Patient Perception of Lower Limb Straightness after Unrestricted Kinematically Aligned Total Knee Arthroplasty: Exploring the Concept of “Inherent Straightness”

Patient Perception of Lower Limb Straightness after Unrestricted Kinematically Aligned Total Knee Arthroplasty: Exploring the Concept of “Inherent Straightness” | 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 Patient Perception of Lower Limb Straightness after Unrestricted Kinematically Aligned Total Knee Arthroplasty: Exploring the Concept of “Inherent Straightness” Toshiya Kano, Yoshinori Soda, Kimihiro Inoue, Mitsuhiro Nakamura This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8194991/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 Mechanical neutrality has long been regarded as the principal alignment target in total knee arthroplasty (TKA). However, radiographic neutrality does not necessarily reflect physiological morphology or patient perception. This study evaluated early postoperative cosmetic straightness after unrestricted kinematic alignment (KA)–TKA and examined its relationship with radiographic and functional parameters. Methods A total of 175 patients (203 knees) who underwent unrestricted KA-TKA were retrospectively reviewed. Pre- and postoperative radiographs, clinical findings, and patient questionnaires were analyzed. Patient perception of straightness was assessed using the Straightness Visual Analog Scale (S-VAS) and Straightness Satisfaction Visual Analog Scale (SS-VAS). Radiographic measurements included the hip–knee–ankle angle (HKAA), medial proximal tibial angle (MPTA), mechanical lateral distal femoral angle (mLDFA), and joint line convergence angle (JLCA). Coronal plane alignment of the knee (CPAK) patterns were also assessed. Correlations were examined between VAS scores and radiographic/clinical parameters. Results Preoperatively, 85.2% of knees were perceived as bowed; all of these were reported as straight after surgery. Among knees not perceived as bowed preoperatively, 60% were newly perceived as straight and 40% remained straight. Postoperative satisfaction was high (S-VAS 88.9 ± 11.6; SS-VAS 92.3 ± 12.9). Radiographs demonstrated substantial changes in coronal alignment, largely due to changes in MPTA and JLCA, resulting in shifts in CPAK patterns. Neither S-VAS nor SS-VAS correlated with HKAA, whereas both correlated moderately with postoperative knee extension (S-VAS r = 0.54; SS-VAS r = 0.59). Conclusions Patients tended to equate straightness with restoration of morphology and improved knee extension rather than radiographic mechanical neutrality. These findings suggest that cosmetic straightness reflects each patient’s inherent sense of limb alignment (“inherent straightness”), complementing conventional alignment metrics in KA-TKA and supporting a more patient-centered understanding of alignment outcomes. Kinematic alignment Total knee arthroplasty Inherent straightness Patient perception Coronal alignment Figures Figure 1 Figure 2 Figure 3 Figure 4 Background Since the late 1970s, mechanical neutrality has been widely regarded as the principal alignment goal in total knee arthroplasty (TKA) for osteoarthritic knees ( 1 , 2 ). This strategy was proposed to improve implant survival by promoting even load distribution between the medial and lateral compartments. Over time, the neutral mechanical axis has also come to be widely interpreted as representing “normal” or physiologic alignment ( 3 – 10 ). However, Bellman et al. ( 11 ) demonstrated that a substantial proportion of skeletally mature adults naturally exhibit varus knee morphology, suggesting that ideal alignment may vary among individuals and does not universally fall within the traditional target of 0° ± 3°. Furthermore, increasing evidence indicates that coronal alignment measured on static radiographs after TKA does not reliably predict dynamic loading during gait ( 12 , 13 ) and shows only weak associations with postoperative functional recovery or long-term implant performance ( 14 , 15 ). Consequently, attention has shifted toward alternative alignment philosophies. Howell and colleagues ( 16 , 17 ) proposed kinematic alignment (KA), an approach that aims to restore the patient’s native bone morphology and soft-tissue balance, thereby attempting to replicate prearthritic knee conditions. To date, no published studies have examined how patients perceive the straightness of their lower limbs as a cosmetic factor after TKA performed using such individualized alignment techniques, and this aspect remains insufficiently understood. In the context of KA, which seeks to reproduce each patient’s physiological morphology, it is clinically relevant to clarify whether patients perceive their limbs as bowed or naturally straight after surgery. Therefore, the purpose of this study was to evaluate whether patients perceive their lower limbs to be straight following unrestricted KA-TKA and to investigate how this perception relates to cosmetic satisfaction, coronal alignment parameters, and early functional findings. Methods Patients A total of 175 patients (203 knees) who underwent unrestricted kinematically aligned total knee arthroplasty (KA-TKA) at our institution were included. The mean age was 76.7 ± 7.1 years; 36 were male and 139 were female. All patients were of Japanese ethnicity. Patients with a history of osteotomy, fracture, or total hip arthroplasty on the affected side were excluded to avoid extra-articular influences. Clinical evaluation Knee extension and flexion angles were assessed preoperatively and one week postoperatively using a standard goniometer with patients in the supine position. Measurements were obtained passively, with the examiner supporting the limb to ensure neutral rotation. Radiographic evaluation Weight-bearing, full-leg standing radiographs were obtained preoperatively and one week postoperatively. Patients stood with their feet 10 cm apart and both patellae facing forward. Radiographic parameters included the medial proximal tibial angle (MPTA), mechanical lateral distal femoral angle (mLDFA), joint line convergence angle (JLCA), and hip–knee–ankle angle (HKAA). Knees were classified according to the Coronal Plane Alignment of the Knee (CPAK) system ( 18 ). Radiographic measurements followed established angle definitions, which are summarized and illustrated in Fig. 1 for clarity. Schematic illustration of radiographic measurements used in this study. The medial proximal tibial angle (MPTA), mechanical lateral distal femoral angle (mLDFA), joint line convergence angle (JLCA), and hip–knee–ankle angle (HKAA) were assessed on weight-bearing radiographs. Dotted lines represent the mechanical axis or joint line, and red arcs indicate the measured angles. For JLCA, medial opening was defined as positive and lateral opening as negative. For HKAA, valgus alignment was defined as positive and varus alignment as negative. Questionnaire survey A study-specific questionnaire was administered one week after surgery to evaluate patients’ perceptions of lower-limb straightness. The survey consisted of five items: Did you feel that your leg was bowed before the surgery? Has your leg been straightened after the surgery? Are you satisfied with the straightness of your leg? What is your straightness score? What is your score for satisfaction with straightness? Questions 1–3 were answered with “yes” or “no,” and questions 4–5 were assessed using a visual analog scale (VAS). Surgical procedures Distal and posterior femoral resection The femoral component was aligned using the calipered technique, as previously described ( 17 , 19 ). After accounting for cartilage wear, distal and posterior resections were performed to match the thickness of the femoral component. Proximal tibial resection The tibial component was aligned using a combination of the calipered technique ( 17 , 19 ) and the soft-tissue–respecting technique ( 20 , 21 ), both integral to unrestricted KA ( 22 ). With the trial femoral component in place, the knee was extended and the lower leg gently pulled distally. A curved gap gauge was inserted into the tibial osteochondral defect to measure defect thickness. These values were compensated using the calipered technique, and cutting blocks were positioned so that the medial and lateral sides matched the thickness of the tibial component. The posterior slope was aligned to the native medial tibial condyle, and tibial rotation was aligned parallel to the long axis of the lateral tibial condyle. The soft-tissue–respecting technique was then used to confirm parallelism between the tibial resection surface and the distal femoral cut in extension. Minor adjustments were performed when joint-surface deformation or defect evaluation warranted correction. The posterior cruciate ligament was preserved in all patients. Data analysis All values are expressed as means ± standard