To propose an optimal therapeutic scheme, finite element analysis was used to evaluate the biomechanical status of femoral head under daily activities.

Non-necrotic femoral head volunteers (11 people) and necrotic femoral head patients (7 cases) were included in this study. All these participants were divided into two groups: control group and abnormal group. The DICOM imaging files of each participant were imported into ScanIP software to form a mask showing the proximal femurs. Then the finite element models of proximal femurs were progressively reconstructed. The generated models were imported into Abaqus, and the forces were added on these models to simulate daily activities, including standing, sitting, upstairs, and squatting etc. The loads and boundary conditions of digital daily activities simulation were collected from Orthoload database. All of the femoral finite element models were progressed in Abaqus under above activity conditions. After the models were processed, stress concentrating region was defined in each models respectively, which expressed the main bearing structure in each model based on the result of finite element analysis. At last, the elastic modulus (E-modulus) and strain of the stress concentrating region in each femoral model were extracted and calculated.

There was no significant difference in age, weight, and height between these two groups. In control group, no significant differences of E-modulus (7 125±745 MPa on left, and 7 112±751 MPa on right) and strain (micro-strain: 952 on left, and 954 on right) were found between their bilateral proximal femurs; however in abnormal group, the patients' E-modulus (5 798±1036 MPa on normal side, and 6 667±888 MPa on necrotic side) and strain (micro-strain: 1 261 on normal side, and 987 on necrotic side) of necrotic side were significantly lower than normal side. As to all the daily activities which were considered in this study, in abnormal group, the E-modulus among each postures of abnormal side were significantly lower than the E-modules of healthy side; the micro-strain in downstairs was also significantly lower than other postures.

Daily activities with different intensity could generate different mechanical effects on femoral head, especially on necrotic femoral head. The higher intensity of posture, the greater damage would be found in necrotic femoral head.

Femur head necrosis; Finite element analysis; Activities of daily living