Anatomy
The mandible consists of the mandibular body, and the mandibular ramus. The fibrocartilaginous symphysis joins the right and left halves of the mandible. The mandibular body hosts the roots of the teeth of the lower arcade, and the mandibular canal, containing the mandibular alveolar artery and the inferior mandibular nerve. The mandibular ramus has three bony prominences, the angular process, the condylar process of the temporomandibular joint, and the large coronoid process dorsally. The masseteric fossa of the mandibular ramus is the insertion site of the thick masseter muscle. It is very thin, and implants for repair of fractures of the mandibular ramus must be placed near the thicker coronoid crest rostrally, and along the caudoventral border in order to achieve sufficient bone purchase.
Incidence of Fractures
Fractures of the feline skull account for about 14.5% of all fractures seen in cats.1,2 Symphyseal fractures are the commonest (74%), followed by body (16%), condyle (7%) and coronoid (4%). They are particularly challenging to deal with because of the small size and thin, dense bone. The main aim when repairing mandibular fractures is to restore normal dental occlusion.
Preoperative Assessment & Preparation for Surgery
Perform a full physical examination and assess the cranial nerves. Regularly repeat neurological examination to look for any deterioration. Thoracic radiography is essential. Careful assessment of the jaw, ability to open and close the mouth and any lateral deviation should be noted. Once the cat is deemed stable enough for anaesthesia take a series of skull radiographs. Take normal lateral, 20° lateral obliques, ventrodorsal and intraoral films.3 It can be difficult to visualise all the fractures on the radiographs, a CT scan will give more information but a careful oral assessment for open fractures, symphyseal separation, a split palate and other injuries is beneficial.
Planning
Consider all management options/how to deliver anaesthesia/surgical technique/route for nutrition.
Endotracheal Tube Placement Via a Pharyngostomy
To be able to assess dental occlusion intraoperatively placement of the endotracheal tube through a pharyngostomy or tracheostomy incision is highly recommended.4 Intermittently removing & replacing the endotracheal tube is not satisfactory. Briefly the procedure for pharyngostomy tube placement is described.4 Cat has endotracheal tube placed normally via the oral route. An area of skin is clipped and aseptically prepared on the left laryngeal area (for right handed people). If the fracture is caudal or there is significant intraoral bruising and oedema select the most appropriate side. The surgeon should scrub his/her hands and don sterile gloves. The endotracheal tube should be uncuffed and able to be disconnected from the connector. The surgeon places the first finger in the piriform fossa just rostral to the hyoid apparatus; this area should present minimal soft tissue to dissect through. Avoid iatrogenic damage to veins, or salivary glands. With a No. 11 or 15 scalpel blade a small stab incision is made 'onto' the surgeons' finger, down to the oral mucosa. Then a pair of small mosquito artery forceps is used to tunnel through the last layer of tissue. The endotracheal tube is disconnected from the connector bent 180° grasped by the artery forceps (it is still in position in the trachea) and pulled back through the pharyngostomy incision. The connector is reconnected, gas reconnected, and the connector sutured to the skin. At the end of surgery the ET tube can be taken back into the more normal oral position and removed routinely.
Feeding
Consider whether cat will be able to eat normally per os postoperatively. If not then need an alternate route for nutrition - nasoesophageal, oesophagostomy or gastrostomy. Need to place oesophagostomy tube and per endoscopic gastrostomy prior to surgical repair if repair involves having to close the cats' mouth.
Facial Fracture Repair Goals
Realignment to normal occlusion
Minimal invasiveness
Minimal morbidity
Early return to self-feeding
Pain control
Treatment Options
A variety of stabilisation techniques have been utilised in the cat4 including interdental wiring, interarcade wiring, interfragmentary wires, plate and screw fixation, external skeletal fixation (ESF), dental acrylic and transarticular ESF.
Conservative - Normal occlusion, closed fractures, stable & pain free
Surgical - Deviation or malocclusion, open fractures & instability
Tape muzzle - very rarely works - may be useful after closed reduction of TMJ luxation.
