Reconstructing Physiological Knee Medial Tightness in Total Knee Arthroplasty is Associated with Superior Clinical Outcomes in Asian Population: A Retrospective Cohort Study with Finite Element Analysis

Reconstructing Physiological Knee Medial Tightness in Total Knee Arthroplasty is Associated with Superior Clinical Outcomes in Asian Population: A Retrospective Cohort Study with Finite Element Analysis | 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 Reconstructing Physiological Knee Medial Tightness in Total Knee Arthroplasty is Associated with Superior Clinical Outcomes in Asian Population: A Retrospective Cohort Study with Finite Element Analysis Jiawei Hou, Yanlin Zhong, Yichen Zhang, Dong Jiang, Yu Xie, Shuai Li, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8952088/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 12 You are reading this latest preprint version Abstract Objective For Asian populations with physiological varus, optimal gap balance in total knee arthroplasty (TKA) remains debated. This study evaluated whether preserving physiological medial is superior to absolute balance. Methods In this retrospective study of 252 knees, patients undergoing primary posterior‑stabilized (PS) TKA were grouped by postoperative medial‑lateral gap difference. Clinical osteoarthritis assessment scores including KSS (Knee Society Score), WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) and FJS-12 (Forgotten Joint Score) were evaluated, comparing postoperative outcomes and their improvements after at least one year of follow-up. Subgroup analyses considered age, varus severity, and BMI. Finite element analysis (FEA) of different balance models were performed for load distribution and stress. Results Both the medially tight and balanced groups achieved superior outcomes compared with the laterally tight group. Moreover, patients with a gap difference of 1.0–1.5 mm (medially tight) demonstrated greater improvements in total, functional, and clinical KSS scores than the balanced group (all p 70 years, medial tightness provided a substantial functional improvement (KSS functional improvements: 37.9 ± 11.7 vs. 26.1 ± 9.84, p = 0.011). Besides, for patients with hip-knee-ankle angle > 10°, 0.5–1.0 mm gap difference (medially tight) contributed to fewer clinical symptoms (KSS clinical improvements:54.2 ± 11.4 vs. 43.9 ± 14.4, p = 0.040). FEA indicated that the medially tight model restored a more physiological load and favorable stress distribution. Conclusion For Asian patients undergoing PS TKA, reconstructing physiological medial tightness is associated with better functional recovery and a more physiological biomechanical environment than absolute balance reconstruction. Knee physiological reconstruction total knee arthroplasty knee medial tightness joint gap difference finite element analysis Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction In 2020, the global population with osteoarthritis (OA) reached 595 million, and a 74.9% rise in the prevalence of knee osteoarthritis is anticipated by the year 2050, posing a substantial health and economic burden ( 1 ) . Despite the rapid development of emerging therapeutic technologies such as platelet-rich plasma, total knee arthroplasty (TKA) is still the definitive surgical solution for end-stage knee OA ( 2 ) . Traditional TKA surgery adheres to the mechanical alignment principle, aiming to achieve neutral limb alignment. The basis of this concept is the anatomical characteristic of a predominance of neutral alignment in European and American populations ( 3 , 4 ) . Empirical observations suggest that the indiscriminate application of mechanical alignment, without accounting for physiological differences, can disrupt native bone alignment and perturb the physiological soft tissue envelope ( 5 ) . In response, kinematic alignment was proposed to preserve the patient's physiological alignment, offering a new direction for physiological joint replacement ( 6 ) . Current research predominantly focuses on the impact of lower limb alignment on clinical outcomes ( 7 ) , leaving the critical factor of medial-lateral gap balance insufficiently explored. Despite satisfactory postoperative radiographic alignment, 15–20% of patients still report symptoms such as pain and tightness ( 8 ) . These symptoms may be linked to improper management of soft tissue balance, potentially leading to abnormal prosthetic load distribution, reduced joint stability, and ultimately impaired functional recovery ( 9 ) . Historically, achieving absolute medial-lateral balanced gap has been considered the "gold standard" in TKA. Nevertheless, a study involving a European/American cohort indicated that patients with mild lateral laxity achieved comparable improvements in postoperative pain relief and joint awareness to those with absolutely balanced gaps ( 10 ) . This raises an important question: is absolute medial-lateral gap balance necessary for all patients? Among Asian populations, the prevalence of varus limb alignment is notably higher, reaching 52.7% in Southeast Asian populations ( 11 ) , and 38.03% in Chinese populations ( 12 ) . In 97% of individuals with varus knees, the medial compartment exhibited a smaller gap than lateral side, due to relative tightness of the medial soft‑tissue envelope ( 13 ) . Could preserving or restoring this physiological state of medial tightness yield equivalent, even potentially superior outcomes compared with a balanced gap? Currently, research specifically targeting Asian populations to clarify the impact of medial-lateral gap difference remains scarce. This study focuses on an Asian cohort. First, it analyzes the physiological medial-lateral gap difference state in healthy knees. Subsequently, it measures the medial-lateral gap difference in patients following primary TKA and correlates this with clinical outcome scores from at least one year of follow-up. The aim is to investigate whether “medial tightness” offers superior clinical prognosis compared to “medial-lateral balance”, and if so, to determine the ideal range for medial-lateral gap difference. To elucidate the biomechanical mechanisms underlying these clinical findings, this study employs finite element modeling to analyze the mechanical conditions on the prosthesis and bone resections under different gap difference states, thereby validating and explaining the clinical conclusions. Materials and method Study design and participant recruitment This study employed a single‑center, retrospective case‑control design. The protocol was approved by the ethics committee of the First Affiliated Hospital of Sun Yat‑sen University (Approval No: [2025]428). We derived the data for this study from the hospital's Joint Surgery Center database. It comprised two participant cohorts: Healthy volunteers: Volunteers who underwent lower‑limb X‑ray examinations at our institution between January 2024 and December 2024 for non‑orthopedic reasons. Inclusion criteria were: age 25‑35 years, no self‑reported knee symptoms, no previous lower‑limb trauma or surgical procedures, and no systemic diseases (e.g. rheumatoid arthritis, gout) potentially affecting the skeletal system. Patients: Patients receiving TKA with a posterior-stabilized (PS) prosthesis at the First Affiliated Hospital of Sun Yat-sen University from August 2019 to August 2024 were enrolled. Inclusion criteria were: age 18–85 years, diagnosis of primary knee OA (Kellgren–Lawrence classification grade IV), preoperative hip-knee-ankle angle (HKA) of affected limb > 0° ( 14 ) , and complete radiographic records. Exclusion criteria included: surgeries affecting function (e.g. hip, spine or ankle surgeries); revision surgery; periprosthetic infection; aseptic loosening or periprosthetic fracture following TKA; secondary knee OA (e.g. due to post‑traumatic arthritis, rheumatoid arthritis, pathological fractures from metastases or myeloma); pain and functional limitations not primarily attributable to knee pathology as confirmed by imaging and clinical examination and concomitant malignant disease or other systemic conditions severely impacting mobility; function or quality of life or other reasons such as loss to follow-up (Fig. 1 ). All patients were followed up preoperatively and at one year postoperatively via telephone by one orthopedic surgeon blinded to the radiographic data. Baseline characteristics and patient‑reported outcome measures were collected during these interviews. Radiographic data collection Bilateral full-length standing anteroposterior radiographs of the lower limbs and standard anteroposterior knee radiographs were obtained for healthy volunteers. For patients, preoperative full‑length standing radiographs of the affected limb and standard anteroposterior knee radiographs taken on postoperative day 1 were collected. All radiographic measurements were conducted independently by three experienced orthopedic surgeons using the UniWeb Version 6.0 clinical measurement system. These assessors were blinded to the clinical follow‑up scores. The measured parameters included: (1) HKA: it is defined as the acute angle subtended by two lines: one from the femoral head center to the knee center, and the other from the knee center to the ankle mortise center. Varus alignment was designated with positive values, while valgus alignment was designated with negative values. ( Fig. 2 a ) . (2) Joint gap difference: On standard anteroposterior knee radiographs, joint gap was the vertical distance from the lowest point of the femoral condyle to the tibial plateau. Joint gap difference (d) was calculated as: d = lateral gap - medial gap. d > 0 indicated relative medial tightness, while d < 0 indicated relative lateral tightness (Fig. 2 b). Grouping and outcome measures Participants were stratified based on the medial‑lateral gap difference (d) into: balanced group (-0.5 mm < d < 0.5 mm), medially tight Group (d ≥ 0.5 mm), laterally tight group (d ≤ -0.5 mm). The medially tight group was further subdivided into 0.5 mm ≤ d < 1.0 mm and d ≥ 1.0 mm subgroups. The laterally tight group was subdivided into − 1.0 mm < d ≤ -0.5 mm and d ≤ -1.0 mm subgroups. The primary outcomes measures included postoperative scores and the magnitude of improvement from the preoperative baseline to one year postoperatively. The following knee osteoarthritis scores were incorporated in this study: the Knee Society Score (KSS) ( 15 ) and its clinical and function subscales, the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) ( 16 ) and the Forgotten Joint Score-12 (FJS-12) ( 17 ) . Statistical analysis Data were analyzed using R studio version 4.5.2. The distribution of gap differences among healthy volunteers was summarized. For patients, age, body mass index (BMI), sex, preoperative varus severity (dichotomized at 10°) and operative side were compared across gap‑difference groups to assess baseline comparability. Appropriate multiple comparison correction was employed to compare postoperative scores and scores improvements between the different gap‑difference groups. The analysis specifically focused on comparisons between the medially tight group and balanced group. If statistically significant difference was observed between d ≥ 1.0 mm subgroup and the balanced group, further stratification at 0.5 mm intervals would be performed until the optimal gap‑difference range was identified or the subgroup sample size fell below 10. To explore the potential influence of the following factors, subgroup analyses were conducted. Each subgroup analysis was based on a single variable, dichotomizing the overall population (1) Age. Based on previous literature indicating poorer TKA outcomes in patients aged ≥ 70 years ( 18 ) , we divided patients into a lower-age group (< 70 years) and a higher-age group (≥ 70 years) (2) Preoperative varus severity. As medial soft‑tissue tightness is reported to commence with varus angles exceeding 10° ( 19 ) , patients were categorized into mild varus (preoperative HKA < 10°) and severe varus (preoperative HKA ≥ 10°) groups. (3) According to WHO classifications ( 20 ) , patients were grouped into normal BMI (BMI < 25.0 kg/m²) and overweight (BMI ≥ 25.0 kg/m²) groups. Fisher's exact test was applied to compare categorical variables. For continuous variables, normality (Shapiro‑Wilk test) and homogeneity of variances were first assessed. Based on these results, appropriate tests were applied: Tukey‑Kramer's test (parametric assumptions met), Games‑Howell test (normally distributed but unequal variances) or Dunn's test (non‑normally distributed). The threshold for statistical significance was set at a corrected p‑value of 0.05. Finite element model development Magnetic resonance imaging (MRI) and computed tomography (CT) scans (slice thickness and spacing: 1.0 mm) were performed on the left knee of a healthy male volunteer (weight: 75 kg, height: 178 cm,). We identified and segmented different anatomical structures of the knee on the MR and CT images using Mimics medical 21.0 (Materialise, Belgium). Utilizing distinct imaging modalities, we separately reconstructed the osseous and soft-tissue components. CT images formed the basis for modeling the femur, tibia, and fibula, whereas MRI data were used to generate individual solid models of the menisci, articular cartilage, medial/lateral collateral ligaments, patellar retinaculum, and cruciate ligaments. The models were imported into Geomagic 2021 (USA) for surface optimization and fitting to eliminate stair‑step artefacts resulting from image noise. The solid models of all components were then imported into SolidWorks 2024 (USA) for assembly, an experienced orthopedic surgeon supervised the procedure. Finally, the assembled model was imported into Ansys 2023 (USA) for meshing, material property assignment, and subsequent mechanical analysis. A three‑dimensional model of the PS prosthesis, comprising the femoral component, polyethylene insert and tibial tray was provided by the manufacturer (Keyibangen, China). Femoral component was positioned using a posterior referencing technique. 