page_title: Orthopedic cast
section_title: Materials
hierarchical_section_title: Orthopedic cast / Materials
caption_attribution_description: A flat sheet of fibreglass casting material 4 layers thick
context_page_description: An orthopedic cast, or simply cast, is a shell, frequently made from plaster or fiberglass, that encases a limb to stabilize and hold anatomical structures—most often a broken bone, 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, 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 + 3 H₂O → 2 + 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.
  Current 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.
context_section_description: Due to the nature of the dressing in that the limb is unreachable during treatment; the skin under the plaster becomes dry and scaly because the discarded outer skin cells are not washed or brushed off. Also, plaster of Paris casts can result in cutaneous complications including macerations, ulcerations, infections, rashes, itching, burns, and allergic contact dermatitis, which may also be due to the presence of formaldehyde within the plaster bandages. In hot weather, staphylococcal infection of the hair follicles and sweat glands can lead to severe and painful dermatitis.
  Other limitations of plaster casts include their weight, which can be quite considerable, thus restricting movement, especially of a child. Removal of the cast requires destroying the cast itself. The process is often noisy, making use of a special oscillating saw that can easily cut the hard cast material but has difficulty cutting soft material like cast padding or skin. Although the removal is often painless, this can be distressing for the patient, especially children.  A cast saw can cut, abrade, or burn skin, but those results are uncommon. Additionally, plaster of Paris casts break down if patients get them wet.
  Due to the limitations of plaster of Paris, surgeons have also experimented with other types of materials for use as splints. An early plastic like material was gutta-percha obtained from the latex of trees found in Malaya. It resembled rubber, but contained more resins. When dry it was hard and inelastic, but when warmed it became soft and malleable. In 1851 Utterhoeven, described the use of splints made from this material for the treatment of fractures. In the 1970s, the development of fibreglass casting tape made it possible to produce a cast that was lighter and more durable than the traditional plaster cast and also resistant to water (though the bandages underneath were not) helping the patient be more active.
  In the 1990s the introduction of new cast lining has meant that fiberglass casts with this liner are completely waterproof, allowing patients to bathe, shower, and swim while wearing a cast. The waterproof cast liner however adds approximately 2 to 3 more minutes to the application time of the cast and increases the cost of the cast.
  Drying time, however, can be inconvenient enough to warrant a cast and bandage moisture protector. These waterproof covers allow for bathing and showering while wearing either a plaster or fiberglass cast. The waterproof cast cover stays tightly around the cast and prevents water from ever reaching it while the patient is in contact with water. The cover can easily be removed to dry, and can be re-used often.
caption: fibreglass and polyurethane casting material, 4ply
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