We have developed a graphics-based model of the human lower extremity with a "deformable" femur. This model characterizes the geometry of the pelvis, femur, and proximal tibia, the kinematics of the hip and tibiofemoral joints, and the paths of the medial hamstrings, iliopsoas, and adductor muscles for an average-sized adult male. The femur of our deformable model can be altered to represent anteversion angles of 0-60°, neck-shaft angles of 110-150°, and/or neck lengths of 35-60 mm. The lesser trochanter torsion angle of the model can be adjusted by as much as 30° anteriorly or 10° posteriorly. Hence, this model enables rapid and accurate estimation of muscle-tendon lengths and moment arms for individuals with a wide range of movement abnormalities and femoral deformities.
Deformable model in action. We can deform the femur of our generic model (left, shaded bone) to resemble the deformed femurs of children with cerebral palsy (wireframe bone) by increasing its femoral anteversion angle (middle) and its neck-shaft angle (right).
Arnold and Delp. Rotational moment arms of the 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, Blemker, and Delp. Evaluation of a deformable musculoskeletal model for estimating muscle-tendon lengths during crouch gait. Annals of Biomedical Engineeering, 2001. (Download PDF)