Finite Element Analysis On The Femoral Revision With Two Types Revision Hip Stems

Objective: To compare the stress distribution on the femur when perform femoral revision with bone defect using cylindrical extensively porous-coated stems and fluted,tapered titanium stems.Methods : 1.The femur of healthy adult volunteer was scanned by CT scan,and obtain the DICOM data of tomographic scanning.Import the femoral DICOM data into Mimics 15.0 software for image processing,acquiring 3D model of bone cortex and cancellous of femur of healthy adult volunteer.Export the two models as.STL files;2.The.STL files of bone cortex and cancellous were imported into Geomagic Studio 2013 software,and the clutter data produced by Mimics15.0 software was cleared.After polygon stage,the curved surface slice was created,and the curved surface slice was fitted surface after the shape processing stage.NURBS surface models of bone cortex and cancellous were less surface,closed and smooth.Export the two models as.IGES files;3.The.IGES files of bone cortex and cancellous were imported into Solidworks 2015 software.Finally,the solid model of femoral bone cortex and cancellous was obtained.By Solidworks 2015 software,assemble the bone cortex and cancellous matter into a solid model of the femur via assembly function.The femoral head and neck were amputated as hip arthroplasty.According to the classification of Parprosky bone defect classification,we simulate four types of femur bone defect: Parprosky IIA,IIB,IIC and IIIA.All solid models of the femur bone defect were stored as the format of.PRT;4.In this experiment,the Echelon revision stem(Simith&Nephew,American)was selected to represent the cylindrical extensively porous-coated stem.and the Wagner SL revision femur stem(Zimmer,American)represent the fluted,tapered titanium stem.By the Solidworks 2015 software,according to the design data of two kinds of revision stems,two specifications of cylindrical extensively porous-coated stems were drawn: size 15 porous-coated straight stem,size 15 porous-coated straight stem Plus,and two specifications of fluted,tapered titanium stems: size 14 190 mm length,size 15 225 mm length.Revision stems of different specifications meet the requirements of different degrees of bone defects.The solid model of the Revision stems were saved as.prt format;5.Selected the corresponding size of revision stem according to the degree of bone defect.By the Solidworks 2015 software,two kinds of solid models of revision stems and four solid models of different degrees of femoral bone defect were assembled like revision hip arthroplasty,and eight models of revision were obtained.Divided revision models into extensively cylindrical stems group and tapered stems group.The revision models were saved as.x_t format;6.The.x_t files of revision models were imported into Ansys Workbench 17.0 software for finite element analysis.Material assignment for bone and stems,regarded the bone defect region as cancellous bone removed and cortical bone thinned to simulate the bone defect.meshed the revision model by meshing tool.Applied the peak load of the joint during adult gait cycle.Finite element analysis was solved after all steps is set up and completed,getting the nephogram of stress distribution and Von Mises value of femur;7.Analysis of the difference of stress distribution at femoral bone defect region between the two groups.In the femoral bone defect region of cylindrical stems group and tapered stems group,25 points of Von Mises value were randomly selected,and the difference of stress distribution in the bone defect region between the two groups was analyzed;Compare the difference of nephogram of the femoral stress distribution between cylindrical stems group and tapered stems group;Extracted Von Mises value at the lateral and medial of coronal plane of the femur between two groups of models,and draw line chart.Compare the difference of line chart of the femoral stress distribution between cylindrical stems group and tapered stems group.Results:1.The nephograms of the femoral stress distribution and line charts showed that the stress of lateral and medial sides of femur was obviously higher than that of anterior and posterior side,besides the stress of lateral and medial sides of femur gradually increased from proximal end to distal end,reaching the peak of stress at the distal end of femur.The maximum Von Mises value of tapered stems group is 91.3 MPa,and that of cylindrical stems group is 5.2 MPa;2.Under the condition of the same degree of bone defect,the stress in the femoral bone defect region was higher in the tapered stems group than cylindrical stems group,and the difference was statistically significant((P<0.05));3.Under the condition of the same degree of bone defect,the nephogram of the femoral stress distribution showed that the stress distribution of the proximal and middle femur in the tapered stems group was more gently,while the stress distribution in the cylindrical stems group was less gently.The line chart showed that the stress changes in the region span 0cm to 10.5cm away from the osteotomy site of tapered stems group of Parprosky II bone defect(IIA?IIB?IIC)were much smoother than the cylindrical stems group of Parprosky II bone defect.In addition the line chart showed that the stress changes in the region span 0cm to 15.5cm away from the osteotomy site of tapered stems group of Parprosky IIIA bone defect were much smoother than the cylindrical stems group of Parprosky IIIA bone defect;4.The line chart showed that the stress changes in the end region of cylindrical stems group were much sharper and the transition was less smoother than tapered stems group.The line chart showed that the increased stress value in the region from 9.0cm to 10.5cm of II(IIA?IIB?IIC)bone defect and 14.0cm to 15.5cm of IIIA bone defect away from the osteotomy site of cylindrical stems group was IIA:25.0MPa ?IIB:23.0MPa?IIC:20.0MPa ?IIIA:23.0MPa,while in the region from 13.5cm to 15.0cm of II(IIA?IIB?IIC)bone defect and 17.0cm to 18.5cm of IIIA bone defect away from the osteotomy site of tapered stems group was IIA:4.0MPa?IIB:2.0MPa?IIC:2.0MPa?IIIA1.50MPa?The nephogram of the femoral stress distribution showed that there was a narrow green band(about 1.5cm width)at the end of porous-coated region of cylindrical stems group,while there was no obvious stress concentration in tapered stems group.Conclusion:1.Under the condition of the same degree of bone defect,there was much higher stress in the femoral bone defect region in fluted,tapered titanium stems revision than cylindrical extensively porous-coated stems revision;besides the tress distribution of the proximal and middle femur in the fluted,tapered titanium stems revision was more gently than the cylindrical extensively porous-coated stems revision;in additions,tress changes in the end of porous-coated region of cylindrical extensively porous-coated stems revision were much sharper and the transition was less smoother than fluted,tapered titanium stems revision.There was obvious femoral stress concentration at the end of porous-coated region of cylindrical extensively porous-coated stems revision,while there was no obvious stress concentration in fluted,tapered titanium stems revision;2.Fluted,tapered titanium stems revision showed higher stress in the femoral bone defect region than that of cylindrical extensively porous-coated stems revision.This may be the reason of the proximal femural pontaneous bone remodeling after the revision with fluted,tapered titanium stems and the proximal femural bone resorption bone resorption due to stress shielding after the revision with cylindrical extensively porous-coated stems;3.The stress concentration in the femur at the end of the porous-coated region after the revision with cylindrical extensively porous-coated stems may be one of the cause of the thigh pain observed.