Evaluation of the External Rotation of femur component in functionally aligned Robotic Assisted Total Knee Arthroplasty

Evaluation of the External Rotation of femur component in functionally aligned 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 Evaluation of the External Rotation of femur component in functionally aligned Robotic Assisted Total Knee Arthroplasty Dr. Sanjay Bhalchandra Londhe, Dr. Ravi Teja Rudraraju, Dr. Ravi Vinod Shah, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4250735/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: The conventional total knee arthroplasty (TKA) for grade 4 knee arthritis lacks individualized strategies for determining femur component rotation, contributing to suboptimal clinical outcomes and heightened patient dissatisfaction. Methods: A retrospective assessment of 100 consecutive active robotic assisted TKA (RA-TKA) patients was performed. Patients with grade 4 knee arthritis receiving RA-TKA were included, whereas prior knee surgery patients were excluded. The functionally aligned TKA (FTKA) trans-epicondylar axis (TEA), posterior condylar axis (PCA), and posterior femoral axis (FAA) were evaluated. The relation between FAA, TEA, and PCA were examined. Negative value denotes internal rotation of the femur component. The study's null hypothesis was that there would not be a statistically significant difference between FAA and the standard 3 degrees of external rotation applied during conventional TKA (C-TKA). The student's t-test was used to compare the mean rotation values (between FTKA and C-TKA) with p-value of less than 0.05 deemed significant. Results: Total 100 patients (Male: Female – 11:89) were studied. The FAA was externally rotated in relation to TEA (mean 1.451° SD 1.023°, p value <0.0001). As regards the PCA, the FAA was externally rotated (mean 2.36° SD 2.221°, p value 0.0002). Conclusion: Functional alignment TKA technique resulted in external rotation of the femur component in respect to TEA and PCA. This negates the null hypothesis indicating statistically significant difference amongst the femur component rotation implanted according to FTKA concept with robotic assisted technology and C-TKA. Robotic assisted total knee arthroplasty Transepicondylar axis Posterior condylar axis Functional alignment Kinematic alignment Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction The rotation of the femoral component plays a crucial role in achieving favorable results following Total Knee Arthroplasty (TKA). The alignment of internal or external rotation of the femur component in TKA significantly influences sustained clinical outcomes [ 1 , 2 ]. Malrotation or improper alignment of the femur component can potentially lead to complications like patellofemoral maltracking and instability [ 3 ], post TKA stiffness [ 4 ]. It can also lead to anterior knee pain, instability during mid-flexion [ 5 , 6 ]. Malrotated femur component can lead to abnormal tortional loading on the tibia component [ 7 ], impingement of the cam post in posterior stabilized (PS) cruciate sacrificing designs causing premature wear and loosening of the components [ 8 ]. There is no universal agreement on determining femur component rotation during the TKA operation. The two different techniques used are measured resection and gap balancing [ 9 , 10 ]. In measured resection, generally used bony landmarks are trans-epicondylar (TEA), posterior condylar (PCA) axes (Fig. 1 ). Studies on cadavers and radiography demonstrate that the TEA is parallel to the flexion-extension axis of the knee [ 7 , 8 ]. The intraoperative measurement of the TEA involves connecting the most prominent point of the lateral epicondyle with the centre of the medial epicondyle sulcus. The knee joint's flexion/extension axis may be accurately replicated and a rectangular gap achieved by using this landmark has been proven to be highly reliable [ 11 , 12 , 13 ]. The visualisation of the TEA during the procedure is challenging as the bony landmarks used for determining the TEA are covered with soft tissues (especially the medial epicondyle sulcus) [ 9 ]. In view of this difficulty PCA has been utilised as a surrogate for TEA during TKA procedure. Various studies have tried to evaluate the usefulness of PCA and TEA for accurately placing the femur component in proper rotation during TKA [ 5 , 8 , 14 , 15 , 16 , 17 ]. In conventional TKA, usually the femur zigs set the femur component in 3 degrees external rotation with respect to PCA. However multiple studies have shown that this method using PCA as a surrogate for the TEA may cause femur component malrotation in 25.5–72% of TKA [ 14 , 15 , 16 , 17 ]. As technology has advanced, the concept of Functional alignment in TKA (FTKA) offers a step up from kinematic alignment. Using robotic-assisted technology (RA-TKA) to refine bone resection, implant location, and/or soft tissue releases, FTKA improves TKA function according to each patient's unique alignment, bone structure, and soft tissue features surrounding the knee [ 18 ]. Replicating natural knee motions and improve patient-reported outcome measures are the two main objectives of FTKA. The study aims explore the relationships between posterior femoral axis of the functionally aligned TKA (FAA), TEA and PCA in patients undergoing RA-TKA. Methods We present a retrospective assessment of the data gathered from prospectively enrolled patients who underwent RA-TKA with Cuvis Joint robot (Curexo Inc, Korea supported by Meril Healthcare Pvt. Ltd, India). The Local Research Ethics Committee has waived the approval due to the retrospective nature of the study. One-hundred consecutive patients who underwent active RA-TKA were retrospectively reviewed by an independent observer. The study comprised patients with grade 4 arthritis of the knee joint receiving RA-TKA. Individuals who previously had the knee surgery were excluded from the study. One week prior to the procedure, patients were required to have a pre-operative CT scan of the leg scanned in hip, knee and ankle (HKA) regions. The scanned images were transferred in the .jpg format. By use of proprietary operating system and dedicated laptop, segmentation and pre-operative planning was performed. The desired alignment of the limb was HKA angle of 0 degrees with acceptable deviation of -3 to + 3 degrees (Fig. 2 ). Planning process involved establishing the HKA center, selecting the tibia and femur bony landmarks, obtaining precise implant position in sagittal, coronal and axial planes, determining the bony resection