":""},{"id":466365530,"identity":"6a35206d-1665-4fa6-8c30-4a5ec62bf445","order_by":1,"name":"Hao-Ming AN","email":"","orcid":"","institution":"the Fourth Medical Center of PLA General Hospital","correspondingAuthor":false,"prefix":"","firstName":"Hao-Ming","middleName":"","lastName":"AN","suffix":""},{"id":466365531,"identity":"f19b6ad6-985e-40ec-9328-a0ee8052a069","order_by":2,"name":"Yun-Hao TANG","email":"","orcid":"","institution":"the Fourth Medical Center of PLA General Hospital","correspondingAuthor":false,"prefix":"","firstName":"Yun-Hao","middleName":"","lastName":"TANG","suffix":""},{"id":466365532,"identity":"c9c09d33-4167-4194-abbe-38d8dfe1fada","order_by":3,"name":"Ming-Feng LI","email":"","orcid":"","institution":"the Fourth Medical Center of PLA General Hospital","correspondingAuthor":false,"prefix":"","firstName":"Ming-Feng","middleName":"","lastName":"LI","suffix":""},{"id":466365533,"identity":"96b27dd4-864b-4543-b568-4bbcc66e58ab","order_by":4,"name":"Rui LI","email":"","orcid":"","institution":"the Fourth Medical Center of PLA General Hospital","correspondingAuthor":false,"prefix":"","firstName":"Rui","middleName":"","lastName":"LI","suffix":""},{"id":466365534,"identity":"709de2ce-da72-4838-9d52-440a5ecf5df7","order_by":5,"name":"Wei CHAI","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAz0lEQVRIiWNgGAWjYDACCQaGA0DSjo2Z+cCBDz9I0JLMz86WeHBmD5FaQIBxZj+P8WEONiJ08M9ufniYp8KC2eAwz4fDDDwM8vxiBwhYcucYUPEZCT6Dw7wbDhdYMBjOnJ2AX4uBRILB4dw2CWawlhk8DAkGtwlqSf9wOPefBOOGwzwPDvOwEaUlB2hLgwTjzGYeBuK0SNzIKTj85xgwkJnZDICBLEHYL/wz0jd/nFFTZ8fGf/jxhw8/bOT5pQlowbCVNOWjYBSMglEwCrADAHgqRFVGPir5AAAAAElFTkSuQmCC","orcid":"","institution":"the Fourth Medical Center of PLA General Hospital","correspondingAuthor":true,"prefix":"","firstName":"Wei","middleName":"","lastName":"CHAI","suffix":""}],"badges":[],"createdAt":"2025-05-24 07:38:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6737486/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6737486/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":84214579,"identity":"fe19776f-f6a4-4b5c-9f15-329cfa4aa863","added_by":"auto","created_at":"2025-06-09 10:32:35","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":273821,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe standard of landmark identification\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn the 3D model of the distal femur reconstructed by \u003cem\u003eMAKO TKA system\u003c/em\u003e, the bony landmark points were marked. The surgical transepicondylar axis is the line between the most prominent point of the lateral epicondyle (Point A) and the sulcus of the medial epicondyle (Point B). The posterior condylar axis is the line connecting the lowest points of the medial (Point C) and lateral posterior condyles (Point D) of the femur. All landmarks were identified twice repeatedly and then averaged.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6737486/v1/948aa256645399166d7bcb63.png"},{"id":84216157,"identity":"2a85577f-75e8-4471-8ad1-5eb7798ed924","added_by":"auto","created_at":"2025-06-09 10:40:35","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":178032,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe workflow of landmark identification by different surgeons\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn the landmark selection interface of the \u003cem\u003eMAKO TKA system\u003c/em\u003e, surgeons obtain the respective TEA (the angle between the transepicondylar axis and the femoral component axis) and PCA (the angle between the posterior condylar axis and the femoral component axis) by marking the anatomical points of the transepicondylar axis while keeping the default values of other landmarks. The procedure was repeated for the posterior condylar axis. The data were standardized: the TEA value when the PCA was adjusted to 0° was recorded as \u003cstrong\u003eα\u003c/strong\u003e, and the PCA value when the TEA was adjusted to 0° was recorded as \u003cstrong\u003eβ\u003c/strong\u003e. The measured value was \u003cstrong\u003eα\u003c/strong\u003e\u003csub\u003e1\u003c/sub\u003e\u003cstrong\u003eβ\u003c/strong\u003e\u003csub\u003e1\u003c/sub\u003e for Surgeon-1 (red) and \u003cstrong\u003eα\u003c/strong\u003e\u003csub\u003e2\u003c/sub\u003e\u003cstrong\u003eβ\u003c/strong\u003e\u003csub\u003e2\u003c/sub\u003e for Surgeon-2 (blue). The values of \u003cstrong\u003eα\u003c/strong\u003e and \u003cstrong\u003eβ\u003c/strong\u003e are defined as positive for external rotation and negative for internal rotation.