deviations. Analyses were performed using R software (version 3.4.1; R Foundation for Statistical Computing, Vienna, Austria). The normality of continuous variables was assessed using the Shapiro–Wilk test. Pre- and postoperative values of range of motion (ROM; extension and flexion), MPTA, mLDFA, JLCA, and HKAA were compared using paired t-tests. Pearson correlation coefficients were calculated to examine associations between straightness VAS (S-VAS) or straightness satisfaction VAS (SS-VAS) and both HKAA and postoperative knee extension. Ninety-five percent confidence intervals (95% CIs) were calculated where appropriate. A post hoc power analysis was conducted using G*Power version 3.1 (Heinrich-Heine-University, Düsseldorf, Germany) based on the observed standard deviations. Scatter plots displayed regression lines only for correlations of at least moderate strength (r ≥ 0.3) to avoid visual overinterpretation of weak associations. A two-sided p-value < 0.05 was considered statistically significant. No adjustments were made for multiple comparisons because the analyses were exploratory in nature. Ethical considerations This retrospective observational study was approved by the institutional ethics committee (approval number: 2025-98) and conducted in accordance with the Ethical Guidelines for Medical and Health Research Involving Human Subjects in Japan and the Declaration of Helsinki. All data were obtained from anonymized reviews of routine clinical and radiographic records. Written informed consent was obtained from all patients for the use of their clinical information for research and publication purposes. Results Range of motion (short-term outcome) One week after surgery, postoperative knee motion differed significantly from preoperative values. The mean extension angle improved from –16.4° ± 9.8° preoperatively to –5.0° ± 5.7° postoperatively, whereas the mean flexion angle decreased from 119.6° ± 14.8° to 110.2° ± 12.8° (both p < 0.01). These findings indicate substantial early correction of the extension deficit, accompanied by a modest reduction in knee flexion. Radiographic alignment The mean preoperative and postoperative radiographic parameters are summarized in Table 1. Postoperatively, both MPTA and JLCA significantly increased (both p < 0.01), indicating that the joint-line orientation was restored toward a more physiological configuration. The HKAA also shifted significantly after surgery (p < 0.01). In contrast, mLDFA did not differ significantly between time points (p = 0.83). Overall, these findings demonstrate that postoperative changes in MPTA and JLCA primarily contributed to the improvement in coronal alignment. Table 1. Changes in radiographic alignment parameters before and after surgery. Parameter Preoperative (mean ± SD) Postoperative (mean ± SD) p-value MPTA (°) 82.4 ± 4.1 85.4 ± 2.2 <0.001 mLDFA (°) 88.4 ± 2.3 88.4 ± 2.6 0.83 JLCA (°) -4.9 ± 4.2 0 ± 0 <0.001 HKAA (°) -10.8 ± 7.9 -3.0 ± 3.4 <0.001 Abbreviations: MPTA = medial proximal tibial angle; mLDFA = mechanical lateral distal femoral angle; JLCA = joint line convergence angle; HKAA = hip–knee–ankle angle. CPAK classification The distribution of CPAK types before and after surgery is shown in Table 2 and Figure 2. Preoperatively, most knees were classified as Type I (150 knees, 73.9%), followed by Type II (35 knees, 17.2%). Postoperatively, the proportion of Type I knees decreased to 44.3% (90 knees), whereas the proportion of Type II knees increased to 35.5% (72 knees), and Type IV increased to 11.8% (24 knees). Overall, the percentage of neutral alignment types (II, V, and VIII) increased from 19.2% preoperatively to 40.4% postoperatively, representing a shift toward more centrally distributed CPAK patterns. Table 2. Distribution of CPAK classification before and after surgery. CPAK type Preoperative, n (%) Postoperative, n (%) Type I 150 (73.9) 90 (44.3) Type II 35 (17.2) 72 (35.5) Type III 6 (3.0) 6 (3.0) Type IV 7 (3.4) 24 (11.8) Type V 4 (2.0) 10 (4.9) Type VI 1 (0.5) 1 (0.5) Abbreviation: CPAK = Coronal Plane Alignment of the Knee. Questionnaire survey Patient responses are summarized in Figure 3. Preoperatively, 173 of 203 knees (85.2%) were perceived as “bowed.” All of these knees were reported as “straight” after surgery. Among the 30 knees not perceived as bowed preoperatively, 18 knees (60.0%) were also reported as straight postoperatively. All patients expressed satisfaction with their postoperative limb straightness. VAS scores The mean postoperative S-VAS was 88.9 ± 11.6 (95% CI: 87.3–90.5), and the SS-VAS was 92.3 ± 12.9 (95% CI: 90.5–94.1). Both distributions skewed toward the upper end of the scale, indicating that patients generally perceived their limbs as nearly straight and were highly satisfied. The post hoc power analysis showed that, with 203 knees and a standard deviation of 11.6, the study had 80% power to detect a 2.3-point difference on the VAS scale, confirming adequate sample size. Correlations Correlation analyses revealed no significant associations between either S-VAS or SS-VAS and postoperative HKAA. In contrast, both indices demonstrated significant positive correlations with postoperative knee extension (S-VAS: r = 0.54, 95% CI 0.43–0.63, p < 0.001; SS-VAS: r = 0.59, 95% CI 0.49–0.67, p < 0.001) (Figure 4). These findings indicate that patient-perceived straightness and satisfaction were more closely related to functional knee extension than to radiographic alignment. Discussion The most important finding of this study was that patients were satisfied that their legs appeared straight after KA-TKA. Many patients in this cohort exhibited femoral cartilage defects with preserved mLDFA, whereas tibial bone defects were common. Consequently, correction of the MPTA led to improvements in overall limb alignment. When these bony and cartilaginous defects were restored, the collapsed articular surface on the osteoarthritic side opened, and the JLCA approached 0°. Because KA-TKA aims to reproduce the prearthritic joint state rather than implanting components into a deformed joint, postoperative changes in alignment and corresponding shifts in CPAK classification should be interpreted as the correction of bone defects rather than unintended deviations in alignment. Patients perceived these alignment changes cosmetically as their legs becoming straight and expressed high satisfaction in the coronal plane. In addition, sensory perception of straightness was influenced by knee extension; when residual extension deficits persisted, satisfaction tended to decrease. This distinction between radiographic correction and perceptual straightness provides a useful context for reconsidering the traditional emphasis on mechanical neutrality. Traditionally, achieving mechanical neutrality (HKAA = 0°) has been regarded as the standard alignment target in TKA. However, the present findings suggest that this radiographic benchmark does not necessarily correspond to patients’ subjective perception of straightness, indicating a potential discrepancy between objective alignment indices and patient-reported experience. Moreover, the assumption that a mechanically neutral axis is universally optimal may overlook inherent morphological diversity across populations, which reflects long-term evolutionary and developmental influences (23–25). Previous epidemiological studies (26, 27) in Asian populations have demonstrated a high prevalence of varus alignment, with reports ranging from one-third to nearly two-thirds of arthritic knees. Comparative analyses further reported that Japanese individuals show greater varus tendencies than Caucasian individuals do (28). Other investigations (29, 30) have confirmed that varus alignment is particularly common among Japanese patients with osteoarthritis, and that progressive varus deformity occurs with advancing age, especially in women (31). A systematic review of the CPAK classification (32) revealed significant differences in arthritic knees between racial groups but not in healthy knees. KA-TKA, which aims to restore the prearthritic morphology, is therefore expected to modify CPAK categories and generate favorable postoperative limb morphology even in Asian populations. In the present cohort, the proportion of CPAK type I knees was particularly high, representing a distinctive distribution in the global context. Despite these baseline characteristics, patients reported excellent postoperative satisfaction with straightness, supporting the ability of KA-TKA to restore physiological morphology in a manner consistent with patient perception. Changes in CPAK phenotype following TKA have been widely documented. Studies of mechanical alignment TKA (33) reported that alterations in CPAK category predicted inferior outcomes in KOOS-12 and FJS-12 scores. Simulation analyses (34) further suggested that, in certain phenotypes (e.g., CPAK type