Splints and Casts
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Introduction
Casts are rigid, circumferential dressings applied to an extremity. They are perhaps the most important treatment for fractures and serious soft tissue injuries. These include stable fractures, reduced dislocations, soft tissue injury, congenital and acquired deformities, and stabilize post-operative repair. Casting takes a great deal of experience to correctly apply, and can compromise skin, blood supply, and nerves if improperly made.
Casts are generally used to immobilize and protect an injured part while facilitating healing. To completely immobilize, a cast must precisely conform to anatomy and cover sufficient area. Failure to sufficiently immobilize can lead to loss of reduction, malalignment, or persistent inflammation.
Types of Splints and Casts
Individual topics discuss various types of immobilization. These include:
Materials
Casting has been used for centuries, beginning with tree bark. Gypsum use began in the 1500s, and plaster/cloth rolls first appeared in the 1920's.
It is ideal to have an area dedicated to casting and splinting.
Stockinette is used as the initial layer for casts. It should extend past toes or fingertips and a few inches above the anticipated proximal end. Ensure wrinkles are removed to prevent pressure points.
Padding comes in a variety of options, including cotton material called Webril. Padding protects skin and bony prominences from plaster, improving comfort and reducing risk of pressure sores. It is common to begin distally, with an extra layer to secure the padding. Overlap by 50% at each turn. Two layers are common. Additional padding may be used over bony prominences, but too much padding will lead to a cast that is too loose. When turning a corner, the edge may be stretched or torn to maintain a smooth application.
Plaster
- easier
- cheaper
- longer shelf life
- low allogenicity
Fibreglass
- lighter
- stronger
- more durable
- more water-resistant
Plaster is supplied as strips or rolls of gauze. The gauze is soaked in water, gently wrung out, and applied over padding. Plaster dries within 10 minutes but takes 48 hours to reach its full strength. Cool water provides more working time and improves cast bonding.
Place each roll in water at room temperature until bubbling stops. Warmer water will speed hardening. Water should be gently removed without leaving finger marks. The first application should overlap 100%, and each subsequent turn should overlap by 50%. Wrinkles may be avoided by tucking and folding the edge. Apply 4-6 layers evenly, and endeavour to cover the entire length with each layer. If only a portion is covered, with the next roll continuing on, cast weakness may result.
Fold the ends of the stockinette over before applying the final layer of plaster.
Smooth and mold the cast using both hands, ensuring it is sculpted to the underlying anatomy. Do not use fingers, as these can lead to pressure areas. Ensure the joint is in proper position of function before the cast hardens.
When water is added to plaster, molecules are incorporated into calcium sulfate hemihydrate in a significant exothermic reaction. A solid, material results, curing over 48-72 hours through evaporation. This process is slowed by low temperature, high humidity, and poor air circulation.
Fibreglass should be applyed in a similar way as plaster. Ensure the water does not get above room temperature. Avoid pulling the material too tightly. As setting occurs quickly, mold the cast between each layer. Two-three layers are usually sufficient, though reinforcement may be added to areas such as those that are walked upon.
Ensure there are no rough edges that remain that can catch the skin. These can be trimmed with scissors, a file, or sandpaper if present.
Additives such as salicylic acid, zinc, and aluminium can be used to accelerate hardening, while gum or glue can be used to slow it.
Flannel is used on occasion for the outer layer of a splint. It should NEVER be used inside a cast or a splint.
Other equipment required includes gloves, patient drape, gown and shoe covers, water source (with drain traps if using plaster), scissors, and Chinese finger traps.
Patient Preparation
Discuss the indications, estimated length of immobilization, and potential impact on function. It is also important to discuss potential problems or complications.
Cleanse, dry, and inspect the skin for damage to the skin. If present, they may require a window to be placed.
Assess for swelling. If significant, a circumferential cast is contraindicated, and a splint would be better used acutely. When swelling has decreased, a cast can again be considered.
Position the patient in such a way that they can comfortably maintain position of function during the casting or splinting.
Resources and References
Topic Development
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