Digital Reconstruction And Three Dimensional Finite Element Analysis Of Skeleton System

ObjectivesDigital medicine is a new medicine- engineering cross subject.It is characterized by a combination of medicine and digital technique.This subject is comprised of medicine,mathematics,information,electronics,mechanics- engineering,et al. Nowadays digital medicine has been one of the important parts of modern medicine. Especially in surgery this subject has caused great revolution.With digital medicine goes deep into and expands in clinical fields,traditional medicine is running to modern medicine,which is characterized by Precision,Personality,Micro-trauma and Long range.At present orthopedists apply digital technique in clinical fields generally. Digital technique is one of doctors' personal techniques and it will develop with the development of digital medicine.This will be one of doctors' basic clinical techniques in 21 century.This study wants to use the digital technology in clinical orthopedics.It contains two departments:(1) Scoliosis is a frequent disease.It has a complicated anatomy and is a kind of three dimensional(3D) deformity in sagittal plane,coronal plane and transverse plane.It is very important to understand the entirety and details of the abnormal spine before operations.This can help us to diagnose and type correctly, make the operation plan,determine the fixation segments,choose suitable pedicle screws,estimate the angles of screws,et al.It is both the emphasis and the difficult point of scoliosis treatment.In the past time doctors had to use X-ray/CT/MR data to do this job,but all these examinations were two dimensional and they can't be used to evaluate the actual information of 3D spine.In part one,we carried out digital 3D reconstruction of deformity spine of scoliosis patients.Then entities of the spines were made using Rapid Prototyping(RP) technology.We utilized the models to guide diagnosis and typing,design operation program and simulate handlings in operation. (2) At present the biomechanical analysis of pelvis by experiment is crude for these reasons:it is difficult to get pelvis specimens,the anatomy structure is very complicated,the conduction of force is anisotropic,specimens made by different persons are various,et al.Nowadays Finite Element Method(FEM) has being an significant device.FEM can get results without many specimens and the experiment error is few.Furthermore FEM is good at reproducibility.In part two,we carried out digital reconstruction of pelvis of a normal adult.Then we analyzed the mechanism of bearing load and damage by FEM.Character One Digital 3D reconstruction and Rapid Prototyping of scoliosis Section One Digital 3D reconstruction of scoliosisMaterials and methods6 patients with scoliosis were chosen randomly from July to September,2007. They were 6 to 21 years old with average 14.There were 1 male and 5 female patients,with 4 were idiopathic scoliosis(IS) and 2 were congenital scoliosis(CS). They all accepted PET-CT scanning of spine before operations with the scanning interval of 1 mm.The cross- section images were preserved in disc by DICOM (Digital Imaging and Communications in Medicine) pattern.Then they were imported into personal computer(PC) and dealt by Mimics(Materialise's Interactive Medical Inage Control System) 8.1 software.From this data a 3D model of pelvis was reconstructed using Mimics.The steps of digital reconstruction in Mimics contained input and segmentation of images,reconstruction of interested portions,et al.Then the digital 3D recon- struetion images of spine and the skeleton structures nearby were got,such as ribs and pelvis.Subsequently we could do various kinds of observation and measuring to the model.ResultsAll 6 patients in this group were undertaken digital 3D reconstruction of spine before operations.We got their 3D images of abnormal spines.Then we could rotate or translate the 3D model to observe the deformity of spine with the 2D images of sagittal,coronal and transverse planes from any angle conveniently.Also we measured every kinds of data from the images,such as angles of scoliosis,kyphosis or rotation of the spine,extent or segments of the deformity,forms or relationship of vertebral bodies and appendixes,transverse or sagittal diameters of pedicles,the deformity of bony thorax or pelvis,et al.So we could understand the global and details of abnormal spine generally and distinctly.The digital model could also help us do surgery design and simulate the manipulation of internal fixation.Section Two Rapid Prototyping of scoliosis and clinical application Materials and methodsBased on Section One,we output the 3D