Experimental Study On The Anterior Column Injury Pilon Fracture Fixed By Prying And Reducing With Horseshoe-ring External Fixation

Pilon fracture is a comminuted fracture of the distal tibia with a serious injury to the tibiotalar articular surface.Clinically,it is often treated with open reduction and internal fixation.This operation has high requirements for soft tissue and a high incidence of postoperative complications.The external fixation scheme has low requirements and little influence on the soft tissue around the fracture and can be quickly applied in an emergency.It is suitable for fixing serious Pilon fractures.Limited internal fixation combined with an external fixator is often used to treat the Pilon fracture,reduce the incidence of complications and improve the postoperative curative effect.However,patients still need to cut and place internal plants to further damage the soft tissue.The external fixator has the function of adjustable and stable fixation and has little damage to soft tissue.At present,some scholars at home and abroad use the external fixator for the final fixation of the Pilon fracture.It is found that it has a high effective rate of the Pilon reduction,a high excellent rate of the postoperative functional score,and is suitable for patients’ early weight-bearing rehabilitation.This subject observed the cases of the Pilon fracture treated with a horseshoe-ring external fixator and found the existing problems.Combined with the"golden needle bone pulling" prying reduction technology of traditional Chinese medicine bone injury in the first Department of the trauma of Wang Jing hospital,the difficulty of closed reduction of articular surface was solved.Combined with the independently innovative Horseshoe-ring external fixator,the treatment scheme configuration of the Pilon fracture external fixator was proposed,which is suitable for the common anterior column injury Pilon fracture in a clinic.This scheme provides stable support by prying the reduction needle,and solves the failure of the fixed articular surface of the half-ring external fixator.The study makes a preliminary experimental study for the theoretical basis of the scheme.Firstly,the artificial bone model is prayed and reset,the horseshoe-ring external fixation configuration is fixed,and its effectiveness is tested by mechanical test.Then use the finite element analysis method to simulate the mechanical theoretical basis of the scheme.By comparing the fixation performance of Unilateral,Ilizarov ring external fixation,and horseshoe-ring external fixation frame,and analyzing the biomechanics of prying reduction Horseshoe-ring external fixation frame in the treatment of Pilon fracture,to explore the effectiveness,stability,and mechanical advantages of the scheme,so as to provide a new external fixation treatment scheme for the treatment of Pilon fracture with anterior column injury.1 Artificial bone test1.1 ObjectiveTo verify the axial stability of prying reduction,horseshoe ring external fixation and frame fixation of anterior column injured Pilon fracture.1.2 MethodsSix artificial bone fracture models of the Pilon fracture with anterior column injury were prepared according to the four-column theory and fixed with prying reduction and a horseshoe-ring external fixator.Install the corresponding proximal tibia,medial tibia fracture block,anterior tibia fracture block,and distal fibula fracture block cursors,place the model into the microcomputer electronic testing machine,and load the load from ON to 70N to 350N to simulate the physiological walking load,load each foot for 3 times,and take the average displacement dynamically captured by each cursor.1.3 ResultsUnder the stress of 70N,the average displacement of the whole fracture fixation model was 1.12±0.53mm;Under 350N stress,the average displacement of the whole fracture fixation model is 3.79±0.87mm.Under the two loads,there was no significant difference in the relative displacement of coordinate axes in all directions(P>0.05),and the displacement was less than 2mm.The fixation of the fibular fracture block was not ineffective.The displacement direction of the lateral fracture block of the distal tibia shifted from posterior,upper,medial,forward,lower and lateral.Only the mean change of sagittal position(0.28 ±0.80mm vs-1.59±1.10mm)had statistical difference(P<0.05).The displacement direction of the medial fracture block of the distal tibia shifted from posterior,upper,medial,forward,lower and lateral.Only the change of the mean value of sagittal position(-0.22±0.52mm vs-1.96±0.76mm)had statistical difference(P 0.05).1.4 ConclusionThis scheme is stable for the bone fracture of the distal tibial articular surface of Pilon fracture.When 3 50N full weight-loading,the relative overall displacement of the fracture block in the sagittal plane is large,and the fracture is not ineffective.This scheme is an effective external fixation scheme suitable for the anterior column Pilon fracture and has good axial mechanical stability.2 Finite element analysis2.1 ObjectiveTo study and establish a model of anterior column injury Pilon fracture combined with fibula fracture with clinical guiding significance.The mechanical mechanism was obtained by simulating prying reset in the model.The fixation performance of the Unilateral,Ilizarov ring external fixator and horseshoe-ring external fixator were compared and analyzed.To analyze the biomechanics of prying reduction and horseshoe-ring external fixator in the treatment of the Pilon fracture with anterior column injury.2.2 Method2.2.1 Finite element analysis of the horseshoe-ring external fixator and common external fixator for fixation of anterior column injured Pilon fracture40 cases of clinical Pilon fracture with anterior column injury were collected.The corresponding fracture lines were measured,and the corresponding literature was consulted to determine the distribution area of fracture lines in the tibial talar plane.Combined with the literature and the height of fracture lines,the finite element model osteotomy was carried out to construct the finite element model of Pilon fracture with