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

knee included tibio-femoral contacts and patello-femoral contacts of the TKA
components, passive soft tissue and active muscle elements.
The external forces (ground reaction and weights), the muscle forces (quadriceps and
hamstrings) and the frictional forces are applied to the knee joint through the machine
(Figure 1). In particular, the machine determines the quadriceps force, at each time step,
in such a way as to maintain a constant predefined vertical hip force during knee
flexion. This is done using a proportional/derivative feedback system.
Figure 1 :The knee simulator model used in this study. It consists of: a base frame (A), a
hip sled (B), a femur block (C), a tibia block (D), a tibia rotation table (E), an
adduction–abduction sled (F) and an antero-posterior sled (G).
The tissues mechanical properties were obtained from Woo et al. [20]. The
discretization of the tendon enables its wrapping around the bone and in the trochlear
groove of the femoral component.
According to the literature works [21-23], the LCL, the anterior and posterior bands of
the MCL, as well as the capsule tissues, were assumed to be elastic with a non-linear
force strain curve describing their behavior.
To avoid any lift-off of the femoral component, the model was initialized prior to the
dynamic simulation until stable bi-condylar contact was established and static
equilibrium was reached.
For each configuration, the internal/external (IE) and abduction/adduction (AA)
rotations and the anterior/posterior (AP) translation of the femoral component with
respect to the tibial component were evaluated and compared during the descent phase
of the loaded squat.
4. RESULTS
The results show that AA rotation and the AP translation are mainly influenced by tibial
components mal-positioning while the IE rotation is affected almost equally from the
soft-tissues position and from tibial component positioning (Figure 2). These results