measurements at distal, anteroposterior (AP), anterior and posterior chamfer cuts and proximal cuts of tibia. The femur implant that fit precisely in all three planes without overhanging or notching was chosen (Fig. 3 ). The implant rotation was kept as close as possible to TEA and negative value denoted relative internal rotation of the femur component. The TEA, PCA and posterior femoral axis (FAA) were evaluated and correlation between FAA, TEA and PCA were determined (Fig. 4 ). The assessment was conducted by an independent observer who was not a member of the core surgical team. The study's null hypothesis was that there would not be a statistically significant difference between FAA and the standard 3 degrees of external rotation applied during conventional total knee arthroplasty (C-TKA). The student's t-test was used to compare the mean rotation values (between FTKA and CTKA) with p-value of less than 0.05 deemed significant. Results We conducted a study involving 100 consecutive patients diagnosed with grade 4 arthritis of the knee joint. Patients’ distribution was: 89% female and 11% males, and the average age of the participants was 68.3 years ( Table 1 ). Table 1 Patient Demographics undergoing robotic assisted total knee arthroplasty. Demographics n = 100 Mean Age, years 68.3 Males, n 11 Females, n 89 Left knees, n 53 Right Knees, n 47 A broad range of variability was observed amongst the FAA, TEA and PCA. The FAA in correlation to TEA was consistently observed to be externally rotated with the mean external rotation of 1.451°±1.023°. This implies a systematic and statistically significant external rotation, as evidenced by the p-value of < 0.0001. The tight range further underscores the consistency of this observed rotation among the study population. Similarly, the analysis of the PCA also demonstrated an external rotation of the FAA. The mean external rotation measured 2.36° with a standard deviation of 2.221°. The associated p-value of 0.0002 reinforces the statistical significance of this finding. Table 2 shows the relationship of FAA to TEA and PCA. The consistency in external rotation observed across both TEA and PCA comparisons implies a robust and reliable pattern in the functional alignment of the TKA. These results contradict the null hypothesis, demonstrating a statistically significant difference in femoral component rotation when implemented according to the FTKA concept with robotic-assisted technology as opposed to C-TKA. Clinically none of the 100 patients experienced any patellofemoral complications or premature loosening at one year follow up. Table 2 Femoral external rotation with respect to transepicondylar axis (TEA) and posterior condylar axis (PCA) in robotic assisted total knee arthroplasty. n = 100 Femoral rotation with TEA (degrees) Femoral rotation with PCA (degrees) Mean value (SD) 1.451 (± 1.023) 2.36 (± 2.221) P value < 0.0001 0.0002 TEA: transepicondylar axis; PCA: posterior condylar axis n: number of patients; SD: standard deviation Discussion The primary outcome of our research indicates that the FAA is externally rotated by 1.45 and 2.36 degrees in relation to TEA and PCA, respectively. Additionally, the study reveals a difference of 0.91 degrees between TEA and PCA. Consequently, the null hypothesis is negated, signifying a statistically significant variance observed among the FAA and standard 3 degrees of external rotation utilized in C-TKA. Precise alignment and rotation of implants play a pivotal role in the success of TKA, as any misalignment can result in issues like abnormal wear, premature loosening, and patellofemoral issues [ 18 , 19 , 20 ]. The fusion of navigation and robotic surgery has ushered in the functional alignment concept, enabling surgeons to utilize 3D simulations and real-time ligament tension data for precise adjustments during knee arthroplasty [ 21 , 22 ]. Research indicates that RA-TKA technology excels in gap balancing and accurately restores the joint line while preserving near-normal knee kinematics [ 22 ]. The improved precision of component placement in the sagittal plane with RA-TKA potentially facilitates greater accuracy in knee gap balancing than C-TKA [ 23 ]. The authors of a previously published prospective randomized study compared the patients who underwent RA-TKA and C-TKA. They noted early increase in maximum knee flexion in RA-TKA cohort (104.1°, 90°–120°) compared to C-TKA (93.3°, 90°–110°) p-value < 0.001 along with noticeable and gradual reduction in post-operative stiffness in the RA-TKA cohort [ 24 ]. A widely accepted standard among surgeons is a ± 3° rotation for implant alignment. The reported resections of the femoral as well as tibial components (coronal plane) in RA-TKA cases are oriented within ± 3° and accuracy of implant alignment in RA-TKA cohort is 94.7% for femoral component and 95% for tibial components whereas in C-TKA cases, the percentages are 87.2% for femoral components and 82.1% for tibial components [ 25 ]. Functional alignment’s primary goal is to position TKA components to reconstruct the joint's plane and obliquity while minimizing damage to soft tissues. Unlike kinematic alignment, functional alignment not only considers bony anatomy, but ensures a balanced alignment of soft tissues [ 26 ]. For satisfactory and optimal TKA outcomes, ensuring accurate rotational alignment of the femoral component is important [ 27 ]. While excessive external rotation may cause post-operative pain (including pain in anterior part of knee), flexion and mid-flexion instability, and stiffness, internal rotation result in patellar maltracking and instability [ 22 , 28 ]. In a study assessing 190 CT scans in which 65% of the healthy knee joints revealed an 3° internal rotation [ 29 ]. The progression of osteoarthritis may increase this rotation because of elevated soft tissue stress caused by growing malalignment of lower limb. To ensure uniform flexion gap alignment during TKA, the femoral component should be rotated in the opposite direction with the equivalent degree value [ 28 ]. Optimal functionality frequently correlates with an external rotation of the femoral component ranging between 3° to a maximum of 5° relative to the posterior condylar line or positioning it at 0° in relation to the transepicondylar line [ 20 ]. The two common landmarks used while deciding the femur component rotation in conventional TKA are TEA and PCA. Several authors suggest utilizing the epicondylar axis as a point of reference for bone cutting and ligament balances to create the most favourable