A person must normally wear a cast for a fractured arm for four-to-six weeks, according to Dr. Danny L. Proffitt answering medical-related questions for HealthTap. Depending on the age of the patient and the type of fracture, some casts must remain in place for 10 weeks, notes KidsHealth.
A cast is a hard plaster or fiberglass bandage that holds bones in place while they heal, explains the University of Rochester Medical Center. A short arm cast, used to treat wrist and forearm injuries, extends from the hand to the area below the elbow. A long arm cast, used to treat elbow, forearm and upper arm fractures, extends from the hand to the upper arm.