Ankle-foot orthoses for rehabilitation and reducing metabolic cost of walking: Possibilities and challenges

People with diseases such as stroke, spinal cord injury, and trauma usually have paretic ankle involvement because of the plantar flexor and dorsiflexor muscle weakness. Individuals with paretic ankle normally have the drop-foot gait, which has the complications of foot-slap after heel contact and toe-drag during the swing phase of a gait cycle. This could cause slow walking speed, short step-length, high metabolic cost, and high risk of tripping. Ankle-foot orthotic intervention is mostly prescribed to treat paretic ankle impairments. In addition, ankle-foot orthoses (AFOs) have been developed to assist human walking, which can reduce the wearer's metabolic cost of walking. To date, three kinds of AFOs have been developed, including the passive AFOs, semi-active AFOs, and active AFOs. This paper provides a systematic review on these three types of AFOs, where the biomechanics of normal and pathological gaits of human, the design concepts of the AFOs, and motion data collection of the human-machine system in human trials are described. The limitations of the currently developed AFOs and future research and development directions of AFOs are discussed, which would provide useful information for researchers to develop suitable AFOs.