Validation of a Novel Kinematic Based Protocol to Study Foot and Ankle Biomechanics

A novel testing protocol was developed to simulate in vivo mechanics of the foot-ankle complex during early stance phase gait in a human cadaveric lower extremity model. A lower leg was mounted in a robotic testing platform with the tibia upright and foot flat on the baseplate. The axial force applied to the tibia was controlled as a function of the vertical ground reaction force (vGRF) set at half body weight (356N) and a 50% vGRF (178N) Achilles tendon load. The loading scenario was repetitively tested over 1° dorsiflexion and 20° plantarflexion in two specimens. Because the platform axes were controlled to within 2microns and 0.0002°, error in calculating the ankle instantaneous axis of rotation (IAR) was ±0.001mm. Mean axial tibia loads, vGRFs, and mean ankle IAR values were analyzed with an ANOVA and a Holm-Sidak post-hoc multiple comparisons test (P<;0.05). Axial forces applied to the tibia were controlled to within ±2N of the target conditions with a maximum deviation of ±6N. Ankle IAR values were significantly different between dorsiflexion and plantarflexion. The customized robotic platform and advanced testing protocol can be programmed to simulate many different loading scenarios appropriate for studying foot biomechanics.