Investigation Of A Bi-Cruciate Ligament Retaining Total Knee Prosthesis Design: A Three Dimensional Finite Element Analysis.

Background: Although total knee arthroplasty(TKA) has made great progress in recent years, knee functions and biomechanics after knee arthroplasty still differ from that of natural knee. The knee joint is a very complicated system made of many subunits that undergo large loads and large relative displacements during various daily activities, and all the subunits function as a whole. So with alteration or loss of any subunits, the present knee prosthesis can lead to loss of stability and physiological dysfunction of the knee. Nowadays almost all knee prosthesis sacrifice the anterior cruciate ligament except unicompartmental knee prosthesis. Also there are many problems with the present bi-cruciate ligament retaining knee prosthesis, such as joint exposure difficulty, non-optimal anchoring, difficulty in regaining proper tension of the ligament. Along with the rapid development of modern life, TKA should not only be a procedure to relieve pain and improve function, but also a good method to improve quality of life of people. So higher requirements are needed in total knee arthroplasty.Objectives: To design a new bi-cruciate retaining knee prosthesis and overcome problems existed in present bi-cruciate ligament retaining designs, and to keep the normal function of the natural knee as much as possible.Methods: 1. Anatomical measurements were made on twenty cadaver knees in order to determine the exact attachment location of the ACL. Then with the help of modern CAD(Computer Aided Design) technology, a new bi-cruciate retaining knee prosthesis was designed. 2. The three dimensional finite element models of an intact knee joint and the knee joint with implantation of the designed prosthesis were constructed with the help of modern CAD(Computer Aided Design) and CAE(Computer Aided Engineering). Then the normal knee model was validated by comparing with previous data. After that, three dimentional finite element analysis was used in the design optimization of the tibia plate. Different kinds of tibia plate designs were compared under axial loads and rotational loads to optimize the tibia plate design. Also four conditions(including intact knee, knee without ACL, knee with implantation of the prosthesis with both cruciate ligaments and knee with implantation of the prosthesis without ACL)were compared in their biomechanical responses under axial loads, rotational loads, posterior femoral drawer forces.Results: 1. A new bi-cruciate retaining knee prosthesis was designed and this design had overcome some disadvantages of the previous bi-cruciate retaining prosthesis. 2. By the combined usage of CAD and CAE computer technology, a three dimensional finite element model of the human knee joint with cartilage, menisci, ligaments was constructed. And the model was validated to be effective and correct in predicting the biomechanical responses of the knee. Then on the basis of this model, a three dimensional finite element model of the knee with implantation of the prosthesis was also constructed. 3. Design optimization of the tibia plate suggested that properly increase of the number of pegs, the length of pegs, the diameter of pegs and placement of pegs more laterally are helpful in improving the anti-rotational ability of the tibia plate. The newly designed four pegged tibia plate with a middle cleavage to accomodate the ACL did not decrease the fixation stability compared with commonly used single post plate. 3. The biomechanics of bi-cruciate retaining total knee prosthesis was close to that of the intact natural knee.Conclusions: 1. The newly designed bi-cruciate ligament retaining knee prosthesis can preserve the normal structure of the knee maximally. 2. Proper design of the pegs in the tibial plate is helpful to achieve best fixation stability.The four pegged tibia plate with a middle cleavage to accomodate the ACL was comparable with the single post tibia plate. 3. Retaining both ACL and PCL can preserve the normal biomechanics of the knee after arthroplasty as much as possible. It is necessary to retain the ACL in total knee arthroplasty.