flexion-extension axis [ 30 ]. Surgeon’s skill and experience with TKA play’s a crucial role in achieving femoral rotation alignment through the TEA during TKA procedure. Previous studies indicate variations in the accuracy of aligning knees with the accurate epicondylar axis employing TEA. Prior study has reported approximately 86.5% of knees to be within 5° range of the true epicondylar axis [ 31 ], while one study noted 90% of them deviated by less than 3° using the TEA [ 6 ], and another research reported rotation in 90.8% cases under 5 degrees from the surgical transepicondylar axis [ 27 ]. Techniques which use the PCA as a reference, assume that it represents the neutral axis of femoral rotation. In the research conducted by Benjamin J it was shown that the PCA predominantly matched the rotational positioning of the implanted femoral component in 62% cases, falling within ± 1° [ 32 ]. Due to individual’s varying wear patterns of the posterior condylar cartilage, it is not appropriate to generalize a fixed alignment of 3° of external rotation relative to the posterior aspect of the femoral condyles. Employing a 3° external rotation factor based on such assumptions may result in excessive external rotation, resulting in unfavourable clinical outcomes [ 33 ]. Our study shows that femoral external rotation with respect to PCA is 2.36 ± 2.221 degrees (as against fixed angle of 3 degrees) indicating statistical significance with p-value < 0.0002. The results of our study, involving femoral rotation with respect to TEA and PCA, demonstrated consistent external rotation in the functional alignment. The mean values, standard deviations, and p-values provided valuable insights into the biomechanics of osteoarthritis and the relationships between TEA, PCA, and FAA. Certain limitation of the studies are as follows: First limitation is our planning of setting the femur component rotation does not account for the gap balancing philosophy method. The gap balancing method initially achieves a balanced gap in extension. Subsequently, it adjusts the rotation of the femur component to attain a balanced rectangular gap relative to the upper tibia resection. The advantage of the RA-TKA is it mainly depends on measured resection philosophy thereby reducing the necessity of soft tissue releases. The second limitation is that the study presents a small series of patients of one ethnicity. Further studies are required at multiple centers involving more number of patients of different ethnicities. The third limitation is study did not evaluate the patient related outcomes (PROMS). Further extension of the present study is ongoing comparing the PROMS of this cohort versus the C-TKA cohorts. To the best of our knowledge, the study's strength lies in its novelty, in which we assessed the relationship between the posterior femoral axis of functionally aligned TKA and commonly used axes (i.e., TEA and PCA) for determining femur component rotation in the conventional method of performing TKA. Our study demonstrated that the FAA significantly differs from the routine 3 degrees of external rotation imparted in the C-TKA using currently available alignment instruments. Conclusion In conclusion, our investigation into the Functional Alignment concept in Total Knee Arthroplasty has yielded compelling results in a cohort of one hundred consecutive patients. The consistent external rotation observed in the functional Alignment Axis in relation to both the TEA and the PCA underscores a distinct departure from traditional alignment approaches. This aligns seamlessly with the fundamental principles of FTKA. The statistical significance of the observed external rotation emphasizes the need for a paradigm shift towards more patient-specific treatments. Our findings challenge the conventional practice of applying a uniform femur component external rotation, often around 3 degrees, across all patients. Instead, we advocate a more individualized and tailored approach, accounting for the unique characteristics of each patient's knee, which is in alignment with the principles of Functional Alignment concept in Total Knee Arthroplasty. Abbreviations 1. Total Knee Arthroplasty: TKA 2. Trans Epicondylar Axis: TEA 3. Posterior Condylar Axis: PCA 4. Functional Alignment in Total Knee Arthroplasty: FTKA 5. Robotic Assisted Total Knee Arthroplasty: RA-TKA 6. Conventional Total Knee Arthroplasty: C-TKA 7. Posterior Femoral Axis of the Functionally Aligned Total Knee Arthroplasty: FAA 8. Patient Reported Outcomes: PROMS Declarations Author Contribution All authors contributed to the study conception and design.SBL is the PI of the study and the senior surgeon. Material preparation, data analysis were performed by RTR and RVS. The first draft of the manuscript was written by RVS, GB, and SV. ZNJ helped with the statistical analysis of the data. All authors commented on previous versions of the manuscript and have read and approved the final manuscript. Acknowledgement We would like to acknowledge Dr. Dolly Singh for revising, finalizing and submitting the final version of the article. We also would like to acknowledge Mr. Nikhil Dhonde for his help in data collection and analysis. References Begum FA, Kayani B, Magan AA, Chang JS, Haddad FS (2021) Current concepts in total knee arthroplasty: mechanical, kinematic, anatomical, and functional alignment. Bone Jt Open 2(6):397-404. doi: 10.1302/2633-1462.26.BJO-2020-0162.R1 Hazratwala K, Gouk C, Wilkinson MPR, O'Callaghan WB (2023) Navigated functional alignment total knee arthroplasty achieves reliable, reproducible and accurate results with high patient satisfaction. 