A Schatzker type IV tibial plateau fracture model was constructed using the patient’s CT image data. The specific steps were as follows: First, CT images including coronal, sagittal, and axial views were acquired and saved in DICOM format. Additionally, 3D model information of the distal femur and tibia was extracted from the CT data. These images were then imported into Mimics 21.0 software (Materialise, Belgium) for three-dimensional (3D) model reconstruction. Subsequently, the reconstructed 3D model was imported into Geomagic 2021 software (Geomagic, Inc.) for further smoothing and fracture line drawing. The Schatzker type IV-A fracture was characterized by a fracture line originating medial to the intercondylar eminence, with the proximal point of the fracture line located 12 mm horizontally medial to the intercondylar eminence and the distal point 28 mm vertically below the tibial plateau (Figures 1A-C). The Schatzker type IV-B fracture was defined by a fracture line originating within the intercondylar eminence, with the proximal point of the fracture line located at the intercondylar eminence (0 mm horizontal distance) and the distal point 33 mm vertically below the tibial plateau (Figures 1D-F).

Ligaments were modeled as spring elements to enhance the realism of joint motion and reinforce the constraints between the femur and tibia. The insertion points of the ligaments were defined based on anatomical video data and existing literature (Lee et al., 2024). The medial collateral ligament (MCL) and lateral collateral ligament (LCL) were constructed as shown in Figures 1H,I. The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) were modeled as illustrated in Figure 1G. The menisci were also incorporated into the model, with their geometry and positioning depicted in Figure 1G.

In this study, all internal fixation components were constructed based on technical parameters provided by the manufacturer (Shanghai Sanyou Medical Instrument Co., Ltd.) (Table 1). The experimental groups were established as previously described (Zhou et al., 2025). The specific experimental grouping schemes were as follows: IMLP Group: Comprised a medial T-shaped plate (placed on the medial side of the tibia) and 8 screws. The proximal 3 screws were inserted at a 5° angle to the tibial plateau, while the distal 5 screws were inserted at angles of 10°, 13°, 6°, 6°, and 1°, respectively. IMLP + 2PMS Group: Based on the IMLP structure, two 4.5 mm diameter tension screws were added to the anteromedial tibia (inserted at angles of 8°, 16°, 7°, 4°, 6°, and 1°). Additionally, two 4.5 mm tension screws were placed posteriorly, parallel to the tibial plateau, to enhance the stability of the posterior fracture fragment. IMLP + 2LTS Group: The medial plate placement followed the IMLP group, with the distal 5 screws inserted at angles of 11°, 14°, 7°, 7°, and 1°. Two 4.5 mm tension screws were placed laterally, parallel to the tibial plateau, to reinforce the fixation of the lateral fracture fragment. PMP + MLP Group: This group consisted of a medial T-shaped plate, a golf-shaped plate, and 15 screws. The golf-shaped plate was fixed to the anteromedial tibia, while the medial plate was fixed to the posteromedial tibia. The screw angles were set according to their specific insertion positions. MLDP Group: Utilized a medial T-shaped plate, a lateral L-shaped plate, and 16 screws. The medial plate was fixed to the medial tibia, and the lateral plate was fixed to the lateral tibia, with screw angles adjusted based on their fixation positions. Finally, the geometric models of Schatzker type IV-A and IV-B tibial fractures were integrated and assembled with various internal fixation models using SolidWorks 2021 software, forming the final research models as illustrated in Figures 2, 3 (Zhou et al., 2025).

It is noteworthy that although medial-lateral double plating (MLDP group) is less commonly used in the treatment of Schatzker type IV-A/B fractures, it was included in this study for two key reasons: (1) Historical Control Significance: Combined plating provides excellent mechanical stability through multi-planar fixation. Double plating (e.g., posteromedial and medial-lateral plates) has been widely adopted in clinical practice, and its biomechanical data can serve as a benchmark reference for evaluating hybrid fixation techniques. (2) Mechanical Comparison Requirement: Lateral plating offers the highest torsional stiffness, which helps quantitatively assess whether hybrid fixation (single plate + screws) can achieve comparable stability.

