| BackgroundTotal Knee Arthroplasty(TKA)is the “golden standard” of managing end-stage knee osteoarthritis(OA)and can relieve pains and restore the motor functions.During the past several decades,the researches focusing on articular joint materials is valuable to prolong the lifespan of the joint implants.However,the surgeons gradually realized that the geometric design of the prosthesis and its effects on the patients' motor functions are equally important to the surgical outcomes and patients' degree of satisfaction.Although the concepts of bionics design and subject-specific design are continually promoting the improvements of prosthesis designing,various studies ha ve demonstrated that the kinematic status of knee joint following TKA cannot completely restore the status of healthy natural knee.Therefore,the kinematic and kinetic assessments of TKA patients would help to detect how TKA procedures influence the kinematics of knee joint and can act as a clinical outcome parameter to provide references for clinical management.Clinicians and artificial joints manufacturers want to know the post-operative kinematics and kinetics status of the TKA subjects' body,as well as the movement and mechanics performances of TKA prostheses in vivo.At present,although there are in vivo direct mechanical measurement methods,these techniques are insufficiency of application due to technical implementation difficulties.Computer models can simulate many analyses of the mechanical process and operation that cannot be completed in lab.They have become an important tool to promote the design and improvement of TKA.With the rising development of computer hardware,computer 3-dimentional model is more and more sophisticated and 3D model of dynamic mechanics research is implemented.Through the establishment of dynamic knee 3D finite element model to simulate the mechanical state of TKA postoperative knee joint activities and the change rule become important means of TKA mechanics research.The biggest problems of 3D finite element analysis is,however,experimental conditions set has a large dispute,and load bearings of prosthesis in vivo have large deviation,personalized analysis of clinical cases cannot be precisely completed.Gait analysis through different means of inspection and evaluation of individual activities,is the quantification of human activities.Quantitative analysis of the gait is an important clinical tool to distinguish normal and abnormal gait.It has been applied to clinical disease assessments,treatment strategy formulation and treatment effect evaluation for a long time.Through checking the gait data collected by calculating the trajectory of motion and force of the activities of the joint,gait analysis can be used to indirectly reflect the TKA joint kinematics and kinetics.Multibody system dynamics is to study the law of motion of the multibody system,the object of the study generally includes several flexible and rigid objects that interconnected to constitute a whole structure.Human kinetics modeling of muscle activity and joint contact force of the gait cycle analysis,helps us to understand the principle of muscle coordination,the force of the bone and soft tissues at the same time.Based on this model,it can be further improved to complete prosthesis loading analysis and in vivo analysis of polyethylene wear prediction.Skeletomuscular multibody dynamics model to predict the joint force and joint movement can be output to subsequent analysis based on the finite element software.The way to obtain the stress and strain is important to artificial knee joint prosthesis wear prediction.Multi-body dynamic model considers the patients' skeletal geometry,artificial joint prosthesis design,the situation of the joints,and muscles and ligaments around the joint,can calculate the joint movement,contact force,muscle and ligament forces at the same time.The above results as boundary conditions of the input parameters to the finite element software can reflect the status of prosthesis of the real stress distribution in the human body.In conclusion,the combination of human multi-body dynamics model and the modeling of finite element analysis method can be a good method to understand the in vivo force of artificial knee joint,and thus improve the prosthetic design and provide theoretical basis for clinical case analysis.The core content of this research was divided into two parts: the first part is to adopt the quantitative three-dimensional gait analysis data of patients after TKA,which belongs to observational study;the second part is to try to establish the individualized musculoskeletal multibody dynamics model through prosthesis 3D data and gait data of patient,in order to more accurately describe the joint activities,and predict the intra-articular stress situation,which belongs to exploratory study.Methods1.Three-Dimensional Gait Analysis Following Total Knee ArthroplastyWe use the three-dimensional markers trajectory motion capture system to collect the ground reaction force that measured with force platform and three-dimensional gait data that collected with skin electricity acquisition device.Data collected include the relative positions and directions of each part of the body,the reaction force between the foot and the ground,time-space parameters and the phases of lower limb muscle activity.Patients were required to walk back and forth on the trail in the speed of daily walking.Feet are completely stepped on force plates are identified as valid data,five to eight times of valid data was collected for each patient.Electromyographic signal with load simulation signal synchronous collected data through a unified work platform.Then use the Cortex real-time operating analysis software