The Finite Element Analysis Of The Stability Of Osteotomy After Hallux Valgus Surgery Based On Wrapped Curtain Method External Fixation

BackgroundHallux valgus is a common deformity of foot, the incidence rate is about 10%, the main symptoms of Hallux valgus are foot bunions, metatarsophalangeal joint medial swelling and pain, walking difficulty, which seriously affects the quality of life. Traditional surgical treatment of hallux valgus have the shortcomings of large soft tissue injuries, higher cost of internal fixation or plaster external fixation, patients suffering, slow recovery, can not take care of themselves after surgery. Integrated traditional Chinese and Western Medicine minimally invasive treatment of hallux valgus have the advantages of simple operation, less pain, less complications, better curative effect etc.The treatment won the second prize of National Scientific and Technological Progress in 2002.Also won the gold medal in the "new thinking, new inventions, new technology" International Fair held in Germany recommended by Ministry of science and technology. Integrated traditional Chinese and Western Medicine minimally invasive treatment of hallux valgus was promoted to the country as one of national top ten outstanding project by the State Administration of Traditional Chinese Medicine. Currently there are more than 20 provincial and municipal hospitals carry out this technology. The excellent rate 98.5% confirmed by early more than 20,000 cases of hallux valgus patients followed up. The standardization system of diagnosis and treatment for hallux valgus has been formed by tutor team through continuous improvement, innovation and development for more than 20 years.Integrated Traditional Chinese and Western Medicine minimally invasive treatment of hallux valgus is the use of the first metatarsal head and neck oblique osteotomy. Traditional Chinese Medicine(TCM) manipulation of valgus deformity and dislocation of joint.According to the principle of "muscle bundle bone".based on Wrapped Curtain Method using a small plywood and paper pad clip principles and a "8"-shaped bandage fixed osteotomy end. Abandon the Western tradition methods such as plate and screws internal fixation and plaster external fixation method.The main technique points of the method lies in:1. The application of minimally invasive techniques in TCM foot and ankle surgery.2. The oblique osteotomy at the first metatarsal head and neck to correct the deformity.3. Chinese bone-setting techniques to correct deformities and joint dislocation.4. Based on a small plywood and paper pad clip principles and the "muscle bundle bone" theory, a "8"-shaped bandage fixed osteotomy end.In recent years, with the application of finite element analysis method in biomechanics, especially in the research of human skeletal structure of mechanics, traditional mechanics experiment almost can not be directly carried out. Therefore, in the mechanical simulation experiment finite element method(FEM) has become an effective method, the biggest advantage of the FEM is no damage to the organism, and can simulate the biomechanical behavior in living tissue. There is not limit to the geometry of the model, stress conditions, etc. With the development of technology, material parameters and related aspects continuous improvement. The simulation of the biomechanical environment and test accuracy is higher and higher.There are 26 bones, one pair sesamoid complex ligament, plantar fascia, tendons and other soft tissues in mechanical structure of the foot to maintain the three-dimensional structure of the foot. In function, foot and ankle support bearing, shock absorption, transfer movement and lever balance etc. Foot biomechanics research rises in recent years with the rising incidence of foot diseases and development of foot surgery in recent years. From a technical point of view, various measurement techniques and the rapid development of computer hardware and software provide the necessary conditions for foot biomechanical study, including motion capture systems, pressure platform. CT and MRI three-dimensional scanning technology, reverse engineering(RE) and finite element analysis(FEA) software software, etc. So that the accuracy of finite element model simulation in the foot biomechanics research is more and more high.Integrated Traditional Chinese and Western Medicine minimally invasive treatment of hallux valgus based on wrapped curtain method with "8"-shaped bandage and sub toe pad external fixation, Patients are able to weight-bearing after the operation. As soon as this method has been mentioned, some Western orthopedics experts questioned it. It is believed by modern medicine that the healing of osteotomy need to keep the stability between the sides of osteotomy to achieve optimal healing. When the human body are in the weight-bearing.foot load increases, especially in the first metatarsal. Some orthopedic surgeons believe that osteotomy without internal fixation and limiting activities will affect the stability of the osteotomy end, may delay the healing of the osteotomy end, and even nonunion occurs. But the fact is the treatment of hallux valgus does not cause osteotomy nonunion after 20 years of clinical application and more than 30,000 cases followed-up. Could minimally invasive technique for the treatment of hallux valgus based on wrapped curtain method with "8"-shaped bandage and sub toe pad external fixation can maintain the osteotomy effective fixed? Will early weight-bearing and walking affect the bone healing? Is the external fixation based on wrapped curtain method scientific? These questions need our theoretical research.At present, the FEA of hallux valgus is rarely reported, the majority of which are static simulation, so it is necessary for us to establish hallux valgus finite element model and do some research on the biomechanical mechanisms of treatment of hallux valgus, in order to further understand the stress distribution and displacement after hallux valgus surgery in different state (static and gait cycle), and to investigate the influence on the osteotomy stability and biomechanics