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6737486/v1/24f430c56eaf426e9c420ab6.png"},{"id":84214578,"identity":"44d7e9cf-9077-422a-a4b4-c331e3dc6938","added_by":"auto","created_at":"2025-06-09 10:32:35","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":77921,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe values of α and β measured by the two surgeons\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eα\u003c/strong\u003e value (black points), TEA (angle between the transepicondylar axis and the femoral component axis) when the PCA (angle between the posterior condylar axis and the femoral component axis) was adjusted to 0°; \u003cstrong\u003eβ\u003c/strong\u003e value (red points), PCA when the TEA was adjusted to 0°. The values of \u003cstrong\u003eα\u003c/strong\u003e and \u003cstrong\u003eβ\u003c/strong\u003e are defined as positive for external rotation and negative for internal rotation.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6737486/v1/349daf1668a833007f07968d.png"},{"id":84216159,"identity":"385a383d-e772-4c46-afbb-bcfc7bf88cfb","added_by":"auto","created_at":"2025-06-09 10:40:35","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":56097,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDistribution of the ∆α and ∆β values\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe \u003cstrong\u003eα\u003c/strong\u003e value is the TEA (the angle between the transepicondylar axis and the femoral component axis) when the PCA (the angle between the posterior condylar axis and the femoral component axis) is adjusted to 0°; the \u003cstrong\u003eβ\u003c/strong\u003e value is the PCA when the TEA is adjusted to 0°. The measured value was \u003cstrong\u003eα\u003c/strong\u003e\u003csub\u003e1\u003c/sub\u003e\u003cstrong\u003eβ\u003c/strong\u003e\u003csub\u003e1\u003c/sub\u003e for Surgeon-1 and \u003cstrong\u003eα\u003c/strong\u003e\u003csub\u003e2\u003c/sub\u003e\u003cstrong\u003eβ\u003c/strong\u003e\u003csub\u003e2\u003c/sub\u003e for Surgeon-2. Define ∆\u003cstrong\u003eα\u003c/strong\u003e (black column)\u003cstrong\u003e \u003c/strong\u003eas \u003cstrong\u003eα\u003c/strong\u003e\u003csub\u003e1\u003c/sub\u003e-\u003cstrong\u003eα\u003c/strong\u003e\u003csub\u003e2\u003c/sub\u003e and ∆\u003cstrong\u003eβ\u003c/strong\u003e (red column)\u003cstrong\u003e \u003c/strong\u003eas \u003cstrong\u003eβ\u003c/strong\u003e\u003csub\u003e1\u003c/sub\u003e-\u003cstrong\u003eβ\u003c/strong\u003e\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6737486/v1/15acf040d19502e77d6380dd.png"},{"id":84217567,"identity":"1d1c053e-2c80-4769-99c7-a08755cf34e9","added_by":"auto","created_at":"2025-06-09 10:56:35","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":190669,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTypical cases with anatomical abnormalities of the medial and lateral condyles\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis is a screenshot from the \u003cem\u003eMAKO TKA system\u003c/em\u003eof three patients’ distal femur models with abnormal abnormalities of the medial and lateral condyles. The dots represent anatomical points (the distal femoral point and the medial and lateral posterior condylar points, respectively).\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6737486/v1/259eee00a1e5961030902856.png"},{"id":90309597,"identity":"072311b8-64bf-4011-8669-2e6d1dafd544","added_by":"auto","created_at":"2025-09-01 09:39:33","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1451230,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6737486/v1/5bc8da94-c868-491d-8fdd-42bea09c5ac4.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"The transepicondylar axis or the posterior condylar axis: Which is the best reference for femoral component rotation in robotic-assisted total knee arthroplasty?","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSurgical robots are efficient tools that have changed the total knee arthroplasty (TKA) process owing to their use in preoperative planning and during surgery [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. However, an issue prone to be overlooked is that the osteotomy plan displayed by the robot is dependent on the landmark identified by engineer (product specialist). The different landmark identification may affect the surgeon's judgment of the osteotomy parameters. Robotic precision for coronal alignment restoration has been confirmed in several studies [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. However, few studies [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] have focused on femoral component rotation in robotic-assisted TKA, which may affect knee biomechanics [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn robotic-assisted TKA, the transepicondylar axis (a line connecting the medial epicondylar sulcus with the most prominent point of the lateral epicondylar sulcus [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]) and the posterior condylar axis (a line connecting the posterior aspect of the medial and lateral femoral condyles [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]) are commonly used to determine the degree of rotation of the femoral component. Which parameter is more suitable as a reference line in robotic-assisted TKA remains to be investigated.