Basics of Splint and Cast Application

GENERAL PRINCIPLES

Splint versus Cast

In many situations, there are both splinting and casting options that will be effective in immobilizing the desired portion of the limb. A splint is not circumferential and, thus, accommodates swelling. In the acute setting, a splint is typically recommended because the eventual amount of soft tissue swelling is unpredictable. Because a cast is circumferential, it is stronger and more rigid. It offers increased stability and the ability to mold in all planes, which makes it more effective in holding reductions of unstable fractures. In the setting of an acute injury, a cast may be applied and is either uni- or bivalved to accommodate soft tissue swelling; however, it will still not be as soft tissue friendly as a splint (Fig. 1-1). Cast saws are designed to limit skin injury, but mechanical and thermal injury can still occur with improper usage. To prevent mechanical injury, place your index finger on the cast as a guard against plunging the saw too deep. To prevent thermal injury do not plow continuously through the cast. Rather, cut a small section of cast the width of the blade then disengage the saw completely prior to cutting the next section.

FIGURE 1-1

Splint and Cast Thickness

The ideal splint or cast is thick enough to have the strength to be rigid and to withstand associated forces while not being unnecessarily heavy or placing the patient at risk for thermal injury during the setting process. For plaster splints, we typically use 8 to 12 layers for
the upper extremity and 12 to 15 layers for the lower extremity. Fiberglass is stronger than plaster, so fewer layers (typically 1/2 to 2/3 of the number of plaster layers) can be used.

Splint and Cast Padding

Cast padding is available in a variety of types and sizes; however, the principles are the same. Padding can be applied in a circumferential manner to the limb or as sheets corresponding to the predetermined length of the splint. Typically, cast padding cannot be applied excessively tight because it is designed to tear beyond an unsafe pressure. A minimum of two layers should be applied in any situation with more padding being required for fragile soft tissue and skin, for thicker casts or splints, around bony prominences, and at the anticipated site for a mold. In the setting of a cast, the padding is typically rolled circumferentially around the limb; while splinting, it may be applied in this manner or as longitudinal sheets along the inside of the splint. Regardless of the method, the padding should be applied slightly farther than the anticipated plaster or fiberglass to ensure adequate protection for the patient. If a cast or splint is to be applied over a wound, ensure that sufficient gauze or other dressing material is applied to absorb blood. When blood that is absorbed by the padding dries it becomes rigid, essentially creating a “blood cast” that will not allow swelling. To prevent this use the longitudinal sheet padding technique whenever bleeding is expected (e.g. open fractures, postoperative splint) (Figs. 1-2 and 1-3).

FIGURE 1-2

FIGURE 1-3

Splint Width

Splinting material comes in a variety of different widths, but is most frequently stocked in 4, 5, and 6 inch widths. The practitioner must chose the correct width based on the size of the patient and the area of the body. If the splint is too narrow, then the strength of the splint will be insufficient to stabilize the limb. On the other hand, an excessively wide splint will be circumferential, reducing the ability of the splint to accommodate swelling. In general, most splints distal to the elbow are made with 4 inch plaster. For the elbow and humerus 5 inch plaster is often used. For the lower extremity 5 or 6 inch plaster is used. However, the width of the splinting material should be adapted for larger (obese or muscular) or smaller (frail or pediatric) patients.

Temperature Concerns

An exothermic reaction occurs when water is added to splinting material, therefore heat is released in close proximity to the patient’s skin. This results in the potential for burns. The amount of heat that reaches the skin is proportional to the plaster thickness, amount of padding, and water temperature. Since the amount of heat is proportional to the plaster thickness, the thinnest splint that is clinically effective should be used. It is very important to accurately measure the length of the splint, because the common practice of folding over the end of the splint to shorten an incorrectly measured splint doubles the plaster thickness at the end. This causes the end of splint to reach high temperatures, possibly resulting in thermal injury. With warmer water, plaster and fiberglass will set in a shorter amount of time but also reach higher temperatures. It is critical to understand that the temperature inside of the cast or splint (closer to the patient) is greater and dissipates slower than the temperature outside. Using cold water is always safest, and we do not recommend using water that is warmer than the ambient room temperature. Finally, the limb should not be placed on a pillow while the splint hardens. Pillows, especially the plastic type that are frequently used in hospitals, will not allow for dissipation of heat resulting in high temperatures near the patient’s skin. The limb must be held as the splint or cast hardens to allow for heat dissipation.

