Total knee arthroplasty (TKA) is one of the most effective surgical interventions for relieving pain and restoring function of knee in patients with advanced osteoarthritis (Cushnaghan et al., 2009; Carr et al., 2012; Price et al., 2018). Due to prolonged degenerative changes and weight-bearing wear, tibial plateau bone cysts are frequently observed during TKA procedures (Burnett et al., 2019; Tanamas et al., 2010). Residual bone defects from these cysts, following tibial plateau resection, can hinder both anatomical reconstruction and functional recovery of the knee joint (Lei et al., 2019; Lombardi et al., 2010).

The widely utilized Anderson Orthopaedic Research Institute (AORI) classification system categorizes knee-related bone defects into three types based on their size and location (Bieganowski et al., 2022; Sheth et al., 2017). Type I defects are characterized by mild bone loss with intact metaphyseal ends and are generally amenable to correction using standard TKA procedures. Type III defects involve extensive damage to the femoral condyles or tibial plateaus, often requiring customized components to effectively address the defect. Type II defects involve metaphyseal bone loss and are further subdivided into subtypes A and B: subtype A affects either the femoral condyles or tibial plateaus, while subtype B involves both. For Type II bone defects, treatment options typically include the cement-screw technique, bone cement filling, and bone grafting (Aggarwal and Baburaj, 2021; Shafaghi et al., 2019). However, a consensus on the optimal surgical approach for addressing bone defects resulting from tibial plateau bone cysts has yet to be established.

Cement filling, bone grafting, and the cement-screw technique are all effective methods for managing Type 2A bone defects, accommodating a range of defect sizes and configurations. Cement filling involves packing cement into the bone defect to enhance stability between the defect area, surrounding tissue, and the implant through adhesion (Qiu et al., 2012). Bone grafting, which includes both autografts and allografts, primarily uses cancellous bone to fill the defect, with the main difference being the source of the graft material (Lotke et al., 2006; Bauman et al., 2009; Wang et al., 2013). The cement-screw technique further augments fixation strength at the defect site by placing screws within the cement; however, precise screw placement is critical to avoid compromising the positioning of the prosthesis (Berend et al., 2014; Özcan et al., 2021; Berend et al., 2015).

Finite-element analysis (FEA) and biomechanical tests are widely utilized methodologies for investigating the biomechanics of orthopaedic implants (Campbell and Glüer, 2017; Lewis et al., 2021; Beitler et al., 2022). FEA provides accurate simulations by modeling bone structures (Siddiqi et al., 2021), while biomechanical tests involve measuring and analyzing experimental data to obtain quantitative insights into the mechanical behavior of skeletal systems (Adames et al., 2023; Schwer et al., 2024). These methods complement each other, with biomechanical tests helping to assess the mechanical properties of bone tissue and validate FEA results (Liu et al., 2022; Pei et al., 2023). Additionally, we have developed a standardized surgical guide to create an anteromedial tibial encapsulated bone defect, ensuring consistency and precision in biomechanical test models.

In this study, we combined FEA and biomechanical tests to explore the biomechanical differences among cement filling, cancellous bone filling, and the cement-screw technique for repairing tibial plateau bone defect in total TKA. Additionally, we compared these methods against a model that did not receive any specific treatment for the bone defect.

Analysis of X-ray data from 31 patients scheduled for TKA surgery, all of whom had preoperative X-rays showing tibial bone cysts, revealed that in 25 of these patients, the cysts were predominantly located in the anteromedial region of the tibial plateau (Table 2). Details of the sizes of the anteromedial bone cysts are provided in Table 3.

FEA results of this study offer a detailed comparison of stress and displacement across different model groups. Under a load of 1050 N, the maximum von Mises stresses for the prosthesis in the four groups were as follows: Group A, 15.059 MPa; Group B, 14.631 MPa; Group C, 14.382 MPa; and Group D, 13.379 MPa (Table 4). Stress concentrations in the prosthesis’s high-stress regions were predominantly located on the medial side near the defect area, with no significant differences observed among the groups (Figure 4A). For the von Mises stresses in the cement below the prosthesis, the maximum values were: Group A, 13.255 MPa; Group B, 12.365 MPa; Group C, 11.926 MPa; and Group D, 10.321 MPa (Table 5). In Group D, a stress concentration zone was noted in the cement area above the screw, while other regions showed no significant differences in stress distribution (Figure 4B). The maximum von Mises stresses of the cancellous bone in the four groups were: Group A, 3.133 MPa; Group B, 2.919 MPa; Group C, 2.835 MPa; and Group D, 11.730 MPa (Table 6). In Group D, a stress concentration was observed near the screw insertion site. While high-stress concentrations were noted at the medial cancellous bone edges in Groups A, B, and C, the medial cancellous bone edges in Group D did not exhibit significant high-stress areas (Figure 4C). Group D showed the lowest maximum von Mises stresses in both the prosthesis and the cement below it, yet the highest maximum von Mises stresses in the cancellous bone. These variations are clearly depicted in the bar graphs (Figures 4D–F), with stress distributions following consistent trends under different loads (Tables 4–6). Additionally, the maximum von Mises stress of screw in Group D model was 25.796 MPa (Figure 4G).