9 mm distal femoral resection was made perpendicular to the mechanical axis in 6° of valgus. The anterior‑posterior femoral resection was externally rotated 3° relative to the posterior condylar line. The anterior chamfer and posterior intercondylar resections were performed according to the prosthesis system's surgical guidelines ( 21 ) . Tibial component placement followed these steps: the proximal tibial cut was made perpendicular to the tibial mechanical axis with 3° of posterior slope. The resection was 8 mm below the intact lateral tibial plateau. The component was positioned centrally in the medial‑lateral direction and aligned with the anterior cortex in the anterior‑posterior direction. Tibial component rotation was aligned to a line connecting the center of the posterior cruciate ligament footprint to the medial third of the tibial tubercle. The polyethylene insert was mounted onto the tibial tray according to the manufacturer's instructions. The virtual implantation process was conducted by an orthopedic surgeon. As simulating a 1‑1.5 mm tightening of the medial ligament under load was technically unfeasible in the model. We reduced the thickness of the medial portion of the polyethylene insert by 1.25 mm to simulate this condition. To preserve the integrity of the bearing surfaces, the insert was virtually split into medial and lateral parts along its neutral plane. A 1.25 mm section was removed from the central portion of medial insert. Upper and lower parts of medial insert were then re‑joined and smoothed. This modified medial section was subsequently re‑joined to the unaltered lateral section. We restored the central post to its original geometry to avoid altering its interaction with the femoral component (Fig. 3 a- 3 c). Material properties and meshing According to the previous studies ( 22 , 23 ) , we assumed all materials in the finite element model to be isotropic, homogeneous and linearly elastic for contact stress analysis. Material properties were assigned based on literature values (Table 1 ) ( 24 , 25 ) . All components were meshed using linear tetrahedral elements. A mesh sensitivity analysis was conducted, resulting in a final element size ranging from 0.5 mm to 5.0 mm for different parts of the model Table 1 Material parameters for the models constructed in this study Tissue Young’s modulus (MPa) Poisson’s ratio Cortical bone 12000 0.3 Trabecular bone 100 0.3 Cartilage 20 0.45 Meniscus 55 0.3 Medial and lateral collateral ligaments 61 0.3 Patellar ligament 46 0.45 Anterior and posterior cruciate ligament 64 0.3 Femoral component 195000 0.3 Tibial component 110000 0.3 Femoral component 685 0.47 Interface contact conditions Contact between femoral cartilage and menisci, between femoral cartilage and tibial cartilage was modelled as frictionless surface‑to‑surface contact with finite sliding. The contact between the femoral component and the tibial polyethylene insert was assigned a coefficient of friction (µ) of 0.04. We defined all other interfaces between components, between implants and bone as tied contacts to simulate the connections within the knee joint ( 26 ) . Boundary and loading conditions To facilitate analysis and comparison, we constrained the distal ends of tibia fibula in all finite element models. Knee models were created at configurations of 0°, 15°, 60° and 90° to simulate different activities of daily life with corresponding loads applied (Fig. 3 d- 3 g) ( 22 , 27 ) . 0° configuration simulated static standing. A compressive load equal to 0.5 times body weight (367.5 N) was applied along the mechanical axis to the proximal femoral surface. 15° configuration simulated the toe‑off phase of gait. A load equal to 2.8 times body weight (2058 N) was applied along the mechanical axis to the proximal femoral surface. 60° configuration simulated stair climbing. A load of 3.3 times body weight (2425.5 N) was applied along the mechanical axis to proximal femur. 90° configuration simulated rising from a seated position. A load of 1000 N was applied along the tibial mechanical axis to proximal femur. Lower magnitude reflects common use of arm support during this activity ( 28 ) . Model validation To validate the model, we compared the maximum stress values in the femoral cartilage, menisci and tibial cartilage of the healthy knee model under a 1000 N vertical load with published experimental data ( 29 ) . The results showed good agreement in terms of peak pressure magnitudes and the distribution of high‑pressure areas, confirming the reliability of the model. Biomechanical parameters The biomechanical parameters involved comparing: The load distribution ratio between the medial and lateral tibial plateaus across healthy knee model, balanced prosthesis model and medially tight prosthesis model under the different configurations. The stress and strain distribution on the polyethylene insert and the tibial resection surface between balanced prosthesis model and medially tight prosthesis model under the different configurations Results Reproducibility All radiographic parameters demonstrated excellent reproducibility, with ICC values ranging from 0.937 to 0.987, exceeding the threshold of 0.80, indicating outstanding interobserver agreement and reliability. Physiological state in the healthy population A total of 19 healthy volunteers (38 knees) were included. The medially tight group was the most prevalent, comprising 24 knees (63.16%), followed by the balanced group with 12 knees (31.58%), and the laterally tight group with 2 knees (5.26%). This indicates a higher physiological prevalence of medial tightness of the knee in the healthy cohort. Association between post-TKA outcomes and joint gap difference A total of 220 patients (252 knees) completed the follow-up. Baseline characteristics are summarized in Table S1 , there were no significant differences between groups. d ≥ 1.0 mm group had significantly greater total KSS improvements (83.8 ± 18.9) compared to the balanced group (70.5 ± 21.0) (p = 8.16 × 10 − ³). d ≥ 1.0 mm group was subsequently divided into 1.0 mm ≤ d < 1.5 mm and d ≥ 1.5 mm groups for further analysis. Baseline characteristics for these refined groups showed no significant differences (Table 2 ) Table 2 Comparison of baseline characteristics among the six joint gap difference groups Item d≤-1.0mm -1.0mm < d≤-0.5mm -0.5mm < d<0.5mm 0.5mm ≤ d < 1.0mm 1mm ≤ d < 1.5mm d ≥ 1.5mm P-value n 39 39 94 34 25 21 Gender = M (%) 7 (17.9) 5 (12.8) 19 (20.2) 2 (5.9) 1 (4.0) 4 (19.0) 0.203 Age (years, mean ± SD) 69.0 ± 5.8 70.3 ± 5.57 68.98 ± 5.8 69.26 ± 5.0 70.08 ± 6.6 70.57 ± 6.2 0.729 BMI (m 2 /kg, mean ± SD) 25.6 ± 3.1 26.36 ± 3.5 25.95 ± 4.1 27.14 ± 3.7 25.10 ± 2.2 26.51 ± 3.6 0.301 HKA Group=Severe (%) 18 (46.2) 18 (46.2) 52 (55.3) 21 (61.8) 18 (72.0) 15 (71.4) 0.147 Side = R (%) 19 (48.7) 16 (41.0) 47 (50.0) 17 (50.0) 15 (60.0) 11 (52.4) 0.804 d means joint gap difference, n means number of patients, BMI means body mass index, HKA means hip-knee-ankle angle, M means male, R means right side, SD means standard deviation. P-value means the significance level for intergroup comparisons. Categorical variables were analyzed using the chi-square test and continuous variables were analyzed using analysis of variance. 1.0 mm ≤ d< 1.5 mm group demonstrated superior improvements in total KSS improvements (88.5 ± 19.5 vs. 70.5 ± 21.0, p = 4.66 × 10 − 3 ), functional KSS improvements (52.9 ± 10.6 vs. 42.8 ± 15.0, p = 0.030) and clinical KSS improvements (35.6 ± 11.2 vs. 27.7 ± 10.7, p = 0.041) compared to the balanced Group (Fig. 4 a- 4 c). Both the 1.0 mm ≤ d < 1.5 mm group and the balanced group outperformed the laterally tight group. For WOMAC improvements, we found no significant difference between the medially tight and balanced groups, both were superior to the laterally tight group. Comparison of postoperative scores showed no statistically significant difference between the medially tight and balanced groups. The medially tight group achieved higher postoperative total KSS, functional KSS, and WOMAC scores than the laterally tight group. We found no significant between-group differences in the FJS-12 scores. (Table 3 , Figure S1 ). Table 3 Comparison of postoperative knee scores and score improvements among different patient groups Item d≤-1.0mm -1.0mm < d≤-0.5mm -0.5mm < d<0.5mm 0.5mm ≤ d < 1.0mm 1mm ≤ d < 1.5mm d ≥ 1.5mm P-value Total KSS improvements 60.4 ± 23.2 70.4 ± 22.0 70.5 ± 21.0 80.3 ± 19.3 88.5 ± 19.5 78.1 ± 16.9 4.466×10 − 5 (Dunn) Clinical KSS improvements 38.7 ± 17.3 44.1 ± 16.0 42.8 ± 15.0 50.6 ± 12.2 52.9 ± 10.6 49.8 ± 15.0 5.341×10 − 4 (Dunn) Functional KSS improvements 21.7 ± 11.9 26.3 ± 11.2 27.7 ± 10.7 29.7 ± 11.1 35.6 ± 11.2 28.3 ± 7.5 2.020×10 − 4 (Dunn) WOMAC improvements 26.3 ± 7.4 30.3 ± 9.7 33.4 ± 8.8 36.9 ± 7.6 37.6 ± 7.4 34.7 ± 6.0 4.212×10 − 8 (T-K) Postoperative total KSS 147.4 ± 19.5 150.5 ± 16.2 154.4 ± 14.6 159.8 ± 9.4 160.5 ± 8.4 152.8 ± 16.4 3.850×10 − 3 (Dunn) Postoperative clinical KSS 86.4 ± 12.9 88.4 ± 9.3 90.2 ± 8.5 93.0 ± 6.4 92.1 ± 6.4 89.2 ± 8.8 0.141 (Dunn) Postoperative Functional KSS 61.0 ± 9.9 62.2 ± 9.4 64.1 ± 8.2 66.8 ± 6.4 68.4 ± 3.7 63.6 ± 8.8 3.933×10 − 3 (Dunn) Postoperative WOMAC 15.9 ± 8.1 14.7 ± 7.8 12.7 ± 6.9 9.88 ± 4.7 8.92 ± 3.4 13.2 ± 6.5 3.391×10 − 4 (Dunn) Postoperative FJS-12 78.3 ± 13.5 77.6 ± 10.0 76.7 ± 13.3 80.8 ± 8.1 82.2 ± 8.9 76.0 ± 18.6 0.463 (Dunn) Data are presented as mean ± standard deviation. d means joint gap difference, KSS means Knee Society Score, WOMAC means Western Ontario and McMaster Universities Osteoarthritis Index, FJS-12 means Forgotten Joint Score-12. P-values were derived from the Kruskal-Wallis test (K-W test) or One-way Analysis of Variance (One-way ANOVA). Dunn means Dunn’s test was used in the multiple comparisons. T-K means Tukey-Kramer's test was used in the multiple comparisons. Subgroup analysis Baseline characteristics were balanced within all groups ( Table S2 -S7 ). In the higher-age subgroup, the 1.0 mm ≤ d < 1.5 mm group showed greater improvements in total KSS improvements (92.6 ± 21.3 vs. 68.5 ± 19.1, p = 2.40 × 10 − 3 ) and functional KSS improvements (37.9 ± 11.7 vs. 26.1 ± 9.84, p = 0.011) than balanced group (Fig. 4 d- 4 e). In the severe varus subgroup, the 0.5 mm ≤ d < 1.0 mm group showed greater improvements in clinical KSS improvements (54.2 ± 11.4 vs. 43.9 ± 14.4, p = 0.040) than balanced group (Fig. 4 f). In other subgroups analyses, no differences in KSS or WOMAC improvements were found between medially tight and balanced groups. Within all subgroups analyses, the medially tight and balanced groups showed better KSS and WOMAC improvements than the laterally tight group. Regarding postoperative scores, there were no significant differences between medially tight and balanced groups within both subgroups. However, specific advantages for the medially tight group over the laterally tight group were noted: in the higher-age subgroup for total KSS, in the mild varus subgroup for total KSS and WOMAC, in the normal BMI subgroup for WOMAC and in the high BMI subgroup for total KSS, functional KSS and WOMAC. We found there are no significant between-group differences in FJS-12 within any of these subgroups ( Table S8-S13, Figures S2 -S7 ). Medial‑lateral load distribution It is illustrated the magnitude and proportion of load transmitted through the medial tibial plateaus for the three models under the four configurations (Fig. 5 ). Across all conditions, the medial plateau bore a greater load in each model. The load borne by the medial and lateral plateaus became more comparable at flexion angles of 60° and 90°, a trend consistent with previous studies ( 27 , 30 ) . Furthermore, it demonstrates that the load proportion of the medial compartment in the medially tight prosthesis model more closely resembled that of the healthy knee model compared to the balanced prosthesis model. The absolute difference (|Δ|) in the proportion of medial plateau load between each prosthesis model and the healthy knee model was calculated (|Δ balanced‑healthy| vs |Δ medially tight‑healthy|): 0°: 5.71% vs 0.49%, 15°: 5.05% vs 0.49%, 60°: 0.77% vs 0.25%, 90°: 4.23% vs 1.64%. Stress and strain distribution Distribution of stress on the polyethylene insert for medially tight and balanced prosthesis models under the four configurations are displayed in Fig. 6 . The results indicate that during knee flexion, The contact area of the femoral component on the tibial insert migrates posteriorly on both the medial and lateral sides. Due to the medial pivoting motion of the knee, the area of stress distribution on the lateral plateau exhibited a greater range of movement during flexion, which is corroborated by prior finite element studies ( 31 ) . Additionally, compared to the balanced model, the medially tight prosthesis model exhibited higher peak stress on medial portion of insert across all simulated conditions: medially tight vs balanced (MPa): 0°: 15.667 vs 12.719, 15°: 49.599 vs 46.023, 60°: 65.150 vs 59.928, 90°: 32.260 vs 21.076. Figure S8 presents the magnitude and distribution of strain for the two prosthesis models. The strain distribution pattern was largely consistent with the stress findings. Representative peak strain values (medially tight vs balanced, mm/mm) were: 0°: 0.026 vs 0.001, 15°: 0.091 vs 0.117, 60°: 0.143 vs 0.089, 90°: 0.054 vs 0.041. It is showed the stress magnitude and distribution on the tibial resection surface for both models in Fig. 7 . It was observed that at flexion angles of 15°, 60° and 90°, The medially tight prosthesis model demonstrated a lower peak stress on the tibial resection surface. (medially tight vs balanced (MPa)): 0°: 7.435 vs 7.018, 15°: 50.916 vs 58.229, 60°: 133.02 vs 137.22, 90°: 31.744 vs 34.388. Furthermore, the area of stress distribution was generally more extensive in the balanced prosthesis model. As the resection surface is primarily load‑bearing for cortical bone, a separate analysis was conducted for cancellous bone stress distribution ( Figure S9 ). The results were largely consistent with those of the full resection surface (medially tight vs balanced (MPa)): 0°: 0.090 vs 0.088, 15°: 1.363 vs 1.507, 60°: 3.329 vs 3.328, 90°: 0.292 vs 0.352. Figure S10 illustrates the strain distribution on the tibial resection surface for both models at different configurations. Strain was primarily concentrated in the cancellous bone region. The strain distribution and magnitude were generally similar between the two prosthesis models (medially tight vs balanced (ε)): 0°: 0.001 vs 0.021, 15°: 0.014 vs 0.016, 60°: 0.034 vs 0.036, 90°: 3.075×10 − 3 vs 3.968×10 − 3 . Discussion This study demonstrates that for Asian patients undergoing TKA, maintaining a medial‑lateral gap difference of 1–1.5 mm ("medial tightness") is associated with superior clinical outcomes, including more pronounced symptom relief and greater functional recovery. Other degrees of medial tightness yielded similar clinical and functional improvements as the balanced group, with both performing significantly better than lateral tight group (particularly d ≤ -1.0 mm). We observed no significant differences in joint awareness among different gap‑difference groups. The Coronal Plane Alignment of the Knee (CPAK) classification system precisely categorizes lower limb alignment, critiquing a "one‑size‑fits‑all" approach to TKA ( 32 ) . Previous research has delineated the prevalence of various knee phenotypes across ethnicities, revealing a higher proportion of varus alignment in Asian populations (39.5%) compared to the predominance of neutral alignment in Caucasian populations (39.7%), thereby providing a scientific foundation for physiological surgery ( 4 ) . A retrospective study showed that outcomes following a standardized surgical protocol differ across CPAK phenotypes ( 33 ) , prompting consideration of physiological knee reconstruction. Existing research has largely focused on lower limb alignment and bone resection techniques, the role of soft‑tissue balance remains underexplored. To address this gap, we aimed to investigate the impact of soft‑tissue balance on clinical outcomes. Within our healthy cohort, medial tightness was found to be prevalent. Okazaki et al. similarly reported the presence of lateral laxity in knee flexion and extension, which may play a functional role in facilitating the normal medial pivoting motion of the knee ( 34 ) . Concurrently, finite element analysis of the healthy knee model confirmed that a greater proportion of the load is borne by the medial compartment. A finite element study analyzing femoral condylar motion trajectories reported anteroposterior translation ranges of 6.8 ± 3.1 mm for the medial condyle and 9.3 ± 4.4 mm for the lateral condyle during 0-100° of flexion ( 31 ) . These findings collectively underscore the strong constraint imposed by the medial collateral ligament and the physiological state of relative medial soft‑tissue tightness. Regarding the post‑TKA population, several prior studies have noted the existence of postoperative lateral soft‑tissue laxity and its association with favorable outcomes. Coffey et al. found that whether mechanical alignment or restricted kinematic alignment was used intraoperatively, the lateral soft tissues were laxer than the medial tissues postoperatively ( 35 ) . A study involving 40 knee samples reported that lateral laxity was related to improved Knee injury and Osteoarthritis Outcome Score (KOOS) (β = 0.465, p = 0.025) ( 36 ) . A cadaveric study elucidated that insufficient lateral laxity during TKA might impede normal tibial internal rotation during knee flexion ( 37 ) . Our study not only confirms that medial tightness is associated with significant post-TKA outcomes in Asian populations but also, for the first time, innovatively defines the optimal gap‑difference range as 1-1.5 mm. Another biomechanical cadaveric study indicated that 75% of the load in a healthy knee is transmitted through the medial compartment, and that laxity of the medial collateral ligament results in a shift of load to the lateral compartment ( 38 ) . Appropriate tightness of the medial collateral ligament helps maintain load within the medial compartment, preserving physiological conditions. Our finite element analysis similarly observed that compared to the balanced model, the proportion of load borne by the medial versus lateral tibial plateau in the medially tight model (1.25 mm reduction) more closely approximated that of the healthy knee. Furthermore, in the medially tight model, a greater proportion of stress was transmitted through the medial plateau. Larger surface area of the medial plateau facilitates better stress distribution ( 39 ) , which may explain why the peak stress on the tibial resection surface was lower and the stress distribution more uniform in the medially tight model compared to the balanced model. This restoration of the knee's native physiological state is a plausible mechanism for its superior outcomes. In the higher-age patient subgroup (≥ 70 years), the prognostic advantage of a 1-1.5 mm gap difference over the balanced group was primarily evident in functional recovery, which was not observed in the lower-age subgroup. Previous studies indicate that approximately 20% of elderly patients with knee OA have osteoporosis preoperatively, and nearly half have osteopenia ( 40 ) , which increases the long‑term revision risk (HR:1.8, 95% CI: 1.6 to 2.1) ( 41 ) . Moreover, it was reported that decreased bone mineral density of tibial plateau occurs predominantly in the medial segment ( 42 ) , fragile bony architecture may be more sensitive to physiological load transfer ratio. Additionally, multiple community‑based studies in Japan report generally weaker muscle strength in the elderly population ( 43 , 44 ) , and muscle deficit is known to hinder postoperative recovery in TKA patients ( 45 ) . Therefore, medial soft‑tissue tightness, by restoring a physiological medial‑lateral load distribution, may better compensate for the negative impact of muscle deficit on recovery. In the severe varus subgroup, the group with a joint gap difference of 0.5-1 mm demonstrated significantly greater improvement in pain and other clinical symptoms compared to the balanced group. A study focusing on the microstructure, bone remodeling levels, and histological characteristics of varus knees revealed that the weight-bearing area of the medial tibial plateau exhibits severe cartilage degeneration and more substantial structural deterioration of the subchondral bone ( 46 ) . Consequently, this region demonstrates a diminished capacity to withstand excessive load distribution. Therefore, a joint gap difference of 0.5-1 mm better balances the requirements for physiological reconstruction and the protection of the vulnerable bone environment of the medial plateau, leading to superior clinical outcomes compared to a 1-1.5 mm gap difference. This study has several limitations: (1) The use of radiographs rather than CT scans may have reduced the precision of gap measurements. However, three experienced arthroplasty surgeons performed the measurements independently, and the average was used to maximize accuracy and objectivity. (2) Due to technical constraints, directly modelling medial ligament tightness resulting in a 1-1.5 mm gap difference was not feasible. We therefore approximated this condition by modelling a prosthesis with a 1.25 mm reduction in medial insert thickness. (3) As a retrospective study, information bias is unavoidable. We attempted to mitigate this by blinding the personnel involved in radiographic measurement and telephone follow‑up. (4) The finite element analysis revealed higher medial insert stress in the medially tight model. This implies that medially tight soft‑tissue state could lead to greater wear on the medial insert, potentially reducing long‑term implant survivorship and increasing revision risk. Limited by patient numbers and research costs, this study did not conduct long‑term follow‑up across gap‑difference groups, which warrants further investigation. (5) The present study investigated the joint gap exclusively in full knee extension; the relationship between gap variations during flexion and post-TKA outcomes remains to be explored. Conclusion This study establishes a physiological target for soft‑tissue balancing in PS TKA. Convergent clinical and biomechanical evidence indicates that for Asian population, reconstructing medial tightness with a 1.0‑1.5 mm medial‑lateral gap difference constitutes a strategy superior to the traditional goal of absolute balance, potentially serving as a key determinant for enhancing postoperative function and patient satisfaction. Abbreviations OA osteoarthritis TKA total knee arthroplasty PS posterior-stabilized d difference KSS Knee Society Score WOMAC Western Ontario and McMaster Universities Osteoarthritis Index FJS-12 Forgotten Joint Score-12 FEA finite element analysis HKA hip-knee-ankle angle BMI body mass index MRI Magnetic resonance imaging CT computed tomography. Declarations Acknowledgments We were grateful for the guidance and support in the finite element analysis provided by Youdao Technology Co., Ltd. (Guangzhou, China). We were thankful to DeepSeek for polishing the article. However, we declared that the artificial intelligence did not generate any scientific conclusions. Author contributions Jiawei Hou conceived, designed and performed research, collected clinical data and drafted the manuscript. Yanlin Zhong performed clinical follow‐up, Yichen Zhang, Dong Jiang and Shuai Li collected clinical data. Yu Xie performed the finite element analysis. Zhiqi Zhang and Guiwu Huang conceived, designed, supervised the study, and revised the manuscript. Jiawei Hou is regarded as first author. Guiwu Huang and Zhiqi Zhang are regarded as the corresponding authors. Funding This study was funded by the National Natural Science Foundation of China (82572796，82172467), the First Affiliated Hospital of Sun Yat-sen University Ke Ling Funding program for Novel and Distinguished talents (R07005), Guangzhou Science Funds (2024A04J6487). Data availability statement The data are available from the corresponding author upon reasonable request and with permission from the First Affiliated Hospital of Sun Yat‑sen University. Ethics approval and consent to participate The study received the approval of the Institutional Ethics Committee for Clinical Research and Animal Trials of the First Affiliated Hospital of Sun Yat-sen University [2025]428. All procedures were conducted in accordance with the Declaration of Helsinki. The requirement for informed consent was waived due to the retrospective design of the study. Consent for publication Not applicable. 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Larger Medial Contact Area and More Anterior Contact Position in Medial-Pivot than Posterior-Stabilized Total Knee Arthroplasty during In-Vivo Lunge Activity. Bioeng (Basel). 2023;10(3):290. 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. 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. Okazaki K, Miura H, Matsuda S, Takeuchi N, Mawatari T, Hashizume M, et al. Asymmetry of mediolateral laxity of the normal knee. J Orthop Sci. 2006;11(3):264–6. Orsi AD, Wakelin EA, Plaskos C, Petterwood J, Coffey S. Restricted kinematic alignment achieves similar relative lateral laxity and greater joint line obliquity compared to gap balancing TKA. 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J Bone Joint Surg Am. 2008;90(12):2724–34. Delsmann MM, Strahl A, Mühlenfeld M, Jandl NM, Beil FT, Ries C, et al. High prevalence and undertreatment of osteoporosis in elderly patients undergoing total hip arthroplasty. Osteoporos Int. 2021;32(8):1661–8. Harris AB, Lantieri MA, Agarwal AR, Golladay GJ, Thakkar SC. Osteoporosis and Total Knee Arthroplasty: Higher 5-Year Implant-Related Complications. J Arthroplasty. 2024;39(4):948–e531. Krause M, Hubert J, Deymann S, Hapfelmeier A, Wulff B, Petersik A, et al. Bone microarchitecture of the tibial plateau in skeletal health and osteoporosis. Knee. 2018;25(4):559–67. Asano Y, Yoshida T, Tsunoda K, Yokoyama K, Watanabe Y, Yoshinaka Y, et al. Sex- and age-related declines in muscle mass, strength, physical performance, and muscle quality among community-dwelling older adults: A cross-sectional study. Exp Gerontol. 2025;210:112862. Hayashida I, Tanimoto Y, Takahashi Y, Kusabiraki T, Tamaki J. Correlation between muscle strength and muscle mass, and their association with walking speed, in community-dwelling elderly Japanese individuals. PLoS ONE. 2014;9(11):e111810. Humphrey TJ, Salimy MS, Jancuska JM, Egan CR, Melnic CM, Alpaugh K, et al. Sarcopenia is an independent risk factor for failure to achieve the 1-year MCID of the KOOS, JR and PROMIS PF-SF10a after TKA. Knee. 2023;42:64–72. Liu K, Chen Y, Miao Y, Xue F, Yin J, Wang L, et al. Microstructural and histomorphological features of osteophytes in late-stage human knee osteoarthritis with varus deformity. Joint Bone Spine. 2022;89(4):105353. Additional Declarations No competing interests reported. Supplementary Files Supplementalmaterial1.xlsx SupplementalMaterial2.docx Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 10 Mar, 2026 Reviews received at journal 10 Mar, 2026 Reviewers agreed at journal 06 Mar, 2026 Reviewers agreed at journal 06 Mar, 2026 Reviewers agreed at journal 05 Mar, 2026 Reviewers agreed at journal 04 Mar, 2026 Reviews received at journal 04 Mar, 2026 Reviewers agreed at journal 04 Mar, 2026 Reviewers invited by journal 04 Mar, 2026 Editor assigned by journal 03 Mar, 2026 Submission checks completed at journal 02 Mar, 2026 First submitted to journal 26 Feb, 2026 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. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8952088","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":601985277,"identity":"f346ce45-b762-49ee-ad42-83eb86805f2f","order_by":0,"name":"Jiawei Hou","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Jiawei","middleName":"","lastName":"Hou","suffix":""},{"id":601985281,"identity":"6b5bc043-062e-48b0-bf5c-cdc01b1b0c7f","order_by":1,"name":"Yanlin Zhong","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Yanlin","middleName":"","lastName":"Zhong","suffix":""},{"id":601985283,"identity":"9b81a3bb-ac63-4bd4-a499-51a8e443d086","order_by":2,"name":"Yichen Zhang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Yichen","middleName":"","lastName":"Zhang","suffix":""},{"id":601985285,"identity":"13345f6f-0570-4439-94f8-9606a70d0fd8","order_by":3,"name":"Dong Jiang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Dong","middleName":"","lastName":"Jiang","suffix":""},{"id":601985286,"identity":"8020834d-0969-437f-a154-241fe0d052d3","order_by":4,"name":"Yu Xie","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Yu","middleName":"","lastName":"Xie","suffix":""},{"id":601985287,"identity":"d60e9daf-612d-4f13-b617-0bfe01544b1a","order_by":5,"name":"Shuai Li","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Shuai","middleName":"","lastName":"Li","suffix":""},{"id":601985288,"identity":"14e3242e-d5cb-4fc7-affb-174538630bc6","order_by":6,"name":"Guiwuh Huang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Guiwuh","middleName":"","lastName":"Huang","suffix":""},{"id":601985289,"identity":"d18a3033-1935-447c-9e58-8f22445e9d8c","order_by":7,"name":"Zhiqi Zhang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABAklEQVRIiWNgGAWjYDACCQY2hgQGCTkGBsbGAwhBIrQYA7U0kKAFCBIbgARxWuRntz978KDMIn1t+2GgLX8O2xscYD54m4fBLg+XFsY5B9INEs5J5G47k9hwgLHtcOKGA2zJ1jwMycW4tDBLJByTSGwDajkA0tJwOMHgAI+ZNA/DAbBTsQE2kHogSjc7/xDmMP5veLXwSCSDdSWY3QDawsB2mHHDAR42vFokJNLYJIB+Mdx2A2hLYlt64szDbMaWcwyScWqRn5H+TPJHWZ282fn0hw8+/LG25zve/PDGmwo7nFqgPoLSCQzNwBABsQzwqkfSwsBQR0jpKBgFo2AUjEAAAN8qWeZVjGQoAAAAAElFTkSuQmCC","orcid":"","institution":"","correspondingAuthor":true,"prefix":"","firstName":"Zhiqi","middleName":"","lastName":"Zhang","suffix":""}],"badges":[],"createdAt":"2026-02-24 03:23:05","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8952088/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8952088/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104311148,"identity":"46ed91f6-d73a-4ec5-b736-591811c961c8","added_by":"auto","created_at":"2026-03-10 10:57:00","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1271710,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThis flowchart illustrates the process of patient enrollment and the reasons for exclusion, culminating in a final patient cohort.