Robotic Assisted Primary Total Knee Arthroplasty for Severe Varus Knee Utilizing an Unconstrained Prosthesis: a retrospective study

Robotic Assisted Primary Total Knee Arthroplasty for Severe Varus Knee Utilizing an Unconstrained Prosthesis: a retrospective study | 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 Robotic Assisted Primary Total Knee Arthroplasty for Severe Varus Knee Utilizing an Unconstrained Prosthesis: a retrospective study Hongmei Zhang, Yuanyuan Li, Lin Jing, Peiyan Hu, Hai Tang, Mingjiang He This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7234889/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 Recent findings indicated that robotic-assisted primary total knee arthroplasty (TKA) utilizing an unconstrained prosthesis for severe varus knee (SVK) showed excellent clinical outcomes. The surgical techniques are valuable to be explored. Methods Patients with SVKs and intact medial and lateral collateral ligaments underwent robotic assisted primary TKAs by using the unconstrained posterior stabilized (PS) prostheses. The osteotomy principle was that the more severe the varus degree, the thinner the resection. Tibial resection was assessed on the lateral plateau, and medial plateau defects were managed with cement, bone grafts, or augments, depending on defect size and depth. The femoral external rotation angle was determined using the transepicondylar axis (TEA) and posterior condylar angle (PCA), rather than the conventional 3°. Radiographic evaluations included the hip-knee-ankle angle (HKAA), PCA, lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), posterior tibial slope (PTS), patella tilt angle (PTA), and Insall-Salvati ratio (ISR). Clinical evaluations comprised the range of motion (ROM) and the Hospital for Special Surgery (HSS) knee score. Results Postoperative improvements were significant for HKAA, LDFA, PCA, MPTA, PTS, and PTA compared to preoperative values: 178.52 ± 1.79° vs. 156.34 ± 1.85°, 90.03 ± 0.39° vs. 83.92 ± 0.42°, 6.53 ± 0.89° vs. 3.32 ± 0.02°, 90.15 ± 0.47° vs. 71.84 ± 0.73°, 5.35 ± 2.02° vs. 7.53 ± 1.34°, and 2.2 ± 1.48° vs. 15.7 ± 6.35°, respectively ( P < 0.05). The ISR showed no significant difference. Postoperative joint line changes were controlled at 1 ± 1.2 mm. Both ROM and HSS scores demonstrated significant improvements at the last follow-up ( P < 0.01). Conclusions The techniques include reducing femoral and tibial resections, controlling patient-specific femoral external rotation, and reconstructing tibial bone defects are effective to manage the SVK utilizing an unconstrained prosthesis, yielding excellent clinical results. total knee arthroplasty robotic assisted severe varus unconstrained prosthesis Figures Figure 1 Figure 2 Figure 3 Introduction De Muylder et al[ 1 ] classified varus knee based on the angle of separation of the mechanical axes of the femur and tibia, defining severe varus knee (SVK) as an angle greater than 20°, which accounts for approximately 10% of all varus knee cases. Many cases of SVK are attributed to a combination of intra-articular and extra-articular factors or solely due to intra-articular factors, presenting as bony structural varus or mixed varus commonly[ 2 – 4 ]. Notable, a proportion of these patients had intact medial and lateral collateral ligaments; however, many were managed with condylar-constrained or hinged prostheses[ 5 – 7 ], despite one of the principles of total knee arthroplasty (TKA) to achieve maximum knee stability with the minimum restriction[ 8 – 11 ]. Additionally, even unconstrained prosthesis to be utilized, performing osteotomy according to standard TKA protocols can result in excessive bone resection and imbalances in the medial and lateral collateral ligaments and flexion-extension gaps. This may necessitate excessive release of the medial collateral ligament (MCL), potentially leading to injury, or requiring sliding osteotomy of condyle, or the use of thicker spacer, which can elevate the joint line and cause patella baja. Robotic assisted TKA can adjust osteotomy plans based on preoperative assessments and achieve precise osteotomy during surgery to accomplish digitization, precision, and individualization[ 12 – 14 ].This can assist surgeons in completing primary TKAs for SVKs utilizing unconstrained prostheses. We reviewed 30 cases involving 37 knees that underwent primary TKAs using the Krobot-5800 robotic system (HURWA, China) for SVKs with intact medial and lateral collateral ligaments from March 2022 to March 2024. All cases utilized unconstrained posterior-stabilized prostheses. Material and Methods Inclusion and Exclusion Criteria Inclusion criteria: 1. Knee varus degree > 20° 2. Intact medial and lateral collateral ligaments with adequate tension 3. Primary TKA utilizing an unconstrained prosthesis 4. Robot-assisted TKA Exclusion criteria: 1. Knee varus degree ≤ 20° 2. Loss of function in the medial or lateral collateral ligaments 3. External knee deformity corrected by prior external knee surgery 4. Use of condylar-constrained or hinged prostheses 5. Certain diseases, including infectious arthritis, joint tumors, and other specific joint diseases. General Information From March 2022 to March 2024, 30 cases involving 37 knees with intact medial and lateral collateral ligaments underwent the Krobot-5800 assisted primary TKAs for SVKs utilizing posterior-stabilized unconstrained prostheses. Among the patients, 5 were men and 25 were women, aged between 61 and 81 years. The underlying conditions included osteoarthritis in 28 cases involving 33 knees and rheumatoid arthritis in 2 cases involving 4 knees. The varus degrees ranged from 21° to 37°, with 20 knees between 21° and 25°, 13 knees between 26° and 30°, and 4 knees over 30°. The prostheses used were A3GT prosthesis (AiKang, China) in 17 cases involving 22 knees, Unique prosthesis (Zhengtian, China) in 3 cases involving 3 knees, and Genesis II prosthesis (Smith & Nephew, USA) in 10 cases involving 12 knees. Bilateral TKA surgeries were performed in 7 cases, with an interval time from 6 to 12 weeks. Due to the reduced bone resection, all cases exhibited tibial medial plateau bone defects. The tibial defects were classified according to the Rand classification[ 15 ]: Rand type A (congruent type) was observed in 3 cases involving 3 knees, Rand type B1 (non-congruent oblique type) in 27 cases involving 34 knees, and no cases of Rand type B2 (non-congruent vertical type). All data were obtained with informed consent from the patients (Ethics Approval Number: WJEC-KT-2020-001-P003). Surgical Technique All surgeries were performed by the first author as the lead surgeon. 1.Minimized resection of the tibial plateau and femoral condyles Minimized osteotomy of the tibial plateau and femoral condyle was performed to adjust the extension gap. The principle was that the more severe the varus degree, the thinner the resection, with resected thickness of femur and tibia controlled to be ≤ 8.0 mm. The tibial osteotomy was referenced at the highest point of the lateral plateau, without considering the amount of resection on the medial plateau or any resultant bone defects after the osteotomy. (Fig. 1 A and B) 2.Patient-specific or increased femoral external rotation Due to the hypertrophy of the posterior medial femoral condyle and the tension in the MCL associated with SVK, appropriate personalized external rotation of the femur facilitated the adjustment of the internal and external balance of the flexion gap. The method involved using the transepicondylar axis (TEA) and the posterior condylar axis (PCA) as references for external rotation adjustments, with a greater external rotation angle corresponding to more severe varus deformity. If the medial gap is narrower than the lateral gap and could not be adjusted through the PCA at the 0° position of TEA, the TEA can be externally rotated; each additional 1° of external rotation release 2 mm of space [ 16 ] (Fig. 2 ). While setting the external rotation angle of the femur to achieve balance in the medial and lateral flexion gaps, it was important to simultaneously determine the amount of posterior condylar resection to ensure equal flexion and extension gaps, avoiding anterior condylar notching. 