based on wrapped curtain method external fixation.Purpose1. To establish and improve hallux valgus foot finite element model and simulate Integrated traditional Chinese and Western Medicine minimally invasive treatment of hallux valgus based on wrapped curtain method with "8"-shaped bandage and sub toe pad external fixation. To establish the finite element model after the operation of Integrated traditional Chinese and Western Medicine minimally invasive osteotomy and manipulation of valgus deformity.2. To research the stress distribution and displacement after the operation of Integrated traditional Chinese and Western Medicine minimally invasive osteotomy and manipulation of valgus deformity based on wrapped curtain method external fixation in different state (static and gait cycle).3. To observe the changes of angle and distance of osteotomy at different time points after operation based on wrapped curtain method external fixation.4. To evaluate the impact on osteotomy end stability after the operation of Integrated traditional Chinese and Western Medicine minimally invasive osteotomy and manipulation of valgus deformity based on wrapped curtain method external fixation. To improve the understanding its scientific nature and provide theoretical and experimental evidence for the treatment.Method1. The establishment of hallux valgus model after Integrated traditional Chinese and Western Medicine minimally invasive osteotomy and manipulation of valgus deformity1.1 Selected a young female volunteer of Hallux valgus, whose right foot Hallux Abductor Valgus angle(HAV) 24°, Intermetatarsal Angle (IMA) 13°, Proximal Articulator Set Angle angle(PASA) 7°, Distal Articulator Set Angle (DASA) 7°, the body weight was 58kg, no foot operation history and other deformities. Using CT to scan the right foot, layer thickness 1mm, interval 1mm, scanned from toe to heel. Keep the ankle joint in neutral position and no weight bearing during the scanning.1.2 Imported foot CT images in Mimics10.01, next Image segmentation and filling, Generating 3D model, Imported into Geomagic Studio 12.0 software, by surface fitting, solid model was generated, and then assembled the bones and ligaments, defined material properties in ABAQUS, all were set to single isotropic linear elastic material, meshed and generated free tetrahedral grid.Then all bones, cartilage, ligaments, etc. were assembled together. Established Rectangular model as the terrain model in ABAQUS, divided hexahedral meshes.1.3 Simulated hallux valgus patients in the balance standing, defining the Achilles tendon,plantar pressure, plantar friction as loading force, The upper surface of the supporting structure and plantar surface were defined as the contact relationship, the friction coefficient is 0.6. Fixed flat plate was completely restrained, double feet were in balance standing in neutral position, the upper end of the tibia and fibula were loaded. The static plantar pressure was measured in foot scan plantar pressure measurement system. The model was validated by comparing the results of the test and the finite element model.1.4 Using CATIA software simulating osteotomy in hallux valgus model, cut the inside of the first metatarsal head osteophytes, oblique cut in the first metatarsal head and neck. In horizontal plane the cutting line kept 20°angle with the perpendicular of axis of the first metatarsal, from distal inside to the proximal outside. In sagittal plane the cutting line kept 15°with the perpendicular of the axis of the first metatarsal, from distal dorsal to proximal plantar. Simulate manual reduction, the distal osteotomy end was pushed 3mm to the outside. Then simulated skin by mechanical loading, establish hallux valgus foot finite element model of Integrated traditional Chinese and Western Medicine minimally invasive osteotomy and manipulation of valgus deformity.2. Researched the stress distribution and displacement after the operation of Integrated traditional Chinese and Western Medicine minimally invasive osteotomy and manipulation of valgus deformity based on wrapped curtain method external fixation2.1 Using established hallux valgus osteotomy finite element model, Simulated wrapped curtain method with "8"-shaped bandage and sub toe pad external fixation by mechanical load mode in ABAQUS software. The elasticity modulus of bandage was 44.61 MPa.2.2 Restraint and load models:model with front loading constraints and conditions.2.3 Calculation of finite element model data:calculated and analysed the stress distribution,displacement,total stress (Miles Stress) and the total amount of displacement of the distal osteotomy plane four nodes (up, down, inside and outside).2.4 Data collection and statistical analysis:acquised with and without external fixation two conditions, comparion of displacement and stress values of osteotomy were made between two conditions.To observe and analyse the impact of external fixation based on wrapped curtain method with "8"-shaped bandage and sub toe pad on the osteotomy end stability. All experimental data were analysed by one way ANOVA in SPSS 13.0 statistical software.3. To research the stress distribution and displacement in different state (static and gait cycle) after the operation.3.1 Plantar reaction force-time curve and tibia axis with ground perpendicular angle-time curve were obtained by plantar pressure testing and three-dimensional motion testing synchronously,two kinds of gait analysis techniques,and were to determine reaction forces and the angle corresponding relationship.3.2 Constraints and loading model:The model based on the stance phase (after Initial Contact instant, the whole foot support phase, accelerated phase and push off) corresponding feet bear the vertical pressure were 110%,90%,110% of body weight were loaded. Model extrinsic foot muscles were through the mechanical loading simulation. Freedom of tibia and fibula was constraint, simulation model to face the vertical load. Vertical loading on the model was done by the simulation of ground.3.3 The calculated data of finite element model:The Von Miles Stress and the total displacement of the osteotomy