Modeling Of Human Foot-Ankle Complex And Relevant Research On Biomechanical Issues

In our country, particularly in recent years, with the continuous economic development and the rising of the living standards, people have more intense demands on how to really improve their quality of life. Biomechanical study of the human body from a mechanical point of view is to study human biology-related theoretical knowledge and motion mechanism, thus provides strong theoretical guidance and help for the development of clinical medicine and rehabilitation medicine. Our Institute's "Chinese Mechanical Virtual Human" project is the National Natural Science Foundation key project which was approved in 2006 (No. 30.53023), whose research goal is to establish a Chinese standard biomechanical system of the human body, including "bones - muscles - ligament", for partial and whole body statics and kinematics, as well as the dynamics studies, so as to solve the medical problems related to biomechanics.The research in this dissertation is an sub-project of the key project "Chinese Mechanical Virtual Human": the human foot-ankle musculoskeletal system modeling and related mechanical research. At the same time, it is also an international collaborative project of our institute with the orthopedics department, Fudan University affiliated Huashan Hospital, and England Rehabilitation Centre for Rehabilitation & Human Performance Research (CRHPR), Salford University, while supported by the British Royal Society (UK Royal Society) (Grant: IPJ/2006/R3).Human foot-ankle not only includes 26 bones, but also the complex structures of ligaments, plantar aponeurosis, muscle and tendon, joint capsules joints and the stable arch structure; From a functional point of view, the foot-ankle complex is a supporting and load-bearing structure to absorb shock and transfer movement. However, in real life and medical care, the ankle biomechanics system was not paid enough attention. With the current continuous understanding of the foot-ankle, its importance gradually displayed. In the human biomechanics field, the foot-ankle biomechanics research is rising in recent years with the development of foot and ankle surgery, mainly due to the following factors: Firstly, from a clinical point of view, with a rising incidence variety of foot diseases, such as the complications of diabetes foot, hallux valgus feet, foot pain and so on, medical researchers are eager to know the causes of foot pathology; Secondly, from a market perspective, the various functions shoes, orthoses and sport shoes have a large consumer market, patients and consumers tend to demand such shoes or fixers which is comfort, having a special function and playing a protective role; Finally, from a technical point of view, a variety of measurement techniques and computer hardware and software provide the necessary conditions for the rapid development of foot biomechanics study, including motion capture system, the pressure platform, the plantar pressure sensors, ultrasonic measurement, three-dimensional CT and MRI scanning technologies, various anti-seeking software and finite element analysis softwares and so on. The research was carried out based on the above background, and the specific research content included the following:(1) Based on the three-dimensional MRI scan images of ankle of one healthy subject, three-dimensional geometric solid models and finite element models under three typical postures (heel-striking, mid-stance and heel-lift) were established. These physical models include detailed geometric information in the foot: all of the foot bones and the distal segments of the tibia and fibula and fibula, ligaments and plantar aponeurosis, joint cartilages and external soft tissue structures, which have high data integrity, high anatomical similarity and revisability. All data of these geometrical and finite element models were proceeded and managed in modular style. The modular structure can be used independently, and feasible for secondary alteration.(2) With healthy young people as research subjects, plantar reaction forces were measured under different walking rhythms (beat per minute). Using this kind of frequency-domain parameter, statistical analysis and regression analysis were used to quantify some of the basic mechanical parameters values and their relationships with walking rhythms, body weight and height. Surface EMGs of four extrinsic muscles (tibialis anterior, peroneus longus, soleus and gastrocnemius) under different states of motion (normal walking, jumping conditions and balanced standing with an anterior shift of CoP) were measured to research their muscle strengths in the course of these movements. These experiments provided the necessary basis and information for the simulation of the foot-ankle model.(3) Aiming at the finite element model under static standing posture, a detailed verification and validation work for the model were carried out. Here, a number of key technical issues, such as major simplifications of the model and assumptions, element selections, joint contact problem handling, material properties and so on were determined by a detailed analysis and comparison; An in vivo validation test was designed to synchronously record foot reaction force, plantar pressure distribution and vertical deformation. These measured results were used to compare to the corresponding model predictions, in order to validate the effectiveness and correctness of the model. This in vivo model validation method combined several commonly used measurement methods effectively, and was unharmful to human body. Meanwhile, based on the validated foot model, we developed a software of the human foot&ankle model which included five parts: geometric model, finite element model, the original data, the relevant parameters and calculation case; all established geometric model and finite element model of the whole model as well as individual skeletal part of the model were provided to the user with different data formats, in this way provide a foot&ankle simulation analysis platform to users for research or medical workers. Currently, this software is the first case at home and abroad.(4) The quasi-static finite element simulation analysis of foot&ankle under three typical postures ( heel-striking, mid-stance and heel off) was carried out for the first time and the external muscle forces were taken into account; FE simulated results (plantar pressure and foot reaction force) were compared with the experimental measurement results and it was found basically the same. The internal mechanics information under the three postures were quantified, including stress/strain in bony structure and tensions in some soft tissues. All these mechanics information were in the first report of domestic and foreign, and provided an important reference for the comprehensive understanding of gait in force within the foot-ankle.(5) Two basic mechanical issues in the foot were studied using the validated finite element model in mid-stance. First, for the standing neutral posture, individual releases of plantar aponeurosis, spring ligament, plantar long and short ligaments ligaments, were simulated respectively and model predictions were compared to the model prediction results under the health status of the same standing. These comparisons in several aspects were used to quantify their importance in maintaining stability in the foot arch. Second, under the standing load, model predicted detailed changes of metatarsal stress/strain distributions caused by the plantar load redistribution, and thereby this quantitative analysis increased our understanding of metatarsal biomechanics and also provided academic support for some requests in orthopedic surgery for hallux valgus program.(6) Cooperated with the Orthopedic Surgery, Shanghai Huashan Hospital, we carried out gait plantar pressure distribution measurement with a normal walking speed. The study goal was to compare the difference of plantar pressure distribution between normal foot and diabetic foot. Meanwhile, finite element model was used to simulate normal young foot, normal elderly foot and diabetic foot respectively and investigated effects of the different mechanical properties of plantar soft tissue layers on the internal biomechanics of the foot-ankle. A comprehensive comparison of the normal foot and diabetic foot from two aspects of external plantar pressure distribution and internal mechanical status provided the mechanical information for the prevention of diabetic patients with foot ulcers.In a word, three-dimensional modular geometry and finite element models of the human foot-ankle musculoskeletal system were established under three typical postures, as a research platform it can be widely used in basic foot mechanics research. For the specific problems in medicine and rehabilitation medicine, the above foot models can be reconstructed to do related mechanical simulation analysis. At the same time this paper has researched several foot and ankle biomechanical problems via experimental measurement and finite element analysis, and quantified the internal and external mechanics information of the foot-ankle, which provided important knowledge for the development of clinic and rehabilitation.