Orthosis are externally applied devices that modify the structural and functional characteristics of the neuromuscular and skeletal systems. Orthotics is the science and art of treating patients using orthosis. An orthotist is an authorized person who designs, measures, and fits orthosis after completing approved education and training. The 20th century saw the greatest improvements in orthotics after both world wars and polio epidemics, as orthotists began adapting prefabricated parts into functional orthoses for specific purposes.