\u003c/p\u003e \u003cp\u003eSome studies have confirmed that the transepicondylar axis is more difficult to identify [\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], and some researchers believe that the posterior condylar axis is more stable [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]; Our study of robotic-assisted TKA osteotomy parameters also confirmed that the coefficient of variation for the transepicondylar axis is greater than that of the posterior condylar axis [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], which suggests that the identification of the landmark location have a direct effect on the osteotomy parameters. However, the magnitude of impact on the judgment of femoral component rotation remains unknown.\u003c/p\u003e \u003cp\u003eTherefore, the aim of this study was to determine the effects of landmark identification by different surgeons on the consistency of the displayed values of the TEA (the angle between the transepicondylar axis and the femoral component axis) and PCA (the angle between the posterior condylar axis and the femoral component axis).\u003c/p\u003e"},{"header":"Material and Methods","content":"\u003cp\u003e In accordance with the Declaration of Helsinki, scientific and ethical committees of our institution approved this study (2024KY074-KS001). We reviewed the distal femoral model data stored in the \u003cem\u003eMAKO TKA system\u003c/em\u003e (\u003cem\u003eStryker, USA\u003c/em\u003e) in our institute. All this cases were performed TKA with MAKO system between June 2021 and March 2024. The exclusion criteria for this study were (1) severe flexion contracture deformities (\u0026gt;\u0026thinsp;15\u0026deg;); (2) severe varus or valgus deformities (\u0026gt;\u0026thinsp;15\u0026deg;); Cases which modeling data was missing in the \u003cem\u003eMAKO TKA system\u003c/em\u003e were not included. Ultimately, 56 patients with unilateral primary knee osteoarthritis were included in the study. Informed written consent has been obtained from all participants.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eLandmark Identification\u003c/h2\u003e \u003cp\u003eIn the 3D model of the distal femur reconstructed by \u003cem\u003eMAKO TKA system\u003c/em\u003e, the bony landmark points were marked by two experienced surgeons following previously published studies, and then each reference axis was determined. The surgical transepicondylar axis [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] is the line between the most prominent point of the lateral epicondyle (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003cb\u003eA\u003c/b\u003e) and the sulcus of the medial epicondyle (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003cb\u003eB\u003c/b\u003e). The posterior condylar axis [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] is the line connecting the lowest points of the medial (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003cb\u003eC\u003c/b\u003e) and lateral posterior condyles (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003cb\u003eD\u003c/b\u003e) of the femur. All landmarks were identified twice repeatedly and then averaged.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Experimental Procedure","content":"\u003cp\u003eAll operations were performed on the \u003cem\u003eMAKO TKA system\u003c/em\u003e, and the TEA (the angle between the transepicondylar axis and the femoral component axis) and PCA (the angle between the posterior condylar axis and the femoral component axis) values were displayed on the preoperative planning interface. All of the operations were performed after the surgery, only using the patient's anatomical model, without interfering with the surgery.\u003c/p\u003e \u003cp\u003eFirst, the transepicondylar axis was selected as the first landmark, and, using the landmark selection interface, surgeon-1 marked the medial and lateral epicondyles to obtain the respective TEA and PCA values while keeping the default values of other landmarks. Since the robot system automatically adjusts the position of the femoral component according to the landmark, thereby affecting the angles [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], the data were standardized: the TEA value when the PCA was adjusted to 0\u0026deg; was recorded as \u003cb\u003eα\u003c/b\u003e. The procedure was repeated for Surgeon-2. The measured value was \u003cb\u003eα\u003c/b\u003e\u003csub\u003e1\u003c/sub\u003e for Surgeon-1 and \u003cb\u003eα\u003c/b\u003e\u003csub\u003e2\u003c/sub\u003e for Surgeon-2.