digital reconstruction model of deformity spine in STL pattern.Then a concrete model of the same spine,which was as equal to the real one,was made by photosensitive colophony using rapid prototyping machine.In this process,the RP technique with compute-assistant and each layer accumulation was utilized.We could realize various kinds of information of the deformity spine from the concrete model directly.And it could be used to design operation program,stimulate the handling of installing screws,et al.The model could also be taken to the operating room and be consulted by surgeon during the operation.ResultsAll 6 patients in this study were undertaken digital 3D reconstruction and rapid prototyping of their spine and every one accepted operations.During the operations we found that the deformity was as same as the reconstruction model before.The appearance and size were completely accord by RP model and real spine.The RP model reflected the concrete information of the abnormal spine exactly and directly. Every patient was operated successfully according to the plans before.The processes of operation were success and the effects were excellent after treatment.There wasn't any syndrome of nerves or vessels.After operation the exhibition of X-ray and CT scanning were satisfying,and the position of pedicle screws were accurate.ConclusionWith the high speedy development of digital medicine and RP technique,they were possible to be used in the diagnosis and treatment in spine diseases.Our study proved the feasibility and reliability of the using of these techniques in clinical practice.Doctors could collect the data of CT scanning to reconstruct the deformity spine digitally to scoliosis patients.Then they made concrete models of the spine using RP technique.Using the RP model,doctors could observe the whole and details of the deformity spine directly from the model,design the operations,stimulate the surgery manipulations and communicate with the patient and his families.At the same time,the RP model made doctors understand the disease deeply and improve the treatment results of operations. Chapter Two Digital reconstruction and three-dimensional FEM analysis of pelvisSection One Establishment of the three-dimensional Finite Element model of pelvisMaterials and MethodsOne common volunteer who was male adult was chosen.He had been got rid of trauma or tumor or deformity of pelvis by X-ray and B-ultrasound examination.Then he got PET-CT scanning.Scanning thickness of each slice was 1 millimeter.The initial two dimensional images of pelvis were output in DICOM format to PC.The digital reconstruction of pelvis based on the data was made by Mimics 8.1 software. The process of reconstruction contained images been input,segmentation of images, pelvis reconstructed,et al.The results were output by STL format(See Chapter One). Then the 3D model accepted post-processing with the software of Freeform.We could modify the 3D model by Freeform,such as smoothening,removing noise and surface-meshing,et al.The results were output in the format of IGES which could be used directly by the software of FEM.Finally the 3D model of pelvis was import by the FEM software of ANSYS 9.0.Through ANSYS we could give units,set up the solid constants,definite the pattern of materials,add ligaments to the pelvis,et al.At the end the model was meshed and a FEM model occurred.ResultsWe got a complete FEM model in ANSYS.He model contained bone structure and some accessory such as ligaments,articular cartilage.This model possessed 241227 nodes and 155194 elements.Based on it people could exert load or damage to the pelvis,or stimulate the processes of operation,such as reset the fracture or fixation,et al.Section Two Finite Element Analysis of Pelvis under static loading Materials and MethodsIn the FEM model of pelvis built in Section One,axial loading were put to it. The model simulated the posture when the body was erecting by two legs.The loading was put to the supine surface of sacrum perpendicularly and distributed to each node averagely with both sides of the acetabulum were constrained.The loading was 500N and the none-line solution was analyzed.After that the stress and strain and displacement nephograms were obtained with the function of post-processing module in ANSYS.At the end the biomechanical stability and intensity of pelvis were analyzed and compared.ResultsThe distribution of stress in two sides of iliac bones was equal.The stress past the ala of sacrum and the sacroiliac joint to the regions near the greater sciatic notch. Then it past the arcuate line to the acetabulum.The peak of stress was 0.434E+07(Pa), appeared at the region