ABSTRACT
BACKGROUND: Three-dimensional finite element analysis has been used by many scholars from department of orthopedics, but the results of postoperative evaluation of hip preserving treatment for osteonecrosis of femoral head are different. OBJECTIVE: To study the biomechanical changes of the femoral head and the biomechanical changes of the proximal femur after greater trochanter bone flap for the treatment of femoral head necrosis using three-dimensional finite element method, and to verify the mechanical safety and effectiveness. METHODS: One case of unilateral femoral head necrosis in ARCOIII stage undergoing parallel vascularized greater trochanter bone flap transplantation was selected. Computed Tomography data of proximal femur were collected before and 6 months after the operation, and preserved in DICOM format. With the aid of computer technology, professional medical modeling software, MIMICS and HYPERMESH, were used to establish the three-dimensional geometric models of the proximal femur. These models were divided into normal group, necrosis group and repair group. Finite element analysis software ANSYS was utilized to simulate human body standing and movement in different situations. The model was divided by free mesh, and given material parameters to establish normal proximal femur, femoral head necrosis and bone defect. Greater trochanter bone flap was applied in repairing three-dimensional finite element model of bone defect. Loads were loaded on different finite element models. The maximum displacement of the femoral head and the stress distribution in the proximal femur of the three groups were observed under different loading models. RESULTS AND CONCLUSION: (1) Under the same load, the maximum displacement of the three sets of models was 0.61 mm in the normal group, 0.66 mm in the necrosis group, and 0.61 mm in the repair group, respectively. Maximum Von Mises stress was greater in necrosis model than in the normal molding. The maximum Von Mises stress gradually decreased in the repair model, and was close to normal value. (2) Three groups of models showed stress concentration above the rotor in femoral neck region. The maximum stress in the trochanteric position was higher in necrosis models than in normal models. The maximum stress in this region gradually increased after repair, but was still lower than the failure stress of bone. (3) The results confirm that the maximum stress and the maximum displacement are closer to the normal value after greater trochanter bone flap for treatment of osteonecrosis of the femoral head. The greater trochanter is safe and reliable for repairing bone defect of femoral head.