I), KA may achieve more favorable soft-tissue balance than MA does. Collectively, these findings highlight the importance of respecting an individual’s baseline bone morphology and ligament balance, factors that likely contributed to the natural sense of straightness reported by patients in the present study. From a broader perspective, these findings have notable clinical implications. For decades, surgeons have equated HKAA = 0° with a “straight leg,” shaping both surgical philosophy and patient expectations. This concept has been reinforced by the notion of “constitutional varus,” derived from radiographic surveys reporting an average HKAA of approximately 3° varus in healthy adults. The present results indicate that patients’ perception of straightness is influenced primarily by the restoration of native morphology and adequate knee extension rather than by achieving radiographic neutrality. This patient-centered alignment can be described as an “inherent straightness”—an alignment that feels physiologically natural to the individual. Distinguishing inherent straightness from radiographic neutrality helps refine current concepts of alignment and underscores the value of individualized anatomical reconstruction in KA-TKA. Limitations This study has several limitations that should be acknowledged. First, it was retrospective and conducted at a single center, which may restrict the generalizability of the findings. Second, patient perception of straightness was assessed using a study-specific VAS instrument that has not undergone formal psychometric validation. Although the questionnaire was intentionally simple to capture early cosmetic impressions, future studies incorporating validated patient-reported outcome measures may strengthen the interpretability of subjective assessments. Third, all evaluations were performed one week postoperatively. Early postoperative perception was intentionally selected as the target outcome because cosmetic awareness is most pronounced during this period; however, the short follow-up limits conclusions regarding longer-term perceptual or functional changes. Fourth, radiographic measurements and ROM assessments were performed by a single observer, and intra- or inter-observer reliability was not assessed. Fifth, correlation analyses were exploratory and based on linear assumptions; therefore, weak correlations should be interpreted with caution. Finally, although KA-TKA aims to restore each patient’s native morphology, it remains uncertain to what extent the reconstructed joint surface replicates the true prearthritic anatomy. Ongoing morphological investigations may help clarify this issue. Nevertheless, the central finding of this study remains consistent: patients reported a high degree of cosmetic satisfaction and perceived straightness of the lower limb after unrestricted KA-TKA, regardless of their postoperative radiographic alignment. Conclusions Patients who underwent unrestricted KA-TKA were highly satisfied with the cosmetic straightness of their legs, even when postoperative alignment did not reach mechanical neutrality (HKAA = 0°). Satisfaction was more closely associated with the restoration of knee extension and physiological morphology than with radiographic coronal alignment. These findings indicate that the alignment patients perceive as “straight” reflects an individualized and natural sense of limb alignment—an “inherent straightness.” Recognizing inherent straightness as a meaningful patient-centered outcome may help refine current concepts of alignment in TKA and complement traditional radiographic metrics. Abbreviations CPAK Coronal Plane Alignment of the Knee HKAA Hip–Knee–Ankle Angle JLCA Joint Line Convergence Angle KA Kinematic Alignment KA-TKA Kinematically Aligned Total Knee Arthroplasty MPTA Medial Proximal Tibial Angle mLDFA Mechanical Lateral Distal Femoral Angle ROM Range of Motion S-VAS Straightness Visual Analog Scale SS-VAS Straightness Satisfaction Visual Analog Scale TKA Total Knee Arthroplasty VAS Visual Analog Scale Declarations Ethics approval and consent to participate This study was conducted in accordance with institutional and national ethical standards and the principles of the Declaration of Helsinki. Ethical approval was obtained from the institutional review board (Approval No. 2025-98). Consent for publication All patients provided consent for publication of anonymized data. Funding No external funding was received for this study. References Freeman MA, Swanson SA, Todd RC. Total replacement of the knee using the Freeman-Swanson knee prosthesis. Clin Orthop Relat Res. 1973(94):153–70. Insall JN, Binazzi R, Soudry M, Mestriner LA. Total knee arthroplasty. Clin Orthop Relat Res. 1985(192):13–22. Lotke PA, Ecker ML. Influence of positioning of prosthesis in total knee replacement. J Bone Joint Surg Am. 1977;59(1):77–9. Bargren JH, Blaha JD, Freeman MA. Alignment in total knee arthroplasty. Correlated biomechanical and clinical observations. Clin Orthop Relat Res. 1983(173):178–83. Tew M, Waugh W. Tibiofemoral alignment and the results of knee replacement. J Bone Joint Surg Br. 1985;67(4):551–6. Aglietti P, Buzzi R. Posteriorly stabilised total-condylar knee replacement. Three to eight years' follow-up of 85 knees. J Bone Joint Surg Br. 1988;70(2):211–6. Berend ME, Ritter MA, Meding JB, Faris PM, Keating EM, Redelman R, et al. Tibial component failure mechanisms in total knee arthroplasty. Clin Orthop Relat Res. 2004(428):26–34. Benjamin J. Component alignment in total knee arthroplasty. Instr Course Lect. 2006;55:405–12. Sabharwal S, Zhao C, Edgar M. Lower limb alignment in children: reference values based on a full-length standing radiograph. J Pediatr Orthop. 2008;28(7):740–6. Fang DM, Ritter MA, Davis KE. Coronal alignment in total knee arthroplasty: just how important is it? J Arthroplasty. 2009;24(6 Suppl):39–43. Bellemans J, Colyn W, Vandenneucker H, Victor J. The Chitranjan Ranawat award: is neutral mechanical alignment normal for all patients? The concept of constitutional varus. Clin Orthop Relat Res. 2012;470(1):45–53. Riviere C, Ollivier M, Girerd D, Argenson JN, Parratte S. Does standing limb alignment after total knee arthroplasty predict dynamic alignment and knee loading during gait? Knee. 2017;24(3):627–33. Miller EJ, Pagnano MW, Kaufman KR. Tibiofemoral alignment in posterior stabilized total knee arthroplasty: Static alignment does not predict dynamic tibial plateau loading. J Orthop Res. 2014;32(8):1068–74. Parratte S, Pagnano MW, Trousdale RT, Berry DJ. Effect of postoperative mechanical axis alignment on the fifteen-year survival of modern, cemented total knee replacements. J Bone Joint Surg Am. 2010;92(12):2143–9. Magnussen RA, Weppe F, Demey G, Servien E, Lustig S. Residual varus alignment does not compromise results of TKAs in patients with preoperative varus. Clin Orthop Relat Res. 2011;469(12):3443–50. Howell S, Hull M. Kinematically aligned TKA with MRI-based cutting guides. Improving Accuracy in Knee Arthroplasty New Delhi, India: Jaypee Brothers Medical Publishers (P) Ltd. 2012:207 – 32. Riviere C, Iranpour F, Auvinet E, Howell S, Vendittoli PA, Cobb J, et al. Alignment options for total knee arthroplasty: A systematic review. Orthop Traumatol Surg Res. 2017;103(7):1047–56. MacDessi SJ, Griffiths-Jones W, Harris IA, Bellemans J, Chen DB. Coronal Plane Alignment of the Knee (CPAK) classification. Bone Joint J. 2021;103-B(2):329–37. Howell SM. Calipered Kinematically Aligned Total Knee Arthroplasty: An Accurate Technique That Improves Patient Outcomes and Implant Survival. Orthopedics. 2019;42(3):126–35. Soda Y. Coronal Alignment of Three Different Types of Implants in Kinematically Aligned Total Knee Arthroplasty: A Comparative Study. 2021. Brown JH. Traction during total knee arthroplasty leads to a bone-conserving tibial resection: a retrospective comparative study. International Journal of Orthopaedics. 2020;7(3):1283–8. Hiranaka T, Suda Y, Saitoh A, Tanaka A, Arimoto A, Koide M, et al. Current concept of kinematic alignment total knee arthroplasty and its derivatives. Bone Jt Open. 2022;3(5):390–7. Horbaly H, Hubbe M, Sylvester AD, Steadman DW, Auerbach BM. Variation in human limb joint articular morphology. Am J Biol Anthropol. 2023;182(3):388–400. Richard D, Liu Z, Cao J, Kiapour AM, Willen J, Yarlagadda S, et al. Evolutionary Selection and Constraint on Human Knee Chondrocyte Regulation Impacts Osteoarthritis Risk. Cell. 2020;181(2):362–81 e28. Dye SF. Functional morphologic features of the human knee: an evolutionary perspective. Clin Orthop Relat Res. 2003(410):19–24. Hsu CE, Chen CP, Wang SP, Huang JT, Tong KM, Huang KC. Validation and modification of the Coronal Plane Alignment of the Knee classification in the Asian population. Bone Jt Open. 2022;3(3):211–7. Nayak M, Kumar V, Kanojiya G, Mellon S, Srivastava DN, Pandit H, et al. A radiographic analysis of alignment in 966 lower extremities with knee pain and its association with osteoarthritis in Indian population. J Orthop. 