\u003c/p\u003e \u003cp\u003eThe posterior condylar axis was selected as the second landmark, and, using the landmark selection interface, surgeon-1 marked the medial and lateral posterior femoral condyles to obtain the respective TEA and PCA values while keeping the default values of other landmarks. Since the robot system automatically adjusts the position of the femoral component according to the landmark, thereby affecting the angles, the data were standardized: the PCA value when the TEA was adjusted to 0\u0026deg; was recorded as \u003cb\u003eβ\u003c/b\u003e. Surgeon-2 repeated the procedure. The measured value was \u003cb\u003eβ\u003c/b\u003e\u003csub\u003e1\u003c/sub\u003e for Surgeon-1 and \u003cb\u003eβ\u003c/b\u003e\u003csub\u003e2\u003c/sub\u003e for Surgeon-2 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo minimize bias, Surgeon-1 and Surgeon-2 operated with mutual blinding. In addition, to circumvent the interference of the previous location, after each operation, return to the landmark selection interface, and the selected points were changed to random landmarks. The values of \u003cb\u003eα\u003c/b\u003e and \u003cb\u003eβ\u003c/b\u003e are defined as positive for external rotation and negative for internal rotation.\u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003ePatient characteristics were subjected to statistical analysis, and a p value\u0026thinsp;\u0026lt;\u0026thinsp;0.05 indicated statistical significance. We performed t tests to compare continuous variables and the chi-square test or Fisher\u0026rsquo;s exact probability test to compare categorical variables. We performed an ICC consistency test to compare the landmark identified by each surgeon and used scatter plots and bar graphs to depict the differences between the landmarks selected by different surgeons. Statistical analyses were performed using SPSS (v27.0), and the figures were drawn with GraphPad Prism, version 9.5 for Windows (GraphPad software).\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eThe characteristics of the patients are shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\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\u003eCharacteristics of the patients (n\u0026thinsp;=\u0026thinsp;56)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCharacteristic\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eValue\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge(yrs)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e67.69\u0026thinsp;\u0026plusmn;\u0026thinsp;5.27 (55\u0026ndash;79)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBMI(kg/m2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e26.40\u0026thinsp;\u0026plusmn;\u0026thinsp;2.54 (19.14\u0026ndash;31.05)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSex (n, % )\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMen\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e19 (33.9%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWomen\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e37 (66.1%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSide (n,% )\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLeft\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e26 (46.4%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRight\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e30 (53.6%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePreoperative HKA(\u0026deg;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e8.01\u0026thinsp;\u0026plusmn;\u0026thinsp;7.47 (-15.8-26.1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePreoperative LDFA(\u0026deg;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e88.22\u0026thinsp;\u0026plusmn;\u0026thinsp;4.12 (74.8\u0026ndash;100.0)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePreoperative MPTA(\u0026deg;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e84.90\u0026thinsp;\u0026plusmn;\u0026thinsp;3.72 (75.2\u0026ndash;95.9)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eQuantitative data are presented as means\u0026thinsp;\u0026plusmn;\u0026thinsp;SDs, with the range in brackets; categorical data are presented as numbers, with the corresponding percentages in brackets; BMI, body mass index; HKA, hip-knee angle, positive for varus, negative for valgus; LDFA, lateral distal femoral angle; MPTA, medial proximal tibial angle.\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\u003eThe values of \u003cb\u003eα\u003c/b\u003e and \u003cb\u003eβ\u003c/b\u003e measured by the two surgeons are detailed in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The above data conformed to a normal distribution after the Kolmogorov-Smirlov test (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe ICC consistency test revealed that both the TEA landmark location (\u003cb\u003eα\u003c/b\u003e) and the PCA landmark location (\u003cb\u003eβ\u003c/b\u003e) were consistent across different surgeons (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05\u003cb\u003e)\u003c/b\u003e. However, the ICC of \u003cb\u003eα\u003c/b\u003e was 0.761, and that of \u003cb\u003eβ\u003c/b\u003e was 0.943 (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Moreover, our data revealed that 26.8% of the ∆\u003cb\u003eα\u003c/b\u003e(\u003cb\u003eα\u003c/b\u003e\u003csub\u003e1\u003c/sub\u003e-\u003cb\u003eα\u003c/b\u003e\u003csub\u003e2\u003c/sub\u003e) values were \u0026gt;\u0026thinsp;2\u0026deg;, 42.9% were within 1\u0026deg;, 5.4% of the ∆\u003cb\u003eβ\u003c/b\u003e(\u003cb\u003eβ\u003c/b\u003e\u003csub\u003e1\u003c/sub\u003e-\u003cb\u003eβ\u003c/b\u003e\u003csub\u003e2\u003c/sub\u003e) values were \u0026gt;\u0026thinsp;2\u0026deg;, and 80.4% were within 1\u0026deg; (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), indicating that the posterior condylar axis seems to have better consistency.