4.2 Skull fractures
The prognosis for skull fractures is dependent upon their location. A fissure fracture of the skull may simply cause minor trauma compared with a displaced depression fracture of the skull into the brain, which may be fatal [14]. Most facial and cranial bones are very flat and are readily rendered bereft of a blood supply, predisposing them to sequestration. In many locations the bones are subtended by a hollow cavity, such as a sinus. The brain is also located beneath portions of the bony shell. Rigid internal fixation may not be a prerequisite to healing. The main task involves the reduction of disfiguring fractures and their maintenance in that location until they have healed.
4.2.1 Etiology
Kicks and collisions are the main causes of skull and facial fractures.
4.2.2 Diagnosis
The diagnosis devolves from the anamnesis and observation [14] (Fig. S4I). Assess the extent of the injury by palpation. Some animals may resent this, causing additional, sometimes dangerous, instability. Radiography is indicated but it may be difficult to pinpoint the exact number of injuries and their extent because overlying structures obscure many details [3]. Computed tomography may be the technique of choice, allowing precise identification of the various fragments. Ultrasonography may also be helpful.
Fig. S4I: Palpation of skull fracture. The index finger demonstrates the instability created by the fracture.
Employ computed tomography to precisely define the extent of the pathology.
4.2.3 Preoperative management
Assess the injury in detail, and issue a prognosis, giving due consideration to quality of life. This is important in skull fractures with brain injury or permanent disfigurement. Address the metabolic state of the patient. Some animals will require fluids and correction of acid-base imbalance. If the animal is unconscious or ataxic, tranquilizers and agents such as intravenous DMSO are indicated to help prevent additional damage due to edema. Prepare a surgical plan and check the availability of any devices needed for the surgical intervention [1]. Decide on the approach through which correction of the problem will be attempted well ahead of time to allow expedient correction. Evaluate the animal for gait abnormalities and determine whether the problem is improving or worsening or if there is no change.
4.2.4 Surgical procedures
The following surgical procedures are carried out dependent upon the characteristics of the injury. Either an open or a closed reconstruction, possibly with the aid of a Richards bone hook, can be performed [15] (Fig. F4R). Depression fractures may have to be elevated. This can be achieved with periosteal elevators and hooks or by preparing a hole in an adjacent bone and then inserting an instrument or bent large-gauge wire through the hole and elevating the depressed fragment from the inside [2, 15] (Fig. F4S). Take care to preserve the tenuous blood supply in an effort to avoid sequestration.
Fig. F4R: Use of a bone hook to reduce a depressed zygomatic arch fracture.
Fig. F4S: Insertion of a Steinmann pin through a small drill hole for elevation of a depressed bone fragment. If necessary the fragment is fixed with cerclage wire.
In selected cases, closed reduction is performed and the fragment kept in place by interdigitation of its serrated edges. This would seem to be the ideal situation but it is only applicable to fractures around the zygomatic arch [16]. Insert cerclage wires through small holes prepared in the fragments and in adjacent bones to act as wire sutures (Fig. S4J, Fig. S4K). In cases with large areas of unstable depressed fractures, contour a bone plate and place it over the depressed bones; then apply wire sutures through the plate holes to hold the plate in position. These wire sutures, which are connected to the adjacent bones as well as to the fragments (Fig. F4T), maintain the normal shape of the skull until healing occurs [1, 17]. The fragments are lifted into their normal positions. The bone plate serves as a buttress and bridge, allowing suspension of the bone fragments. If deemed necessary, place a bone graft over the repositioned fragments.
Fig. F4T: A reconstruction plate is contoured to the shape of the head over a comminuted fracture of the skull. Through strategically placed wire sutures the underlying bone fragments are stabilized. It is important that the plate is anchored on the healthy bone on either side of the fractures. Once the fractures are healed the implants are removed.
Fig. S4J: A comminuted fracture of the rostral sinus region was approached surgically. Several small fragments were removed because they were totally devoid of blood supply. The larger pieces were reduced and fixed in place with a wire suture.
Fig. S4K: Closure was uncomplicated after repair of the fracture.
Use a bone plate as a buttress or bridge, from which fragments may be suspended.
If the defect cannot be corrected by reduction, it can be filled with silicone [18] or fluorocarbon implants [19]. These materials appear to be well tolerated.
Reconstructive procedures are indicated in cases of bone defects. With time, some of the bone may slough and leave wide areas of exposed sinuses. Merely closing the skin over these defects proves inadequate because beneath them lies an air-filled cavity. Typically, the skin becomes desiccated and necrotic (Fig. S4L).
Two types of reconstructive procedures can be effective: periosteal flaps and muscle flaps. Periosteal flaps are prepared in the area adjacent to the bone defect with their bases at the edge of the bone defect [20]. The flaps are then inverted, drawn over the bone defect, and sutured either to each other or to the periosteum of the opposite side (Fig. S4M). Apply a cancellous bone graft over the latter, and suture the skin (Fig. S4N). It may be necessary to perform relief incisions and/or transportation flaps to allow adequate coverage of the bone graft [20] (Fig. S4O, Fig. S4P). The other technique involves selection of a special muscle. It is dissected free from the surrounding tissues and transected at its tendon of insertion [21].