The following material parameters were adopted for simulation analysis in this study: The titanium alloy implant model was assigned an elastic modulus of 110,000 MPa and a Poisson’s ratio of 0.3. Cortical bone was modeled with an elastic modulus of 17,000 MPa and a Poisson’s ratio of 0.3. Trabecular bone was assigned an elastic modulus of 5,000 MPa and a Poisson’s ratio of 0.3. Cartilage was modeled with an elastic modulus of 12 MPa and a Poisson’s ratio of 0.45. The menisci were assigned an elastic modulus of 80 MPa and a Poisson’s ratio of 0.3. For ligaments, a single spring stiffness was applied to each insertion site (Table 2). All materials, including implants and bone tissues, were assumed to be isotropic and linearly elastic (Zhou et al., 2025).

During normal gait, the biomechanical load on the knee joint is approximately two to three times the body weight (Taylor et al., 2004), with the medial and lateral plateaus bearing about 60% and 40% of the load, respectively (Zhou et al., 2025). For a healthy adult weighing 75 kg, the compressive force on the tibial plateau during standing is calculated as follows:

75 kg × 9.8 N/kg×85.6% = 629.16 N (Gao et al., 2022). Walking and running exert forces on the tibial plateau that are two to three times greater than during standing (Tai et al., 2009). Accordingly, the following axial loads were applied to the models to simulate different activity levels: 300 N (bipedal standing), 600 N (single-leg standing), 1200 N (walking), 1800 N (running), 2400 N (vigorous activities). For all loading conditions, 60% of the load was distributed to the medial compartment to reflect physiological load distribution.

For modeling the plate-screw and screw fixation systems, the contact between implants and bone tissue was simulated using a Coulomb friction model with a friction coefficient of 0.3. The mechanical behavior of the locking screw mechanism was simulated using a node coupling method, which achieved rigid connections between plates and screws through shared common nodes. Additionally, to accurately characterize the mechanical interaction between the tibia and fibula, a fully bonded contact algorithm was employed to simulate load transfer mechanisms between them (Zhou et al., 2025).

This study conducted numerical simulations using the finite element analysis software ANSYS Workbench 2021 R1. Material properties were assigned to each component according to the parameters listed in Table 2. Following model importation, finite element meshing was performed for five experimental models with different configurations, with detailed node and element counts for each model provided in Table 3. After completing these preprocessing steps, loads were applied according to predefined boundary conditions. The static structural analysis module was employed to obtain key mechanical parameters, including stress distributions and displacement fields of the internal fixation system, fracture fragments, and tibial shaft. It should be specifically noted that all mechanical data in this study were derived directly from simulation results generated by ANSYS Workbench 2021 R1.

Finite element analysis revealed that under a 1200 N load, the implant displacement in the five groups of Schatzker type IV-A tibial plateau fracture models, ranked from smallest to largest, was approximately: PMP + MLP (8.5051 mm) < IMLP + 2LTS (8.5355 mm) <IMLP + 2PMS (8.5362 mm) <MLDP (8.5944 mm) <IMLP (8.7010 mm). However, no significant differences were observed in the numerical values. The peak implant stress values were as follows: IMLP + 2PMS (124.210 MPa) <IMLP + 2LTS (155.080 MPa) <MLDP (159.070 MPa) <PMP + MLP (160.820 MPa) < IMLP (248.280 MPa). These data indicate that the IMLP + 2PMS group performed best in reducing implant stress, while the IMLP + 2LTS group achieved stress reduction comparable to the MLDP and PMP + MLP groups. This suggests that adding two tension screws either posteromedially or laterally to a medial plate significantly reduces the stress experienced by the implant. Figures 7A–J displays the stress distribution and displacement nephograms of the implant in the five fixation models. The peak stress consistently occurred at the connection point between the distal-most screw and the plate in the tibia.

Analysis of the internal fixation stress and displacement results for the five fixation methods under a 1200 N load in Schatzker type IV-B tibial plateau fractures (Figures 7K–T) revealed that the peak stress consistently occurred at the connection point between the distal-most screw and the plate in the tibia. The peak implant stress values were as follows: IMLP + 2PMS (115.640 MPa) <MLDP(154.610 MPa) < IMLP + 2LTS (162.650 MPa) < PMP + MLP (192.460 MPa) < IMLP (246.560 MPa). Notably, the IMLP group exhibited the highest peak stress of 246.560 MPa. In contrast, the IMLP + 2PMS group demonstrated the lowest peak implant stress (115.640 MPa), indicating its superior performance in reducing stress concentration within the implant. However, the MLDP and IMLP + 2LTS groups also achieved relatively low peak stress levels (154.610 MPa and 162.650 MPa, respectively), suggesting that supplementing a medial plate with two tension screws (either posteromedially or laterally) significantly reduces stress on the implant. Regarding fracture fragment displacement, the values were as follows: PMP + MLP (8.5052 mm) < IMLP + 2LTS (8.5376 mm) < IMLP + 2 PMS (8.5377 mm) < MLDP (8.5919 mm) < IMLP (8.7022 mm). No significant differences were observed in the numerical values, indicating that all fixation systems exhibited high overall stiffness and stability. This is critical for maintaining fracture reduction and resisting early functional loading.

