How to Take Care of a Cast: Keeping It Dry and Clean

What Is Cast Care?

Picture of a healthcare professional putting a pink cast on a patient's lower leg.
Picture of a healthcare professional putting a pink cast on a patient's lower leg.

Why Do Doctors Put Casts on Broken Bones?

  • The function of a cast is to rigidly protect and immobilize an injured bone or joint. It serves to hold the broken bone in proper alignment to prevent it from moving while it heals.
  • Casts may also be used to help rest a bone or joint to relieve pain that is caused by moving it (such as when a severe sprain occurs, but no broken bones).

What Are the Different Types of Casts?

  • Different types of casts and splints are available, depending on the reason for the immobilization and/or the type of fracture.

What Are Casts Made of?

  • Casts are usually made of either plaster or fiberglass material.

What Are the Types of Broken Bones (Fractures), and How Long Do They Take to Heal?

  • A fractured bone is the same as a broken bone. Most fractures happen because of a single and sudden injury. Fractures are usually diagnosed by X-ray (even when a fracture is apparent on physical exam, an X-ray helps confirm the fracture and establish its severity and the bones involved ).
    • A simple (or closed) fracture has intact skin over the broken bone.
    • An open fracture is also called a compound fracture. This means that a cut or wound exists on the skin near the broken bone. If the cut is very severe, the edges of the bone may be seen coming out from the wound.
    • A stress fracture can result from many repeated small stresses on a bone. Microscopic fractures form and, if not given time to heal, can join to form a stress fracture. These types of fractures are usually seen in athletes or soldiers who perform repetitive vigorous activities.
    • A pathologic fracture happens with minimal or no apparent injury to an abnormal bone. This is usually caused by an underlying weakness or problem with the bone itself, such as osteoporosis or a tumor.
  • When a bone is fractured, it may require a reduction (realignment) to put the ends of the fracture back into place. A doctor will do this by moving the fractured bone into alignment with his or her hands. If a bone has a fracture but is not out of position or deformed, no reduction is necessary. This reduction can be performed in the emergency department, a doctor's office or, if the reduction is complicated, might even occur in the operating room.
  • Once the ends of the bone are aligned, the injured bone requires support and protection while it heals. A cast or splint usually provides this support and protection.
  • Many factors affect the rate at which a fracture heals and the amount of time a person needs to wear a cast. Ask your doctor how much time the specific fracture will take to heal.

Is a Fiberglass or Plaster Cast Better, and How Do They Put Them On?

Many different sizes and shapes of casts are available depending on what body part needs to be protected. A doctor decides which type and shape is best for each person.

Cast application

  • Before casting material is applied (plaster or fiberglass), a "stockinette" is usually placed on the skin where the cast begins and ends (for example, at the hand and near the elbow for a wrist cast). This stockinette protects the skin from the casting material.
  • After the stockinette is placed, soft cotton padding material (also called cast padding or Webril) is rolled on. This cotton padding layer provides both additional padding to protect the skin and elastic pressure to the fracture to aid in healing.
  • Next, the plaster or fiberglass cast material is rolled on while it is still wet.
  • The cast will usually begin to feel hard about 10 to 15 minutes after it is put on, but it takes much longer to be fully dry and hard.
  • Be especially careful with a plaster cast for the first 1 to 2 days because it can easily crack or break while it is drying and hardening. It can take up to 24 to 48 hours for the cast to completely harden.

Plaster casts

  • A plaster cast is made from rolls or pieces of dry muslin that have starch or dextrose and calcium sulfate added.
  • When the plaster gets wet, a chemical reaction happens (between the water and the calcium sulfate) that produces heat and eventually causes the plaster to set, or get hard, when it dries.
  • A person can usually feel the cast getting warm on the skin from this chemical reaction as it sets.
  • The temperature of the water used to wet the plaster affects the rate at which the cast sets. When colder water is used, it takes longer for the plaster to set, and a smaller amount of heat is produced from the chemical reaction.
  • Plaster casts are usually smooth and white.

Fiberglass casts

  • Fiberglass casts are also applied starting from a roll that becomes wet.
  • After the roll is wet, it is rolled on to form the cast. Fiberglass casts also become warm and harden as they dry.
  • Fiberglass casts are rough on the outside and look like a weave when dry. Fiberglass are available in many colors.