near the greater sciatic notch.The stress at the anterior ring of pelvis was small.This result indicated that the main weight loading and stability structure was at the posterior part of pelvis.On the other hand function of the anterior part was supporting mainly.The strain concentrated at two sides of the sacroiliac joints,and it was very small just 0.004527-0.022633.The strain at pubic symphysis was little very much and it could be ignored.The strain of bone was almost zero.The peak value of displacement appeared at the median sacral crest.It was 0.164E-03m (0.164mm).The displacement extended to two sides until the iliac ala.And it gradually reduced to zero from the center to the side.Section Three Three Dimension FEM Analysis of pelvis under Extorsion loadingMaterials and MethodsIn the FEM model of pelvis built in Section One,the loading of 500N was given to the left anterior superior iliac spine.The direction of the loading was flatly rearwards.This state simulated the loading of pelvis when it was paid extorsion loading.ResultsThe stress transmitted in two ways.In the first way it was rearwards to the superior part of the sacrum past the sacroilial joint at the same side.In the second way the stress passed forward to the pubis at opposite side.In the way it past the pubis and pubic symphysis at the same side.The peak value of stress appeared at the promontory of the same side of sacrum.It was 0.240E+08(Pa).The minimum of the stress appeared at the supra-half of sacroilial joint at the same side.The loading of the anterior ring of pelvis was relatively greater than it was perpendicularly.The stress of the real pelvis was analyzed alone using the function of segment in ANSYS.We found that in the anterior ring of pelvis the stress at the medium of upper branch of pubis at the same side was greatest,and it was 0.0142 E+08(Pa).Similarly the stress at the medium of upper branch of pubis at the opposite and at the lower branch of pubis at both sides was greater.The peak value of strain appeared at lower- forward of the sacroi- lial joint at the same side and it reached 0.35.While it was smallest at supra- rearward of the sacroilial joint.And it was smaller at the sacroilial joint opposite.The strain at pubic symphysis was greater and it reached 0.22.The peak value of displacement was at the point of loading and it was 0.0035m.The displacements at ilium,ischium and branch of pubis at the same side were relatively greater.And it was smaller at the branch of pubis and the half part of ilium lateral opposite.The smallest value appeared at supra- half part of the sacroilial joint at the same side.Section Four Three Dimension FEM Analysis of internal fixed pelvisMaterials and Methods In the FEM model of pelvis built in Section One,one of the sacroiliac joints simulated dislocation.Then an internal fixation system was installed before the injured joint.Axial loading and extorsion loading were put to the pelvis in turn.The loading was 500N.Then the none-line analysis was carried out.ResultsThe internal system generated stress concentration under axial loading.The max of stress was 0.599E+90(Pa) which was as much as 100 times than the equal state of the normal pelvis.At the same time only the normal sacroiliac joint existed strain. The fixed joint lost strain at all.The max of displacement was at the fixed sacroiliac joint.The value was 0.342mm.The internal system existed stress concentration similarly under extorsion loading and the value was 0.265E+10(Pa).The maximal value of strain appeared at the pubic symphysis.The strain was as 4.5 times much as the normal pelvis.The distribution of displacement was similarly as the normal pelvis.The displacement of the point of bared loading was largest and it was very small at the fixed sacroiliac joint.The distribution was as similar to the normal pelvis.ConclusionsWe utilized the data of CT scanning of pelvis which was from a normal male adult.The data was input to PC and was reconstructed to digital model in Mimics. Then the results was imported to ANSYS and been analyzed by FEM.We gave loading perpendicularly and extorsion loading to the pelvis model.In the two situations the tendency of changing of stress,strain and displacement was according to it in experiments using specimens in vitro or in the theories.It proved the efficacy and reliability of the 3D finite element model.Then we simulate the state of dislocation of one sacroiliac joint and been internal fixed.The stability of internal fixation was analyzed.Afterward we will use it to analyze every situations of the pelvis all-sided,such as fracture,fixation,dislocation of the sacroilial joint,part excision,et al.