The impact of sagittal cortical support on stability after internal fixation of intertrochanteric femoral fractures: a finite element analysis

The impact of sagittal cortical support on stability after internal fixation of intertrochanteric femoral fractures: a 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 The impact of sagittal cortical support on stability after internal fixation of intertrochanteric femoral fractures: a finite element analysis Jinhu Miao, Jin Dai, Zhihao Chen, Yadong Liu, Guoxi Shao This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5415730/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Objective: To explore the optimal sagittal cortical support reduction mode with proximal femoral bionic nails (PFBN) for treating intertrochanteric femoral fractures (ITFFs) with medial wall defects to prevent internal fixation failure. Methods: A 64-year-old healthy male volunteer with no history of hip or systemic disease was recruited. High-resolution computed tomography images with a slice thickness of 0.602 mm of his right femur were obtained. These images were used to establish three-dimensional (3D) models. The lesser trochanter and medial wall were cut off to create an AO Foundation/Orthopaedic Trauma Association (AO/OTA) type 31-A1.3 pertrochanteric fracture model. PFBN was used to simulate fixation. Under the conditions of coronal anatomical reduction, eighteen different fracture sagittal reduction modes were examined, which included intact or defective medial walls, as well as neutral, negative 5%,10%,15%,20%, and positive 5%,10%,15%,20%, were simulated. A load of 600 N was applied to simulate a 60 kg elderly patient standing on one leg. The models were subjected to finite element analysis (FEA). The displacement and von Mises stress distributions were analyzed. Results: Under the conditions of an intact or defective medial wall, the 10% positive sagittal cortical support reduction pattern showed minimal stress and displacement. In the case of medial wall defects, with 20% loss of reduction in both negative and positive sagittal mal reduction, the maximum equivalent stresses were 188.52 MPa and 211.21 MPa, respectively, which are 2.66 and 2.98 times greater than the maximum equivalent stress of 70.761 MPa observed when the medial wall was intact. Meanwhile, the 20% negative reduction pattern seemed to have the largest displacement. Conclusion: Under the conditions of an intact or defective medial wall, the 10% positive sagittal support reduction pattern showed the best mechanical stability for ITFF. The negative support reduction pattern was prone to fixation failure and should be avoided during an operation. Sagittal cortical support Intertrochanteric femoral fracture Internal fixation Finite element analysis Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction With the intensification of population aging, the incidence of ITFF has significantly increased, with unstable fractures accounting for approximately 50%-60% 1 . Unstable intertrochanteric fractures (UITFFs) primarily include comminuted fractures of the posterior medial wall, lateral wall defects, and reverse oblique fractures, with the comminuted fracture of the posterior medial wall (AO/OTA 31A1.3 type) being the most common 2 . Due to the defect of the medial wall, this type of fracture may lead to complications related to internal fixation devices in 10%-27% of patients during treatment, such as device displacement, hip varus deformity, and femoral neck shortening 3 . Therefore, for ITFF associated with medial wall defects, early surgical intervention is recommended to achieve stable fixation, facilitate early functional rehabilitation, and reduce complications and mortality rates 4 . Traditional surgical fixation methods include extramedullary and intramedullary fixation. The dynamic hip screw (DHS), as a representative of extramedullary fixation, has become the "gold standard" for treating trochanteric fractures due to its ability to adequately expose the fracture site, minimal damage to the gluteus Medius, and relatively low cost 5 . However, since the DHS is an off-center extramedullary fixation, its standalone application in intertrochanteric fractures with medial wall defects presents a problem of insufficient medial support 6,7 . Relevant studies indicate that if the medial wall is not addressed during surgery, the incidence of hip varus deformity can be as high as 10%-16% 8 . Biomechanical research suggests that for UITFFs classified as 31A2.1, the combination of DHS with cerclage wiring around the lesser trochanter can significantly enhance structural stability, increasing maximum load and stiffness. It is recommended to apply cerclage wiring above the lesser trochanter and below the greater trochanter to facilitate intraoperative manipulation 9 . Traditional intramedullary fixation systems have certain biomechanical advantages over extramedullary fixation; however, they still struggle to effectively reconstruct medial support through minimally invasive approaches, making it difficult to achieve anatomical reduction of the medial fragment. This can lead to secondary instability of the fracture, resulting in varus deformity of the proximal fracture fragment 10,11 . Reports in the literature indicate that the failure rates of these implants range from 8% to 56%, including withdrawal, cut-out, and varus collapse 12 .Nam et al. 13 used a modified "candy wire cerclage technique" to stabilize 22 cases of UITFFs involving the lesser trochanter, successfully restoring normal anatomy of the proximal femur, preserving iliopsoas function, allowing early patient mobilization, reducing limping and hip pain, and achieving favorable outcomes. Ehrnthaller et al. 14 treated UITFFs classified as 31A2 by combining Proximal femoral nail anti-rotation (PFNA) with cerclage fixation of the medial wall fragment, demonstrating that overall stiffness increased by 30% under an axial load of 200 N and by 38% under a load of 400 N, indicating that fixation of the lesser trochanter significantly enhances overall structural stability. Liu et al. 15 utilized a ring plate in conjunction with InterTAN for UITFFs involving the lesser trochanter, finding that compared to the control group, patients exhibited significantly improved hip function scores, and recommended fixation of the lesser trochanter when the patient's condition allows. However, while combined fixation restores the anatomical structure of the medial wall and improves postoperative stability, the use of wires or plates and the additional surgical incisions can increase operative and anesthetic times, elevate the risk of intraoperative bleeding and infection, potentially compromise blood supply to the fracture site, and in severe cases lead to femoral artery injury, resulting in pseudoaneurysms and thigh compartment syndrome 16 . Furthermore, biomechanical studies by Ceynowa et al. 17 also confirmed that reconstructing the medial wall with cerclage wiring does not significantly enhance axial stability of the fixation. Therefore, prioritizing a single intramedullary fixation method to improve overall stability, reduce complications associated with internal fixation devices, and avoid further soft tissue damage is a trend in the treatment of ITFFs. PFBN developed based on the principles of triangular stable structures and lever balance reconstruction theory, utilizes a cross-combination of pressure and tension screws to achieve bionic reconstruction of the compressive trabecular bone and tensile trabecular bone in the proximal femur. This cross-point configuration is closer to the physiological pivot point, effectively resisting postoperative pressure and stress from fractures. Its dual triangular structure not only reconstructs the damaged Ward triangle area but also significantly enhances overall stability 18,19 . Research by Cheng et al. 20 indicates that the stable fixation provided by the triangular structure helps reduce femoral neck shortening associated with DHS and PFNA. Furthermore, PFBN demonstrates distinct advantages in stress distribution and biological stability. Zhao et al. 21 treated 12 cases of UITFFs (31A2.3) with PFBN internal fixation, and follow-up assessments one year later showed good Harris and Parker scores. Therefore, using PFBN for the treatment of UITFFs with concomitant medial wall defects not only offers excellent stability but also minimizes additional soft tissue damage, making it a significant research focus on recent years for managing UITFFs. Currently, there is a relatively large body of biomechanical research on internal fixation of ITFF. However, studies focusing on the biomechanical characteristics of PFBN internal fixation under different sagittal alignments in the presence of medial wall defects are limited. This study aims to utilize FEA to explore the mechanical effects of different sagittal alignment patterns on the stability of PFBN internal fixation for ITFF with concomitant medial wall defects, thereby quantifying the concept of sagittal cortical support and providing a theoretical basis for clinical treatment. 