Discussion

Introduction:
Fractures of the head, particularly of the mandible, are common in horses. In a recent review, fractures involving the head comprised 12% of all incidents and were the second most common injuries after splint bone fractures. Many head fractures are treated surgically and generally the prognosis is very good (Hug 2009). This applies not only to open fractures but also to severely displaced fractures. Cerclage wire is frequently used for repair of skull fractures because it is inexpensive and has a broad range of applications. The use of locking compression plates (LCP) and screws is very appropriate in skull fractures. Special small- sized interlocking implants are available to manage selected fractures successfully.

Fractures of the facial skull:
Periosteal elevators or Langenbeck retractors can be effectively applied for fracture reduction. A specially designed reduction instrument manufactured in 2 sizes (2.4 mm and 3.5 mm), has recently become available. It consists of an horizontal cross handle, connected to a tap-like rod that is twisted into the bone fragment. Depending on the size of the fragment a 1.8 or 2.4 mm drill hole is prepared and the instrument inserted into the bone fragment.
Once the displaced fragments are reduced into proper alignment, most skull fractures may be repaired using No. 2 polydioxanone sutures or 1 - 1.2mm (20 or 18 gauge) cerclage wire. Great care should be used when tightening a cerclage, because the bones of the facial skull are usually thin and can easily be cut by the wire. The advantage of using the Flapfix-System is that the titanium rosettes provide a large contact area with the bone fragments, which minimises iatrogenic bone damage potentially occurring during fracture fixation. Large fractures are amenable to repair using suitable plates. Locking compression plates like the 3.5 LCP reconstruction plates or the 2.4 mm Unilock are favoured by most surgeons because they allow a very stable fixation. Usually only few short screws of 8 - 14 mm length are required for a stable fixation.
Fractures of the orbit present a special challenge because, in addition to the bony eye socket, associated structures such as the globe or neighbouring parts of the nervous system may be involved. The outer parts of the orbit consist of solid bone and are therefore amenable to fixation with surgical plates, whereas the deeper parts are thin and do not usually allow repair using implants. Reconstruction plates (2.7 mm or 3.5 mm) are suitable for fixation because they are easily adapted to the shape of the bones.

Jaw fractures:
Mandibular fractures are the most common head fractures in the horse. Rostral fractures are the least stable fractures because the cheek teeth and muscles, which provide some stability, are lacking in this region. Incisive bone and mandibular fractures are often open toward the oral cavity, since fracture fragments are usually sharp and there is very little soft tissue covering the bones. Because most jaw fractures are unstable and dislocated, conservative treatment is rarely successful and should therefore not be attempted. The majority of rostral fractures are amenable to wire fixation. For rostral fractures an interdental continuous wire-loop splint described by Obwegeser can be used. It allows the application of uniform tension between all the teeth that are engaged in the splint (Furst et al. 2010).
Many fractures of the body or the ramus of the mandible can be fixed using screws and plates. Although the oral side of the mandible and maxilla is the tension surface, plates are applied ventral to the mandible, where the thick cortex provides a stable fixation. Dynamic compression plates can be used but locking compression plates are presently preferred, because they provide better stability (Kuemmerle et al. 2009). In areas with only one cortex and a predominance of spongy bone, locking screws provide good stability. Depending on the size of the horse, narrow 3.5 or 4.5 LCP are used. Fractures of the mandibular interdental space may be uni- or bilateral and the fragments are often severely dislocated and highly mobile. Very unstable and bilateral mandibular fractures require fixation with one or 2 plates, in addition to intraoral wire fixation that engages the premolars. Teeth that are involved in the fracture should not be removed because this decreases the stability of the fracture. Open and dislocated fractures of the horizontal part of the mandibular branch require surgical treatment and fixation using screws and plates is the treatment of choice. The ventral margin of the mandible is very strong and suitable for the placement of multiple screws.
Fractures of the vertical part of the mandibular branch are rare. Transverse fractures with minimal dislocation are treated conservatively, whereas unstable fractures and those with more severe dislocation require surgical treatment. Plating the ventral and caudal aspect of the vertical ramus can be difficult because access for drilling and placing the screws is limited by the parotid area and the wing of the atlas.