Dynamic Finite Element Analysis Of Calcaneal Fractures

BackgroundThe calcaneus is the largest tarsal bone in a human foot.It plays an important role in the body’s weight-bearing and walking functions.Calcaneal fracture is the most common tarsal fracture,usually caused by a sudden high-energy impact on the heel.The most common causes of injuries are falls from heights,car accidents and explosions from the heel of the feet.Intra-articular calcaneal fracture is a serious and complex injury that often leads to functional disability of the lower limbs.At present,the analysis of the calcaneal fracture pattern was the result of direct observation from the experiment,and there were still some differences.The stress change of the calcaneus during the fall remains unclear,and quantitative analysis is lacking.There is no relevant research on the mechanical changes of the calcaneus under different injury models is still unknown.ObjectivesWe aimed to use several 3D reconstruction softwares to build multiple finite element models including the talus,calcaneus,ligament,and baseboard-The analysis method of finite element explicit dynamics was used to quantitatively analyze the stress distribution and size changes of the calcaneus in the two injury states of the heel falling on the ground and the talus impacting the calcaneus and the bottom plate impacting the heel.It was used to verify the pattern of calcaneal fracture,analyze the factors affecting calcaneal fracture,and provide research methods and theoretical basis for the study of other fractures.MethodUsing CT data from a healthy male volunteer,three-dimensional reconstruction software such as Mimics,Geomagic studio,and Solidworks were used to establish three-dimensional models of the talus and calcaneus.A static mechanical model of the calcaneus,the model of the talus impacting the calcaneus at a speed of 5-10m/s with varus and valgus 5°-20°/s,and the baseboard impacting of the heel at a speed of 5-10m/s with the calcaneus varus and valgus 5°-20°/s was established using the software of Ansys Workbench.Finite element explicit dynamics method was implemented to solve the models.Stress values of the posterior,middle,and anterior subtalar articular surface,calcaneocubic articular surface,bottom of the calcaneal body,medial and lateral cortex under each initial condition were extracted.The stress changes and stress distribution of various parts of the calcaneus under these different conditions change were analyzed.ResultsThe static mechanical model of the calcaneus,the heel-falling model and the baseboard impacting heel model were established respectively.The results of static analysis verified the validity of the calcaneal model.In the heel-falling model,the posterior subtalar articular surface reached the peak stress first when the talus impacted the calcaneus,and the stress was mainly concentrated on the posterior subtalar articular surface,anterior subtalar articular surface,medial cortex and Gissane angle.With the increase of the impact velocity of the talus,the stress increased range of each part was from 7.11%to 140.58%,and the parts where the stress was concentrated and the order of stress peaks had changed.Stress changes of the calcaneus during talar varus and valgus were from-5.50%to 9.90%and-1.75%to 4.70%,respectively.The absolute value of the stress change was small.In the model of the baseboard impacting the heel,the middle subtalar joints and the Gissane angle reached the stress peak first.The stress was concentrated on the posterior subtalar articular surface,the calcaneocuboid articular surface,the bottom of the calcaneal body,the Gissane angle,and the medial cortex.With the increase of the impact speed of the baseboard,the stress increased range of each part was 37.75%to 269.00%,and the part where the stress was concentrated and the order of stress peaks had changed.The magnitude of stress changes during calcaneus varus and valgus was from-8.34%to 12.77%and-20.56%to 2.51%,respectively.However,the absolute value of stress change was small.ConclusionThe dynamic finite element model can reflect the stress quantity and distribution changes of the calcaneus in a very short period of time under two injury status of heel-falling and baseboard impacting the heel,and validated calcaneal fracture pattern.Speed was the most important factor leading to calcaneal fractures.The magnitude of stress and the time sequence of stress peaks appearance may be important factors in determining the starting location and moving towards of the fracture.This method can be widely used in the research of fracture patterns and injury protection.