Abstract
We constructed four shoehorn type ankle foot orthoses with different frontal plane alignments and plastic thicknesses, and measured the strain of the orthosis during walking and the change in plantar flexion decelerating force. When the frontal plane alignment of the orthosis was more valgus than the alignment of the body at mid stance, externally rotational strain of the lower leg portion of the orthosis occurred. The externally rotational strain was become greater as flexibility increased, and the plantar flexion decelerating force was decreased. In the case of low flexibility, although the externally rotational strain decreased, landing on the lateral portion of the plantar surface (foot flat stage) was observed, which is a cause of lateral instability of orthosis. These results suggest that the clinical observation of knee locking during gait caused by externally rotational strain together with insufficient plantar flexion decelerating force is not only due to issues related to flexibility of the orthosis and the initial dorsiflexion angle, but may be caused by mal-alignment frontal plane alignment.
