A cast is a rigid, protective shell applied to an injured limb to immobilize the surrounding joints and maintain the correct alignment of a fractured bone. This external stabilization is necessary for the healing process, allowing bone tissue to regenerate and fuse properly. Healthcare professionals carefully execute the procedure, holding the injured area in a precise anatomical position until the bone achieves sufficient structural integrity.
Comparing Casting Materials
The two primary materials used for creating a cast are Plaster of Paris and fiberglass, each having distinct properties that influence their selection. Plaster of Paris, made from gypsum, is heavier and requires a longer period for the chemical reaction to fully cure, often taking 24 to 72 hours to reach maximum strength. This material excels in molding, conforming smoothly to complex contours of the limb, which is beneficial for initial applications or injuries requiring very precise shaping.
Fiberglass, a synthetic material coated with a water-activated resin, is significantly lighter and more durable than plaster. It sets much faster, hardening enough to support the limb within minutes, though it may take an hour or two to achieve full rigidity. While generally more expensive, its lighter weight and increased breathability often make fiberglass the preferred choice for long-term immobilization and patient comfort.
Preparing the Area for Application
Before the hardening material is applied, a series of preparatory steps are taken to protect the patient’s skin and soft tissues from the cast’s rigid exterior. The first layer applied directly to the skin is a soft, cotton or synthetic tube called a stockinette, which acts as a gentle barrier to prevent irritation. The stockinette must be applied smoothly, avoiding any wrinkles that could create pressure points or cause skin breakdown underneath the cast.
Following the stockinette, a thick layer of soft padding is wrapped circumferentially around the limb. This padding provides cushioning over bony prominences like the heel, elbow, or ankle, which are susceptible to pressure sores. Proper padding also absorbs moisture and heat generated by the setting cast material, preventing potential thermal injury to the skin.
The Step-by-Step Application Process
The application of the casting material begins with the clinician holding the injured limb in the correct anatomical alignment, which is maintained throughout the process. The rolls of plaster or fiberglass are prepared by briefly immersing them in water; the temperature is carefully controlled, as warmer water accelerates the setting time. The chemical reaction between the water and the material causes it to become pliable and begin the hardening process.
The material is then wrapped around the padded limb, starting at the distal end (farthest from the body) and moving proximally toward the body. Each layer is overlapped by approximately half the width of the roll, a technique that ensures uniform thickness and strength across the entire cast. The healthcare provider must apply even tension without creating constricting bands that could compromise circulation or nerve function.
As the material is wrapped, the clinician uses the palms of their hands to gently mold the cast, shaping it to the natural contours of the limb, especially around joints and bony landmarks. This molding ensures a snug fit that maximizes immobilization and prevents the limb from shifting inside the cast. Once the final layer is applied, the excess stockinette and padding are folded back over the raw cast material, creating a soft, finished rim that prevents skin irritation.
Immediate Post-Application Care
Immediately after the casting material is applied and molded, the limb must be held in position until the cast is firm enough to maintain its shape (setting time). For fiberglass, this occurs within five to fifteen minutes, while plaster may take slightly longer. Although the cast is set, it has not reached its maximum strength and remains vulnerable to denting or pressure until the full cure is complete.
Medical staff conduct immediate checks to monitor the limb’s neurovascular status, ensuring blood flow and nerve function are not restricted by the new cast. This involves checking capillary refill time, assessing the pulse, and testing sensation and motor function distal to the cast. The patient is instructed to keep the casted limb elevated above the level of the heart for the first 48 to 72 hours to reduce swelling and discomfort.
Patients are advised to avoid applying pressure to the cast during the initial setting period and to report any signs of complications immediately. These signs can indicate excessive swelling and the potential for a serious condition like compartment syndrome:
- Persistent or worsening pain.
- Numbness.
- Tingling.
- A feeling of burning.
The cast must be protected from moisture and impact until it is fully cured and has achieved its supportive function.