Mandibular Symphyseal Separations
These are the commonest skull injuries seen in cats. These can be easily stabilised by use of a cerclage wire of heavy gauge orthopaedic wire (20 or 22 ga, 1.0 or 0.8 mm). The wire should be placed in a manner that minimally disrupts the soft tissue. A large gauge hypodermic needle (14 or 16 ga) is prebent to a 5/8ths semi-circle. This is then taken between chin skin and bone and the orthopaedic wire threaded back through. With the separation held in reduction the wire is then twisted tight with the twist left on the ventral chin or between lip and gum. Generally the wire can be removed after four weeks. It is important to accurately reduce the symphyseal separation, especially in the presence of other fractures; a malunion can prevent normal occlusion.4
Mandibular Body Fractures
Plate
The mandible is not an easy bone to use plating techniques for stabilisation of fractures. The bone is thin which is not ideal for secure screw placement. Tooth roots and the mandibular artery, vein and nerve all should be avoided when placing screws. The plate should therefore be placed on the ventral surface to avoid these structures although the tension side is the oral side. Plating should only be considered for simple fractures that can be very accurately reduced. Any malalignment may lead to dental malocclusion which will be difficult to correct. Locking plates may be more useful than non-locking implants as if plate contouring is not perfect they should not distort the fracture fragments (Unilock 2.0 mm).4
Dental Composite4
Ideally need 4 intact canine teeth to apply dental composite to - pumiced, acid etched, mouth left open approximately 1 cm, canines overlapped by 2 mm. Remove composite 6 week post op with cat under GA. Advantages of the technique are that it is fairly atraumatic, easy & rapid to apply, and fairly inexpensive. Main complications are need special equipment, composite breaks in about 50% cases and cats may experience excessive salivation.
Interarcade/Interarcuate Wiring4
Wire placed between tooth roots (PM2 and PM2), or through holes in the bone, in mandible and maxilla. Cats try to open mouth and also excessively salivate. Potentially useful if broken or absent canine teeth and for very caudal fractures.
ESF
Mandibular ESF is probably one of the most useful options, except for very caudal fractures, it is versatile, easy to check occlusion, not reliant on having intact teeth and allows oral food intake. Place small (1.6 mm) threaded pins through each mandible on ventral aspect - avoid pins crossing mandible unless sure occlusion is correct. Use tubing and acrylic to connect transosseous pins.
Transarticular External Skeletal Fixation (TESF)4
One or more pins placed in both the mandible and maxilla and then connected together by use of pins and clamps, elastic bands or wire. Technique allows cat to eat orally if mouth left slightly open - useful for caudal fractures.
MAMA BEARD
(Mandibular And MAxillary BiEncircling And Reduction Device!) - Simple technique particularly for caudal fractures and for very young kittens with lots of developing teeth. Technique involves placing an encircling piece of 50b monofilament nylon between skin and bone around the jaw with occlusion maintained - need to keep jaw tightly close to maintain correct occlusion.5 Need intact canine teeth and an amenable cat. Cat needs to have minimal pharyngeal swelling and careful observation after surgery in case of respiratory distress. Scissors or blade kept handy to cut suture if required.
Partial Mandibulectomy
The indications for this are rare but include heavily contaminated fractures and fractures where nutritional secondary hyperparathyroidism is present - e.g., when iatrogenic fractures occur in the elderly cat after a dental involving tooth removal.
Complications & Outcome
In Umphlets study (1) complications occurred in 25% of cases with malocclusion and soft tissue infection being the commonest problems. Fractures took around 6–10 weeks to heal.
