Finite Element Modeling And Biomechanical Function Analysis In Locomotor System Of Ostrich (Struthio Camelus) Foot

The ostrich is the only extant bird that is both didactyl and exhibits a permanentlyelevated metatarsophalangeal joint, it is capable of remarkable speed and exceptionalendurance in their native Africa of desert and grassland environment. Ostrich foot consistsof bone, articular cartilage, ligaments and soft tissue, etc; it belongs to light distal legsegments without muscle. This study embarks from the biomechanics principle, based onthe anatomy experiment, the medical image data acquisition, reverse engineering and thefinite element analysis technology. In this study, ostrich foot motor system composite modelis established, and verified it by biomechanical experiment. This article analyzed the stressdistribution characteristics of bone, cartilage, and soft tissue of ostrich under static anddynamic impact. This study explores the heavy load and shock-absorbing mechanism ofostrich foot, providing important theoretical basis for bionic research and design of softground equipment, such as bionic mechanicals, travel on sand vehicles, two-legged robots,artificial limbs, desert adventure, and lunar rover walking system and so on.With gross anatomy theory and method, this study determined the exact distributionlocation and anatomy characteristics of the bone, cartilage, ligaments and tendons of theostrich foot. The relationship between the foot structure and its high performancecharacteristics is studied. The study found that bone is the framework of ostrich; it contains9pieces of phalanges and1piece of tarsometatarsus. The length of4th digit is half3rd digit,the3rd digit assume most of body weight, and4th digit maintaining its balance. The toe padprotect the phalanx with functions of energy absorption, shock absorption and heatinsulation. The elevated metatarsophalangeal joint forms the arch structure, reducing thegrip size and can absorb shock and store energy.The feature sizes of the ostrich foot are measured by using morphology metrologymethod. The mechanical parameter of tarsometatarsus was obtained by using themechanical testing machine. The results showed that limit load, compressive strength andelastic modulus of compact bone is1.62±0.20KN,0.30±0.06KN and183.91±14.87MPa,respectively. The limit load, compressive strength and elastic modulus of compact bone are 5.4,8.1and2.0times than spongy bone. It showed that the compact is the main pressurestructure.This study obtained the medical image data of ostrich under the condition of steadystance phase by CT and MRI scan. And then Established the three-dimensional motorsystem composite model is of ostrich foot, this model contains10pieces of bone,18piecesof articular cartilage, soft tissue and75ligament elements. Computing the model by3kindsof different load, and performing an experiment in vitro ostrich foot combined with plantarpressure test system and dynamic image analytic system. Comparative analysis shows thatplantar pressure distribution simulated result has same trend with experiment, whichverified the ostrich foot composite model is effective.The composite model of ostrich is using to numerical simulation calculation understatic and dynamic impact process in the stance phase. Calculation results show that whenthe ostrich static stand evenly, the equivalent stress of bone is the largest, second is articularcartilage, soft tissue is small; the largest stress occurred in metatarsophalangeal jointposterior, its special structure is equivalent to a "buffer" and "steering", to protect the foot.For digit parts, the stress in3rd digit is larger than the4th digit, and the stress in shaftphalanx is bigger than the base and head of phalanx. The stress in medial significantlygreater than the lateral, the back is greater than the plantar side. The maximum equivalentstress, contact peak stress in phalanx is gradually reduced from proximal to distal.Maximum stress appears in the3rd digit at the posterior-lateral position, and then is theanteromedial. When there is plus instantaneous speed imposed to ostrich foot, soft tissue invirtue of its structure and deformation characteristics, absorb the impact force and partitioneffectively, have played an important role in energy absorption and shock absorption.