Tibial shaft stress is a critical indicator that requires careful balance, as both excessively low and high stress levels can adversely affect fracture healing and postoperative recovery. Ideally, stress distribution in the tibial shaft should be as uniform as possible, closely resembling normal physiological conditions. For Schatzker Type IV-A Fractures under 1200 N Load: The stress and displacement nephograms of the tibial shaft for the five fixation methods are shown in Figures 8A–J. The results indicate that the tibial shaft stress in all groups aligned with the ideal state. Specifically, the peak tibial shaft stress values (from smallest to largest) were as follows: IMLP + 2PMS (53.067 MPa) < MLDP (53.078 MPa) < IMLP + 2LTS (60.043 MPa) < IMLP (64.698 MPa) < PMP + MLP (64.844 MPa). Among these, the IMLP + 2LTS group exhibited the most uniform stress distribution in the tibial shaft. Regarding tibial shaft displacement (from smallest to largest): PMP + MLP (8.8510 mm) < IMLP + 2PMS (8.8579 mm) < MLDP (8.8817 mm) < IMLP + 2LTS (8.8888 mm) < IMLP (8.8898 mm). No significant differences were observed among the groups.

For Schatzker Type IV-B Fractures under 1200 N Load: Figures 8K–O displays the stress distribution in the tibial shaft for the five fixation models. In the IMLP and MLDP groups, peak stress was located at the proximal screw holes, while in the IMLP + 2PMS, PMP + MLP, and IMLP + 2LTS groups, peak stress occurred at the inferior aspect of the tibial tuberosity. The MLDP group showed the lowest peak stress (53.069 MPa). The PMP + MLP group exhibited the highest peak stress (84.813 MPa). The IMLP + 2LTS (59.219 MPa) and IMLP + 2PMS (53.017 MPa) groups demonstrated intermediate peak stress values with relatively uniform stress distribution. No significant differences were observed in tibial shaft displacement among the groups.

Finally, we analyzed the stress and displacement of the fracture fragments (Figures 9, 10). For Schatzker Type IV-A Fractures: The peak stress values of fracture fragments (from smallest to largest) were as follows: MLDP (25.7490 MPa) < IMLP + 2LTS (25.8950 MPa) < PMP + MLP (27.1460 MPa) < IMLP + 2PMS (27.0470 MPa) < IMLP (29.8960 MPa). The MLDP and IMLP + 2LTS groups demonstrated the best performance in terms of fracture fragment stress, with values significantly lower than the compressive strength limit of cancellous bone. Notably, the IMLP + 2LTS group offered the additional advantage of being minimally invasive. Stress distribution (Figure 9C) indicated effective support of fracture fragments without significant stress concentration points. No notable differences were observed in fracture fragment displacement among the groups, suggesting that all five fixation methods provided sufficient stability for primary fracture healing.

For Schatzker Type IV-B Fractures: Detailed examination of the equivalent stress nephograms revealed that stress distribution in all models was primarily concentrated around the screw holes and the distal aspect of the fracture surface. The IMLP group exhibited the highest fracture fragment stress (38.430 MPa). The MLDP group showed the lowest fracture fragment stress (17.2920 MPa). Notably, the IMLP + 2LTS (23.4890 MPa) and IMLP + 2PMS (21.8480 MPa) groups achieved fracture fragment stress levels comparable to the MLDP group. This finding indicates that supplementing a medial plate with posteromedial or lateral tension screws effectively reduces stress concentration in the fracture fragments. No significant differences were observed in fracture fragment displacement among the groups.

