Finite Element Analysis Of Screw Fracture Of Middle And Lower Tibia Combined With Posterior Malleolus With Four Internal Fixation Methods

Background:Middle and lower 1/3 spiral fracture of tibia combined with posterior malleolus fracture is a special type of compound fracture with a high incidence and it often occurs in low energy trauma.Due to the injury mechanism of the spiral fracture of the middle and lower 1/3 of the tibia combined with posterior malleolus fracture,the displacement of the posterior ankle fracture is often not obvious,which is hard to be found in conventional X-rays and usually misdiagnosed.The incidence of traumatic arthritis is greatly increased in the case of a spiral fracture of the middle and lower 1/3 of the tibia and a massive fracture of the posterior ankle.Currently,there is no unified treatment plan for the treatment of the middle and lower 1/3 spiral fracture of the tibia combined with the posterior malleolus fracture,the main treatment plans are as follows:tibial intramedullary needle combined with posterior ankle plate,tibial intramedullary needle combined with posterior ankle hollow nail,tibial minimally invasive plate combined with posterior ankle plate,tibial minimally invasive plate combined with posterior ankle hollow nail.At present,there is no clinical conclusion about which method is the best among the four internal fixation methods.There are many clinical efficacy studies of four internal fixation methods,but there is a lack of finite element simulation of biomechanical effects.Objective:Four biomechanical model types of internal fixation were established to treat the spiral fracture of the middle and lower 1/3 of the tibia combined with posterior malleolus fracture,which concludes tibial intramedullary needle combined with posterior ankle plate,tibial intramedullary needle combined with posterior ankle hollow nail,tibial minimally invasive plate combined with posterior ankle plate,tibial minimally invasive plate combined with posterior ankle hollow nail,then the biomechanical model of spiral fracture of the middle and lower 1/3 of the tibia combined with posterior malleolus fracture is analyzed by finite element biomechanics analysis software.Finally,the models and analysis can provide the proof for the clinical treatment of spiral fracture of the middle and lower 1/3 of the tibia combined with posterior malleolus fracture.Methods:Establish a spiral fracture model of the middle and lower 1/3 of the tibia and a posterior malleolus fracture that accounts for 50% of the distal articular surface of the tibia by the three-dimensional finite element software,and add the four biomechanical model types of spiral fracture of the middle and lower 1/3 of the tibia combined with posterior malleolus fracture,tibial intramedullary needle combined with posterior ankle plate,tibial intramedullary needle combined with posterior ankle hollow nail,tibial minimally invasive plate combined with posterior ankle plate,tibial minimally invasive plate combined with posterior ankle hollow nail,to the established model.Then apply the corresponding constraints and loads of the four groups of models(vertical axial stress 1000N;torsional stress10N)to simulate the human body’s situation of force and displacement after the operation of middle and lower 1/3 spiral fracture of the tibia combined with a massive fracture of the posterior ankle under the same movement mode,finally analyse the experimental results for comparative analysis.The setting standards of experiment are:(1)The fracture displacement of the end of the middle and lower 1/3 of the tibia and the posterior malleolus fracture is greater than 1mm,which is not conducive to fracture healing,and the fracture displacement greater than 2mm can increase the incidence of traumatic arthritis;(2)the stress of tibial intramedullary needles and locking nails,tibial plates and screws,posterior ankle hollow nails,posterior ankle plates and screws,greater than 450 MPa can cause irreversible deformation of the internal fixation;internal fixation stress greater than 600 MPa can cause the internal fixation to break;(3)tibia bone stress greater than 120 Mpa can lead to bone stress absorption.Results:Through the comparative analysis of data of four types internal fixation output by Ansys17.0,tibial intramedullary needle combined with posterior ankle plate,tibial intramedullary needle combined with posterior ankle hollow nail,tibial minimally invasive plate combined with posterior ankle plate,tibial minimally invasive plate combined with posterior ankle hollow nail,the conclusions are as follows:(1)Comparing the four groups of internal fixation methods,the displacement of the broken ends of the middle and lower 1/3 tibial fractures combined with the posterior malleolus fractures were all less than 1mm,which do not reach the setting standards of 1mm and 2mm.(2)The stress values of the fracture ends of the four groups of internal fixation are all less than the setting standard of 120 Mpa under two different situations of loads.And the stress at the fracture end of the posterior malleolus fracture in the tibial intramedullary needle combined with posterior ankle hollow nail group was significantly reduced compared with the other three groups.(3)Under two different situations of loads,the maximum stress value of the four groups of internal fixation methods is less than 450 Mpa,and the four groups of internal fixation methods do not reach the setting standards of450 Mpa and 600 Mpa.The maximum stress value of the tibial internal fixation in the tibial intramedullary needle combined with posterior ankle hollow nail group was smaller than the other three groups.Conclusion:(1)The results of the four different internal fixation methods under the two different situations of force loads did not exceed the setting standards in this article,and there was no obvious fracture displacement,broken nails and broken steel plates.(2)Both groups,the tibial intramedullary needle combined with posterior ankle hollow nail group and the tibial minimally invasive plate combined with posterior ankle hollow nail group,performed better over the other two groups in terms of stress of the fracture end and internal fixation stress distribution,so the stability of fixing of these two groups are higher than the other two groups.(3)The tibial intramedullary needle combined with posterior ankle hollow nail group has better distributed stress,better anti-axial and torsional loading ability.Comparatively speaking,the tibial intramedullary needle combined with posterior ankle hollow nail group has more advantages,and the surgical method is more minimally invasive.