| ObjectiveAs the improving of people's living standards,the number of obese patients with knee osteoarthritis has gradually increasing.Total Knee arthroplasty is an effective method for the treatment of osteoarthritis.Using of tibial stem in the treatment of obese patients with knee replacement is an effective way to reduce the incidence of postoperative aseptic loosening.However,it is still unclear whether the length of the tibial stem affects the stress distribution and what the optimal length would be for patients with a high BMI.Therefore,we performed a three-dimensional finite element(FE)modeling study to investigate the stress distribution and shielding on the tibial implant platform for different tibial stem lengths.Methods1.A tibia in a female volunteer patient with osteoarthritis processed the computed tomography.Using Mimics15.0 software to process image data and 3D reconstruction.Three dimensional solid model of the tibia was derived and importedthe STL format into Unigraphics NX8.5 software,and then simulating the step of total knee replacement operation,establishing the three dimensional solid model of tibial.The tibial side,30 mm,60mm and 100 mm length of stem extension of the knee prosthesis were introduced into the software.Three dimensional dynamic finite element model is established by dividing the mesh,assigning the material properties of each part,determining the coordinate system,loading and boundary conditions with a finite element analysis software FEMAP.2.The model of virtual tibial prosthesis with different stem length extension.The control group A was the standard tibial plateau,with no extension stem connection.The experimental group B was connected with the 30 mm extension stem by standard tibial plateau prosthesis.The experimental group C was used as the standard tibial plateau prosthesis with 60 mm extension stem.The experimental group D was used as the standard platform prosthesis with 100 mm extension stem.Each model is independent of each other.FEMAP finite element software was used to calculate the biomechanical characteristics of four groups of 3D finite element models.Result1.In the standard platform and the 3 groups of different length extension group,the lateral stress of each group was the highest.The stress of the tibial prosthesis wing is higher,and the maximum stress is on the standard platform(0mm).In the use of30 mm,60mm,and 100 mm extension rod,respectively 37.93 + 1.25 MPa,34.62 +3.85 MPa and 36.70 + 2.97 MPa.Comparing with the control group,the stress values of the three groups were significantly reduced,and the difference was statistically significant.There was no significant difference between the experimental groups.2.In the control group A,experimental group B and experimental group C model,the medial stress of the tibial plateau were 4.09 + 0.85 MPa,+ 3.98 + 0.73 MPa and + 3.88 + 0.80 MPa,and there was no significant difference between the three groups.But in the experimental group D(100mm extension),the medial plateau stress decreased significantly to 1.55 + 0.29 MPa,and there was significant differencebetween the other three groups.In the control group A and experimental group B model,posterior tibial plateau stress was 11.68 + 1.01 MPa and 10.34 + 2.05,there were statistically significant differences between the two groups(P < 0.05),A,B two group and experimental group C and D have statistical significance on difference in rear platform(P < 0.05).There was no statistically significant difference between the experimental group and the posterior platform of C and D.3.In the control group A(0mm standard platform),the stress at the tibial plateau24.2cm reached a peak value of 43.3MPa.In the experimental group model,using the extended pole does not change the axial stress transmission mode,but the location of peak stress to the distal conduction,the use of 30 mm,60mm and 100 mm extension rod stress peak increased gradually,reached 60.52 MPa,66.31 MPa and 78.61 MPa respectively,the distance between the tibial plateau were 26.6cm,28.3cm and30.6cm.4.In the three experimental groups,the stress of the proximal tibial cortex decreased with the extension of the extension rod,and the 100 mm extension group was the most significant.100 mm prolonged stress shielding large area is located in the base within 6cm bar group,up to 82.39%;60mm extension rod group,within the6 cm region from the base of stress shielding of the maximum maximum 67.83%;30mm extension rod,the maximum stress shielding region and the base distance less than 2cm,the maximum stress shielding rate 39.48%.The three have statistical difference.ConclutionThe use of the extension rod can be dispersed to a certain extent tibial stress;extension rod of the proximal tibia of varying degrees of stress shielding,long extension rod is more obvious;the extension rod stress conduction to the distal tibia,the extension rod is longer,will make the tibia stress,increase operation after the tibia pain incidence;knee arthroplasty,increase the extension rod of the tibial plateau front and lateral stress had no significant effect,long extension rod will disperse the medial tibial plateau stress,and use the shorter extension bar can significantly reduce theposterior tibial stress. |
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