EXPLICIT FINITE ELEMENT ANALYSIS OF MENISCAL BEARING KNEE UNDEVARIOUS SIMULATED CONDITIONS

Abstract

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 the kinematics and the internal stresses within a single analysis of the Meniscal Bearing Knee (MBK, Zimmer, Warsaw, IN) prosthesis

The MBK is a mobile-bearing prosthesis (rotating and AP-gliding) with complete femorotibial 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. No abnormal alignment or soft tissue imbalance were assumed. 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 amedially-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.

Peak contact stresses for each activity evaluated were below 11 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 rollback in flexion without increasing contact stresses.

Explicit FE analysis is an efficient screening tool before in-vivo or in-vitro testing. It provides a means of testing the effect of variables such as change in prosthetic design, surgical techniques and applied loads on knee forces and kinematics.