| Articular cartilage is a kind of viscoelastic soft tissue with high moisture content and porosity.It has unique properties such as shock absorption and low friction force,and occupies a special position and function in the joint functional structure of human body.Because of articular cartilage movement and poor regeneration ability that hemal,lymphatic canal and nerve organization is lacking.Damaged cartilage after injury cannot repair normally.Therefore,it is of great scientific significance and clinical value to study the biomechanical mechanism of articular cartilage injury and evaluate the effect of cartilage repairing dynamically and objectively.The injury of articular cartilage is closely related to the biomechanical environment of subchondral bone.Articular cartilage is composed of a small number of chondrocytes and a large amount of extracellular matrix of chondrocytes.The matrix is mainly composed of collagen fibers and glycoproteins.From the joint surface to the bone marrow cavity,articular cartilage is divided into four layers:the superficial layer,the transitional layer,the columnar layer,and the calcified layer.The layers are tightly coupled.The accumulation of local compression and friction can lead to cartilage ossification,fibrosis,cracks,etc.Sports injury or fracture can cause different degrees of acute injury to articular cartilage.During a normal gait cycle,the knee cartilage bears the weight of the body's axial compression during the standing phase,and the knee cartilage bears both axial compression and torsion in the case of squatting or body torsion.Therefore,the biomechanical environment of all parts of the knee joint,especially the femoral condyle,is closely related to the biomechanical mechanism of cartilage injury in the knee joint.Acute cartilage injury of the knee refers to cartilage injury caused by acute sports injury or fracture which involving articular surface,IKDC score and Lysholm score of knee joint function are common scoring methods to evaluate knee joint function,but they have the disadvantages of subjective evaluation,unquantifiable and dynamic evaluation.MRI is the most commonly used objective method to evaluate cartilage injury repair.MOCART score for articular cartilage transplantation and T2 mapping for cartilage injury are also common evaluation methods.However,MRI has the disadvantage of relying on personal experience,being expensive and unable to observe dynamically and so on.How to explore the relationship between the repair of acute cartilage injury and the motor function of knee joint through in vivo kinematics method,so as to evaluate the repair effect of cartilage injury indirectly,objectively and dynamically,which can guide the optimization of the diagnosis and treatment program of acute cartilage injury.At present,domestic and foreign studies of this subject are relatively rare.Therefore,in order to explore the biomechanical mechanism of knee cartilage injury in sports,and to further study in vivo kinematic evaluation method of knee cartilage injury repair based on gait,we conducted this study.We divided the study into two parts.Part i:the biomechanical study of femoral condylar cartilage under normal gait.Part ii:in vivo kinematic study of cartilage repair after type C fracture of femoral condyleChapter 1:the biomechanical study of femoral condylar cartilage under normal gait[Background]The biomechanical characteristics of bone joints are closely related to the traumatic mechanism of intra-articular structural injury.In order to guide the clinical development of the prevention and treatment of such diseases,it is necessary to maximize the simulation of the biomechanical environment of bone and joint movement in normal human body.[Objective]To establish a finite element biomechanical model of knee joint including femoral condyle cartilage,and study the dynamic biomechanical characteristics of femoral condyle cartilage in normal gait cycle.[Methods and Results]The knee joint of a healthy adult volunteer was scanned with 64-slice CT and 3.0T MRI 3D sequence.The scanned DICOM data of knee joint were imported into the Mimics 3D modeling software,and the 3D anatomical models of bone tissue and soft tissue were reconstructed respectively by using the functions of threshold value and regional growth.The bone tissue and soft tissue models were assembled in Mimics software to generate a 3D model including the femoral condyle cartilage of the knee joint.The geometric model is generated after processing.Then the 3d solid model of knee joint was established in SolidWorks2018 software.Finally,in the finite element analysis software Abaqus2018,the material parameters of each part of the model are established respectively,and the analysis types are defined as static analysis and dynamic explicit analysis respectively.The contact type between the cartilage and meniscus is defined as frictionless contact,and the rest of the contact types are set as fixed connections.Boundary conditions and loads were set.The lower surface of the tibial model was set as fixed.The loading was divided into two cases:the first case was to apply a gravity load of 700N to the femur with the command of concentrated force,and then to apply a torsional load of 5N·m with the bending moment command.In the second case,a gravity load of 700N is applied to the femur with the command of concentrated force,and then a dynamic bending load from 0° to 90° is applied with the command of rotation Angle.Finally,the model is meshed and submitted for calculation.The results are as follows:we establish a dynamic 3D finite element model.The model included femoral condyle cartilage and meniscus,anterior and posterior foramen ligaments,and medial and lateral collateral ligaments.The statically stable structure of the model has 67870 nodes and 314211 elements.The stress and displacement cloud maps of each part of the knee joint were output under static and dynamic conditions.The results showed that there was a stress concentration region in the middle of the load-bearing region of the cartilage of the medial and lateral femoral condyle.The stress concentration zone extends deep into the subchondral bone.Cartilage is damaged by stress concentration.The biomechanical characteristics of the cartilage surface are closely related to the subchondral bone.Under dynamic working conditions,with the increase of knee flexion Angle,the stress concentration area in the load-bearing area of the medial and lateral condyles of the femur is constantly moving backward,suggesting that the flexion and extension motion amplitude and frequency of the knee will cause the