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Hyderabad","correspondingAuthor":false,"prefix":"Dr.","firstName":"Ravi","middleName":"Teja","lastName":"Rudraraju","suffix":""},{"id":291132129,"identity":"5d86b0db-7c8b-4ff9-ac3b-3d43e8edd72a","order_by":2,"name":"Dr. Ravi Vinod Shah","email":"","orcid":"","institution":"Criticare Asia Hospital, Andheri, Mumbai","correspondingAuthor":false,"prefix":"Dr.","firstName":"Ravi","middleName":"Vinod","lastName":"Shah","suffix":""},{"id":291132130,"identity":"b15c58dd-15d1-46f7-8748-c84d4629f2eb","order_by":3,"name":"Dr. Govindkumar Baranwal","email":"","orcid":"","institution":"Criticare Asia Hospital, Andheri, Mumbai","correspondingAuthor":false,"prefix":"Dr.","firstName":"Govindkumar","middleName":"","lastName":"Baranwal","suffix":""},{"id":291132131,"identity":"0a034ed6-c7a2-4103-a523-48593c7ec166","order_by":4,"name":"Dr. Suneet Velankar","email":"","orcid":"","institution":"Criticare Asia Hospital, Andheri, Mumbai","correspondingAuthor":false,"prefix":"Dr.","firstName":"Suneet","middleName":"","lastName":"Velankar","suffix":""},{"id":291132132,"identity":"e18b02f8-1a42-46d4-8458-d70e7137d40b","order_by":5,"name":"Zara Namjoshi","email":"","orcid":"","institution":"Criticare Asia Hospital, Andheri, Mumbai","correspondingAuthor":false,"prefix":"","firstName":"Zara","middleName":"","lastName":"Namjoshi","suffix":""}],"badges":[],"createdAt":"2024-04-11 07:06:40","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4250735/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4250735/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":54914098,"identity":"dd92b6fc-ce3f-4980-a582-95d6f73870d5","added_by":"auto","created_at":"2024-04-18 13:47:29","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":51012,"visible":true,"origin":"","legend":"\u003cp\u003erepresentative image of measured resection using bony landmarks- trans-epicondylar axis (TEA), posterior condylar axis (PCA).\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4250735/v1/4ab1c9649297d750de3b0325.jpg"},{"id":54914101,"identity":"a2a67657-b02e-416e-a227-0f33bc611528","added_by":"auto","created_at":"2024-04-18 13:47:30","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":31632,"visible":true,"origin":"","legend":"\u003cp\u003erepresentative image of alignment of the limb with Hip-Knee-Ankle (HKA) angle of 0 degrees.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4250735/v1/abefc2dc236a2cc43d631c35.jpg"},{"id":54914103,"identity":"f7160f77-bff3-47f6-bd97-706e4f50f563","added_by":"auto","created_at":"2024-04-18 13:47:30","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":69474,"visible":true,"origin":"","legend":"\u003cp\u003erepresentative image of femoral implant fit in coronal, sagittal and axial plane.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4250735/v1/5b23ac7d8a5d5ddd383471ba.jpg"},{"id":54914102,"identity":"0a105ef6-f24e-4f2c-a7a8-9d2694dd9a07","added_by":"auto","created_at":"2024-04-18 13:47:30","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":51916,"visible":true,"origin":"","legend":"\u003cp\u003eThe trans-epicondylar (TEA), posterior condylar (PCA) axes and posterior femoral axis (FAA) of the functionally aligned TKA (FTKA).\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4250735/v1/34434bee394c2427562cf5b8.jpg"},{"id":56313250,"identity":"92b1b2a8-9674-42d9-bdd0-bccfa33e5b08","added_by":"auto","created_at":"2024-05-11 16:46:50","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":484175,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4250735/v1/e44e572c-693e-480c-95f4-26dedb061806.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Evaluation of the External Rotation of femur component in functionally aligned Robotic Assisted Total Knee Arthroplasty","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe rotation of the femoral component plays a crucial role in achieving favorable results following Total Knee Arthroplasty (TKA). The alignment of internal or external rotation of the femur component in TKA significantly influences sustained clinical outcomes [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Malrotation or improper alignment of the femur component can potentially lead to complications like patellofemoral maltracking and instability [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], post TKA stiffness [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. It can also lead to anterior knee pain, instability during mid-flexion [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Malrotated femur component can lead to abnormal tortional loading on the tibia component [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], impingement of the cam post in posterior stabilized (PS) cruciate sacrificing designs causing premature wear and loosening of the components [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. There is no universal agreement on determining femur component rotation during the TKA operation. The two different techniques used are measured resection and gap balancing [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. In measured resection, generally used bony landmarks are trans-epicondylar (TEA), posterior condylar (PCA) axes (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eStudies on cadavers and radiography demonstrate that the TEA is parallel to the flexion-extension axis of the knee [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. The intraoperative measurement of the TEA involves connecting the most prominent point of the lateral epicondyle with the centre of the medial epicondyle sulcus. The knee joint's flexion/extension axis may be accurately replicated and a rectangular gap achieved by using this landmark has been proven to be highly reliable [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The visualisation of the TEA during the procedure is challenging as the bony landmarks used for determining the TEA are covered with soft tissues (especially the medial epicondyle sulcus) [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. In view of this difficulty PCA has been utilised as a surrogate for TEA during TKA procedure. Various studies have tried to evaluate the usefulness of PCA and TEA for accurately placing the femur component in proper rotation during TKA [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. In conventional TKA, usually the femur zigs set the femur component in 3 degrees external rotation with respect to PCA. However multiple studies have shown that this method using PCA as a surrogate for the TEA may cause femur component malrotation in 25.5\u0026ndash;72% of TKA [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAs technology has advanced, the concept of Functional alignment in TKA (FTKA) offers a step up from kinematic alignment. Using robotic-assisted technology (RA-TKA) to refine bone resection, implant location, and/or soft tissue releases, FTKA improves TKA function according to each patient's unique alignment, bone structure, and soft tissue features surrounding the knee [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Replicating natural knee motions and improve patient-reported outcome measures are the two main objectives of FTKA. The study aims explore the relationships between posterior femoral axis of the functionally aligned TKA (FAA), TEA and PCA in patients undergoing RA-TKA.