No form of orthopedic therapy has been used….and misused….more and over a longer period than external coaptation. Casts, splints, slings, and support bandages trace their origins to the earliest medical practitioners. The ancient Egyptians and the writings of Hippocrates described the use of splints for fracture immobilization. Over the centuries everything from flour and egg whites to animal fat and starch were added to bandages to stiffen them and improve stability at the fracture site. As has so often been the case, especially in the field of orthopedics, major advances in fracture management with external coaptation occurred as the result of treating battle casualties during wartime. In the mid 19th century, plaster of Paris bandages were developed during the Crimean War and other European conflicts (1).
Today, although materials have changed, the techniques are much the same and external coaptation is widely used….and misused. In fact, no therapeutic technique is associated with more complications and unsatisfactory outcomes than external coaptation. However, it must be pointed out that external coaptation shares an important characteristic with every other form of orthopedic therapy: proper case and patient selection is essential to successful outcomes. Largely because external coaptation techniques are relatively inexpensive and non-invasive they are frequently applied in situations where there is a high probability of complications. Practitioners, confronted with financial or other constraints on more appropriate surgical treatment will frequently be tempted to practice “don’t just stand there, do something medicine!”
Although every case is unique, there are many instances including most femoral and humeral fractures, where resorting to external coaptation violates the medical maxim of “first do no harm.” Although plaster of Paris remains in use due to its low cost and moldability, its poor radiolucency, susceptibility to moisture, and relative density has seen it give way to a range of synthetic casting materials lead by fiberglass resins. These casting materials are economical, strong, resistant to moisture, and harden rapidly; however, they are less easy to work with and mold than plaster of Paris.
Meticulous attention to the indications for cast use is the key to success with this technique. These indications include a closed fracture below the elbow or stifle and above the metacarpal/metatarsal phalangeal joints where it is possible to immobilize the joint above and the joint below the fracture. Fractures appropriate for cast immobilization are those in which closed reduction can be accomplished and maintained with at least 50% of the fracture ends surface area in apposition. In addition, fractures that are expected to heal relatively rapidly should be chosen to lessen the chance of cast-related complications (2–5).
As a general guideline, placing the limb in a comfortable, standing angle during casting is preferred, although there are a few instances in which increasing the degree of flexion or extension at a joint may improve fracture reduction or reduce strain on soft tissue injuries. Examples of this include placing the hock in somewhat more extension than the standing angle to protect a surgical repair of a damaged gastrocnemius tendon, placing the stifle in somewhat more extension than normal to maintain reduction of a Saltar-Harris II fracture of the proximal tibial physis, or placing the carpus in flexion to protect surgical repair of digital flexor tendons.
Two to six layers of casting material will be required to provide sufficient rigidity to the cast depending on patient size (4).
“Bivalving” a cast is a useful technique that has many applications. This involves applying the cast, allowing it to set, and then cutting it into two halves by cutting longitudinally down the medial and lateral aspects of the cast. The cast is then replaced on the limb and wrapped with elastic bandaging material. Bivalving allows the cast to be easily removed if swelling develops or underlying soft tissues need to be examined. In addition, the caudal half of the cast can be used as a splint in the later stages of fracture healing (2–5).
Splints come in two main categories: preformed splints in several sizes such as mason metasplints or tibial splints, and “made-to-measure” splints formed to the individual patient’s limb using casting tape or moldable plastics. Preformed splints are convenient but frequently don’t provide a good enough fit. For example, mason metasplints are commonly used in radius and ulna fractures even though they do not immobilize the elbow (the “joint above” the fracture) and thus do a poor job of immobilizing the fracture. Molding several layers of casting tape to the limb for the entire length that is needed produces better fracture stability and a more comfortable splint for the animal (2,5).
