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

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.