An orthopedic cast is a rigid shell designed to immobilize a fractured or injured limb, which is necessary for proper healing. The cast holds the bone fragments in correct anatomical alignment, preventing movement that could disrupt the repair process. This stabilization allows the body’s natural mechanisms to bridge the break with new bone tissue over several weeks. A successful cast application requires precision, starting long before the hardening material is applied.
Preparing the Injury Site
Before the first layer of casting material is applied, the clinician must ensure the limb is correctly positioned and prepped. Initial checks often involve X-rays to confirm the alignment of the fracture is acceptable for casting. The skin is then cleaned and dried to prevent irritation or infection from being sealed beneath the cast material.
The limb must be held in a specific position of function throughout the entire application, which is crucial for maximizing recovery and later mobility. For example, a wrist might be placed in slight extension, while an ankle is held at a 90-degree angle. The choice of material is also decided at this stage, primarily between plaster of Paris and fiberglass. Plaster is easier to mold, making it suitable for displaced or complex fractures, but fiberglass is lighter, more durable, and porous, which is often more comfortable for the patient.
The Step-by-Step Application
The application process begins with the first protective layer, the stockinette, a soft, tubular knitted fabric. This sleeve is rolled directly onto the skin, extending beyond the intended borders of the cast. The stockinette acts as a barrier, protecting the skin from direct contact with the hard cast and helping to absorb initial moisture and sweat.
The second layer involves wrapping soft cotton or synthetic padding over the stockinette, moving from the limb’s distal end toward the body. This padding provides essential cushioning, particularly over bony prominences like the elbow or ankle, which are susceptible to pressure sores. Adequate padding prevents the rigid cast shell from creating dangerous pressure points and helps prevent thermal burns that can occur during the hardening process.
Next, the outer casting material, either rolls of fiberglass or plaster, is submerged briefly in water to activate the material. The clinician wraps the wet material circumferentially around the padded limb, overlapping each layer by approximately half its width. This requires a specialized wrapping technique that maintains light, even pressure without causing wrinkles or excessive tightness.
While the material is still wet and pliable, the technician carefully molds the cast to the contours of the limb, ensuring maximum structural support. For instance, a plaster cast may use “longuettes,” which are reinforced strips laid into the layers to enhance strength. The process concludes with folding the excess stockinette and padding over the edges and securing them with the final layer of casting material, creating a smooth, protective border.
Setting Time and Immediate Checks
Once the final layer of material is applied, the setting process begins, which varies significantly between materials. Fiberglass casts start hardening almost immediately after water activation. They are usually rigid enough for light use within 10 to 15 minutes, fully curing in one to two hours. Plaster casts take longer to set, often requiring 24 to 72 hours to achieve full strength and dryness.
The clinician performs immediate neurovascular checks to ensure the cast is not compromising circulation or nerve function. These checks involve assessing the exposed fingers or toes for color, temperature, and capillary refill time, which should be less than three seconds. The patient is also asked to move the exposed digits to check for motor function and report any signs of tingling, numbness, or excessive pain, which can indicate nerve compression.
The patient is given initial instructions to elevate the cast above heart level for the first 48 hours to manage swelling. They are advised to support the cast to prevent indentations and to avoid putting any weight on it until it has achieved its hardened state. These steps are important for preventing complications like compartment syndrome and ensuring the cast maintains its shape for effective healing.