Mechanical Analysis Of TCM Thread-hanging Therapy For Anal Fistula Based On Three-dimensional Finite Element Mode

Objective:The purpose of this study is to establish a three-dimensional finite element model of the anal canal by collecting the MRI image data of patients with anal fistula,observe the anatomical structure of the muscles around the anal canal,simulate the internal and external sphincter injury models with different degrees caused by seton therapy,conduct static analysis,and observe the overall stress and the overall deformation degree of the model under the simulated state.To provide a basis for exploring the mechanism of seton therapy.Methods:Patients with anal fistula who met the inclusion criteria were selected and underwent enhanced MRI scanning of the anal canal to obtain the MRI image data of the patient’s anal canal.The image data were imported into Mimics21.0 medical image processing software to generate a three-dimensional model of the anal canal based on the image data.The thickness of the internal anal sphincter,the width of the internal anal sphincter,the anorectal Angle,and the thickness of the sphincter space were measured.The data were imported into Geomagic Warp software for further processing,and then SolidWorks software was used to format and assemble the model.Finally,the Workbench software was imported for mechanical analysis.The lower 1/3 transection,lower 2/3 transection,and total transection of the internal sphincter were constructed at the 6 point of lithotomy position in simulated seton surgery for anal fistula.The models of lower 1/3 transection(subcutaneous part),lower 2/3 transection(subcutaneous part and superficial part),and total transection of external sphincter were used for stress analysis and deformation analysis under the same value of anal canal resting pressure.The results were exported and compared to draw conclusions.Results:A three-dimensional finite element model of the anal canal was established,and the anatomical relationship of the muscles around the anal canal was clarified.The results showed that the thickness of the internal anal sphincter was 4.5mm,the width of the internal anal sphincter was 27.29mm,the anorectal Angle was 126.93°,and the thickness of the sphincter space could not be measured.Mechanical analysis results:when the anal canal resting pressure was uniformly set as 10Pa,the stress and deformation degree of the simulation model were greater than those of the original model.The specific values are:the overall maximum deformation of the original model is 0.25mm,and the overall maximum stress is 5.35 × 10-4Mpa.The maximum deformation was 0.26mm and the maximum stress was 5.70 × 10-4 Mpa in the model of internal sphincter transection(1/3).The maximum deformation was 0.28mm and the maximum stress was 1.02 × 10-3Mpa in the model of internal sphincter amputation(2/3).The overall maximum deformation and the overall maximum stress of the internal sphincter transection model were 2.5mm and 1.08 × 10-3 Mpa,respectively.The overall maximum deformation and stress of the external sphincter transection(subcutaneous part)model were 0.25mm and 6.23 × 10-4 Mpa,respectively.The overall maximum deformation of the model of external sphincter amputation(subcutaneous and superficial)was 0.26mm and the overall maximum stress was 6.18 × 10-4 Mpa.The overall maximum deformation and stress of the model with complete trandivision of the external sphincter were 0.47mm and 7.53 × 10-4 mpa,respectively.Conclusion:The MRI image data of the anal canal can be converted into a more intuitive three-dimensional finite element model by various three-dimensional finite element modeling software on the market,which provides help for the study of the mechanism of seton therapy.The original 3D model can be set to simulate different degrees of internal and external sphincter transection after seton treatment.After analyzing these models,the overall stress contrast and deformation contrast of the model can be obtained,which has certain reference value for how to design the surgical method.This modeling analysis method can be applied to the study of anal fistula seton surgery.How to establish more accurate procedural evaluation standards and processes is the direction of the next research.