What’s the Difference Between Orthotics and Prosthetics. There are many reasons why people might require assistive devices such as orthotics & prosthetics. If you are new to these devices, there are some things that you should know, particularly surrounding the difference between the two. The major difference between orthotics and prosthetics is that while an orthotic device is used to enhance a person’s limb, a prosthetic device is used to replace a limb entirely.