| ObjectiveOsteonecrosis of the femoral head is a common joint disease in the clinical diagnosis and treatment of orthopedics and trauma department.The pathological process of this disease is complicated,and collapse is the key to the outcome.Collapse of femoral head is the result of the comprehensive action of biology and biomechanics.The role of mechanical mechanism in preventing and predicting collapse has been widely described,and simulation studies emerge in endlessl.The geometric reconstruction of necrotic area is the basis of simulation research on osteonecrosis of the femoral head.At present,researchers usually use reverse engineering software to adjust the space and shape indicated by clinical necrotic classification in order to achieve the purpose of "reconstruction on demand".However,in order to facilitate clinical using and promotion,the image classification system is usually highly simplified or aimed at a certain aspect of the description,the location distribution is not defined explicitly and there is a lack of morphological data.Therefore,the existing clinical necrosis classification system can not meet the needs of finite element analysis,and "reconstruction on demand" lacks effective parameter standards.On the other hand,the existing finite element analysis mostly uses CT/MRI data based on supine position to simulate the standing posture and directly set the load,but the attitude difference between supine position and standing position may lead to the inaccuracy of the analysis results,while the more complex multi-posture finite element simulation not only needs to solve the problem of coordinate transformation of each limb during pose transformation.It is also necessary to extract the muscle response data under the corresponding posture to solve the joint force and moment level.Due to the limitation of finite element elements,muscle finite element simulation with active power is still difficult.The multi-body dynamic simulation model based on inverse dynamics has significant advantages in solving these problems.Therefore,this study intends to:1.measure the three-dimensional space and morphological parameters of the necrotic lesions by reverse engineering and divide them into modules,and assign the necrotic types according to the distribution probability,so as to establish a set of "reconstruction on demand" standards for finite element necrosis analysis.2.construct the joint simulation framework of multi-body dynamic model and finite element model through musculoskeletal simulation,and explore the mechanical level of the above standards in musculoskeletal simulation with the guidance of the theory of "emphasizing both muscles and bones".Methods1.A series of case observation and study method was used to review the patients with JIC C1 and C2 non-traumatic ONFH treated by the Department of Articular Orthopaedics,the first affiliated hospital of GZTCM from January 2019 to December 2020.No collapse of the femoral head was found on X-ray films and CT scanning was performed at the same time.The imaging data were collected and the general data were statistically described.Based on the reverse engineering software,the reference coordinate system for individual identification was established,and the method of dividing the longitude and latitude regions of the earth was used for reference.The femoral head was regarded as a sphere and divided into 144 standardized module units,which was used as a reference system to establish a CAD evaluation model.Based on the CT DICOM format data of patients,the parameters of space and shape of necrotic area were evaluated combined with the longitude and latitude division system of JIC.According to the statistical data,the plane heat map and threedimensional heat map of necrotic area distribution were drawn,and the longitude and latitude distribution levels of two-dimensional and three-dimensional distribution of femoral head C1 and C2 necrosis were visually displayed.2.Based on the longitude and latitude division system,the probability of necrosis of each unit was clustered,and ten distribution probability models of 90%,80%,70%,60%,50%,40%,30%,20%,10% and 0% were assigned and the corresponding modules were rebuilt.The CT data of two healthy volunteers were collected to reconstruct the geometric models of hip joint.At the same time,the walking gait data of volunteers were collected based on three-dimensional motion capture equipment to drive the musculoskeletal multibody dynamic models to complete the corresponding gait movements.After the corresponding gait simulation of the multi-body dynamic models were completed,the kinematics and inverse dynamics data were extracted to verify the simulation degree of the models.The data of main muscle strength around hip,joint reaction force and moment were connected in series to the finite