A New Design Of Total Knee Replacements And The Mechanical Evaluation On Prostheses

The knee joint is the largest joint in the body and it is also one of the most complex joints.It moves with a complex set of translations and rotations and bears the most part of body weight in our daily live.The common causes of knee pain and loss of knee function in clinic are osteoarthritis,rheumatoid arthritis and post traumatic arthritis.Total knee replacement(TKR),as one of the most effective methods in clinic is widely used in the treatment of knee joint diseases.About 440,000 total knee replacements are carried out worldwide each year.Although the patient satisfaction rate of TKR is high,the number of patients who need revision surgery is significant.The main reasons for TKR failure are: irregular kinestate of total knee prostheses,the significant change of contact stress level,early wear of the UHMWPE.In this research,a novel method was used to design total knee prostheses.This new method improved the articular surface of the femoral component with less design parameters than off-the-shelf TKRs.Meanwhile,this new designed knee prosthesis was supposed to have a good stability and flexibility during the gait cycle.In this research,static and dynamic simulation were used to evaluate the mechanical performance of this new designed TKR component during the gait cycle.The stability of knee implant models was evaluated on the magnitude of overlapped volume.Simulated results were compared with theoretical results,which were got from formula calculation of Hertz contact mechanics.The theoretical evaluation method was discussed in this paper,whether it could evaluate the mechanical performance of the knee joint prosthesis in the design phase.The result of stability evaluation indicated that the new designed femoral component provided enough stability in lower flexion angle,on the contrary,this component provided flexibility in conditions of high flexion.This characteristic has positive influence on the kinematic of the knee joint,and more close to the vivo human knee joint.The result of static simulation indicated that this new design preserved implants from abrupt change of the stress during the gait cycle and keep the tibial component from early wear.In addition,considered the influence from soft tissue(ligaments and muscles),a dynamic model of the lower limb was built in this research.This new design improved the distribution of contact stress on the articular surface and decreased the stress on the medial condyle surface.The simulated results indicated that the length of bearing space(BS)gradually decrease with the increase of flexion angle.Under low flexion,a longer BS can provide good stability for knee joint.On the contrary,a shorter BS means knee joint can get a better flexibility and easier tibial rotation at high flexion.