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-8952088/v1/ab10100aa1955663174f1303.png"},{"id":104311290,"identity":"adff6913-3b2b-4d7c-9d63-d661e7e45f3f","added_by":"auto","created_at":"2026-03-10 10:57:15","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":5976927,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSchematic diagram illustrates the methodology for measuring the HKA angle and the joint gap difference of a knee. \u003c/strong\u003e(a) L\u003csub\u003e1\u003c/sub\u003e means the femoral mechanical axis, L\u003csub\u003e2\u003c/sub\u003e means the tibial mechanical axis. The HKA angle was defined as the acute angle formed between the L\u003csub\u003e1\u003c/sub\u003e and L\u003csub\u003e2\u003c/sub\u003e.\u003cstrong\u003e \u003c/strong\u003e(b)\u003cstrong\u003e \u003c/strong\u003eMedial joint gap (d₁) and lateral joint gap (d₂) were measured separately. The joint gap difference (d = d₂ − d₁) was calculated to assess relative joint gap tightness. A positive value (d \u0026gt; 0) indicates relative medial tightness, whereas a negative value (d \u0026lt; 0) indicates relative lateral tightness.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-8952088/v1/897648333989e3784255a831.png"},{"id":104311236,"identity":"b2360592-f301-4aea-b1c6-40c12310d9ea","added_by":"auto","created_at":"2026-03-10 10:57:09","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":4225315,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThis figure shows the medially tight model with the medially tight insert and the magnitude and direction of forces applied to the finite element model under four configurations.\u003c/strong\u003e (a) Posterior view of the medially tight knee finite element model (b) Anterior view of the medially tight knee finite element model (c) Anterior view of the medially tight insert, with the medial joint gap (Gap\u003csub\u003eM\u003c/sub\u003e) and lateral joint gap (Gap\u003csub\u003eL\u003c/sub\u003e) labeled. The lateral joint gap is 1.25 mm larger than the medial joint gap (Δ=1.25 mm).\u003cstrong\u003e \u003c/strong\u003eGap\u003csub\u003eM\u003c/sub\u003e means medial joint gap; Gap\u003csub\u003eL\u003c/sub\u003e means lateral joint gap. (d) 0° flexion (standing): A force of 367.5 N (0.5 times body weight) was applied along the mechanical axis.\u003cstrong\u003e \u003c/strong\u003e(e) 15° flexion (toe-off phase of gait): A force of 2058 N (2.8 times body weight) was applied along the mechanical axis.\u003cstrong\u003e \u003c/strong\u003e(f) 60° flexion (stair climbing): A force of 2425.5 N (3.3 times body weight) was applied along the mechanical axis.\u003cstrong\u003e \u003c/strong\u003e(g) 90° flexion (sit-to-stand): A force of 1000 N was applied along the tibial mechanical axis, reflecting reduced load due to hand support.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-8952088/v1/1a1a91cb90ad7e8fb0a420cd.png"},{"id":104311234,"identity":"57a4d76d-c5c2-4403-9898-04d1c7bb8b6c","added_by":"auto","created_at":"2026-03-10 10:57:08","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":4102824,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe medially tight group demonstrated superior post-TKA outcomes compared to the balanced group across the evaluated metrics.\u003c/strong\u003e The x‑axis represents difference joint gap difference groups, the y‑axis shows clinical outcomes. P‑values above bars indicate significance between adjacent groups. (a) Multiple comparisons of total KSS improvements (b) Multiple comparisons of functional KSS improvement. (c) Multiple comparisons of clinical KSS improvements. (d) Multiple comparisons of total KSS improvement within elderly subgroup. (e) Multiple comparisons of functional KSS improvement within elderly subgroup. (f) Multiple comparisons of clinical KSS improvement within severe varus subgroup.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-8952088/v1/1737120d12acc1ece283eb44.png"},{"id":104311265,"identity":"d810136e-3fd0-41c0-8dae-1ec3fcd99ccd","added_by":"auto","created_at":"2026-03-10 10:57:13","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":3452912,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe figure illustrates the patterns of load distribution in the medial compartment for each of the three models under four configurations\u003c/strong\u003e. X-axis represents different configurations, and y-axis shows proportion of the load transfer through the medial compartment.\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-8952088/v1/3f09f92db5d57dc980e4f5d7.png"},{"id":104311314,"identity":"943d7354-0ecc-499d-b637-76c93999c0eb","added_by":"auto","created_at":"2026-03-10 10:57:24","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":5074802,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThis figure maps the insert stress distribution of the balanced model (left) and the medially tight model (right) under four configurations\u003c/strong\u003e(a) stress distribution at 0° flexion. (b) stress distribution at 15° flexion. (c) stress distribution at 60° flexion. (d) stress distribution at 90° flexion.\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-8952088/v1/36fc2b04540434d4c38ca6c1.png"},{"id":104311237,"identity":"2aaca84c-8b7a-4150-a4ea-a47c859a4827","added_by":"auto","created_at":"2026-03-10 10:57:09","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":3351118,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThis figure demonstrates cancellous bone resection surfaces stress distribution of the balanced model (left) and the medially tight model (right) under four configurations\u003c/strong\u003e. (a) stress distribution at 0° flexion; (b) stress distribution at 15° flexion; (c) stress distribution at 60° flexion; (d) stress distribution at 90° flexion.\u003c/p\u003e","description":"","filename":"Figure7.png","url":"https://assets-eu.researchsquare.com/files/rs-8952088/v1/b62269dd89950a47eac03610.png"},{"id":104405724,"identity":"b2959a78-2564-41ff-8fd3-517c74e33b70","added_by":"auto","created_at":"2026-03-11 12:23:40","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":28243699,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8952088/v1/13129238-8df8-4987-88c2-7546fde8e08d.pdf"},{"id":104311309,"identity":"c3319962-5cc3-40f5-ae5f-5a3e0b76fa2b","added_by":"auto","created_at":"2026-03-10 10:57:22","extension":"xlsx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":30724,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementalmaterial1.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-8952088/v1/092e59bce28b3438b36bb7e8.xlsx"},{"id":104311302,"identity":"d1590aab-b632-4b7e-889a-0b1abff1bfdb","added_by":"auto","created_at":"2026-03-10 10:57:18","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":6066967,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementalMaterial2.docx","url":"https://assets-eu.researchsquare.com/files/rs-8952088/v1/3de87dd18389de0cac7128ae.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Reconstructing Physiological Knee Medial Tightness in Total Knee Arthroplasty is Associated with Superior Clinical Outcomes in Asian Population: A Retrospective Cohort Study with Finite Element Analysis","fulltext":[{"header":"Introduction","content":"\u003cp\u003eIn 2020, the global population with osteoarthritis (OA) reached 595\u0026nbsp;million, and a 74.9% rise in the prevalence of knee osteoarthritis is anticipated by the year 2050, posing a substantial health and economic burden\u003csup\u003e(\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e)\u003c/sup\u003e. Despite the rapid development of emerging therapeutic technologies such as platelet-rich plasma, total knee arthroplasty (TKA) is still the definitive surgical solution for end-stage knee OA \u003csup\u003e(\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e)\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eTraditional TKA surgery adheres to the mechanical alignment principle, aiming to achieve neutral limb alignment. The basis of this concept is the anatomical characteristic of a predominance of neutral alignment in European and American populations\u003csup\u003e(\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e)\u003c/sup\u003e. Empirical observations suggest that the indiscriminate application of mechanical alignment, without accounting for physiological differences, can disrupt native bone alignment and perturb the physiological soft tissue envelope\u003csup\u003e(\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e)\u003c/sup\u003e. In response, kinematic alignment was proposed to preserve the patient's physiological alignment, offering a new direction for physiological joint replacement \u003csup\u003e(\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e)\u003c/sup\u003e. Current research predominantly focuses on the impact of lower limb alignment on clinical outcomes \u003csup\u003e(\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e)\u003c/sup\u003e, leaving the critical factor of medial-lateral gap balance insufficiently explored.\u003c/p\u003e \u003cp\u003eDespite satisfactory postoperative radiographic alignment, 15\u0026ndash;20% of patients still report symptoms such as pain and tightness \u003csup\u003e(\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e)\u003c/sup\u003e. These symptoms may be linked to improper management of soft tissue balance, potentially leading to abnormal prosthetic load distribution, reduced joint stability, and ultimately impaired functional recovery\u003csup\u003e(\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e)\u003c/sup\u003e. Historically, achieving absolute medial-lateral balanced gap has been considered the \"gold standard\" in TKA. Nevertheless, a study involving a European/American cohort indicated that patients with mild lateral laxity achieved comparable improvements in postoperative pain relief and joint awareness to those with absolutely balanced gaps\u003csup\u003e(\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e)\u003c/sup\u003e. This raises an important question: is absolute medial-lateral gap balance necessary for all patients? Among Asian populations, the prevalence of varus limb alignment is notably higher, reaching 52.7% in Southeast Asian populations\u003csup\u003e(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e)\u003c/sup\u003e, and 38.03% in Chinese populations \u003csup\u003e(\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e)\u003c/sup\u003e. In 97% of individuals with varus knees, the medial compartment exhibited a smaller gap than lateral side, due to relative tightness of the medial soft‑tissue envelope \u003csup\u003e(\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e)\u003c/sup\u003e. Could preserving or restoring this physiological state of medial tightness yield equivalent, even potentially superior outcomes compared with a balanced gap?\u003c/p\u003e \u003cp\u003eCurrently, research specifically targeting Asian populations to clarify the impact of medial-lateral gap difference remains scarce. This study focuses on an Asian cohort. First, it analyzes the physiological medial-lateral gap difference state in healthy knees. Subsequently, it measures the medial-lateral gap difference in patients following primary TKA and correlates this with clinical outcome scores from at least one year of follow-up. The aim is to investigate whether \u0026ldquo;medial tightness\u0026rdquo; offers superior clinical prognosis compared to \u0026ldquo;medial-lateral balance\u0026rdquo;, and if so, to determine the ideal range for medial-lateral gap difference. To elucidate the biomechanical mechanisms underlying these clinical findings, this study employs finite element modeling to analyze the mechanical conditions on the prosthesis and bone resections under different gap difference states, thereby validating and explaining the clinical conclusions.\u003c/p\u003e"},{"header":"Materials and method","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy design and participant recruitment\u003c/h2\u003e \u003cp\u003eThis study employed a single‑center, retrospective case‑control design. The protocol was approved by the ethics committee of the First Affiliated Hospital of Sun Yat‑sen University (Approval No: [2025]428). We derived the data for this study from the hospital's Joint Surgery Center database. It comprised two participant cohorts:\u003c/p\u003e \u003cp\u003eHealthy volunteers: Volunteers who underwent lower‑limb X‑ray examinations at our institution between January 2024 and December 2024 for non‑orthopedic reasons. Inclusion criteria were: age 25‑35 years, no self‑reported knee symptoms, no previous lower‑limb trauma or surgical procedures, and no systemic diseases (e.g. rheumatoid arthritis, gout) potentially affecting the skeletal system.\u003c/p\u003e \u003cp\u003ePatients: Patients receiving TKA with a posterior-stabilized (PS) prosthesis at the First Affiliated Hospital of Sun Yat-sen University from August 2019 to August 2024 were enrolled. Inclusion criteria were: age 18\u0026ndash;85 years, diagnosis of primary knee OA (Kellgren\u0026ndash;Lawrence classification grade IV), preoperative hip-knee-ankle angle (HKA) of affected limb\u0026thinsp;\u0026gt;\u0026thinsp;0\u0026deg; \u003csup\u003e(\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e)\u003c/sup\u003e, and complete radiographic records. Exclusion criteria included: surgeries affecting function (e.g. hip, spine or ankle surgeries); revision surgery; periprosthetic infection; aseptic loosening or periprosthetic fracture following TKA; secondary knee OA (e.g. due to post‑traumatic arthritis, rheumatoid arthritis, pathological fractures from metastases or myeloma); pain and functional limitations not primarily attributable to knee pathology as confirmed by imaging and clinical examination and concomitant malignant disease or other systemic conditions severely impacting mobility; function or quality of life or other reasons such as loss to follow-up (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAll patients were followed up preoperatively and at one year postoperatively via telephone by one orthopedic surgeon blinded to the radiographic data. Baseline characteristics and patient‑reported outcome measures were collected during these interviews.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eRadiographic data collection\u003c/h3\u003e\n\u003cp\u003eBilateral full-length standing anteroposterior radiographs of the lower limbs and standard anteroposterior knee radiographs were obtained for healthy volunteers. For patients, preoperative full‑length standing radiographs of the affected limb and standard anteroposterior knee radiographs taken on postoperative day 1 were collected. All radiographic measurements were conducted independently by three experienced orthopedic surgeons using the UniWeb Version 6.0 clinical measurement system. These assessors were blinded to the clinical follow‑up scores.