ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

3.3 Finite Element Model
3.3.1 Meshing
The solid 3D knee joint assembly model was then
exported to ABAQUS V6.11-2 (HKS, USA), and
meshed using hexahedral elements (Figure 2).
Following mesh convergence sensitivity analyses, the
osseous tissues were meshed with an element size of 7
mm while 1 mm was used for the soft tissues.
3.3.2 Material Properties
The material properties [6, 7, 8, 9 and 10] assigned to
the osseous and soft tissues were obtained from the
literature and summarised in Table 1.
Table1: Material properties assigned to the different tissues in the knee joint
3.3.3 Boundary Conditions
Attachments of each ligament, meniscal horns and cartilage to the corresponding bone
were modelled by merging the nodes on the corresponding surfaces in Abaqus.
Frictionless cartilage-cartilage and cartilage-meniscus contact surfaces were simulated
by creating contact elements between the corresponding surfaces.
3.3.4 Verification of Model with Cadaveric Experiment
Fig. 2: Finite element
mesh of a cadaveric knee.
Tissues Young’s Modulus (MPa) Poisson’s Ratio
Bones 1000 0.3
Cartilage 50 0.45
Meniscus 112 0.45
Ligaments 400 0.45
The same cadaveric specimen that was used to obtain the MRI dataset was mounted in
an inverted posture (femur inferior, tibia superior) within a six-degree-of-freedom
Kawasaki robot based knee joint testing system. The distal end of the femur was
mechanically grounded. The proximal tibia was affixed to the 6 degree of freedom load
cell within the robot gripper. A pressure transducer (model 4010N, Tekscan Inc., USA)
was inserted within the tibio-femoral joint to measure medial and lateral compartment
loading values. A 300N axial force and 0 to 12Nm ramped bending moment were
applied to the distal end of the tibia, simulating different varus-valgus moments at 20°
of flexion. The same loading conditions were applied to the FE model to compare the
contact force and peak pressure values in the medial and lateral compartments. The
results, summarised in Table 2 and Figure 3, show good agreement of the knee joint
contact mechanics between our FE and in vitro studies.