Dynamic Finite Element Modeling And Biomechanical Function Coupling Analysis Of The Human Foot Complex During Locomotion

The human foot is an immensely complex structure comprising numerous bones, muscles, ligaments and synovial joints, playing very important role in lots of human sports and activities. Biomechanical functions and characteristics of the human foot are research hotspots in foot biomechanics, and are also the solid biological data base of bionic engineering. Meantime, it is of great significance in science and its application for many related fields, such as foot diseases therapy, sports protection, rehabilitation and orthopedic instruments design, computer aid design and manufacture of artificial limb, fine design of humanoid robot's foot, etc.Combined with experimental test, foot medical images, inverse engineering technique, finite element method, biological coupling theory and extenics, human foot finite element modeling and biomechanical function coupling analysis during locomotion were conducted in this dissertation. In the dissertation, based on the multiple rigid-body model of human lower limb and foot, a novel infrared reflective tracking marker system was designed. The marker system had been used successfully in multi-locomotion test, such as walking, running, turning etc., to study the human foot biomechanics combined with stereophotogrammetry motion capture system and technique; A 2-dimensional subject-specific dynamic finite element model of the human foot complex was proposed based on individualized medical imaging data and the loading conditions derived from gait measurements on the same subject. With the help of this model, main parameter estimation of human normal walking and foot plantar stress distribution can be got successfully, and the model can also be used for analyzing some related foot diseases; Foot muscle modeling method based on Slipring connector element was proposed through running multiple simulations. On the basis of medical images and anatomy, a 3-dimenstional human foot musculoskeletal finite element model comprising 29 bones,85 ligaments,12 muscle groups and foot plantar was established. To our knowledge, it is the most complicated foot musculoskeletal finite element model in foot biomechanics research field. The 3-dimensional foot model can predict the stress distribution of foot plantar and bony structure effectively in gait simulation; finally, systematic coupling analysis of specific foot biomechanical functions (vibration and energy absorption, foot musculoskeletal functional system) was carried out based on biological coupling theory. And the corresponding extension models of these two biological coupling systems were established by Extenics method, to describe coupling information in formalization. This kind of illustration of biological coupling system can be useful to build a biological functional knowledge base and manage data, and can also be recognized as the basis of the combination of bionic engineering and an intelligent computer processing technique. The detailed research work and conclusions obtained of the dissertation are as follows:1. Human foot medical images were collected with the aid of medical imaging technique and instrument. Foot medical imaging data is the foundation of foot finite element modeling work (2-dimensional,3-dimensional). Two different kinds of foot medical images were collected, they are CT images (with interval 1.5mm,157 images in total) and MR images (with interval 2mm,104 images in total), respectively.2. The lower limb of 13 segments human multiple rigid-body model was adopted, furthermore, the foot segment of the lower limb was redefined into five segments, they are hind foot, mid-foot, medial fore-foot, lateral fore-foot and phalanx, respectively. The new model was introduced by kinetic description method. According to the model and specific foot measurement requirements, a novel infrared reflective tracking marker system was designed. The marker system was consisted of 53 reflective markers in total, including 32 technical markers and 21 anatomical landmarks, and was used to track the motion the motion of pelvis, femur, shank and foot segments. The system had been used successfully in multi-locomotion experimental test, such as walking, running, jumping, turning, etc., to study the human foot biomechanics.3. Measurement platform comprising 12 infrared camera motion analysis system,6 force plates array and 1 metre-long pressure plate, was built to study foot biomechanics during locomotion. Based on the measurement platform and tracking marker system, the 3-dimensional human motion experiments of 7 subjects were successfully conducted. Each subject had been measured for six kinds of state of motion. They are slow walking/running, normal walking/running and fast walking/running, respectively. Conclusions were drawn from measurement results:in the state of walking, whatever slow speed, normal speed or fast speed, the ground reaction force of the same subject has two main components; they are the force componets along O-X and O-Y direction, respectively; under these three different walking conditions, for the same subject, the similar development trend of right ankle joint force and torque were found; the ankle joint force components (along O-X and O-Y direction) and the ankle joint torque in sagittal plane play very important role during human locomotion; by the comparison among these three walking conditions, it is also found that there is no big difference in the ankle joint force components (along O-X and O-Y direction) and the ankle joint torque in sagittal plane between slow walking and normal walking condition, whereas, the magnitude of ankle joint force components and torque increased during fast walking. The similar conclusions were also derived from running experimental test.4. A 2-dimensional subject-specific dynamic finite element model of the human foot complex was proposed based on individualized medical imaging data and the loading conditions derived from gait measurements. Normal walking gait simulation was conducted by the help of the proposed 2-dimensional model. Through the comparison of ground reaction force (GRF), the trajectory of center of pressure (COP), foot rotation angle (FRA) and foot plantar stress distribution between simulation results and measurement, it is showed the simulation results all are agreed well with the measurement. Material sensitivity analysis was carried out to study the biomechanical effects of soft tissue stiffening (+5%,+10%) and softening (-5%,-10%) on above FE calculated results. It is showed that there is no significant effect on GRF, GRA and COP trajectory whatever stiffening or softening the soft tissue, besides plantar stress distribution. With the increase of soft tissue stiffness, the maximum von Mises stress on foot model increased as well, and the magnitude of stress decreased along with the soft tissue softening. Slow release effect of stress was proposed on the basis of material sensitivity analysis results. That is, in the stance phase, due to the decrease of soft tissue stiffness, the flexibility and adaptability of the whole foot plantar were reinforced. Therefore, under the same loading condition, it is easy to deform to absorb more energy or work done by external forces, furthermore, abate the strength of interaction forces between foot-ground contact to make the human foot avoiding possible danger and damage caused by high stress. At the same time, the conclusion may give a help to explain tissue breakdown syndrome of diabetic feet.5. By use of commercial software (Mimics, Solidworks, Geomagic and Rhinocreos), a 3-dimenstional human foot skeletal model comprising 29 bones and foot plantar was established. Then, combined with foot ligaments anatomy,85 ligaments including plantar fascia were constructed by the help of truss elements; Foot muscle modeling method based on Slipring connector element was proposed through running multiple simulations. Finally, based on the foot skeletal-ligament model,12 muscle groups were integrated into the 3-dimensional foot model by using slipring connector elements and mid-reference points. To our knowledge, it is the most complicated foot musculoskeletal finite element model in foot biomechanics research field. Mid-stance phase during locomotion was simulated by the model. Through the analysis of simulation results of foot plantar stress distribution, bony structure stress, ligaments and plantar fascia, it is showed the proposed 3-dimensional foot model worked effectively in gait simulation. And it may be used in some foot related fields, such as foot diseases therapy, sports protection, computer aid design and manufacture of artificial limb, etc.6. Based on biological coupling theory, systematic coupling analysis of specific foot biomechanical function (vibration and energy absorption) was carried out by combining finite element method and experimental measurement results. The corresponding coupling mechanism is the following:1) Reticular fiber structure and fat cells material are coupling elements of foot pad vibration and energy absorption functional coupling system; these two coupling elements are connected with each other by cross-link coupling way; during locomotion, the foot pad energy absorption function was implemented with fully equipoise parallel pattern.2) Foot arc structure and plantar fascia are coupling elements of foot arc vibration and energy absorption functional coupling system; these two coupling elements are connected with each other by immovable coupling way; the corresponding biological function was implemented with compound non-fully equipoise parallel pattern.3) The vibration and energy absorption biomechanical function of whole foot was coupling result of foot pad coupling system and foot arc coupling system. These two coupling system are the basic elements, and connected each other by up-down orientation coupling way; during locomotion, the whole foot vibration and energy absorption function was implemented with combined non-fully equipoise parallel pattern.7. Based on biological coupling theory, systematic coupling analysis of foot musculoskeletal functional system was carried out. Dynamic coupling conception was proposed, and the corresponding basic element, coupling way and implement pattern of biological function were also discussed. The conclusion is the following:the implementation of foot functional motion was dynamic coupling result of foot muscle-tendon and foot bony structure system. Foot muscle-tendon is an active coupling system; muscle and tendon are the basic elements of the system and connected with each other by closely overlapping coupling way; the active coupling system implemented the function of generating and transferring muscle force with non-fully equipoise parallel pattern. Whilst, foot bony structure is a passive coupling system; foot bones and ligaments are basic elements of the system and connected each other with immovable coupling way; the passive coupling system receive acting muscle force from muscle-tendon active coupling system with second-level combined non-fully equipoise parallel pattern, and generate corresponding foot action. Therefore, muscle-tendon active coupling system and foot bony structure passive coupling system are connected with each other with dynamic dominance coupling way; the specific foot functional motion or action during locomotion was implemented with combined non-fully equipoise parallel pattern.8. An extension model of biological coupling system was proposed based on basic element theory of Extenics. By use of the model, the coupling analysis information of foot biomechanical function (part 7) were all described in formalization, so as to facilitate building biological function knowledge base, data management and bionic engineering general design.Human foot biomechanics study is one of the research fronts of biomechanics field, which is related to human anatomy, human physiology, mathematics, mechanics, kinematics, and biomedical engineering, etc. and therefore, it is a highly comprehensive topic. This dissertation mainly focused on human foot finite element modeling and biomechanical function coupling analysis during locomotion. Specific-subject based finite element foot models were proposed, supply an innovative and more proper method for dynamic foot finite element modeling during locomotion, and facilitate the further study of dynamic response of foot musculoskeletal system and tissue mechanics.