Total knee arthroplasty (TKA) has achieved excellent clinical outcomes and functional performances. However, there is a need for greater implant longevity and higher flexion by younger and Asian patients. We determined the relationship between mobility and stability of TKA product because they are essential for much further functional upgrading. This research evaluated the geometry characteristics of femorotibial surfaces quantitatively by measuring their force of constraint by computer simulation and mechanical test. We measured the force of constraint of femorotibial surfaces in order to evaluate the property of femorotibial surfaces. A total knee system was used for this evaluation, and has an asymmetrical joint surface, which restores the anatomical jointline in both sagittal and coronal planes, and is expected to permit normal kinematics, with cruciate-retaining fixed type. We performed computer simulation using finite element analyses (FEA) and mechanical tests using knee simulator to measure the force of constraint regarding anterior-posterior (AP) and internal-external (IE) rotational direction in extension position, 90-degree flexion and a maximum flexion of 140-degree. In the FEA, Young's modulus and Poisson's ratio were set to 213 GPa and 0.3 for Co-Cr-Mo alloy as the femoral component, and 1 GPa and 0.3 for UHMWPe as the tibial insert, respectively. The force load to AP direction of tibial tray was measured when the femoral component moved plus or minus 10 millimeters. The moment load to IE rotational direction of tibial tray was measured when the femoral component moved plus or minus 20 degrees. The vertical load of 710 N was loaded on the femoral component during these measurements.Introduction
Methods
Total knee arthroplasty (TKA) has achieved excellent clinical outcomes and functional performances. However, younger and Asian patients require even greater implant longevity and higher flexion. It is necessary for much further functional upgrading to design TKA with mobility and stability. Therefore, we determined the relationship between mobility and stability of TKA. We evaluated the force of constraint of femorotibial surfaces in two types of designs in order to measure the property of femorotibial surfaces. The anatomical geometry knee (AGK) has an asymmetrical design, which restores the anatomical jointline in both sagittal and coronal planes, and is expected to permit normal kinematics, with cruciate-retaining fixed type. The functional designed knee (FDK) has a symmetrical design, and enhances concave femorotibial surfaces with cruciate-retaining mobile type. We performed mechanical tests to measure the force of constraint regarding anterior-posterior (AP) and internal-external (IE) rotational direction in extension position, 90-degree flexion and a maximum flexion of 140-degree. The force load to AP direction of tibial tray was measured when the femoral component moved plus or minus 10 millimeters. The moment load to IE rotational direction of tibial tray was measured when the femoral component moved plus or minus 20 degrees. The vertical load of 710N has been loaded on the femoral component during this test.Background:
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