1 Introduction

Knee osteoarthritis is a common degenerative disease of the tibiofemoral joint.¹ High tibial osteotomy (HTO), especially medial open wedge high tibial osteotomy (MOWHTO), is a joint-preserving treatment for selected patients with mild-to-moderate disease.^2,3 It can relieve symptoms and improve function by unloading the medial compartment ^4–9.

Accurate postoperative alignment is central to HTO planning. The correction target is commonly described by the weight-bearing line (WBL) ratio on a full-length standing radiograph, where the tibial plateau width is scaled from 0% at the medial edge to 100% at the lateral edge.^10,11 Although the Fujisawa point (62.5%) is widely used, its role as a universal target remains debated ^12–16.

Current clinical studies usually determine the target WBL point or range from postoperative follow-up and functional outcomes.^14,17 However, the tissue-level mechanical basis for WBL selection remains incompletely defined, especially for cartilage and meniscal stress redistribution. Cadaveric studies provide important information but cannot fully characterize internal stress patterns under different alignments.¹⁸ Finite element analysis can complement these data under controlled loading conditions.

Therefore, we developed a full-length lower-limb FE model that included tibiofemoral cartilage, menisci, and major ligaments. We simulated progressive WBL lateralization from 50% to 100% of the tibial plateau width and quantified von Mises stresses in cartilage and the menisci under a representative walking load. The aims were to characterize stress redistribution across WBL targets and to identify a stress-based target range that balances medial unloading with avoidance of excessive lateral-compartment stress under the current assumptions.

2 Materials and methods

2.1

2.1 Construction of a full-length three-dimensional model of the knee and lower limb

This study was ruled exempt from formal review by the Ethical Committee of Guizhou medical university, given the participant provided written informed consent. After obtaining consent, a full-length CT scan of the lower limb was performed on a healthy volunteer (male, 24 years old, height 175 cm, weight 60 kg), with a layer thickness of 0.625 mm. An MRI scan of the knee joint was then performed, with a layer thickness of 0.700 mm. DICOM images were imported into Mimics (v21.0, Materialise, Leuven, Belgium). Bone geometry was segmented from CT using Hounsfield unit–based thresholds. Articular cartilage and menisci were segmented from MRI using a semi-manual workflow. An orthopaedic surgeon performed the segmentation, and the final contours were reviewed for anatomical consistency. The reconstructed surfaces were exported as STL files for further processing (Fig. 1A and B).

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Fig. 1 Construction of the subject-specific finite element model and simulated weight-bearing line (WBL) settings. (A) MRI-based segmentation and three-dimensional reconstruction of the knee structures. (B) Generation and meshing of the finite element model for biomechanical analysis of the cartilage and meniscus. (C) Full-length lower-limb models with simulated WBL positions ranging from 50% to 100%. (D) Representative standing anteroposterior radiograph showing the medial compartment of interest. (E) Representative intraoperative photographs and gross articular specimens, with corresponding stress maps illustrating regions of stress concentration.

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3 Results

3.2

3.2 Von Mises stress distribution in the medial-lateral compartment of the knee joint

In the baseline neutral configuration (WBL = 50%), the medial tibial cartilage showed a mean von Mises stress of 0.161 MPa and a peak stress of 0.606 MPa, whereas the lateral tibial cartilage showed a mean of 0.116 MPa and a peak of 0.479 MPa (Fig. 2A and B). For the meniscus, the medial meniscus showed a mean stress of 0.797 MPa and a peak stress of 1.677 MPa, whereas the lateral meniscus showed a mean stress of 0.558 MPa and a peak stress of 4.293 MPa (Fig. 3A and B). As the WBL shifted laterally from 50% to 100%, stress concentration progressively migrated from the medial to the lateral compartment in both cartilage and menisci (Figs. 2 and 3). Medial-compartment stresses decreased, whereas lateral-compartment stresses increased, indicating redistribution of mechanical demand toward the lateral side with progressive valgus alignment. Correspondingly, femoral cartilage contact decreased in the medial compartment and increased in the lateral compartment (Fig. 4A).

