Foot anatomy specialization for postural sensation and control

Abstract

Wright WG, Ivanenko YP, Gurfinkel VS. Foot anatomy specialization for postural sensation and control. J Neurophysiol 107: 1513-1521, 2012. First published December 7, 2011 doi:10.1152/jn.00256.2011.-Anthropological and biomechanical research suggests that the human foot evolved a unique design for propulsion and support. In theory, the arch and toes must play an important role, however, many postural studies tend to focus on the simple hinge action of the ankle joint. To investigate further the role of foot anatomy and sensorimotor control of posture, we quantified the deformation of the foot arch and studied the effects of local perturbations applied to the toes (TOE) or 1st/2nd metatarsals (MT) while standing. In sitting position, loading and lifting a 10-kg weight on the knee respectively lowered and raised the foot arch between 1 and 1.5 mm. Less than 50% of this change could be accounted for by plantar surface skin compression. During quiet standing, the foot arch probe and shin sway revealed a significant correlation, which shows that as the tibia tilts forward, the foot arch flattens and vice versa. During TOE and MT perturbations (a 2-to 6-mm upward shift of an appropriate part of the foot at 2.5 mm/s), electromyogram (EMG) measures of the tibialis anterior and gastrocnemius revealed notable changes, and the root-mean-square (RMS) variability of shin sway increased significantly, these increments being greater in the MT condition. The slow return of RMS to baseline level (Ͼ30 s) suggested that a very small perturbation changes the surface reference frame, which then takes time to reestablish. These findings show that rather than serving as a rigid base of support, the foot is compliant, in an active state, and sensitive to minute deformations. In conclusion, the architecture and physiology of the foot appear to contribute to the task of bipedal postural control with great sensitivity. foot deformation; proprioception; human posture control THE HUMAN FOOT IS A UNIQUE structure, formed by numerous bones and joints and fastened by the three layers of ligaments.

Kinematic gait analysis of a young man after amputation of the toes

“…Then, we need to adapt our locomotor pattern to compensate for the dysfunction. The research revealed that even a partial loss of the toes not only changes the anatomical structure of the foot but also modifies the gait pattern [9,23]. We need to bear in mind that the toes are a crucial element in increasing the weight-bearing area during walking [6], as well as the first metatarsophalangeal joint complex, an important component in both stance and propulsive phases of gait [16].…”

“…Human foot bones form three strong arches: two lengthwise and one across the foot. Arch structures and toes are recognised as critical to gait because of the large range of motion displayed by the ankle [23].…”

Effects of Foot Arch Structure on Postural Stability

“…Wright et al [4] reported that foot arch deformations and body sway were significantly correlated during quiet standing, indicating that the arch was related to postural sway. Kelly et al [5] have reported that there is a correlation in the change of CoP and the activity of the plantar intrinsic foot muscles.…”

“…Because most of the previous studies used a large scale device to investigate the role of the foot arch on postural control, subject selection was limited. Wright et al [4] used a linear transducer and force plate to examine the relationship between the deformation of the foot arch and CoP sway in seven subjects. Kelly et al [5] measured body sway and muscle activity of the plantar intrinsic muscles in ten young people, using a wire electrode electromyogram and force plate.…”

“…Movability of the foot arch has not been considered in previous studies. Recent research has reported that foot arch deformations and body sway revealed a significant correlation during quiet standing, indicating that the arch of the foot is related to postural sway [4]. Foot structure has individual characteristic in every person and becomes deformed with aging.…”