With the rapid increase in the global elderly population and life expectancy, the number of hip fractures in this population is also increasing (Lindskog and Baumgaertner, 2004; Chang et al., 2020). In elderly individuals, hip fractures encompass both femoral neck fractures and femoral intertrochanteric fractures, with intertrochanteric fractures representing approximately 40% of all hip fractures (Adeyemi and Delhougne, 2019). Surgical intervention is the first line of treatment and includes extramedullary fixation, intramedullary fixation, and joint replacement. Extramedullary dynamic hip screw (DHS) fixation is the preferred option for stable intertrochanteric fractures. However, owing to the severe complications associated with DHS, it is not the preferred choice for unstable intertrochanteric fractures (Ecker et al., 1975; Haidukewych, 2009). In such cases, intramedullary nailing is necessary. Studies have reported favorable outcomes for intramedullary nail fixation (Tawari et al., 2015). Nevertheless, complications may arise after intramedullary fixation, including intramedullary nail fractures, screw blade withdrawal, and non-union. These complications are often linked to suboptimal fracture reduction, screw blade positioning, and inadequate screw blade length. They are closely related to the stability and integrity of the lateral intertrochanteric wall (Bohl et al., 2014; Yu et al., 2016).

Professor Gotfried first proposed the importance of the lateral wall in the prognosis of femoral intertrochanteric fractures in 2004, defining the lateral femoral wall as the proximal extension of the femoral shaft or the lateral femoral cortex distal to the vastus ridge (Gotfried, 2004). The intact lateral wall provides biomechanical and lateral support for the proximal femur, thus improving stability, whereas lateral wall fractures can lead to uncontrollable excessive fracture collapse and varus (Gotfried, 2004; Gupta et al., 2010). In 2018, the Orthopaedic Trauma Association improved the classification system for femoral intertrochanteric fractures by adding lateral intertrochanteric wall fractures (Meinberg et al., 2018). The integrity of the lateral wall is considered the main prognostic factor for hip intertrochanteric fractures (Hsu et al., 2013; Hsu et al., 2015; Gao et al., 2018). At present, intramedullary nail fixation is the preferred choice for patients with primary or iatrogenic lateral wall fractures. Nevertheless, intramedullary nail fixation alone may not adequately address the complete reconstruction of the fractured lateral wall. Enhanced fixation through devices such as ring ligation, additional screws, or plates is needed to reconstruct the fractured lateral wall (Mohamed et al., 2020). However, the internal fixation devices for lateral wall fracture reconstruction have not reached a unified standard.

The ortho-bridge system (OBS) (Wang et al., 2014)—an original internal fixation system developed by China Tianjin Weiman Biomaterials Co., Ltd.—finds extensive clinical use in China for fracture fixation of the upper and lower extremities and pelvis fracture fixation. It consists of connecting rods, locking screws, and fixation blocks (Figure 1). Following the application of the bridge internal fixation system, combined with proximal femoral nail antirotation (PFNA) fixation for femoral intertrochanteric fractures accompanied by lateral wall fractures, we conducted a finite-element analysis to investigate the biomechanical changes of the lateral wall of the femur, proximal femur and intramedullary nail when OBS is used versus no OBS, as well as the mechanical advantages of OBS. These findings serve as a basis for future clinical applications.

Treatment of femoral intertrochanteric fractures combined with lateral wall fractures is a difficult challenge for orthopaedic surgeons. Currently, there is no unified clinical standard on whether and how to fix the lateral wall. In this study, we tried to repair the lateral wall with OBS in order to increase the stability of intramedullary nail.

