History

The use of immobilization to treat acute fractures dates back to the era of the Fifth Dynasty of Egypt (2498–2345 BCE) when bark was used to splint fractures of the forearm. Gypsum, from which plaster of Paris is derived, was initially used around the sixteenth century in parts of the Ottoman Empire. With the development, in 1927, of the hard-coated plaster of Paris rolls, a binder was incorporated that improved the adherence of the plaster to the cloth. Since then, various additives have been used to either accelerate (salicylic acid, zinc, or aluminum) or slow down (gums or glue) the setting process.

Currently, fiberglass is the most common material used in casting. It has the advantages of being stronger and lighter (approximately two to three times stronger for any given thickness) than plaster, and it creates less heat during application. However, it is more difficult to mold. The cost of fiberglass continues to be more than that of plaster, but in recent years this difference has decreased significantly. In addition to newer casting materials, the development of synthetic padding (Gore-Tex) has allowed most casts to survive significant exposure to water without damage.

Indications

• A variety of stable, acute fractures

• Dislocations that have been reduced

• Injuries to the soft tissues, including muscle, tendon, and ligament

• Congenital and acquired deformities (e.g., correction of talipes equinovarus, congenital clubfoot)

• For the stabilization and protection of vascular, tendon, and nerve injuries following surgical repair

The most common diagnosis for which the primary care clinician uses cast immobilization is the stable, nondisplaced, closed fracture of a long bone. The primary care clinician often treats fractures involving the radius or ulna, phalanges, metacarpals, metatarsals, and malleoli. (See Chapter 190, Fracture Care.) Other conditions include certain grade III ligament sprains (e.g., ankle), Achilles tendon disruptions, and tendonitis refractory to other forms of therapy.

Cast Application Equipment

• Rubber gloves

• Gown and shoe covers for the clinician

• Patient towels or drapes

• Stockinette (2-, 3-, and 4-inch widths)

• Felt padding, soft cotton (e.g., Webril), or synthetic (e.g., polyester) bandages (2-, 3-, 4-, and 6-inch widths)

• Synthetic waterproof cast liner (e.g., Gore Procel, Scotchcast Wet or Dry, Delta-Dry, Waterpruf)

• Rubber heels (walking cast)

• Cast removal protective strip (e.g., De-Flex) to eventually protect skin from cast saw

• Casting material (Fig. 187-1)

• Plaster (e.g., plaster of Paris, avoid thicker than 10 ply, which can cause thermal injury to patient)

• Synthetic (e.g., fiberglass)

• Water source (if using plaster, should have traps in drains and water temperature less than 24° C/75° F)

• Elastic (e.g., Ace) bandages (2-, 3-, 4-, and 6-inch widths)

• Slings

• Scissors

• Chinese finger traps

• Leg stand

Figure 187-1 Materials needed for casting: cotton padding, synthetic casting material or plaster rolls, cast spreader, cast cutter (not shown), and plaster strips.

When water is added to the plaster, the water molecules are incorporated into the calcium sulfate hemihydrate (i.e., plaster of Paris) molecules with a resultant exothermic reaction. The powdery white substance is converted into a solid, rock-hard material, and a significant amount of heat is generated. A curing process then follows over the next few days, characterized by continued water evaporation; this process is accelerated by low humidity, high ambient temperature, and increased air circulation.

Synthetic materials require immersion in water to activate the curing process, with generally less heat generated than plaster. Attention to water temperature in this process is especially important, because water that is too warm (>24° C/75° F) can lead to rapid curing and significant difficulty in application. Water at higher than these temperatures or plaster of Paris thicker than 10 ply can also result in thermal injury to the patient.

Advantages of plaster casts over fiberglass include low cost, ease of molding, long shelf-life, and low allergenicity. Synthetic cast material is more expensive, but this margin has narrowed in the years since fiberglass was introduced. Fiberglass has also improved in its ease of application and continues to be superior in strength, durability, weight, water resistance, and drying time. Both materials are available in multiple sizes, ranging from 2 to 5 inches in width for general, circumferential cast use.

Ideally, a single room or area in the clinic, emergency department, or hospital should be dedicated to the application of casts and splints. This room should have a plaster trap in the sink, and all materials should be easily available. Rubber gloves, gowns, shoe covers, and towels or drapes should be available to protect both the clinician and patient from the inevitable exposure to casting materials. An easily cleaned examination table, stool, and leg stand can greatly facilitate the process of cast application.

Common Cast Types

See Chapter 190, Fracture Care.