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eWe present a retrospective assessment of the data gathered from prospectively enrolled patients who underwent RA-TKA with Cuvis Joint robot (Curexo Inc, Korea supported by Meril Healthcare Pvt. Ltd, India). The Local Research Ethics Committee has waived the approval due to the retrospective nature of the study. One-hundred consecutive patients who underwent active RA-TKA were retrospectively reviewed by an independent observer. The study comprised patients with grade 4 arthritis of the knee joint receiving RA-TKA. Individuals who previously had the knee surgery were excluded from the study. One week prior to the procedure, patients were required to have a pre-operative CT scan of the leg scanned in hip, knee and ankle (HKA) regions. The scanned images were transferred in the .jpg format. By use of proprietary operating system and dedicated laptop, segmentation and pre-operative planning was performed. The desired alignment of the limb was HKA angle of 0 degrees with acceptable deviation of -3 to +\u0026thinsp;3 degrees (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003ePlanning process involved establishing the HKA center, selecting the tibia and femur bony landmarks, obtaining precise implant position in sagittal, coronal and axial planes, determining the bony resection measurements at distal, anteroposterior (AP), anterior and posterior chamfer cuts and proximal cuts of tibia. The femur implant that fit precisely in all three planes without overhanging or notching was chosen (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe implant rotation was kept as close as possible to TEA and negative value denoted relative internal rotation of the femur component. The TEA, PCA and posterior femoral axis (FAA) were evaluated and correlation between FAA, TEA and PCA were determined (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe assessment was conducted by an independent observer who was not a member of the core surgical team. The study's null hypothesis was that there would not be a statistically significant difference between FAA and the standard 3 degrees of external rotation applied during conventional total knee arthroplasty (C-TKA). The student's t-test was used to compare the mean rotation values (between FTKA and CTKA) with p-value of less than 0.05 deemed significant.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eWe conducted a study involving 100 consecutive patients diagnosed with grade 4 arthritis of the knee joint. Patients\u0026rsquo; distribution was: 89% female and 11% males, and the average age of the participants was 68.3 years \u003cb\u003e(\u003c/b\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u003cb\u003e).\u003c/b\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\u003ePatient Demographics undergoing robotic assisted total knee arthroplasty.\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\u003eDemographics\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;100\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMean Age, years\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e68.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMales, n\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e11\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFemales, n\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e89\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLeft knees, n\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e53\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRight Knees, n\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e47\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\u003eA broad range of variability was observed amongst the FAA, TEA and PCA. The FAA in correlation to TEA was consistently observed to be externally rotated with the mean external rotation of 1.451\u0026deg;\u0026plusmn;1.023\u0026deg;. This implies a systematic and statistically significant external rotation, as evidenced by the p-value of \u0026lt;\u0026thinsp;0.0001. The tight range further underscores the consistency of this observed rotation among the study population.\u003c/p\u003e \u003cp\u003eSimilarly, the analysis of the PCA also demonstrated an external rotation of the FAA. The mean external rotation measured 2.36\u0026deg; with a standard deviation of 2.221\u0026deg;. The associated p-value of 0.0002 reinforces the statistical significance of this finding. Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the relationship of FAA to TEA and PCA. The consistency in external rotation observed across both TEA and PCA comparisons implies a robust and reliable pattern in the functional alignment of the TKA. These results contradict the null hypothesis, demonstrating a statistically significant difference in femoral component rotation when implemented according to the FTKA concept with robotic-assisted technology as opposed to C-TKA. Clinically none of the 100 patients experienced any patellofemoral complications or premature loosening at one year follow up.\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\u003eFemoral external rotation with respect to transepicondylar axis (TEA) and posterior condylar axis (PCA) in robotic assisted total knee arthroplasty.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;100\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFemoral rotation with TEA (degrees)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFemoral rotation with PCA (degrees)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMean value (SD)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.451 (\u0026plusmn;\u0026thinsp;1.023)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.36 (\u0026plusmn;\u0026thinsp;2.221)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP value\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.0002\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e \u003cp\u003eTEA: transepicondylar axis; PCA: posterior condylar axis\u003c/p\u003e \u003cp\u003en: number of patients; SD: standard deviation\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe primary outcome of our research indicates that the FAA is externally rotated by 1.45 and 2.36 degrees in relation to TEA and PCA, respectively. Additionally, the study reveals a difference of 0.91 degrees between TEA and PCA. Consequently, the null hypothesis is negated, signifying a statistically significant variance observed among the FAA and standard 3 degrees of external rotation utilized in C-TKA. Precise alignment and rotation of implants play a pivotal role in the success of TKA, as any misalignment can result in issues like abnormal wear, premature loosening, and