2. Materials And Methods 2.1. Ethical approval This study was approved by the ethics of the Second Hospital of Jilin University. Written informed consent was obtained from the volunteer. 2.2. Establishment of the finite element models Fig.1 depicts the building procedures for modeling sixteen forms of sagittal cortical support in treating ITFs. First, we collected from the Second Hospital of Jilin University a set of high-resolution computed tomography (CT) patient data (a 64-year-old Chinese man, 165 cm, 60kg) with a slice thickness of 0.602 mm. This collection of CT data is imported into MIMICS 21 (Materialize, Leuven, Belgium) to rebuild the geometry of his femur based on the tissue’s gray value and the area segmentation. Then we additionally segmented the cortical and cancellous bone and rebuilt the cancellous bone using Boolean operation. The Boolean operation is to use all the masks of the femur to subtract the cortical bone from the Boolean operation to get the cancellous bone. Second, the rebuilt model files were imported into Geomagics 13 (3D Systems, Rock Hill, NC) for smoothing, meshing, additional processing and the generation of non-uniform rational B-spline (NURBS)-wrapped surfaces. Thirdly, the model files were loaded into Creo Parametric 7 (PTC, Boston, MA) to reconstruct ITFF patterns. We created two sets of ITFF models, one for the medial wall intact(AO/OTA 31A1.2),one for the medial defect(AO/OTA 31A1.3) 22 , the medial wall defect is one of the distinction between the models, seen as Fig.1(d1 and d2). Each model set consists of fractures of the neutral, backwards 5%,10%,15%,20% and forwards 5%,10%,15%,20% sagittal cortical supports, seen as Fig. 2. According to the view put forward by Chang et al. 23 , the proximal femur located in front of the distal femur is a positive support, on the contrary, it is a negative support, so we name the model backwards 5%,10%,15%,20% as negative 5%,10%,15%,20% and forwards as positive respectively. The PFBN model was also developed in Creo according to the size of the intramedullary nail provided by the manufacturer, complete the assembly of the intramedullary nail model, and export the geometric model file, seen as Fig. 1(c). Then, 18 fractured models and the PFBN model were assembled, and the tip-apex distance was adjusted to within 20mm.These models were then loaded into ANSYS Workbench 2022R1（ANSYS, Cannonsburg, PA, USA）for subsequent static analysis (one-legged stance). The elastic modulus and Poisson’s ratio of various structural materials are listed in Table 1 19 . 2.3. Loading force settings The contact conditions were set as friction contact, the friction coefficient between bone and bone was 0.46, the friction coefficient between bone and main nail was 0.42 24 . The relationship the nail and the nail and between the other nail and bone and between the cortical bone and cancellous bone were set as the bonding constraint. Set the 30 mm diameter range above the femoral head as the loading surface, and set the restraint surface at the femoral condyle to be fully fixed(Fig.3) 19 .The load condition is set to 600 N, and the direction was 10 adduction on the coronal plane and 9 adduction on the sagittal plane 25 . 2.4. Mesh sensitivity analysis To ensure the mesh size of the FEA results in this study, a mesh convergence test was performed. Using the automatic mesh generation function of the ANSYS program used for the analysis, finite element models with femur mesh sizes of 4.0 mm,3.5 mm, 3.0 mm, and intramedullary nail mesh sizes of 2.5 mm,2.0 mm and 1.8 mm were created, and the mesh convergence was tested for anatomical reduction with the medial wall intact. The convergence criterion used was a change of＜5%, and the smaller, the better 26 . Table 2 summarizes the number of elements, maximum equivalent stress, the difference from the previous group for each mesh size. Considering the results, the optimal mesh sizes of femur and internal fixation are 3.0mm and 1.8mm respectively, could meet the accuracy requirements of the analysis and this was applied to all cases for the analysis. 2.5. Model validation To verify the reliability of the model, the fully assembled femur model was imported into Ansys Workbench 2022R1 software, and the cortical bone and cancellous bone were given corresponding Young's modulus and Poisson's ratio. The distal end of the model was fixed, and the vertical load was applied to the femoral head and then calculated. The results show that the stress value was like that of the reference and was concentrated in the medial femoral shaft and transmitted downward, which shows that the experimental results were valid, and the model was reliable 18,19,27 . Since the convergence difference of the results of the FEA in this study was less than 5%, it could be considered that there was a unique solution, and statistical analysis was not required 2 . 3. Results 3.1 Total Displacement of the models The maximum displacements of the 18 models are shown in Table 3 and Fig. 4. With the increase of poor sagittal reduction, regardless of the integrity / defect of the medial wall, the negative cortical support displacement gradually increased; within 10% of the positive cortical support, the displacement value decreased, but after more than 10%, the displacement value began to increase. 3.2 Von mises stresses (VMS) distribution The VMS distributions of the main nail and fracture plane in 18 fixation patterns are shown in Fig.5 and Fig.6. The peak VMS values of the main nail, pressure nail, tension nail and fracture plane are listed in Table 4 and Fig.7. Regardless of the integrity / defect of the medial wall, the 10% of the positive cortical support reduction pattern showed minimal stress on the intramedullary nail, tension nail and fracture surface. From the stress distribution nephograms Fig.5, it could be seen that stress was mainly concentrated at the junction of the pressure nail and the main nail. From the stress distribution nephograms Fig.6, it could be seen that stress was mainly concentrated at the posterolateral wall. In the case of the same poor reduction, the maximum stress of the medial wall defect is significantly larger than that of the intact medial wall, as seen from Fig.7. 4. Discussion The destruction of the medial wall significantly reduces the stability of the proximal femur postoperatively and is closely associated with complications such as coxavalga deformity, shortening of the femoral neck, failure of internal fixation, and even the need for revision surgery 14,28-30 . As shown in Table 4 and Fig.7, under conditions of medial wall defect, the maximum stress values of the intramedullary nail, compression screw, and tension screw are all higher than those observed when the medial wall is intact with the same reduction pattern. This suggests that the medial wall plays a critical role in the transmission of compressive stresses, femoral stiffness, and the maintenance of stability at the proximal femur 31,32 . As early as 1949, Evans recognized the importance of the medial wall in the reduction of hip fractures and proposed the Evans classification based on the integrity of the posterior medial wall (including the lesser trochanter) 33 . Nie et al. 29 reported that the ultimate failure load of the femur in the medial wall defect group was 476 N, whereas it was 1596 N in the lateral wall defect group, with a statistically significant difference (P < 0.001). This indicates that the impact of medial wall defects on the stability of the proximal femur is more significant, and the stability of the medial wall is evidently more important than that of the lateral wall. A retrospective case study by Chen et al. 34 indicated that the postoperative loss of reduction rate due to medial wall comminution was as high as 20%. Therefore, restoring the anatomical integrity of the medial wall is crucial for enhancing the stability of the overall model and reducing the risk of internal fixation failure. According to the 2018 AO/OTA classification system 22 ，when the thickness of the lateral wall exceeds 20.5 mm, it is defined as a simple fracture with an intact lateral wall (A1 type). If accompanied by a medial wall defect, it is classified as type 31A1.3. In this intertrochanteric fracture type, the defect in the medial wall results in the loss of support for the proximal femoral fracture fragment from the medial cortex. This study utilized the method described by Wu et al. 9 to remove part of the medial wall to simulate a 31A1.3 type ITFF. The mechanical stability of internal fixation for ITFF plays a crucial role in promoting fracture healing and functional recovery in patients. Studies have shown that stable postoperative fixation can increase overall strength by approximately 30% 35 . Kaufer (1980) proposed that