| BackgroundAdolescent idiopathic scoliosis(AIS) has a morbility of 2%～3%in teenagers,which threatens physical and mental health of teenagers seriously.And the therapic method has been improved greatly,the curative effect has raised a lot.But there are many problems that wait us for studying,in which the biomechanics study of scoliosis is the most important aspect.Spinal biomechanical research methods include animal experiment,physical experiment,cadaver experiment,and so on.The model of scoliosis had not been found in natural animals,and it is difficult to select material.And it is very difficult to get human specimen of scoliosis.With the development of computer,finite element method has been becoming a modern computing method,which can be repeated in study,and it can change any quality and quantitation,and also can provid local and internal reaction mechanismHueter-Volkmann law presumes that the growth of the bone will be suppressed when the stress adding to the bone increases,and the growth of the bone will be accelerated when the stress adding to the bone decreases.The law can explain the progression of AIS in the period of growth peak.The brace can get therapic effect through balancing the stress of convex and concave disc by exerting orthopedic force.In our research,we chose a patients of AIS with Risser sign 3 degree,whose AIS type is Lenk type IA-and PUMC typeⅡa.We construct a FEM of AIS,and research the characteristics of different orthopedic force,and also research distribution change of disc stress after brace treatment in order to predict the effect of brace therapy,which provides a quantization index for AIS biomechanical study.Part oneObjective:Construct a 3-diamensions finite element model of AIS and check the validity of the model,which provides a platform for the next study.Methods:Chose a patient with AIS,and used spiral CT to get spinal successive scanning with layer thickness of 1 millimeter.And the images were saved as a form of DICOM.Used the Mimics to form a 3-diamensions geometric model of AIS,and divided mesh in Hypermesh, and assign the mesh with specific materials attribute.Compared the model with upstanding posterior-anterior X-Ray,supine posterior-anterior X-Ray and lateral flexion X-Ray of supine posterior-anterior position.Chose T12-L2 and L3-S1 to compare with related results of biomechanics empirical study.Results:1.The Cobb'angle of upstanding posterior-anterior X-Ray,supine posterior-anterior X-Ray and lateral flexion X-Ray in left and right supine position were 40°,31°,44°,19°,and 41°,30°,40°,20°in finite element model corresponding.2.Compared the center of mass deviated from sacral middle line between X-Ray and finite element model,P＞0.10,which considered no differences between them.3.Chose T12-L2 and L3-S1 to compare with related results of biomechanics empirical study,the stiffness of the model was in the boundary of related results.Conclusions:1.Based on Dicom document with CT scanning,used software of Mimics and Hypermesh,we constructed a finite element model of AIS from T1 to sacral bone.The model included vertebral body,intervertebral discs,ligaments,costal bone,costal cartilage and sternum from T1 to sacral bone.2.Compared the model with X-Ray and related results of biomechanics,the model meet them very well,which demonstrated the reliability and validity of the model,and it provides a digital platform for the next study. Part twoObjective:To make use of the model constructed in upper chapter in researching characteristics of different orthopedic forces.Methods:1.Limitate the movement of T1 in X and Y orientation,fix the pelvis,and exert 20N,40N,60N at three costal bones in convex side of apex vertebrae,and compare the reshaping effect.2.Limitate the movement of T1 in X and Y orientation,fix the pelvis,exert longitudinal force of 100N,200N,400N at the upper surface of T1 vertebrae,and compare the reshaping effect.3.Limitate the movement of T1 in X and Y orientation,fix the pelvis,exert torque of 10N.m,20N.m,40N.m at T8 and T9,and compare the reshaping effect.Results:1.After exerting transversal force of 20N,40N and 60N,the Cobb's degree change from 31°initially to be 26°,20°and 15°correspondingly, and the rotational angle of T9 decreased by 1.234°,2.501°,3.674°.2.After exerting longitudinal force of 100N,200N and 400N,the Cobb's degree change from 31°initially to be 25°,18°and 13°correspondingly,and the rotational angle of T9 decreased by 0.09°,0.21°,0.33. 3.After exerting torque of 10N.m,20N.m and 40N.m in vertebraes of T8 and T9,the Cobb's degree change from 31°initially to be 26°,24°and 22°correspondingly,and the rotational angle of T9 decreased by 10.781°,18.423°,30.795°.Conclusions:1.Analyzing biomechanical characterastics of different orthopedic force using finite element method,which provides biomechanical basis for deformity correction with instrument and brace therapy.2.Analyzing scoliotic orthopedic force using finite element method, which provides general and local quantization index for 3D correction of scoliosis.3.The reshaping effect of transversal force is much more great than longitudinal force when the Cobb's degree is small.4.The efficiency of orthopedic forces are different:transversal force and longitudinal force perform spinal derotation function mainly,and rotary strength perform vertebral derotation function mainly.Part threeObjective:Make use of the FEM of AIS in part one to analyse distribution change of disc stress in the convex side and concave side in order to predict curative effect of brace. Methods:1.Characteristic of spinal biomechanics in standing positionConstrained condition:fix the pelvis and restrict its movement,and exert gravity load correspondingly.Measure the distribution of disc stress and ligament stress,and predict the increasing height of vertebrae and wedge angle of vertebrae after one year.2.Reshaping effect of braceConstrained condition:fix the pelvis and restrict its movement,and restrict T3 and T4 movement in X-axis and Y-axis.Loading:exert gravity load in each segment of spine correspondingly,and exert lateral force of 0N,10N,20N,30N,40N,60N, 80N,100N at three costal bones in convex side of apex vertebrae.Calculate the mean stress in convex side and concave side,and also the stress ratio between the convex side and the concave side,and predict the increasing height of vertebrae and wedge angle of vertebrae after one year.Results:1.In up standing position,the stress in concave side is higher than the convex side in the discs between T6 to T11 segment,and the stress ratio between the convex side and the concave side is smaller than one. And the ratio in the disc of T8/9 is the most smallest,which is 0.23.2.The stress ratio between the convex side and the concave side is increasing following with the increasement of orthopedic force.When the orthopedic force increases to 30N,the stress ratio between the convex side and the concave side get to 1.00 in T6/7 disc.But when the orthopedic force increases to 100N,the stress ratio between the convex side and the concave side is still smaller than one.3.With the increasing of orthopedic force,the wedge angle in T6-T11 are decreasing gradually,and the total wedge angle change predicted in one year is becoming decrease.And when the force adds up to 100N, the total wedge angle change predicted in one year becomes negative number.Conclusions:1.It is the first time we use finite element method to research the disc stress in the convex side and concave side,and use the disc stress in the convex side and concave side to predict therapeutic efficacy of the brace,which provides a new method for predicting therapeutic efficacy of the brace.2.The study of the disc stress in the convex side and concave side using finite element method provides a new quantization index for improvement of the brace.3.In standing position,the stress in the concave side is much more higher than the convex side,and the ratio of disc stress in the convex side to the concave side has a tendency of becoming small towards apex vertebrae.
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