3. Management of tibial plateau bone defects For Rand type A and B1 defects with a depth of ≤ 5 mm and an area of ≤ 1/3 of the medial plateau after initial osteotomy, bone cement filling or autologous cancellous bone grafting was used. For type B1 defects with a depth of > 5 mm and an area of > 1/3 of the medial plateau, structural bone grafting was performed using trimmed femoral posterior condyle with cancellous bone screws fixation, or metal augments employed to repair the defects. For type B2 defects, treatment involved the use of metal augments in conjunction with an extended stem [ 17 – 19 ]. Evaluation Criteria Functional indicators included the statistical analysis of all patients' knee range of motion (ROM) before surgery and at 3 months, 6 months, and the last follow-up after surgery, as well as the hospital for special surgery knee score (HSS). Imaging indicators included obtaining anteroposterior, lateral, and full-length weight-bearing X-ray films of both lower limbs for all patients before surgery and during follow-up, as well as patellar axial line and lateral X-ray at 30° knee flexion. The measurements were: hip-knee-ankle angle (HKAA), lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), posterior tibial slope (PTS), insall-salvati ratio (ISR)[ 20 ], and patellar tilt angle (PTA). Preoperative and postoperative CT scans at 3 months were performed for preoperative planning and measurement of PCA. (Fig. 3 A-D) Data Analyses Statistical analysis was performed using SPSS version 24.0 (SPSS, USA). Measurement data were expressed as mean ± standard deviation ( \(\:\stackrel{-}{x}\) ± s). The comparison of preoperative and postoperative follow-up data was conducted using paired sample t-tests, with a significance level (α) set at two-sided 0.05. Results General Results The follow-up period ranged from 6 to 30 months, with an average of 19.5 ± 5.12 months. The average thickness of osteotomy on the lateral tibial plateau was 6.3 mm (range: 5.5 to 8.0 mm), and on the medial plateau, it was 2.3 mm (range: 0 to 2.5 mm). The average thickness of osteotomy on the femoral distal medial condyle was 5.5 mm (range: 4.3 to 8.0 mm), and on the lateral condyle, it was 6.5 mm (range: 4.5 to 7.6 mm).For the management of tibial plateau defects during surgery: 3 knees with Rand type A defects received autogenous cancellous bone impaction grafting; in type B1 defects, 8 knees received bone cement filling, 15 knees underwent cancellous bone grafting, 9 knees underwent structural bone grafting with cancellous bone screws for fixation following the trimming of the lateral tibial plateau or medial femoral condyle, and 2 knees were treated with metal wedges. There were no cases of Rand type B2 defects. Functional Evaluations The postoperative ROM was significant improved:109.5 ± 9.13° ( t = -14.80, P < 0.01), 122.3 ± 8.90° ( t = -23.61, P < 0.01) and 121.6 ± 7.71° ( t = -23.94, P < 0.01) at 3 months, 6 months and last follow-up respectively, compared to the preoperative value of 83.8 ± 9.54°. Postoperative HSS score showed significant improvement: 76.6 ± 5.56 ( t = -23.35, P < 0.01), 88.2 ± 4.32 ( t = -28.80, P < 0.01) and 86.1 ± 4.89 ( t = -30.66, P < 0.01) at 3 months, 6months and last follow-up respectively, compared to the preoperative score of 38.5 ± 7.46.(Table.1) Imaging Findings Standard X-rays taken during each follow-up included weight-bearing full-length images of both lower limbs, anteroposterior and lateral films of both knees, axial line of the patella, and lateral film at 30° knee flexion. Measurements included HKAA, LDFA, MPTA, PTS, PTA, and ISR. At 3 months postoperatively, a CT scan was performed to measure PCA. The results showed statistical significant differences in HKAA, LDFA, PCA, MPTA, PTS, and PTA ( P < 0.01), indicating that the severe varus deformity had been effectively corrected and there was good congruence in the patellofemoral joint. Detailed data at 3 months postoperatively are shown in Table 2 . The ISR showed no statistically significant difference between the preoperative value of 1.10 ± 0.15 and postoperative1.00 ± 0.10 ( t = 0.97, P = 0.34), indicating that the decreased osteotomy during surgery did not result in a significant change in patellar height compared to preoperative measurement. The postoperative change in the joint line was controlled within 1.0 ± 1.2 mm, with 28 knees showing an upward or downward shift within 1.0 mm, and 9 knees showing a shift between 1.1 mm and 2.0 mm. Table 1 Comparison table of ROM and HSS score of knee joint(n = 37) Observational Index Before Surgery 3 Months After Surgery 6 Months After Surgery Last Follow-up ROM(°) 83.8 ± 9.54 109.5 ± 9.13* 122.3 ± 8.90* 121.6 ± 7.71* HSS(score) 38.5 ± 7.46 76.6 ± 5.56* 88.2 ± 4.32* 86.1 ± 4.89* Note: Compared with observational index before surgery, * P < 0.01 Table 2 Comparison table of HKAA, LDFA, PCA, MPTA, PTS and PTA 3 months after surgery and before surgery(n = 37, \(\:\stackrel{-}{x}\) ±s, °) Time HKAA LDFA PCA MPTA PTS PTA Before Surgery 156.34 ± 1.85 83.92 ± 0.42 6.53 ± 0.89 71.84 ± 0.73 7.53 ± 1.34 15.7 ± 6.35 After Surgery 178.52 ± 1.79 90.03 ± 0.39 3.32 ± 0.02 90.15 ± 0.47 5.35 ± 2.02 2.20 ± 1.48° t value 32.90 19.93 -23.97 38.37 -16.53 -24.43 P value 0.000 0.000 0.000 0.000 0.000 0.000 Discussion For SVK, the challenge lies in completing TKA using an unconstrained prosthesis while avoiding the utilization of constrained or hinged prostheses. The most crucial aspect is to ensure the structural and functional integrity of the medial and lateral collateral ligaments of the knee, which aligns with the fundamental requirements of an unconstrained prosthesis. We summarize three techniques utilized in robotic assisted TKA surgery: adjusting the resection volume and femoral condyle external rotation angle based on the TEA and PCA of each knee specific condition, calculating the amount of bone defect on the tibial plateau, and preparing components such as grafts, metal augments, and extension rods to achieve patient-specific, digital, and precise solutions, thus overcoming the empirical and blind nature of conventional TKA. The tension of MCL and knee flexion contracture are often associated with SVK. Some surgeons advocate for increased bone resection during TKA to accommodate soft tissue tension[ 21 ]. However, we found that the medial femoral condyle and tibial plateau often experience osteophyte formation due to long-term high-stress stimulation. The protruding osteophytes could stretch the MCL and other soft tissues. Thorough removal of these osteophytes significantly relieved the high tension in the medial soft tissues to create more space [ 22 , 23 ]. Additionally, the lateral collateral ligament (LCL) and other lateral soft tissues may have become lax due to prolonged stretching. If conventional osteotomy was performed or if the osteotomy amount was arbitrarily increased, a significant increase in the extension gap could occur after thoroughly removing the osteophytes, potentially exceeding the flexion gap. To achieve a balance between the extension and flexion gaps, it might have been necessary to increase the flexion gap or select a smaller prosthesis, both of which would have resulted in greater bone volume loss and necessitated the use of thicker polyethylene liners, thereby raising the joint line and potentially causing patellar baja and other complications [ 24 , 25 ]. In conclusion, minimized osteotomy of the tibial plateau and femoral condyle can avoid an excessive extension gap. An increasing number of surgeons recognize that the resection of the tibial plateau and femoral condyle during primary TKA of SVK should be minimized. Mullaji et al[ 26 ] used computer navigation assisted TKA for patients with fixed