bone quality, the shape of the fracture fragments, the quality of reduction, and the internal fixation device and its positioning are the main factors affecting the postoperative stability of fracture fixation, with the latter three factors being amenable to improvement through surgical techniques 36 . Due to anatomical reasons, the proximal intertrochanteric fracture fragment tends to displace outward and posteriorly. If the distal fracture fragment can be stably reduced and provide sufficient cortical contact for the proximal fragment, it will help counteract the valgus and posterior displacement of the proximal fragment, thus significantly improving the overall postoperative stability and strength of the internal fixation device. Chang et al. 23 introduced the concept of "positive support" from the anterior medial cortex during reduction, noting that for UITFFs, fluoroscopic reduction with "negative support" from the anterior medial cortex may result in the loss of cortical support and should therefore be avoided. Positive support from the anterior medial cortex can prevent further sliding of the proximal fragment, achieving secondary stable contact, and providing favorable conditions for fracture healing. For type 31A1.3 intertrochanteric fractures, the loss of cortical support between the proximal and distal fragments due to medial wall defect makes sagittal plane cortical support particularly important. Table 3 and Fig.4 show that under the conditions of an intact/defective medial wall, the displacement increases as the sagittal negative support increases. When the medial wall is defective and the sagittal negative support reaches 20%, the maximum displacement value reaches 6.2 mm, with displacement concentrated at the top of the proximal femoral fracture fragment, which is prone to varus displacement. This is consistent with the results of previous FEA 2 .Related studies have shown that when the displacement after fracture fixation exceeds 2-3 mm, it may lead to bone resorption and micromotion of the internal fixation device, increasing the risk of internal fixation failure 37 . In this case, the larger the displacement, the poorer the overall stability of the model, which may lead to delayed union or even nonunion of the fracture. When the sagittal positive support is 5%-10%, the maximum displacement values under the intact/defective medial wall conditions are 4.324 mm and 4.409 mm (5% positive support), and 4.18 mm and 4.247 mm (10% positive support), which are all lower than the maximum displacement values of the intact/defective medial wall in the neutral position (4.471 mm and 4.567 mm). Moreover, when the positive support is 10%, the maximum displacement value is the smallest. This indicates that positive support helps maintain the stability of the model, which is consistent with the findings of Shao et al. 35 . However, when the sagittal positive support exceeds 10%, the displacement value continues to increase, indicating a decline in the overall stability of the model. From Table 3 and Fig.4, it can be concluded that under either intact or defective medial wall conditions, a neutral position or sagittal positive support within the 5%-10% range helps maintain the overall stability of the model, while reduction patterns with negative support or positive support exceeding 10% should be avoided. As shown in Table 4 and Fig.7, with the increase of sagittal positive support from 5% to 10%, the maximum stress values show a decreasing trend compared to the neutral position. Under the conditions of both intact and defective medial walls, the percentage changes in the maximum stress values are 1.141%-2.585% and 0.115%-1.141%, respectively. When the sagittal positive support reaches 10% and the medial wall is intact, the maximum stress value is the smallest. The maximum stress is primarily borne by the intramedullary nail, and the stress is mainly concentrated at the junction between the main intramedullary nail and the pressure screw (as shown in Fig.5). Although the stress variation is relatively small, it remains significant for elderly patients with osteoporotic fractures. This result is consistent with the findings of Liu et al. 27 , where simulation of a 4 mm anterior shift during PFNA treatment of a type 31A1 ITFF resulted in reduced internal fixation stress, indicating that moderate positive support helps improve the overall stability of the model and promote fracture healing. When the medial wall is intact, with the increase of sagittal negative support, the maximum stress on the tension screw gradually increases, while the maximum stress on the pressure screw gradually decreases, (as shown in Table 4). This may be due to the fact that, when the medial wall is intact, part of the stress is transmitted and dispersed through the medial wall, while another part is transferred via the tension screw to the internal fixation system, thus reducing the stress on the pressure screw. Additionally, as shown in Fig.6, when the medial wall is intact, the maximum stress on the fracture surface is primarily concentrated on the medial femoral calcar, which further supports the pathway of stress transmission from the intertrochanteric medial wall through the femoral calcar downward. As Bigelow 38 described, the femoral calcar, in combination with the anterior wall, serves as a physiological axis providing mechanical support to the proximal femur. When the medial wall is defective, the maximum stress on the fracture surface is primarily concentrated on the posterior-lateral wall (as shown in Fig.6), indicating that the posterior-lateral wall plays an important role in resisting varus and posterior displacement of the proximal femur. If the intertrochanteric fracture involves the posterior-lateral wall, internal fixation failure is more likely, which is consistent with the study by Xing et al. 39 , indicating that defects in the posterior-lateral wall are a risk factor for internal fixation failure in UITFFs. When the medial wall is defective and the sagittal reduction is improperly negative or positive displaced by 20%, the stresses on the main intramedullary nail are 188.52 MPa and 211.21 MPa, which are 2.66 and 2.98 times the stress value (70.761 MPa) seen with an intact medial wall and anatomically reduced fracture ends. Nevertheless, these stress values remain below the maximum yield strength of titanium alloy (750-900 MPa), indicating that the PFBN internal fixation system is safe under static conditions 40 . However, according to Bergmann et al. 41 , during normal walking and stair climbing, the loads on the hip joint are 211%-285% and 227%-316% of body weight, respectively. Therefore, during postoperative rehabilitation and walking, there is a potential risk of failure and fracture of the internal fixation device due to stress concentration. Although the results of this FEA show that when anatomical reduction and sagittal positive support are within the 5%-10% range, both the maximum displacement and maximum stress values of the overall model are relatively small (as shown in Fig.4 and Fig.7), which helps maintain the overall stability of the model, they still cannot completely offset the increased displacement and stress in the proximal femoral anatomical structures caused by medial wall defects. Therefore, if conditions allow, it is still recommended to restore the anatomical structure and integrity of the medial wall. For patients with medial wall defects or those in whom the anatomical structure of the medial wall cannot be restored, some researchers have developed new types of proximal femoral biomimetic intramedullary nails, which include an additional support screw below the pressure screw. FEA simulating screw cutout and using PFBN, PFNA, and DHS for revision fixation has shown that the new biomimetic proximal femoral intramedullary nail demonstrates significant advantages in terms of femoral displacement, stress, and internal fixation system displacement and stress 42 . Additionally, Chen et al. 43 designed a proximal femoral totally bionic nail, which adds a lateral wall screw behind the pressure screw, passing through the lateral cortical bone to fix it to the medial cortical bone of the femur. FEA indicated that compared with PFBN, the lateral wall screw further disperses the stress on the main intramedullary nail, tension screw, and pressure screw, helping to improve the overall stability of post-operative ITFFs and reduce the risk of hip varus deformity. In this study, the FEA of a type 31A1.3 intertrochanteric femoral fracture with PFBN fixation showed that the maximum stress values of the internal fixation device and various anatomical structures of the proximal femur did not reach their yield strength, proving that PFBN is an effective internal fixation method. Moreover, this fixation method avoids the additional soft tissue damage caused by the combined use of wires or plates to fix the medial wall in other methods, reducing