| ObjectiveTo investigate the feasibility of reconstructing three dimensional dynamic finite element model based on two-dimensional CT and MRI image data from knee joint. An osteotomy was simulated in the three-dimensional model and virtual knee replacement operation was made with posterior cruciate-substituting fixed-bearing and rotating-platform prosthesis model. The prosthesis surface peak conact stress changes were analyzed when the prosthesis sizes were mismatch by finite element method. To provide a theoretical basis for clinical work.Methods1. Nine adults were chosen to get two-dimensional images of both knee joint by MRI scaning and lower extremity by CT scaning. The images were imported to Mimics 16.0 software in DICOM format, the three-dimension digital models of the knee joint including bone, cartilage, meniscus, ligaments and tendons based on two-dimensional MRI image data and the lower extremity three-dimension models based on two-dimensional CT image data were reconstructed.2. The 5 sets of posterior cruciate-substituting fixed-bearing (FB) and rotating-platform (RB) total knee prosthesis were respectively chosen and obtained point cloud data by laser scanning. The data was imported to Geomagic Studio 12 software in STL format to reconstruct a fixed-bearing (FB) and rotating-platform (RB) total knee prosthesis geometry model. Virtual osteotomy according to standard operating method in the three-dimension digital knee model and different knee replacement prosthesis were choosed and installed in the resceted knee model according to clinical operating standards. The three-dimension model were meshed and material properties of various parts of the knee were defined, The dynamic coordinate system of knee models was established and the load and defined boundary conditions were applied.Then the three-dimension dynamic finite element model was reconstructed finally.3. The prosthesis size mismatch of fixed-bearing (FB) was simulated by computer in the 3D knee joint model. In experimental group A (F>T), the size 2 femoral prosthesis was mached with size 1.5 tibial prosthesis, the size 2.5 femoral prosthesis was mached with size 2 tibial prosthesis, the size 3 femoral prosthesis was mached with size 2.5 tibial prosthesis. In experimental group B (F<T), the size 2 femoral prosthesis was mached with size 2.5 tibial prosthesis, the size 2.5 femoral prosthesis was mached with size 3 tibial prosthesis, the size 3 femoral prosthesis was mached with size 4 tibial prosthesis. In control group C (F=T), the size 2 femoral prosthesis was mached with size 2 tibial prosthesis, the size 2.5 femoral prosthesis was mached with size 2.5 tibial prosthesis, the size 3 femoral prosthesis was mached with size 3 tibial prosthesis. By using Abaqus software, the biomechanical characteristics of the artificial knee joint replacement prosthesis were analyzed at 0°,30°,60°,90°,120° of knee flexion respectively.The maximal equivalent stress of different groups of the prosthesis were made statistical analysis using SPSS 19.0 software. Significance level α=0.05.4. The prosthesis of rotating-platform(RB)prosthesis size mismatch was simulated by computer in the knee joint model. In experimental group A (F>T), the size 2 femoral prosthesis was mached with size 1.5 tibial prosthesis, the size 2.5 femoral prosthesis was mached with size 2 tibial prosthesis, the size 3 femoral prosthesis was mached with size 2.5 tibial prosthesis. In experimental group B (F<T), the size 2 femoral prosthesis was mached with size 2.5 tibial prosthesis, the size 2.5 femoral prosthesis was mached with size 3 tibial prosthesis, the size 3 femoral prosthesis was mached with size 4 tibial prosthesis. In control group C (F=T), the size 2 femoral prosthesis was mached with size 2 tibial prosthesis, the size 2.5 femoral prosthesis was mached with size 2.5 tibial prosthesis, the size 3 femoral prosthesis was mached with size 3 tibial prosthesis. By using Abaqus software, the biomechanical characteristics of the artificial knee joint replacement prosthesis were analyzed at 0°,30°,60°,90°,120° of knee flexion respectively. The maximal equivalent stress of different groups of the prosthesis were made statistical analysis using SPSS 19.0 software. Significance level α=0.05.Results1. The peak contact stresss of posterior cruciate-substituting fixed-bearing and rotating-platform medial and lateral polyethylene gasket increased gradually during knee model flexed from 0° to 90°. The peak contact stresss increased to the maximum value at 90° of knee