\u003c/p\u003e \u003cp\u003eThe measured parameters included:\u003c/p\u003e \u003cp\u003e(1) HKA: it is defined as the acute angle subtended by two lines: one from the femoral head center to the knee center, and the other from the knee center to the ankle mortise center. Varus alignment was designated with positive values, while valgus alignment was designated with negative values. \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea\u003cb\u003e)\u003c/b\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e(2) Joint gap difference: On standard anteroposterior knee radiographs, joint gap was the vertical distance from the lowest point of the femoral condyle to the tibial plateau. Joint gap difference (d) was calculated as: d\u0026thinsp;=\u0026thinsp;lateral gap - medial gap. d\u0026thinsp;\u0026gt;\u0026thinsp;0 indicated relative medial tightness, while d\u0026thinsp;\u0026lt;\u0026thinsp;0 indicated relative lateral tightness (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb).\u003c/p\u003e\n\u003ch3\u003eGrouping and outcome measures\u003c/h3\u003e\n\u003cp\u003eParticipants were stratified based on the medial‑lateral gap difference (d) into: balanced group (-0.5 mm\u0026thinsp;\u0026lt;\u0026thinsp;d \u0026lt; 0.5 mm), medially tight Group (d\u0026thinsp;\u0026ge;\u0026thinsp;0.5 mm), laterally tight group (d \u0026le; -0.5 mm). The medially tight group was further subdivided into 0.5 mm\u0026thinsp;\u0026le;\u0026thinsp;d \u0026lt; 1.0 mm and d\u0026thinsp;\u0026ge;\u0026thinsp;1.0 mm subgroups. The laterally tight group was subdivided into \u0026minus;\u0026thinsp;1.0 mm\u0026thinsp;\u0026lt;\u0026thinsp;d \u0026le; -0.5 mm and d \u0026le; -1.0 mm subgroups.\u003c/p\u003e \u003cp\u003eThe primary outcomes measures included postoperative scores and the magnitude of improvement from the preoperative baseline to one year postoperatively. The following knee osteoarthritis scores were incorporated in this study: the Knee Society Score (KSS)\u003csup\u003e(\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e)\u003c/sup\u003e and its clinical and function subscales, the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)\u003csup\u003e(\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e)\u003c/sup\u003e and the Forgotten Joint Score-12 (FJS-12)\u003csup\u003e(\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e)\u003c/sup\u003e.\u003c/p\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eData were analyzed using R studio version 4.5.2. The distribution of gap differences among healthy volunteers was summarized. For patients, age, body mass index (BMI), sex, preoperative varus severity (dichotomized at 10\u0026deg;) and operative side were compared across gap‑difference groups to assess baseline comparability.\u003c/p\u003e \u003cp\u003eAppropriate multiple comparison correction was employed to compare postoperative scores and scores improvements between the different gap‑difference groups. The analysis specifically focused on comparisons between the medially tight group and balanced group. If statistically significant difference was observed between d\u0026thinsp;\u0026ge;\u0026thinsp;1.0 mm subgroup and the balanced group, further stratification at 0.5 mm intervals would be performed until the optimal gap‑difference range was identified or the subgroup sample size fell below 10.\u003c/p\u003e \u003cp\u003eTo explore the potential influence of the following factors, subgroup analyses were conducted. Each subgroup analysis was based on a single variable, dichotomizing the overall population\u003c/p\u003e \u003cp\u003e(1) Age. Based on previous literature indicating poorer TKA outcomes in patients aged\u0026thinsp;\u0026ge;\u0026thinsp;70 years \u003csup\u003e(\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e)\u003c/sup\u003e, we divided patients into a lower-age group (\u0026lt;\u0026thinsp;70 years) and a higher-age group (\u0026ge;\u0026thinsp;70 years)\u003c/p\u003e \u003cp\u003e(2) Preoperative varus severity. As medial soft‑tissue tightness is reported to commence with varus angles exceeding 10\u0026deg; \u003csup\u003e(\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e)\u003c/sup\u003e, patients were categorized into mild varus (preoperative HKA\u0026thinsp;\u0026lt;\u0026thinsp;10\u0026deg;) and severe varus (preoperative HKA\u0026thinsp;\u0026ge;\u0026thinsp;10\u0026deg;) groups.\u003c/p\u003e \u003cp\u003e(3) According to WHO classifications \u003csup\u003e(\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e)\u003c/sup\u003e, patients were grouped into normal BMI (BMI\u0026thinsp;\u0026lt;\u0026thinsp;25.0 kg/m\u0026sup2;) and overweight (BMI\u0026thinsp;\u0026ge;\u0026thinsp;25.0 kg/m\u0026sup2;) groups.\u003c/p\u003e \u003cp\u003eFisher's exact test was applied to compare categorical variables. For continuous variables, normality (Shapiro‑Wilk test) and homogeneity of variances were first assessed. Based on these results, appropriate tests were applied: Tukey‑Kramer's test (parametric assumptions met), Games‑Howell test (normally distributed but unequal variances) or Dunn's test (non‑normally distributed). The threshold for statistical significance was set at a corrected p‑value of 0.05.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eFinite element model development\u003c/h3\u003e\n\u003cp\u003eMagnetic resonance imaging (MRI) and computed tomography (CT) scans (slice thickness and spacing: 1.0 mm) were performed on the left knee of a healthy male volunteer (weight: 75 kg, height: 178 cm,). We identified and segmented different anatomical structures of the knee on the MR and CT images using Mimics medical 21.0 (Materialise, Belgium). Utilizing distinct imaging modalities, we separately reconstructed the osseous and soft-tissue components. CT images formed the basis for modeling the femur, tibia, and fibula, whereas MRI data were used to generate individual solid models of the menisci, articular cartilage, medial/lateral collateral ligaments, patellar retinaculum, and cruciate ligaments. The models were imported into Geomagic 2021 (USA) for surface optimization and fitting to eliminate stair‑step artefacts resulting from image noise. The solid models of all components were then imported into SolidWorks 2024 (USA) for assembly, an experienced orthopedic surgeon supervised the procedure. Finally, the assembled model was imported into Ansys 2023 (USA) for meshing, material property assignment, and subsequent mechanical analysis.\u003c/p\u003e \u003cp\u003eA three‑dimensional model of the PS prosthesis, comprising the femoral component, polyethylene insert and tibial tray was provided by the manufacturer (Keyibangen, China). Femoral component was positioned using a posterior referencing technique. 9 mm distal femoral resection was made perpendicular to the mechanical axis in 6\u0026deg; of valgus. The anterior‑posterior femoral resection was externally rotated 3\u0026deg; relative to the posterior condylar line. The anterior chamfer and posterior intercondylar resections were performed according to the prosthesis system's surgical guidelines\u003csup\u003e(\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e)\u003c/sup\u003e. Tibial component placement followed these steps: the proximal tibial cut was made perpendicular to the tibial mechanical axis with 3\u0026deg; of posterior slope. The resection was 8 mm below the intact lateral tibial plateau. The component was positioned centrally in the medial‑lateral direction and aligned with the anterior cortex in the anterior‑posterior direction. Tibial component rotation was aligned to a line connecting the center of the posterior cruciate ligament footprint to the medial third of the tibial tubercle. The polyethylene insert was mounted onto the tibial tray according to the manufacturer's instructions. The virtual implantation process was conducted by an orthopedic surgeon.\u003c/p\u003e \u003cp\u003eAs simulating a 1‑1.5 mm tightening of the medial ligament under load was technically unfeasible in the model. We reduced the thickness of the medial portion of the polyethylene insert by 1.25 mm to simulate this condition. To preserve the integrity of the bearing surfaces, the insert was virtually split into medial and lateral parts along its neutral plane. A 1.25 mm section was removed from the central portion of medial insert. Upper and lower parts of medial insert were then re‑joined and smoothed. This modified medial section was subsequently re‑joined to the unaltered lateral section. We restored the central post to its original geometry to avoid altering its interaction with the femoral component (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea-\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eMaterial properties and meshing\u003c/h2\u003e \u003cp\u003eAccording to the previous studies\u003csup\u003e(\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e)\u003c/sup\u003e, we assumed all materials in the finite element model to be isotropic, homogeneous and linearly elastic for contact stress analysis. Material properties were assigned based on literature values (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e)\u003csup\u003e(\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e)\u003c/sup\u003e. All components were meshed using linear tetrahedral elements. A mesh sensitivity analysis was conducted, resulting in a final element size ranging from 0.5 mm to 5.0 mm for different parts of the model\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\u003eMaterial parameters for the models constructed in this study\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTissue\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eYoung\u0026rsquo;s modulus (MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePoisson\u0026rsquo;s ratio\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCortical bone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e12000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTrabecular bone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCartilage\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.45\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMeniscus\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMedial and lateral\u0026nbsp;collateral ligaments\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePatellar ligament\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.45\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnterior and posterior cruciate ligament\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFemoral component\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e195000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTibial component\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e110000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFemoral component\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e685\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.47\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eInterface contact conditions\u003c/h3\u003e\n\u003cp\u003eContact between femoral cartilage and menisci, between femoral cartilage and tibial cartilage was modelled as frictionless surface‑to‑surface contact with finite sliding. The contact between the femoral component and the tibial polyethylene insert was assigned a coefficient of friction (\u0026micro;) of 0.04. We defined all other interfaces between components, between implants and bone as tied contacts to simulate the connections within the knee joint\u003csup\u003e(\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e)\u003c/sup\u003e.\u003c/p\u003e\n\u003ch3\u003eBoundary and loading conditions\u003c/h3\u003e\n\u003cp\u003eTo facilitate analysis and comparison, we constrained the distal ends of tibia fibula in all finite element models. Knee models were created at configurations of 0\u0026deg;, 15\u0026deg;, 60\u0026deg; and 90\u0026deg; to simulate different activities of daily life with corresponding loads applied (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed-\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg)\u003csup\u003e(\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e)\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e0\u0026deg; configuration simulated static standing. A compressive load equal to 0.5 times body weight (367.5 N) was applied along the mechanical axis to the proximal femoral surface.\u003c/p\u003e \u003cp\u003e15\u0026deg; configuration simulated the toe‑off phase of gait. A load equal to 2.8 times body weight (2058 N) was applied along the mechanical axis to the proximal femoral surface.\u003c/p\u003e \u003cp\u003e60\u0026deg; configuration simulated stair climbing. A load of 3.3 times body weight (2425.5 N) was applied along the mechanical axis to proximal femur.\u003c/p\u003e \u003cp\u003e90\u0026deg; configuration simulated rising from a seated position. A load of 1000 N was applied along the tibial mechanical axis to proximal femur. Lower magnitude reflects common use of arm support during this activity\u003csup\u003e(\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e)\u003c/sup\u003e.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eModel validation\u003c/h2\u003e \u003cp\u003eTo validate the model, we compared the maximum stress values in the femoral cartilage, menisci and tibial cartilage of the healthy knee model under a 1000 N vertical load with published experimental data\u003csup\u003e(\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e)\u003c/sup\u003e. The results showed good agreement in terms of peak pressure magnitudes and the distribution of high‑pressure areas, confirming the reliability of the model.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eBiomechanical parameters\u003c/h2\u003e \u003cp\u003eThe biomechanical parameters involved comparing:\u003c/p\u003e \u003cp\u003eThe load distribution ratio between the medial and lateral tibial plateaus across healthy knee model, balanced prosthesis model and medially tight prosthesis model under the different configurations.\u003c/p\u003e \u003cp\u003eThe stress and strain distribution on the polyethylene insert and the tibial resection surface between balanced prosthesis model and medially tight prosthesis model under the different configurations\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eReproducibility\u003c/h2\u003e \u003cp\u003eAll radiographic parameters demonstrated excellent reproducibility, with ICC values ranging from 0.937 to 0.987, exceeding the threshold of 0.80, indicating outstanding interobserver agreement and reliability.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003ePhysiological state in the healthy population\u003c/h2\u003e \u003cp\u003eA total of 19 healthy volunteers (38 knees) were included. The medially tight group was the most prevalent, comprising 24 knees (63.16%), followed by the balanced group with 12 knees (31.58%), and the laterally tight group with 2 knees (5.26%). This indicates a higher physiological prevalence of medial tightness of the knee in the healthy cohort.