 This study will collect information on the different ways that people walk, that is, their gait, when they use ankle braces. Patients will visit NIH on at least three and as many as nine separate occasions. A physical therapist will perform a physical examination to determine how patients move, how strong they are and what their comfortable walking speed is. Then patients will sit on a chair while a camera apparatus takes special pictures of their legs, a procedure lasting up to 2 hours. Patients will be asked to return to learn how to walk with the custom Passive Dynamic Ankle-Foot Orthosis PD-AFO-a unique ankle brace designed to improve walking ability by providing natural support to the lower limb. 