Effects of prosthetic foot forefoot flexibility on gait of unilateral transtibial prosthesis users

Abstract

Abstract-Five solid-ankle experimental prosthetic feet were used in this double-blind randomized crossover study to determine the effects of forefoot flexibility on gait of 14 unilateral transtibial prosthesis users. Flexibility in experimental feet was altered by changing the number of flexural hinges in their forefoot sections. When experimental prosthetic foot conditions were compared, measured prosthetic ankle dorsiflexion range of motion increased as much as 3.3° with increasing flexibility (p < 0.001) and the foot's anterior moment arm (measured as the effective foot length ratio) increased as much as 23% of the foot length with decreasing flexibility (p < 0.001). Subjects also showed increases in the difference between sound and prosthetic ankle moments as high as 0.53 Nm/kg in late stance phase of walking as flexibility decreased (p < 0.001). The difference between first peaks of the vertical ground reaction forces on the sound and prosthetic sides increased as much as 9% of body weight when subjects used the foot with the greatest flexibility (p = 0.001). The results of this study suggest solid-ankle prosthetic foot designs with overly flexible forefoot sections can cause a "drop-off" effect in late stance phase and during the transition of loading between prosthetic and contralateral limbs.

Effects of prosthetic foot forefoot flexibility on oxygen cost and subjective preference rankings of unilateral transtibial prosthesis users

“…Our foot conditions were designed to cover this range of roll-over shape radii. Unfortunately, the measured roll-over shapes for the most flexible feet (F1 and F2) in the gait analysis part of the study were found to be highly variable and generally higher than their designed values [16]. This problem potentially arises because the moment arm for each cut is reduced in the F1 and F2 conditions, not allowing the cuts to close in the appropriate timing to achieve the designed roll-over shape radius.…”

“…Their metabolic rate versus foot radius curve has a fairly wide "valley" near the minimum. The effective rocker radii of feet used in this study, as estimated from measurements made during the gait analysis session [16], most likely resided within this valley. Walking speeds during energy expenditure testing on a level treadmill varied from 0.65 to 1.20 m/s.…”

“…Use of the F1 foot led to a noticeable "limp" in many of the participants' gaits and many complained that the foot had insufficient forefoot support during walking and standing. The lack of forefoot support in the F1 foot led to a "drop-off" effect during terminal stance on the prosthetic side and an increased loading on the sound limb [16]. It is not clear whether the preference ranking results relate to F3 and F4 feet having flexibilities closer to that of the nondisabled ankle-foot system, yielding better function for walking, or to these feet more closely matching the flexibilities of their usual prosthetic feet.…”

“…The participant walked at a freely selected speed previously determined from the treadmill accommodation sessions. These speeds tended to be slower than the participants' comfortable over ground walking speeds [16]. Each participant performed all walking trials at the same speed and at an inclination of 0° (level).…”

“…Recruitment criteria included having a minimum of 1 year of experience walking on a definitive prosthesis, being a functional ambulator without serious complications, having the ability to walk without the use of assistive devices such as canes or walkers, and having an age between 18 and 80 years. Participants in the study were involved in four visits: (1) consent and initial anthropometric measurements to allow for prosthetic foot fabrication, (2) alignment and accommodation, (3) gait analysis with each foot [16], and (4) energy expenditure testing with each foot.…”