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eAssociation between post-TKA outcomes and joint gap difference\u003c/h2\u003e \u003cp\u003eA total of 220 patients (252 knees) completed the follow-up. Baseline characteristics are summarized in \u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e, there were no significant differences between groups. d\u0026thinsp;\u0026ge;\u0026thinsp;1.0 mm group had significantly greater total KSS improvements (83.8\u0026thinsp;\u0026plusmn;\u0026thinsp;18.9) compared to the balanced group (70.5\u0026thinsp;\u0026plusmn;\u0026thinsp;21.0) (p\u0026thinsp;=\u0026thinsp;8.16 \u0026times; 10\u003csup\u003e\u0026minus;\u003c/sup\u003e\u0026sup3;). d\u0026thinsp;\u0026ge;\u0026thinsp;1.0 mm group was subsequently divided into 1.0 mm\u0026thinsp;\u0026le;\u0026thinsp;d \u0026lt; 1.5 mm and d\u0026thinsp;\u0026ge;\u0026thinsp;1.5 mm groups for further analysis. Baseline characteristics for these refined groups showed no significant differences (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\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 of baseline characteristics among the six joint gap difference groups\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\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 \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eItem\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ed\u0026le;-1.0mm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-1.0mm\u0026thinsp;\u0026lt;\u0026thinsp;d\u0026le;-0.5mm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-0.5mm\u0026thinsp;\u0026lt;\u0026thinsp;d\u0026lt;0.5mm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.5mm\u0026thinsp;\u0026le;\u0026thinsp;d\u0026thinsp;\u0026lt;\u0026thinsp;1.0mm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1mm\u0026thinsp;\u0026le;\u0026thinsp;d\u0026thinsp;\u0026lt;\u0026thinsp;1.5mm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003ed\u0026thinsp;\u0026ge;\u0026thinsp;1.5mm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eP-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003en\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGender\u0026nbsp;=\u0026nbsp;M\u0026nbsp;(%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7\u0026nbsp;(17.9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5\u0026nbsp;(12.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e19\u0026nbsp;(20.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2\u0026nbsp;(5.9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u0026nbsp;(4.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4\u0026nbsp;(19.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.203\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge\u0026nbsp;(years, mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e69.0\u0026thinsp;\u0026plusmn;\u0026thinsp;5.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e70.3\u0026thinsp;\u0026plusmn;\u0026thinsp;5.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e68.98\u0026thinsp;\u0026plusmn;\u0026thinsp;5.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e69.26\u0026thinsp;\u0026plusmn;\u0026thinsp;5.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e70.08\u0026thinsp;\u0026plusmn;\u0026thinsp;6.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e70.57\u0026thinsp;\u0026plusmn;\u0026thinsp;6.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.729\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBMI\u0026nbsp;(m\u003csup\u003e2\u003c/sup\u003e/kg, mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25.6\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26.36\u0026thinsp;\u0026plusmn;\u0026thinsp;3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e25.95\u0026thinsp;\u0026plusmn;\u0026thinsp;4.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e27.14\u0026thinsp;\u0026plusmn;\u0026thinsp;3.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e25.10\u0026thinsp;\u0026plusmn;\u0026thinsp;2.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e26.51\u0026thinsp;\u0026plusmn;\u0026thinsp;3.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.301\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHKA Group=Severe (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18\u0026nbsp;(46.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18\u0026nbsp;(46.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e52\u0026nbsp;(55.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e21\u0026nbsp;(61.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e18\u0026nbsp;(72.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e15\u0026nbsp;(71.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.147\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSide\u0026thinsp;=\u0026thinsp;R (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e19\u0026nbsp;(48.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e16\u0026nbsp;(41.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e47\u0026nbsp;(50.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e17\u0026nbsp;(50.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e15\u0026nbsp;(60.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e11\u0026nbsp;(52.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.804\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"8\"\u003ed means joint gap difference, n means number of patients, BMI means body mass index, HKA means hip-knee-ankle angle, M means male, R means right side, SD means standard deviation. P-value means the significance level for intergroup comparisons. Categorical variables were analyzed using the chi-square test and continuous variables were analyzed using analysis of variance.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e1.0 mm\u0026thinsp;\u0026le;\u0026thinsp;d\u0026lt; 1.5 mm group demonstrated superior improvements in total KSS improvements (88.5\u0026thinsp;\u0026plusmn;\u0026thinsp;19.5 vs. 70.5\u0026thinsp;\u0026plusmn;\u0026thinsp;21.0, p\u0026thinsp;=\u0026thinsp;4.66 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e), functional KSS improvements (52.9\u0026thinsp;\u0026plusmn;\u0026thinsp;10.6 vs. 42.8\u0026thinsp;\u0026plusmn;\u0026thinsp;15.0, p\u0026thinsp;=\u0026thinsp;0.030) and clinical KSS improvements (35.6\u0026thinsp;\u0026plusmn;\u0026thinsp;11.2 vs. 27.7\u0026thinsp;\u0026plusmn;\u0026thinsp;10.7, p\u0026thinsp;=\u0026thinsp;0.041) compared to the balanced Group (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea-\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec). Both the 1.0 mm\u0026thinsp;\u0026le;\u0026thinsp;d \u0026lt; 1.5 mm group and the balanced group outperformed the laterally tight group. For WOMAC improvements, we found no significant difference between the medially tight and balanced groups, both were superior to the laterally tight group.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eComparison of postoperative scores showed no statistically significant difference between the medially tight and balanced groups. The medially tight group achieved higher postoperative total KSS, functional KSS, and WOMAC scores than the laterally tight group. We found no significant between-group differences in the FJS-12 scores. (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, \u003cb\u003eFigure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of postoperative knee scores and score improvements among different patient groups\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\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 \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eItem\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ed\u0026le;-1.0mm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-1.0mm\u0026thinsp;\u0026lt;\u0026thinsp;d\u0026le;-0.5mm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-0.5mm\u0026thinsp;\u0026lt;\u0026thinsp;d\u0026lt;0.5mm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.5mm\u0026thinsp;\u0026le;\u0026thinsp;d\u0026thinsp;\u0026lt;\u0026thinsp;1.0mm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1mm\u0026thinsp;\u0026le;\u0026thinsp;d\u0026thinsp;\u0026lt;\u0026thinsp;1.5mm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003ed\u0026thinsp;\u0026ge;\u0026thinsp;1.5mm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eP-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal KSS improvements\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e60.4\u0026thinsp;\u0026plusmn;\u0026thinsp;23.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e70.4\u0026thinsp;\u0026plusmn;\u0026thinsp;22.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e70.5\u0026thinsp;\u0026plusmn;\u0026thinsp;21.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e80.3\u0026thinsp;\u0026plusmn;\u0026thinsp;19.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e88.5\u0026thinsp;\u0026plusmn;\u0026thinsp;19.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e78.1\u0026thinsp;\u0026plusmn;\u0026thinsp;16.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e4.466\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e (Dunn)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eClinical KSS improvements\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e38.7\u0026thinsp;\u0026plusmn;\u0026thinsp;17.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e44.1\u0026thinsp;\u0026plusmn;\u0026thinsp;16.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e42.8\u0026thinsp;\u0026plusmn;\u0026thinsp;15.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e50.6\u0026thinsp;\u0026plusmn;\u0026thinsp;12.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e52.9\u0026thinsp;\u0026plusmn;\u0026thinsp;10.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e49.8\u0026thinsp;\u0026plusmn;\u0026thinsp;15.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e5.341\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e (Dunn)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFunctional KSS improvements\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e21.7\u0026thinsp;\u0026plusmn;\u0026thinsp;11.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e26.3\u0026thinsp;\u0026plusmn;\u0026thinsp;11.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e27.7\u0026thinsp;\u0026plusmn;\u0026thinsp;10.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e29.7\u0026thinsp;\u0026plusmn;\u0026thinsp;11.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e35.6\u0026thinsp;\u0026plusmn;\u0026thinsp;11.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e28.3\u0026thinsp;\u0026plusmn;\u0026thinsp;7.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e2.020\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e (Dunn)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWOMAC improvements\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e26.3\u0026thinsp;\u0026plusmn;\u0026thinsp;7.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e30.3\u0026thinsp;\u0026plusmn;\u0026thinsp;9.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e33.4\u0026thinsp;\u0026plusmn;\u0026thinsp;8.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e36.9\u0026thinsp;\u0026plusmn;\u0026thinsp;7.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e37.6\u0026thinsp;\u0026plusmn;\u0026thinsp;7.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e34.7\u0026thinsp;\u0026plusmn;\u0026thinsp;6.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e4.212\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e (T-K)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePostoperative total KSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e147.4\u0026thinsp;\u0026plusmn;\u0026thinsp;19.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e150.5\u0026thinsp;\u0026plusmn;\u0026thinsp;16.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e154.4\u0026thinsp;\u0026plusmn;\u0026thinsp;14.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e159.8\u0026thinsp;\u0026plusmn;\u0026thinsp;9.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e160.5\u0026thinsp;\u0026plusmn;\u0026thinsp;8.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e152.8\u0026thinsp;\u0026plusmn;\u0026thinsp;16.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e3.850\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e (Dunn)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePostoperative clinical KSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e86.4\u0026thinsp;\u0026plusmn;\u0026thinsp;12.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e88.4\u0026thinsp;\u0026plusmn;\u0026thinsp;9.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e90.2\u0026thinsp;\u0026plusmn;\u0026thinsp;8.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e93.0\u0026thinsp;\u0026plusmn;\u0026thinsp;6.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e92.1\u0026thinsp;\u0026plusmn;\u0026thinsp;6.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e89.2\u0026thinsp;\u0026plusmn;\u0026thinsp;8.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.141 (Dunn)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePostoperative Functional KSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e61.0\u0026thinsp;\u0026plusmn;\u0026thinsp;9.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e62.2\u0026thinsp;\u0026plusmn;\u0026thinsp;9.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e64.1\u0026thinsp;\u0026plusmn;\u0026thinsp;8.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e66.8\u0026thinsp;\u0026plusmn;\u0026thinsp;6.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e68.4\u0026thinsp;\u0026plusmn;\u0026thinsp;3.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e63.6\u0026thinsp;\u0026plusmn;\u0026thinsp;8.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e3.933\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e (Dunn)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePostoperative WOMAC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e15.9\u0026thinsp;\u0026plusmn;\u0026thinsp;8.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e14.7\u0026thinsp;\u0026plusmn;\u0026thinsp;7.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e12.7\u0026thinsp;\u0026plusmn;\u0026thinsp;6.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e9.88\u0026thinsp;\u0026plusmn;\u0026thinsp;4.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e8.92\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e13.2\u0026thinsp;\u0026plusmn;\u0026thinsp;6.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e3.391\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e (Dunn)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePostoperative FJS-12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e78.3\u0026thinsp;\u0026plusmn;\u0026thinsp;13.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e77.6\u0026thinsp;\u0026plusmn;\u0026thinsp;10.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e76.7\u0026thinsp;\u0026plusmn;\u0026thinsp;13.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e80.8\u0026thinsp;\u0026plusmn;\u0026thinsp;8.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e82.2\u0026thinsp;\u0026plusmn;\u0026thinsp;8.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e76.0\u0026thinsp;\u0026plusmn;\u0026thinsp;18.