the incidence of related complications, shortening the surgical time, and aiding in fracture healing. Furthermore, whether there is a medial wall defect, the displacement and stress of the overall model are small within the neutral position and sagittal positive support range of 5%-10%, suggesting that these reduction patterns offer better overall stability and should be the preferred reduction methods. This FEA is a mechanical study on the effects of different sagittal reduction patterns on the overall stability after PFBN internal fixation in cases of ITFFs with medial wall defects. However, there are some limitations in this study. First, the finite element model is idealized, with anatomical structures simplified, and factors such as muscles, ligaments, and tendons are not considered. As a result, the model may not fully reflect the true biomechanical characteristics, potentially leading to discrepancies between the simulated stress distribution and stability results and actual conditions. Second, this analysis is primarily based on static conditions of the hip joint, neglecting the impact of dynamic loading on the results. Moreover, the study lacks clinical data, which reduces the clinical applicability of the findings. Therefore, future studies should incorporate more comprehensive dynamic simulations and clinical validation to enhance the reliability and clinical guidance of the results. 5. Conclusion This study indicates that both the neutral position and sagittal positive support within the 5%-10% range provide good support under conditions of both intact and defective medial walls, while sagittal negative support tends to lead to fixation instability. Therefore, during surgery, positive support should be achieved whenever possible, and negative support should be avoided. Although the double triangular structure of the PFBN internal fixation system can improve the overall stability of the model and provide some resistance to rotation, it cannot completely eliminate the mechanical effects caused by medial wall defects. In cases of severe medial wall defects, the use of auxiliary support screws or lateral wall screws should be considered to further distribute the stress on other internal fixation devices and enhance overall stability. Abbreviations PFBN Proximal Femoral Bionic Nail ITFFs Intertrochanteric femoral fractures UITFFs Unstable intertrochanteric fractures FEA Finite element analysis DHS Dynamic hip screw PFNA Proximal femoral nail anti-rotation AO/OTA AO Foundation/Orthopaedic Trauma Association VMS Von mises stresses Declarations Acknowledgements There are no financial and personal relationships with other people or organizations that could inappropriately influence our work for all authors of this paper. Author contributions: MJH and SGX developed the idea. MJH and CZH wrote an initial draft of the manuscript. LYD was responsible for data collection. MJH and DJ were responsible for model building and finite element analysis. MJH and CZH wrote the final version of the manuscript. All authors read and approved the final manuscript. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Availability of data and materials Please contact author for data requests. Declarations Ethics approval and consent to participate This article does not contain any studies with human participants or animals performed by any of the authors. This study received approval from the Institutional Review Board (IRB) of the Second Hospital of Jilin University. Informed consent was obtained from all individual participants included in the study. All methods were performed in accordance with the Declarations of Helsinki. 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Proximal femoral bionic nail (PFBN)-an innovative surgical method for unstable femoral intertrochanteric fractures. Int Orthop 47 , 1089-1099, doi:10.1007/s00264-023-05696-y (2023). Meinberg, E. G., Agel, J., Roberts, C. S., Karam, M. D. & Kellam, J. F. Fracture and Dislocation Classification Compendium-2018. J Orthop Trauma 32 Suppl 1 , S1-s170, doi:10.1097/bot.0000000000001063 (2018). Chang, S. M. et al. Anteromedial cortical support reduction in unstable pertrochanteric fractures: a comparison of intra-operative fluoroscopy and post-operative three dimensional computerised tomography reconstruction. Int Orthop 42 , 183-189, doi:10.1007/s00264-017-3623-y (2018). Tucker, S. M., Wee, H., Fox, E., Reid, J. S. & Lewis, G. S. Parametric Finite Element Analysis of Intramedullary Nail Fixation of Proximal Femur Fractures. J Orthop Res 37 , 2358-2366, doi:10.1002/jor.24401 (2019). Nüchtern, J. V. et al. Malpositioning of the lag screws by 1- or 2-screw nailing systems for pertrochanteric femoral fractures: a biomechanical comparison of gamma 3 and intertan. J Orthop Trauma 28 , 276-282, doi:10.1097/bot.0000000000000008 (2014). Lorza, R. L. et al. Comparative Analysis of Healthy and Cam-Type Femoroacetabular Impingement (FAI) Human Hip Joints Using the Finite Element Method. Applied Sciences-Basel 11 , doi:10.3390/app112311101 (2021). Liu, J. et al. Sagittal support rather than medial cortical support matters in geriatric intertrochanteric fracture: A finite element analysis study. Heliyon 10 , e28606, doi:10.1016/j.heliyon.2024.e28606 (2024). Ren, H. et al. Effect of lesser trochanter posteromedial wall defect on the stability of femoral intertrochanteric fracture using 3D simulation. J Orthop Surg Res 15 , 242, doi:10.1186/s13018-020-01763-x (2020). Nie, B., Chen, X., Li, J., Wu, D. & Liu, Q. The medial femoral wall can play a more important role in unstable intertrochanteric fractures compared with lateral femoral wall: a biomechanical study. J Orthop Surg Res 12 , 197, doi:10.1186/s13018-017-0673-1 (2017). Marmor, M., Liddle, K., Pekmezci, M., Buckley, J. & Matityahu, A. The effect of fracture pattern stability on implant loading in OTA type 31-A2 proximal femur fractures. J Orthop Trauma 27 , 683-689, doi:10.1097/BOT.0b013e31828bacb4 (2013). Apel, D. M., Patwardhan, A., Pinzur, M. S. & Dobozi, W. R. Axial loading studies of unstable intertrochanteric fractures of the femur. Clin Orthop Relat Res , 156-164 (1989). Liu, C. C., Xing, W. Z., Zhang, Y. X., Pan, Z. H. & Feng, W. L. Three-dimensional finite element analysis and comparison of a new intramedullary fixation with interlocking intramedullary nail. Cell Biochem Biophys 71 , 717-724, doi:10.1007/s12013-014-0254-4 (2015). Evans, E. M. The treatment of trochanteric fractures of the femur. J Bone Joint Surg Br 31b , 190-203 (1949). Chen, S. Y. et al. A new fluoroscopic view for evaluation of anteromedial cortex reduction quality during cephalomedullary nailing for intertrochanteric femur fractures: the 30° oblique tangential projection. BMC Musculoskelet Disord 21 , 719, doi:10.1186/s12891-020-03668-6 (2020). Shao, Q. et al. Positive or negative anteromedial cortical support of unstable pertrochanteric femoral fractures: A finite element analysis study. Biomed Pharmacother 138 , 111473, doi:10.1016/j.biopha.2021.111473 (2021). Kaufer, H. Mechanics of the treatment of hip injuries. Clin Orthop Relat Res , 53-61 (1980). Kumar, V., Bakhtari, A. R., Himanshu, P. & Akhtar, W. in Advances in Engineering Design. (eds Preeti Joshi, Shakti S. Gupta, Anoop Kumar Shukla, & Sachin Singh Gautam) 507-516 (Springer Singapore). Bigelow, H. J. The true neck of the femur: its structure and pathology. 1875. Clin Orthop Relat Res , 4-7, doi:10.1097/00003086-199711000-00002 (1997). Ye, K. F. et al. Loss of the posteromedial support: a risk factor for implant failure after fixation of AO 31-A2 intertrochanteric fractures. Chin Med J (Engl) 133 , 41-48, doi:10.1097/cm9.0000000000000587 (2020). Levadnyi, I., Awrejcewicz, J., Goethel, M. F. & Loskutov, A. Influence of the fixation region of a press-fit hip endoprosthesis on the stress-strain state of the "bone-implant" system. Comput Biol Med 84 , 195-204, doi:10.1016/j.compbiomed.2017.03.030 (2017). Bergmann, G. et al. Hip contact forces and gait patterns from routine activities. J Biomech 34 , 859-871, doi:10.1016/s0021-9290(01)00040-9 (2001). Chen, P., Fan, Z., Xu, N. & Wang, H. A biomechanical investigation of a novel intramedullary nail used to salvage failed internal fixations in intertrochanteric fractures. J Orthop Surg Res 18 , 632, doi:10.1186/s13018-023-04112-w (2023). Chen, X. et al. A Novel Internal Fixation Design for the Treatment of AO/OTA-31A3.3 Intertrochanteric Fractures: Finite Element Analysis. Orthop Surg 16 , 1684-1694, doi:10.1111/os.14041 (2024). Tables Tables 1 to 4 are available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files Tables.