anterior column injury.The effectiveness of modeling was verified by comparing it with a load of previous literature.On the fracture model,Unilateral,Ilizarov ring,and horseshoe ring external fixators were assembled respectively to fix the metatarsal and calcaneus.Two loading distances of 70N and 350N were loaded vertically downward on the cross-section of the tibia and fibula to simulate the swing stage and static standing stage of gait.The stress and displacement of each needle path,each fracture block,and each external fixator were compared,and the mechanical characteristics of Pilon fracture with anterior column injury fixed by each external fixator were analyzed.2.2.2 Finite element study on prying reduction of the articular surface of Pilon fracture with anterior column injuryIn the fracture model,each fracture block was displaced 2mm in each direction to simulate the minimum displacement and joint instability in the surgical indications.Based on the principle of prying reduction and fracture fixation,prying Kirschner wires are assembled in each fracture block respectively,and the horizontal plane of x-axis displacement is positive to the lateral malleolus;The y-axis is the coronal plane,and upward is positive;The z-axis is the sagittal plane,the forward is positive,the coordinate system is set,the displacement reset is at the speed of 2mm/s,and the time is set to 1s.Take 1/3 points outside the prying needle as the stress output point to output the prying reset mechanics.2.2.3 Finite element analysis of horseshoe ring external fixator combined with local puncture for fixation of Pilon fracture with anterior column injuryA prying reduction Horseshoe Ring external fixator was installed on the fracture model to fix the metatarsal and calcaneus,and two loading distances of 70 N and 350 n were loaded vertically downward on the cross-section of the tibia and fibula to simulate the swing stage and static standing stage of gait,analyze the stress and displacement of each prying needle,each fracture block and external fixation of this scheme,and analyze its mechanical characteristics.2.3 Results2.3.1 Finite element analysis of the horseshoe-ring external fixator and common external fixator for fixation of anterior column injured Pilon fractureAn effective model of Pilon fracture with fibula fracture with anterior column injury was established.It was found that the vertical displacement of foot arch in the finite element model was close to that in the literature;Plantar pressure and stress distribution were similar to those measured by normal healthy people;The stress distribution of external fixator and needle path is similar to that in the literature,and the model verification is effective.The needle track stress of the Unilateral external fixator under two kinds of loads is small;The stress of other needle paths is small except for the half needle of tibial thread(70N:249.94MPa;350N:249.03MPa)of horseshoe ring external fixator;Except for the proximal tibia(70N:541.14MPa;350N:548.49MPa)of Ilizarov ring external fixator,the stress of other needle paths is small.In the stress results of Kirschner wire,the half needle of the thread of the horseshoe-ring external fixator is large(70N:645.56MPa;350N:646.61MPa),and the stress of metatarsal bone is large(446.76MPa);Ilizarov ring external fixation has large stress in the proximal tibia(70N:609.18MPa;350N:607.01MPa).The stress distribution diagram shows that the overall and needle path bone stress of the Unilateral external fixator is concentrated,the stress of the Ilizarov ring external fixator is concentrated in the proximal tibia,and the stress of the horseshoe-ring external fixator is dispersed.The stress displacement at the fracture end shows that the maximum displacement of the Unilateral and Ilizarov ring external fixator under 350N load is 6.36mm and 8.67mm,which may cause fixation failure.The overall maximum displacement of the horseshoe-ring is less than 2mm.The horseshoe ring external fixator is more stable and the mechanics are more dispersed.2.3.2 Finite element study on prying reduction of the articular surface of Pilon fracture with anterior column injuryKirschner wire prying can effectively reduce fracture displacement.The reduction order is to reduce the medial fracture block first,the anterolateral fracture block,and then the anterior fracture block.The stress of the medial deltoid ligament is the largest when it is restored,so it can play a role in ligament restoration.2.3.3 Finite element analysis of horseshoe ring external fixator combined with local puncture for fixation of Pilon fracture with anterior column injuryThe overall maximum stress of the external fixator is less than the fracture yield stress of the Kirschner wire,and the configuration is stable.The displacement diagram shows that the overall stability of the proximal tibial threaded half needle external fixator is the most important.The prying reduction needle transmits the stress of the fracture block to the Horseshoe Ring and plays the role of prying support.Under the two loads,the fretting of each fracture end is within the range of favorable fracture healing.The stress displacement results of the articular surface show that there is no 1mm step in displacement under 350N load,the fracture is not invalid,and the cartilage is not easy to be damaged.2.4 ConclusionThis study effectively constructs a clinically representative finite element model of Pilon fracture with anterior column injury.The prying reduction sequence is first medial,then anterolateral,and finally the front can be effectively reduced.The prying reduction needle transmits the stress of the fracture block to the horseshoe ring to play the role of prying support.The horseshoe ring external fixator provides stronger stability than the Unilateral and Ilizarov ring external fixator.The treatment scheme of prying reduction Horseshoe Ring external fixator can produce the stress and micro-movement at the fracture end conducive to fracture healing during weight-bearing,which is in line with the principle of combining dynamic and static treatment of fracture and has biomechanical advantages.