\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\u003eICC consistency test between two surgeons\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=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;56\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSurgeon-1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSurgeon-2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eICC (\u003cem\u003eP-Value\u003c/em\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eα\u003c/b\u003e value\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.28\u0026thinsp;\u0026plusmn;\u0026thinsp;3.06\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.36\u0026thinsp;\u0026plusmn;\u0026thinsp;3.40\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.761 (\u0026lt;\u0026thinsp;0.001)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eβ\u003c/b\u003e value\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.19\u0026thinsp;\u0026plusmn;\u0026thinsp;2.82\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.22\u0026thinsp;\u0026plusmn;\u0026thinsp;3.29\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.943 (0.000)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"4\" nameend=\"c4\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eα\u003c/b\u003e value, the angle between the transepicondylar axis and the femoral component axis when the angle between the posterior condylar axis and the femoral component axis was adjusted to 0\u0026deg;; \u003cb\u003eβ\u003c/b\u003e value, the angle between the posterior condylar axis and the femoral component axis when the angle between the transepicondylar axis and the femoral component axis was adjusted to 0\u0026deg;; Define the values of \u003cb\u003eα\u003c/b\u003e and \u003cb\u003eβ\u003c/b\u003e as positive for external rotation and negative for internal rotation; Quantitative data are presented as means\u0026thinsp;\u0026plusmn;\u0026thinsp;SDs\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"},{"header":"Discussion","content":"\u003cp\u003eThis is the first study to quantitatively evaluate the differences in femoral component rotation due to landmarks identified by different surgeons directly on the \u003cem\u003eMAKO TKA system\u003c/em\u003e. Our data revealed that the ICC of the TEA (0.761) was smaller than the ICC of the PCA (0.943), and 26.8% of patients had an observer difference\u0026thinsp;\u0026gt;\u0026thinsp;2\u0026deg; for the TEA, whereas 5.4% of patients had an observer difference\u0026thinsp;\u0026gt;\u0026thinsp;2\u0026deg; for the PCA, which may have caused problems with surgical planning.\u003c/p\u003e \u003cp\u003eOur data revealed that the posterior condylar axis was significantly more consistently identified than the transepicondylar axis was (the ICCs of \u003cb\u003eα\u003c/b\u003e and \u003cb\u003eβ\u003c/b\u003e were 0.761 and 0.943, respectively). Jerosch [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] reported that the range of anatomical points chosen by each surgeon during the operation varied by 22.3 mm on the medial epicondyle and 13.8 mm on the lateral epicondyle; even experienced surgeons experience difficulty in identifying its location [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] which was in line with our results. Morover, our results indicated that, in 26.8% of patients, the observer difference was \u0026gt;\u0026thinsp;2\u0026deg; for the TEA and up to 12\u0026deg;, which may significantly affect the degree of femoral component rotation. Numerous studies have shown that incorrect rotation of the femoral component is associated with many complications, including patellofemoral maltracking [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], anterior knee pain [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], stiffness [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], flexion instability [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], abnormal torsional stress on the tibial component leading to wear or loosening [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], and cam post impingement in a posterior-stabilized knee [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Therefore, the difference caused by landmark selection warrants attention considering the significant observer difference for the TEA. Although the transepicondylar axis is considered the most accurate landmark for locating the flexion axis of the knee [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], such a large variation can cause confusion for doctors during surgery.