Orthotics is a specialty within the medical field concerned with the design, manufacture and application of orthoses. An orthosis (plural: orthoses) is "an externally applied device used to modify the structural and functional characteristics of the neuromuscular and skeletal system". An orthotist is the primary medical clinician responsible for the prescription, manufacture and management of orthoses. An orthosis may be used to Control, guide, limit and/or immobilize an extremity, joint or body segment for a particular reason, To restrict movement in a given direction, To assist movement generally, To reduce weight bearing forces for a particular purpose, To aid rehabilitation from fractures after the removal of a cast, To otherwise correct the shape and/or function of the body, to provide easier movement capability or reduce pain. Orthotics combines knowledge of anatomy and physiology, pathophysiology, biomechanics and engineering. Patients who benefit from an orthosis may have a condition such as spina bifida or cerebral palsy, or have experienced a spinal cord injury or stroke. Equally, orthoses are sometimes used prophylactically or to optimise performance in sport.