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Deviations from normal foot structure are thought to result in hyper or hypo mobility preventing the foot from providing sufficient stability or mobility at appropriate times during the stance phase of gait. Such deviations in foot structure are often suggested as a risk factor for the development of common foot and ankle injuries. Though foot structure is believed to influence function its effect on foot motion and mechanisms thought to allow stability during the end of stance phase remain poorly understood. The purpose of this study was to determine the extent to which arch height affects foot kinematics during gait using a four segment foot model.
Subjects included 17 healthy individuals with a wide range of arch heights and no past history of foot pathology. A three-dimensional motion tracking system was used to determine kinematics of the hallux, first metatarsal, forefoot, calcaneus and tibia during gait while subjects ambulated at a predetermined walking velocity of 0.78 statures/s. AP and lateral radiographs were used to determine coordinate system orientation for the first metatarsal, forefoot and calcaneus. The sagittal plane angle between the first metatarsal and calcaneus was used to represent foot structure.
No association was observed between foot structure, as represented by arch height, and foot kinematics as represented by excursion or coupling during the stance phase of gait. This surprising result provides no evidence to support the assertion that foot structure influences mobility during gait in individuals without foot pathology.
The kinematic patterns observed were highly consistent between individuals and provide new insight into the mechanisms underlying the formation of a rigid lever for pushoff at the end of stance phase. Supination, consisting of forefoot and first metatarsal adduction and plantarflexion along with hindfoot inversion, was found to occur at approximately 76 percent stance. Kinematic coupling associated with activation of the windlass mechanism is consistent with the concept of supination and occurs shortly after forward rotation of the first metatarsal and hallux dorsiflexion.
In conclusion, deviation from normal foot structure appears to have little or no influence on foot mobility or intersegmental coupling due to activation of the windlass mechanism.