In recent years, with the development of sports medicine, scholars have paid more and more attention to the biomechanical effect of fibula. Domestic and foreign scholars have conducted relevant studies on the biomechanical effect of fibula in lower limbs [9, 11–15]. Zahn et al demonstrated that in patients with severe osteoporosis the weight bearing of fibular is critical due to the reduced bone quality in the elderly . Moreover, they confirmed the advantage of an internal fixation method that restores the stability of the distal fibula in osteoporosis patients with distal fibular fractures. Jabara et al explained the importance of the stability of fibular and proximal tibiofifibular joint . They emphasized that neglect proximal tibiofifibular joint instability may be the reason for the failure of an reconstruction of the posterolateral corner or knee ligament. Through the study of the proximal tibiofibular joint, Calabro et al found that the fibula assumed the role of load-bearing and dispersing the torsion stress of the lower limb [12–14]. At the same time, patients with proximal tibiofibular joint dislocation had complications such as knee pain and weakness. Teresa et al described the kinematics of the proximal tibiofibular joint and its relation to the ankle and knee movements by an exploratory cadaver study .
According to the study of Morin, the combined fractures of the distal of tibia and fibula is a common orthopedic injury . Javdan et al described that fibular fractures in 77.7% of the cases are common with tibial fractures . However, it's still controversial about the necessity of fibular fixation in fibula and distal tibia fractures. Strauss et al has examined the effect of fibular fixation in cases of distal tibiafibula fractures and particularly in the setting of distal tibia fractures in both laboratory and clinical settings and has verified fibular fixation is helpful to maintaining the tibia fracture reduction . Previous studies have shown that effective fixation of fibula fractures improves the force line following internal fixation of tibial fractures and reduces tibial reduction failure [19–20]. Elhence et al recommended fibula fixation for all distal fractures when two fractures are in the same plane and the tibial fracture is relatively stable . However, Rouhani et al concluded that there was no advantage of the fixation of fibula to the treatment outcome of tibia diaphysis distal third fractures . However, the literature on the application of fracture mechanics to study the biomechanical effects of fibula in lower limbs is rare.
In recent decades, researchers have carried out a lot of experiments and studies on fracture problems [23–25]. This led to the emergence and development of fracture mechanics. At present, finite element analysis is used to study fracture, mainly considering the occurrence mechanism of fracture after falling external force, and by calculating Von Mises equivalent stress and combining with fracture failure criteria. However, the basis for judgment is limited to the starting point of fracture failure, which does not fully reflect the actual fracture situation. LS-DYNA software is the most famous universal explicit dynamic analysis program in the world, which can simulate various complex problems in the real world, and is especially 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, even in the simulation of muscle active response force. Lin et al described the influence of regional difference in bone mineral density on hip fracture site by fracture mechanics .
In our research,we found that the fibula carries about 7% of the axial load of the lower leg. A study using a biostatic model has found that the fibula bears 1/6 of the weight of the lower leg . The results of Trainotti showed that fibula bears about 6.4% of body weight . We believe that the differences in the results are due to differences in measurement methods.
At the same time, we compared the normal model with the fibula defect model and found that the tibia with the fibula defect was more prone to fracture and the complete fracture occurred faster. Under axial loading, fibula can disperse stress and delay the time of tibial fracture, but the presence of fibula does not affect the location of tibial stress concentration, and basically does not affect the direction and development of cracks.
In addition, Fan et al described that distal tibial fractures account for 37.8% of all tibial fractures . They believe the fractures of the distal tibia typically occur because of axial and rotational forces on the lower extremity. In our research, this was confirmed by the typical distal fracture of the tibia following axial loading.
There are some limitations to this study. In this fracture analysis, only one load vector was set, and the simulation of fracture caused by different external forces would be more helpful to understand the mechanism of tibial fracture. In addition, this study only made a mechanical comparison for the middle-aged people with normal bone. Bone mineral density and bone strength can affect the fracture type and stress distribution . Therefore, further study is needed for osteoporosis patients. Moreover, more biomechanical studies and related clinical research should be performed.