Ortheses perform additional duties when compared to braces. The term orthesis originates from the Old Greek orthos, which means correct or aligned, and thesis meaning position or stance. An orthosis is a corrective aid that is shaped as an external support device. Ortheses are not to be confused with prostheses. Prostheses are substitutes for missing body parts, while ortheses are functional aids for corrective use for function and form of a body part.

Ortheses (so-called segment ortheses) are available for almost every joint in the body. As opposed to braces, whose material is elastic and flexible, an orthesis must be rigid. Thus they consist of mechanical variably strong and partly rigid elements. Often times metal and plastic strips equipped with Velcro straps or sleeve devices are used.