Research On Biomechanics Of Avascular Necrosis Of Femoral Head And Prediction Of Its Collaps Risk

Avascular necrosis of the femoral head is one of a common orthopedic disease.To predict collaps risk of this kind of femoral head is of key importance for hip preservation.At present,the method of composing both imaging and finite element methods is used to reveal the mechanical performance and collaps risk of the femoral head at standing or other instant moment.However,the contact area of the femoral head is constantly changing during walking movement.This would then lead to variation of both the magnitude and direction of the stress.Whereas,the research on biomechanics of the femoral head under dynamic condition is still lacking.Therefore,the biomechanics performance and collapse risk prediction of avascular necrosis of femoral head under different necrosis volume and location both at static and dynamic condition were studied.First of all,a patient-specified CAD model which could been used in dynamical simulation was establish based on volunteer’s CT image.Moreover,a finite element model of the normal femoral head was established and verified using commercial software of ABAQUS.Secondly,nine groups of finite element(FE)models of different avascular necrosis for the femoral head were established.Then the biomechanics performance and collaps risk of the femoral head for different necrotic volume and necrotic location were calculated using the above FE method under a static load of 3000 N.Finally,same nine groups of FE models for dynamic analysis were established.The biomechanics performance and collaps risk of the femoral head for different necrotic volume size and different necrotic location in one cycle of walking were also analyzed.The results showed that: 1.The larger of the necrosis volume(2α)or the closer of the necrosis location(β)to the superior center,the higher of the maximum stress at the interface between the necrotic area and the normal bone tissue of the femoral head for both static(3000N)and dynamic(walking)conditions.This would finally lead to higher risk of the femoral head collaps.Besides,the size of the necrosis volume was more important than the location of the necrosis for the risk of femoral head collaps.2.Except for mild necrosis(2α=60°)at the location of necrosis(β=30°,β=60°),the maximum stress peak at the interface between the normal tissue of the femoral head and the necrosis under walking dynamic load and the maximum stress peak in the necrotic area were lower than those under static load.However,this variation trend reversed for another 7 groups.The results of collaps risk prediction were as follows: in the case of mild necrosis,the site of necrosis(β=0°)would not collapse under static load,and there would be collaps risk under dynamic load.No collaps would occur at the site of necrosis(β=30°,β=60°).In moderate necrosis,collaps occurred at the necrotic site(β=0°)and was of collaps risk at the necrotic site(β=30°)but not happened at the necrotic site(β=60°).In severe necrosis,collaps occurred at both the necrotic site(β=0° and β=30°)and collaps risk occurred at the necrotic site(β= 60°).The results of this study provided valuable theoretical reference for surgeons to cure the necrotic femoral head.