There are related clinical reports on the treatment of lateral wall fracture with steel wire or steel plate, Kulkarni SG et al. reported that fixing the lateral wall with steel wire can provide better stability and reduce complications such as fracture collapse (Kulkarni et al., 2017). Gupta RK et al. reported that the lateral wall fixation of 46 patients was performed using the trochanteric stabilising plate (TSP), and most of them recovered well. They believe that TSP ensures a better abductor function due to stability provided to the greater trochanter. However, there may be persistent pain in the hip region because of impingement of the proximal part of the trochanteric stabilising plate (Gupta et al., 2010). But there is no biomechanical report at present. Huang et al. reported the biomechanical analysis of the treatment of subtrochanteric fracture of femur with steel wire (Huang et al., 2021). Although the steel wire increased the local stress, it improved the stability of the medial femur. Encircling steel wire can also increase the stability of lateral wall, but whether to increase local stress during treatment needs biomechanical verification, and the biomechanical and clinical comparative study of internal fixators is needed to further improve the treatment of lateral wall reconstruction.

The instability of intertrochanteric fractures is often associated with the incomplete lateral wall of the femur. In such cases, intramedullary nail treatment becomes the preferred choice. Consequently, in this study, we employed PFNA fixation for the models. Significant variations in von Mises stresses on the lateral wall were observed between the two models. The maximum stress of the lateral wall of the double-fixation model was lower than 60 MPa, whereas that of the single-fixation model was 86.819 MPa. According to Wolff’s law and the study of Frost (Frost, 1994; Frost, 2004), bone tissue is absorbed when the strain is less than 50–100 microstrain and the stress is lower than 1–2 MPa. When the strain of the bone exceeds 1,000–1,500 microstrain and the stress is higher than approximately 20 MPa, the bone tissue grows. However, when the strain of the bone exceeds approximately 3,000 microstrain and the stress is higher than approximately 60 MPa, the bone tissue is damaged. Therefore, the use of OBS can effectively reduce the stress on the lateral wall and ensure that the bone tissue grows safely without stress shielding of the implant, whereas the von Mises stress of the lateral wall of the femur cannot grow well when the lateral wall of the femur is moved. Anatomically, the lateral wall is the lateral femoral cortex of the distal femoral crest, which provides lateral support (Varshney et al., 2022). Single-fixation refers to the loss of integrity of the lateral wall of the femur. When proximal femoral antirotation intramedullary nail-Asia (PFNA-II) is used, some scholars believe that the integrity of the lateral wall may not be important, because the metal lateral wall of the nail replaces the lateral cortex in osteoporosis (Boopalan et al., 2012; Abram et al., 2013). Studies by Shi et al. (2021) have shown that even when PFNA-II is used, the imaging and functional results of patients with lateral wall fractures are worse than those of individuals with intact lateral walls. Additionally, lateral wall fractures increase the risk of postoperative complications and reoperation (Palm et al., 2007). Gupta et al. considered that the strength of the lever arm and abductor muscle can be maintained when the lateral wall is reconstructed (Gupta et al., 2010); therefore, When conditions permit, the lateral wall of the femur should be fixed for fractures of the lateral intertrochanteric wall, whether it is a preoperative fracture or an intraoperative or postoperative intertrochanteric fracture, as reported by Gotfried (2004). In this study, the maximum von Mises stress of the proximal femur exceeded 60 MPa. However, Figure 6 shows that the distribution of the maximum stress was not near the fracture line, and the stress near the fracture line remains below 60 MPa, which does not hinder the normal healing of bones. Our findings suggest that the OBS device can effectively stabilize lateral wall fractures of the femur, thereby mitigating biomechanical deficiencies and lowering the risk of postoperative complications.

OBS affected the biomechanics of the intramedullary nail system and proximal femur bone in the model. In this study, the maximum von Mises stress was observed on the main nail of the single-fixation model. When the lateral wall of the femur was fixed with the OBS device, the maximum von Mises stress of the main intramedullary nail, the maximum von Mises stress of the screw blade, and the maximum stress of the proximal femur bone decreased significantly. Previous studies have shown that implants share part of the load borne by bone (Ridzwan et al., 2007). In the present study, we found that the implant can share not only the stress of the bone but also the load of each part of the intramedullary nail with internal fixation. As shown in Figures 7–9, no stress concentration was observed in the proximal femur. Part of the lateral wall of the femur belongs to the trabecular tension area of the proximal femur, and the force is tension (Stiehl et al., 2007; Nawathe et al., 2014). Internal fixation design must resist tension. Scholars (Ding et al., 2022) have developed the triangular support intramedullary nail to fix the intertrochanteric fracture of the femur, which proposes the triangular fixation theory of the proximal femur to better resist the tension in the femur. Internal plants placed in tension zones to resist the transverse tension of the femur, reduce the shear force, and reduce the stress on the intramedullary nail—particularly the shear force of the screw blade. This biomechanical feature can reduce the likelihood of postoperative internal fixation failure.