varus knees that were difficult to reduce, performing precise bone resection through navigation and soft tissue tension sensing techniques. They found that the resection volume was below 8 mm and believed that the greater the varus angle of the knee and the more relaxed the lateral structures of the knee, the smaller the resection volume, with SVK resection controlled at 6 mm to 7 mm. Ranawat et al[ 27 ] performed TKA in 31 cases involving 34 knees with SVK accompanied by flexion contracture, where the osteotomy thickness ranged from 8mm to 10 mm. Our experience indicated that, in cases of SVK with medial tibial plateau wear and subsidence, the tibial osteotomy should reference the highest point of the lateral plateau, aiming for minimal bone resection without considering the thickness of the medial plateau resection or any resultant bone defects. Medial tibial plateau defect can be reconstructed using bone cement filling, autogenous bone grafting, or thicker augments. Similarly, the femoral condyle should be minimally resected. Our outcomes showed that the change in joint line was controlled at 1.1 ± 1.2 mm and the ISR was 1.03 ± 0.10, indicating that minimal osteotomy did not lead to significant changes in joint line, thus preventing the occurrence of patellar alta or baja. The external rotation of the femoral component during TKA surgery is closely related to the patellar tracking, affecting the patellar tilt angle, the knee flexion and extension function, the incidence of anterior patellar complications, and the longevity and revision rates of the prosthesis [ 28 , 29 ]. William et al [ 30 ] reported that severe internal rotation of the femoral component significantly affected the load transfer between the femur and tibia, leading to subluxation of the patellofemoral joint, and the severity of internal rotation was positively correlated with the incidence of patellofemoral complications. In our cases, the PTA decreased significantly after surgery, indicating that patellar tracking had been corrected. This improvement resulted from individualized external rotation resection of the femoral condyle and prosthesis placement. Due to the hypertrophy of the posterior medial femoral condyle in SVK, a traditional approach addressing a 3° external rotation resection of the femoral condyle might result in the prosthesis being positioned internally rotated. The solution involves referencing the PCL, PCA, and TEA. Most studies believe that the TEA, being closest to the flexion-extension axis of the knee joint, is the most reliable reference for external rotation of the femur[ 31 , 32 ]. We propose using TEA and PCA as mutual references for femoral external rotation alignment to be more accurate. In SVK, the patient-specific external rotation of the femur often requires a larger resection of the medial-posterior condyle to relieve the tension of the MCL in the flexed position. Thorough removal of osteophytes helps achieve balance in the medial and lateral flexion gaps without excessively releasing the MCL. In our group of 37 knees that underwent TKA, the femoral PCA improved from a preoperative measurement of 6.53 ± 0.89° (maximum 8.0°) to 3.32 ± 0.02°, achieving balance instantly in the medial and lateral flexion gaps without excessive MCL release. In cases of SVK, the tension in the MCL and other medial soft tissues sometimes requires release; however, the degree and sequence of soft tissue release also influence the positioning of femoral external rotation[ 33 , 34 ]. Our experience indicates that performing appropriate femoral external rotation osteotomy and removing the posterior osteophyte thoroughly before MCL release can avoid excessive MCL release and the internal rotation placement of the femoral prosthesis. If the medial gap is narrower than the lateral gap and could not be adjusted through the PCA at the TEA 0° position, the TEA can be externally rotated. The variations in medial tibial plateau bone defects in SVK necessitate reconstructing the tibial plateau to ensure the tibial prosthesis’s long-term stability[ 35 ]. If tibial plateau osteotomy had been performed based on medial bone defects, it would have resulted in excessive lateral resection and the use of a thicker polyethylene insert. This would have weakened the tibial plateau bone bed support strength for the prosthesis, reduced the tibial component size, and led to early subsidence and loosening of the tibial tray. Therefore, tibial plateau osteotomy should reference the lateral plateau with minimal resection and tibial plateau bone defects can be resolved with bone grafting or the addition of augments. In this group of cases, tibial defects of different Rand types were treated individually, and postoperative follow-up revealed that graft healing was successful without bone desorption, tibial plateau subsidence, or prosthetic loosening. Conclusions In conclusion, using an unconstrained prosthesis successfully achieves knee stability and satisfactory clinical outcomes in SVK case with intact medial and lateral collateral ligaments by addressing minimal osteotomy, patient-specific femoral external rotation and tibial plateau bone defects. Abbreviations SVK: Severe varus knee TKA: Total knee arthroplasty MCL: Medial collateral ligament TEA: Transepicondylar axis PCA: Posterior condylar axis ROM: Range of motion HSS: Hospital for special surgery knee score HKAA: Hip-knee-ankle angle LDFA：Lateral distal femoral angle MPTA：Medial proximal tibial angle PTS：Posterior tibial slope ISR: Insall-salvati ratio PTA: Patellar tilt angle Declarations Ethics approval and consent to participate Approval was received by the Medical Ethics Committee of Wangjing Hospital of Chinese Academy of Chinese Medical Sciences and obtained the unique identification number of research registration (WJEC-KT-2020-001-P003). Written informed consent for participation was obtained from all participants. Consent for publication Not applicable. Availability of data and materials The corresponding author can be contacted via email to obtain all data for legitimate purposes. Competing interests The authors declare no competing interests. Funding This work was supported by Beijing Science and Technology Commission, Zhongguancun Science and Technology Park Management Committee- Capital clinical diagnosis and treatment technology research and demonstration application project [grant number: Z191100006619023] Authors' contributions All authors were involved in the conception and design. HZ contributed to conceptualization, methodology, funding acquisition, and writing - original draft preparation. YL participated in writing - original draft preparation. LJ conducted formal analysis and provided supervision. PH was responsible for software development and validation. HT handled visualization tasks. MH performed data curation and investigation. All authors read and approved the final manuscript. Acknowledgements Not applicable. Clinical trial number Not applicable. References De Muylder J, Victor J, Cornu O, Kaminski L, Thienpont E. 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Ng CK, Chen JY, Yeh JZY, Ho JPY, Merican AM, Yeo SJ. Distal Femoral Rotation Correlates With Proximal Tibial Joint Line Obliquity: A Consideration for Kinematic Total Knee Arthroplasty. J Arthroplasty. 2018;33(6):1936-44. Nodzo SR, Staub TM, Jancuska JM, Cobler-Lichter MD, Boyle KK, Rachala S. Flexion Space Balancing Through Component Positioning and Its Relationship to Traditional Anatomic Rotational Landmarks in Robotic Total Knee Arthroplasty. J Arthroplasty. 2020;35(6):1569-75. Lee SY, Lim HC, Jang KM, Bae JH. What Factors Are Associated With Femoral Component Internal Rotation in TKA Using the Gap Balancing Technique? Clin Orthop Relat Res. 2017;475(8):1999-2010. Gao YH, Li SQ, Yang C, Liu JG, Dong N, Qi X. Favorable femoral component rotation achieved in severe varus deformity by using the gap-balancing technique. Knee. 2016;23(5):867-70. Nourishirazi R, Firoozabadi MA, Hassanzadeh M, Toofan H, Karimpour M, Mortazavi SMJ. Biomechanical study of effect of tibial posteromedial defect depth and area on primary TKA implant stability. Knee. 2024;49:249-56. 