Research On Biomechanics Of Artificial Hip-Host Bone System

Since the hip arthroplasty was applied in practice, the clinicalcomplications related with it had always been a key concern. At present,the main failure of the hip replacement was aseptic loosening with thecomplicated reasons. The particle produced by interfacial fretting wear wasthe dominant factor, and the stress shielding on the fixed prosthesis was theother factor. Both of the factors lead to bone dissolution and absorption,and result in the failure of artificial hip joint replacement.This dissertation is based on the two key projects"mechanical virtualhuman of China"and"design of artificial joints for Asia race"supportedby National Natural Science Foundation of China. The three-dimensionalgeometrical model and finite element analysis model of femur wereestablished and the finite element analysis on the biomechanics caused byprosthesis aseptic loosening under gait and stair climbing was made. Thecalculations related to stress shielding effect, micromotion research andjoint interfacial stress distribution. The main contents are listed asfollowing:1) The geometric model of femur was established based oncryosectional image data using medical image processing technology andreverse engineering method. Base on the geometric model of femur, thefinite element meshing model provided a basis for the subsequent researchwas also established.2) The FEA models of intact femur and the femur implanted wereestablished, and with the models the stress distribution on the femur underthe gait and stair climbing was carried out. There was no stress shieldingeffect on the femoral medial side because of the stress outward deflection, while the lateral and anterior and posterior sides of the femur had a greaterstress shielding phenomenon. At the same time, anterior and posteriorsides'stress shielding of the femur is more sensitive to the elastic modulusthan the medial and lateral sides.3) Based on the FEA femoral models implanted with differentartificial hip stems, the micromotions between femur and stem werecalculated and the micromotion distribution on the four paths was alsoobtained. In addition, the interference's effects on the femoral primarystabilities of different stems were analyzed. The proximal micromotion islarger the distal and the medical micromotion was also smaller than theother three sides. A certain range of interference fit has a significant impacton the micromotion and greater interference fit should be given to themedical and anterior sides of the femur than the lateral and posterior sidesto reduce the micromotion.4) With the finite element analysis method, the interfacial stressdistribution between the femur and stem under gait and stair climbing wascarried out and the stress difference's effect on femur was analyzed. Themedical and lateral axial stress was greater than the anterior and posterioraxial stress on the three stems, and meanwhile two of the stems had stressconcentration on the distal medical side, but the third stem had no stressconcentration because of the shape of stem. Large stress difference lead toserious interfacial loosening and wear was found on the interfacial medicaland lateral sides.In short, this thesis established a human biomechanical model offemur, and meanwhile the biomechanical problems related to the artificialhip failure were carried out. The results got from the finite elementanalysis could provide a theoretical basis and useful information for thedesign of the prosthesis and the postoperative rehabilitation training.