Variable stiffness orthosis for gait normalization in patients with toe walking

Abstract

Duchenne muscular dystrophy (DMD) is an X-linked recessive neuro-muscular disorder that causes progressive muscle degeneration. DMD patients tend to walk on their tip toes because of their weak calf muscles and currently do not have many options for managing the fatigue induced by supporting most of the foot strike impact with the ball of their feet. Patients with Idiopathic Toe Walking (ITW) suffer from similar symptoms and lack of physical support when walking. The addition of external heel support through an orthosis attached on the exterior of the heel of the shoe may help reduce this fatigue and correct the tip toe gait of DMD and ITW patients, enabling them to walk for longer distances unassisted. In order to study the effect of additional heel support with an orthosis, a custom orthosis with variable stiffness cushioning was designed. A healthy subject walked with simulated tip toe walking observed in DMD and ITW patients on a treadmill for three thirty-second trials, each with a cushioning material of rubber, gel, or foam added to the orthosis. The force on the foot, calf muscle activity, and video were recorded. Controls of "normal" walking and tip toe walking without prototypes were used for baseline comparisons. Material firmness and Young's modulus were measured for each of the materials with a compression test using a texture analyzer. There was a significant decrease in muscle activity from the tip toe control with the foam orthosis for both feet and for all orthosis materials for the right foot. There was also a significant improvement in heel-to-ball force ratios for all orthosis materials compared to the tip toe control. There was no observed correlation between material firmness and Young's modulus with muscle activity or heel-to-ball force ratio. The gait analysis from the video showed a gait appearance closer to that of the normal control than the tip toe control with the orthoses..