Slings are a relatively uncommon form of external coaptation. Velpeau slings bandage the forelimb against the body wall with the paw in slight internal rotation. The sling is most often utilized to immobilize the shoulder, especially after reduction of luxations, but it is also an effective way of keeping the animal from bearing weight on the forelimb to protect other injuries. The same can be accomplished with a carpal flexion splint which is also an effective way to protect repairs to digital flexor tendons (5). The most well-known sling in veterinary medicine is the Ehmer sling which prevents the patient from weight-bearing on the bandaged hindlimb and keeps the femoral head internally rotated to lessen the likelihood of reluxation after reduction of a craniodorsal coxofemoral luxation (2,5). Ehmer slings are the object of much controversy, however, as the incidence of soft tissue complications such as swelling, dermatitis, ulceration, and tissue necrosis can be very high and there is relatively little evidence in the literature that they have a significant impact on reluxation rate (6).
The support bandage in most common use in small animal orthopedics is the Robert Jones bandage named after 19th century British surgeon Sir Robert Jones. Jones was a pioneer in orthopedic surgery and radiography. He also described a common 5th metatarsal fracture that he sustained himself on the dance floor! The bandage for which he is best known is seldom mentioned in his writings (7). It consists of a roll or rolls of heavy cotton covered with layers of tightly applied bandaging material to provide uniform compression to the skin surface of the limb. In veterinary orthopedics the Robert Jones bandage may be the best example we have of the misuse of external coaptation, again not because of a deficiency in the technique but because of inappropriate case selection. The Robert Jones bandage is applicable for very short-term reduction and prevention of soft tissue inflammation, and the temporary stabilization of non-displaced, stable fractures distal to the stifle or elbow (1,5). The elastic qualities of the bandaging material provide the compression to the surface of the limb that can minimize inflammation and provide some stability to underlying fractures, but that same elasticity means that the compression is very temporary. Pressure transducers under these bandages have demonstrated that compression lasts for as little as 2 to 5 minutes in some applications but likely no more than 24 to 48 hours in the extreme (7,8). That makes the Robert Jones bandage wholly inappropriate for any use beyond a day or two.
No discussion of external coaptation would be complete without consideration of the potential complications associated with these techniques. Complications are not infrequent; one report placed the rate of soft tissue complication with casting at 63% (8). Complications can arise because of the difficulties inherent in cast or bandage management and owner compliance with animal patients. They can arise because of less than ideal case selection, but they can also arise in situations where case selection and patient management are optimal. Complications with external coaptation take three forms:
- Malunion, delayed union, or non-union. Complications related to fracture healing most often pertain to case selection. For example, external coaptation of a distal, transverse radius and ulna fracture in a 2-year-old Pomeranian would be expected to have a high probability of nonunion due to high interfragmentary strain at the fracture site and poor intra- and extra-osseous blood supply to the healing fracture. In such a case, external coaptation is not able to provide rigid enough fixation to produce consistently positive results (5).
- Fracture disease. Fracture disease refers to joint stiffness, muscle atrophy, and disuse osteopenia associated with prolonged casting of a limb (2). While some of these effects may be reversible, particularly with physiotherapy, some permanent disability may remain.
- Soft tissue injury. Soft tissue injury with external coaptation is frustratingly common. It is most often seen under casts but is by no means limited to this technique. A recent publication found soft tissue injury in nearly 2/3 of 60 animals that had been casted ranging in severity from mild dermatitis to pressure sores and sepsis to avascular necrosis of soft tissues. All sight hounds in this survey developed soft tissue injury and mixed breeds were at less risk (8). The investigators were not able to demonstrate any protective value in weekly cast changes, nor in owner education and monitoring. They concluded that even the most observant owners were unreliable in detecting soft tissue injury and that the only way to detect cast sores was to remove the cast. Their examination of the literature produced no conclusive data and thus no consensus on the matter of cast padding. Recommendations vary as to the amount of padding to use, if any at all, and how it should be applied with no indication that there is any “best method” (8). Ultimately, management of soft tissue injury caused by casts resulted in an increase in costs from 4% to 121% of the original surgery cost for these owners.