How Do You Prevent Getting Water Inside Your Cast, and What Remedies Help Pain and Inflammation?

  • A doctor may want the person to use ice to help decrease the swelling of the injured body part. (Check with a physician before using ice.)
  • To keep the cast from becoming wet, put ice inside a sealed plastic bag and place a towel between the cast and the bag of ice.
  • Apply ice to the injury for 15 minutes each hour for the first 24 to 48 hours.
  • Try to keep the cast and injured body part elevated above the level of the heart, especially for the first 48 hours after the injury occurs.
  • Elevation will help to decrease the swelling and pain at the site of the injury.
  • Propping the cast up on several pillows may be necessary to help elevate the injured area, especially while asleep.

How Can You Prevent a Cast From Breaking, and How Do You Keep it Clean and Dry?

Always keep the cast clean and dry.

  • Loose cast. If the cast becomes very loose as the swelling goes down, call the doctor for an appointment, especially if the cast is rubbing against the skin.
  • Protect the cast from water. Cover the cast with a plastic bag or wrap the cast to bathe (and check the bag for holes before using the bag a second time). Some drug stores or medical suppliers have cast covers - plastic bags with Velcro straps or rubber gaskets to seal out water for protection during bathing.
  • Fiberglass casts and water. If a fiberglass cast gets damp, dry it (make sure it dries completely). Because a fiberglass cast allows air through it, a hairdryer on the cool setting should do the trick (do not try to dry it using a hairdryer without a cool setting - you could burn yourself). If you have any trouble getting the cast dry, call your doctor to find out if the cast needs to be replaced.
  • Very wet under cast. If the cast gets wet enough that the skin gets wet under the cast, contact the doctor. If the skin is wet for a long period of time, it may break down, and infection may occur.
  • Odors in a cast. Sweating enough under the cast to make it damp may cause mold or mildew to develop. Call the doctor if mold or mildew or any other odor comes from the cast.
  • Don't break a cast. Do not lean on or push on the cast because it may break.
  • Do not put anything inside a cast. Do not try to scratch the skin under the cast when it itches with any sharp objects; it may break the skin under the cast and lead to an infection. Do not put any powders or lotions inside the cast.
  • Don't trim the rough edges of a cast. Do not trim the cast or break off any rough edges because this may weaken or break the cast. If a fiberglass cast has a rough edge, use a metal file to smooth it. If rough places irritate the skin, call the doctor for an adjustment.
  • Use an arm sling. An arm sling may be needed for support if the cast is on the hand, wrist, arm, or elbow. Wrapping a towel or cloth around the strap that goes behind the neck can help protect the skin on the neck from becoming sore and irritated.
  • Do not walk on the cast. If the cast is on the foot or leg, do not walk on or put any weight on the injured leg, unless the doctor allows it.
  • Walking boots. If the doctor allows walking on the cast, be sure to wear the cast boot (if given one by the doctor). The boot is to keep the cast from wearing out on the bottom and has a tread to keep people in casts from falling.
  • Crutches. Crutches may be needed to walk if a cast is on the foot, ankle, or leg. Make sure the crutches have been adjusted properly before leaving the hospital or the doctor's office and make sure you understand and can demonstrate proper use of crutches.

How Are Casts Removed?

  • Do not try to remove the cast.
  • When it is time to remove the cast, the doctor will take it off with a cast saw and a special tool.
    • A cast saw is a specialized saw made just for taking off casts. It has a flat and rounded metal blade that has teeth and vibrates back and forth at a high rate of speed.
    • The cast saw is made to vibrate and cut through the cast but not to cut the skin underneath.
    • After several cuts are made in the cast (usually along either side), it is then spread and opened with a special tool to lift the cast off.
    • The underlying layers of cast padding and stockinette are then cut off with scissors.
  • After a cast is removed, depending on how long the cast has been on, the underlying body part may look different than the other uninjured side.
    • The skin may be pale or a different shade.
    • The pattern and length of hair growth may also be different.
    • The injured part may even look smaller or thinner than the other side because some of the muscles have atrophied or weakened because they have not been used since the cast was put on.
    • If the cast was over a joint, the joint is likely to be stiff. It will take rehabilitation and some time and patience before the joint regains its full range of motion.

What Are the Complications of Wearing a Cast?

Many potential complications are related not only to wearing a cast but also to the healing of the underlying fracture.