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.463 (Dunn)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"8\"\u003eData are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation. d means joint gap difference, KSS means Knee Society Score, WOMAC means Western Ontario and McMaster Universities Osteoarthritis Index, FJS-12 means Forgotten Joint Score-12. P-values were derived from the Kruskal-Wallis test (K-W test) or One-way Analysis of Variance (One-way ANOVA). Dunn means Dunn\u0026rsquo;s test was used in the multiple comparisons. T-K means Tukey-Kramer's test was used in the multiple comparisons.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eSubgroup analysis\u003c/h2\u003e \u003cp\u003eBaseline characteristics were balanced within all groups (\u003cb\u003eTable \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e-S7\u003c/b\u003e). In the higher-age subgroup, the 1.0 mm\u0026thinsp;\u0026le;\u0026thinsp;d\u0026thinsp;\u0026lt;\u0026thinsp;1.5 mm group showed greater improvements in total KSS improvements (92.6\u0026thinsp;\u0026plusmn;\u0026thinsp;21.3 vs. 68.5\u0026thinsp;\u0026plusmn;\u0026thinsp;19.1, p\u0026thinsp;=\u0026thinsp;2.40 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e) and functional KSS improvements (37.9\u0026thinsp;\u0026plusmn;\u0026thinsp;11.7 vs. 26.1\u0026thinsp;\u0026plusmn;\u0026thinsp;9.84, p\u0026thinsp;=\u0026thinsp;0.011) than balanced group (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed-\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee). In the severe varus subgroup, the 0.5 mm\u0026thinsp;\u0026le;\u0026thinsp;d\u0026thinsp;\u0026lt;\u0026thinsp;1.0 mm group showed greater improvements in clinical KSS improvements (54.2\u0026thinsp;\u0026plusmn;\u0026thinsp;11.4 vs. 43.9\u0026thinsp;\u0026plusmn;\u0026thinsp;14.4, p\u0026thinsp;=\u0026thinsp;0.040) than balanced group (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef). In other subgroups analyses, no differences in KSS or WOMAC improvements were found between medially tight and balanced groups. Within all subgroups analyses, the medially tight and balanced groups showed better KSS and WOMAC improvements than the laterally tight group.\u003c/p\u003e \u003cp\u003eRegarding postoperative scores, there were no significant differences between medially tight and balanced groups within both subgroups. However, specific advantages for the medially tight group over the laterally tight group were noted: in the higher-age subgroup for total KSS, in the mild varus subgroup for total KSS and WOMAC, in the normal BMI subgroup for WOMAC and in the high BMI subgroup for total KSS, functional KSS and WOMAC. We found there are no significant between-group differences in FJS-12 within any of these subgroups (\u003cb\u003eTable S8-S13, Figures \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e-S7\u003c/b\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eMedial‑lateral load distribution\u003c/h2\u003e \u003cp\u003eIt is illustrated the magnitude and proportion of load transmitted through the medial tibial plateaus for the three models under the four configurations (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Across all conditions, the medial plateau bore a greater load in each model. The load borne by the medial and lateral plateaus became more comparable at flexion angles of 60\u0026deg; and 90\u0026deg;, a trend consistent with previous studies\u003csup\u003e(\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e)\u003c/sup\u003e. Furthermore, it demonstrates that the load proportion of the medial compartment in the medially tight prosthesis model more closely resembled that of the healthy knee model compared to the balanced prosthesis model. The absolute difference (|Δ|) in the proportion of medial plateau load between each prosthesis model and the healthy knee model was calculated (|Δ balanced‑healthy| vs |Δ medially tight‑healthy|): 0\u0026deg;: 5.71% vs 0.49%, 15\u0026deg;: 5.05% vs 0.49%, 60\u0026deg;: 0.77% vs 0.25%, 90\u0026deg;: 4.23% vs 1.64%.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eStress and strain distribution\u003c/h2\u003e \u003cp\u003eDistribution of stress on the polyethylene insert for medially tight and balanced prosthesis models under the four configurations are displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The results indicate that during knee flexion, The contact area of the femoral component on the tibial insert migrates posteriorly on both the medial and lateral sides. Due to the medial pivoting motion of the knee, the area of stress distribution on the lateral plateau exhibited a greater range of movement during flexion, which is corroborated by prior finite element studies\u003csup\u003e(\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e)\u003c/sup\u003e. Additionally, compared to the balanced model, the medially tight prosthesis model exhibited higher peak stress on medial portion of insert across all simulated conditions: medially tight vs balanced (MPa): 0\u0026deg;: 15.667 vs 12.719, 15\u0026deg;: 49.599 vs 46.023, 60\u0026deg;: 65.150 vs 59.928, 90\u0026deg;: 32.260 vs 21.076. \u003cb\u003eFigure S8\u003c/b\u003e presents the magnitude and distribution of strain for the two prosthesis models. The strain distribution pattern was largely consistent with the stress findings. Representative peak strain values (medially tight vs balanced, mm/mm) were: 0\u0026deg;: 0.026 vs 0.001, 15\u0026deg;: 0.091 vs 0.117, 60\u0026deg;: 0.143 vs 0.089, 90\u0026deg;: 0.054 vs 0.041.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIt is showed the stress magnitude and distribution on the tibial resection surface for both models in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. It was observed that at flexion angles of 15\u0026deg;, 60\u0026deg; and 90\u0026deg;, The medially tight prosthesis model demonstrated a lower peak stress on the tibial resection surface. (medially tight vs balanced (MPa)): 0\u0026deg;: 7.435 vs 7.018, 15\u0026deg;: 50.916 vs 58.229, 60\u0026deg;: 133.02 vs 137.22, 90\u0026deg;: 31.744 vs 34.388. Furthermore, the area of stress distribution was generally more extensive in the balanced prosthesis model. As the resection surface is primarily load‑bearing for cortical bone, a separate analysis was conducted for cancellous bone stress distribution (\u003cb\u003eFigure S9\u003c/b\u003e). The results were largely consistent with those of the full resection surface (medially tight vs balanced (MPa)): 0\u0026deg;: 0.090 vs 0.088, 15\u0026deg;: 1.363 vs 1.507, 60\u0026deg;: 3.329 vs 3.328, 90\u0026deg;: 0.292 vs 0.352.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eFigure S10\u003c/b\u003e illustrates the strain distribution on the tibial resection surface for both models at different configurations. Strain was primarily concentrated in the cancellous bone region. The strain distribution and magnitude were generally similar between the two prosthesis models (medially tight vs balanced (ε)): 0\u0026deg;: 0.001 vs 0.021, 15\u0026deg;: 0.014 vs 0.016, 60\u0026deg;: 0.034 vs 0.036, 90\u0026deg;: 3.075\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e vs 3.968\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis study demonstrates that for Asian patients undergoing TKA, maintaining a medial‑lateral gap difference of 1\u0026ndash;1.5 mm (\"medial tightness\") is associated with superior clinical outcomes, including more pronounced symptom relief and greater functional recovery. Other degrees of medial tightness yielded similar clinical and functional improvements as the balanced group, with both performing significantly better than lateral tight group (particularly d \u0026le; -1.0 mm). We observed no significant differences in joint awareness among different gap‑difference groups.\u003c/p\u003e \u003cp\u003eThe Coronal Plane Alignment of the Knee (CPAK) classification system precisely categorizes lower limb alignment, critiquing a \"one‑size‑fits‑all\" approach to TKA \u003csup\u003e(\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e)\u003c/sup\u003e. Previous research has delineated the prevalence of various knee phenotypes across ethnicities, revealing a higher proportion of varus alignment in Asian populations (39.5%) compared to the predominance of neutral alignment in Caucasian populations (39.7%), thereby providing a scientific foundation for physiological surgery \u003csup\u003e(\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e)\u003c/sup\u003e. A retrospective study showed that outcomes following a standardized surgical protocol differ across CPAK phenotypes \u003csup\u003e(\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e)\u003c/sup\u003e, prompting consideration of physiological knee reconstruction. Existing research has largely focused on lower limb alignment and bone resection techniques, the role of soft‑tissue balance remains underexplored. To address this gap, we aimed to investigate the impact of soft‑tissue balance on clinical outcomes.\u003c/p\u003e \u003cp\u003eWithin our healthy cohort, medial tightness was found to be prevalent. Okazaki et al. similarly reported the presence of lateral laxity in knee flexion and extension, which may play a functional role in facilitating the normal medial pivoting motion of the knee \u003csup\u003e(\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e)\u003c/sup\u003e. Concurrently, finite element analysis of the healthy knee model confirmed that a greater proportion of the load is borne by the medial compartment. A finite element study analyzing femoral condylar motion trajectories reported anteroposterior translation ranges of 6.8\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1 mm for the medial condyle and 9.3\u0026thinsp;\u0026plusmn;\u0026thinsp;4.4 mm for the lateral condyle during 0-100\u0026deg; of flexion \u003csup\u003e(\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e)\u003c/sup\u003e. These findings collectively underscore the strong constraint imposed by the medial collateral ligament and the physiological state of relative medial soft‑tissue tightness.\u003c/p\u003e \u003cp\u003eRegarding the post‑TKA population, several prior studies have noted the existence of postoperative lateral soft‑tissue laxity and its association with favorable outcomes. Coffey et al. found that whether mechanical alignment or restricted kinematic alignment was used intraoperatively, the lateral soft tissues were laxer than the medial tissues postoperatively \u003csup\u003e(\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e)\u003c/sup\u003e. A study involving 40 knee samples reported that lateral laxity was related to improved Knee injury and Osteoarthritis Outcome Score (KOOS) (β\u0026thinsp;=\u0026thinsp;0.465, p\u0026thinsp;=\u0026thinsp;0.025) \u003csup\u003e(\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e)\u003c/sup\u003e. A cadaveric study elucidated that insufficient lateral laxity during TKA might impede normal tibial internal rotation during knee flexion \u003csup\u003e(\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e)\u003c/sup\u003e. Our study not only confirms that medial tightness is associated with significant post-TKA outcomes in Asian populations but also, for the first time, innovatively defines the optimal gap‑difference range as 1-1.5 mm. Another biomechanical cadaveric study indicated that 75% of the load in a healthy knee is transmitted through the medial compartment, and that laxity of the medial collateral ligament results in a shift of load to the lateral compartment \u003csup\u003e(\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e)\u003c/sup\u003e. Appropriate tightness of the medial collateral ligament helps maintain load within the medial compartment, preserving physiological conditions. Our finite element analysis similarly observed that compared to the balanced model, the proportion of load borne by the medial versus lateral tibial plateau in the medially tight model (1.25 mm reduction) more closely approximated that of the healthy knee. Furthermore, in the medially tight model, a greater proportion of stress was transmitted through the medial plateau. Larger surface area of the medial plateau facilitates better stress distribution \u003csup\u003e(\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e)\u003c/sup\u003e, which may explain why the peak stress on the tibial resection surface was lower and the stress distribution more uniform in the medially tight model compared to the balanced model. This restoration of the knee's native physiological state is a plausible mechanism for its superior outcomes.\u003c/p\u003e \u003cp\u003eIn the higher-age patient subgroup (\u0026ge;\u0026thinsp;70 years), the prognostic advantage of a 1-1.5 mm gap difference over the balanced group was primarily evident in functional recovery, which was not observed in the lower-age subgroup. Previous studies indicate that approximately 20% of elderly patients with knee OA have osteoporosis preoperatively, and nearly half have osteopenia \u003csup\u003e(\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e)\u003c/sup\u003e, which increases the long‑term revision risk (HR:1.8, 95% CI: 1.6 to 2.1) \u003csup\u003e(\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e)\u003c/sup\u003e. Moreover, it was reported that decreased bone mineral density of tibial plateau occurs predominantly in the medial segment \u003csup\u003e(\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e)\u003c/sup\u003e, fragile bony architecture may be more sensitive to physiological load transfer ratio. Additionally, multiple community‑based studies in Japan report generally weaker muscle strength in the elderly population \u003csup\u003e(\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e)\u003c/sup\u003e, and muscle deficit is known to hinder postoperative recovery in TKA patients \u003csup\u003e(\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e)\u003c/sup\u003e. Therefore, medial soft‑tissue tightness, by restoring a physiological medial‑lateral load distribution, may better compensate for the negative impact of muscle deficit on recovery.\u003c/p\u003e \u003cp\u003eIn the severe varus subgroup, the group with a joint gap difference of 0.5-1 mm demonstrated significantly greater improvement in pain and other clinical symptoms compared to the balanced group. A study focusing on the microstructure, bone remodeling levels, and histological characteristics of varus knees revealed that the weight-bearing area of the medial tibial plateau exhibits severe cartilage degeneration and more substantial structural deterioration of the subchondral bone\u003csup\u003e(\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e)\u003c/sup\u003e. Consequently, this region demonstrates a diminished capacity to withstand excessive load distribution. Therefore, a joint gap difference of 0.5-1 mm better balances the requirements for physiological reconstruction and the protection of the vulnerable bone environment of the medial plateau, leading to superior clinical outcomes compared to a 1-1.5 mm gap difference.