Wrapping Cast Material around Joints

When a joint is immobilized in a position of some flexion, there will be a concave and convex side. The tendency is to place an excessive amount of casting material on the concave side while leaving the convex side too thin. To avoid this error, consider placing sheets of cut material or “fan-folding” along the convex side (Figs. 1-4 through 1-6).

Splint Overwrapping Material

One of the advantages of a splint over a cast is that the noncircumferential nature of the splint accommodates swelling of the soft tissue. With this concept in mind, select an appropriate material to overwrap the splint. Commonly used materials are bias (stockinette cut with a bias to create a single layer) and elastic bandages. Bias is preferred to elastic bandages for 3 reasons. Bias allows for the release of heat reducing the likelihood of thermal injury, and moisture reducing skin maceration and splint/cast weight as the plaster dries. Additionally, bias more uniformly distributes compression as the splint is wrapped. A gauze roll is a poor choice because it does not expand and is circumferentially restrictive. Similarly, tape should be applied in a nonrestricting manner.

FIGURE 1-4

FIGURE 1-5

FIGURE 1-6

Molding

Molding of a cast or a splint is essential. It is important in maintaining a reduction by neutralizing deforming forces and in preventing movement or slipping through contours to the corresponding limb. Molds can also be dangerous to the soft tissues if not performed correctly. A proper mold occurs over broad surfaces to prevent areas of high pressure. Fingertips should never be used. Instead, use the palm of the hand or the thenar eminence. Additional cast padding can be used in areas of anticipated molds; however, it should be recognized that while additional layers of padding offer increased protection, excessive padding can increase the likelihood that the reduction will be lost once the swelling subsides. Plaster or fiberglass can be used. Plaster takes more time to set, allowing additional time for cast or splint application and molding; however, with an experienced assistant, fiberglass may be easier to mold since the position is required to be held for a shorter duration of time.

Wedging Casts

Wedging a cast is performed to correct fracture malalignment during the early stages of nonoperative treatment. The first step is to determine the plane of malalignment by reviewing the patient’s radiographs. For example, a varus malalignment of a tibia fracture will be seen on the AP radiograph. The apex of the deformity is then located to determine the location of the cast wedge. Either an opening wedge or a closing wedge can be performed. In the previous example of a varus malalignment of the tibia, an opening wedge can be performed on the medial side or a closing wedge on the lateral side to correct the deformity. We usually prefer an opening wedge to a closing wedge because the latter can result in skin becoming incarcerated in the closed wedge or bunching of cast padding. To perform an opening wedge, the cast is sectioned for three quarters of its circumference at the apex of the deformity. There are a number of techniques to determine the size of the wedge. We draw a longitudinal line representing the long axis of the bone on each side of the fracture. Cast wedges are then placed until this line becomes straight. A radiograph is then taken to confirm acceptable alignment. The opening is then padded, and the cast is rewrapped with fiberglass or plaster.

THE UPPER EXTREMITY

Coaptation Splint

Description of Procedure

Use the patient’s unaffected arm to approximate the length of the splint. The appropriate length extends from the axilla along the medial aspect of the arm, around the elbow, and over the shoulder to at least the level of the acromioclavicular joint, preferably slightly longer (Fig. 1-7).
Apply sufficient cast padding (see “Cast Padding” section discussed previously).
With the elbow bent to 90°, apply the splint as high as possible in the axilla without causing discomfort or compression of the sensitive soft tissue or neurovascular structures in
this area. The splint courses along the medial aspect of the arm, around the elbow, up the lateral aspect of the arm, and over the shoulder toward the neck (Fig. 1-8).
Wrap the splint with bias, and apply the desired mold (Fig. 1-9).