Immediate complications

Compartment syndrome

  • Compartment syndrome is a very serious complication that can happen because of a tight cast or a rigid cast that restricts severe swelling.
  • Compartment syndrome happens when pressure builds within a closed space that cannot be released. This elevated pressure can cause damage to the structures inside that closed space or compartment - in this case, the muscles, nerves, blood vessels, and other tissues under the cast.
  • This syndrome can cause permanent and irreversible damage if it is not discovered and corrected in time.
  • Signs of compartment syndrome
    • Severe pain
    • Numbness or tingling
    • Cold, pale, or blue-colored skin
    • Difficulty moving the joint and fingers or toes below the affected area.
  • If any of these symptoms occur, call the doctor or go to the emergency department immediately. The cast may need to be loosened or replaced.

A pressure sore or cast sore can develop on the skin under the cast from excessive pressure by a cast that is too tight or poorly fitted.

Delayed complications

  • Healing problems
    • Malunion: The fracture may heal incorrectly and leave a deformity in the bone at the site of the break. (Union is the term used to describe the healing of a fracture.)
    • Nonunion: The edges of the broken bone may not come together and heal properly.
    • Delayed union: The fracture may take longer to heal than is usual or expected for a particular type of fracture.
  • Children are at risk for a growth disturbance if their fracture goes through a growth plate. The bone may not grow evenly, causing a deformity, or it may not grow any further, causing one limb to be shorter than the other.
  • Arthritis may eventually result from fractures that involve a joint. This happens because joint surfaces are covered by cartilage, which does not heal as easily or as well as bone. Cartilage may also be permanently damaged at the time of the original injury.

When to Call Your Doctor about Cast Complications?

  • Check the cast and the skin around the edges of the cast everyday. Look for any damage to the cast, or any red or sore areas on the skin.
  • Call the doctor immediately if any of the following happen:
    • The cast gets wet, damaged, or breaks.
    • Skin or nails on the fingers or toes below the cast become discolored, such as blue or gray.
    • Skin, fingers, or toes below the cast are numb, tingling, or cold.
    • The swelling is more than before the cast was put on.
    • Bleeding, drainage, or bad smells come from the cast.
    • Severe or new pain occurs.

Bone Fracture (Broken Bone)

  • Bone fracture, broken bone, and bone crack all mean the same thing. The bone has been damaged such that it is no longer intact. None of these terms indicate the severity of the bone damage.
  • Bones break when they cannot withstand a force or trauma applied to them. Sometimes the bones are so weak that they cannot withstand the force of gravity, such as compression fractures of the back in the elderly.
  • Fracture descriptions help explain how the breakage appears. For example, these descriptions may tell whether or not the fragments are aligned (displaced fracture) and whether or not there is skin overlying the injury is damaged (compound fracture).
1.. Amendola A, Twaddle B. Compartment syndromes. In: Browner BD, Jupiter JB, Levine AM, Trafton PG, eds. Skeletal Trauma. 2nd ed. Philadelphia, Pa:WB Saunders Co;1998:365-389.

2. Latta L, Sarmiento A, Zych G. Principles of nonoperative fracture treatment. In: Browner BD, Jupiter JB, Levine AM, Trafton PG, eds. Skeletal Trauma. 2nd ed. Philadelphia, Pa:WB Saunders Co;1998:237-266.

3. Rosen P, Barkin RM, eds. Emergency Medicine: Concepts and Clinical Practice. 4th ed. St. Louis, Mo:Mosby-Year Book;1998:620-622.

4. Salter RB. Fractures and joint injuries. In: Textbook of Disorders and Injuries of the Musculoskeletal System. 2nd ed. Baltimore, Md:Lippincott Williams & Wilkins;1983:349-426.

5. Simon R, Koenigsknecht S. Fracture principles. In: Emergency Orthopedics: The Extremities. 3rd ed. Norwalk, Conn:Appleton & Lange;1996:3-20, 517-36.

6. Simon RR, Koenigsknecht SJ. Treatment of fractures. In: Emergency Orthopedics: The Extremities. 2nd ed. Norwalk, Conn:Appleton & Lange;1987:7-15.

7. Tintinalli JE, Menkes JS. Immobilization techniques. In: Tintinalli JE, Kelen GD, eds. Emergency Medicine: A Comprehensive Study Guide. 5th ed. New York, NY:McGraw-Hill;2000:1747-1753.