Objective To analyze the influence of total hip arthroplasty (THA) on the process of proximal femoral bone remodeling by using the Wolff bone remodeling theory. Methods According to control equation of bone remodeling, the program of bone remodeling was written in Python language. Preoperative femur model and postoperative femur and prosthesis finite element models were established respectively in ABAQUS software. The process of bone reconstruction before and after THA operation was compared to analyze the effect of prosthesis implantation on mechanical properties of the femur in the middle and long term after THA operation. Results The stress in proximal femur continued to decrease after prosthesis implantation, and the stress site was transferred from the femoral head to the prosthesis, resulting in an obvious stress shielding phenomenon. Bone loss in the stress shielding area was serious. The femoral shaft cortical bone became thinner and the stress shielding was relieved. The medial side at the bottom of the prosthesis was compressed, and the stress was significantly higher than that of the lateral side, where the bone was unevenly distributed. Conclusions After THA operation, obvious stress shielding occured at proximal medial side of the femur, leading to bone loss and prosthesis loosening. The difference in stress levels on both sides at the bottom of the prosthesis resulted in an uneven bone distribution, causing the discordance between the prosthesis and the femur, as well as postoperative pain in the middle part of the thigh.

Objective To analyze interface stress of cemented tibial prosthesis platform and determine the interface stress damage area, so as to provide references for stress failure of tibial platform in clinical single condylar replacement. Methods The full cycle gait was simulated by human dynamics software to obtain the load-bearing condition of knee joint. A complete model of the knee joint was established by medical imaging and three-dimensional (3D) reconstruction software, and unicompartmental replacement was performed. The distribution of interfacial stress of tibial prosthesis platform after single condylar replacement was analyzed by finite element method. ResultsIn gait, force and angle of the knee joint changed periodically with time, a cycle lasted 1.3 s, and the peak of knee joint resultant force was 760 N. The maximum shear stress of the interface was 11.82 MPa and the maximum tensile stress was 6.849 MPa, both occurred at inner front end of the corner of prosthesis cement interface. The maximum interface stress of titanium alloy prosthesis was lower than that of stainless steel prosthesis. Conclusions The decrease in elastic modulus of prosthesis can reduce the maximum principal stress at the interface. Considering the interface stress, titanium alloy prosthesis is better than stainless steel prosthesis. The area of tibial prosthetic platform interface damage is mainly at the medial anterior and posterior corners and lateral middle ends,so improving the ability of prosthesis cement bonding in this area can prevent the loosening of tibial prosthesis of unicompartmental knee joint.The findings have practical implications for the prevention of tibial prosthetic platform loosening after unicompartmental knee arthroplasty in clinic.