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-7234889","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":501363075,"identity":"82e6cf56-dd16-4451-a8d2-5069ca397a91","order_by":0,"name":"Hongmei Zhang","email":"","orcid":"","institution":"Wangjing Hospital of China Academy of Chinese Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Hongmei","middleName":"","lastName":"Zhang","suffix":""},{"id":501363076,"identity":"fcfcfc33-f92b-45a6-a518-243939284a5f","order_by":1,"name":"Yuanyuan Li","email":"","orcid":"","institution":"Wangjing Hospital of China Academy of Chinese Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Yuanyuan","middleName":"","lastName":"Li","suffix":""},{"id":501363077,"identity":"5c5c8613-2c0c-4e6c-83a4-7a4268c2f70a","order_by":2,"name":"Lin Jing","email":"","orcid":"","institution":"Wangjing Hospital of China Academy of Chinese Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Lin","middleName":"","lastName":"Jing","suffix":""},{"id":501363078,"identity":"92f4a11b-9085-4940-8c27-87c93f5bba29","order_by":3,"name":"Peiyan Hu","email":"","orcid":"","institution":"Wangjing Hospital of China Academy of Chinese Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Peiyan","middleName":"","lastName":"Hu","suffix":""},{"id":501363079,"identity":"f9eaba15-f0a0-43e8-a777-096b31f1c6f7","order_by":4,"name":"Hai Tang","email":"","orcid":"","institution":"Wangjing Hospital of China Academy of Chinese Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Hai","middleName":"","lastName":"Tang","suffix":""},{"id":501363080,"identity":"87245e88-4991-4027-b9c1-229b6dddb880","order_by":5,"name":"Mingjiang He","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA00lEQVRIiWNgGAWjYHACNiBmBiLmAwc+GNjYEaGDGaqFnS3x4YyCtGQStPDzGBvzfDjE2EBIA//s88ceV1RYy/E3M5hJ2xgcYGZgP3x0Az4tEueS2Q3PnEk3ljjMkCadY3CHj4EnLe0GXmvOMLNJNrYdTtzAzHAMqOUZM4MEjxleLfIILYxt0hYGhxkbCGkxQGhhZjZmIEaL4RlmM8kGsF/YGB/2GKQlsxHyi9wZxmeSDaAQ6z//4cCPPzZ2/OyHj+H3PgZgI035KBgFo2AUjAJsAAC64ENDYVgBBAAAAABJRU5ErkJggg==","orcid":"","institution":"Wangjing Hospital of China Academy of Chinese Medical Sciences","correspondingAuthor":true,"prefix":"","firstName":"Mingjiang","middleName":"","lastName":"He","suffix":""}],"badges":[],"createdAt":"2025-07-28 14:23:19","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7234889/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7234889/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":89282317,"identity":"241c0068-dcb9-4f2c-b8bd-332c7cecf946","added_by":"auto","created_at":"2025-08-18 10:42:02","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":408003,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Osteotomy of the lateral tibial condyle: 7.0 mm; osteotomy of the medial tibial condyle: 1.3 mm. (B). Osteotomy of the lateral femoral condyle: 7.6 mm; osteotomy of the medial femoral condyle: 4.5 mm.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7234889/v1/dd95b0d4c53807d80d174100.png"},{"id":89282318,"identity":"d07b57b8-3625-410c-bc6d-ade6f37a3697","added_by":"auto","created_at":"2025-08-18 10:42:02","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":151890,"visible":true,"origin":"","legend":"\u003cp\u003eAn increase of 0.9°in TEA external rotation will release 1.8 mm in the medial gap during flexion.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7234889/v1/94c35d7b7b82d59b4b88fb10.png"},{"id":89282765,"identity":"67330c5c-ce0c-457c-adcc-e5ae3e86fb6a","added_by":"auto","created_at":"2025-08-18 10:50:02","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":395576,"visible":true,"origin":"","legend":"\u003cp\u003eMeasurement diagrams of angles and values before and after surgery: (A) HKAA: The angle between the mechanical axes of the femur and tibia in the coronal plane; LDFA: The lateral angle between the mechanical axis of the femur and the tangent to the distal ends of the medial and lateral femoral condyles (joint line) in the coronal plane; MPTA: The medial angle between the mechanical axis of the tibia and the knee joint line in the coronal plane. (B) ISR: On the lateral view of the knee joint, the maximum diagonal length of the patella (LP, represented by the blue line B) and the length of the patellar tendon (LT, represented by the red line A) were measured, and the ratio of the two (LP/LT) was calculated. (C) PTA: The angle between the extension line of the patellar width and the extension line connecting the highest points of the medial and lateral femoral condyles. (D) PCA: The angle between TEA and the tangent to the posterior condyle line (PCL) of the femur.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7234889/v1/a70ab1c70c914d93423bc372.png"},{"id":91406428,"identity":"eae5ae69-dfa2-4f99-b3e3-685e5e3c129a","added_by":"auto","created_at":"2025-09-16 07:54:50","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1655648,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7234889/v1/291dfa53-07ce-4251-85a4-ea1e39544122.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Robotic Assisted Primary Total Knee Arthroplasty for Severe Varus Knee Utilizing an Unconstrained Prosthesis: a retrospective study","fulltext":[{"header":"Introduction","content":"\u003cp\u003eDe Muylder et al[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] classified varus knee based on the angle of separation of the mechanical axes of the femur and tibia, defining severe varus knee (SVK) as an angle greater than 20\u0026deg;, which accounts for approximately 10% of all varus knee cases. Many cases of SVK are attributed to a combination of intra-articular and extra-articular factors or solely due to intra-articular factors, presenting as bony structural varus or mixed varus commonly[\u003cspan additionalcitationids=\"CR3\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Notable, a proportion of these patients had intact medial and lateral collateral ligaments; however, many were managed with condylar-constrained or hinged prostheses[\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], despite one of the principles of total knee arthroplasty (TKA) to achieve maximum knee stability with the minimum restriction[\u003cspan additionalcitationids=\"CR9 CR10\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Additionally, even unconstrained prosthesis to be utilized, performing osteotomy according to standard TKA protocols can result in excessive bone resection and imbalances in the medial and lateral collateral ligaments and flexion-extension gaps. This may necessitate excessive release of the medial collateral ligament (MCL), potentially leading to injury, or requiring sliding osteotomy of condyle, or the use of thicker spacer, which can elevate the joint line and cause patella baja.\u003c/p\u003e\u003cp\u003eRobotic assisted TKA can adjust osteotomy plans based on preoperative assessments and achieve precise osteotomy during surgery to accomplish digitization, precision, and individualization[\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].This can assist surgeons in completing primary TKAs for SVKs utilizing unconstrained prostheses. We reviewed 30 cases involving 37 knees that underwent primary TKAs using the Krobot-5800 robotic system (HURWA, China) for SVKs with intact medial and lateral collateral ligaments from March 2022 to March 2024. All cases utilized unconstrained posterior-stabilized prostheses.\u003c/p\u003e"},{"header":"Material and Methods","content":"\u003cp\u003e\u003cem\u003eInclusion and Exclusion Criteria\u003c/em\u003e\u003c/p\u003e\u003cp\u003eInclusion criteria: 1. Knee varus degree\u0026thinsp;\u0026gt;\u0026thinsp;20\u0026deg; 2. Intact medial and lateral collateral ligaments with adequate tension 3. Primary TKA utilizing an unconstrained prosthesis 4. Robot-assisted TKA\u003c/p\u003e\u003cp\u003eExclusion criteria: 1. Knee varus degree\u0026thinsp;\u0026le;\u0026thinsp;20\u0026deg; 2. Loss of function in the medial or lateral collateral ligaments 3. External knee deformity corrected by prior external knee surgery 4. Use of condylar-constrained or hinged prostheses 5. Certain diseases, including infectious arthritis, joint tumors, and other specific joint diseases.