Effects of Knee and Ankle Movements on Foot Impact Forces in Human Walking

Excessive repetitive impacts in human walking lead to lower extremity orthopaedic disorders such as degenerative joint disease and prosthetic loosening. In this study, two planar models, corresponding to free or fixed ankle joints, were used to examine movements of the knee and ankle joints that affect foot impact forces and their attenuation during level walking. A kinetic approach was used to describe the relationship between the landing style of the leg and the impact at heel contact. Human subjects with free and fixed ankle joints were studied to verify the models. Free and fixed ankle groups showed a significant difference with regard to acceleration (p<0.005). The attenuation capacity of acceleration for healthy subjects with a freed ankle joint was 59.9±12.1 (mean ±SD)%, while the capacity for the same subjects with a fixed joint was 27.4±28.9%. The movements of the knee and ankle joints at landing on the ground played important roles in attenuating impulsive force.