Jaw fractures are a common traumatic pathology in our domestic patients. Separations of the mandibular symphysis are seen in cats perhaps more than any other orthopaedic injury. As a fibrous union and a prominent area of the rostral face, it is at risk primarily in road traffic accidents and sometimes in high-rise falls. This article will challenge some of the well-established techniques and present the reader with an alternative and more reliable technique for repair.
Symphyseal separations account for between 11 and 20 percent of all orthopaedic traumas and 73 percent of all craniofacial injuries in cats. Visually, they can be very easy to diagnose, and the injury is often clear on conscious examination (Figure 1). However, radiographic or CT imaging of the skull is still essential as approximately a third of these cats will also have other craniofacial trauma. It is this additional craniofacial trauma that is likely to affect the outcome of surgical treatment.
The traditional technique
The most commonly-described technique for repairing symphyseal separations is to place a cerclage wire around the rostral mandible (Figure 2). This can be done by passing the wire through two large hypodermic needles placed either side of the rostral mandible. Once placed, the cerclage wire is tightened and knotted outside the skin on the ventral aspect of the mandible.
There are, however, some significant concerns regarding this repair. Firstly, the position of the wire around the rostral mandible is often close to the neurovascular bundle that emerges from the middle mental foramen. As the wire is tightened, there is a significant risk of crushing this bundle between the bone and the wire, which is likely to be a source of post-operative discomfort. Secondly, as the wire passes from the oral cavity through to the submucosa and then out of the skin, the wire is easily contaminated by plaque and food debris from the oral cavity.
This is a useful technique to master as it provides a more straightforward and reliable repair to this
very common orthopaedic injury
Thirdly, the knot ventral to the mandible is a challenge to cover and will often leave a sharp structure that can traumatise the patient and its owners or veterinary staff. Finally, and most significantly, the cerclage wire, when tightened, has the potential to rotate or collapse the mandibles, resulting in a malocclusion.
With no other injuries, the caudal articular surfaces of the mandible will counteract this rotation. But if there is a caudal trauma, this stability can be lost, and the mandibles will be compressed and rotated. This can be seen in these two cases: in the first, skull radiography reveals a condylar fracture of the right mandibular condyle (Figures 3A and B). This destabilises the mandible, and as the cerclage wire is tightened, the right mandible becomes externally rotated (Figures 3C and D). From this, a malocclusion develops, which prevents full mouth closure.
In the second case, there is a caudal luxation of the left temporomandibular joint, which again destabilises the mandible. This time, as the cerclage wire has been tightened, the mandible has been compressed lingually and then inwardly rotated. This again results in a malocclusion, whereby the left mandibular canine tooth is now making contact with the palatal mucosa, causing extensive damage and discomfort (Figure 4).
An alternative technique
These complications can be avoided by using an alternative technique to repair the separation. Indeed, it is my opinion that this technique is altogether a more straightforward one, and a technique that is easy to achieve in general practice. This alternative technique uses a wire and acrylic intra-oral splint to stabilise the rostral mandible.
Initially, the mandibular canine teeth are scaled to remove calculus and polished lightly with a pumice polish. The tooth surfaces are then irrigated and air-dried using an air-water syringe.
The teeth are etched with phosphoric acid and a bonding agent such as Optibond is applied and light-cured.
A bleb of acrylic is then placed 2-3mm above the gingival margin on the buccal aspect of the mandibular canine teeth to act as a retainer (Figure 5A). Just apical to this, a figureeight orthopaedic wire is placed around the mandibular canine teeth, knotted and tightened in light compression, with the knot then folded to sit adjacent to the distal aspect of one of the mandibular canine teeth (Figure 5B). The wire will sit on the cusps of the mandibular incisor teeth.
With the wire in place, further acrylic is then applied to the surface of the mandibular canine teeth, and also covering the wire (Figure 5C). The wire and acrylic, when used together, are stronger than either material used on its own. The acrylic can then be shaped with an acrylic burr to allow full mouth closure and to ensure the splint is comfortable within the mouth. The splint allows a much more controlled fixation, with accurate apposition of the separation, and because of the position of the splint it is unlikely to cause disruption to the occlusion, even if a caudal fracture is present. The splint is rigid enough to stabilise not only the symphysis, but the whole mandible with caudal fractures supported by the masticatory muscles. The splint is left in place for three to six weeks, until the separation has healed, and is then removed by simply sectioning the splint using a cutting tungsten carbide fissure burr in the high-speed dental handpiece.
This technique may be new to some readers, but it is a useful technique to master as it provides a more straightforward and reliable repair to this very common orthopaedic injury.
