We have developed a seven segment, seven degree-of-freedom model of the human lower extremity to examine how surgical changes in musculoskeletal geometry and muscle architecture affect muscle force and its moment about the joints. This model represents a subject that is about 1.8 m tall and has the strength of a young, adult male. We defined the lines of action of forty-three muscle-tendon actuators based on their anatomical relationships to three-dimensional surface representations of the bones. A model for each actuator was formulated to compute its isometric force-length relation. The kinematics of the lower extremity were specified by modeling the hip, knee, ankle, subtalar, and metatarsophalangeal joints. Thus, the force and joint moment that each muscle-tendon actuator develops can be computed for any body position. The joint moments calculated with the model compare well with experimentally measured isometric joint moments.
Delp, Loan, Hoy, Zajac, Topp, Rosen. "An interactive graphics-based model of the lower extremity to study orthopaedic surgical procedures." IEEE Transactions on Biomedical Engineering, 1990. (Download PDF)
Delp. "Surgery simulation: A computer-graphics system to analyze and design musculoskeletal reconstructions of the lower limb." Stanford University, Ph.D. Thesis, 1990. (Download PDF)