Biomechanical And MRI Study On Predicting The Collapse Of Non-traumatic Avascular Necrosis Of Femoral Head

Purpose:This study uses theory of finite element to analyze degree of risks for differents sizes of collapse after necrosis of femoral head,explore critical risk value of collapse after necrosis of femoral head and provide effective and feasible approach of prediction for clinic combined with MRI performance.Materials and Methods:Part 1.Constructing of normal acetabulum-cartilage-femoral head three-dimensional Finite element model:1.A normal hip joint from an adult male volunteer subject was scanned by MRI and the images of every coronal section were obtained.A acetabulum-cartilage-femoral head 3D reconstruction model was constructed with MATLAB and ANSYS software.2.Different bone material parameters were adopted according to the relation to physiological condition,and divide elements in ANSYS software,and the acetabulum-cartilage-femoral head 3-D orthotropy finite element model was constructed.3.The model was validated in contrast to the date of literature.Part 2.Biomechanical study on predicting the collapse of avascular necrosis of the femoral head:1.Fifty different size and different depth of necrosis 3-D FE models were constructed.2.Put a kind of pressure on each model which simulation of normal walking.And analyze the regular pattern of the stress distribution on different model.3.The parameters of different part on different model was analysis using ANOVA.Part 3.MRI study on predicting the collapse of avascular necrosis of the femoral head:To select 22 patients(39 hips)diagnosed avascular necrosis of femoral head by MRI.Evaluation all MRI appearance of 39 hips. Include:bone marrow edema,joint effusion,characteristic of signal intensity and position of the lesion.Measured the volume and surface area of the necrosis zone on each case,then calculated the volume ratio and ratio of NASA.Follow-up the patients from 1.5～7 years.The correlative risk factors were analyzed and screened with the logistic regression analysis.Analyse the detection results of ratio of NASA and volum ratio by ROC curve.Select the maximum value of Youden index as the critical point to predict the collapse of femoral head and to definite the sensitive,specificity and accurate.Results:1.A 3D orthotropy FE model of acetabulum-cartilage-femoral head was established successfully,including 89 961 nods of 448 159 units.The maximal displacement occurrence on the femoral head,and the maximal Von Mises stress occurs on femur neck.The stress analysis was the same as the results of literature and the actuality.2.In normal condition,the cortical shell bore 59%of the total pressure, and the cancellous bore the rest.3.The stress was redistribution after the development of osteonecrosis of femoral head.The enduring pressure of cortical shell will increase with the rising ratio of necrosis articular surface area(NASA)to whole articular surface area(WASA)of the femoral head.When the ratio of NASA reached 5%,the enduring pressure of cortical shell would occupy the 61%of total pressure,while the ratio of NASA reached 50%,the enduring pressure of cortical shell would occupy the 76%of total pressure.4.There was little pressure on necrosis zone.It bored not more than 5%of total pressure while the ratio of NASA reached 50%.5.The depth of necrosis zone had a little influence on the load-bearing of normal cortical shell with the same ratio of NASA.6.There were no obviously changes of stress in normal cancellous and necrosis portion while the depth increased when the ratio of NASA was the same.7.The stress was concentrations obviously around the cortical shell boundary of the necrosis potion especially when the ratio of NASA was 25%or more. Therefore,the critical value is about 25%of the ratio of NASA.8.The stress was also concentration around cancellous boundary of the necrosis portion with the increased the width of necrosis zone.The analysis of patients showed that:1.In the 39 cases of femoral head necrosis,21 hip collapsed and 18 hip did not.2.On logistic regression analysis,bone marrow edema,joint effusion,characteristic of signal intensity and position of the lesion,volum ratio,and ratio of NASA were the risk factors.3.The area under ROC curves for ratio of NASA was large than that for volum ratio(0.987 vs 0.902).4.The critical value for ratio of NASA was 26.7%,the ture positive rate was 95.2%,ture negative rate was 94.4%.Youden's index was 89.6。Conclusion:1.In normal condition,the cortical shell bore 59%of the total pressure, and the cancellous bore the rest.2.The stress was redistribution after the development of osteonecrosis of femoral head.The enduring pressure of cortical shell will increase with the rising ratio of necrosis articular surface area(NASA)to whole articular surface area(WASA)of the femoral head.while the ratio of NASA reached 50%,the enduring pressure of cortical shell would occupy the 76%of total pressure.3.The stress was concentrations obviously around the cortical shell boundary of the necrosis potion.4.The depth of necrosis zone had a little influence on the load-bearing of normal cortical shell.5.Ratio of NASA is more sensitive and accurate for prediction collapse of necrosis femoral head then volum ratio.6.The critical value for ratio of NASA to predict the collapse of femoral head was about 25%.