Mechanical performance and collapse risk prediction of avascular necrosis of femoral head under walking movement
Gao Yongchang1, 3, Fu Yantao1, Zhao Xin1, Cui Qingfeng1, Zhang Zhifeng2, Chen Shibin1
1National Engineering Laboratory for Highway Maintenance Equipment, School of Engineering Machinery, Chang’an University, Xi’an 710064, Shaanxi Province, China; 2Department of Joint Surgery, The Second Affiliated Hospital of Inner Mongolia Medical University, Hohhot 010030, Inner Mongolia Autonomous Region, China; 3Dabo Medical Technology Co., Ltd., Xiamen 361000, Fujian Province, China
Abstract: BACKGROUND: Avascular necrosis of the femoral head is a refractory orthopedic disease that seriously affects the normal life of patients. Hip preservation is recommended for young patients due to the limited prosthesis longevity and revision. Accurate prediction of the mechanical properties of the necrotic area in the early stage and then intervention is the key to hip preservation.
OBJECTIVE: To establish a dynamic contact mechanics finite element model of necrotic femoral head based on human hip CT data and predict effects of both necrotic volume magnitude and its position on biomechanics of the necrotic region under walking movement.
METHODS: CT data of a volunteer were collected and then geometry model of the hip was rebuilt. Finite element model of the necrotic femoral head was established using the Abaqus software. Nine different necrotic femoral models were constructed by combined both three different necrotic volume magnitudes (small, medium and big volume) and three different necrotic positions (coincided with, medium deviated with and kept away from the line of the force). The Von Mises of the necrotic region for all models were predicted under both 3 000 N static load and dynamical loads of one whole ISO walking gait cycle. The collapse risk for all models was evaluated based on collapse criterion.
RESULTS AND CONCLUSION: (1) More approaching of the necrotic region to the line of force and bigger collapse volume made the maximum Von Mises increasing. This also enlarged the collapse risk of the necrotic region. (2) For different load types, walking movement increased the maximum Von Mises of the necrotic region than that of the value under static load under the same necrotic volume and location. (3) In conclusion, dynamic load would result in increasing of the maximum Von Mises of the necrotic region comparing to static load during exercise. Therefore, the risk of local collapse will increase due to greater Von Mises. However, the overall collapse risk is lower than that of static load due to the dynamic change of bearing area. This factor should be carefully considered by surgeons when they evaluate the mechanical performance of the necrotic femoral head.
Key words: avascular necrosis of femoral head, walking movement, finite element analysis, collapse risk, stress