External coaptation can be an effective means of stabilising a fracture when it is used appropriately and can be used for first aid, method of primary repair, after surgery or following the removal of implants.

To maximise the chance of successful healing, both the patient and the fracture should be assessed before use of external coaptation as the sole means of stabilisation. The object of fracture assessment is to establish the precise nature of the fracture together with any associated injuries. In general this involves assessing biological, biomechanical and clinical factors in order to estimate the chances for successful treatment and determine the best form of management (Figure 1).

As a general rule, external coaptation is an acceptable mode of fracture repair for young animals with rapid healing potential since the device need not be in place for prolonged periods of time, although this rule is not proven in toy breeds where a high rate of non-unions and malunions has been associated with external coaptation of antebrachial fractures. Thus it is important to consider the breed of dog as well.

Figure 1. Factors used for fracture assessment.

The location of the fracture is a very important consideration. Femoral and humeral fractures do not lend themselves to external coaptation since the device will tend to act as a pendulum, resulting in further distraction and displacement of the fragments leading to non-union or malunion. Animals with femoral or humeral fractures should be cage rested pending definitive repair. Fractures below the elbow or stifle may be amenable to external coaptation; however for closed reduction to be effective at least 50% of the proximal and distal fracture fragments should be in contact.

Fracture configuration is another important consideration since external casts and splints are only effective at resisting bending forces. Shearing, distractive and compressive forces are not neutralised. Consequently external coaptation is a poor method of sole repair for oblique or comminuted fractures because both types of fractures present all of these forces. Transverse fractures are best suited for splints and casts since the primary force involved is bending which can be effectively neutralised. Fractures with an intact adjacent bone (ulna or fibula) can also be considered for external coaptation since the intact bone serves as an anatomical splint and can help to resist rotational and bending forces. Greenstick fractures that occur in young animals where the periosteum is still intact are also suitable candidates for casts and splints.

Where risk assessment identifies factors that may delay or prolong fracture healing or concurrent injuries are present then alternative means of definitive stabilisation should be considered.

Temporary splints and bandages should be considered as a method of emergency first aid in order to prevent fragment motion, which may cause pain, induce further soft tissue trauma and potentially convert a closed fracture into an open fracture. Support dressings supplemented with splints can also be suitable to manage open fractures, allowing dressings to be removed daily while the wounds are managed appropriately. This helps reduce the risk of infection, and provides time for tissue swelling to reduce before definitive repair.

The advantages of external coaptation over other forms of repair are preservation of blood supply and minimal disruption of the fracture site adhering to the principles of biological osteosynthesis. Provided adequate stability can be provided by the device then indirect bone healing is usually rapid with minimal risk of infection and without the need for placement of implants. In young growing animals there is no interference with growth potential, and dressings can be changed on a regular basis as the device is outgrown.

Although a cost-effective way of stabilising certain fractures, there are frequent complications that can arise. These problems most frequently occur through inappropriate selection of cases or application of the device. Inadequate stabilisation will result in non-union. Failure to incorporate one joint above and below the fracture will allow excessive motion of the fracture fragments resulting in high strain at the fracture site and failure of ossification of the fibrous callus. This important rule eliminates the use of external coaptation above the elbow or stifles.

Other common complications include rub sores, pressure sores, dermatitis and swelling of surrounding tissues due to improper placement of the cast or splint. Dressings that are too loose may slip and rub along the skin. Likewise too much padding can result in pressure sores; uneven distribution of pressure or wrapping the limb too tight can cause swelling of the distal extremities due to tourniquet effect. Definitive external coaptation should not be applied until swelling has subsided.

Methods of External Coaptation

Robert Jones Bandage

This restricts motion, reduces soft tissue swelling and provides appropriate temporary stabilisation of fractures below the elbow or stifle until definitive fracture repair can be performed or until swelling has subsided to allow placement of a cast. With prolonged application the padding will become loose allowing movement at the fracture site. The dressing comprises three layers: a contact layer (usually a non-adherent dressing over traumatic or surgical wounds), a secondary layer of rolled cotton (to provide padding and compression) and a tertiary layer (to protect the first two layers). Overall thickness should be 4-8 cm.

Modified Robert Jones Bandage

This differs from the Robert Jones bandage in thickness and, although it provides less support, it is useful postoperatively to minimise swelling.

Splints

Splints are composed of relatively rigid material and do not encompass the entire limb. They are used for stabilising stable fractures in young animals and for postoperative support of repairs and luxations. In general moulded splints are more effective than pre-made splints since they are made to custom fit the patient reducing the risk of soft tissue irritation. Mason metasplints are the most common pre-made splints used in veterinary patients for distal antebrachial fractures and postoperative support of carpal arthrodesis. Spica and Schroeder Thomas splints are rarely used but can be effective for preoperative stabilisation of fractures.

Casts

These can be an effective form of rigid external stabilisation for fractures when applied properly. The aim is to achieve 50% overlap of the fracture fragment ends with minimal axial or rotational deformity (<5%). The secondary layer should provide adequate padding without being too thick. This is to ensure adequate stabilisation since the further away from the bone the cast material is the less rigid the stabilisation. If there are open wounds then the cast can be split (bivalved) to aid in the process of redressing and wound management.

Casting materials most commonly used in veterinary patients generally comprise a polyester fabric impregnated with a clear polyurethane resin. The polyester fabric is extensible in all directions which makes it very conformable in use. When exposed to water or moisture the resin undergoes a polymerisation reaction, which causes the bandage to harden and become rigid. Casts are lightweight, strong and translucent to X-rays, allowing postoperative radiographic evaluation of the fracture without cast removal. Once set, the resin is not adversely affected by moisture, but immersion in water is not recommended as it will prove difficult to dry the underlying padding. Such casting materials generally have a shelf-life of approximately 2 years.

Care for Bandages

Owners should be properly instructed about care of the dressing. Bandages should be kept clean and dry at all times. Limbs should be monitored for signs of swelling, discomfort, drainage and odour. If any of these signs are noticed or the bandage loosens then the owner should be instructed to contact their veterinary surgeon immediately so that the dressing can be changed and the limb evaluated and treated appropriately.

Summary

Although casts and splints are suitable for the management of certain fractures and are seen as the cheap alternative to other forms of fracture stabilisation, they do require relatively intensive management with regular veterinary assessments, as well as owner and patient compliance. If used inappropriately or applied incorrectly then complications can result in a significant overall expense and intense management that may well exceed that associated with other fixation devices.