Objective A simplified pelvic model of a patient was established,and periacetabular osteotomy(PAO)was simulated to investigate its effects on the stress in the sacroiliac joints in the standing position.Methods The anterior center edge angle(ACEA)and lateral center edge angle(LCEA)of the patient's hip model were adjusted,and 27 postoperative models were obtained.Finite element calculations and analyses of each model were performed during single-leg standing and double-leg standing.Furthermore,an investigation of the stress variations and distributions on the sacroiliac cartilage was conducted in combination with a hip joint stress analysis.Results During single-leg standing,the maximum stress on the sacroiliac cartilage of a healthy individual was 18.2 MPa.With an increase in the anterior center edge angle(ACEA),the von Mises stress of the sacroiliac cartilage decreased from 34.5 MPa to 19.8 MPa.The maximum von Mises stress in the acetabular cartilage decreased from 4.767 MPa to 2.7 MPa.Before the ACEA attained 36°,the maximum von Mises stress exhibited a downward trend.After it attained 36°,the stress distribution began to increase,and the stress distribution improved significantly.During double-leg standing,the minimum and maximum von Mises stresses on the sacroiliac cartilage of the affected leg side were 2.8 and 6.5 MPa,respectively.The sacroiliac cartilage stress on the normal leg side did not vary significantly,and the stress difference between the two leg sides decreased gradually.Conclusions PAO can improve the hip joint stress and sacroiliac joint stress.Additionally,the improvement of sacroiliac joint stress is identical to that of hip joint stress.Prior to surgery,a comprehensive planning of the hip and sacroiliac joints can be used as a reference by doctors.This is of high significance for patients with developmental dysplasia of the hip(DDH)to achieve better outcomes.

Objective To establish a three-dimensional finite element model of knee joint in patients with mild knee osteoarthritis in the absence of CT and MRI with thin layer thickness,and to analyze the stress distributions of the tibial plateau.Methods A female patient with mild knee osteoarthritis was selected as the study object,and received serial CT scan from pelvis to distal tibia of fibula.The obtained files in DICOM format were imported into Mimics software for extracting the bony structures of knee joint through threshold segmentation,and then optimizing the extracted structures with Edit Masks,Cavity Fill and Region Grow.The generated model of bony structures was imported into 3-matic for smoothing and wrapping,and Geomagic Wrap was used for bony structure processing with mesh doctor inspection,surface defect repair and surface fitting.The cartilages,meniscus and ligaments were established by contour extension,and assembled with bony structures in SolidWorks in the way of origin coincidence.After defining material properties and contact relationships,meshing,and setting constraints and loads in ANSYS software,the stress distributions of the tibial plateau when standing with both legs were analyzed.Results A complete knee joint model including bony structure,cartilage and ligament was successfully established.When standing with two legs,the peak value of contact stress was about 1.21 MPa,and the maximum stress was 0.72 MPa at the medial middle of tibial plateau and lateral tibial plateau.The 62.7%and 37.3%of the total load were borne by the inner and outer compartments.Conclusion The model of the total knee joint is established with CT extraction and software rendering,and the finite element analysis results meet clinical expectations,indicating that the model established by the proposed method is reliable and can be used for follow-up research.

Objective A simplified pelvic model of a patient was established,and periacetabular osteotomy(PAO)was simulated to investigate its effects on the stress in the sacroiliac joints in the standing position.Methods The anterior center edge angle(ACEA)and lateral center edge angle(LCEA)of the patient's hip model were adjusted,and 27 postoperative models were obtained.Finite element calculations and analyses of each model were performed during single-leg standing and double-leg standing.Furthermore,an investigation of the stress variations and distributions on the sacroiliac cartilage was conducted in combination with a hip joint stress analysis.Results During single-leg standing,the maximum stress on the sacroiliac cartilage of a healthy individual was 18.2 MPa.With an increase in the anterior center edge angle(ACEA),the von Mises stress of the sacroiliac cartilage decreased from 34.5 MPa to 19.8 MPa.The maximum von Mises stress in the acetabular cartilage decreased from 4.767 MPa to 2.7 MPa.Before the ACEA attained 36°,the maximum von Mises stress exhibited a downward trend.After it attained 36°,the stress distribution began to increase,and the stress distribution improved significantly.During double-leg standing,the minimum and maximum von Mises stresses on the sacroiliac cartilage of the affected leg side were 2.8 and 6.5 MPa,respectively.The sacroiliac cartilage stress on the normal leg side did not vary significantly,and the stress difference between the two leg sides decreased gradually.Conclusions PAO can improve the hip joint stress and sacroiliac joint stress.Additionally,the improvement of sacroiliac joint stress is identical to that of hip joint stress.Prior to surgery,a comprehensive planning of the hip and sacroiliac joints can be used as a reference by doctors.This is of high significance for patients with developmental dysplasia of the hip(DDH)to achieve better outcomes.