The morphology and position of the tibial plateau directly influence lower limb alignment and the knee’s mechanical environment, serving as a cornerstone for maintaining joint function and stability (Tscherne and Lobenhoffer, 1993). Consequently, the mechanical stability of implants is critical for postoperative bone healing and functional recovery (Prat-Fabregat and Camacho-Carrasco, 2016; Hörmandinger et al., 2024). While double-plate fixation offers excellent mechanical stability, the extensive surgical exposure required is associated with significant trauma, increased blood loss, and higher risks of soft tissue complications (Stannard et al., 2010; Honkonen, 1994). The key finding of this study is that the hybrid fixation mode (medial plate combined with tension screws: IMLP + 2PMS/IMLP + 2LTS) achieved superior or comparable performance to traditional double-plate fixation in the core mechanical metric—implant stress—while significantly outperforming single-plate fixation. Under a 1200 N load, the IMLP + 2PMS group exhibited the lowest peak implant stress among all groups (IV-A: 124.21 MPa; IV-B: 115.64 MPa), even surpassing the traditional double-plate MLDP group (IV-A: 159.07 MPa; IV-B: 154.61 MPa). This phenomenon carries profound biomechanical implications: The medial locking plate, with its angular stability, forms the primary framework resisting axial compression forces; The posteromedial or lateral tension screws act as “neutralization screws,” effectively countering shear stresses and rotational moments in the coronal and sagittal planes. This “main load-bearing framework + auxiliary anti-slip” design effectively disperses stress concentrated at the distal end of the medial plate, significantly reducing the risk of implant failure due to metal fatigue. This provides crucial mechanical assurance for young patients expecting early weight-bearing and high-intensity functional rehabilitation.

Notably, the peak stress in all models was concentrated at the screw-plate junction in the distal tibia, indicating this region as a mechanical weak point. Clinically, optimizing screw configuration in this area (e.g., increasing screw density or utilizing locking designs) is essential to prevent mechanical failure. It must be emphasized that the inclusion of lateral double plating in this study was solely for biomechanical comparison and is not recommended as a primary clinical solution.

Stress distribution within fracture fragments serves as a direct indicator of fixation efficacy (Wang et al., 2019). Although no significant differences were observed in fracture fragment displacement across groups—demonstrating that all configurations provided initial stability—the internal stress distribution revealed the indispensable value of posteromedial tension screws (PMS). For type IV-B fractures, the IMLP + 2PMS group exhibited significantly lower fracture fragment stress (21.85 MPa) compared to the IMLP group (38.43 MPa) and approached the level of the MLDP group (17.29 MPa). This indicates that PMS plays a critical role in supporting and compressing the posteromedial fragment. The underlying mechanism lies in the fact that Schatzker type IV fractures typically result from varus-internal rotation forces, rendering the posteromedial fragment susceptible to posterior-directed tensile stresses. PMS counteracts this displacement by applying compression perpendicular to the fracture line, whereas a solitary medial plate primarily resists axial loads and offers insufficient control over shear forces. Furthermore, from the three-column theory perspective, type IV fractures often involve the posterior column, making isolated medial fixation inadequate for stability. For fractures involving both the medial and posterior columns, medial or posteromedial buttress fixation is essential to prevent reduction loss, which explains the high clinical incidence of reduction failure after isolated medial plating (Luo et al., 2010). The insertion direction of posteromedial tension screws is precisely perpendicular to the articular surface of the posteromedial fragment, enabling direct and effective support, restoring articular congruity, and resisting posterior-inferior collapse.

An ideal fixation system should stabilize the fracture while maintaining normal stress conduction in the tibial shaft (Aihemaiti et al., 2022). The study found that double-plate fixation (particularly the PMP + MLP group) generated significant stress concentration peaks around the proximal screw holes of the tibia (reaching up to 84.81 MPa in type IV-B fractures), which not only reflects stress shielding but also represents a potential risk factor for refracture after implant removal. In contrast, the hybrid fixation groups (e.g., IMLP + 2LTS for IV-A; IMLP + 2PMS for IV-B) demonstrated a smoother and more uniform stress distribution in the tibial shaft, closely resembling normal physiological load transfer. This characteristic of “elastic fixation” allows the bone to bear its appropriate share of the load, promoting physiological bone remodeling and healing. From a long-term perspective, this approach may yield better outcomes by reducing the risks of stress shielding-induced bone loss and refracture.

