A Three-Dimensional Finite Element Study On Axial Rotation Of Tibial Prosthesis Of Unicompartment Knee Arthroplasty

Objective: The axial rotation of the tibial prosthesis has a significant effect on the knee joint function and the prosthesis life after of unicompartment knee arthroplasty.However,there are few studies on the appropriate placement.In this study,three-dimensional finite element model of mobile-bearing UKA knee joint was reconstructed from knee image data,and UKA knee joint models with different axial rotation angles of tibial prosthesis are established.The effect of axial rotation of tibial prosthesis on biomechanical and kinematic changes of knee joint was studied to find the optimal implantion axial angle.Methods:The knee of a healthy adult male volunteer was scanned with sliced Computed Tomography and Magnetic Resonance Imaging.The CT and MRI data were imported into Mimics 21.0 for image data processing and reconstruction of three-dimensional models of bone and soft tissue of the knee joint.The models of various structures of the knee were imported into NX 10 for assembling the 3D model of the normal knee.The perpendicular of the cortical tangent line in the posterior margin of the anterolateral tibial plateau is used as a reference,and sagittal osteotomy of tibia were performed at different angles and other computer simulations of osteotomy operations were performed?Then,the UKA prosthesis model was attached to the knee joint model after osteotomy,and 7 threedimensional solid models of the knee joint after UKA were obtained with the rotation angle of the tibial prosthesis from 9° external rotation to 9° internal rotation.These models were imported into Abaqus 6.14 for material assignment,cell type setting,mesh generation and contact setting.A concentrated force of 500 N perpendicular to the ground was applied to the point which is the midpoint of the medial and lateral condyle of the femur to simulate gravity.A temoriss force of 400 N is applied to the action of the knee joint,and the temoriss' action direction is parallel to the direction of the femoral shaft,pointing to the origin of the temoriss.The femur moves at full degrees of freedom relative to the tibia under the control of the force exerted by the temoriss.The peak Von Mises stresses and displacements of bone and prosthesis were calculated.The degree of freedom of the femur was restrained,the middle point of the internal and external condyle of the tibia was set as the reference point,and 132 N was applied to the reference point of the tibia to simulate tibia front and back drawer experiments.The displacement distance of tibia was calculated by finite element simulation and compared with in vitro experimental data Results: A three-dimensional finite element UKA model that established in this study was verified with the results of previous biomechanical experiments,and it has strong reliability to be used to study the biomechanics and kinematics of UKA knee joint.For the three-dimensional finite element UKA model with different axial rotation angles of the tibial prosthesis,the stress of the PE was the least when the tibial prosthesis was rotated 3° in vitro.Increased external or internal rotation angle will lead to increased stress,which may accelerate PE wearing and affecting the life of the prosthesis.The displacement distance of the femoral prosthesis in the fore and aft direction is at least 7.1mm when the external rotation of the tibial prosthesis was 9°.The displacement distance of the femoral prosthesis medial and lateral direction was at least 2.3mm when the external rotation of the tibia prosthesis is 3°.The excessive external or internal rotation of the tibial prosthesis caused the reduction of the posterior displacement and increase of the lateral displacement,indicating that the rotation of the prosthesis has influence in the flexion and extension process of the knee joint.while the external rotation of the tibial prosthesis had little influence on the kinematics of the knee joint.It has the minimal effect when the rotation angle of the tibial prosthesis was 3° external.The peak VonMises stress in medial cortical bone was the least when the tibial prosthesis was rotated in neutral position.The peak VonMises stress increased significantly when tibial prosthesis external or internal totaion exceeded 6°.This may be due to unexplained postoperative pain and aseptic loosening of the prosthesis.Conclusion: The biomechanics and kinematics after mobile-bearing unicompartmental knee arthroplasty can be affected by the axial rotation of the tibia prosthesis.The axial rotation of the tibial prosthesis can obtain better biomechanical and kinematic performance between neutral position and external rotation 3°,which is a suitable axial rotation position of the tibial prosthesis.It can reduce the wear of polyethylene gasket after UKA surgery,the loosening of tibia prosthesis,the postoperative knee pain of unknown reasons and other complications,which is expected to improve the postoperative treatment effect of UKA and extend the survival life of UKA prosthesis.