\u003c/p\u003e \u003cp\u003eOn the other hand, based on our data, the observer difference was within 1\u0026deg; for the PCA in 80.4% of patients, thus the posterior condylar line seems to be a more informative landmark under robotic-assisted TKA. In general, the posterior condylar axis\u0026thinsp;+\u0026thinsp;3\u0026deg; is usually used to determine the external rotation of the femoral component during surgery [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. However, ethnic groups also have an effect on the angle between the posterior condylar line and transepicondylar axis [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], so 3\u0026deg; is not accurate for all patients. Besides, in the robotic-assisted TKA, how much PCA is appropriate remains to be further studied. Therefore the experience of femoral rotation in manual TKA may not be applicable to robotic-assisted TKA, and we recommend the use of double landmarks cross-checking.\u003c/p\u003e \u003cp\u003eSurgeons who choose the transepicondylar axis may think that the transepicondylar axis is closer to the flexion axis of the knee [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], whereas the posterior condylar line is based on 3\u0026ndash;4\u0026deg; internally rotated in relation to the transepicondylar axis [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. However, this anatomical-based definition does not seem important in robotic ligament balancing workflow, and we may need a more stable metric to evaluate the parameter boundaries for each surgery. It seems that the posterior condylar line is more competent to this criterion. However, it does not mean that the transepicondylar axis should be out of history, but rather that when the transepicondylar axis is chosen as a reference, more attention should be paid to the accuracy of landmark identification, especially when it is too far out of line compared to experience.\u003c/p\u003e \u003cp\u003eWe analyzed cases with excessive differences in landmark location and selected three typical samples (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Two representative anatomically abnormal types of the medial and lateral condyles were included in the following typical patients: first, the lateral condylar prominence was so flat that the depression point was not recognizable, and second, two prominences were present in the medial condylar. Surgeons who choose different anatomical points will experience a difference of more than 2\u0026deg;. Thus, surgeons should focus more intently on landmark location during the second preoperative examination.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThere are several limitations in our study. First, only two surgeons were compared, and differences may vary from surgeon to surgeon; however, the tendency for the TEA to have a greater dispersion is clear. Second, only the \u003cem\u003eMAKO TKA system\u003c/em\u003e was used, and results may vary among other robots. Last, the sample size was small, so large-sample studies are needed in the future.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe posterior condylar axis was significantly more consistently identified than the transepicondylar axis was during robotic-assisted TKA by different surgeons. To avoid inappropriate femoral component rotation due to inaccurate identification, the surgeon should check the position of the landmarks, especially in patients with anatomical abnormalities.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eTKA, total knee arthroplasty;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTEA, the angle between the transepicondylar axis and the femoral component axis;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003ePCA, the angle between the posterior condylar axis and the femoral component axis;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eICC, the intraclass correlation coefficient.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEthical approval for this study was obtained from IEC, the Fourth Medical Center of PLA General Hospital (2024KY074-KS001).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors received no financial or material support for the research, authorship, and publication of this article.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was supported by the Beijing Science and Technology Plan \"AI+ Health Collaborative Innovation Cultivation\" project (No. Z221100003522014).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eThis study was conducted under the guidance of R.L. and W.C. The article was written by Q.