were calculated and analysed in different periods of gait cycle, Statistical analysis were made.4. The X-ray study of the stability of osteotomy based on Wrapped Curtain Method external fixation after operationBy retrospective study, selected patients 63 cases (120 feet) of hallux valgus operated by minimally invasive osteotomy manipulation in Orthopedics Department 2 of Wangjing Hospital of China Academy of Chinese Medical Sciences from November 2014 to March 2015,postoperative based on "Wrapped Curtain" method by "8" bandage and sub toe pad extemal fixation, immediately after the operation,2 weeks,6 weeks,3 months were treated with feet weight-bearing X-ray examination, recorded Angle displacement index (Angle α, β) and displacement index(Distance M,N) values, and statistically analysed the difference between the angle and distance at different time points.Results1. A hallux valgus dimensional finite element model was established, model reconstructed bone, cartilage, intrinsic muscles, skin and other tissues, the total number of nodes was 209,832, the total number of units was 333,776. The static plantar pressure was measured in foot scan plantar pressure measurement system. Through the test results of finite element and plantar pressure measurement system comparison, pressure mainly concentrated in calcaneus, the second and third metatarsal, the force area was substantially the same.2. By means of mechanical load module in ABAQUS software, Simulated working conditions of external fixation based on wrapped curtain method with "8"-shaped bandage and sub toe pad. Within the 4 nodes in distal osteotomy plane, the maximum stress was 0.067 MPa without external fixation, the maximum stress was 1.258 MPa with the external fixation. Stress was mainly distributed in the outer edge of the osteotomy. The maximum absolute displacement was 0.363mm without external fixation, The maximum absolute displacement was 0.716mm with external fixation. The two largest displacement were both in the Z-axis direction. ANOVA statistical analysis confirmed that the 4 nodes absolute displacement and stress were significant different (P<0.01) with and without external fixation. Selected proximal and distal osteotomy surface 4 nodes correspond to each other, analysed the corresponding to the two nodes deformation distance. The maximum relative displacement was 0.10149mm without external fixation. While the maximum relative displacement was 0.046391mm with external fixation. ANOVA statistical analysis confirmed that the 4 nodes relative displacement were statistically significant (P<0.05) with and without external fixation.3. First peak moment:after Initial Contact instant,0.24s in the stance phase, and tibial axis whith ground vertical angle was -4.3 degrees, vertical loading force of 621N. The valley moment:the whole foot support phase,0.40s in the stance phase, tibial axis whith ground vertical angle was 4.5 degrees, vertical loading force of 564N. Second peak moment:under accelerated push off,0.63s in the stance phase, tibial axis whith ground vertical angle 27.3 degrees, vertical loading force of 632N.The finite element analysis of stance phase in gait cycle:The total displacement of the first peak conditions was 0.133mm, the Von Mises stress of 1.3 MPa. The total displacement of the valley conditions was 0.183mm, Von Mises stress of 3.4 MPa; The total displacement of the first peak conditions was 0.115mm, Von 24.8 MPa Mises stress. The relative displacement in The X-axis and Z-axis,and total displacement in different conditions had significant difference (P<0.01), but there was no difference of Y axial displacement (P>0.05).4. In Tests of Between-Subjects Effects,Angle a and Distance M values comparisons had no statistical difference in different time points (P>0.05),while Angle β, Distance N values were statistically different (P<0.05), but in Post Hoc Tests, Angle p and Distance N values comparisons between groups had no statistical difference (P>0.05)Conclusion1. By CT scan, reverse engineering software and FEA software, we successfully establish a three-dimensional finite element model and minimally invasive osteotomy and TCM manipulation of hallux valgus model. The reliability test of the finite element model is carried out by the foot scan plantar pressure measurement system and the reliability of the model is verified.2. It is confirmed that the wrapped curtain method external fixation system could effectively reduce osteotomy displacements by finite element analysis, which keeps osteotomy fretting, moderate stress, does not affect fracture healing of osteotomy.3. It is confirmed in the gait cycle by gait analysis technique of the three instants that the wrapped curtain method could maintain osteotomy relatively stable, moderate stress, help osteotomy healing, which is a safe and effective method of external fixation.4. It is confirmed from clinical practice that curtain wrap method could maintain the osteotomy stability, with the presence of micro-osteotomy moving, fracture healing are indirect,which conforms to elastic fixed criterion.5. By the finite element analysis of the biomechanical mechanism of Integrated Chinese and Western medicine minimally invasive technique for the treatment of hallux valgus, we improve the understanding its scientific nature and provide theoretical and experimental evidence for the treatment.Innovation1. Establish a minimally invasive osteotomy and TCM manipulation of hallux valgus finite element model and the external fixation finite element model based on wrapped curtain method, which open up a new way for evaluation of hallux valgus surgical methods and for the study of prognosis.2. The combination of finite element analysis software, three-dimensional motion testing system, and Foot scan plantar pressure measurement system, Simulate the conditions in gait cycle phase. Static and dynamic three-dimensional finite element analysis prove that wrapped curtain method external fixation is scientific, which provides an experimental basis in enriching and improving the theory of Integrated traditional Chinese and Western Medicine treatment of hallux valgus.