\u003c/p\u003e \u003cp\u003eThis study has several limitations: (1) The use of radiographs rather than CT scans may have reduced the precision of gap measurements. However, three experienced arthroplasty surgeons performed the measurements independently, and the average was used to maximize accuracy and objectivity. (2) Due to technical constraints, directly modelling medial ligament tightness resulting in a 1-1.5 mm gap difference was not feasible. We therefore approximated this condition by modelling a prosthesis with a 1.25 mm reduction in medial insert thickness. (3) As a retrospective study, information bias is unavoidable. We attempted to mitigate this by blinding the personnel involved in radiographic measurement and telephone follow‑up. (4) The finite element analysis revealed higher medial insert stress in the medially tight model. This implies that medially tight soft‑tissue state could lead to greater wear on the medial insert, potentially reducing long‑term implant survivorship and increasing revision risk. Limited by patient numbers and research costs, this study did not conduct long‑term follow‑up across gap‑difference groups, which warrants further investigation. (5) The present study investigated the joint gap exclusively in full knee extension; the relationship between gap variations during flexion and post-TKA outcomes remains to be explored.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis study establishes a physiological target for soft‑tissue balancing in PS TKA. Convergent clinical and biomechanical evidence indicates that for Asian population, reconstructing medial tightness with a 1.0‑1.5 mm medial‑lateral gap difference constitutes a strategy superior to the traditional goal of absolute balance, potentially serving as a key determinant for enhancing postoperative function and patient satisfaction.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eOA\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eosteoarthritis\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\"\u003ePS\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eposterior-stabilized\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ed\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003edifference\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eKSS\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eKnee Society Score\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eWOMAC\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eWestern Ontario and McMaster Universities Osteoarthritis Index\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eFJS-12\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eForgotten Joint Score-12\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eFEA\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003efinite element analysis\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eHKA\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ehip-knee-ankle angle\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eBMI\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ebody mass index\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eMRI\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eMagnetic resonance imaging\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eCT\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ecomputed tomography.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe were grateful for the guidance and support in the finite element analysis provided by Youdao Technology Co., Ltd. (Guangzhou, China). We were thankful to DeepSeek for polishing the article. However, we declared that the artificial intelligence did not generate any scientific conclusions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJiawei Hou conceived, designed and performed research, collected clinical data and drafted the manuscript. Yanlin Zhong performed clinical follow‐up, Yichen Zhang, Dong Jiang and Shuai Li collected clinical data. Yu Xie performed the finite element analysis. Zhiqi Zhang and Guiwu Huang conceived, designed, supervised the study, and revised the manuscript. Jiawei Hou is regarded as first author. Guiwu Huang and Zhiqi Zhang are regarded as the corresponding authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was funded by the National Natural Science Foundation of China (82572796，82172467), the First Affiliated Hospital of Sun Yat-sen University Ke Ling Funding program for Novel and Distinguished talents (R07005), Guangzhou Science Funds (2024A04J6487).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data are available from the corresponding author upon reasonable request and with permission from the First Affiliated Hospital of Sun Yat‑sen University.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study received the approval of the Institutional Ethics Committee for Clinical Research and Animal Trials of the First Affiliated Hospital of Sun Yat-sen University [2025]428. All procedures were conducted in accordance with the Declaration of Helsinki. The requirement for informed consent was waived due to the retrospective design of the study.\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\u003eConflict of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe author claimed that the study was conducted without any commercial or financial relationships being interpreted as potential conflicts of interest.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eGlobal regional, national burden of osteoarthritis. 1990\u0026ndash;2020 and projections to 2050: a systematic analysis for the Global Burden of Disease Study 2021. Lancet Rheumatol. 2023;5(9):e508\u0026ndash;22.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePerruccio AV, Young JJ, Wilfong JM, Denise Power J, Canizares M, Badley EM. Osteoarthritis year in review 2023: Epidemiology \u0026amp; therapy. Osteoarthritis Cartilage. 2024;32(2):159\u0026ndash;65.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eInsall J, Scott WN, Ranawat CS. The total condylar knee prosthesis. A report of two hundred and twenty cases. J Bone Joint Surg Am. 1979;61(2):173\u0026ndash;80.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ede Geofroy B, Ghabi A, Fairag R, Machado A, Gonzalez JF, Micicoi G. Varus and neutral coronal knee phenotypes dominate globally: insights from a systematic review and meta-analysis of the CPAK classification. Knee. 2025;57:488\u0026ndash;505.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBellemans J, Colyn W, Vandenneucker H, Victor J. 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J Clin Med. 2021;10(14):3095.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBellemans J, Vandenneucker H, Vanlauwe J, Victor J. The influence of coronal plane deformity on mediolateral ligament status: an observational study in varus knees. Knee Surg Sports Traumatol Arthrosc. 2010;18(2):152\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFan H, Kouvari M, Guo C, Liu Z, Zhang X, Wang H, et al. A comprehensive comparison of two commonly used BMI thresholds for non-communicable diseases and multimorbidity in the Chinese population. Clin Nutr. 2025;48:70\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eInnocenti B, Bellemans J, Catani F. Deviations From Optimal Alignment in TKA: Is There a Biomechanical Difference Between Femoral or Tibial Component Alignment? J Arthroplasty. 2016;31(1):295\u0026ndash;301.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eInnocenti B. 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Computational study on the effect of malalignment of the tibial component on the biomechanics of total knee arthroplasty: A Finite Element Analysis. Bone Joint Res. 2017;6(11):623\u0026ndash;30.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWoiczinski M, Steinbr\u0026uuml;ck A, Weber P, M\u0026uuml;ller PE, Jansson V, Schr\u0026ouml;der C. Development and validation of a weight-bearing finite element model for total knee replacement. Comput Methods Biomech Biomed Engin. 2016;19(10):1033\u0026ndash;45.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCastellarin G, Bori E, Rapallo L, Pianigiani S, Innocenti B. Biomechanical analysis of different levels of constraint in TKA during daily activities. Arthroplasty. 2023;5(1):3.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBurastero G, Pianigiani S, Zanvettor C, Cavagnaro L, Chiarlone F, Innocenti B. 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Exp Gerontol. 2025;210:112862.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHayashida I, Tanimoto Y, Takahashi Y, Kusabiraki T, Tamaki J. Correlation between muscle strength and muscle mass, and their association with walking speed, in community-dwelling elderly Japanese individuals. PLoS ONE. 2014;9(11):e111810.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHumphrey TJ, Salimy MS, Jancuska JM, Egan CR, Melnic CM, Alpaugh K, et al. Sarcopenia is an independent risk factor for failure to achieve the 1-year MCID of the KOOS, JR and PROMIS PF-SF10a after TKA. Knee. 2023;42:64\u0026ndash;72.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu K, Chen Y, Miao Y, Xue F, Yin J, Wang L, et al. Microstructural and histomorphological features of osteophytes in late-stage human knee osteoarthritis with varus deformity. Joint Bone Spine. 2022;89(4):105353.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"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":"journal-of-orthopaedic-surgery-and-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"josr","sideBox":"Learn more about [Journal of Orthopaedic Surgery and Research](http://josr-online.biomedcentral.com)","snPcode":"13018","submissionUrl":"https://submission.nature.com/new-submission/13018/3","title":"Journal of Orthopaedic Surgery and Research","twitterHandle":"@MSKmedBMC","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Knee physiological reconstruction, total knee arthroplasty, knee medial tightness, joint gap difference, finite element analysis","lastPublishedDoi":"10.21203/rs.3.rs-8952088/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8952088/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eObjective\u003c/h2\u003e \u003cp\u003eFor Asian populations with physiological varus, optimal gap balance in total knee arthroplasty (TKA) remains debated. This study evaluated whether preserving physiological medial is superior to absolute balance.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eIn this retrospective study of 252 knees, patients undergoing primary posterior‑stabilized (PS) TKA were grouped by postoperative medial‑lateral gap difference. Clinical osteoarthritis assessment scores including KSS (Knee Society Score), WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) and FJS-12 (Forgotten Joint Score) were evaluated, comparing postoperative outcomes and their improvements after at least one year of follow-up. Subgroup analyses considered age, varus severity, and BMI. Finite element analysis (FEA) of different balance models were performed for load distribution and stress.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eBoth the medially tight and balanced groups achieved superior outcomes compared with the laterally tight group. Moreover, patients with a gap difference of 1.0\u0026ndash;1.5 mm (medially tight) demonstrated greater improvements in total, functional, and clinical KSS scores than the balanced group (all p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Among patients\u0026thinsp;\u0026gt;\u0026thinsp;70 years, medial tightness provided a substantial functional improvement (KSS functional improvements: 37.9\u0026thinsp;\u0026plusmn;\u0026thinsp;11.7 vs. 26.1\u0026thinsp;\u0026plusmn;\u0026thinsp;9.84, p\u0026thinsp;=\u0026thinsp;0.011). Besides, for patients with hip-knee-ankle angle\u0026thinsp;\u0026gt;\u0026thinsp;10\u0026deg;, 0.5\u0026ndash;1.0 mm gap difference (medially tight) contributed to fewer clinical symptoms (KSS clinical improvements:54.2\u0026thinsp;\u0026plusmn;\u0026thinsp;11.4 vs. 43.9\u0026thinsp;\u0026plusmn;\u0026thinsp;14.4, p\u0026thinsp;=\u0026thinsp;0.040). FEA indicated that the medially tight model restored a more physiological load and favorable stress distribution.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eFor Asian patients undergoing PS TKA, reconstructing physiological medial tightness is associated with better functional recovery and a more physiological biomechanical environment than absolute balance reconstruction.\u003c/p\u003e","manuscriptTitle":"Reconstructing Physiological Knee Medial Tightness in Total Knee Arthroplasty is Associated with Superior Clinical Outcomes in Asian Population: A Retrospective Cohort Study with Finite Element Analysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-10 10:56:05","doi":"10.21203/rs.3.rs-8952088/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-03-10T15:46:20+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-10T09:16:11+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"19173726920768748950174304003520085378","date":"2026-03-06T15:35:23+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"118590944592902510175006514785276329058","date":"2026-03-06T09:26:32+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"631748448147029458743324016699727387","date":"2026-03-05T05:29:48+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"162557141544790798419053107011446747054","date":"2026-03-04T20:19:41+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-04T15:20:05+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"123806656899946209883474471448328435537","date":"2026-03-04T09:05:15+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-03-04T07:15:50+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-03T05:58:31+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-02T15:24:38+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Orthopaedic Surgery and Research","date":"2026-02-27T02:03:57+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-orthopaedic-surgery-and-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"josr","sideBox":"Learn more about [Journal of Orthopaedic Surgery and Research](http://josr-online.biomedcentral.com)","snPcode":"13018","submissionUrl":"https://submission.nature.com/new-submission/13018/3","title":"Journal of Orthopaedic Surgery and Research","twitterHandle":"@MSKmedBMC","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"4ae3ca8a-a497-49a9-97e6-f741b695723c","owner":[],"postedDate":"March 10th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-16T16:53:15+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-10 10:56:05","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8952088","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8952088","identity":"rs-8952088","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}