A key insight from this series of studies is that Schatzker type IV-A, IV-B, and IV-C fractures may require differentiated internal fixation strategies. Although both IV-A and IV-B fractures originate medial to the intercondylar eminence, their fracture line trajectories and involved column structures exhibit subtle yet critical differences. Type IV-B fractures are located more medially and directly involve the posteromedial weight-bearing area. Analysis indicates that for type IV-B fractures, IMLP + 2PMS demonstrates superior performance in reducing fracture fragment stress, while for type IV-A fractures, IMLP + 2LTS exhibits better overall stress distribution (Figure 11).

In contrast to type IV-A and IV-B fractures, type IV-C tibial plateau fractures extend laterally to the intercondylar eminence, which imposes higher demands on biomechanical stability. However, pure type IV-C fractures are relatively rare in clinical practice and are often accompanied by fractures of the lateral intercondylar eminence, posteromedial column, or partial lateral plateau. Our previous research on Schatzker type IV-C tibial plateau fractures also demonstrated that IMLP + 2LTS can enhance stability while minimizing surgical trauma (Zhou et al., 2025). This suggests that clinical decision-making should integrate the Schatzker classification, Wahlquist subtyping, three-column theory, and 3D CT imaging to meticulously evaluate fracture line patterns, the location of major fracture fragments, and posterior column involvement. A “tailored” approach to internal fixation selection—where the direction and placement of auxiliary screws are optimized based on specific fracture morphology—represents the next frontier in precision treatment.

The core clinical significance of this study lies in demonstrating that optimized fixation configurations can significantly reduce surgical invasiveness without compromising stability. First, Minimally Invasive Advantages: The IMLP + 2PMS/IMLP + 2LTS techniques require only a single incision (medial approach) combined with percutaneous screw placement, substantially reducing soft tissue dissection compared to double-plating (medial + lateral/posteromedial dual incisions). This approach significantly lowers the risk of wound complications. The reduction in soft tissue damage is not merely about incision length but fundamental differences in surgical approach: double-plating (MLDP) inevitably requires two extensive exposures—a lateral incision (e.g., anterolateral approach) and a medial incision (e.g., posteromedial approach)—both involving layered fascial dissection, muscle elevation (e.g., lifting the tibialis anterior muscle for posteromedial plating), and periosteal stripping. In contrast, hybrid fixation (IMLP with two tension screws) requires only one main medial incision for plate placement, with additional screws inserted via minimal percutaneous incisions, resulting in negligible soft tissue damage. Second, Broad Applicability: For patients with osteoporosis or high-energy trauma (poor soft tissue conditions), the hybrid fixation method (medial plate with screws) avoids extensive exposure, reduces the risk of periosteal blood supply disruption, and FEA-confirmed mechanical reliability supports early weight-bearing. This makes it an optimal choice for elderly patients and those with soft tissue injuries. Finally, efficiency and cost-effectiveness: Reducing the number of plates used can shorten surgical time and lower material costs.

This study has several limitations. First, the finite element analysis (FEA) model was based on linear elastic material assumptions, which cannot simulate biological changes during bone healing or material plastic deformation. Second, the impact of bone quality variations was not systematically evaluated. Future work will employ parametric modeling methods (e.g., adjusting cortical bone thickness by ±20% and trabecular bone elastic modulus by ±30%) to quantify the range of mechanical performance fluctuations. Additionally, the Schatzker type IV-A/B fractures investigated in this study correspond to the “extension-varus” pattern within the three-column classification system. Further comprehensive analysis is needed for flexion-varus and hyperextension-varus fracture types. Moreover, segmentation, fracture modeling, and implant placement were strictly performed by four co-authors under the guidance of the two corresponding authors according to the experimental protocol. While this ensured clinical relevance, formal inter-observer variability assessment has not been conducted and represents a potential direction for future research. Finally, the finite element model was constructed based on CT data from a single typical patient. Although it effectively reflects the core biomechanical mechanisms of Schatzker type IV fractures, it must be acknowledged that individual differences (such as bone density and fracture comminution) may affect the generalizability of the results. Future studies should incorporate diverse geometric models (including subgroups with osteoporosis and high-energy comminuted fractures) to further validate the robustness of fixation strategies.

Future research will focus on: 1) Developing more sophisticated nonlinear finite element models that integrate muscle forces and dynamic loading conditions; 2) Conducting cadaveric biomechanical experiments to validate the FEA conclusions; and 4) Implementing multicenter, prospective randomized controlled trials (RCTs) to empirically test the superiority of this classification-guided optimized fixation strategy across biomechanical, radiological, and patient-reported functional outcomes.