Cast (orthopedic)

An orthopedic cast, body cast, plaster cast, or surgical cast, is a shell, frequently made from plaster or fiberglass, encasing a limb (or, in some cases, large portions of the body) to stabilize and hold anatomical structures, most often a broken bone (or bones), in place until healing is confirmed. It is similar in function to a splint.

Plaster bandages consist of a cotton bandage that has been combined with plaster of paris, which hardens after it has been made wet. Plaster of Paris is calcined gypsum (roasted gypsum), ground to a fine powder by milling. When water is added, the more soluble form of calcium sulfate returns to the relatively insoluble form, and heat is produced.

The setting of unmodified plaster starts about 10 minutes after mixing and is complete in about 45 minutes; however, the cast is not fully dry for 72 hours.

Nowadays bandages of synthetic materials are often used, often knitted fiberglass bandages impregnated with polyurethane, sometimes bandages of thermoplastic. These are lighter and dry much faster than plaster bandages. However, plaster can be more easily moulded to make a snug and therefore more comfortable fit. In addition, plaster is much smoother and does not snag clothing or abrade the skin.

The earliest methods of holding a reduced fracture involved using splints. These are rigid strips laid parallel to each other alongside the bone. The Ancient Egyptians used wooden splints made of bark wrapped in linen. They also used stiff bandages for support that were probably derived from embalming techniques. The use of plaster of Paris to cover walls is evident, but it seems it was never used for bandages. Ancient Hindus treated fractures with bamboo splints, and the writings of Hippocrates discuss management of fractures in some detail, recommending wooden splints plus exercise to prevent muscle atrophy during the immobilization. The ancient Greeks also used waxes and resins to create stiffened bandages and the Roman Celsus, writing in AD 30, describes how to use splints and bandages stiffened with starch. Arabian doctors used lime derived from sea shells and albumen from egg whites to stiffen bandages. The Italian School of Salerno in the twelfth century recommended bandages hardened with a flour and egg mixture as did Medieval European bonesetters, who used casts made of egg white, flour, and animal fat. By the sixteenth century the famous French surgeon Ambroise Paré (1517–1590), who championed more humane treatments in medicine and promoted the use of artificial limbs, made casts of wax, cardboard, cloth, and parchment that hardened as they dried.

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