patellofemoral issues [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The fusion of navigation and robotic surgery has ushered in the functional alignment concept, enabling surgeons to utilize 3D simulations and real-time ligament tension data for precise adjustments during knee arthroplasty [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Research indicates that RA-TKA technology excels in gap balancing and accurately restores the joint line while preserving near-normal knee kinematics [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. The improved precision of component placement in the sagittal plane with RA-TKA potentially facilitates greater accuracy in knee gap balancing than C-TKA [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The authors of a previously published prospective randomized study compared the patients who underwent RA-TKA and C-TKA. They noted early increase in maximum knee flexion in RA-TKA cohort (104.1\u0026deg;, 90\u0026deg;\u0026ndash;120\u0026deg;) compared to C-TKA (93.3\u0026deg;, 90\u0026deg;\u0026ndash;110\u0026deg;) p-value\u0026thinsp;\u0026lt;\u0026thinsp;0.001 along with noticeable and gradual reduction in post-operative stiffness in the RA-TKA cohort [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. A widely accepted standard among surgeons is a\u0026thinsp;\u0026plusmn;\u0026thinsp;3\u0026deg; rotation for implant alignment. The reported resections of the femoral as well as tibial components (coronal plane) in RA-TKA cases are oriented within \u0026plusmn;\u0026thinsp;3\u0026deg; and accuracy of implant alignment in RA-TKA cohort is 94.7% for femoral component and 95% for tibial components whereas in C-TKA cases, the percentages are 87.2% for femoral components and 82.1% for tibial components [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFunctional alignment\u0026rsquo;s primary goal is to position TKA components to reconstruct the joint's plane and obliquity while minimizing damage to soft tissues. Unlike kinematic alignment, functional alignment not only considers bony anatomy, but ensures a balanced alignment of soft tissues [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. For satisfactory and optimal TKA outcomes, ensuring accurate rotational alignment of the femoral component is important [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. While excessive external rotation may cause post-operative pain (including pain in anterior part of knee), flexion and mid-flexion instability, and stiffness, internal rotation result in patellar maltracking and instability [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. In a study assessing 190 CT scans in which 65% of the healthy knee joints revealed an 3\u0026deg; internal rotation [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. The progression of osteoarthritis may increase this rotation because of elevated soft tissue stress caused by growing malalignment of lower limb. To ensure uniform flexion gap alignment during TKA, the femoral component should be rotated in the opposite direction with the equivalent degree value [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Optimal functionality frequently correlates with an external rotation of the femoral component ranging between 3\u0026deg; to a maximum of 5\u0026deg; relative to the posterior condylar line or positioning it at 0\u0026deg; in relation to the transepicondylar line [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The two common landmarks used while deciding the femur component rotation in conventional TKA are TEA and PCA. Several authors suggest utilizing the epicondylar axis as a point of reference for bone cutting and ligament balances to create the most favourable flexion-extension axis [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Surgeon\u0026rsquo;s skill and experience with TKA play\u0026rsquo;s a crucial role in achieving femoral rotation alignment through the TEA during TKA procedure. Previous studies indicate variations in the accuracy of aligning knees with the accurate epicondylar axis employing TEA. Prior study has reported approximately 86.5% of knees to be within 5\u0026deg; range of the true epicondylar axis [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e], while one study noted 90% of them deviated by less than 3\u0026deg; using the TEA [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], and another research reported rotation in 90.8% cases under 5 degrees from the surgical transepicondylar axis [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTechniques which use the PCA as a reference, assume that it represents the neutral axis of femoral rotation. In the research conducted by Benjamin J it was shown that the PCA predominantly matched the rotational positioning of the implanted femoral component in 62% cases, falling within \u0026plusmn;\u0026thinsp;1\u0026deg; [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Due to individual\u0026rsquo;s varying wear patterns of the posterior condylar cartilage, it is not appropriate to generalize a fixed alignment of 3\u0026deg; of external rotation relative to the posterior aspect of the femoral condyles. Employing a 3\u0026deg; external rotation factor based on such assumptions may result in excessive external rotation, resulting in unfavourable clinical outcomes [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Our study shows that femoral external rotation with respect to PCA is 2.36\u0026thinsp;\u0026plusmn;\u0026thinsp;2.221 degrees (as against fixed angle of 3 degrees) indicating statistical significance with p-value\u0026thinsp;\u0026lt;\u0026thinsp;0.0002.\u003c/p\u003e \u003cp\u003eThe results of our study, involving femoral rotation with respect to TEA and PCA, demonstrated consistent external rotation in the functional alignment. The mean values, standard deviations, and p-values provided valuable insights into the biomechanics of osteoarthritis and the relationships between TEA, PCA, and FAA.