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5415730","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":377451873,"identity":"89a977ff-d93a-47a7-b4b1-9d78d55f0f6f","order_by":0,"name":"Jinhu Miao","email":"","orcid":"","institution":"The Second Hospital of Jilin University","correspondingAuthor":false,"prefix":"","firstName":"Jinhu","middleName":"","lastName":"Miao","suffix":""},{"id":377451874,"identity":"63fc236e-8c95-4164-811e-abd21d891968","order_by":1,"name":"Jin Dai","email":"","orcid":"","institution":"The Second Hospital of Jilin 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06:59:19","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":19690,"visible":true,"origin":"","legend":"","description":"","filename":"Tables.docx","url":"https://assets-eu.researchsquare.com/files/rs-5415730/v1/14ab121463aeeb2281f79e61.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"The impact of sagittal cortical support on stability after internal fixation of intertrochanteric femoral fractures: a finite element analysis","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWith the intensification of population aging, the incidence of ITFF has significantly increased, with unstable fractures accounting for approximately 50%-60%\u003csup\u003e1\u003c/sup\u003e. Unstable intertrochanteric fractures (UITFFs) primarily include comminuted fractures of the posterior medial wall, lateral wall defects, and reverse oblique fractures, with the comminuted fracture of the posterior medial wall (AO/OTA 31A1.3 type) being the most common\u003csup\u003e2\u003c/sup\u003e. Due to the defect of the medial wall, this type of fracture may lead to complications related to internal fixation devices in 10%-27% of patients during treatment, such as device displacement, hip varus deformity, and femoral neck shortening\u003csup\u003e3\u003c/sup\u003e. Therefore, for ITFF associated with medial wall defects, early surgical intervention is recommended to achieve stable fixation, facilitate early functional rehabilitation, and reduce complications and mortality rates\u003csup\u003e4\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eTraditional surgical fixation methods include extramedullary and intramedullary fixation. The dynamic hip screw (DHS), as a representative of extramedullary fixation, has become the \u0026quot;gold standard\u0026quot; for treating trochanteric fractures due to its ability to adequately expose the fracture site, minimal damage to the gluteus Medius, and relatively low cost\u003csup\u003e5\u003c/sup\u003e. However, since the DHS is an off-center extramedullary fixation, its standalone application in intertrochanteric fractures with medial wall defects presents a problem of insufficient medial support\u003csup\u003e6,7\u003c/sup\u003e. Relevant studies indicate that if the medial wall is not addressed during surgery, the incidence of hip varus deformity can be as high as 10%-16%\u003csup\u003e8\u003c/sup\u003e. Biomechanical research suggests that for UITFFs classified as 31A2.1, the combination of DHS with cerclage wiring around the lesser trochanter can significantly enhance structural stability, increasing maximum load and stiffness. It is recommended to apply cerclage wiring above the lesser trochanter and below the greater trochanter to facilitate intraoperative manipulation\u003csup\u003e9\u003c/sup\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTraditional intramedullary fixation systems\u0026nbsp;have certain biomechanical advantages over extramedullary fixation; however, they still struggle to effectively reconstruct medial support through minimally invasive approaches, making it difficult to achieve anatomical reduction of the medial fragment. This can lead to secondary instability of the fracture, resulting in varus deformity of the proximal fracture fragment\u003csup\u003e10,11\u003c/sup\u003e. Reports in the literature indicate that the failure rates of these implants range from 8% to 56%, including withdrawal, cut-out, and varus collapse\u003csup\u003e12\u003c/sup\u003e.Nam et al.\u003csup\u003e13\u003c/sup\u003e used a modified \u0026quot;candy wire cerclage technique\u0026quot; to stabilize 22 cases of UITFFs involving the lesser trochanter, successfully restoring normal anatomy of the proximal femur, preserving iliopsoas function, allowing early patient mobilization, reducing limping and hip pain, and achieving favorable outcomes. Ehrnthaller et al.\u003csup\u003e14\u003c/sup\u003e treated UITFFs classified as 31A2 by combining Proximal femoral nail anti-rotation (PFNA) with cerclage fixation of the medial wall fragment, demonstrating that overall stiffness increased by 30% under an axial load of 200 N and by 38% under a load of 400 N, indicating that fixation of the lesser trochanter significantly enhances overall structural stability. Liu et al.\u003csup\u003e15\u003c/sup\u003e utilized a ring plate in conjunction with InterTAN for UITFFs involving the lesser trochanter, finding that compared to the control group, patients exhibited significantly improved hip function scores, and recommended fixation of the lesser trochanter when the patient\u0026apos;s condition allows. However, while combined fixation restores the anatomical structure of the medial wall and improves postoperative stability, the use of wires or plates and the additional surgical incisions can increase operative and anesthetic times, elevate the risk of intraoperative bleeding and infection, potentially compromise blood supply to the fracture site, and in severe cases lead to femoral artery injury, resulting in pseudoaneurysms and thigh compartment syndrome\u003csup\u003e16\u003c/sup\u003e. Furthermore, biomechanical studies by Ceynowa et al.\u003csup\u003e17\u003c/sup\u003e also confirmed that reconstructing the medial wall with cerclage wiring does not significantly enhance axial stability of the fixation. Therefore, prioritizing a single intramedullary fixation method to improve overall stability, reduce complications associated with internal fixation devices, and avoid further soft tissue damage is a trend in the treatment of ITFFs.\u003c/p\u003e\n\u003cp\u003ePFBN developed based on the principles of triangular stable structures and lever balance reconstruction theory, utilizes a cross-combination of pressure and tension screws to achieve bionic reconstruction of the compressive trabecular bone and tensile trabecular bone in the proximal femur. This cross-point configuration is closer to the physiological pivot point, effectively resisting postoperative pressure and stress from fractures. Its dual triangular structure not only reconstructs the damaged Ward triangle area but also significantly enhances overall stability\u003csup\u003e18,19\u003c/sup\u003e. Research by Cheng et al.\u003csup\u003e20\u003c/sup\u003e indicates that the stable fixation provided by the triangular structure helps reduce femoral neck shortening associated with DHS and PFNA. Furthermore, PFBN demonstrates distinct advantages in stress distribution and biological stability. Zhao et al.\u003csup\u003e21\u003c/sup\u003e treated 12 cases of UITFFs (31A2.3) with PFBN internal fixation, and follow-up assessments one year later showed good Harris and Parker scores. Therefore, using PFBN for the treatment of UITFFs with concomitant medial wall defects not only offers excellent stability but also minimizes additional soft tissue damage, making it a significant research focus on recent years for managing UITFFs.\u003c/p\u003e\n\u003cp\u003eCurrently, there is a relatively large body of biomechanical research on internal fixation of ITFF. However, studies focusing on the biomechanical characteristics of PFBN internal fixation under different sagittal alignments in the presence of medial wall defects are limited. This study aims to utilize FEA to explore the mechanical effects of different sagittal alignment patterns on the stability of PFBN internal fixation for ITFF with concomitant medial wall defects, thereby quantifying the concept of sagittal cortical support and providing a theoretical basis for clinical treatment.\u003c/p\u003e"},{"header":"2. Materials And Methods","content":"\u003cp\u003e\u003cstrong\u003e2.1. Ethical approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was approved by the ethics of\u0026nbsp;the Second Hospital of Jilin University. Written informed consent was obtained from the volunteer.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.2. Establishment of the finite element models\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFig.1\u0026nbsp;depicts the building procedures for modeling sixteen forms of sagittal cortical support in treating ITFs. First, we collected from the Second Hospital of Jilin University a set of high-resolution computed tomography (CT) patient data (a 64-year-old Chinese man, 165 cm, 60kg) with a slice thickness of 0.602 mm. This collection of CT data is imported into MIMICS 21 (Materialize, Leuven, Belgium) to rebuild the geometry of his femur based on the tissue\u0026rsquo;s gray value and the area segmentation. Then we additionally segmented the cortical and cancellous bone and rebuilt the cancellous bone using Boolean operation. The Boolean operation is to use all the masks of the femur to subtract the cortical bone from the Boolean operation to get the cancellous bone. Second, the rebuilt model files were imported into Geomagics 13 (3D Systems, Rock Hill, NC) for smoothing, meshing, additional processing and the generation of non-uniform rational B-spline (NURBS)-wrapped surfaces. Thirdly, the model files were loaded into Creo Parametric 7 (PTC, Boston, MA) to reconstruct ITFF patterns. We created two sets of ITFF models, one for the medial wall intact(AO/OTA 31A1.2),one for the medial defect(AO/OTA 31A1.3)\u003csup\u003e22\u003c/sup\u003e, the medial wall defect is one of the distinction between the models, seen as Fig.1(d1 and d2). Each model set consists of fractures of the neutral, backwards 5%,10%,15%,20% and forwards 5%,10%,15%,20% sagittal cortical supports, seen as Fig. 2. According to the view put forward by Chang et al.