Orthopedic casts are rigid shells designed by healthcare professionals to treat fractures and severe soft tissue injuries. Their primary function is to immobilize an injured limb, holding the broken bones in a precise and stable alignment. This stability allows the body’s natural healing processes to bridge the fracture gap and restore bone integrity. The cast restricts movement, ensuring bony fragments remain undisturbed throughout healing.
Understanding Cast Materials
The choice of casting material is determined by the specific injury, the duration of immobilization, and the required fit. Plaster of Paris, a traditional material, is derived from gypsum. When soaked in water, the plaster becomes highly moldable, making it effective for conforming to complex bone contours or for initial application when swelling is anticipated. Plaster casts tend to be heavier and less durable, and they lose structural integrity if they become wet, requiring careful protection from moisture.
Fiberglass is the alternative material, a synthetic product made from plastic resins reinforced with glass fibers. It is significantly lighter, offering greater comfort for the patient during long-term use. This material sets quickly and cures to a strength superior to plaster, forming a shell that is generally more water-resistant. Fiberglass is often preferred for simple, stable fractures or when the initial swelling has subsided due to its strength and light weight.
The Casting Procedure Explained
Before the cast material is applied, the limb must be properly prepared to protect the underlying skin and ensure a comfortable fit. The medical professional begins by cleaning the skin and then slipping a soft, tubular fabric, called a stockinette, over the entire area to be covered. This material acts as a barrier, preventing direct contact between the skin and the subsequent layers.
Next, a layer of synthetic padding, often cotton or polyester, is wrapped circumferentially over the stockinette. Extra padding is carefully placed over bony areas, such as the ankle or elbow, to prevent pressure sores where the hard cast might press against the skin. The goal is to create a continuous, smooth layer of cushioning without wrinkles, which could otherwise create localized pressure points under the cast.
The casting material, whether plaster or fiberglass tape, is then dipped into lukewarm water to initiate the chemical hardening reaction. The wet material is immediately wrapped around the padded limb in continuous, overlapping layers, starting distally and working proximally. During this wrapping process, the technician uses the flat palms of their hands to gently mold the material to the limb’s shape, ensuring the bone fragments remain in their correct anatomical position. Using the palms avoids creating indentations in the soft material that could harden into painful pressure spots.
Multiple layers are applied to achieve the necessary thickness and strength, typically requiring eight to ten layers for plaster or two to four for fiberglass. Once the final layer is applied, the edges of the cast are carefully folded back and smoothed to create a non-irritating cuff at the skin line. The technician holds the limb in the precise position dictated by the injury until the material has set sufficiently to maintain its shape independently.
Curing and Immediate Aftercare
The time it takes for a cast to harden involves two phases: the setting time and the full curing time. Fiberglass casts begin to set quickly, often within minutes, but require 12 to 24 hours to reach maximum strength and be fully cured. Plaster casts have a longer setting time, taking 8 to 15 minutes to become firm, and may need 48 to 72 hours before they are completely dry and capable of bearing weight.
During this initial curing period, the patient is instructed to protect the cast from pressure and moisture. Patients must avoid resting the wet cast on sharp edges that could deform the shape and create internal pressure points as it hardens. Swelling is common immediately following an injury, so patients are advised to elevate the casted limb above the level of the heart continuously for the first two to three days. Elevation helps reduce swelling and prevents the cast from becoming too tight.
Vigilant monitoring for signs of circulatory compromise is a primary concern during the first few days after application. Patients must watch for symptoms such as excessive numbness, persistent tingling, a burning sensation, or fingers or toes becoming pale and cold. These symptoms indicate that swelling is causing dangerous pressure inside the cast, requiring immediate medical attention to prevent damage to nerves or blood vessels.
Safe Cast Removal
When the bone is fully healed, the cast is removed using a specialized electric tool called an oscillating cast saw. The saw blade does not spin in a full circle like a traditional saw but instead vibrates rapidly back and forth over a very small angle. This unique oscillating action allows the blade to cut easily through the hard, rigid material of the cast.
The safety of the saw comes from the principle that it requires resistance to cut, meaning the hard cast material is cut but the soft skin underneath is not. When the blade contacts the soft cotton padding or skin, the tissue moves with the blade’s vibration, preventing a laceration. The technician cuts the cast down both sides, creating two halves, which are then gently pried apart using a tool called a cast spreader.
After the cast is split and the protective padding is peeled away, the limb is finally exposed. The skin underneath often appears dry, pale, and flaky due to the buildup of dead skin cells and lack of air circulation. Muscles in the area may also look noticeably smaller or feel stiff because of the prolonged period of immobilization, which is a temporary change that resolves with time and use.