Abstract
Introduction: Static finite-element (FE) analysis has been extensively used to examine polyethylene stresses in Total Knee Arthroplasty (TKA). The aim of this study was to use an explicit-dynamic FE approach with force driven models to simulate both kinematics and internal stresses within a single analysis of the Meniscal Bearing Knee (MBK, Zimmer, Warsaw, IN).
Material and methods: The MBK is a mobile-bearing prosthesis (rotating and AP-gliding) with complete femoro-tibial conformity throughout motion owing to spherical femoral condyles. The FE meshes of the MBK were created from data obtained from the manufacturer as Initial Graphics Exchange Specification (IGES) files. Three-dimensional FE models of the original MBK design and of two modified versions (MBK-Flex and MBK-PS) were generated in Hypermesh 5.1 software. The tibial insert was modeled as a flexible body with 82212 noded solid tetrahedral elements (Poisson ratio: 0.46). The femoral and tibial components were modeled as rigid bodies. Linear soft tissue constraints (30 N/mm AP and 0.6 N-m/degree rotational displacements) were included. Axial load was 4.9mm medially displaced to achieve a medially-biased (60–40) condylar load allocation. Waveforms to simulate gait, stair-climbing and deep-knee-bending with the FE models were obtained from the proposed International Standards Organization 14243–1 and from literature data.
Results: Peak contact stresses for each activity evaluated were below 14 MPa for both the original and modified MBK versions. Kinematics analysis showed similar amount of displacements (average rotations: 3.7°: average AP-glide: 2.5mm) for the various design during gait. In simulated stair-climbing and deep-knee-bending the PS version showed a more reproducible pattern of posterior roll-back in flexion without increasing contact stresses.
Conclusion: Explicit FE analysis is an efficient screening tool before in-vivo or in-vitro testing. It allows to test the effects of variables such as change in prosthetic design, surgical techniques and loads on knee forces and kinematics.
Theses abstracts were prepared by Professor Roger Lemaire. Correspondence should be addressed to EFORT Central Office, Freihofstrasse 22, CH-8700 Küsnacht, Switzerland.