\u003csup\u003e23\u003c/sup\u003e , the proximal femur located in front of the distal femur is a positive support, on the contrary, it is a negative support, so we name the model backwards 5%,10%,15%,20% as negative 5%,10%,15%,20% and forwards as positive respectively.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe PFBN model was also developed in Creo according to the size of the intramedullary nail provided by the manufacturer, complete the assembly of the intramedullary nail model, and export the geometric model file, seen as Fig. 1(c). Then, 18 fractured models and the PFBN model were assembled, and the tip-apex distance was adjusted to within 20mm.These models were then loaded into ANSYS Workbench 2022R1（ANSYS, Cannonsburg, PA, USA）for subsequent static analysis (one-legged stance). The elastic modulus and Poisson\u0026rsquo;s ratio of various structural materials are listed in Table 1\u003csup\u003e19\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.3. Loading force settings\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe contact conditions were set as friction contact, the friction coefficient between bone and bone was 0.46, the friction coefficient between bone and main nail was 0.42\u003csup\u003e24\u003c/sup\u003e. The relationship the\u003c/p\u003e\n\u003cp\u003enail and the nail and between the other nail and bone and between the cortical bone and cancellous bone were set as the bonding constraint. Set the 30 mm diameter range above the femoral head as the loading surface, and set the restraint surface at the femoral condyle to be fully fixed(Fig.3)\u003csup\u003e19\u003c/sup\u003e.The load condition is set to 600 N, and the direction was 10 adduction on the coronal plane and 9 adduction on the sagittal plane\u003csup\u003e25\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.4. Mesh sensitivity analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;To ensure the mesh size of the FEA results in this study, a mesh convergence test was performed. Using the automatic mesh generation function of the ANSYS program used for the analysis, finite element models with femur mesh sizes of 4.0 mm,3.5 mm, 3.0 mm, and intramedullary nail mesh sizes of 2.5 mm,2.0 mm and 1.8 mm were created, and the mesh convergence was tested for anatomical reduction with the medial wall intact. The convergence criterion used was a change of＜5%, and the smaller, the better\u003csup\u003e26\u003c/sup\u003e. Table 2 summarizes the number of elements, maximum equivalent stress, the difference from the previous group for each mesh size. Considering the results, the optimal mesh sizes of femur and internal fixation are 3.0mm and 1.8mm respectively, could meet the accuracy requirements of the analysis and this was applied to all cases for the analysis.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.5. Model validation\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo verify the reliability of the model, the fully assembled femur model was imported into Ansys Workbench 2022R1 software, and the cortical bone and cancellous bone were given corresponding Young\u0026apos;s modulus and Poisson\u0026apos;s ratio. The distal end of the model was fixed, and the vertical load was applied to the femoral head and then calculated. The results show that the stress value was like that of the reference and was concentrated in the medial femoral shaft and transmitted downward, which shows that the experimental results were valid, and the model was reliable\u003csup\u003e18,19,27\u003c/sup\u003e. Since the convergence difference of the results of the FEA in this study was less than 5%, it could be considered that there was a unique solution, and statistical analysis was not required\u003csup\u003e2\u003c/sup\u003e.\u003c/p\u003e"},{"header":"3. Results","content":"\u003cp\u003e\u003cstrong\u003e3.1 Total Displacement of the models\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe maximum displacements of the 18 models are shown in Table 3 and Fig. 4. With the increase of poor sagittal reduction, regardless of the integrity / defect of the medial wall, the negative cortical support displacement gradually increased; within 10% of the positive cortical support, the displacement value decreased, but after more than 10%, the displacement value began to increase.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2 Von mises stresses (VMS) distribution \u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe VMS distributions of the main nail and fracture plane in 18 fixation patterns are shown in Fig.5 and Fig.6. The peak VMS values of the main nail, pressure nail, tension nail and fracture plane are listed in Table 4 and Fig.7. Regardless of the integrity / defect of the medial wall, the 10% of the positive cortical support reduction pattern showed minimal stress on the intramedullary nail, tension nail and fracture surface. From the stress distribution nephograms Fig.5, it could be seen that stress was mainly concentrated at the junction of the pressure nail and the main nail. From the stress distribution nephograms Fig.6, it could be seen that stress was mainly concentrated at the posterolateral wall. In the case of the same poor reduction, the maximum stress of the medial wall defect is significantly larger than that of the intact medial wall, as seen from Fig.7.\u003c/p\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eThe destruction of the medial wall significantly reduces the stability of the proximal femur postoperatively and is closely associated with complications such as coxavalga deformity, shortening of the femoral neck, failure of internal fixation, and even the need for revision surgery\u003csup\u003e14,28-30\u003c/sup\u003e. As shown in Table 4 and Fig.7, under conditions of medial wall defect, the maximum stress values of the intramedullary nail, compression screw, and tension screw are all higher than those observed when the medial wall is intact with the same reduction pattern. This suggests that the medial wall plays a critical role in the transmission of compressive stresses, femoral stiffness, and the maintenance of stability at the proximal femur\u003csup\u003e31,32\u003c/sup\u003e . As early as 1949, Evans recognized the importance of the medial wall in the reduction of hip fractures and proposed the Evans classification based on the integrity of the posterior medial wall (including the lesser trochanter)\u003csup\u003e33\u003c/sup\u003e. Nie et al.\u003csup\u003e29\u003c/sup\u003e reported that the ultimate failure load of the femur in the medial wall defect group was 476 N, whereas it was 1596 N in the lateral wall defect group, with a statistically significant difference (P \u0026lt; 0.001). This indicates that the impact of medial wall defects on the stability of the proximal femur is more significant, and the stability of the medial wall is evidently more important than that of the lateral wall. A retrospective case study by Chen et al.\u003csup\u003e34\u003c/sup\u003e indicated that the postoperative loss of reduction rate due to medial wall comminution was as high as 20%. Therefore, restoring the anatomical integrity of the medial wall is crucial for enhancing the stability of the overall model and reducing the risk of internal fixation failure. According to the 2018 AO/OTA classification system\u003csup\u003e22\u003c/sup\u003e，when the thickness of the lateral wall exceeds 20.5 mm, it is defined as a simple fracture with an intact lateral wall (A1 type). If accompanied by a medial wall defect, it is classified as type 31A1.3. In this intertrochanteric fracture type, the defect in the medial wall results in the loss of support for the proximal femoral fracture fragment from the medial cortex. This study utilized the method described by Wu et al. \u003csup\u003e9\u003c/sup\u003e to remove part of the medial wall to simulate a 31A1.3 type ITFF.