2020;20:207–12. Hovinga KR, Lerner AL. Anatomic variations between Japanese and Caucasian populations in the healthy young adult knee joint. J Orthop Res. 2009;27(9):1191–6. Toyooka S, Osaki Y, Masuda H, Arai N, Miyamoto W, Ando S, et al. Distribution of Coronal Plane Alignment of the Knee Classification in Patients with Knee Osteoarthritis in Japan. J Knee Surg. 2023;36(7):738–43. Nomoto K, Hanada M, Hotta K, Matsuyama Y. Distribution of coronal plane alignment of the knee classification does not change as knee osteoarthritis progresses: a longitudinal study from the Toei study. Knee Surg Sports Traumatol Arthrosc. 2023;31(12):5507–13. Harada K, Mori Y, Kamimura M, Aki T, Koyama T, Aizawa T. Impact of Aging and Knee Osteoarthritis on Lower Limb Alignment and CPAK Classification: Gender Differences in a Japanese Cohort. J Clin Med. 2024;13(20). Zhao G, Ma C, Luo Z, Ma J, Wang J. A systematic review of geographic differences in knee phenotypes based on the coronal plane alignment of the knee (CPAK) classification. Arthroplasty. 2025;7(1):26. Konishi T, Hamai S, Tsushima H, Kawahara S, Akasaki Y, Yamate S, et al. Pre- and postoperative Coronal Plane Alignment of the Knee classification and its impact on clinical outcomes in total knee arthroplasty. Bone Joint J. 2024;106-B(10):1059–66. Arai N, Toyooka S, Masuda H, Kawano H, Nakagawa T. Kinematic Alignment Achieves a More Balanced Total Knee Arthroplasty Than Mechanical Alignment among CPAK Type I Patients: A Simulation Study. J Clin Med. 2024;13(12). 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-8194991","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":552481074,"identity":"47a6d4c3-f264-47a5-b9e5-ce8bb0745edf","order_by":0,"name":"Toshiya 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13:54:02","extension":"xml","order_by":23,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":81222,"visible":true,"origin":"","legend":"","description":"","filename":"921d539d01244ad78422227db8b27d391structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-8194991/v1/7a5a0c548590ecf1beee88b6.xml"},{"id":97259661,"identity":"a1f7d583-4bda-40fd-90f7-efbfbdcb910a","added_by":"auto","created_at":"2025-12-02 13:54:00","extension":"html","order_by":24,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":90573,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8194991/v1/4b56a0a9cc89b740964c3017.html"},{"id":97259610,"identity":"5c91e87c-6666-4952-a200-d0b266e19787","added_by":"auto","created_at":"2025-12-02 13:53:56","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":2651588,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eRadiographic definitions of coronal alignment parameters.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-8194991/v1/5b99232df79f4920b3861bf3.png"},{"id":97259671,"identity":"129bc44a-2c33-44eb-8728-e9eeb37003c9","added_by":"auto","created_at":"2025-12-02 13:54:02","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":590973,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScatter plots of CPAK classification.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(A) Preoperative distribution plotted by arithmetic hip–knee–ankle angle (aHKA, x-axis) and joint line obliquity (JLO, y-axis). (B) Postoperative distribution. Dotted lines indicate the Coronal Plane Alignment of the Knee (CPAK) classification thresholds of aHKA = –2° to 2° and JLO = 177° to 183°.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-8194991/v1/0f107fb5e2ce740f88179a9f.png"},{"id":97259669,"identity":"856fa74c-50d4-42da-842e-a031d821e08d","added_by":"auto","created_at":"2025-12-02 13:54:02","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":296927,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePatient-reported perception of lower-limb alignment.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(A) Response to the question: “Did you feel that your leg was bowed before the surgery?” (n = 203).\u003c/p\u003e\n\u003cp\u003e(B) Response to the question: “Has your leg been straightened after the surgery?” among patients who preoperatively perceived their legs as bowed (n = 173).\u003c/p\u003e\n\u003cp\u003e(C) Response to the question: “Has your leg been straightened after the surgery?” among patients who preoperatively did not perceive their legs as bowed (n = 30).\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-8194991/v1/2b2849e60ad88aa64f9a8211.png"},{"id":97259615,"identity":"c9cea20b-7d77-4bb6-a90d-3d481ed78f0e","added_by":"auto","created_at":"2025-12-02 13:53:57","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":705518,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eRelationships between patient-reported straightness scores and radiographic/clinical parameters.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eScatter plots showing the relationships between straightness visual analog scale (S-VAS) or satisfaction with straightness VAS (SS-VAS) and radiographic/clinical parameters. Regression lines are shown only for correlations with r ≥ 0.3.\u003c/p\u003e\n\u003cp\u003e(A) S-VAS versus hip–knee–ankle angle (HKA): weak correlation (r = 0.186, 95% CI 0.049–0.315, p = 0.008).\u003c/p\u003e\n\u003cp\u003e(B) S-VAS versus postoperative knee extension angle: moderate correlation (r = 0.535, 95% CI 0.429–0.626, p \u0026lt; 0.001).\u003c/p\u003e\n\u003cp\u003e(C) SS-VAS versus HKA: weak correlation (r = 0.164, 95% CI 0.027–0.295, p = 0.019).\u003c/p\u003e\n\u003cp\u003e(D) SS-VAS versus postoperative knee extension angle: moderate correlation (r = 0.586, 95% CI 0.487–0.669, p \u0026lt; 0.001).\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-8194991/v1/b7d7d51cbc6f115c7b33e529.png"},{"id":99315011,"identity":"2176da59-a645-4069-aaaf-8749456998a9","added_by":"auto","created_at":"2025-12-31 16:25:52","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6907181,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8194991/v1/3069c831-b0fc-40d0-8b09-4a4f65a2f280.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Patient Perception of Lower Limb Straightness after Unrestricted Kinematically Aligned Total Knee Arthroplasty: Exploring the Concept of “Inherent Straightness”","fulltext":[{"header":"Background","content":"\u003cp\u003eSince the late 1970s, mechanical neutrality has been widely regarded as the principal alignment goal in total knee arthroplasty (TKA) for osteoarthritic knees (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e). This strategy was proposed to improve implant survival by promoting even load distribution between the medial and lateral compartments. Over time, the neutral mechanical axis has also come to be widely interpreted as representing \u0026ldquo;normal\u0026rdquo; or physiologic alignment (\u003cspan additionalcitationids=\"CR4 CR5 CR6 CR7 CR8 CR9\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e). However, Bellman et al. (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e) demonstrated that a substantial proportion of skeletally mature adults naturally exhibit varus knee morphology, suggesting that ideal alignment may vary among individuals and does not universally fall within the traditional target of 0\u0026deg; \u0026plusmn; 3\u0026deg;.\u003c/p\u003e\u003cp\u003eFurthermore, increasing evidence indicates that coronal alignment measured on static radiographs after TKA does not reliably predict dynamic loading during gait (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e) and shows only weak associations with postoperative functional recovery or long-term implant performance (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e). Consequently, attention has shifted toward alternative alignment philosophies. Howell and colleagues (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e) proposed kinematic alignment (KA), an approach that aims to restore the patient\u0026rsquo;s native bone morphology and soft-tissue balance, thereby attempting to replicate prearthritic knee conditions.\u003c/p\u003e\u003cp\u003eTo date, no published studies have examined how patients perceive the straightness of their lower limbs as a cosmetic factor after TKA performed using such individualized alignment techniques, and this aspect remains insufficiently understood. In the context of KA, which seeks to reproduce each patient\u0026rsquo;s physiological morphology, it is clinically relevant to clarify whether patients perceive their limbs as bowed or naturally straight after surgery. Therefore, the purpose of this study was to evaluate whether patients perceive their lower limbs to be straight following unrestricted KA-TKA and to investigate how this perception relates to cosmetic satisfaction, coronal alignment parameters, and early functional findings.