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Fig. 2 Von Mises stress distribution in the tibial cartilage under different simulated WBL positions. (A) Representative stress contour maps of the medial tibial cartilage at WBL positions from 50% to 100%. (B) Representative stress contour maps of the lateral tibial cartilage at WBL positions from 50% to 100%. The stress distribution progressively shifted from the medial to the lateral compartment as the WBL moved laterally.

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Fig. 3 Von Mises stress distribution in the menisci under different simulated WBL positions. (A) Representative stress contour maps of the medial meniscus at WBL positions from 50% to 100%. (B) Representative stress contour maps of the lateral meniscus at WBL positions from 50% to 100%. Increasing lateralization of the WBL reduced stress in the medial meniscus and increased stress in the lateral meniscus, particularly in the horn regions.

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Fig. 4 Von Mises stress distribution in the femoral cartilage under different simulated WBL positions. (A) Representative stress contour maps of the femoral cartilage at WBL positions from 50% to 100%. As the WBL shifted laterally, stress in the medial femoral cartilage decreased, whereas stress concentration became more evident in the lateral compartment.

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3.4

3.4 Identification of a stress-based transition point for WBL targeting

The predefined WBL configurations were evaluated to characterize how medial unloading and lateral stress elevation co-varied with progressive WBL lateralization. Fig. 5 summarizes the changes in mean and peak von Mises stresses of cartilage and menisci across WBL ratios. With increasing WBL, medial-compartment stresses decreased, whereas lateral-compartment stresses increased in a gradual but non-linear manner. Using the reference criterion defined in Section 2.4, the lateral tibial cartilage reached the reference stress level at approximately WBL = 64% under the 600 N walking load (Fig. 5). Beyond this point, further lateralization was associated with additional increases in lateral-compartment stresses (Fig. 6). Accordingly, WBL ≈64% was considered a biomechanically favorable target point within the current model assumptions.

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Fig. 5 Quantitative comparison of cartilage and meniscal stresses under different simulated WBL positions. (A) Maximum von Mises stress in the medial and lateral tibial cartilage. (B) Mean von Mises stress in the medial and lateral tibial cartilage. (C) Maximum von Mises stress in the medial and lateral menisci. (D) Mean von Mises stress in the medial and lateral menisci. The dashed red lines indicate the reference wear-line thresholds used for comparison with the finite element results.

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Fig. 6 Overall trends in mean and maximum von Mises stress in the menisci and cartilage with progressive lateralization of the WBL. (A) Mean von Mises stress of the lateral meniscus, medial meniscus, lateral cartilage, and medial cartilage across WBL positions from 50% to 100%. (B) Maximum von Mises stress of the lateral meniscus, medial meniscus, lateral cartilage, and medial cartilage across WBL positions from 50% to 100%. Progressive lateralization of the WBL was associated with a decrease in medial compartment stress and a corresponding increase in lateral compartment stress.

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4 Discussion

In this study, we used a subject-specific finite element model to examine how progressive lateralization of the weight-bearing line (WBL) influences stress redistribution in tibiofemoral cartilage and menisci under a representative compressive load. Three main findings emerged. First, shifting the WBL laterally reduced stresses in the medial compartment while increasing stresses in the lateral compartment. Second, meniscal stresses were generally higher than cartilage stresses, and stress concentration tended to move from the meniscal body toward the horns, with earlier concentration in the posterior horn of the lateral meniscus. Third, a stress-based transition behavior was observed around WBL ≈64%, beyond which lateral-compartment stresses continued to rise.

Malalignment is closely associated with the development and progression of knee osteoarthritis, and HTO is widely used to treat medial compartment disease in patients with tibial deformity ^4,31–34. Precise alignment targeting is therefore central to HTO planning. Our simulations provide a mechanical explanation for this issue. As the WBL moved laterally, medial cartilage and meniscal stresses progressively decreased, which is consistent with the intended unloading mechanism of HTO. At the same time, lateral cartilage and meniscal stresses increased, indicating that excessive lateralization may transfer mechanical demand to the lateral compartment. These findings support selecting the postoperative target as a balance, rather than relying on a single fixed point for all patients.

In the present model, increasing the WBL from 50% to 100% progressively reduced medial cartilage and meniscal stresses while increasing the corresponding lateral stresses. This pattern is consistent with the clinical observation that the medial compartment is more commonly affected in varus knees.^35,36 At the same time, the marked rise in lateral-compartment stress at more lateral targets suggests that excessive correction may increase mechanical demand on tissues that are intended to be protected.