flexion.2. The peak contact stressses of the same size posterior cruciate-substituting fixed-bearing medial and lateral polyethylene gasket were analyzed with ANOVA method, the p value was less than 0.05. The peak contact stressses were statistical significance between medial and lateral polyethylene gasket. The pdak contact stressses of medial polyethylene gasket was greater than that of the lateral polyethylene gasket.3. There was statistical significance between the experimental group A (F>T) and control group C(F=T) (P<0.05) about the peak contact stressses on posterior cruciate-substituting fixed-platform medial polyethylene gasket at 0°,30°,60°,90°, 120° of knee flexion. There was statistical significance between the experimental group B (F<T) and control group C(F=T) (P<0.05) about the peak contact stressses on posterior cruciate-substituting fixed-platform medial polyethylene gasket at 0°,30°, 60°,90°,120° of knee flexion.4.The posterior cruciate-substituting fixed-bearing medial polyethylene gasket peak contact stressses of experimental group A and experimental group B at 0°,90° of knee flexion were compared, there were no statistical significant. But the peak contact stressses of the two groups at 30°,60°,120° of knee flexion were compared, the p values was less than 0.05, there were statistical significant.The fixed-bearing medial polyethylene gasket peak contact stressses of experimental group A were greater than that of experimental group B.5. There was statistical significance between the experimental group A (F>T) and control group C(F=T) (P<0.05) about the peak contact stressses on posterior cruciate-substituting fixed-bearing lateral polyethylene gasket at 0°,30°,60°,90°, 120° of knee flexion. There was statistical significance between the experimental group B (F<T) and control group C(F=T) (P<0.05) about the peak contact stressses on posterior cruciate-substituting fixed-bearing lateral polyethylene gasket at 0°,30°, 60°,90°,120° of knee flexion.6. The peak contact stressses on posterior cruciate-substituting rotating-platform medial polyethylene gasket of experimental group B at 0°,30°,60°,90°,120° of knee flexion were greater than peak contact stressses of other two groups. The peak contact stressses of control group C were smallest in the three groups. The medial polyethylene gasket peak contact stressses of the three groups were increased to the maximum value at 90° of knee flexion.7. There was statistical significance between the experimental group A (F>T) and control group C (F=T) (P<0.05) about the peak contact stressses on posterior cruciate-substituting rotating-platform medial polyethylene gasket at 0°,30° of knee flexion. There was statistical significance between the experimental group B (F<T) and control group C (F=T) (P<0.05) about the peak contact stressses on posterior cruciate-substituting rotating-platform medial polyethylene gasket at 0°,30° of knee flexion. There was no statistical significance between the experimental group A (F>T) and experimental group B (F<T) (P>0.05) about the peak contact stressses on posterior cruciate-substituting rotating-platform medial polyethylene gasket at 0°,30° of knee flexion of knee flexion. There was statistical significance between the experimental group B (F<T) and control group C (F=T) (P<0.05) about the peak contact stressses on posterior cruciate-substituting rotating-platform medial polyethylene gasket at 60° of knee flexion. There was no statistical significance between the experimental group A (F>T) and control group C (F=T) (P>0.05) about the peak contact stressses on posterior cruciate-substituting rotating-platform medial polyethylene gasket at 60° of knee flexion of knee flexion. There was no statistical significance between the experimental group B (F<T) and control group C (F=T) (P>0.05) about the peak contact stressses on posterior cruciate-substituting rotating-platform medial polyethylene gasket at 60° of knee flexion of knee flexion. There was no statistical significance between the experimental group A (F>T) and control group C (F=T) (P>0.05) about the peak contact stressses on posterior cruciate-substituting rotating-platform medial polyethylene gasket at 90°,120° of knee flexion. There was no statistical significance between the experimental group B (F<T) and control group C (F=T) (P>0.05) about the peak contact stressses on posterior cruciate-substituting rotating-platform medial polyethylene gasket at 90°,120° of knee flexion. There was no statistical significance between the experimental group