Foot and ankle injuries were usually caused by high energy falls in many people . People who were healthy and active had a higher risk of falling. Because they might perform more dangerous activities, such as climbing ladders to roofs . The heel drop was a rather quick process. During this process, there was a considerable reaction force between the foot and the ground. Studies had found that this force was about 8 to 14 times the body weight of the human body . When the impact load exceeded the endurance limitation of the human musculoskeletal system, damage would occur. Researching the biomechanics of the calcaneus during this process was critical for understanding the mechanism of high energy trauma in the hind foot.
The main finding of this study was that with the increase of the velocity, the amplitude of the stress increased in each area of the calcaneus and the location of the stress concentration changed. The speed when the foot falling to the ground was related to the height of the fall, which determined the impact load at the heel when landing . The impact velocity of the foot during walking and running was between 0.52 m/s and 0.72 m/s . In sports such as skiing, impact velocity might reach 14.0 m/s at a drop height of 10 meters . Funk et al.  found that about 93% of the specimens had calcaneal fractures under an impact of 5.0 m/s. This study found that with the increase of the impact velocity of the talus, the stress of the calcaneus also increased significantly. The stress of the medial wall, lateral wall and calcanecubic joints increased the most. Falling speed was the most important factor leading to calcaneal fractures. For every 1m/s increased in speed, the stress of each area of the calcaneus could increase by about 50% at most. Therefore, reducing the influence of the talus on the calcaneus during a fall was the principal way to reduce calcaneal fractures.
Yoganandan et al.  simulated the intra-articular and extra-articular fractures of the calcaneus by applying axial loads on the feet of the cadaver specimen, and conducted experimental studies on the loads required to produce calcaneal fractures. It turned out that the greater the loads, the easier the damage was the calcaneus. Another study had shown that axial compression was dominant in calcaneal fractures, and as the impact speed increased, the chance of calcaneal injury increased. However, stress changes of the calcaneus were not reported in these studies. This study performed a quantitative analysis. The results of this study reflect the relationship between the speed and stress of various regions of the calcaneus, as well as the relationship between the stress and time. With increasing the speed of the talus, the stress increasing in various regions were not consistent due to the anatomical characteristics of the calcaneus. This resulted in different areas of calcaneal fractures at different speed. Therefore, calcaneal fracture lines were diverse.
Another finding of this study was that the initial positions of calcaneal fractures might be related to the sequence of stress peaks. There were still many controversies about the various position and direction of fracture lines, even primary fracture lines [16, 18]. The comminution and displacement of calcaneal fractures, and the combination of various fracture lines produced various fracture morphology. The study of Utheza et al.  believed that the main fracture line was variable, but always centered on the sustentaculum tali. Warrick et al.  believed that the fracture line extended forward and outward from a point on the medial wall of the calcaneus to various positions behind the sustentaculum tali. In this study, we found stress concentrations in the posterior, anterior, and intermediate subtalar joints, the medial wall, and the Gissane angle. These stress concentration locations were basically the same as the locations of fracture in the model proposed by Carr et al. . Obviously, when the stress peak appeared early and the regional stress exceeded the limit load of the bone, the starting point of the calcaneal fracture might appear at this time. As the stress concentration areas of the calcaneus increased, the sites of possible fracture increased, which led to compound fracture lines.
There were some shortcomings in this study. First of all, the forefoot, midfoot and heel soft tissues were not created in this study. In fact, the soft tissues of the foot and many joints could absorb energy. The damping properties of muscles, skin and cartilage could reduce the stress, transfer and consume high energy generated by the impact process. However, these factors did not affect the mechanical characteristics of the talus on the calcaneus. Secondly, the human weight was not applied to the calcaneus. The results obtained could roughly reflect the calcaneal stress distribution and the degree of change, but the conclusions have limitations. In fact, impact injury of the calcaneus was a very complicated process. A more accurate finite element model, more precise material properties and boundary conditions were needed in order to make the simulation technology closer to reality. More research will be needed in the future.