\u003c/p\u003e \u003cp\u003eCertain limitation of the studies are as follows: First limitation is our planning of setting the femur component rotation does not account for the gap balancing philosophy method. The gap balancing method initially achieves a balanced gap in extension. Subsequently, it adjusts the rotation of the femur component to attain a balanced rectangular gap relative to the upper tibia resection. The advantage of the RA-TKA is it mainly depends on measured resection philosophy thereby reducing the necessity of soft tissue releases. The second limitation is that the study presents a small series of patients of one ethnicity. Further studies are required at multiple centers involving more number of patients of different ethnicities. The third limitation is study did not evaluate the patient related outcomes (PROMS). Further extension of the present study is ongoing comparing the PROMS of this cohort versus the C-TKA cohorts. To the best of our knowledge, the study's strength lies in its novelty, in which we assessed the relationship between the posterior femoral axis of functionally aligned TKA and commonly used axes (i.e., TEA and PCA) for determining femur component rotation in the conventional method of performing TKA. Our study demonstrated that the FAA significantly differs from the routine 3 degrees of external rotation imparted in the C-TKA using currently available alignment instruments.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn conclusion, our investigation into the Functional Alignment concept in Total Knee Arthroplasty has yielded compelling results in a cohort of one hundred consecutive patients. The consistent external rotation observed in the functional Alignment Axis in relation to both the TEA and the PCA underscores a distinct departure from traditional alignment approaches. This aligns seamlessly with the fundamental principles of FTKA.\u003c/p\u003e \u003cp\u003eThe statistical significance of the observed external rotation emphasizes the need for a paradigm shift towards more patient-specific treatments. Our findings challenge the conventional practice of applying a uniform femur component external rotation, often around 3 degrees, across all patients. Instead, we advocate a more individualized and tailored approach, accounting for the unique characteristics of each patient's knee, which is in alignment with the principles of Functional Alignment concept in Total Knee Arthroplasty.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003e1. Total Knee Arthroplasty: TKA\u003c/p\u003e\n\u003cp\u003e2. Trans Epicondylar Axis: TEA\u003c/p\u003e\n\u003cp\u003e3. Posterior Condylar Axis: PCA\u003c/p\u003e\n\u003cp\u003e4. Functional Alignment in Total Knee Arthroplasty: FTKA\u003c/p\u003e\n\u003cp\u003e5. Robotic Assisted Total Knee Arthroplasty: RA-TKA\u003c/p\u003e\n\u003cp\u003e6. Conventional Total Knee Arthroplasty: C-TKA\u003c/p\u003e\n\u003cp\u003e7. Posterior Femoral Axis of the Functionally Aligned Total Knee Arthroplasty: FAA\u003c/p\u003e\n\u003cp\u003e8. Patient Reported Outcomes: PROMS\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAll authors contributed to the study conception and design.SBL is the PI of the study and the senior surgeon. Material preparation, data analysis were performed by RTR and RVS. The first draft of the manuscript was written by RVS, GB, and SV. ZNJ helped with the statistical analysis of the data. All authors commented on previous versions of the manuscript and have read and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eWe would like to acknowledge Dr. Dolly Singh for revising, finalizing and submitting the final version of the article. We also would like to acknowledge Mr. Nikhil Dhonde for his help in data collection and analysis.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBegum FA, Kayani B, Magan AA, Chang JS, Haddad FS (2021) Current concepts in total knee arthroplasty: mechanical, kinematic, anatomical, and functional alignment. Bone Jt Open 2(6):397-404. doi: 10.1302/2633-1462.26.BJO-2020-0162.R1\u003c/li\u003e\n\u003cli\u003eHazratwala K, Gouk C, Wilkinson MPR, O\u0026apos;Callaghan WB (2023) Navigated functional alignment total knee arthroplasty achieves reliable, reproducible and accurate results with high patient satisfaction. Knee Surg Sports Traumatol Arthrosc 31(9):3861-3870. doi: 10.1007/s00167-023-07327-w\u003c/li\u003e\n\u003cli\u003eVerlinden C, Uvin P, Labey L, Luyckx JP, Bellemans J, Vandenneucker H (2010) The influence of malrotation of the femoral component in total knee replacement on the mechanics of patellofemoral contact during gait: an in vitro biomechanical study. J Bone Joint Surg Br 92(5):737-42. doi: 10.1302/0301-620X.92B5.22603\u003c/li\u003e\n\u003cli\u003eClark G, Steer R, Wood D (2023) Functional alignment achieves a more balanced total knee arthroplasty than either mechanical alignment or kinematic alignment prior to soft tissue releases. Knee Surg Sports Traumatol Arthrosc 31(4):1420-1426. doi: 10.1007/s00167-022-07156-3\u003c/li\u003e\n\u003cli\u003eCastelli CC, Falvo DA, Iapicca ML, Gotti V (2016) Rotational alignment of the femoral component in total knee arthroplasty. 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BMC Musculoskelet Disord 24:660. https://doi.org/10.1186/s12891-023-06781-4\u003c/li\u003e\n\u003cli\u003eFranceschini V, Nodzo SR, Gonzalez Della Valle A (2016) Femoral Component Rotation in Total Knee Arthroplasty: A Comparison Between Transepicondylar Axis and Posterior Condylar Line Referencing. J Arthroplasty 31(12):2917-2921. doi: 10.1016/j.arth.2016.05.032 \u003c/li\u003e\n\u003cli\u003eNejima S, Kumagai K, Kobayashi H, Yamada S, Akamatsu T, Ogino T, Sotozawa M, Inaba Y (2021) Coronal shaft bowing of the femur affects varus inclination of the surgical transepicondylar axis in varus knee osteoarthritis. Knee Surg Sports Traumatol Arthrosc 29(3):814-819. doi: 10.1007/s00167-020-06025-1\u003c/li\u003e\n\u003cli\u003eNam JH, Koh YG, Kim PS, Park JH, Kang KT (2020) Effect of the presence of the articular cartilage on the femoral component rotation in total knee arthroplasty in female and varus osteoarthritis knees. J Orthop Surg Res 15(1):499. doi: 10.1186/s13018-020-02030-9 \u003c/li\u003e\n\u003cli\u003eMiller MC, Berger RA, Petrella AJ, Karmas A, Rubash HE (2001) Optimizing femoral component rotation in total knee arthroplasty. Clin Orthop Relat Res 392:38-45. doi: 10.1097/00003086-200111000-00005\u003c/li\u003e\n\u003cli\u003eLongstaff LM, Sloan K, Stamp N, Scaddan M, Beaver R (2009) Good alignment after total knee arthroplasty leads to faster rehabilitation and better function. J Arthroplasty 24(4):570-578. doi:10.1016/j.arth.2008.03.002 \u003c/li\u003e\n\u003cli\u003eAglietti P, Sensi L, Cuomo P, Ciardullo A (2008) Rotational position of femoral and tibial components in TKA using the femoral transepicondylar axis. Clin Orthop Relat Res 466(11):2751-5. doi: 10.1007/s11999-008-0452-8\u003c/li\u003e\n\u003cli\u003evan der Linden-van der Zwaag HM, Valstar ER, van der Molen AJ, Nelissen RG (2008) Transepicondylar axis accuracy in computer assisted knee surgery: a comparison