Cast away

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Mar 01, 2007


New developments: Casts continue to evolve to reduce the stress on an injured tendon, ligament or bone.
For most adolescents it was a rite of passage. Signed and decorated by their friends, it was that itchy, white-plaster cast on his/her wrist, arm or ankle. It may have been acquired from a bike, skateboard or skiing mishap, a sports injury from football or hockey or just a fall on the ice.

These casts were heavy, scratchy and hot. The same was true in equine practice. Expertise and experience were required to successfully apply a functional plaster leg cast. They figured prominently in attempts to repair fractures in legendary horses such as Ruffian and yet, many times, poor acceptance by the horse or the development of cast sores limited their usefulness.

Still, the plaster cast was a part of advanced orthopedic care in the 1900s and figured prominently in both human and equine fracture repair.

New developments in materials ensued, however, and fiberglass soon became the casting material of choice. By the 1980s that old crumbly, itchy plaster cast was beginning to disappear for both humans and horses. Fiberglass casts were 20-times stronger than plaster, one-fourth the weight and both durable and waterproof. They became commonly used for many equine injuries ranging from angular limb deformities to tendon injuries to laceration repair stability as well as for support in fracture fixation.

Fiberglass is still used today but medical advances march on. Once again, new developments in materials and methods of bracing may soon make even fiberglass casts obsolete in equine practice.

Limiting range of motion

Fiberglass casts are currently used in equine practice for a number of reasons. A primary use is for the immobilization of the distal or lower limb following tendon repair or similar surgery. Keeping the limb from flexing and extending reduces the stress on the injured tendon or ligament and allows the area time to heal. Fiberglass casting is similarly used following plastic or reconstructive surgery to limit the range of motion of the limb and allow a period of initial healing without skin edges being pulled apart. Transfixation casts, which use pins placed through bones and incorporated in the cast, are used as aids in the fixation of fractures. Occasionally fiberglass casts are used alone to treat some types of non-displaced or simple fractures in certain areas. Casts are especially useful for the treatment of hoof-wall defects and some heel-bulb lacerations.

Proper case selection for cast use is important. Practice and experience are required for correct application. There are certain principles for fiberglass casting that should always be followed. Patient motion during the casting process and during the curing of the cast itself can cause pressure points and poor cast fit so general anesthesia is usually recommended.

This first principle can be problematic for many equine cases and especially so for practitioners attempting to treat a horse in a field or barn. Some equine injuries are unstable enough that the risk of anesthesia and recovery may further jeopardize these patients. Indeed, many horses have been successfully repaired surgically only to have problems occur during recovery which may include failure of the surgical implants and/or cast damage. Standing tranquilization and good handling techniques may make cast application possible with select cases and while not optimum, such procedures can still be successful.

The area to be placed in a cast should be clean and dry. Draining incisions, open wounds or lacerations must be covered with non-adherent dressings and these casts will need to be removed and replaced more frequently to allow examination and monitoring of the wounds. Minimal cast padding should be used over possible pressure points. Too much padding leads to slippage and rotation of the cast, and improper fit cause sores and compromises cast function. Casting principles state that the cast should be long enough to immobilize the joints above and below the lesion and that the upper and lower ends of the cast should be sealed with a collar of elastic adhesive tape to eliminate the entrance of foreign material.