\u003c/p\u003e\u003cp\u003e\u003cem\u003eGeneral Information\u003c/em\u003e\u003c/p\u003e\u003cp\u003eFrom March 2022 to March 2024, 30 cases involving 37 knees with intact medial and lateral collateral ligaments underwent the Krobot-5800 assisted primary TKAs for SVKs utilizing posterior-stabilized unconstrained prostheses. Among the patients, 5 were men and 25 were women, aged between 61 and 81 years. The underlying conditions included osteoarthritis in 28 cases involving 33 knees and rheumatoid arthritis in 2 cases involving 4 knees. The varus degrees ranged from 21\u0026deg; to 37\u0026deg;, with 20 knees between 21\u0026deg; and 25\u0026deg;, 13 knees between 26\u0026deg; and 30\u0026deg;, and 4 knees over 30\u0026deg;. The prostheses used were A3GT prosthesis (AiKang, China) in 17 cases involving 22 knees, Unique prosthesis (Zhengtian, China) in 3 cases involving 3 knees, and Genesis II prosthesis (Smith \u0026amp; Nephew, USA) in 10 cases involving 12 knees. Bilateral TKA surgeries were performed in 7 cases, with an interval time from 6 to 12 weeks. Due to the reduced bone resection, all cases exhibited tibial medial plateau bone defects. The tibial defects were classified according to the Rand classification[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]: Rand type A (congruent type) was observed in 3 cases involving 3 knees, Rand type B1 (non-congruent oblique type) in 27 cases involving 34 knees, and no cases of Rand type B2 (non-congruent vertical type). All data were obtained with informed consent from the patients (Ethics Approval Number: WJEC-KT-2020-001-P003).\u003c/p\u003e\u003cp\u003e\u003cem\u003eSurgical Technique\u003c/em\u003e\u003c/p\u003e\u003cp\u003eAll surgeries were performed by the first author as the lead surgeon.\u003c/p\u003e\u003cp\u003e\u003cem\u003e1.Minimized resection of the tibial plateau and femoral condyles\u003c/em\u003e\u003c/p\u003e\u003cp\u003eMinimized osteotomy of the tibial plateau and femoral condyle was performed to adjust the extension gap. The principle was that the more severe the varus degree, the thinner the resection, with resected thickness of femur and tibia controlled to be \u0026le;\u0026thinsp;8.0 mm. The tibial osteotomy was referenced at the highest point of the lateral plateau, without considering the amount of resection on the medial plateau or any resultant bone defects after the osteotomy. (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA and B)\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003e2.Patient-specific or increased femoral external rotation\u003c/em\u003e\u003c/p\u003e\u003cp\u003eDue to the hypertrophy of the posterior medial femoral condyle and the tension in the MCL associated with SVK, appropriate personalized external rotation of the femur facilitated the adjustment of the internal and external balance of the flexion gap. The method involved using the transepicondylar axis (TEA) and the posterior condylar axis (PCA) as references for external rotation adjustments, with a greater external rotation angle corresponding to more severe varus deformity. If the medial gap is narrower than the lateral gap and could not be adjusted through the PCA at the 0\u0026deg; position of TEA, the TEA can be externally rotated; each additional 1\u0026deg; of external rotation release 2 mm of space [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). While setting the external rotation angle of the femur to achieve balance in the medial and lateral flexion gaps, it was important to simultaneously determine the amount of posterior condylar resection to ensure equal flexion and extension gaps, avoiding anterior condylar notching.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003e3. Management of tibial plateau bone defects\u003c/em\u003e\u003c/p\u003e\u003cp\u003eFor Rand type A and B1 defects with a depth of \u0026le;\u0026thinsp;5 mm and an area of \u0026le;\u0026thinsp;1/3 of the medial plateau after initial osteotomy, bone cement filling or autologous cancellous bone grafting was used. For type B1 defects with a depth of \u0026gt;\u0026thinsp;5 mm and an area of \u0026gt;\u0026thinsp;1/3 of the medial plateau, structural bone grafting was performed using trimmed femoral posterior condyle with cancellous bone screws fixation, or metal augments employed to repair the defects. For type B2 defects, treatment involved the use of metal augments in conjunction with an extended stem [\u003cspan additionalcitationids=\"CR18\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003cem\u003eEvaluation Criteria\u003c/em\u003e\u003c/p\u003e\u003cp\u003eFunctional indicators included the statistical analysis of all patients' knee range of motion (ROM) before surgery and at 3 months, 6 months, and the last follow-up after surgery, as well as the hospital for special surgery knee score (HSS).\u003c/p\u003e\u003cp\u003eImaging indicators included obtaining anteroposterior, lateral, and full-length weight-bearing X-ray films of both lower limbs for all patients before surgery and during follow-up, as well as patellar axial line and lateral X-ray at 30\u0026deg; knee flexion. The measurements were: hip-knee-ankle angle (HKAA), lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), posterior tibial slope (PTS), insall-salvati ratio (ISR)[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], and patellar tilt angle (PTA). Preoperative and postoperative CT scans at 3 months were performed for preoperative planning and measurement of PCA. (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA-D)\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003eData Analyses\u003c/em\u003e\u003c/p\u003e\u003cp\u003eStatistical analysis was performed using SPSS version 24.0 (SPSS, USA). Measurement data were expressed as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{-}{x}\\)\u003c/span\u003e\u003c/span\u003e \u0026plusmn; s). The comparison of preoperative and postoperative follow-up data was conducted using paired sample t-tests, with a significance level (α) set at two-sided 0.05.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cem\u003eGeneral Results\u003c/em\u003e\u003c/p\u003e\u003cp\u003eThe follow-up period ranged from 6 to 30 months, with an average of 19.5\u0026thinsp;\u0026plusmn;\u0026thinsp;5.12 months. The average thickness of osteotomy on the lateral tibial plateau was 6.3 mm (range: 5.5 to 8.0 mm), and on the medial plateau, it was 2.3 mm (range: 0 to 2.5 mm). The average thickness of osteotomy on the femoral distal medial condyle was 5.5 mm (range: 4.3 to 8.0 mm), and on the lateral condyle, it was 6.5 mm (range: 4.5 to 7.6 mm).For the management of tibial plateau defects during surgery: 3 knees with Rand type A defects received autogenous cancellous bone impaction grafting; in type B1 defects, 8 knees received bone cement filling, 15 knees underwent cancellous bone grafting, 9 knees underwent structural bone grafting with cancellous bone screws for fixation following the trimming of the lateral tibial plateau or medial femoral condyle, and 2 knees were treated with metal wedges. There were no cases of Rand type B2 defects.