A (F>T) and experimental group B (F<T) (P>0.05) about the peak contact stressses on posterior cruciate-substituting rotating-platform medial polyethylene gasket at 90°,120° of knee flexion.8. There was statistical significance between the experimental group A (F>T) and experimental group B (F<T) (P<0.05) about the peak contact stressses on posterior cruciate-substituting rotating-platform lateral polyethylene gasket at 0° of knee flexion. There was statistical significance between experimental group B (F<T) and control group C(F=T) (P<0.05) about the peak contact stressses on posterior cruciate-substituting rotating-platform lateral polyethylene gasket at 0° of knee flexion. There was no statistical significance between the control group C (F=T) and experimental group A (F>T) (P>0.05) about the peak contact stressses on posterior cruciate-substituting rotating-platform lateral polyethylene gasket at 0° of knee flexion. There was statistical significance between experimental group B (F<T) and control group C(F=T) (P<0.05) about the peak contact stressses on rotating-platform lateral polyethylene gasket at 30° of knee flexion. There was statistical significance between experimental group A (F>T) and control group C(F=T) (P<0.05) about the peak contact stressses on posterior cruciate-substituting rotating-platform lateral polyethylene gasket at 30° of knee flexion. There was no statistical significance between the experimental group B (F<T) and experimental group A (F>T) (P>0.05) about the peak contact stressses on posterior cruciate-substituting rotating-platform lateral polyethylene gasket at 30° of knee flexion. There was statistical significance between experimental group B (F<T) and control group C (F=T) (P<0.05) about the peak contact stressses on posterior cruciate-substituting rotating-platform lateral polyethylene gasket at 60°,90° of knee flexion. There was no statistical significance between the experimental group B (F<T) and experimental group A (F>T) (P>0.05) about the peak contact stressses on posterior cruciate-substituting rotating-platform lateral polyethylene gasket at 120° of knee flexion. There was no statistical significance between the control group C (F=T) and experimental group A (F>T) (P>0.05) about the peak contact stressses on posterior cruciate-substituting rotating-platform lateral polyethylene gasket at 120° of knee flexion. There was no statistical significance between the experimental group B (F<T) and experimental group A (F>T) (P>0.05) about the peak contact stressses on posterior cruciate-substituting rotating-platform lateral polyethylene gasket at 120° of knee flexion.9. The peak contact stressses of patella cartilage increased during knee flexed. There was no statistical significance between posterior cruciate-substituting fixed-bearing knee prosthesis and rotating-platform knee prosthesis (P>0.05) about the peak contact stressses on patella cartilage at 0°,30°,60°,90°,120° of knee flexion.Conclusion1. A fidelity 3-digital knee dynamic finite element model which includes bones, articular cartilage, menisci and ligaments based on two-dimensional CT and MRI image data were reconstructed. The model could be used for the study of biomechanics in the virtual knee replacement model.2. The peak contact stresss of posterior cruciate-substituting fixed-bearing and rotating-platform medial and lateral polyethylene gasket increased gradually during knee model deep flexion. The peak contact stresss increased to the maximum value at 90° of knee flexion. The polyethylene gasket wear rate increased during knee deep flexion.3. The size of the posterior cruciate-substituting fixed-bearing femoral prosthesis and tibial prosthesis was mismatch could lead to the polyethylene gasket wear increased, which would reduce the lifetime of the prosthesis.4. The peak contact stresss change of the polyethylene gasket was not particularly evident when the posterior cruciate-substituting rotating platform femoral prosthesis size and tibial prosthesis size was mismatch. The polyethylene gasket long-term wear increase might not be obvious.5. When the femoral prosthesis and tibial prosthesis was mismatch, posterior cruciate-substituting rotating platform knee prosthesis may be a better choice.6. There was no statistical significance between posterior cruciate-substituting fixed-bearing knee prosthesis and rotating-platform knee prosthesis about the peak contact stressses on patella cartilage at 0°,30°,60°,90°,120° of knee flexion. |
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