ORTHETICS in the treatment of the patient with musculoskeletal disease and disability may be prescribed for temporary use during rehabilitation or may be permanently needed. In either case, the purpose of orthetics and their areas of usefulness are specific. Orthetic devices may be indicated: (1) for support and protection of musculoskeletal structure, (2) as a functional replacement or assistive device for a functionally inadequate body part, (3) as an efficiency mechanism for the conservation of body energy expenditure, (4) or for multiples of these reasons. An orthetic device may be as simple as a metatarsal rocker bar to protect arthritic metatarsal heads, as mechanically compact and complex as a motorized wheelchair, or as futuristic as an electronic talking machine. Basically, however, regardless of complexity demanded by need, device design should conform to the same rules. They should be maximally efficient, effective, and simple in operation. They should be designed