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003ePatients\u003c/h2\u003e\u003cp\u003eA total of 175 patients (203 knees) who underwent unrestricted kinematically aligned total knee arthroplasty (KA-TKA) at our institution were included. The mean age was 76.7\u0026thinsp;\u0026plusmn;\u0026thinsp;7.1 years; 36 were male and 139 were female. All patients were of Japanese ethnicity. Patients with a history of osteotomy, fracture, or total hip arthroplasty on the affected side were excluded to avoid extra-articular influences.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eClinical evaluation\u003c/h3\u003e\n\u003cp\u003eKnee extension and flexion angles were assessed preoperatively and one week postoperatively using a standard goniometer with patients in the supine position. Measurements were obtained passively, with the examiner supporting the limb to ensure neutral rotation.\u003c/p\u003e\n\u003ch3\u003eRadiographic evaluation\u003c/h3\u003e\n\u003cp\u003eWeight-bearing, full-leg standing radiographs were obtained preoperatively and one week postoperatively. Patients stood with their feet 10 cm apart and both patellae facing forward. Radiographic parameters included the medial proximal tibial angle (MPTA), mechanical lateral distal femoral angle (mLDFA), joint line convergence angle (JLCA), and hip\u0026ndash;knee\u0026ndash;ankle angle (HKAA). Knees were classified according to the Coronal Plane Alignment of the Knee (CPAK) system (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e). Radiographic measurements followed established angle definitions, which are summarized and illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e for clarity.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eSchematic illustration of radiographic measurements used in this study.\u003c/p\u003e\u003cp\u003eThe medial proximal tibial angle (MPTA), mechanical lateral distal femoral angle (mLDFA), joint line convergence angle (JLCA), and hip\u0026ndash;knee\u0026ndash;ankle angle (HKAA) were assessed on weight-bearing radiographs. Dotted lines represent the mechanical axis or joint line, and red arcs indicate the measured angles. For JLCA, medial opening was defined as positive and lateral opening as negative. For HKAA, valgus alignment was defined as positive and varus alignment as negative.\u003c/p\u003e\n\u003ch3\u003eQuestionnaire survey\u003c/h3\u003e\n\u003cp\u003eA study-specific questionnaire was administered one week after surgery to evaluate patients\u0026rsquo; perceptions of lower-limb straightness. The survey consisted of five items:\u003c/p\u003e\u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eDid you feel that your leg was bowed before the surgery?\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eHas your leg been straightened after the surgery?\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eAre you satisfied with the straightness of your leg?\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eWhat is your straightness score?\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eWhat is your score for satisfaction with straightness?\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003c/p\u003e\u003cp\u003eQuestions 1\u0026ndash;3 were answered with \u0026ldquo;yes\u0026rdquo; or \u0026ldquo;no,\u0026rdquo; and questions 4\u0026ndash;5 were assessed using a visual analog scale (VAS).\u003c/p\u003e\n\u003ch3\u003eSurgical procedures\u003c/h3\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003eDistal and posterior femoral resection\u003c/h2\u003e\u003cp\u003eThe femoral component was aligned using the calipered technique, as previously described (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e). After accounting for cartilage wear, distal and posterior resections were performed to match the thickness of the femoral component.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eProximal tibial resection\u003c/h3\u003e\n\u003cp\u003eThe tibial component was aligned using a combination of the calipered technique (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e) and the soft-tissue\u0026ndash;respecting technique (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e), both integral to unrestricted KA (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e). With the trial femoral component in place, the knee was extended and the lower leg gently pulled distally. A curved gap gauge was inserted into the tibial osteochondral defect to measure defect thickness. These values were compensated using the calipered technique, and cutting blocks were positioned so that the medial and lateral sides matched the thickness of the tibial component. The posterior slope was aligned to the native medial tibial condyle, and tibial rotation was aligned parallel to the long axis of the lateral tibial condyle. The soft-tissue\u0026ndash;respecting technique was then used to confirm parallelism between the tibial resection surface and the distal femoral cut in extension. Minor adjustments were performed when joint-surface deformation or defect evaluation warranted correction. The posterior cruciate ligament was preserved in all patients.\u003c/p\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003eData analysis\u003c/h2\u003e\u003cp\u003eAll values are expressed as means\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviations. Analyses were performed using R software (version 3.4.1; R Foundation for Statistical Computing, Vienna, Austria). The normality of continuous variables was assessed using the Shapiro\u0026ndash;Wilk test. Pre- and postoperative values of range of motion (ROM; extension and flexion), MPTA, mLDFA, JLCA, and HKAA were compared using paired t-tests.\u003c/p\u003e\u003cp\u003ePearson correlation coefficients were calculated to examine associations between straightness VAS (S-VAS) or straightness satisfaction VAS (SS-VAS) and both HKAA and postoperative knee extension. Ninety-five percent confidence intervals (95% CIs) were calculated where appropriate. A post hoc power analysis was conducted using G*Power version 3.1 (Heinrich-Heine-University, D\u0026uuml;sseldorf, Germany) based on the observed standard deviations. Scatter plots displayed regression lines only for correlations of at least moderate strength (r\u0026thinsp;\u0026ge;\u0026thinsp;0.3) to avoid visual overinterpretation of weak associations.\u003c/p\u003e\u003cp\u003eA two-sided p-value\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant. No adjustments were made for multiple comparisons because the analyses were exploratory in nature.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003eEthical considerations\u003c/h2\u003e\u003cp\u003e This retrospective observational study was approved by the institutional ethics committee (approval number: 2025-98) and conducted in accordance with the Ethical Guidelines for Medical and Health Research Involving Human Subjects in Japan and the Declaration of Helsinki. All data were obtained from anonymized reviews of routine clinical and radiographic records. Written informed consent was obtained from all patients for the use of their clinical information for research and publication purposes.\u003c/p\u003e\u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003eRange of motion (short-term outcome)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOne week after surgery, postoperative knee motion differed significantly from preoperative values. The mean extension angle improved from \u0026ndash;16.4\u0026deg; \u0026plusmn; 9.8\u0026deg; preoperatively to \u0026ndash;5.0\u0026deg; \u0026plusmn; 5.7\u0026deg; postoperatively, whereas the mean flexion angle decreased from 119.6\u0026deg; \u0026plusmn; 14.8\u0026deg; to 110.2\u0026deg; \u0026plusmn; 12.8\u0026deg; (both p \u0026lt; 0.01). These findings indicate substantial early correction of the extension deficit, accompanied by a modest reduction in knee flexion.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRadiographic alignment\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe mean preoperative and postoperative radiographic parameters are summarized in Table 1. Postoperatively, both MPTA and JLCA significantly increased (both p \u0026lt; 0.01), indicating that the joint-line orientation was restored toward a more physiological configuration. The HKAA also shifted significantly after surgery (p \u0026lt; 0.01). In contrast, mLDFA did not differ significantly between time points (p = 0.83). Overall, these findings demonstrate that postoperative changes in MPTA and JLCA primarily contributed to the improvement in coronal alignment.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1. Changes in radiographic alignment parameters before and after surgery.