element model to complete the finite element analysis of eight gait phases in a single gait cycle.The change of acetabular contact stress in single gait cycle was analyzed.On this basis,we combined with the modular probability models of necrotic distribution to simulate the mechanics of necrotic hip joint in the middle of the support phase,and compared the stress levels of different JIC C1 and C2 types and different probability models of necrotic distribution.Results1.General data: in this study,the data of 56 patients with osteonecrosis of the femoral head were collected,including 32 males and 24 females,aged from 18 to 60 years old,with an average age of 33.72 ±17.53.there were 67 hips in ARCO II stage,19 hips in,ARCO III A stage,39 hips in JIC C1 and 47 hips in JIC C2.All the patients were scanned by CT at the same time and the corresponding DICOM format data were obtained to complete the simulation reconstruction.2.According to the plane heat map and three-dimensional heat map of the necrotic area(JIC C type)of all 86 hips,the necrotic area(JIC C type)of 86 hips had obvious aggregation and centrality,which showed that the necrotic area was concentrated in the northern and eastern half(upper and anterior part of the femoral head),and the hot area spread around with N5E2,N6E2,N2E3,N3E3,N4E3,N5E3 and N6E3 as the center(90%probability distribution area).The necrotic aggregation and concentration areas of the outer ring and the inner ring were basically the same,but there were still differences.The longitude range of the hot area of the inner ring was larger than that of the outer ring,and the latitude range was smaller than that of the outer ring.The overall distribution of the necrotic area was a slightly flattened cone from the outside to the inside.3.Statistics of the distribution characteristics of all 47 necrotic areas(JIC C2)in the longitude and latitude division areas showed that the hot spots of 47 hips necrotic areas(JIC C2)spread around with N2E2,N3E2,N4E2,N5E2,N6E2,N2E3,N3E3,N4E3,N5E3,N6E3,N4E4 as the center(90% probability distribution area).The distribution characteristics of all 39 hip necrotic areas(JIC C1)in longitude and latitude were statistically analyzed.The hot spots of 39 hip necrotic areas(JIC C1)were diffused in a circular gradient with N5E2,N6E2,N3E3,N4E3,N5E3,N6E3 and N5E4 as the center(90% probability distribution area).The distribution of JIC C1 and C2 necrosis had obvious aggregation characteristics in the longitude and latitude division,and the necrotic area was mainly distributed in the northern and eastern half(superior and anterior part of the femoral head).Comparing the two distribution heat maps,the center of C2 hot zone shifted to0 °longitude level compared with C1 hot spot(anterior lateral side of femoral head).Chisquare test showed that the distribution of JIC C1 and C2 necrosis in the outer ring was statistically significant,and the difference was mainly at the longitude level of E1 L and E2 L.compared with the heat map,it was observed that the difference of E1 L and E2 L at the latitude level of S1-N4 was the main distribution difference of C1 and C2 necrosis.On the whole,the distribution range of C2 necrosis was larger than that of C1,which was mainly reflected in the longitude range,but there was no significant difference in latitude range,which made the three-dimensional morphology of C2 necrosis wider and flatter as a whole.4.Musculoskeletal multi-body dynamic simulation results: the obtained gait data could successfully drive the Musculoskeletal multi-body dynamic simulation model to complete the action simulation.The change trend of left hip flexion and extension(sagittal rotation),extension(coronal rotation)and internal and external rotation(cross-sectional rotation)of each model in the single gait cycle was basically consistent with the results collected and analyzed by BTS gait analyzer.The reverse dynamic data of the main muscles(groups)around the left hip in the single gait cycle were normalized,and the curve showed that the changes of muscle strength of the main muscles(groups)around the left hip of each model showed obvious gait phase distribution characteristics.the change trend of muscle strength of the same muscle(group)in each model was basically the same,but the peak level was different.The peak muscle strength of gluteus maximus,gluteus medius,biceps femoris,quadriceps femoris and adductor major muscle appeared in the early and middle stages of the support phase,while the peak muscle strength of gluteus minimus,iliopsoas,adductor and short external rotator muscles appeared at the end of the support phase and the early stage of the swing phase.During the whole gait,the peak muscle strength of gluteus medius in each muscle(group)was more than 0.8 times of body weight.Compared with the literature data,the reaction