A closed-loop cadaveric foot and ankle loading model

Investigations of human foot and ankle biomechanics rely chiefly on cadaver experiments. The application of proper force magnitudes to the cadaver foo t and ankle is essential to obtain valid biomechanical data. Data for exter nal ground reaction forces are readily available from human motion analysis . However, determining appropriate forces for extrinsic foot and ankle musc les is more problematic. A common approach is the estimation of forces from muscle physiological cross-sectional areas and electromyographic data. We have developed a novel approach for loading the Achilles and posterior tibi alis tendons that does not prescribe predetermined muscle forces. For our l oading model, these muscle forces are determined experimentally using indep endent plantarflexion and inversion angle feedback control. The independent (input) parameters - calcaneus plantarflexion, calcaneus inversion, ground reaction forces, and peroneus forces - are specified. The dependent (outpu t) parameters - Achilles force, posterior tibialis force, joint motion, and spring ligament strain - are functions of the independent parameters and t he kinematics of the foot and ankle. We have investigated the performance o f our model for a single, clinically relevant event during the gait cycle. The instantaneous external forces and foot orientation determined from huma n subjects in a motion analysis laboratory were simulated in vitro using cl osed-loop feedback control. Compared to muscle force estimates based on phy siological cross-sectional area data and EMG activity at 40% of the gait cy cle, the posterior tibialis force and Achilles force required when using po sition feedback control were greater. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.