Currently the standard of peritrochanteric fracture treatment is stable fixation, which allows early full weightbearing mobilization of the patient (Macheras et al., 2012), However, most clinical patients may not be able to walk with full weight in the early postoperative period. The peak hip joint contact force during walking is 3.5–5 times of body weight, and studies conducted after hip prosthesis placement have shown that the peak hip joint contact force during the gait cycle is about 300% of body weight, but the maximum contact force reaches 409% of body weight in patients with gait disorders, and the hip joint peak force is higher when walking up and down stairs. In the case of unreasonable daily activities, such as accidental tripping, it can reach 900% (Bergmann et al., 2001). Therefore, patients must avoid unsafe activities in the early postoperative period. Based on previous studies, 4.2 times of body weight was applied to the femoral head (Fan et al., 2022). The peak joint reaction force during walking was selected for measurement to obtain the data at this limit state. In the follow-up study, it is possible to consider the actual weight of the patient and conduct a more detailed stratified load study, which may enhance the accuracy and comprehensiveness of the study.

In contrast to steel wires and plates, OBS can also be placed in a suitable position through shaping, but in OBS, the screw position is not completely fixed because the position of the connecting rod and fixing block is not fixed, and the screw is fixed according to the position of the fixing block, allowing us to place the nail flexible The position distribution of the screws is shown in the OBS model (Figure 5). Three screws are located in the front and back of the femur, and two screws are located at the proximal end, relative to the spatial distribution of the connecting rod and intramedullary nail; therefore, the lateral wall is fixed in multiple planes, and the length of screw placement exceeds that of the steel plate, even double-layer cortical fixation, and fixation is more reliable than single cortical fixation (Lenz et al., 2012; Lenz et al., 2016). We have combined OBS with PNFA in clinic, but there may be differences between the finite element analysis and the actual clinical use, and the analysis results need to be verified by clinical use in the future.

This study has several limitations. First, the femur and the implants exhibit anisotropic behavior. To reduce the complexity of the analysis, the materials were simplified as homogeneous, isotropic, and elastic materials. Second, our model exclusively conducts static analyses and does not encompass dynamic assessments. Consequently, future investigations should incorporate various forms of dynamic loading. Intertrochanteric fracture of femur mostly occurs in elderly women, so there may be some deviation in the research. In this study, we exclusively compared the biomechanical properties of OBS in conjunction with PFNA and simple PFNA fixation for intertrochanteric fractures with lateral wall involvement. To gain a more comprehensive understanding of lateral wall fixation options for the femur, including steel plate and steel wire fixation, further research is warranted. Additionally, we did not delve into the selection of subdivided internal fixation methods based on the classification of lateral femoral wall fractures in this study. Subsequent research efforts should explore the nuances of different types of lateral femoral wall fractures and the corresponding choice of internal fixation techniques.

We conducted a biomechanical comparison between OBS combined with PFNA and PFNA alone for treating femoral intertrochanteric and lateral wall fractures. OBS was found to effectively reduce stress on the lateral wall of the femur, promoting the safe growth of bone tissue without internal stress shielding. Moreover, it significantly reduced the maximum stress of the intramedullary nail and minimized the overall displacement of the model. The personalized design allows multiple-plane fixation of the femoral lateral wall. According to the findings of our study, we recommend the utilization of OBS fixing the lateral wall of the femur in cases of intertrochanteric fractures combined with lateral wall fractures. This approach promises to enhance the biomechanical stability of the fixation, potentially leading to improved clinical outcomes. Further clinical studies are encouraged to validate these biomechanical results and provide valuable insights into the practical implications of this fixation technique.