Abstract:

BACKGROUND: Previous studies have reported that femoral head finite element models are mostly modeled with single or few samples for specific biomechanical research, but there is little research on model stability.

OBJECTIVE: To compare the models of normal femoral head and osteonecrosis of the femoral head with multiple samples, and to analyze the accuracy and stability of the models through the comparison of stress distribution and mechanical parameters, so as to provide mechanical basis for prevention and treatment of collapse of osteonecrosis of the femoral head.

METHODS: Totally 20 sides uncollapsed of osteonecrosis of the femoral head one year of non-surgical treatment were selected as the experimental group, and the healthy side of 20 patients with unilateral osteonecrosis of the femoral head were set as the normal group. The CT data of the femoral head were collected to establish the finite element model. The stress distribution of normal femoral head and osteonecrosis of the femoral head, the maximum equivalent stress and the maximum total deformation at the weight-bearing area of the femoral head were observed and compared. This study was approved by the Medical Ethics Committee of Wangjing Hospital of China Academy of Chinese Medical Sciences. Patients signed the informed consent. 

RESULTS AND CONCLUSION: (1) The finite element models of normal proximal femur, non-necrotic proximal femur and necrotic bone were established. The number of elements and nodes were 502 568±114 196, 692 608±154 678; 449 954±125 824, 623 311±171 401; 19 133±13 167, 27 577±19 131, respectively. (2) When the load was set by simulating one-foot standing position, the cloud image showed that when 2.5 times body weight applied to the weight-bearing area of the femoral head; the surface stress of the weight-bearing area of the normal femoral head was uniform. The stress was uniformly distributed in the femoral head along the stress trabeculae, and the calcar femorale bears the most. The stress concentration area appeared on the surface of the weight-bearing area and the necrotic area of osteonecrosis of the femoral head. The stress was scattered and distributed on the inner and outer sides of the femoral neck and the femoral head of osteonecrosis of the femoral head produced more deformation than the normal femoral head. (3) The maximum total deformation of the weight-bearing area of the osteonecrosis of the femoral head and the normal femoral head was (4.14±1.31) mm and (1.36±0.22) mm and the maximum equivalent stress was (1.94±0.77) MPa and (0.75±0.19) MPa, respectively, and with statistically significance (P < 0.05). Moreover, two groups of data tend to be concentrated and the models are stable. Through the comparison of multi-sample normal femoral head and osteonecrosis of the femoral head, the CT gray-assigned method reflects the actual mechanical properties of osteonecrosis of the femoral head, and has good accuracy and stability. 

Key words: CT gray-assigned method, osteonecrosis of femoral head, finite element model, number of elements, number of nodes, stress distribution, maximum equivalent stress, maximum total deformation