Orthoses are externally applied devices used to modify the structural and functional characteristics of the neuromusculoskeletal systems; prostheses are externally applied devices used to replace, wholly or in part, an absent or deficient body segment. Included are, e.g. body-powered and externally powered external orthoses, prostheses, orthopaedic footwear. Excluded are endo-prostheses, which are not part of this document.

Orthoses that are designed to modify the structural and functional characteristics of the neuromusculoskeletal systems of the spine and skull; the device may be custom fabricated to meet the functional needs of the individual user or prefabricated to meet a particular set of functional requirements; the prefabricated devices may be adjustable to fit an individual user, or they may be ready-to-use so that adjustment is not possible or no adjustment is necessary for any user.