Impact Load Transmission of Human Knee Joint Using in Vitro Drop-Tower Test and Three-Dimensional Finite Element Simulation

The purpose of this study was to investigate the transmission mechanism of the three-dimensional impact stress in the human knee joint. In this study, two fresh specimens were prepared to search the impact stress by two methods: the impact testing with drop tower apparatus and the finite element simulation. In the testing, the specimens were installed in the apparatus, and an impact load was applied to each specimen by dropping 1 kg weights. The mini-pressure transducers were implanted in the joints of the femur and tibia, and the stress transmission was measured. Under the intact load condition, the impact compressive stress values of 0.140 to 0.320 MPa were observed. In the impact simulation, the 3D modeling with the hexahedral finite elements was developed, and the way the impact load was passing through the cancellous bone could be visualized. The simulation results of the compressive stress in the cancellous bone and the strain in the cortical bone surface were in considerably agreement with the testing results. The stress distribution calculated from the simulation showed that the removal of the meniscus affected the load transmission mechanism. As for the reason, it was considered that when sliding interfaces between the femoral cartilage and tibial cartilage are reduced, the impact load cannot be transmitted to the interior of the joint, causing the stress shielding inside.