Maxillary Fractures
Maxillary fractures are less common than mandibular fractures, or when they occur they tend to be fatal, due to concurrent brain damage or more rostral involving the nose and occurring concurrent with mandibular fractures. Treatment of maxillary fractures is unnecessary unless there is displacement, which can interfere with restoring normal occlusion even if displacement is only minor. Fractures through the cancellous bone are often compression fractures and the thin bone is poor at fragment holding. A useful option for such maxillary fractures to restore dental occlusion is to realign the mandible to match the maxillary malalignment. This can be done by malaligning a concurrent mandibular symphyseal separation or by performing an osteotomy of the mandibular symphysis to realign the mandible with the maxillary malalignment.6
Temporomandibular Joint
The feline temporomandibular joint is a very stable hinge joint due to close congruity between the mandibular fossa of the temporal bone, and the condylar process of the mandible.7 Cats have a large retroarticular process caudally, and also a large bony process rostral to the temporomandibular joint, contributing to joint stability.7 The temporomandibular joint contains a fibrocartilaginous meniscus. Fractures close to or involving the temporomandibular joint (TMJ) can be very challenging to stabilise.7 One option is to place a transarticular ESF or a MAMA BEARD for approximately two weeks. With the latter option an alternative route for nutrition must be provided such as a nasoesophageal, pharyngostomy or gastrostomy tube. Another option, which relies on having intact canine teeth, is to use dental acrylic.8 Occasionally after fractures or trauma in this area the TMJ will fuse due to excessive bone production.9 Excision of the joint can successfully improve the range of motion in the jaw.
Dislocation of the TMJ
The TMJ will usually dislocate in a craniodorsal direction. Reduction should be attempted by placing a small lever (pen or toothbrush) across the mouth caudally and then closing the mouth with the lever in place - this action should displace the mandible ventrally and caudally. Once reduced the jaw should not re-dislocate, but if this occurs then temporary transarticular stabilisation may be necessary.
Ankylosis of the Temporomandibular Joint
Ankylosis of the temporomandibular joint is a rare chronic condition, causing significant patient morbidity due to difficulty or inability to feed and lack of grooming behaviour. True ankylosis involves the temporomandibular joint itself, whereas false ankylosis is caused by periarticular structures. True ankylosis is more common in cats and is usually a sequel of trauma, such as temporomandibular joint luxations and fractures, or fractures of the zygomatic arch.
Clinical signs include progressive difficulty with eating, limited mobility of the lower jaw, and inability to open the mouth. Ankylosis can occur uni- or bilaterally.
Conservative treatment is usually unsuccessful, and is therefore only tried in less severe or early cases. It involves stretching of the jaws under general anesthesia. Recurrence is prevented by manually forcing the jaws open several times a day, and by administration of corticosteroids. However, most cats have to undergo excisional arthroplasty of the temporomandibular joint to treat true ankylosis, or excision of parts of the zygomatic arch for false ankylosis.
References
1. Umphlet RC, Johnson AL. Mandibular fractures in the cat. A retrospective study. Vet Surg. 1988;17(6):333–337.
2. Hill FWG. A survey of bone fractures in the cat. J Small Anim Pract. 1977;18:457–463.
3. Ticer JW, Spencer CP. Injury of the feline temporomandibular joint: radiographic signs. J Am Vet Radiol Soc. 1978;19:146–156.
4. Voss K, Langley-Hobbs SJ, et al. Mandible and maxilla. In: Montavon PM, Voss K, Langley-Hobbs SJ, eds. Feline Orthopedic Surgery and Musculoskeletal Disease. Elsevier Saunders; 2009.
5. Nicholson I, Radke H, Langley-Hobbs SJ. Treatment of caudal mandibular fracture and temporomandibular joint fracture-luxation using a bi-gnathic encircling and retaining device. Vet Comp Orthop Traumatol. 2010;23(2):102–108.
6. Buchet M, Boudrieau RJ. Correction of malocclusion secondary to maxillary impaction fractures using a mandibular symphyseal realignment in eight cats. J Am Anim Hosp Assoc. 1999;35(1):68–76.
7. Caporn TM. Traumatic temporomandibular joint luxation in a cat and treatment by condylar tethering. Vet Comp Orthop Traumatol. 1995;8:61–65.
8. Bennett JW, Kapatkin AS Maretta SM. Dental composite fixation of mandibular fractures and luxations in 11 cats and 6 dogs. Vet Surg. 1996;23(3):190–194
9. Sullivan M. Temporomandibular ankylosis in the cat. J Small Anim Pract. 1989;30:401–405.