\u003c/p\u003e\u003cp\u003e\u003cem\u003eFunctional Evaluations\u003c/em\u003e\u003c/p\u003e\u003cp\u003eThe postoperative ROM was significant improved:109.5\u0026thinsp;\u0026plusmn;\u0026thinsp;9.13\u0026deg; (\u003cem\u003et =\u003c/em\u003e -14.80, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), 122.3\u0026thinsp;\u0026plusmn;\u0026thinsp;8.90\u0026deg; (\u003cem\u003et =\u003c/em\u003e -23.61, \u003cem\u003eP\u0026thinsp;\u0026lt;\u003c/em\u003e\u0026thinsp;0.01) and 121.6\u0026thinsp;\u0026plusmn;\u0026thinsp;7.71\u0026deg; (\u003cem\u003et =\u003c/em\u003e -23.94, \u003cem\u003eP\u0026thinsp;\u0026lt;\u003c/em\u003e\u0026thinsp;0.01) at 3 months, 6 months and last follow-up respectively, compared to the preoperative value of 83.8\u0026thinsp;\u0026plusmn;\u0026thinsp;9.54\u0026deg;. Postoperative HSS score showed significant improvement: 76.6\u0026thinsp;\u0026plusmn;\u0026thinsp;5.56 (\u003cem\u003et =\u003c/em\u003e -23.35, \u003cem\u003eP\u0026thinsp;\u0026lt;\u003c/em\u003e\u0026thinsp;0.01), 88.2\u0026thinsp;\u0026plusmn;\u0026thinsp;4.32 (\u003cem\u003et =\u003c/em\u003e -28.80, \u003cem\u003eP\u0026thinsp;\u0026lt;\u003c/em\u003e\u0026thinsp;0.01) and 86.1\u0026thinsp;\u0026plusmn;\u0026thinsp;4.89 (\u003cem\u003et =\u003c/em\u003e -30.66, \u003cem\u003eP\u0026thinsp;\u0026lt;\u003c/em\u003e\u0026thinsp;0.01) at 3 months, 6months and last follow-up respectively, compared to the preoperative score of 38.5\u0026thinsp;\u0026plusmn;\u0026thinsp;7.46.(Table.1)\u003c/p\u003e\u003cp\u003e\u003cem\u003eImaging Findings\u003c/em\u003e\u003c/p\u003e\u003cp\u003eStandard X-rays taken during each follow-up included weight-bearing full-length images of both lower limbs, anteroposterior and lateral films of both knees, axial line of the patella, and lateral film at 30\u0026deg; knee flexion. Measurements included HKAA, LDFA, MPTA, PTS, PTA, and ISR. At 3 months postoperatively, a CT scan was performed to measure PCA. The results showed statistical significant differences in HKAA, LDFA, PCA, MPTA, PTS, and PTA (\u003cem\u003eP\u0026thinsp;\u0026lt;\u003c/em\u003e\u0026thinsp;0.01), indicating that the severe varus deformity had been effectively corrected and there was good congruence in the patellofemoral joint. Detailed data at 3 months postoperatively are shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The ISR showed no statistically significant difference between the preoperative value of 1.10\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15 and postoperative1.00\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10 (\u003cem\u003et\u0026thinsp;=\u003c/em\u003e\u0026thinsp;0.97, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.34), indicating that the decreased osteotomy during surgery did not result in a significant change in patellar height compared to preoperative measurement. The postoperative change in the joint line was controlled within 1.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2 mm, with 28 knees showing an upward or downward shift within 1.0 mm, and 9 knees showing a shift between 1.1 mm and 2.0 mm.\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\u003eComparison table of ROM and HSS score of knee joint(n\u0026thinsp;=\u0026thinsp;37)\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eObservational\u003c/p\u003e\u003cp\u003eIndex\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eBefore\u003c/p\u003e\u003cp\u003eSurgery\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3 Months\u003c/p\u003e\u003cp\u003eAfter Surgery\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e6 Months\u003c/p\u003e\u003cp\u003eAfter Surgery\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eLast\u003c/p\u003e\u003cp\u003eFollow-up\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eROM(\u0026deg;)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e83.8\u0026thinsp;\u0026plusmn;\u0026thinsp;9.54\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e109.5\u0026thinsp;\u0026plusmn;\u0026thinsp;9.13*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e122.3\u0026thinsp;\u0026plusmn;\u0026thinsp;8.90*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e121.6\u0026thinsp;\u0026plusmn;\u0026thinsp;7.71*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHSS(score)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e38.5\u0026thinsp;\u0026plusmn;\u0026thinsp;7.46\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e76.6\u0026thinsp;\u0026plusmn;\u0026thinsp;5.56*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e88.2\u0026thinsp;\u0026plusmn;\u0026thinsp;4.32*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e86.1\u0026thinsp;\u0026plusmn;\u0026thinsp;4.89*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"5\"\u003eNote: Compared with observational index before surgery, *\u003cem\u003eP\u0026thinsp;\u0026lt;\u003c/em\u003e\u0026thinsp;0.01\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\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\u003eComparison table of HKAA, LDFA, PCA, MPTA, PTS and PTA 3 months after surgery and before surgery(n\u0026thinsp;=\u0026thinsp;37, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{-}{x}\\)\u003c/span\u003e\u003c/span\u003e\u0026plusmn;s, \u0026deg;)\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"7\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHKAA\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eLDFA\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003ePCA\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eMPTA\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003ePTS\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003ePTA\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBefore\u003c/p\u003e\u003cp\u003eSurgery\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e156.34\u0026thinsp;\u0026plusmn;\u0026thinsp;1.85\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e83.92\u0026thinsp;\u0026plusmn;\u0026thinsp;0.42\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e6.53\u0026thinsp;\u0026plusmn;\u0026thinsp;0.89\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e71.84\u0026thinsp;\u0026plusmn;\u0026thinsp;0.73\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e7.53\u0026thinsp;\u0026plusmn;\u0026thinsp;1.34\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e15.7\u0026thinsp;\u0026plusmn;\u0026thinsp;6.35\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAfter\u003c/p\u003e\u003cp\u003eSurgery\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e178.52\u0026thinsp;\u0026plusmn;\u0026thinsp;1.79\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e90.03\u0026thinsp;\u0026plusmn;\u0026thinsp;0.39\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e90.15\u0026thinsp;\u0026plusmn;\u0026thinsp;0.47\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e5.35\u0026thinsp;\u0026plusmn;\u0026thinsp;2.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e2.20\u0026thinsp;\u0026plusmn;\u0026thinsp;1.48\u0026deg;\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003et\u003c/em\u003e value\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e32.90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e19.93\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-23.97\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e38.37\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-16.53\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e-24.43\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eP\u003c/em\u003e value\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.000\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\u003eFor SVK, the challenge lies in completing TKA using an unconstrained prosthesis while avoiding the utilization of constrained or hinged prostheses. The most crucial aspect is to ensure the structural and functional integrity of the medial and lateral collateral ligaments of the knee, which aligns with the fundamental requirements of an unconstrained prosthesis. We summarize three techniques utilized in robotic assisted TKA surgery: adjusting the resection volume and femoral condyle external rotation angle based on the TEA and PCA of each knee specific condition, calculating the amount of bone defect on the tibial plateau, and preparing components such as grafts, metal augments, and extension rods to achieve patient-specific, digital, and precise solutions, thus overcoming the empirical and blind nature of conventional TKA.