| ObjectiveTo study the feasibility of constructing three dimensional dynamic finite element model based on two-dimensional CT and MRI image data from the knee joint. Virtual the prosthesis matching situation through computer technology. Analysis the prosthesis surface contact stress changes when mismatching the prosthesis size by finite element method. To provide the basis for the choice of artificial joint prosthesis.Methods1. A adult young man was chosen to get two-dimensional images of both knee joint by MRI scaning and all lower limb length by CT scaning. The images was imported to Mimics software in DICOM format, and three-dimensional digital model of the knee joint including bone, cartilage, meniscus, ligaments and tendons were reconstructioned.2. The full range of artificial knee joint prosthesis were chosen and obtained point cloud data by laser scanning. The data was imported to Imageware software in STL format, and 3-D digital model of the artificial knee joint prosthesis were reconstructioned. The best clinical bone cutting angle and implant placement position measurement were simulathed by computer. Appropriate prosthesis were chosen for installation and simulathed cutting bone of knee joint model in accordance with TKA operating standards. The model grids were divided and material properties were defined, calculated the knee joint dynamic coordinate system, stress and boundary condition. The three-dimensional dynamic finite element model was reconstructed finally.3. The prosthesis size mismatching was simulathed by computer with the same knee joint. In experimental group A, the size 3 femoral prosthesis was mached with size 2.5 tibial prosthesis (F>T). In experimental group B, the size 3 femoral prosthesis was matched with size 4 tibial prosthesis (F<T). In control group the size 3 femoral prosthesis was matched with size 3 tibial prosthesis (F=T). By using ABAQUS software, and analyzed the biomechanical characteristics of the artificial knee joint replacement prosthesis contact, with flexion from 0 degree to 120 degree of the knee three-dimensional dynamic finite element model.4. The data was analyzed by SPSS 19.0 software, compared the maximum equivalent stress on polyethylene gasket by using no repeated two-factor variance analysis. Significant level a=0.05.Results1. In the the process of knee flexion movement with vertical stress after TKA, the femur moved slide and extorsion when rolled relative to the tibia femoral bone in the range of 0 degree to 90 degree flexion angle. The medial femoral condyle slided to posterior, the lateral condyle lifted up and internal rotation in the range from 90 degree to 120 degree flexion angle.2. In the the process of knee flexion movement with vertical stress after TKA, stress gradually focused on the medial posterior part of polyethylene gasket with flexion degree deepening, and its reached a relatively high peak stress when near to 120 degree angle.3. The knee flexion movement from 0 degree to 120 degree, there was statistical significance between the experimental group (F>T and F<T) and control group (F=T) at the maximum equivalent stress on medial polyethylene gasket (P<0.05).4. The knee flexion movement from 0 degree to 80 degree, there was statistical significance between the experimental group (F>T and F<T) and control group (F=T) at the maximum equivalent stress on lateral polyethylene gasket (P<0.05). When the flexion movement more than 50 degree, the lateral femoral condyle lifted up.5. The knee flexion movement from 0 degree to 40 degree, there was no statistical significance between the experimental group 1 (F>T) and control group (F=T) at the maximum equivalent stress on ineuiai anud laierai puryeinyiene gasket (p＞0.05). The knee flexion movement from 0 degree to 40 degree, there was statistical significance between the experimental group 2 (F<T) and control group (F=T) at the maximum equivalent stress on medial polyethylene gasket (P<0.05), there was no statistical significance between the experimental group 2 (F<T) and control group (F=T)at the maximum equivalent stress on lateral polyethylene gasket (P>0.05). The knee flexion movement from 40 degree to 80 degree, there was no statistical significance between the experimental group (F>T and F<T) and control group (F=T) at the maximum equivalent stress on medial and lateral polyethylene gasket (P>0.05). When the knee flexion movement more than 80 degree there was statistical significance between the experimental group (F>T and F<T) and control group (F=T) at the maximum equivalent stress on medial and lateral polyethylene gasket (P<0.05).Conclusion1. The effective knee three-dimensional dynamic finite element model could combined on the two-dimensional images based of CT and MRI with finite element method, established an The model coucld be used for the study of biomechanics in the TKA knee joint.2. With the knee joint flexion degree deepening after total knee arthroplasty, the contact stress increased in the polyethylene gasket posterior part, and more likely to wear.3. The TKA knee joint flexion movement form 0 degree to 40 degree, the maximum equivalent stress increased in the medial polyethylene gasket when the femoral prosthesis size was less than the tibia prosthesis size, and enhanced the more risk for the polyethylene gasket.4. When the knee flexed more than 90 degree, the maximum equivalent stress increased in the polyethylene gasket medial posterior part obviously when the femoral prosthesis size and the tibia prosthesis size mismatching, and that might induce the wear of the polyethylene gasket.5. During the knee joint flexed movement of repeatedly, it might lead to the tibia platform polyethylene gasket long-term wear increased when the femoral prosthesis size and the tibia prosthesis size mismatching, and reduce the prosthesis using time.And the risk was higher when the femoral prosthesis size was less than the tibia prosthesis size.6. When the Femoral prosthesis and tibial prosthesis size matching, it beneficial to extend the service life of the prosthesis. |
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