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

double limb support position of the stance phase of gait. A varus bending moment of
12Nm was then applied to the knee joint, simulating knee adduction moment. A
pretension was applied to the ligaments to eliminate slack. Sensitivity analyses were
carried out on element size and material properties of the different tissues to identify
those parameters that the FE results are sensitive to. A 10° wedge of bone was removed
using virtual surgery from the well-aligned knee joint model and the corresponding
stress patterns were analysed.
4. RESULTS
Figure 3 illustrates the stress distributions in the tibio-femotal compartments obtained
from in vitro and computational studies for the loading conditions of a 300N axial
force and a 12 Nm varus bending moment. The intra-articular pressure, as measured by
the Tekscan transducer is shown in Figure 3a. The normal stress (MPa) for the finite
element model derived from the imaging data of the same cadaver specimen under
identical loading conditions is shown in Figure 3b. The medial and lateral
compartment forces (N) and peak pressure (MPa) from the experimental data is shown
in Table II.
Locations and values of compartmental forces and peak tibio-femoral contact stresses
predicted from the FE model corroborated with those measured during the
corresponding in-vitro tests on the cadaveric knee.
The peak pressure in the tibial cartilage of the simulated intact knee was 2.44 MPa.
After carrying out a simulation on the malaligned knee the peak pressure increased to
2.52 MPa. The area of tibial cartilage exposed to a pressure greater than 2 MPa in the
malaligned knee increased by 36% compared to the well aligned knee. A bending
moment of 6 Nm and a 10° varus malalignment results in an increase in compressive
loading of the medial tibio-femoral compartment from 68.6% to 94.0%.
(b)
(a)
Faxial=300N Faxial=300N; Mvarus=12Nm
Figure 3: Preliminary results: (a) in vitro contact pressure distribution and (b) computer
simulated pressure distribution in the medial and lateral tibial cartilage. The left side of each
figure displays the pressure resulting from Faxial =300N; the right side of each figure displays
the pressure resulting from Faxial=300N and Mvarus=12Nm.