\u003c/p\u003e\u003cp\u003eThe tension of MCL and knee flexion contracture are often associated with SVK. Some surgeons advocate for increased bone resection during TKA to accommodate soft tissue tension[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. However, we found that the medial femoral condyle and tibial plateau often experience osteophyte formation due to long-term high-stress stimulation. The protruding osteophytes could stretch the MCL and other soft tissues. Thorough removal of these osteophytes significantly relieved the high tension in the medial soft tissues to create more space [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Additionally, the lateral collateral ligament (LCL) and other lateral soft tissues may have become lax due to prolonged stretching. If conventional osteotomy was performed or if the osteotomy amount was arbitrarily increased, a significant increase in the extension gap could occur after thoroughly removing the osteophytes, potentially exceeding the flexion gap. To achieve a balance between the extension and flexion gaps, it might have been necessary to increase the flexion gap or select a smaller prosthesis, both of which would have resulted in greater bone volume loss and necessitated the use of thicker polyethylene liners, thereby raising the joint line and potentially causing patellar baja and other complications [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. In conclusion, minimized osteotomy of the tibial plateau and femoral condyle can avoid an excessive extension gap.\u003c/p\u003e\u003cp\u003eAn increasing number of surgeons recognize that the resection of the tibial plateau and femoral condyle during primary TKA of SVK should be minimized. Mullaji et al[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] used computer navigation assisted TKA for patients with fixed varus knees that were difficult to reduce, performing precise bone resection through navigation and soft tissue tension sensing techniques. They found that the resection volume was below 8 mm and believed that the greater the varus angle of the knee and the more relaxed the lateral structures of the knee, the smaller the resection volume, with SVK resection controlled at 6 mm to 7 mm. Ranawat et al[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] performed TKA in 31 cases involving 34 knees with SVK accompanied by flexion contracture, where the osteotomy thickness ranged from 8mm to 10 mm. Our experience indicated that, in cases of SVK with medial tibial plateau wear and subsidence, the tibial osteotomy should reference the highest point of the lateral plateau, aiming for minimal bone resection without considering the thickness of the medial plateau resection or any resultant bone defects. Medial tibial plateau defect can be reconstructed using bone cement filling, autogenous bone grafting, or thicker augments. Similarly, the femoral condyle should be minimally resected. Our outcomes showed that the change in joint line was controlled at 1.1\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2 mm and the ISR was 1.03\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10, indicating that minimal osteotomy did not lead to significant changes in joint line, thus preventing the occurrence of patellar alta or baja.\u003c/p\u003e\u003cp\u003eThe external rotation of the femoral component during TKA surgery is closely related to the patellar tracking, affecting the patellar tilt angle, the knee flexion and extension function, the incidence of anterior patellar complications, and the longevity and revision rates of the prosthesis [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. William et al [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] reported that severe internal rotation of the femoral component significantly affected the load transfer between the femur and tibia, leading to subluxation of the patellofemoral joint, and the severity of internal rotation was positively correlated with the incidence of patellofemoral complications. In our cases, the PTA decreased significantly after surgery, indicating that patellar tracking had been corrected. This improvement resulted from individualized external rotation resection of the femoral condyle and prosthesis placement.\u003c/p\u003e\u003cp\u003eDue to the hypertrophy of the posterior medial femoral condyle in SVK, a traditional approach addressing a 3\u0026deg; external rotation resection of the femoral condyle might result in the prosthesis being positioned internally rotated. The solution involves referencing the PCL, PCA, and TEA. Most studies believe that the TEA, being closest to the flexion-extension axis of the knee joint, is the most reliable reference for external rotation of the femur[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. We propose using TEA and PCA as mutual references for femoral external rotation alignment to be more accurate. In SVK, the patient-specific external rotation of the femur often requires a larger resection of the medial-posterior condyle to relieve the tension of the MCL in the flexed position. Thorough removal of osteophytes helps achieve balance in the medial and lateral flexion gaps without excessively releasing the MCL. In our group of 37 knees that underwent TKA, the femoral PCA improved from a preoperative measurement of 6.53\u0026thinsp;\u0026plusmn;\u0026thinsp;0.89\u0026deg; (maximum 8.0\u0026deg;) to 3.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u0026deg;, achieving balance instantly in the medial and lateral flexion gaps without excessive MCL release.\u003c/p\u003e\u003cp\u003eIn cases of SVK, the tension in the MCL and other medial soft tissues sometimes requires release; however, the degree and sequence of soft tissue release also influence the positioning of femoral external rotation[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. Our experience indicates that performing appropriate femoral external rotation osteotomy and removing the posterior osteophyte thoroughly before MCL release can avoid excessive MCL release and the internal rotation placement of the femoral prosthesis. If the medial gap is narrower than the lateral gap and could not be adjusted through the PCA at the TEA 0\u0026deg; position, the TEA can be externally rotated.\u003c/p\u003e\u003cp\u003eThe variations in medial tibial plateau bone defects in SVK necessitate reconstructing the tibial plateau to ensure the tibial prosthesis\u0026rsquo;s long-term stability[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. If tibial plateau osteotomy had been performed based on medial bone defects, it would have resulted in excessive lateral resection and the use of a thicker polyethylene insert. This would have weakened the tibial plateau bone bed support strength for the prosthesis, reduced the tibial component size, and led to early subsidence and loosening of the tibial tray. Therefore, tibial plateau osteotomy should reference the lateral plateau with minimal resection and tibial plateau bone defects can be resolved with bone grafting or the addition of augments. In this group of cases, tibial defects of different Rand types were treated individually, and postoperative follow-up revealed that graft healing was successful without bone desorption, tibial plateau subsidence, or prosthetic loosening.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn conclusion, using an unconstrained prosthesis successfully achieves knee stability and satisfactory clinical outcomes in SVK case with intact medial and lateral collateral ligaments by addressing minimal osteotomy, patient-specific femoral external rotation and tibial plateau bone defects.