The magnitude and distribution of cartilage and meniscal stresses were broadly comparable to those reported in prior FE studies using similar loading magnitudes and linear elastic material assumptions. Ding et al.²¹ also applied a 600 N axial load and reported high stress in the anteroinferior medial tibial cartilage and meniscal body. Differences in absolute stress values across studies are expected because they depend on subject-specific anatomy, cartilage thickness, segmentation strategy, and contact or boundary definitions. We therefore interpret agreement mainly at the level of overall trends rather than exact numerical matching.

The unexpectedly higher peak stress in the lateral meniscus under the neutral configuration likely reflected local geometric sensitivity in the model, particularly the thin “white-zone” region and subject-specific morphology, which may have amplified focal stress concentration. This interpretation is supported by the mean stress results, which followed the same overall pattern as cartilage loading: in the neutral configuration, mean stress remained higher in the medial meniscus than in the lateral meniscus (0.797 vs 0.558 MPa).

Clinically, our results suggest that WBL ≈64% may represent a biomechanically favorable target under the current assumptions because it balances medial unloading with a relatively limited increase in lateral-compartment stress. However, this point should not be interpreted as a universal safe threshold. The lateral compartment, including the meniscus, varies substantially across patients with respect to degeneration, thickness, and integrity. In patients with compromised lateral meniscal or cartilage status, a more conservative target may be reasonable, but this requires dedicated modeling and clinical validation.

Several limitations should be acknowledged. First, all tissues were modeled as linear elastic, homogeneous, and isotropic materials, which may affect absolute stress magnitudes. Second, the model did not incorporate shear stress–related outcomes or joint line convergence angle effects, which may be relevant after osteotomy. Third, the analysis was based on a single healthy subject under a simplified static loading condition; patient-specific variation, dynamic gait loading, and muscle forces were not explicitly modeled. Finally, the unexpectedly high lateral meniscal peak stress in the neutral configuration may reflect sensitivity to local geometry and thickness definitions. Additional sensitivity analyses and cohort-based validation are needed to confirm the robustness of the transition point and improve generalizability.

5 Conclusions

This finite element study indicates that lateralization of the weight-bearing line (WBL) redistributes mechanical demand across the tibiofemoral joint. As the WBL shifted laterally, stresses in the medial compartment decreased, whereas stresses in the lateral compartment increased. Meniscal stresses were generally higher than cartilage stresses, and stress concentration tended to move toward the horn regions with progressive lateralization. Using the predefined stress-based reference criterion, a transition behavior was observed around WBL ≈64% under the current loading and modeling assumptions. This point may serve as a biomechanical reference for balancing medial unloading against increasing lateral-compartment stress in the simulated condition, but validation in pathological cohorts and under more physiological loading conditions is required before clinical generalization.

Ethical statement

This study was ruled exempt from formal review by the Ethical Committee of Guizhou medical university, given the participant provided written informed consent. Written informed consent was obtained from the participant before CT and MRI acquisition. The study was conducted in accordance with the ethical standards of the responsible institutional committee and the Declaration of Helsinki.

Participant consent statement

The participant provided written informed consent for study participation and for the use of anonymized imaging data for research and publication.

CRediT author statement

Zihao Zou: Conceptualization, Methodology, Formal analysis, Investigation, Visualization, Writing – original draft.

Zhanyu Wu: Methodology, Software, Validation, Data curation, Writing – review & editing.

Daizhu Yuan: Investigation, Data curation, Resources.

Jialin He: Validation, Resources, Investigation.

Long Yang: Conceptualization, Supervision, Project administration, Funding acquisition, Writing – review & editing.

Chuan Ye: Conceptualization, Supervision, Project administration, Funding acquisition, Writing – review & editing.

Funding statement

This study was supported by the Department of Science and Technology of Guizhou Province [2026]322 and Guizhou Medical University Incubation Program (gyfynsfc-2022-19). The funding sources had no role in study design, data collection, data analysis, data interpretation, manuscript preparation, or the decision to submit the article for publication.