Gait Cycle Basics: Part 4
Pronation as a shock absorber
Heel strike, a traumatic deceleration event with the transfer of weight from one extremity to the other, creates shock which must be attenuated. This is accomplished by 4 distinct mechanisms:
1. ankle plantar flexion at heelstrike, followed by eccentric contraction of the pretibial muscles to decelerate foot fall.
2. subtalar pronation. As the coefficient of friction between the calcaneus and the ground increases, the talus slides anterior on the calcaneus while plantar flexing, adducting and everting. This motion causes concomitant internal rotation of the lower leg. Both these actions cause a time delay, allowing force to be absorbed over a longer period of time.
3. knee flexion. This is a reaction to the heel rocker, forward motion of the tibia, and passive tension in the posterior compartment. It is slowed by eccentric contraction of the quadriceps
4. contralateral pelvic drop, which is decelerated by the ipsilateral hip abductors (primarily gluteus medius). This occurs as weight is suddenly dropped on the contralateral limb
The rockers and shock attenuation are dependent on the integrity of the joints involved, their associated ligaments and cartilage, the functionality of the musculature crossing them and their neuromuscular integrity along with appropriate cortical control of the actions. Being physical medicine practitioners, we understand that the anatomy and physiology cannot be separated and must consider these different components while evaluating the patient.
The Gait Guys….Yup, we ARE foot nerds….Hey, someone has to do it….