Orthotics is the medical field concerned with the application and manufacture of orthoses, devices which support or correct the function of a limb or the torso. The term is derived from the Greek "ortho", to straighten. Sciences such as materials engineering, gait analysis, anatomy and physiology, and psychology contribute to the work done by orthotists, the professionals engaged in the field or orthotics. Individuals who benefit from an orthosis have sustained a physical impairment such as a stroke, spinal cord injury, or a congenital abnormality such as spina bifida or cerebral palsy.