Under a load of 1050 N, the maximum displacements of the prosthesis in Groups A, B, C, and D were 2.330 mm, 2.329 mm, 2.329 mm, and 2.327 mm, respectively (Supplementary Table SII). The maximum displacements of the cement below the prosthesis in these groups were 2.329 mm, 2.328 mm, 2.328 mm, and 2.327 mm, respectively (Supplementary Table SIII). The maximum displacements of the cancellous bone were 2.326 mm, 2.326 mm, 2.326 mm, and 2.325 mm, respectively (Supplementary Table SIV). There were no significant differences in displacement distributions among the various components (Figures 5A–C). Notably, Group D demonstrated the smallest displacements across all components (Figures 5D–F). This trend in displacement was consistent across different loading conditions (Supplementary Tables S2–S4). Additionally, the screw displacement in Group D models was 2.168 mm (Figure 5G).

Additionally, under a load of 1050 N, in Group B, the maximum von Mises stress in the defect area filled with cancellous bone was 0.913 MPa, whereas Groups C and D showed maximum stresses of 1.903 MPa and 6.589 MPa, respectively, in the defect area filled with cement (Figure 6A). The maximum von Mises stress of the defect area in group D was the highest among the three groups (Figure 6B). Group B had a displacement of 2.181 mm in the defect area filled with cancellous bone, while Groups C and D showed displacements of 2.181 mm and 2.179 mm, respectively, in the defect areas filled with bone cement (Figure 6C). The displacement of the defect area in group D was the lowest among the three groups (Figure 6D).

Under a load of 700 N, the study revealed that Group D exhibited the lowest maximum von Mises stress in the prosthesis, at 8.920 MPa, and in the cement below the prosthesis, at 7.000 MPa, compared to the other groups (Tables 4, 5). Conversely, Group D showed the highest maximum von Mises stress in the cancellous bone, reaching 7.820 MPa (Table 6). The stress distribution patterns among the groups at 700 N load were consistent with those observed at a 1050 N load (Figures 7A–C). These differences in maximum von Mises stress among components also align with observations at 1050 N and are clearly depicted in the bar graphs (Figures 7D–F). Additionally, the maximum von Mises stress in the screws of Group D models was 17.197 MPa (Figure 7G). Group B experienced a maximum von Mises stress of 0.609 MPa in the defect area filled with cancellous bone, while Groups C and D had maximum stresses of 1.269 MPa and 4.393 MPa, respectively, in the defect areas filled with cement (Supplementary Figure S4A). The maximum von Mises stress of the defect area in group D was the highest among the three groups (Supplementary Figure S4B).

Table 7 displays the vertical displacements of each model under static compression tests with three different axial loads. The cement-screw technique group demonstrated the smallest displacements. Notably, at axial loads of 700 N and 1050 N, the displacements in the cement-screw technique group were significantly smaller compared to the other three groups, with statistically significant differences (p < 0.05). Even at a load of 350 N, the displacement in the cement-screw technique group was significantly smaller than that in both the untreated group and the cancellous bone filling group (p < 0.05) (Figure 8).

During TKA, residual tibial bone defects resulting from tibial bone cysts can significantly impact the reconstruction of knee joint anatomy and function (Lombardi et al., 2010; Cuckler, 2004; Bush et al., 2006). Consequently, managing tibial bone defects presents a technical challenge in TKA. A single tibial bone defect is classified as AORI Type 2A according to the Anderson Orthopaedic Research Institute (AORI) classification system (Sheth et al., 2017). Techniques such as bone filling, bone cement filling, and cement-screw technique are employed to address AORI Type 2A tibial bone defect. However, there is no consensus on which technique provides the optimal postoperative outcomes in TKA. Currently, the selection of technical parameters is often guided by the practices of experienced surgeons or personal experience, rather than robust evidence. In the realm of modern precision surgery, advancements in the accuracy and biomechanical stability of managing bone defects resulting from bone cysts are anticipated (Bargar, 2007; Chi et al., 2014). This study aims to compare the efficacy of these three techniques against no treatment for managing anteromedial tibial bone defect during TKA.

