Finite Element Analysis Of Implantable Implants Through Femoral Amputation

The patient’s quality of life and mobility were severely affected because of the transfemoral amputation(TFA).The daily needs of amputees are met by the use of socket-type prostheses for many years.However,skin problems such as pressure ulcers,dermatitis,fistula formation,hyperhidrosis,itching,and acne may occur at the site where the socket contacts the skin,which seriously affects the use of prosthetics.An implantable osseointegrated prosthesis concept was proposed to overcome these problems.This prosthesis eliminates skin and soft tissue problems associated with socket prostheses.The femur can be mechanically stimulated to ensure bone quality due to the fixation in the femur.This is a new way to improve the quality of life of amputees.However,implantable osseointegrated prostheses still have problems such as implant loosening and periprosthetic fractures in clinic,so their biomechanical research has important clinical value.The implant and the bone form a new mechanical system,so the finite element analysis under heel-strike and toe-off loads was performed on the femur before and after implantation.The results showed that the stress-strain distribution of the femur changed significantly after implantation of the prosthesis.Compared with preoperatively,the femur developed severe stress shielding after implantation,and the stress on the femur decreased by 47.27%(heel strike)and 24.62%(toe off).The cracking of the bone-implant interface will affect the interface stress,so the finite element simulation calculation is carried out for different cracking states of the bone-implant interface.The results show that the interfacial compressive stress and shear stress increase significantly when the bone-implant interface is cracked,and mainly distributed in the proximal region of the implant.The maximum shear stress can reach 10.86MPa(heel strike)and 17.33MPa(toe off),far exceeding the yield stress of the bone-implant interface.At the same time,interfacial cracking also causes stress concentration on the bone in the proximal region of the implant,which explains the clinical symptoms of proximal implant fractures.Functionally graded materials(FGM)implants are proposed to address the stress shielding problem.FGM is a new type of material that is composed of two or more materials and exhibits continuous gradient changes in structure.Nine different functionally graded implant models were established.The results show that when the implant material is close to hydroxyapatite ceramic and the structure is hard on the inside and soft on the outside,the femur has the best stress-strain response,which can effectively deal with the problem of stress shielding.Due to the development of material science,combined with the simulation results of FGM implants,the outer PEEK implant model was proposed,and four kinds of implant models with different PEEK thickness were established.The results show that the best thickness of the outer layer of PEEK is 80%,which can not only effectively improve the stress shielding,but also bear a lower stress value on the implant.Therefore,its advantages should be properly considered when designing the implant in terms of material.