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

determined. The higher ratio value on intensity of results from the reaction torque
and will produce larger forces on the constraint such as 4 $ and 5 $ .
To validate the modeling approach, a comprehensive experimental data set was
accessed to determine the IAK during gait. The Grand Challenge Competition to Predict
In Vivo Knee Loads” [1] data included motion capture, fluoroscopy data, ground
reaction forces, electromyography, medial and lateral knee contact forces, and strength
data. The data was collected from an instrumented right knee replacement in an adult
male subject (mass 65 kg, height 1.7 m). The gait trial for said subject involved a
medial-lateral trunk sway gait pattern similar to that reported [6]. This study used the
following framework to predict constraint forces. The inputs were a reciprocally
connected knee model, experimental kinematics (i.e., x-y-z trajectories of marker data at
patella, shank and thigh), knee medial and lateral (static only) and ground reaction
forces that were all obtained from the instrumented right knee of the subject. The “knee
radiograph” contained a frontal plane view of the knee region and provided information
about the alignment of contact forces at the medial and lateral compartments. In Step 1,
the experimental kinematics were used to generate the ISA of the shank and thigh that
best approximated the experimental kinematics. In Step 2, the three axes theorem [7]
was used to obtain the ISA of the knee joint (i.e. IAK) from the previously obtained two
axes. In Step 3, a reciprocally connected knee model was used to locate a set of screw
axes of contact forces that were reciprocally connected to the IAK. Then, we tested the
simple computational framework through readily accessible benchmark data [1]:
passive muscle contraction and GRF are compounded into a wrench which is reciprocal
to the IAK and resolved into component wrenches of the constraints belonging to the
reciprocal screw system.
4. RESULTS
Figure 2: The knee joint provides the
instantaneous screw $ which is reciprocal
to the impulsive ground reaction force $ .
No combination of angular velocity at the
$ will cause instantaneous translational
movement, and any force at the ground
contact will cause no rotation at $ . The
reaction forces (and torques) of the GRF
will then be taken by the structures of the
limbs (i.e. the femur is the largest bone)
than they would have been taken by joint
constraints.
In the model presented in this paper, the static equilibrium condition was considered so
that the smaller forces could be estimated: Passive muscle contraction (Muscle in Figure
3) and given GRF are compounded into a wrench which is reciprocal to the IAK and
resolved into component wrenches (Medial and Lateral Contacts in Figure 4
respectively) belonging to the reciprocal screw system. The muscle forces must
compound into a wrench on the given screw. The forces in the medial and lateral