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We have created models of three
lower extremity cadaveric specimens and four subjects with cerebral
palsy from MR images. The models characterize the geometry of the
pelvis, femur, and proximal tibia, the kinematics of the hip and
tibiofemoral joints, and the paths of the hamstrings, iliopsoas,
and adductor muscles. We have quantified the accuracy of
muscle-tendon lengths and moment arms estimated using these models
by comparing hip and knee flexion moment arms estimated from the
models of the specimens to the moment arms determined experimentally
on the same specimens. Errors in the hip and knee flexion moment
arms of the muscles, averaged over functional ranges of motion,
were less than 4 mm (within 10%). Based on these analyses, we believe
that the models provide accurate estimates of muscle-tendon lengths
and moment arms in vivo.
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The
four subjects with cerebral palsy who were imaged ranged in age
from 7 to 27 years and are shown here. The subjects exhibited different
levels of walking ability and degrees of femoral deformity. None
of the subjects had undergone previous orthopaedic surgery, and
all were able to ambulate without orthoses or other assistance.
We have used these MR-based models, in conjuction with kinematic
data obtained from gait analysis, to examine causes of the excessive
knee flexion and hip internal rotation in persons with crouch gait.
We have also used the MR-based models to help evaluate and improve
a generic model of the lower extremity
with a deformable femur. |
Arnold, Blemker, and Delp. Evaluation
of a deformable musculoskeletal model for estimating muscle-tendon lengths during crouch gait. Annals of Biomedical Engineering,
2001. (Download
PDF)
Arnold and Delp. Rotational moment arms of the medial hamstrings and adductors vary with femoral geometry and limb position: implications for the treatment of internally-rotated gait. Journal of Biomechanics, 2001. (Download PDF)
Arnold, Asakawa, and Delp. Do
the hamstrings and adductors contribute to excessive internal rotation
of the hip in persons with cerebral palsy? Gait and Posture,
2000. (Download PDF)
Arnold, Salinas, Asakawa, and Delp. Accuracy
of muscle moment arms estimated form MRI-based musculoskeletal models
of the lower extremity. Computer Assisted Surgery, 2000.
(Download PDF) |