\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"3\" cellpadding=\"0\"\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eParameter\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003ePreoperative (mean \u0026plusmn; SD)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003ePostoperative (mean \u0026plusmn; SD)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003ep-value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eMPTA (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e82.4 \u0026plusmn; 4.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e85.4 \u0026plusmn; 2.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003emLDFA (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e88.4 \u0026plusmn; 2.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e88.4 \u0026plusmn; 2.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.83\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eJLCA (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e-4.9 \u0026plusmn; 4.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0 \u0026plusmn; 0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eHKAA (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e-10.8 \u0026plusmn; 7.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e-3.0 \u0026plusmn; 3.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eAbbreviations: MPTA = medial proximal tibial angle; mLDFA = mechanical lateral distal femoral angle; JLCA = joint line convergence angle; HKAA = hip\u0026ndash;knee\u0026ndash;ankle angle.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCPAK classification\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe distribution of CPAK types before and after surgery is shown in Table 2 and Figure 2. Preoperatively, most knees were classified as Type I (150 knees, 73.9%), followed by Type II (35 knees, 17.2%). Postoperatively, the proportion of Type I knees decreased to 44.3% (90 knees), whereas the proportion of Type II knees increased to 35.5% (72 knees), and Type IV increased to 11.8% (24 knees). Overall, the percentage of neutral alignment types (II, V, and VIII) increased from 19.2% preoperatively to 40.4% postoperatively, representing a shift toward more centrally distributed CPAK patterns.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2. Distribution of CPAK classification before and after surgery.\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"3\" cellpadding=\"0\"\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eCPAK type\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003ePreoperative, n (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003ePostoperative, n (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eType I\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e150 (73.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e90 (44.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eType II\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e35 (17.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e72 (35.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eType III\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e6 (3.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e6 (3.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eType IV\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e7 (3.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e24 (11.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eType V\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4 (2.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e10 (4.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eType VI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1 (0.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1 (0.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eAbbreviation: CPAK = Coronal Plane Alignment of the Knee.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eQuestionnaire survey\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePatient responses are summarized in Figure 3. Preoperatively, 173 of 203 knees (85.2%) were perceived as \u0026ldquo;bowed.\u0026rdquo; All of these knees were reported as \u0026ldquo;straight\u0026rdquo; after surgery. Among the 30 knees not perceived as bowed preoperatively, 18 knees (60.0%) were also reported as straight postoperatively. All patients expressed satisfaction with their postoperative limb straightness.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eVAS scores\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe mean postoperative S-VAS was 88.9 \u0026plusmn; 11.6 (95% CI: 87.3\u0026ndash;90.5), and the SS-VAS was 92.3 \u0026plusmn; 12.9 (95% CI: 90.5\u0026ndash;94.1). Both distributions skewed toward the upper end of the scale, indicating that patients generally perceived their limbs as nearly straight and were highly satisfied. The post hoc power analysis showed that, with 203 knees and a standard deviation of 11.6, the study had 80% power to detect a 2.3-point difference on the VAS scale, confirming adequate sample size.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorrelations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCorrelation analyses revealed no significant associations between either S-VAS or SS-VAS and postoperative HKAA. In contrast, both indices demonstrated significant positive correlations with postoperative knee extension (S-VAS: r = 0.54, 95% CI 0.43\u0026ndash;0.63, p \u0026lt; 0.001; SS-VAS: r = 0.59, 95% CI 0.49\u0026ndash;0.67, p \u0026lt; 0.001) (Figure 4). These findings indicate that patient-perceived straightness and satisfaction were more closely related to functional knee extension than to radiographic alignment.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe most important finding of this study was that patients were satisfied that their legs appeared straight after KA-TKA. Many patients in this cohort exhibited femoral cartilage defects with preserved mLDFA, whereas tibial bone defects were common. Consequently, correction of the MPTA led to improvements in overall limb alignment. When these bony and cartilaginous defects were restored, the collapsed articular surface on the osteoarthritic side opened, and the JLCA approached 0°. Because KA-TKA aims to reproduce the prearthritic joint state rather than implanting components into a deformed joint, postoperative changes in alignment and corresponding shifts in CPAK classification should be interpreted as the correction of bone defects rather than unintended deviations in alignment. Patients perceived these alignment changes cosmetically as their legs becoming straight and expressed high satisfaction in the coronal plane. In addition, sensory perception of straightness was influenced by knee extension; when residual extension deficits persisted, satisfaction tended to decrease. This distinction between radiographic correction and perceptual straightness provides a useful context for reconsidering the traditional emphasis on mechanical neutrality.\u003c/p\u003e\n\u003cp\u003eTraditionally, achieving mechanical neutrality (HKAA = 0°) has been regarded as the standard alignment target in TKA. However, the present findings suggest that this radiographic benchmark does not necessarily correspond to patients’ subjective perception of straightness, indicating a potential discrepancy between objective alignment indices and patient-reported experience. Moreover, the assumption that a mechanically neutral axis is universally optimal may overlook inherent morphological diversity across populations, which reflects long-term evolutionary and developmental influences (23–25).\u003c/p\u003e\n\u003cp\u003ePrevious epidemiological studies (26, 27) in Asian populations have demonstrated a high prevalence of varus alignment, with reports ranging from one-third to nearly two-thirds of arthritic knees. Comparative analyses further reported that Japanese individuals show greater varus tendencies than Caucasian individuals do (28). Other investigations (29, 30) have confirmed that varus alignment is particularly common among Japanese patients with osteoarthritis, and that progressive varus deformity occurs with advancing age, especially in women (31).\u003c/p\u003e\n\u003cp\u003eA systematic review of the CPAK classification (32) revealed significant differences in arthritic knees between racial groups but not in healthy knees. KA-TKA, which aims to restore the prearthritic morphology, is therefore expected to modify CPAK categories and generate favorable postoperative limb morphology even in Asian populations. In the present cohort, the proportion of CPAK type I knees was particularly high, representing a distinctive distribution in the global context. Despite these baseline characteristics, patients reported excellent postoperative satisfaction with straightness, supporting the ability of KA-TKA to restore physiological morphology in a manner consistent with patient perception.