Frequently Asked Questions About Casts

What are the different kinds of casts?

A cast, which keeps a bone from moving so it can heal, is essentially a big bandage that has two layers — a soft cotton layer that rests against the skin and a hard outer layer that prevents the broken bone from moving.

These days, casts are made of either:

• plaster of paris: a heavy white powder that forms a thick paste that hardens quickly when mixed with water. Plaster of paris casts are heavier than fiberglass casts and don't hold up as well in water.
• synthetic (fiberglass) material: made out of fiberglass, a kind of moldable plastic, these casts come in many bright colors and are lighter and cooler. The covering (fiberglass) on synthetic casts is water-resistant, but the padding underneath is not. You can, however, get a waterproof liner. The doctor putting on the cast will decide whether a fiberglass cast with a waterproof lining is appropriate.

How is a cast put on?

First, several layers of soft cotton are wrapped around the injured area. Next, the plaster or fiberglass outer layer is soaked in water. The doctor wraps the plaster or fiberglass around the soft first layer. The outer layer is wet but will dry to a hard, protective covering. Doctors sometimes make tiny cuts in the sides of a cast to allow room for swelling.

Can plaster of paris casts get wet?

Absolutely not! A wet cast may not hold the bone in place because the cast could start to dissolve in the water and could irritate the skin underneath it, possibly leading to infection. So your child shouldn't swim and should use a plastic bag or special sleeve (available online or sometimes at pharmacies) to protect the cast from water. And instead of a shower, your child may need to take a sponge bath.

Can synthetic (fiberglass) casts get wet?

Although the fiberglass itself is waterproof, the padding inside a fiberglass cast is not. So it's still important to try to keep a fiberglass cast from getting wet. If this is a problem, talk to the doctor about getting a waterproof liner. Fiberglass casts with waterproof liners let kids continue bathing or even go swimming during the healing process. Although the liner allows for evaporation of water and sweat, it's still fragile. Also, only certain types of breaks can be treated with this type of cast. Your doctor will determine if the fracture may be safely treated with a waterproof cast.

Is it OK to have people sign and draw on my child's cast?

Definitely! That often makes the whole broken bone experience more bearable for kids. Permanent markers usually work best; washable ones can smear. Feel free to encourage siblings, family members, and classmates to sign it, draw pictures on it, or decorate it with stickers. The doctor might even let your child keep the adorned cast as a souvenir.

What if my child has an itch in the cast?

Try blowing some air in the cast with a hair dryer — be sure to use the cool setting, though. And you should never pour baby powder or oils in the cast to try to relieve itching or try to reach the itch with long, pointed object such as a pencil or hanger — these could scratch or irritate your child's skin and can lead to an infection.

What if the cast gets a crack?

This can happen if the cast is hit or crushed, has a weak spot, or if the injured area begins to swell underneath. Call your doctor as soon as you notice a crack. In most cases, a simple repair can be done to the cast without needing to remove it or change it.

What if the cast causes my child's fingers or toes to turn white, purple, or blue, or if the skin around the edges of the cast gets red or raw?

The cast may be too tight. Redness and rawness are typically signs that the cast is wet inside, from sweat or water. Sometimes, kids pick at or remove the padding from the edges of fiberglass casts. They shouldn't do this, though, because the fiberglass edges can rub on the skin and cause irritation. Call your doctor to have the problem fixed right away.

Why aren't some types of broken bones put in casts right away?

Some kinds of fractures don't need casts to heal. Certain fractures of larger long bones, such as the femur (thighbone), are hard to keep straight in a cast. Although doctors used to commonly put many of these kinds of fractures in traction (a way of gently pulling the bone straight), these days, surgery is often used instead.

Do all broken bones need casts?

It's not practical to cast ribs and collarbones (clavicles). Even displaced collarbones (in which pieces on either side of the break are out of line) heal well with a sling or special strap called a "figure-of-eight clavicle strap," which the child wears like a vest. Some non-displaced finger and toe fractures (in which the pieces on either side of the break line up) that don't involve the joint or the growing part of a child's bone (called the growth plate) may heal well with a splint or buddy taping (taping the injured digit to the adjacent unaffected finger or toe).

Will my child feel pain when the broken bone is in a cast?

Some pain is expected for the first few days, but it's usually not severe. The doctor may recommend acetaminophen or ibuprofen to ease pain.

How are casts taken off?

The doctor will use a small electrical saw to remove the cast. Although it may look and sound scary to your child, the process is actually quick and painless. The saw's blade isn't sharp — it has a dull, round blade that vibrates up and down. The vibration is strong enough to break apart the fiberglass or plaster, but shouldn't hurt your child's skin and may even tickle.

What will the injured area look and feel like when the cast is removed?

Once the cast is off, the injured area will probably look and feel pretty weird to your child: The skin will be pale, dry, or flaky; hair will look darker; and the area (muscles especially) will look smaller or weaker. Don't worry, though — this is all temporary. And depending on the type and location of the fracture, the doctor may also give your child special exercises to do to get the muscles around the broken bone back in working order.

Reviewed by: Peter G. Gabos, MD
Date reviewed: November 2010