stress concentration position of the articular surface to move backward,which is easy to cause squat pain.The location where the femoral condyle bone spongy is connected with the bone cortex and the intercondylar fossa has a concentrated displacement area,which is consistent with the prone place of the fracture line of the clinical distal femoral fracture type C fracture.There was a concentration of displacement in the load-bearing area of the medial and lateral condyle of the femur,and with the increase of knee flexion Angle,the displacement concentration area moved continuously to the rear,which was consistent with the prone area of the medial and lateral condyle fracture(Hoffa fracture).And the fracture line may be closer to the back as the flexion Angle increases.The data of 20 maximum stress and displacement nodes in three regions of the femoral condyle were extracted and analyzed statistically.Under the two conditions,the node stress and displacement in the trochlear area and the medial and lateral condyle area of the femoral condyle were statistically significant by the independent sample T test(P<0.05).The mean values of stress and displacement increase with the buckling Angle.The mean stress and displacement under dynamic working conditions are basically greater than that under static working conditions,which indicates that the increase of flexion and extension motion amplitude and frequency of knee joint will increase the risk of cartilage damage.[Conclusion]The sports biomechanical characteristics of cartilage can reveal the mechanism of cartilage trauma.Dynamic finite element analysis can simulate the sport biomechanical characteristics of the femoral condyle cartilage in a normal gait.This will provide biomechanical guidance for the prevention and treatment of knee cartilage injury diseases and intra-articular fractures.Chapter 2:in vivo kinematic study of cartilage repair after type C fracture of femoral condyle[Background]Arthroscopy is the most direct method for evaluating the efficacy of articular cartilage repair.It can also be evaluated by imaging methods such as MRI.But these methods have their drawbacks.And it's hard to do dynamic evaluation.To explore the relationship between articular cartilage injury and motion characteristics of knee joint can guide the prevention and treatment of such diseases and optimize the motion plan.[Objective]This project is to investigate the therapeutic effect of acute cartilage injury caused by C type fracture of distal femur on knee joint movement.[Methods and Results]The clinical data of 50 cases of distal femoral C fractures treated by surgery were retrospectively analyzed.The surgical incision of all patients was selected by the distal anterolateral approach of femur,and the internal fixation material was selected by the distal femoral condyle support plate.Baseline data on each patient's height,weight,and age were recorded,including the imaging profile of the knee joint and the assessment of cartilage damage.All subjects underwent X-ray examination 6 months,1 year and 2 years after surgery.The complications of malformation,nonunion of bone and traumatic cartilage injury were analyzed.Nonunion is considered if the fracture line does not disappear or blur within 1 year.Recht scoring was used to assess the severity of traumatic cartilage injury.VAS,IKDC and Lysholm scores were obtained to assess knee function.Protractor was used to measure the subjects knee range of motion.All subjects were tested with a new gait analysis system based on infrared navigation(Opti_-knee,Innomotion Inc.,Shanghai,China),and Knee 6DOF motion data were collected.Pearson correlation was used to analyze the relationship between knee function score,VAS,IKDC,Lysholm score and knee kinematics.The statistical results showed that in this group of 50 cases,24(48%)of the left knee,26(52%)of the right knee,C1(17 cases),C2(15 cases),and C3(18 cases).The mean follow-up time was 40.8±15.1 months,the mean age was 21.8±8.1 years,the body mass index(BMI)was 20.4±4.3kg/m2,the average activity was 132.3±30.8 degrees,the average VAS score was 1.8±2.4 points,the average IKDC score was 58.8± 13.6 points,and the average Lysholm score was 90.1±14.2 points.All subjects underwent X-ray examination,and no fracture nonunion was found and no serious deformity was found.In this study,MRI was used to examine the knee joint of the patients,and it was found that 70%of the patients(35 cases)with type C fractures of the distal femur were accompanied by cartilage injury in the trochlear area(Reht standard),with 21 cases of degree ? injury,7 cases of degree ?injury,4 cases of degree ? injury,and 3 cases of degree ? injury.Pearson correlation analysis test showed that the cartilage damage in the femoral trochlear area was significantly correlated with the IKDC score(P<0.05).IKDC score decreased with the increase of injury degree in the femoral pulley region.Statistical analysis of gait characteristics of patients with 6DOF showed that the intermediate/external rotation of standing phase was significantly correlated with IKDC and Lysholm scores and the maximum ROM of knee joint(P<0.05,negative correlation).The flexion and extension of knee gait,time of tiptoe off the ground,ROM of flexion and extension were significantly correlated with the maximum ROM of knee joint(P<0.05,positive correlation).The anterior/posterior translation ROM was significantly correlated with the maximum ROM of knee joint(P<0.05,positive correlation)‘The medial/lateral translational ROM was positively correlated with the maximum ROM of the knee joint(P<0.05,P<0.05).In this study,the protractor was used to examine the maximum knee bend Angle of patients,and Pearson correlation analysis test was used to detect that the maximum knee bend Angle of patients had a significant correlation with IKDC score(P<0.05).With the increase of knee bend Angle,IKDC score increased,but there was no significant difference with VAS and Lysholm scores.[Conclusion]MRI is an objective method to evaluate the therapeutic effect of cartilage injury.There was a significant correlation between MRI Reht rating and IKDC score of knee joint function(P<0.05).The function of knee joint can reflect the therapeutic effect of cartilage injury indirectly.Furthermore,we found that the motion characteristics of the knee joint with six degrees of freedom were related to the IKDC score of joint function.Therefore,the motion characteristics of knee joint with six degrees of freedom can indirectly reflect the therapeutic effect of femoral condyle cartilage injury. |
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