\u003c/p\u003e\n\u003cp\u003eChanges in CPAK phenotype following TKA have been widely documented. Studies of mechanical alignment TKA (33) reported that alterations in CPAK category predicted inferior outcomes in KOOS-12 and FJS-12 scores. Simulation analyses (34) further suggested that, in certain phenotypes (e.g., CPAK type I), KA may achieve more favorable soft-tissue balance than MA does. Collectively, these findings highlight the importance of respecting an individual’s baseline bone morphology and ligament balance, factors that likely contributed to the natural sense of straightness reported by patients in the present study.\u003c/p\u003e\n\u003cp\u003eFrom a broader perspective, these findings have notable clinical implications. For decades, surgeons have equated HKAA = 0° with a “straight leg,” shaping both surgical philosophy and patient expectations. This concept has been reinforced by the notion of “constitutional varus,” derived from radiographic surveys reporting an average HKAA of approximately 3° varus in healthy adults. The present results indicate that patients’ perception of straightness is influenced primarily by the restoration of native morphology and adequate knee extension rather than by achieving radiographic neutrality. This patient-centered alignment can be described as an “inherent straightness”—an alignment that feels physiologically natural to the individual. Distinguishing inherent straightness from radiographic neutrality helps refine current concepts of alignment and underscores the value of individualized anatomical reconstruction in KA-TKA.\u003c/p\u003e"},{"header":"Limitations","content":"\u003cp\u003eThis study has several limitations that should be acknowledged. First, it was retrospective and conducted at a single center, which may restrict the generalizability of the findings. Second, patient perception of straightness was assessed using a study-specific VAS instrument that has not undergone formal psychometric validation. Although the questionnaire was intentionally simple to capture early cosmetic impressions, future studies incorporating validated patient-reported outcome measures may strengthen the interpretability of subjective assessments. Third, all evaluations were performed one week postoperatively. Early postoperative perception was intentionally selected as the target outcome because cosmetic awareness is most pronounced during this period; however, the short follow-up limits conclusions regarding longer-term perceptual or functional changes. Fourth, radiographic measurements and ROM assessments were performed by a single observer, and intra- or inter-observer reliability was not assessed. Fifth, correlation analyses were exploratory and based on linear assumptions; therefore, weak correlations should be interpreted with caution. Finally, although KA-TKA aims to restore each patient’s native morphology, it remains uncertain to what extent the reconstructed joint surface replicates the true prearthritic anatomy. Ongoing morphological investigations may help clarify this issue. Nevertheless, the central finding of this study remains consistent: patients reported a high degree of cosmetic satisfaction and perceived straightness of the lower limb after unrestricted KA-TKA, regardless of their postoperative radiographic alignment.\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003ePatients who underwent unrestricted KA-TKA were highly satisfied with the cosmetic straightness of their legs, even when postoperative alignment did not reach mechanical neutrality (HKAA = 0°). Satisfaction was more closely associated with the restoration of knee extension and physiological morphology than with radiographic coronal alignment. These findings indicate that the alignment patients perceive as “straight” reflects an individualized and natural sense of limb alignment—an “inherent straightness.” Recognizing inherent straightness as a meaningful patient-centered outcome may help refine current concepts of alignment in TKA and complement traditional radiographic metrics.\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eCPAK\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eCoronal Plane Alignment of the Knee\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eHKAA\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eHip\u0026ndash;Knee\u0026ndash;Ankle Angle\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eJLCA\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eJoint Line Convergence Angle\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eKA\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eKinematic Alignment\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eKA-TKA\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eKinematically Aligned Total Knee Arthroplasty\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eMPTA\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eMedial Proximal Tibial Angle\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003emLDFA\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eMechanical Lateral Distal Femoral Angle\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eROM\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eRange of Motion\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eS-VAS\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eStraightness Visual Analog Scale\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eSS-VAS\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eStraightness Satisfaction Visual Analog Scale\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eTKA\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eTotal Knee Arthroplasty\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eVAS\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eVisual Analog Scale\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003cbr\u003e\u0026nbsp;This study was conducted in accordance with institutional and national ethical standards and the principles of the Declaration of Helsinki. Ethical approval was obtained from the institutional review board (Approval No. 2025-98).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003cbr\u003e\u0026nbsp;All patients provided consent for publication of anonymized data.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003cbr\u003e\u0026nbsp;No external funding was received for this study.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eFreeman MA, Swanson SA, Todd RC. Total replacement of the knee using the Freeman-Swanson knee prosthesis. Clin Orthop Relat Res. 1973(94):153\u0026ndash;70.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eInsall JN, Binazzi R, Soudry M, Mestriner LA. Total knee arthroplasty. Clin Orthop Relat Res. 1985(192):13\u0026ndash;22.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLotke PA, Ecker ML. Influence of positioning of prosthesis in total knee replacement. J Bone Joint Surg Am. 1977;59(1):77\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBargren JH, Blaha JD, Freeman MA. Alignment in total knee arthroplasty. Correlated biomechanical and clinical observations. Clin Orthop Relat Res. 1983(173):178\u0026ndash;83.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTew M, Waugh W. Tibiofemoral alignment and the results of knee replacement. J Bone Joint Surg Br. 1985;67(4):551\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAglietti P, Buzzi R. Posteriorly stabilised total-condylar knee replacement. Three to eight years' follow-up of 85 knees. J Bone Joint Surg Br. 1988;70(2):211\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBerend ME, Ritter MA, Meding JB, Faris PM, Keating EM, Redelman R, et al. Tibial component failure mechanisms in total knee arthroplasty. Clin Orthop Relat Res. 2004(428):26\u0026ndash;34.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBenjamin J. Component alignment in total knee arthroplasty. Instr Course Lect. 2006;55:405\u0026ndash;12.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSabharwal S, Zhao C, Edgar M. Lower limb alignment in children: reference values based on a full-length standing radiograph. J Pediatr Orthop. 2008;28(7):740\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFang DM, Ritter MA, Davis KE. Coronal alignment in total knee arthroplasty: just how important is it? J Arthroplasty. 2009;24(6 Suppl):39\u0026ndash;43.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBellemans J, Colyn W, Vandenneucker H, Victor J. The Chitranjan Ranawat award: is neutral mechanical alignment normal for all patients? The concept of constitutional varus. Clin Orthop Relat Res. 2012;470(1):45\u0026ndash;53.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRiviere C, Ollivier M, Girerd D, Argenson JN, Parratte S. Does standing limb alignment after total knee arthroplasty predict dynamic alignment and knee loading during gait? Knee. 2017;24(3):627\u0026ndash;33.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMiller EJ, Pagnano MW, Kaufman KR. Tibiofemoral alignment in posterior stabilized total knee arthroplasty: Static alignment does not predict dynamic tibial plateau loading. J Orthop Res. 2014;32(8):1068\u0026ndash;74.