A cast is a rigid dressing used to immobilize a fractured bone or soft tissue injury. It is made of strips impregnated with plaster or fiberglass material. The injured area is first covered with a layer of padding made of cotton or synthetic materials to protect the skin from irritation. The plaster or fiberglass strips are then dipped in water and applied over the padding to form the cast.
In general, casts are applied to injured limbs to support and protect the bones and soft tissue. The cast helps to reduce the pain, swelling, and muscle spasms following the injury. If the bone is broken, the cast holds the fractured bone ends in correct alignment during the healing process. A cast, because of its rigid properties, will also provide protection from further injury. Body casts are used to prevent movement of the vertebrae of the back and may be used after a traumatic injury to the spine or a surgical repair of the vertebrae.
For health professionals
Wet casts must be handled carefully, using only the palms of the hands, because a wet cast can be dented or compressed if handled too much after application. Dents or compression of the cast can cause pressure or irritation to the skin beneath the dressing, which may develop sores or ulcers.
Patients in a hip cast or body cast should be repositioned every two hours during the first 24 hours to allow even drying of the cast and every two hours when awake thereafter to avoid developing pressure sores on the skin.
The use of crutches may be recommended for patients with a leg cast or a sling for patients with an arm cast for use during the first 24-48 hours. Patients should be instructed to rest and keep the affected limb elevated on a pillow as much as possible during the first 24 hours.
Of the two types of materials used for the hard supportive layer of cats, fiberglass has the advantages of being lighter, longer-wearing, and better able to "breathe" than plaster. Fiberglass is less trouble for the patient, because plaster casts are more likely to lose their shape if they become wet than fiberglass casts. It is also easier for x rays to penetrate fiberglass than plaster casts. Plaster, on the other hand, is less expensive and is easier to mold or shape to the body. A plaster cast will harden in 15-30 minutes but takes 24-48 hours to dry completely. A fiberglass cast will dry faster, in 15-30 minutes, but the force of the patient's full body weight may cause the cast to crack in the first 24 hours after application.
Casts are usually applied by physicians or orthopedic technicians, with the assistance of other health professionals. If the bone is broken, the physician will first place the fractured bone into alignment. Stockinette cut to size is applied to the limb and then cast padding (cotton batting) is wrapped around the extremity. The physician dips the casting material in water, squeezes out excess water and then applies it wet over the cast padding to form the cast. After applying the cast, the physician will roll the stockinette over the edges of the cast to provide smooth edges at the top, bottom and any openings on the cast. The patient's toes and fingertips are not covered by the cast. The cast is then usually placed on pillows elevated above the patient's heart level for 15-20 minutes to dry.
A health professional will assist the patient in removing any clothing that will be difficult to pull over the cast later. The patient is positioned with the affected extremity resting on a pillow. The skin around the affected area is gently cleansed and thoroughly dried. The patient may be given medication for pain as directed by the physician. After the cast has been applied, extra pillows are placed under the cast to elevate it. The patient should be kept warm and comfortable while the cast is drying. It is helpful to explain to the patient that the cast will feel warm at first but then cool and damp as the material dries.
Aftercare includes measuring the patient for crutches or a sling as appropriate. In addition, patients should be given aftercare instructions as follows:
- The cast should be kept dry. Water weakens plaster casts and may cause skin irritation beneath the cast. The patient should use two layers of plastic to keep the cast dry while bathing or showering.
- To decrease swelling and pain in the first 24-48 hours, the patient should place crushed ice in a plastic bag, covered with a pillow case or towel, on the cast over the injury every 15 minutes per hour while awake.
- Dirt, sand, or powder should be kept away from the inside of the cast. Cast boots can be purchased to cover the foot area of a leg cast.
- Padding should not be pulled out of the cast. In addition, the patient should not stick coat hangers, knitting needles, or similar items inside the cast in order to scratch itchy skin.
- The patient should not break off or trim the edges of the cast without consulting the physician.
- The cast should be inspected regularly. If it develops cracks or soft spots, the physician should be notified.
- The patient should never attempt to remove the cast. The physician will remove the cast at the appropriate time with a special saw that cuts through the casting material but will not damage skin.
A serious complication that can occur after cast application is known as compartment syndrome. This is a rare phenomenon that occurs when a cast is too tight. As the affected limb swells, the cast acts as a closed compartment, tightly compressing the nerves and blood vessels. Compartment syndrome can cause permanent nerve damage or loss of limb due to decreased circulation and oxygen to the tissue. Patients should be instructed to call the physician at once if any of the following signs or symptoms appear:
- increased pain combined with the feeling that the cast is too tight
- numbness and tingling in the hand or foot
- burning and stinging sensations
- excessive swelling in the part of the limb below the cast
- inability to actively move the toes or fingers
Another complication of cast application is that the injury may not heal properly. In some cases the bone endings are set incorrectly, producing a deformity; or do not unite at all. Either may require surgical correction. Delayed union of the bone endings may occur in elderly or malnourished patients; their casts may need to remain in place for a longer period of time.
Cast application is an effective treatment for a fractured bone, serious soft tissue injury or surgical joint repair. Casts generally remain in place until bone healing occurs (four to six weeks). The physician will order x rays to monitor bone healing. X rays can be done through the cast. As bone healing occurs and the limb strengthens, the physician may replace the initial cast with a shorter one or a splinted cast that can be removed for bathing. When the cast is removed, the patient's skin will appear dry and the muscles of the limb may be slightly wasted. Skin care with moisturizers and special exercises to regain muscle strength or to relieve joint stiffness may be ordered by the physician.
Health care team roles
Cast application is usually performed by a physician but may be performed by a specially trained orthopaedic technician under the direction of the physician. The licensed nurse will assess the inpatient patient in a medical setting with a newly casted limb for the first 24-48 hours after cast application. In the outpatient setting, the licensed nurse will observe the patient for the first hour after cast application and instruct the patient and patients family about cast care, signs and symptoms of complications and the importance of follow-up visits with the physician for routine reassessment and cast removal.
Compartment syndrome— A potentially serious complication of cast application, caused by pressure of the cast on the nerves and blood vessels in the injured limb.
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Brown, Jennifer, M.D., and Richard Krause, M.D. Cast Care from AAEM Emergency Medicine and Family Health Guide. EMedicine Online, April 2001. 〈http://www.emedicine.com/aaem/topic495.htm〉.
Care of Casts and Splints. American Academy of Orthopaedic Surgeons. About Orthopaedics Online, 2000. 〈http://www.orthoinfo.aaos.org〉.
"Cast Care." McKinley Health Center Online, June 1999. 〈http://www.mckinley.uiuc.edu/handouts/castcare.html〉.
Cast Protocol. Department of Nursing. UNC Online, March 1998. 〈http://www.med.unc.edu/nursing/manuals/protocol/CASTCARE.pdf〉.