Bone filling can be utilized for defects of various sizes and shapes, effectively restoring bone volume. However, it carries risks such as prolonged surgical time, nonunion, delayed healing, disease transmission, infection, and graft resorption (Lotke et al., 2006; Bauman et al., 2009; Wilke et al., 2019). Bone cement filling and the cement-screw technique are also applicable for defects of differing sizes and shapes (Berend et al., 2014; Panegrossi et al., 2014). These methods not only fill the defects but also adhere to the surrounding tissues. Additionally, the implantation of screws in the cement-screw technique can further enhance stability at the defect site.

In the methodology section, we developed a representative tibial bone defect model based on clinical cases of tibial bone cysts and integrated the advantages of FEA with biomechanical test to address the limitations inherent in each method when used in isolation. To overcome the challenges posed by variability in traditional experimental models, we innovatively designed and 3D-printed surgical guides to produce customized and standardized cutting models. Given that the average depth of the tibial anteromedial bone cysts in our clinical cases is approximately 8 mm and that the typical resection depth of the medial tibial plateau during clinical tibial plateau cutting is about 2 mm, we set the tibial bone defect depth in our finite-element model to 6 mm. Additionally, based on the average anteroposterior and mediolateral dimensions of the bone cysts from clinical data, and to ensure design accuracy and applicability, we designed a hemispherical drill bit with a 6 mm radius to create standardized defects. We further simulated stress distribution and displacement for each model under three different loading conditions using FEA. Static compression tests were then conducted under these three different loads to replicate knee joint loading scenarios and measure model displacement.

The biomechanical properties of implants are crucial for their stability (Bori et al., 2022; Apostolopoulos et al., 2022). An effective approach to defect management not only reduce stress of the surrounding components but also facilitates efficient transfer of stress from the proximal tibia to the distal tibia, thereby reducing the risk of periprosthetic fractures and implant loosening (Lescun et al., 2020; Khan et al., 2016). Our FEA results show that in the cement-screw group, the maximum stress in both the tibial prosthesis and the cement below it is minimized. Additionally, the maximum stress in the cancellous bone and the defect area is maximized, with the smallest area of high stress concentration observed at the medial platform of the cancellous bone. These findings indicate that the cement-screw technique effectively distributes stress across the tibial prosthesis and surrounding components, while also efficiently transferring stress from the proximal to the distal tibia.

In the untreated group, the lack of cancellous bone on the tibial plateau hinders the transfer of stress from the defect area to the distal region. Conversely, when the defect is filled with cancellous bone or bone cement, the intact cancellous bone surface serves as an intermediary for load transfer, promoting stress distribution to the distal region. The use of high modulus of elasticity screws combined with cement offers improved support and stability to the defect area, thereby enhancing the efficiency of load transfer to the distal regions (Siddiqi et al., 2021). According to Wolff’s Law, bone structures adapt to resist applied forces, with bone mass decreasing under excessively low stress (Teichtahl et al., 2015; Wang et al., 2021; Barak et al., 2011). Therefore, effective load transfer can help maintain adequate bone volume under the prosthesis following TKA.

Although FEA revealed no significant differences in component displacements between the cement-screw group and the other three groups, static compression tests highlighted the distinctions among the models. In all four models, the cement-screw group demonstrated the smallest displacements under all three loading conditions, with significant differences observed at 700 N and 1050 N loads compared to the other groups. These findings emphasize the alignment between FEA and biomechanical tests, confirming that the cement-screw technique provides superior biomechanical performance.

This study has several limitations. First, we used synthetic bone rather than cadaveric bone for biomechanical tests. However, synthetic bone offers standardized dimensions and properties, and can be used with standardized bone defect models and drill bit to ensure consistency between experimental samples and accuracy of results. Second, tibial defects in clinical practice vary widely, and our study focused on only one type of inclusive defect. However, the bone defect model used is representative of anteromedial inclusive defect on the tibial plateau resulting from bone cysts encountered in recent TKA surgeries. Despite these limitations, our study offers valuable methodological insights for future research on managing various types and locations of bone defects.

In summary, our study highlights the effectiveness of using cement-screw technique to repair residual tibial bone defects from bone cysts during TKA. This approach effectively reduces Von Mises stress in surrounding components and minimizes model displacement. Therefore, to optimize the biomechanical strength of the prosthesis and improve implant survival rates, we recommend adopting cement-screw technique for managing inclusive tibial bone defect following tibial plateau bone cyst in TKA.