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eParratte S, Pagnano MW, Trousdale RT, Berry DJ. Effect of postoperative mechanical axis alignment on the fifteen-year survival of modern, cemented total knee replacements. J Bone Joint Surg Am. 2010;92(12):2143\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMagnussen RA, Weppe F, Demey G, Servien E, Lustig S. Residual varus alignment does not compromise results of TKAs in patients with preoperative varus. Clin Orthop Relat Res. 2011;469(12):3443\u0026ndash;50.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHowell S, Hull M. Kinematically aligned TKA with MRI-based cutting guides. Improving Accuracy in Knee Arthroplasty New Delhi, India: Jaypee Brothers Medical Publishers (P) Ltd. 2012:207\u0026thinsp;\u0026ndash;\u0026thinsp;32.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRiviere C, Iranpour F, Auvinet E, Howell S, Vendittoli PA, Cobb J, et al. Alignment options for total knee arthroplasty: A systematic review. Orthop Traumatol Surg Res. 2017;103(7):1047\u0026ndash;56.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMacDessi SJ, Griffiths-Jones W, Harris IA, Bellemans J, Chen DB. Coronal Plane Alignment of the Knee (CPAK) classification. Bone Joint J. 2021;103-B(2):329\u0026ndash;37.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHowell SM. Calipered Kinematically Aligned Total Knee Arthroplasty: An Accurate Technique That Improves Patient Outcomes and Implant Survival. Orthopedics. 2019;42(3):126\u0026ndash;35.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSoda Y. Coronal Alignment of Three Different Types of Implants in Kinematically Aligned Total Knee Arthroplasty: A Comparative Study. 2021.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBrown JH. Traction during total knee arthroplasty leads to a bone-conserving tibial resection: a retrospective comparative study. International Journal of Orthopaedics. 2020;7(3):1283\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHiranaka T, Suda Y, Saitoh A, Tanaka A, Arimoto A, Koide M, et al. Current concept of kinematic alignment total knee arthroplasty and its derivatives. Bone Jt Open. 2022;3(5):390\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHorbaly H, Hubbe M, Sylvester AD, Steadman DW, Auerbach BM. Variation in human limb joint articular morphology. Am J Biol Anthropol. 2023;182(3):388\u0026ndash;400.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRichard D, Liu Z, Cao J, Kiapour AM, Willen J, Yarlagadda S, et al. Evolutionary Selection and Constraint on Human Knee Chondrocyte Regulation Impacts Osteoarthritis Risk. Cell. 2020;181(2):362\u0026ndash;81 e28.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDye SF. Functional morphologic features of the human knee: an evolutionary perspective. Clin Orthop Relat Res. 2003(410):19\u0026ndash;24.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHsu CE, Chen CP, Wang SP, Huang JT, Tong KM, Huang KC. Validation and modification of the Coronal Plane Alignment of the Knee classification in the Asian population. Bone Jt Open. 2022;3(3):211\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eNayak M, Kumar V, Kanojiya G, Mellon S, Srivastava DN, Pandit H, et al. A radiographic analysis of alignment in 966 lower extremities with knee pain and its association with osteoarthritis in Indian population. J Orthop. 2020;20:207\u0026ndash;12.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHovinga KR, Lerner AL. Anatomic variations between Japanese and Caucasian populations in the healthy young adult knee joint. J Orthop Res. 2009;27(9):1191\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eToyooka S, Osaki Y, Masuda H, Arai N, Miyamoto W, Ando S, et al. Distribution of Coronal Plane Alignment of the Knee Classification in Patients with Knee Osteoarthritis in Japan. J Knee Surg. 2023;36(7):738\u0026ndash;43.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eNomoto K, Hanada M, Hotta K, Matsuyama Y. Distribution of coronal plane alignment of the knee classification does not change as knee osteoarthritis progresses: a longitudinal study from the Toei study. Knee Surg Sports Traumatol Arthrosc. 2023;31(12):5507\u0026ndash;13.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHarada K, Mori Y, Kamimura M, Aki T, Koyama T, Aizawa T. Impact of Aging and Knee Osteoarthritis on Lower Limb Alignment and CPAK Classification: Gender Differences in a Japanese Cohort. J Clin Med. 2024;13(20).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZhao G, Ma C, Luo Z, Ma J, Wang J. A systematic review of geographic differences in knee phenotypes based on the coronal plane alignment of the knee (CPAK) classification. Arthroplasty. 2025;7(1):26.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKonishi T, Hamai S, Tsushima H, Kawahara S, Akasaki Y, Yamate S, et al. Pre- and postoperative Coronal Plane Alignment of the Knee classification and its impact on clinical outcomes in total knee arthroplasty. Bone Joint J. 2024;106-B(10):1059\u0026ndash;66.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eArai N, Toyooka S, Masuda H, Kawano H, Nakagawa T. Kinematic Alignment Achieves a More Balanced Total Knee Arthroplasty Than Mechanical Alignment among CPAK Type I Patients: A Simulation Study. J Clin Med. 2024;13(12).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Kinematic alignment, Total knee arthroplasty, Inherent straightness, Patient perception, Coronal alignment","lastPublishedDoi":"10.21203/rs.3.rs-8194991/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8194991/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e\u003cp\u003eMechanical neutrality has long been regarded as the principal alignment target in total knee arthroplasty (TKA). However, radiographic neutrality does not necessarily reflect physiological morphology or patient perception. This study evaluated early postoperative cosmetic straightness after unrestricted kinematic alignment (KA)\u0026ndash;TKA and examined its relationship with radiographic and functional parameters.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e\u003cp\u003eA total of 175 patients (203 knees) who underwent unrestricted KA-TKA were retrospectively reviewed. Pre- and postoperative radiographs, clinical findings, and patient questionnaires were analyzed. Patient perception of straightness was assessed using the Straightness Visual Analog Scale (S-VAS) and Straightness Satisfaction Visual Analog Scale (SS-VAS). Radiographic measurements included the hip\u0026ndash;knee\u0026ndash;ankle angle (HKAA), medial proximal tibial angle (MPTA), mechanical lateral distal femoral angle (mLDFA), and joint line convergence angle (JLCA). Coronal plane alignment of the knee (CPAK) patterns were also assessed. Correlations were examined between VAS scores and radiographic/clinical parameters.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003ePreoperatively, 85.2% of knees were perceived as bowed; all of these were reported as straight after surgery. Among knees not perceived as bowed preoperatively, 60% were newly perceived as straight and 40% remained straight. Postoperative satisfaction was high (S-VAS 88.9\u0026thinsp;\u0026plusmn;\u0026thinsp;11.6; SS-VAS 92.3\u0026thinsp;\u0026plusmn;\u0026thinsp;12.9). Radiographs demonstrated substantial changes in coronal alignment, largely due to changes in MPTA and JLCA, resulting in shifts in CPAK patterns. Neither S-VAS nor SS-VAS correlated with HKAA, whereas both correlated moderately with postoperative knee extension (S-VAS r\u0026thinsp;=\u0026thinsp;0.54; SS-VAS r\u0026thinsp;=\u0026thinsp;0.59).\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e\u003cp\u003ePatients tended to equate straightness with restoration of morphology and improved knee extension rather than radiographic mechanical neutrality. These findings suggest that cosmetic straightness reflects each patient\u0026rsquo;s inherent sense of limb alignment (\u0026ldquo;inherent straightness\u0026rdquo;), complementing conventional alignment metrics in KA-TKA and supporting a more patient-centered understanding of alignment outcomes.\u003c/p\u003e","manuscriptTitle":"Patient Perception of Lower Limb Straightness after Unrestricted Kinematically Aligned Total Knee Arthroplasty: Exploring the Concept of “Inherent Straightness”","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-02 13:53:50","doi":"10.21203/rs.3.rs-8194991/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":"bf099416-8853-496e-b108-2e412752022e","owner":[],"postedDate":"December 2nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-12-29T01:38:42+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-02 13:53:50","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8194991","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8194991","identity":"rs-8194991","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}