-D.W. The statistical analysis was performed by Q.-D.W. and H.-M.A. The clinical assessment was done by W.G. and W.S. All authors read and approved the final manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eLiow MH, Xia Z, Wong MK, Tay KJ, Yeo SJ, Chin PL. Robot-assisted total knee arthroplasty accurately restores the joint line and mechanical axis. A prospective randomised study. J Arthroplasty. 2014;29(12):2373-7.\u003c/li\u003e\n\u003cli\u003eHampp EL, Chughtai M, Scholl LY, Sodhi N, Bhowmik-Stoker M, Jacofsky DJ, et al. Robotic-Arm Assisted Total Knee Arthroplasty Demonstrated Greater Accuracy and Precision to Plan Compared with Manual Techniques. J Knee Surg. 2019;32(3):239-50.\u003c/li\u003e\n\u003cli\u003eSong EK, Seon JK, Yim JH, Netravali NA, Bargar WL. Robotic-assisted TKA reduces postoperative alignment outliers and improves gap balance compared to conventional TKA. Clin Orthop Relat Res. 2013;471(1):118-26.\u003c/li\u003e\n\u003cli\u003eOussedik S, Abdel MP, Victor J, Pagnano MW, Haddad FS. Alignment in total knee arthroplasty. Bone Joint J. 2020;102-b(3):276-9.\u003c/li\u003e\n\u003cli\u003eMehli\u0026szlig; V, Strauch Leira M, Serrano Olaizola A, Scior W, Graichen H. Proven accuracy for a new dynamic gap measurement in navigated TKA. Knee Surg Sports Traumatol Arthrosc. 2019;27(4):1189-95.\u003c/li\u003e\n\u003cli\u003eElkins JM, Jennings JM, Johnson RM, Brady AC, Parisi TJ, Dennis DA. Component Rotation in Well-Functioning, Gap Balanced Total Knee Arthroplasty Without Navigation. J Arthroplasty. 2023;38(6s):S204-s8.\u003c/li\u003e\n\u003cli\u003eKia M, Wright TM, Cross MB, Mayman DJ, Pearle AD, Sculco PK, et al. Femoral Component External Rotation Affects Knee Biomechanics: A Computational Model of Posterior-stabilized TKA. Clin Orthop Relat Res. 2018;476(1):113-23.\u003c/li\u003e\n\u003cli\u003eChurchill DL, Incavo SJ, Johnson CC, Beynnon BD. The transepicondylar axis approximates the optimal flexion axis of the knee. Clin Orthop Relat Res. 1998(356):111-8.\u003c/li\u003e\n\u003cli\u003eOlcott CW, Scott RD. A comparison of 4 intraoperative methods to determine femoral component rotation during total knee arthroplasty. J Arthroplasty. 2000;15(1):22-6.\u003c/li\u003e\n\u003cli\u003eArima J, Whiteside LA, McCarthy DS, White SE. Femoral rotational alignment, based on the anteroposterior axis, in total knee arthroplasty in a valgus knee. A technical note. J Bone Joint Surg Am. 1995;77(9):1331-4.\u003c/li\u003e\n\u003cli\u003eKatz MA, Beck TD, Silber JS, Seldes RM, Lotke PA. Determining femoral rotational alignment in total knee arthroplasty: reliability of techniques. J Arthroplasty. 2001;16(3):301-5.\u003c/li\u003e\n\u003cli\u003eBerger RA, Rubash HE, Seel MJ, Thompson WH, Crossett LS. Determining the rotational alignment of the femoral component in total knee arthroplasty using the epicondylar axis. Clin Orthop Relat Res. 1993(286):40-7.\u003c/li\u003e\n\u003cli\u003eJang ES, Connors-Ehlert R, LiArno S, Geller JA, Cooper HJ, Shah RP. Accuracy of Reference Axes for Femoral Component Rotation in Total Knee Arthroplasty: Computed Tomography-Based Study of 2,128 Femora. J Bone Joint Surg Am. 2019;101(23):e125.\u003c/li\u003e\n\u003cli\u003eConti MS, Kleeblad LJ, Jones CW, Pearle AD, Sculco PK. Distal Femoral Rotation is not Associated With Preoperative Proximal Tibial Varus Angle in Patients With Isolated Medial Compartment Osteoarthritis. J Arthroplasty. 2019;34(2):281-5.\u003c/li\u003e\n\u003cli\u003eWei QD, An HM, Gu W, Sun W, Li R, Chai W. Characteristics of Resection Parameters in Robot-Assisted Total Knee Arthroplasty With the Ligament Balancing Workflow. Orthop Surg. 2025;17(3):841-7.\u003c/li\u003e\n\u003cli\u003eNo A. MAKO Surgical Corp. MAKO TKA Surgical Guide. 2016 [Available from: https://www.strykermeded.com/media/2223/mako-tka-surgical-guide.pdf.\u003c/li\u003e\n\u003cli\u003eJerosch J, Peuker E, Philipps B, Filler T. Interindividual reproducibility in perioperative rotational alignment of femoral components in knee prosthetic surgery using the transepicondylar axis. Knee Surg Sports Traumatol Arthrosc. 2002;10(3):194-7.\u003c/li\u003e\n\u003cli\u003eFranceschini V, Nodzo SR, Gonzalez Della Valle A. Femoral Component Rotation in Total Knee Arthroplasty: A Comparison Between Transepicondylar Axis and Posterior Condylar Line Referencing. J Arthroplasty. 2016;31(12):2917-21.\u003c/li\u003e\n\u003cli\u003eAkagi M, Oh M, Nonaka T, Tsujimoto H, Asano T, Hamanishi C. An anteroposterior axis of the tibia for total knee arthroplasty. Clin Orthop Relat Res. 2004(420):213-9.\u003c/li\u003e\n\u003cli\u003eBarrack RL, Schrader T, Bertot AJ, Wolfe MW, Myers L. Component rotation and anterior knee pain after total knee arthroplasty. Clin Orthop Relat Res. 2001(392):46-55.