to define each spot,extraction the 3D spatial coordinates of each point.Then the space geometry method was used to calculate the gait parameters,combined with the test data collected before parameter adjustment and optimization.The output parameters included joint reaction force,angle of the joints and muscle activity signals.All the parameters were contra between operation leg and the contralateral leg.2.Subject-Specific Multibody Dynamics Modeling Following Total Knee ArthroplastyData were collected from a patients underwent total knee arthroplasty to establish the subject-specific musculoskeletal multibody dynamics model.The data including CT three-dimensional reconstruction for bone geometric model,three-coordinate scanning to obtain the 3D model of artificial joint prostheses and three-dimensional gait analysis data.Based on "Force Dependent Kinematic"(FDK method)and the theory of elastic base,TKA postoperative lower limb bone multi-body dynamic model was established by integrating artificial knee joint prosthesis to lower limb skeletal muscle model to predict the joint moment of flexion and extension in the gait cycle and contact force of tibiofemoral joint and patellofemoral joint.Results1.Three-Dimensional Gait Analysis Following Total Knee ArthroplastyGait parameters of space-time parameters between operation side and healthy side showed no statistical significance(P > 0.05).Operation side hip,knee,ankle joint reaction force of operation side is less than the healthy side,but the difference was not statistically significant(P > 0.05).Compared with the healthy side,the average hip flexion angle has not changed,but the maximum flexion angle and maximum extension angle are significantly smaller,and the difference is statistically significant(P = 0.039,P < 0.001 respectively).Knee flexion angle and the largest flexion mobility in operation side and healthy side showed no significant difference(P = 0.185,P = 0.185 respectively),but the maximum extension angle increased in operation side than that of healthy side with statistically significant difference(P < 0.001).The valgus angle and the largest knee varus-valgus ROM of the operation side were greater than that of the contralateral side,which showed statistically significant difference(P = 0.023,P = 0.002).Ankle dorsiflexion angle,maximum plantar flexion angle and the largest flexion ROM did not differ significantly between both sides(P = 0.286,P = 0.286,P = 0.151).Bilateral glutes signal did not change,while the signal of the hamstrings in the operation side was greater than the healthy side,but the difference was not statistically significant(P > 0.05).The EMG signal of tibialis anterior in operation side is abate,the signal peak value of the difference was statistically significant(P = 0.036).2.Subject-Specific Multibody Dynamics Modeling Following Total Knee ArthroplastyWe successfully established the subject-specific musculoskeletal multi-body dynamic model of predicting the joint moment of flexion and extension in the gait cycle and contact force of tibiofemoral joint and patellofemoral joint.We found that the maximum flexion angles of tibiofemoral joint and patellofemoral joint in operation side showed no significant difference of patellofemoral joint,while the maximum extension angles were lower than that of healthy side.The moments of three orientations are all showed increased trends.The peak value of flexion(extension)moment increased about 59.2%,adduction(abduction)moment increased about 18.6%,internal rotation(external rotation)moment increased about 3.5%.The contact forces of tibiofemoral joint and patellofemoral joint in operation side were lower than that of the healthy side.The peak value decreased about 5.8% in tibiofemoral joint and about 20.5% in patellofemoral joint.Conclusions1.The results showed that the TKA operation did not affect the space-time parameters of gait,in other words walking function in patients of TKA returned to normal at 12 months following operations.But the joint kinematics results showed that there is a relative limitation of knee extension in operation side when compared with the healthy side.The internal/external rotation and the varus/valgus of knee were also changed and result in the secondary changes in hip and ankle joints.The results of s EMG prompted that the stability of TKA knee was decreased and need to mobilize more muscle to maintain dynamic balance of knee joint.As an objective and quantitative evaluation method,three-dimensional gait analysis is very suitable of being a supplement to current clinical evaluations and provide more additional information for clinical decision making.2.Based on FDK method and elastic theory,we integrated artificial knee joint prosthesis into the limb musculoskeletal model,realize the precise modeling of lower limb and considered the stability of the ligaments around the joint.We successfully predicted the postoperative TKA knee joint movement and contact force of tibiofemoral joint and patellofemoral joint.The results showed that the maximum flexion angles of tibiofemoral joint and patellofemoral joint in operation side showed no significant difference of patellofemoral joint,while the maximum extension angles were lower than that of healthy side.The moments of three orientations are all showed increased trends.The contact forces of tibiofemoral joint and patellofemoral joint in operation side were lower than that of the healthy side.The model has a good commonality and can be further optimized to any individual biomechanics study of TKA to provide accessed and methods in the researches of clinical outcome assessment,prosthesis designing and prosthesis wear analysis. |
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