Orthopedic Cast

An orthopedic cast, body cast or surgical cast, is a shell, frequently made from plaster, encasing a limb (or, in some cases, large portions of the body) to hold 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 impregnated with plaster of paris, which hardens after it has been made wet. Plaster of Paris is calcined 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.

2 (CaSO₄·½ H₂O) + 3 H₂O → 2 (CaSO₄.2H₂O) + Heat

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.