Biomechanical Effects of Load on Foot and Ankle Kinematics

A novel loading protocol was utilized to assess the kinematic response of the ankle joint complex for active and passive loading scenarios during simulation of stance phase gait in a human cadaveric lower extremity model. Passive (5N axial tibia load, no Achilles load) and active (530N axial tibia load, 178N Achilles load) loading conditions were repetitively tested over 10° dorsiflexion and 20° plantarflexion in two specimens. Target axial tibia loads were established by a 356N vertical ground reaction force (vGRF) in the neutral orientation. Applied tibia load was controlled within ±2N. Measurements included mean axial tibia loads, peak vGRFs, and mean positional values of the ankle instantaneous axis of rotation (IAR). All data were statistically analyzed with an ANOVA and Holm-Sidak post-hoc multiple comparisons test (P<;0.05) to assess repeatability of the loading parameters and compare IAR values between loading and movement scenarios. Mean IAR values differed by less than 1mm within each repetitive load and movement test. Statistical differences in IAR patterns occurred between dorsiflexion and plantarflexion, and between active and passive loading. Loading of the ankle joint and Achilles tendon played a major role in the kinematic response of a healthy foot and ankle.