level and change trend of hip joint reaction data are basically the same in the literature data.in the single gait cycle,the hip reaction force shows a "single trough and double peaks" curve distribution,and the first wave peak stress is in the load-bearing reaction period.the peak stress of the second wave is at the end of the support phase,and the trough stress is in the middle of the supporting phase.The average peak value of wave in the model was 2.5-3.0 times body weight.5.The results of finite element analysis of normal hip joint: the CPRESS stress cloud map of the surface of acetabular cartilage showed the distribution range and magnitude of acetabular contact stress in the whole gait cycle.The maximum CPRESS stress distribution of cephalic cartilage in each gait phase mainly appeared in the top of the cartilage on the femoral head side and the top dome of the cartilage on the acetabular side,and decreased radially to the periphery with the peak area as the center.The maximum peak stress of acetabular cartilage appeared at the end of the brace phase,which was 6.92 MPa,which was basically consistent with the distribution trend of hip reaction data of multi-body dynamic model.The peak stress area of the cortical bone of the femoral head was located in the corresponding cortical bone area under the corresponding cartilage contact stress area,and the maximum peak stress appears at the end of the brace phase was 23.42 MPa.6.Finite element analysis results of necrotic hip joint in the Midstance phase: the probability distribution models of each necrotic area were reconstructed and analyzed by finite element method.The maximum peak stress of cortical bone in necrotic group was37.2MPa(0% model 1C2),the minimum peak stress was 18.93MPa(90% model 2C1),and the average peak stress of cortical bone in necrotic group was 29.67 ±4.32.The peak stress of cortical bone in the weight-bearing area of each model was significantly different in the necrotic groups.In C1 necrosis group,the maximum peak stress of cortical bone in weightbearing area was 36.12 MPa,and in C2 necrosis group,the maximum peak stress of cortical bone in weight-bearing area was 37.2MPa,and the maximum peak stress appeared in 0%probability necrosis model.Paired t-test compared the peak stress of cortical bone in the weight-bearing area of C1 and C2 necrotic groups in different probability distribution models,and the results were statistically significant.The peak stress of cortical bone in C1 and C2 necrotic weight-bearing area increased with the decrease of probability distribution.In the multivariate analysis of variance,Dunnett's test was used to compare the difference of peak stress in the load area between each distribution probability model and the normal model.The results showed that 90% and 80% of the distribution probability models had no statistical significance compared with the normal group,and the results of 70%,60%,50%,40%,30%,20%,10% and 0% were statistically significant compared with the normal group.Sidak's test compared the stress difference of the cortical bone of the femoral head in the weight-bearing area among the distribution probability model groups,and the results showed that there was no significant difference in stress between the adjacent distribution probability groups.Conclusions1.The longitude and latitude division system of the femoral head can reflect the spatial and morphological distribution of JIC type C necrosis,and parameterize,visualize,standardize and modularize the data.2.JIC C1 and C2 necrosis have obvious aggregation characteristics and form hot areas in the horizontal distribution of longitude and latitude,which is centered on N5E2,N6E2,N2E3,N3E3,N4E3,N5E3 and N6E3 units,and the heat spreads to the periphery with a circular gradient,which is the main distribution feature of JIC C type necrosis.3.The distribution difference of E1 L and E2 L units at the latitude level of S1-N4 is the key to the identifying of JIC C1 and C2 necrosis and exploring difference of mechanical properties.4.The modular reconstruction of necrotic area based on longitude and latitude region division system can optimize the modeling scheme and realize "reconstruction on demand".Modular reconstruction of units with 70% and 20% probability of JIC C1 and C2 necrosis is recommended to reduce the data bias caused by selection.5.The simulation framework of "gait analysis—multi-body dynamics—finite element" can realize the inverse dynamic analysis of the corresponding gait based on the real gait data and realize the study of "muscle-bone" mechanics of hip joint from macro to micro in series with finite element model.the idea of "emphasizing both muscles and bones" plays an important role in the simulation study of osteonecrosis of the femoral head. |
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