The Study Of Computational Models In Numerical Simulation Of Pectus Excavatum With Scoliosis

The pectus excavatum(PE)is a common thoracic deformity disease.It refers to the sternums,rib cartilages and some ribs which form the anterior thoracic wall,which is concave to the spine.Found in the clinical,patients with pectus excavatum are often associated with scoliosis symptoms.Studies have reported that scoliosis symptoms of the major patient whose sternal deformity and scoliosis were in the same direction improved after the minimally invasive surgery;in the other hand,scoliosis symptoms increased.At present,through the establishment of numerical simulation model to predict the effect of minimally invasive orthopedic surgery and guide the design of clinical orthopedic surgery program has been applied,it has played a positive role to improve the treatment effect.The computational models that have been used in numerical simulation include: solid model based on three-dimensional reconstruction and beam element model.The solid model based on three-dimensional reconstruction has the advantages of accuracy in modelling and computation.But the modeling method of solid model is complex,the modeling cycle is long,the patients need to wait for a long time after admission,and cannot meet the needs of the rapid design of the clinical orthopedic surgery program.The beam element model has the advantage of simple modeling method and short modeling period.But it has been found in the study that the results of scoliosis which were predicted by the beam element model in numerical simulation were different from the clinical results.It is reported that patients who were predicted scoliosis would be improved in the numerical simulation has increased scoliosis after surgery.Therefore,the study of the beam element cannot accurately predict the deformation of scoliosis,to develop a convenient and rapid modeling method which can accurately predict the results of minimally invasive orthopedic surgery of PE with scoliosis is of great significance for the reduction of pain,improvement of the treatment and promotion the application of numerical simulation in the design of minimally invasive orthopedic surgery.In this paper,a method of creating thoracic three-dimensional solid model based on structure and size of thoracic model was developed,which greatly shortened the modeling time of thoracic model and preserved the advantages of three-dimensional solid model.The three-dimensional reconstruction model,the beam element model and the simplified three-dimensional solid model were used to simulate the PE minimally invasive procedure with three computational models,respectively,with CT scans of a typical PE with scoliosis patient.Compared with the results of clinical minimally invasive orthopedic surgery,the three calculation models can accurately predict the displacement of the sternum,but the three models predicted the correction results of scoliosis significantly differently,in which the correction results of scoliosis predicted by the three-dimensional solid model and thesimplified three-dimensional solid model were close to the results of orthopedic surgery,but there were still a large gap to the results of the beam element model.In order to explain the reason of the differences between the three numerical models,a composite model consisting of the sixth thoracic vertebra and the sixth rib was defined to study the biomechanical properties of the assembly model.The vertebras and ribs of the assembly model were created by three-dimensional reconstruction model,simplified three-dimensional solid model and beam element model,respectively.The displacement of the upper and lower thoracic spine was restrained in the simulation,and the orthopedic displacement of the sixth rib was applied according to the numerical simulation results of the sternum.The results showed that the displacement and stress distributions of the beam element model were significantly different from those of the three-dimensional solid model and the simplified three-dimensional solid model.There are many factors that affect the correction of PE with scoliosis.The main factors include the direction and depth of pectus excavatum,the scoliosis direction,angle and position.The main difficulty in the numerical simulation of the minimally invasive correction of the PE with scoliosis is the lack of research on the factors affecting the minimally invasive orthopaedic correction.The parametric research of the three-dimensional reconstruction solid model is unable to obtain the necessary research progress for heavy workload.In this paper,we developed a simplified three-dimensional solid model of PE with scoliosis to study the effects of different deformations on the sternum elevation displacement and scoliosis.The results of numerical simulation showed that the thoracic disease had been improved after thoracic elevation.For scoliosis,if the thoracic deformation and the arcuate deformity of the scoliosis were located in the opposite side,the PE surgery may reduce the lateral bending of the spine;if the thoracic deformation and the arcuate deformity of the scoliosis were located in the same side,the PE surgery may increase the lateral bending of the spine,which is mainly relevant to the location of the arcuate deformity of scoliosis.