The effects of constraining OpenSim inverse
kinematics to a bone pin marker defined range
1 University of Ottawa,
Canada2 University of Copenhagen,
Denmark
INTRODUCTION
AIM
To determine the effect of applying bone pin marker
defined ranges of knee motion in OpenSim IK solutions.
ISBS XXIV Congress
July 18th-22th 2016
Tsukuba, Japan
The generic models available in the OpenSim repository contain knee
joint ranges that are not physiologically realistic3. In the NoBP
condition, nonphysiological oscillations in translations were observed
even when knee flexion angle was constant indicating that they were
the result of STA and were removed once the BP constraints were
applied. These kinetic differences will also have an impact on
quantifying joint contact and ligament loading, which will likely facilitate
more accurate injury assessments through musculoskeletal modelling.
Therefore, caution should be expressed when using the results from
musculoskeletal modelling as STA and optimizations can introduce
error in both the kinematics and kinetic solutions. This error is
amplified during ballistic and high impact tasks such as jump landing.
DISCUSSION & CONCLUSION
1. Benoit et al. Gait Posture. 24: 152-64, 2006.
2. Potvin et al. J Biomech. Submitted.
3. Xu et al. Com Meth Biomech Biomed Eng. 18: 1217-1224, 2015.
METHODS
Thirty one healthy active young adults (15 males & 16
females; 25.7± 5.7 years) participated in this study.
Participants completed 3-5 successful jump lunges
where they were asked to stand on their non-test limb
and jump forward onto a force plate, land on their test
limb and maintain balance for two seconds (Fig 1).
All data were processed through a
Matlab - OpenSim API. The
Gait4392 model was adapted to
include 37 degrees of freedom
(dof), 46 lower limb muscles,
patellae, and six dof at the knee.
Data were scaled and processed
through IK and inverse dynamics
(ID) to achieve the no bone pin
constrained (NoBP) results. Bone
pin data from Benoit et al.1 were processed to create
boundary envelopes of each knee dof as a function of
knee flexion angle to be used as the full ranges of
motion for each of the knee model's 5 other dofs (Fig
2). The same scaled models were then subjected to IK
and ID once again (BP) where the calculations were
completed at each time point (every 0.01s) and the
knee dofs were adjusted so that their kinematics were
constrained to the bone pin range associated with the
current knee flexion angle at that instant in time.
Paired sample
T-tests through
statistical parametric
mapping were used
to test kinematic and
Kinetic differences
between the two
conditions at
α < 0.05.
RESULTS
Figure 3: Mean and standard deviation
clouds for all 6 knee dofs kinematics. Black
vertical line represents heel contact while
blue horizontal line represents period of
significant different between the two
conditions
REFERENCES
Figure 1: OpenSim
model of the jump lunge
When BP constraints were applied,
significant differences were observed
for all six knee dof (Fig 3). BP results
yield a significantly more flexed
knee; although these differences
were only a few degrees. BP knee IK
results were also more adducted and
externally rotated throughout the
movement. Significant differences
were also observed for anterior/
posterior and distraction/
compression (DC trans) translations
throughout the entire jump lunge
while medial/lateral translations were
only significant pre and 50 ms post
contact.
Large discrepancies were observed
in the DC trans (Fig. 4A) shortly after
contact. In NoBP, DC trans was
shown to oscillate in a range of 8 mm
to a max of 20 mm of compression
during this movement, which is
nonphysiological (Fig. 4B). This is
likely due to the inertia observed in
the skin causing soft tissue artifact
(STA) approximately 20-150 ms after
the large impact force at contact.
Since OpenSim uses motion capture data as input while
solving inverse kinematic (IK), it is subjected to soft
tissue artifact as the commonly used surface markers
do not correctly represent the underlying rigid body
bones1. These errors cause nonphysiological
movement of bodies in the OpenSim simulations.
Figure 2: Bone pin defined ranges for all 6 knee
dof as a function of knee flexion. Potvin et al.2
Significant differences in kinetic results were also observed for all six
knee dof from initial contact onwards. After contact, BP constraints
produced a significantly greater flexor moment albeit it clinically small
(max diff: 0.18 Nm/kg). The BP solutions also solved for greater knee
abductor (max diff: 0.23 Nm/kg) and external rotator joint moments
(max diff: 0.05 Nm/kg) after contact. With respect to translation forces,
the BP solutions produced smaller posterior shear forces (max diff:
0.51 N/kg), and greater medial shear (max diff: 0.46 N/kg) and
compressive forces (max diff: 0.82 N/kg) at the knee joint.
KINEMATICS
KINETICS
Figure 4: A) Example participant displaying
the distraction/compression results with
unfiltered (blue) and filtered (black) NoBP
constraints compared to unfiltered BP
constrained results (red). B) Participant with
20 mm of compression 130 ms after contact
Ext
Flex
Add
Abd
Ant
Lat
Med
Com
Dis
Int
Ext
Post
-100 0 100 200 300-5
0
5
10
15
20
25
time (ms)
Kn
ee
Dis
/Co
m T
ran
s (
mm
) Com
Dis
A B
-40 -30 -20 -10 0
-40
-20
0
Kne
e F
lex/
Ext
Ang
le (°
)
-40 -30 -20 -10 0-10
-5
0
5
10
15
Kne
e A
bd/A
dd A
ngle
(°)
-40 -30 -20 -10 0-15
-10
-5
0
5
10
Knee Flex/Ext Angle (°)
Kne
e In
t/Ext
Rot
Ang
le (°
)
-40 -30 -20 -10 0-10
-5
0
5
Kne
e M
ed/L
at T
rans
(mm
)
-40 -30 -20 -10 0
-5
0
5
10
15
Kne
e A
nt/P
ost T
rans
(mm
)
-40 -30 -20 -10 0-20
-10
0
10
Knee Flex/Ext Angle (°)
Kne
e D
is/C
om T
rans
(mm
)
Ext
Flex
Add
Abd
Ant
Lat
Med
Com
Dis
Int
Ext
Post