\u003c/p\u003e\n\u003cp\u003eThe mechanical stability of internal fixation for ITFF plays a crucial role in promoting fracture healing and functional recovery in patients. Studies have shown that stable postoperative fixation can increase overall strength by approximately 30%\u003csup\u003e35\u003c/sup\u003e. Kaufer (1980) proposed that bone quality, the shape of the fracture fragments, the quality of reduction, and the internal fixation device and its positioning are the main factors affecting the postoperative stability of fracture fixation, with the latter three factors being amenable to improvement through surgical techniques\u003csup\u003e36\u003c/sup\u003e. Due to anatomical reasons, the proximal intertrochanteric fracture fragment tends to displace outward and posteriorly. If the distal fracture fragment can be stably reduced and provide sufficient cortical contact for the proximal fragment, it will help counteract the valgus and posterior displacement of the proximal fragment, thus significantly improving the overall postoperative stability and strength of the internal fixation device. Chang et al.\u003csup\u003e23\u003c/sup\u003e introduced the concept of \u0026quot;positive support\u0026quot; from the anterior medial cortex during reduction, noting that for UITFFs, fluoroscopic reduction with \u0026quot;negative support\u0026quot; from the anterior medial cortex may result in the loss of cortical support and should therefore be avoided. Positive support from the anterior medial cortex can prevent further sliding of the proximal fragment, achieving secondary stable contact, and providing favorable conditions for fracture healing. For type 31A1.3 intertrochanteric fractures, the loss of cortical support between the proximal and distal fragments due to medial wall defect makes sagittal plane cortical support particularly important.\u003c/p\u003e\n\u003cp\u003eTable 3\u0026nbsp;and Fig.4 show that under the conditions of an intact/defective medial wall, the displacement increases as the sagittal negative support increases. When the medial wall is defective and the sagittal negative support reaches 20%, the maximum displacement value reaches 6.2 mm, with displacement concentrated at the top of the proximal femoral fracture fragment, which is prone to varus displacement. This is consistent with the results of previous FEA \u003csup\u003e2\u003c/sup\u003e.Related studies have shown that when the displacement after fracture fixation exceeds 2-3 mm, it may lead to bone resorption and micromotion of the internal fixation device, increasing the risk of internal fixation failure \u003csup\u003e37\u003c/sup\u003e. In this case, the larger the displacement, the poorer the overall stability of the model, which may lead to delayed union or even nonunion of the fracture. When the sagittal positive support is 5%-10%, the maximum displacement values under the intact/defective medial wall conditions are 4.324 mm and 4.409 mm (5% positive support), and 4.18 mm and 4.247 mm (10% positive support), which are all lower than the maximum displacement values of the intact/defective medial wall in the neutral position (4.471 mm and 4.567 mm). Moreover, when the positive support is 10%, the maximum displacement value is the smallest. This indicates that positive support helps maintain the stability of the model, which is consistent with the findings of Shao et al.\u003csup\u003e35\u003c/sup\u003e. However, when the sagittal positive support exceeds 10%, the displacement value continues to increase, indicating a decline in the overall stability of the model. From Table 3 and Fig.4, it can be concluded that under either intact or defective medial wall conditions, a neutral position or sagittal positive support within the 5%-10% range helps maintain the overall stability of the model, while reduction patterns with negative support or positive support exceeding 10% should be avoided.\u003c/p\u003e\n\u003cp\u003eAs shown in Table 4 and Fig.7, with the increase of sagittal positive support from 5% to 10%, the maximum stress values show a decreasing trend compared to the neutral position. Under the conditions of both intact and defective medial walls, the percentage changes in the maximum stress values are 1.141%-2.585% and 0.115%-1.141%, respectively. When the sagittal positive support reaches 10% and the medial wall is intact, the maximum stress value is the smallest. The maximum stress is primarily borne by the intramedullary nail, and the stress is mainly concentrated at the junction between the main intramedullary nail and the pressure screw (as shown in Fig.5). Although the stress variation is relatively small, it remains significant for elderly patients with osteoporotic fractures. This result is consistent with the findings of Liu et al. \u003csup\u003e27\u003c/sup\u003e , where simulation of a 4 mm anterior shift during PFNA treatment of a type 31A1 ITFF resulted in reduced internal fixation stress, indicating that moderate positive support helps improve the overall stability of the model and promote fracture healing. When the medial wall is intact, with the increase of sagittal negative support, the maximum stress on the tension screw gradually increases, while the maximum stress on the pressure screw gradually decreases, (as shown in Table 4). This may be due to the fact that, when the medial wall is intact, part of the stress is transmitted and dispersed through the medial wall, while another part is transferred via the tension screw to the internal fixation system, thus reducing the stress on the pressure screw. Additionally, as shown in Fig.6, when the medial wall is intact, the maximum stress on the fracture surface is primarily concentrated on the medial femoral calcar, which further supports the pathway of stress transmission from the intertrochanteric medial wall through the femoral calcar downward. As Bigelow \u003csup\u003e38\u003c/sup\u003e described, the femoral calcar, in combination with the anterior wall, serves as a physiological axis providing mechanical support to the proximal femur. When the medial wall is defective, the maximum stress on the fracture surface is primarily concentrated on the posterior-lateral wall (as shown in Fig.6), indicating that the posterior-lateral wall plays an important role in resisting varus and posterior displacement of the proximal femur. If the intertrochanteric fracture involves the posterior-lateral wall, internal fixation failure is more likely, which is consistent with the study by Xing et al. \u003csup\u003e39\u003c/sup\u003e , indicating that defects in the posterior-lateral wall are a risk factor for internal fixation failure in UITFFs. When the medial wall is defective and the sagittal reduction is improperly negative or positive displaced by 20%, the stresses on the main intramedullary nail are 188.52 MPa and 211.21 MPa, which are 2.66 and 2.98 times the stress value (70.761 MPa) seen with an intact medial wall and anatomically reduced fracture ends. Nevertheless, these stress values remain below the maximum yield strength of titanium alloy (750-900 MPa), indicating that the PFBN internal fixation system is safe under static conditions \u003csup\u003e40\u003c/sup\u003e. However, according to Bergmann et al. \u003csup\u003e41\u003c/sup\u003e , during normal walking and stair climbing, the loads on the hip joint are 211%-285% and 227%-316% of body weight, respectively. Therefore, during postoperative rehabilitation and walking, there is a potential risk of failure and fracture of the internal fixation device due to stress concentration.\u003c/p\u003e\n\u003cp\u003eAlthough the results of this FEA show that when anatomical reduction and sagittal positive support are within the 5%-10% range, both the maximum displacement and maximum stress values of the overall model are relatively small (as shown in Fig.4\u0026nbsp;and Fig.7), which helps maintain the overall stability of the model, they still cannot completely offset the increased displacement and stress in the proximal femoral anatomical structures caused by medial wall defects. Therefore, if conditions allow, it is still recommended to restore the anatomical structure and integrity of the medial wall. For patients with medial wall defects or those in whom the anatomical structure of the medial wall cannot be restored, some researchers have developed new types of proximal femoral biomimetic intramedullary nails, which include an additional support screw below the pressure screw. FEA simulating screw cutout and using PFBN, PFNA, and DHS for revision fixation has shown that the new biomimetic proximal femoral intramedullary nail demonstrates significant advantages in terms of femoral displacement, stress, and internal fixation system displacement and stress\u003csup\u003e42\u003c/sup\u003e. Additionally, Chen et al. \u003csup\u003e43\u003c/sup\u003e designed a proximal femoral totally bionic nail, which adds a lateral wall screw behind the pressure screw, passing through the lateral cortical bone to fix it to the medial cortical bone of the femur. FEA indicated that compared with PFBN, the lateral wall screw further disperses the stress on the main intramedullary nail, tension screw, and pressure screw, helping to improve the overall stability of post-operative ITFFs and reduce the risk of hip varus deformity. In this study, the FEA of a type 31A1.3 intertrochanteric femoral fracture with PFBN fixation showed that the maximum stress values of the internal fixation device and various anatomical structures of the proximal femur did not reach their yield strength, proving that PFBN is an effective internal fixation method. Moreover, this fixation method avoids the additional soft tissue damage caused by the combined use of wires or plates to fix the medial wall in other methods, reducing the incidence of related complications, shortening the surgical time, and aiding in fracture healing. Furthermore, whether there is a medial wall defect, the displacement and stress of the overall model are small within the neutral position and sagittal positive support range of 5%-10%, suggesting that these reduction patterns offer better overall stability and should be the preferred reduction methods.