of the CT-based measured axis versus the CAS-determined axis. Comput Aided Surg 13(4):200-6. doi: 10.3109/10929080802240134 \u003c/li\u003e\n\u003cli\u003eRivi\u0026egrave;re C, Villet L, Jeremic D, Vendittoli PA (2021) What you need to know about kinematic alignment for total knee arthroplasty. Orthop Traumatol Surg Res 107(1S):102773. doi: 10.1016/j.otsr.2020.102773 \u003c/li\u003e\n\u003cli\u003eHe R, Sun ML, Xiong R, Yang PF, Lei K, Liu LM, Yang L, Guo L (2022) A Newly Designed \u0026quot;SkyWalker\u0026quot; Robot Applied in Total Knee Arthroplasty: A Retrospective Cohort Study for Femoral Rotational Alignment Restoration. Orthop Surg 14(8):1681-1694. doi: 10.1111/os.13365\u003c/li\u003e\n\u003cli\u003eSong EK, Seon JK, Yim Ji-H, Netravali NA, Bargar WL (2013) Robotic-assisted TKA Reduces Postoperative Alignment Outliers and Improves Gap Balance Compared to Conventional TKA. Clinical Orthopaedics and Related Research 471(1):118-126. doi: 10.1007/s11999-012-2407-3\u003c/li\u003e\n\u003cli\u003eKayani B, Konan S, Tahmassebi J, Oussedik S, Moriarty PD, Haddad FS (2020) A prospective double-blinded randomised control trial comparing robotic arm-assisted functionally aligned total knee arthroplasty versus robotic arm-assisted mechanically aligned total knee arthroplasty. Trials 21(1):194. doi: 10.1186/s13063-020-4123-8\u003c/li\u003e\n\u003cli\u003eZhang J, Ndou WS, Ng N, Gaston P, Simpson PM, Macpherson GJ, Patton JT, Clement ND (2022) Robotic-arm assisted total knee arthroplasty is associated with improved accuracy and patient reported outcomes: a systematic review and meta-analysis. Knee Surg Sports Traumatol Arthrosc 30(8):2677-2695. doi: 10.1007/s00167-021-06464-4 \u003c/li\u003e\n\u003cli\u003eDoan G (2021) An Accuracy and Precision Analysis of the VELYS\u0026trade; Robotic Assisted Solution for Total Knee Arthroplasty. Electronic Theses and Dissertations. 1909. https://digitalcommons.du.edu/etd/1909\u003c/li\u003e\n\u003cli\u003eSeo JG, Moon YW, Lim JS, Park SJ, Kim SM (2012) Mechanical axis-derived femoral component rotation in extramedullary total knee arthroplasty: a comparison between femoral transverse axis and transepicondylar axis. Knee Surg Sports Traumatol Arthrosc 20(3):538-45. doi: 10.1007/s00167-011-1597-7\u003c/li\u003e\n\u003cli\u003eMaciąg BM, Kordyaczny T, Maciąg GJ, Łapiński M, Jegierski D, Świderek J, Tsitko H, Dorocińska M et al (2023) Comparison of Femoral Component Rotation between Robotic-Assisted vs. Soft-Tissue Tensor Total Knee Arthroplasty with Anatomic Implants. Medicina (Kaunas) 59(5):880. doi: 10.3390/medicina59050880 \u003c/li\u003e\n\u003cli\u003eNewman CR, Walter WL, Talbot S (2018) Femoral rotational asymmetry is a common anatomical variant. Clin Anat 31(4):551-559. doi: 10.1002/ca.23053\u003c/li\u003e\n\u003cli\u003eMukartihal R, Bhat VK, Das R, Chandan S, Patil SS, Rathnakar V, Gurava Reddy AV, Annapareddy A (2023) Relationship between femoral component placement and patient-specific anatomical rotational landmarks in robotic arm assisted total knee Arthroplasty- a multicentric study. J Orthop 45:87-90. doi: 10.1016/j.jor.2023.10.010\u003c/li\u003e\n\u003cli\u003eKinzel V, Ledger M, Shakespeare D (2005) Can the epicondylar axis be defined accurately in total knee arthroplasty? Knee 12(4):293-6. doi: 10.1016/j.knee.2004.09.003.\u003c/li\u003e\n\u003cli\u003eBenjamin J (2008) Determining femoral component position using CAS and measured resection. Clin Orthop Relat Res 466(11):2745-50. doi: 10.1007/s11999-008-0426-x\u003c/li\u003e\n\u003cli\u003ePatel AR, Talati RK, Yaffe MA, McCoy BW, Stulberg SD (2014) Femoral component rotation in total knee arthroplasty: an MRI-based evaluation of our options. J Arthroplasty 29(8):1666-70. doi: 10.1016/j.arth.2014.02.033\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 total knee arthroplasty, Transepicondylar axis, Posterior condylar axis, Functional alignment, Kinematic alignment","lastPublishedDoi":"10.21203/rs.3.rs-4250735/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4250735/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe conventional total knee arthroplasty (TKA) for grade 4 knee arthritis lacks individualized strategies for determining femur component rotation, contributing to suboptimal clinical outcomes and heightened patient dissatisfaction.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA retrospective assessment of 100 consecutive active robotic assisted TKA (RA-TKA) patients was performed. Patients with grade 4 knee arthritis receiving RA-TKA were included, whereas prior knee surgery patients were excluded. The functionally aligned TKA (FTKA) trans-epicondylar axis (TEA), posterior condylar axis (PCA), and posterior femoral axis (FAA) were evaluated. The relation between FAA, TEA, and PCA were examined. Negative value denotes internal rotation of the femur component. The study's null hypothesis was that there would not be a statistically significant difference between FAA and the standard 3 degrees of external rotation applied during conventional TKA (C-TKA). The student's t-test was used to compare the mean rotation values (between FTKA and C-TKA) with p-value of less than 0.05 deemed significant.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTotal 100 patients (Male: Female – 11:89) were studied. The FAA was externally rotated in relation to TEA (mean 1.451° SD 1.023°, p value \u0026lt;0.0001). As regards the PCA, the FAA was externally rotated (mean 2.36° SD 2.221°, p value 0.0002).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFunctional alignment TKA technique resulted in external rotation of the femur component in respect to TEA and PCA. This negates the null hypothesis indicating statistically significant difference amongst the femur component rotation implanted according to FTKA concept with robotic assisted technology and C-TKA.\u003c/p\u003e","manuscriptTitle":"Evaluation of the External Rotation of femur component in functionally aligned Robotic Assisted Total Knee Arthroplasty","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-18 13:47:25","doi":"10.21203/rs.3.rs-4250735/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":"7063b111-8909-4510-ab7e-8202a91a4354","owner":[],"postedDate":"April 18th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-05-11T16:38:41+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-18 13:47:25","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4250735","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4250735","identity":"rs-4250735","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}