In recent years, with advances in sports medicine, researchers have paid increasing attention to the biomechanical effects of the fibula. Domestic and foreign researchers have conducted relevant studies on the biomechanical effects of the fibula in lower limbs[9, 11–15]. Zahn RK et al.  have demonstrated that in patients with severe osteoporosis, the weight bearing of the fibula is critical, owing to the diminished bone quality in older people. Moreover, the authors confirmed the advantage of an internal fixation method that restores the stability of the distal fibula in patients with osteoporosis with distal fibular fractures. Jabara et al. have explained the importance of the stability of the fibular and proximal tibiofifibular joint. They have emphasized that neglecting proximal tibiofifibular joint instability may be the reason for the failure of a reconstruction of the posterolateral corner or knee ligament. In studying the proximal tibiofibular joint, Calabro et al.[12–14] have found that the fibula had roles in load-bearing and dispersing the torsion stress on the lower limb. Moreover, patients with proximal tibiofibular joint dislocation have complications such as knee pain and weakness. Alves-da-Silva T et al. have described the kinematics of the proximal tibiofibular joint and its relationship to ankle and knee movements in an exploratory cadaver study.
According to a study by Morin, combined fractures of the distal of tibia and fibula are a common orthopedic injury. Javdan et al. have described that 77.7% of fibular fractures occur together with tibial fractures. However, the necessity of fibular fixation in fibular and distal tibial fractures remains controversial. Strauss et al. have examined the effects of fibular fixation in distal tibialfibular fractures, particularly distal tibial fractures, in both laboratory and clinical settings; their results have verified that fibular fixation is helpful in maintaining tibial fracture reduction. Previous studies have shown that effective fixation of fibular fractures improves the force line after internal fixation of tibial fractures and decreases tibial reduction failure[19–20]. Elhence et al. have recommended fibular fixation for all distal fractures when two fractures are in the same plane, and the tibial fracture is relatively stable. However, Rouhani et al. have concluded that there was no advantage of fixation of the fibula in the treatment outcomes of tibial diaphysis distal third fractures. However, the literature on the application of fracture mechanics to study the biomechanical effects of the fibula in lower limbs is scarce.
In recent decades, researchers have performed many experiments and studies on fracture problems[23–25], thus resulting in the emergence and development of fracture mechanics. At present, finite element analysis is used to study fracture, mainly by considering the mechanism of fracture after external force from falling, and by calculating the Von Mises equivalent stress and combining it with fracture failure criteria. However, the basis for judgment of Von Mises equivalent stress is limited to the starting point of fracture failure, which does not fully reflect the actual fracture situation. LS-DYNA software, the most widely used universal explicit dynamic analysis program worldwide, can simulate various complex problems in the real world and is particularly suitable for solving nonlinear dynamic impact problems of various nonlinear structures. At present, LS-DYNA software is widely used in the field of dynamic analysis, and is even used in the simulation of muscle active response force. Lin et al. have described the influence of regional differences in bone mineral density on hip fracture sites, on the basis of fracture mechanics.
In our research, we found that the fibula carries approximately 7% of the axial load on the lower leg. A study using a biostatic model has found that the fibula bears one-sixth of the weight on the lower leg . The results of Trainotti et al. have shown that the fibula bore approximately 6.4% of the body weight. We believe that the differences in the results were due to differences in measurement methods.
We additionally compared the normal model with the fibular defect model and found that tibias with fibular defects were more prone to fracture, and complete fracture occurred faster. Under axial loading, the fibula can disperse stress and delay the time of tibial fracture, although the presence of the fibula does not affect the location of tibial stress concentration, and essentially does not affect the direction and development of cracks.
In addition, Fan et al. have reported that distal tibial fractures accounted for 37.8% of all tibial fractures. They believed that fractures of the distal tibia typically occurred because of axial and rotational forces on the lower extremity. In our research, this hypothesis was confirmed by the typical distal fracture of the tibia after axial loading.
There were some limitations to this study. In this fracture analysis, only the load vector was set; the simulation of fractures caused by different external forces would be more helpful to understand the mechanism of tibial fracture. In addition, this study performed a mechanical comparison in only middle-aged people with normal bones. Bone mineral density and bone strength can affect the fracture type and stress distribution. Therefore, further study is needed in patients with osteoporosis. More biomechanical studies and related clinical research should be performed.