\u003c/p\u003e\n\u003cp\u003eThis FEA is a mechanical study on the effects of different sagittal reduction patterns on the overall stability after PFBN internal fixation in cases of ITFFs with medial wall defects. However, there are some limitations in this study. First, the finite element model is idealized, with anatomical structures simplified, and factors such as muscles, ligaments, and tendons are not considered. As a result, the model may not fully reflect the true biomechanical characteristics, potentially leading to discrepancies between the simulated stress distribution and stability results and actual conditions. Second, this analysis is primarily based on static conditions of the hip joint, neglecting the impact of dynamic loading on the results. Moreover, the study lacks clinical data, which reduces the clinical applicability of the findings. Therefore, future studies should incorporate more comprehensive dynamic simulations and clinical validation to enhance the reliability and clinical guidance of the results.\u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eThis study indicates that both the neutral position and sagittal positive support within the 5%-10% range provide good support under conditions of both intact and defective medial walls, while sagittal negative support tends to lead to fixation instability. Therefore, during surgery, positive support should be achieved whenever possible, and negative support should be avoided. Although the double triangular structure of the PFBN internal fixation system can improve the overall stability of the model and provide some resistance to rotation, it cannot completely eliminate the mechanical effects caused by medial wall defects. In cases of severe medial wall defects, the use of auxiliary support screws or lateral wall screws should be considered to further distribute the stress on other internal fixation devices and enhance overall stability.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003ePFBN \u0026nbsp; \u0026nbsp; \u0026nbsp;Proximal Femoral Bionic Nail\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eITFFs \u0026nbsp; \u0026nbsp; \u0026nbsp;Intertrochanteric femoral fractures\u003c/p\u003e\n\u003cp\u003eUITFFs \u0026nbsp; \u0026nbsp; Unstable intertrochanteric fractures\u003c/p\u003e\n\u003cp\u003eFEA \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Finite element analysis\u003c/p\u003e\n\u003cp\u003eDHS \u0026nbsp; \u0026nbsp; \u0026nbsp; Dynamic hip screw\u003c/p\u003e\n\u003cp\u003ePFNA \u0026nbsp; \u0026nbsp; \u0026nbsp;Proximal femoral nail anti-rotation\u003c/p\u003e\n\u003cp\u003eAO/OTA \u0026nbsp; \u0026nbsp;AO Foundation/Orthopaedic Trauma Association\u003c/p\u003e\n\u003cp\u003eVMS \u0026nbsp; \u0026nbsp; \u0026nbsp;Von mises stresses\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThere are no financial and personal relationships with other people or organizations that could inappropriately influence our work for all authors of this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMJH and SGX developed the idea. MJH and CZH wrote an initial draft of the manuscript. LYD was responsible for data collection. MJH and DJ were responsible for model building and finite element analysis. MJH and CZH wrote the final version of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePlease contact author for data requests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis article does not contain any studies with human participants or animals performed by any of the authors. This study received approval from the Institutional Review Board (IRB) of\u0026nbsp;the Second Hospital of Jilin University. Informed consent was obtained from all individual participants included in the study. All methods were performed in accordance with the Declarations of Helsinki.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot\u0026nbsp;applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eYang, A. 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A biomechanical investigation of a novel intramedullary nail used to salvage failed internal fixations in intertrochanteric fractures. \u003cem\u003eJ Orthop Surg Res\u003c/em\u003e\u003cstrong\u003e18\u003c/strong\u003e, 632, doi:10.1186/s13018-023-04112-w (2023).\u003c/li\u003e\n\u003cli\u003eChen, X.\u003cem\u003e et al.\u003c/em\u003e A Novel Internal Fixation Design for the Treatment of AO/OTA-31A3.3 Intertrochanteric Fractures: Finite Element Analysis. \u003cem\u003eOrthop Surg\u003c/em\u003e\u003cstrong\u003e16\u003c/strong\u003e, 1684-1694, doi:10.1111/os.14041 (2024).\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTables 1 to 4 are available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Sagittal cortical support, Intertrochanteric femoral fracture, Internal fixation, Finite element analysis","lastPublishedDoi":"10.21203/rs.3.rs-5415730/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5415730/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eObjective: \u003c/strong\u003eTo explore the optimal sagittal cortical support reduction mode with proximal femoral bionic nails (PFBN) for treating intertrochanteric femoral fractures (ITFFs) with medial wall defects to prevent internal fixation failure.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods: \u003c/strong\u003eA 64-year-old healthy male volunteer with no history of hip or systemic disease was recruited. High-resolution computed tomography images with a slice thickness of 0.602 mm of his right femur were obtained. These images were used to establish three-dimensional (3D) models. The lesser trochanter and medial wall were cut off to create an AO Foundation/Orthopaedic Trauma Association (AO/OTA) type 31-A1.3 pertrochanteric fracture model. PFBN was used to simulate fixation. Under the conditions of coronal anatomical reduction, eighteen different fracture sagittal reduction modes were examined, which included intact or defective medial walls, as well as neutral, negative 5%,10%,15%,20%, and positive 5%,10%,15%,20%, were simulated. A load of 600 N was applied to simulate a 60 kg elderly patient standing on one leg. The models were subjected to finite element analysis (FEA). The displacement and von Mises stress distributions were analyzed.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults: \u003c/strong\u003eUnder the conditions of an intact or defective medial wall, the 10% positive sagittal cortical support reduction pattern showed minimal stress and displacement. In the case of medial wall defects, with 20% loss of reduction in both negative and positive sagittal mal reduction, the maximum equivalent stresses were 188.52 MPa and 211.21 MPa, respectively, which are 2.66 and 2.98 times greater than the maximum equivalent stress of 70.761 MPa observed when the medial wall was intact. Meanwhile, the 20% negative reduction pattern seemed to have the largest displacement.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion:\u003c/strong\u003e Under the conditions of an intact or defective medial wall, the 10% positive sagittal support reduction pattern showed the best mechanical stability for ITFF. The negative support reduction pattern was prone to fixation failure and should be avoided during an operation.\u003c/p\u003e","manuscriptTitle":"The impact of sagittal cortical support on stability after internal fixation of intertrochanteric femoral fractures: a finite element analysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-17 06:59:14","doi":"10.21203/rs.3.rs-5415730/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"9231f45b-b882-46a4-8435-72c2fc3cc834","owner":[],"postedDate":"December 17th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-12-25T04:53:07+00:00","versionOfRecord":[],"versionCreatedAt":"2024-12-17 06:59:14","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5415730","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5415730","identity":"rs-5415730","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}