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Predicting the Effects of Muscle Activation on Knee, Thigh, and Hip Injuries in Frontal Crashes Using a Finite-Element Model with Muscle Forces from Subject Testing and Musculoskeletal Modeling
Technical Paper
2009-22-0011
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English
Abstract
In a previous study, the authors reported on the development of
a finite-element model of the midsize male pelvis and lower
extremities with lower-extremity musculature that was validated
using PMHS knee-impact response data. Knee-impact simulations with
this model were performed using forces from four muscles in the
lower extremities associated with two-foot bracing reported in the
literature to provide preliminary estimates of the effects of
lower-extremity muscle activation on knee-thigh-hip injury
potential in frontal impacts. The current study addresses a major
limitation of these preliminary simulations by using the AnyBody
three-dimensional musculoskeletal model to estimate muscle forces
produced in 35 muscles in each lower extremity during emergency
one-foot braking. To check the predictions of the AnyBody Model,
activation levels of twelve major muscles in the hip and lower
extremities were measured using surface EMG electrodes on 12
midsize-male subjects performing simulated maximum and 50% of
maximum braking in a laboratory seating buck. Comparisons between
test results and the predictions of the AnyBody Model when it was
used to simulate these same braking tests suggest that the AnyBody
model appropriately predicts agonistic muscle activations but under
predicts antagonistic muscle activations.
Simulations of knee-to-knee-bolster impacts were performed by
impacting the knees of the lower-extremity finite element model
with and without the muscle forces predicted by the validated
AnyBody Model. Results of these simulations confirm previous
findings that muscle tension increases knee-impact force by
increasing the effective mass of the KTH complex due to tighter
coupling of muscle mass to bone. They also indicate that muscle
activation preferentially couples mass distal to the hip, thereby
accentuating the decrease in femur force from the knee to the hip.
However, the reduction in force transmitted from the knee to the
hip is offset by the increased force at the knee and by increased
compressive forces at the hip due to activation of lower-extremity
muscles. As a result, approximately 45% to 60% and 50% to 65% of
the force applied to the knee is applied to the hip in the
simulations without and with muscle tension, respectively. The
simulation results suggest that lower-extremity muscle tension has
little effect on the risk of hip injuries, but it increases the
bending moments in the femoral shaft, thereby increasing the risk
of femoral shaft fractures by 20%-40%. However, these findings may
be affected by the inability of the AnyBody Model to appropriately
predict antagonistic muscle forces.
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