Short-Arm Casts

Short-arm casts are generally indicated in the treatment of stable sprains of the wrist, as well as some stable fractures of the distal radius, ulna, carpal bones, and metacarpals. Clinicians performing cast immobilization should be aware of those fractures requiring orthopedic evaluation for possible open reduction and internal fixation. Materials required for short-arm cast applications include a 3-inch stockinette, two rolls of 3-inch cast padding (the waterproof liner replaces the need for both stockinette and padding), and two to four rolls of either 3- or 4-inch plaster bandage (or 2- or 3-inch fiberglass bandage). In general, adult males will require 4-inch plaster (3-inch fiberglass) and children will require 3-inch plaster (2-inch fiberglass). Adolescents and females may require either size depending on preference and size of extremity. The patient should be supine or seated, with the arm abducted 90 degrees and the elbow flexed 90 degrees. The wrist should be slightly extended and in a position of function (Fig. 187-2). Chinese finger traps attached to the patient and suspended from above can support the arm and assist in maintaining the position of function. The cast extends from the proximal forearm (approximately 1 inch distal to the flexion crease of the elbow) distally to include the palm and dorsum of the hand, completely covering the forearm. The metacarpal-phalangeal (MCP) joints are allowed complete motion, with the cast stopping just proximal to the distal palmar crease (Fig. 187-3). Extra padding should be applied over the ulnar styloid. Short-arm casts only partially immobilize the wrist joint and allow movement of the thumb, including opposition with the fifth digit. In addition, they allow for supination and pronation to occur because the elbow is not included. An adaptation of the short-arm cast is the short-arm thumb spica, in which the thumb is included to the level of the interphalangeal (IP) joint (Fig. 187-4). This type of cast may be used for injuries to the scaphoid, trapezium, or first metacarpal, or for any injury requiring wrist and thumb immobilization.

Figure 187-2 Position of the wrist in the application of arm casts.

Figure 187-3 Appearance of a completed short-arm cast. Note that the thumb and fingers are free to move.

Figure 187-4 Short-arm cast with thumb spica.

Long-Arm Casts

Long-arm casts can be fashioned by extending a short-arm cast proximally, with the elbow maintained in 90 degrees of flexion. The padding and plaster should be extended to the proximal humerus, ending 2 to 3 fingerbreadths below the axilla. Be careful to provide extra padding over the pressure point at the olecranon. Plenty of padding should also be placed over the proximal end of the cast or the patient will complain of the sharp edges.

Short-Leg Casts

Short-leg casts are generally indicated in the treatment of some stable ligamentous injuries to the ankle, and stable fractures of the ankle, calcaneus, tarsals, and metatarsals. Materials include a 4-inch stockinette and three rolls of 4-inch cast padding (or waterproof liner). Use of fiberglass is generally preferred in these casts because of its increased durability. With fiberglass casts, three rolls of 4-inch fiberglass bandage are generally needed. An extra reinforcing strip of heavy-duty fiberglass can also be used posteriorly along the bottom of the foot up the back of the leg. For plaster casts (used less often), materials vary widely based on personal preference, but they usually include two to three rolls of 6-inch plaster bandage and an adequate number of plaster splint strips (again for posterior and foot reinforcement), with size based on patient limb size. Application of the short-leg cast is achieved either in the sitting position, with the leg hanging over the table, or prone, with the knee flexed to 90 degrees to help relax the gastrocnemius muscle. The ankle is usually held at a 90-degree angle to the leg, but this angle may be altered depending on the type of injury. A foot-stand or assistant can provide support to the foot. The cast extends from just below the knee joint, usually including the fibular head, distally to the base of the toes, including the metatarsal heads (Fig. 187-5). Again, the ankle joint is only partially immobilized, since the cast does not involve both the joint above and below. For walking short-leg casts (Fig. 187-6), a posterior reinforcing strip is placed and molded after application of the second roll of fiberglass bandage and before placing the final roll. The walker can be applied the same day or at a later time. If applied initially, patients have a tendency to walk on it before the primary cast is dry enough, leading to breakdown of the cast.

Figure 187-5 Appearance of a completed short-leg cast. The cast should hold the ankle at 90 degrees. In addition, the proximal end of the cast should be far enough from the knee to eliminate the possibility of skin irritation with knee flexion.

Figure 187-6 Short-leg cast with walker.

Long-Leg Casts

Long-leg casts can be fashioned by extending a short-leg cast proximally up to the groin. The padding and plaster should be extended to the proximal femur, ending several fingerbreadths below the groin. The knee is in slight flexion and the foot is at 90 degrees. There should be no internal or external rotation of the foot. The knee should be supported in this slight flexion while the cast sets. To maintain strength, make sure there is adequate overlap of the casting material when extending proximally from the knee. In addition, make sure extra padding is provided over the pressure point at the anterior patella. Plenty of padding should also be placed over the proximal end of the cast or the patient will complain of the sharp edges.

Other types of common casts and splints are shown in Figure 187-7. Even with splints, where casting materials do not totally surround the extremity, there is generally a layer of stockinette around the entire area followed by the padding, then the casting material. The casting material is held in place with an Ace wrap or similar material.