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eSVK: Severe varus knee\u003c/p\u003e\n\u003cp\u003eTKA: Total knee arthroplasty\u003c/p\u003e\n\u003cp\u003eMCL: Medial collateral ligament\u003c/p\u003e\n\u003cp\u003eTEA: \u0026nbsp;Transepicondylar axis\u003c/p\u003e\n\u003cp\u003ePCA: Posterior condylar axis\u003c/p\u003e\n\u003cp\u003eROM: Range of motion\u003c/p\u003e\n\u003cp\u003eHSS: Hospital for special surgery knee score\u003c/p\u003e\n\u003cp\u003eHKAA: Hip-knee-ankle angle\u003c/p\u003e\n\u003cp\u003eLDFA：Lateral distal femoral angle\u003c/p\u003e\n\u003cp\u003eMPTA：Medial proximal tibial angle\u003c/p\u003e\n\u003cp\u003ePTS：Posterior tibial slope\u003c/p\u003e\n\u003cp\u003eISR: \u0026nbsp;Insall-salvati ratio\u003c/p\u003e\n\u003cp\u003ePTA: \u0026nbsp;Patellar tilt angle\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eApproval was received by the Medical Ethics Committee of Wangjing Hospital of Chinese Academy of Chinese Medical Sciences and obtained the unique identification number of research registration (WJEC-KT-2020-001-P003). Written informed consent for participation was obtained from all participants.\u0026nbsp;\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 corresponding author can be contacted via email to obtain all data for legitimate purposes.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by Beijing Science and Technology Commission, Zhongguancun Science and Technology Park Management Committee- Capital clinical diagnosis and treatment technology research and demonstration application project [grant number: Z191100006619023]\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors were involved in the conception and design. HZ contributed to conceptualization, methodology, funding acquisition, and writing - original draft preparation. YL participated in writing - original draft preparation. LJ conducted formal analysis and provided supervision. PH was responsible for software development and validation. HT handled visualization tasks. MH performed data curation and investigation. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical trial number\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eDe Muylder J, Victor J, Cornu O, Kaminski L, Thienpont E. Total knee arthroplasty in patients with substantial deformities using primary knee components. 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J Knee Surg. 2021;34(2):142-6.\u003c/li\u003e\n\u003cli\u003eVakharia RM, Rodriguez HC, Roche MW. Medial Varus Proximal Tibial Resection is Superior to Pie-Crusting of the Medial Collateral Ligament During Primary Total Knee Arthroplasty. J Arthroplasty. 2023;38(6S):S169-S76.\u003c/li\u003e\n\u003cli\u003eKato K, Ogawa H, Matsumoto K, Akiyama H. Surgical procedures for the prevention of extension-flexion gap imbalance in total knee arthroplasty. J Orthop. 2021;25:224-9.\u003c/li\u003e\n\u003cli\u003eDos-Santos G, Gutierres M, Leite MJ, Barros AS. Pseudo-patella baja after total knee arthroplasty: Radiological evaluation and clinical repercussion. Knee. 2021;33:334-41.\u003c/li\u003e\n\u003cli\u003eMullaji A, Lingaraju AP, Shetty GM. Computer-assisted total knee replacement in patients with arthritis and a recurvatum deformity. J Bone Joint Surg Br. 2012;94(5):642-7.\u003c/li\u003e\n\u003cli\u003eRanawat CS, Meftah M, Ranawat AS. 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Distal Femoral Rotation Correlates With Proximal Tibial Joint Line Obliquity: A Consideration for Kinematic Total Knee Arthroplasty. J Arthroplasty. 2018;33(6):1936-44.\u003c/li\u003e\n\u003cli\u003eNodzo SR, Staub TM, Jancuska JM, Cobler-Lichter MD, Boyle KK, Rachala S. Flexion Space Balancing Through Component Positioning and Its Relationship to Traditional Anatomic Rotational Landmarks in Robotic Total Knee Arthroplasty. J Arthroplasty. 2020;35(6):1569-75.\u003c/li\u003e\n\u003cli\u003eLee SY, Lim HC, Jang KM, Bae JH. What Factors Are Associated With Femoral Component Internal Rotation in TKA Using the Gap Balancing Technique? Clin Orthop Relat Res. 2017;475(8):1999-2010.\u003c/li\u003e\n\u003cli\u003eGao YH, Li SQ, Yang C, Liu JG, Dong N, Qi X. Favorable femoral component rotation achieved in severe varus deformity by using the gap-balancing technique. Knee. 2016;23(5):867-70.\u003c/li\u003e\n\u003cli\u003eNourishirazi R, Firoozabadi MA, Hassanzadeh M, Toofan H, Karimpour M, Mortazavi SMJ. Biomechanical study of effect of tibial posteromedial defect depth and area on primary TKA implant stability. Knee. 2024;49:249-56.\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":"total knee arthroplasty, robotic assisted, severe varus, unconstrained prosthesis","lastPublishedDoi":"10.21203/rs.3.rs-7234889/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7234889/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e\u003cp\u003eRecent findings indicated that robotic-assisted primary total knee arthroplasty (TKA) utilizing an unconstrained prosthesis for severe varus knee (SVK) showed excellent clinical outcomes. The surgical techniques are valuable to be explored.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e\u003cp\u003ePatients with SVKs and intact medial and lateral collateral ligaments underwent robotic assisted primary TKAs by using the unconstrained posterior stabilized (PS) prostheses. The osteotomy principle was that the more severe the varus degree, the thinner the resection. Tibial resection was assessed on the lateral plateau, and medial plateau defects were managed with cement, bone grafts, or augments, depending on defect size and depth. The femoral external rotation angle was determined using the transepicondylar axis (TEA) and posterior condylar angle (PCA), rather than the conventional 3\u0026deg;. Radiographic evaluations included the hip-knee-ankle angle (HKAA), PCA, lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), posterior tibial slope (PTS), patella tilt angle (PTA), and Insall-Salvati ratio (ISR). Clinical evaluations comprised the range of motion (ROM) and the Hospital for Special Surgery (HSS) knee score.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003ePostoperative improvements were significant for HKAA, LDFA, PCA, MPTA, PTS, and PTA compared to preoperative values: 178.52\u0026thinsp;\u0026plusmn;\u0026thinsp;1.79\u0026deg; vs. 156.34\u0026thinsp;\u0026plusmn;\u0026thinsp;1.85\u0026deg;, 90.03\u0026thinsp;\u0026plusmn;\u0026thinsp;0.39\u0026deg; vs. 83.92\u0026thinsp;\u0026plusmn;\u0026thinsp;0.42\u0026deg;, 6.53\u0026thinsp;\u0026plusmn;\u0026thinsp;0.89\u0026deg; vs. 3.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u0026deg;, 90.15\u0026thinsp;\u0026plusmn;\u0026thinsp;0.47\u0026deg; vs. 71.84\u0026thinsp;\u0026plusmn;\u0026thinsp;0.73\u0026deg;, 5.35\u0026thinsp;\u0026plusmn;\u0026thinsp;2.02\u0026deg; vs. 7.53\u0026thinsp;\u0026plusmn;\u0026thinsp;1.34\u0026deg;, and 2.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.48\u0026deg; vs. 15.7\u0026thinsp;\u0026plusmn;\u0026thinsp;6.35\u0026deg;, respectively (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The ISR showed no significant difference. Postoperative joint line changes were controlled at 1\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2 mm. Both ROM and HSS scores demonstrated significant improvements at the last follow-up (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01).\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e\u003cp\u003eThe techniques include reducing femoral and tibial resections, controlling patient-specific femoral external rotation, and reconstructing tibial bone defects are effective to manage the SVK utilizing an unconstrained prosthesis, yielding excellent clinical results.\u003c/p\u003e","manuscriptTitle":"Robotic Assisted Primary Total Knee Arthroplasty for Severe Varus Knee Utilizing an Unconstrained Prosthesis: a retrospective study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-18 10:41:57","doi":"10.21203/rs.3.rs-7234889/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":"72677768-c7fe-43dd-b6f2-d90a1f0d7021","owner":[],"postedDate":"August 18th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-09-16T07:53:43+00:00","versionOfRecord":[],"versionCreatedAt":"2025-08-18 10:41:57","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7234889","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7234889","identity":"rs-7234889","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}