FIGURE 1-7

FIGURE 1-8

FIGURE 1-9

Long Arm Posterior Splint

Description of Procedure

Use the patient’s unaffected arm to approximate the length of the splint. The appropriate length extends along the posterior aspect of the arm and forearm beginning just distal to the shoulder and ending at the metacarpal heads. The forearm is routinely placed in neutral rotation; however, it may also be placed in supination or pronation (Fig. 1-10).
Apply sufficient cast padding (see “Cast Padding” section discussed previously).
With the elbow bent to 90° and the forearm supinated, apply the splint along the posterior aspect of the arm, elbow, wrist, and hand, ending at the metacarpal heads.
Wrap the splint with bias (Fig. 1-11).

FIGURE 1-10

FIGURE 1-11

Long Arm Cast

Description of Procedure

Apply sufficient cast padding (see “Cast Padding” section discussed previously) (Fig. 1-12).
Begin wrapping plaster or fiberglass at the hand and wrist and continue proximally to the upper arm (Fig. 1-13).
Maintenance of consistent wrist, forearm, and elbow position during the application of the cast is essential, as manipulation of these joints after the plaster or fiberglass has been applied will create wrinkles or distortion of the casting material that can become pressure points, placing the patient at risk for ulceration.
While the plaster or fiberglass is still pliable, apply and hold the desired mold.

Tips and Other Considerations

A long arm cast can be applied in two stages, if desired. First, apply a short arm cast (see “Short Arm Cast”), leaving some uncovered cast padding at the proximal portion of the cast. After the short arm cast has been appropriately molded and has hardened, extend the cast padding above the elbow; do not wrap cast padding over the plaster or fiberglass on the
forearm that has already hardened (this will prevent the extended casting material from adhering to the short arm cast). Next, extend the casting material above the elbow. In order to avoid a weak transition point, begin wrapping cast material far distal to the transition point.

FIGURE 1-12

FIGURE 1-13

Hanging Arm Cast

Description of Procedure

Apply a long arm cast with the elbow at 90° and the forearm in neutral rotation (see “Long Arm Cast”). The cast must extend 2 cm or more above the fracture site.
Drop a plumb line from the midline of the neck to the cast and secure a ring to the cast at this point.
To correct varus angulation, place the ring more dorsally (away from the body). To correct valgus angulation, place the ring more volarly (toward the body) (Fig. 1-14).
To correct apex anterior angulation, place the ring more distally. To correct apex posterior angulation, place the ring more proximally (Fig. 1-14).
Then suspend the cast by wrapping a strap through the ring and around the shoulders.

FIGURE 1-14

Single and Double Sugar-Tong Splint

Description of Procedure

Use the patient’s unaffected arm to approximate the length of the splint. With the elbow bent 90° and the forearm in neutral rotation, the lower, or “single,” portion should extend from just proximal to the metacarpal heads at the first palmar crease (to allow for full flexion of the MCP joints) on the palmar surface of the hand, along the volar surface of the forearm, around the elbow, and dorsally along the forearm and hand to the distal most aspect of the metacarpal heads.
Apply sufficient cast padding (see “Cast Padding” section discussed previously).
Apply the splint as described above, and wrap with bias (Figs. 1-15 through 1-17).
After the plaster or fiberglass has set, the upper portion can be applied if desired. The upper, or “double,” portion extends medially from the axilla, around the elbow, and laterally as proximal as desired (but at least as proximal as its medial extent).
Apply sufficient cast padding (see “Cast Padding” section discussed previously) if not already done.
Apply the splint as described above, and wrap with bias (Figs. 1-18 and 1-19).
While the plaster or fiberglass is still pliable, apply and hold the desired mold.