\u003c/li\u003e\n\u003cli\u003eBoldt JG, Stiehl JB, Hodler J, Zanetti M, Munzinger U. Femoral component rotation and arthrofibrosis following mobile-bearing total knee arthroplasty. Int Orthop. 2006;30(5):420-5.\u003c/li\u003e\n\u003cli\u003eRomero J, St\u0026auml;helin T, Binkert C, Pfirrmann C, Hodler J, Kessler O. The clinical consequences of flexion gap asymmetry in total knee arthroplasty. J Arthroplasty. 2007;22(2):235-40.\u003c/li\u003e\n\u003cli\u003ePuloski SK, McCalden RW, MacDonald SJ, Rorabeck CH, Bourne RB. Tibial post wear in posterior stabilized total knee arthroplasty. An unrecognized source of polyethylene debris. J Bone Joint Surg Am. 2001;83(3):390-7.\u003c/li\u003e\n\u003cli\u003ePoilvache PL, Insall JN, Scuderi GR, Font-Rodriguez DE. Rotational landmarks and sizing of the distal femur in total knee arthroplasty. Clin Orthop Relat Res. 1996(331):35-46.\u003c/li\u003e\n\u003cli\u003eMurgier J, Chantalat \u0026Eacute;, Li K, Chiron P, Telmon N, Huang W, et al. Distal femoral torsion: Differences between caucasians and asians. A multicentre computed tomography study of 515 distal femurs. Orthop Traumatol Surg Res. 2018;104(7):997-1001.\u003c/li\u003e\n\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":"Robotic-assisted Surgery, Total knee arthroplasty, Femoral component rotation, Landmark","lastPublishedDoi":"10.21203/rs.3.rs-6737486/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6737486/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eObjective\u003c/h2\u003e \u003cp\u003eFor robotic-assisted total knee arthroplasty (TKA), accurate identification of landmarks may have a direct impact on the displayed value for femoral component rotation. The aim of this study was to determine the effects of landmark identification by different surgeons on the consistency of the displayed values of the TEA (the angle between the transepicondylar axis and the femoral component axis) and PCA (the angle between the posterior condylar axis and the femoral component axis).\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eThe anatomical data of 56 patients who underwent robotic-assisted TKA at our institution and whose landmarks (the transepicondylar axis and the posterior condylar axis) were identified by the two surgeons using the \u003cem\u003eMAKO TKA system\u003c/em\u003e. After the data were standardized, the TEA value when the PCA was adjusted to 0\u0026deg; was recorded as \u003cb\u003eα\u003c/b\u003e, and the PCA value when the TEA was adjusted to 0\u0026deg; was recorded as \u003cb\u003eβ\u003c/b\u003e. The measured value was \u003cb\u003eα\u003c/b\u003e\u003csub\u003e1\u003c/sub\u003e\u003cb\u003eβ\u003c/b\u003e\u003csub\u003e1\u003c/sub\u003e for Surgeon-1 and \u003cb\u003eα\u003c/b\u003e\u003csub\u003e2\u003c/sub\u003e\u003cb\u003eβ\u003c/b\u003e\u003csub\u003e2\u003c/sub\u003e for Surgeon-2. The values of \u003cb\u003eα\u003c/b\u003e and \u003cb\u003eβ\u003c/b\u003e are defined as positive for external rotation and negative for internal rotation.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eThe ICC consistency test of \u003cb\u003eα\u003c/b\u003e was 0.761, and that of \u003cb\u003eβ\u003c/b\u003e was 0.943. Our data revealed that 26.8% of the ∆\u003cb\u003eα\u003c/b\u003e(\u003cb\u003eα\u003c/b\u003e\u003csub\u003e1\u003c/sub\u003e-\u003cb\u003eα\u003c/b\u003e\u003csub\u003e2\u003c/sub\u003e) values were \u0026gt;\u0026thinsp;2\u0026deg;, 42.9% were within 1\u0026deg;, 5.4% of the ∆\u003cb\u003eβ\u003c/b\u003e(\u003cb\u003eβ\u003c/b\u003e\u003csub\u003e1\u003c/sub\u003e-\u003cb\u003eβ\u003c/b\u003e\u003csub\u003e2\u003c/sub\u003e) values were \u0026gt;\u0026thinsp;2\u0026deg;, and 80.4% were within 1\u0026deg;.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eThe posterior condylar axis was significantly more consistently identified than the transepicondylar axis was during robotic-assisted TKA by different surgeons. To avoid inappropriate femoral component rotation due to inaccurate identification, the surgeon should check the position of the landmarks, especially in patients who have anatomical abnormalities.\u003c/p\u003e\u003ch2\u003eLevel of Evidence\u003c/h2\u003e \u003cp\u003eLevel III, diagnostic study.\u003c/p\u003e","manuscriptTitle":"The transepicondylar axis or the posterior condylar axis: Which is the best reference for femoral component rotation in robotic-assisted total knee arthroplasty?","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-09 10:32:31","doi":"10.21203/rs.3.rs-6737486/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":"5d2b2eb0-ca41-41e9-b879-7fb34a648897","owner":[],"postedDate":"June 9th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-09-01T09:39:22+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-09 10:32:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6737486","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6737486","identity":"rs-6737486","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}