13.3 Diagnostics

Definitive assessment of maxillofacial injuries should be performed once the patient has been stabilized from the initial trauma. High‐impact forces such as automobile trauma or a fall from heights commonly result in maxillofacial fracture or luxation of the temporomandibular joint (TMJ) and often have sequelae such as pulmonary contusions, hemorrhage, myocardial damage, and neurologic effects. Primary repair of maxillofacial trauma should be delayed if abnormalities of the respiratory, circulatory, or neurologic systems are present. Serial neurologic examinations should be performed to assess final neurologic status. A gentle, awake examination can be performed as an initial assessment. Obvious abnormalities of the occlusion such as open‐mouth appearance (not associated with respiratory distress), lateral deviation of the mandible, or inability to close the mouth can be indicative of a maxillofacial, mandibular fracture or TMJ luxation or fracture. Changes in the appearance of the normal facial structure can indicate a depressed or displaced maxillofacial fracture, and similarly changes in the position of the globe can indicate an orbital or zygomatic fracture.

Once the patient has been stabilized, more comprehensive diagnostic modalities can be initiated. General anesthesia should be safely administered to allow for full evaluation of the oral cavity and skull without causing excessive pain or resistance from the patient. Digital palpation may reveal crepitus, instability, or physical inability to completely close the mouth. Visualization of bony structures is common since the trauma often causes damage to the thin layer of soft tissues overlaying the bones. Sharp fracture fragments can also penetrate the soft tissues and result in an open fracture. Following gross examination of the skull and oral cavity, dental and survey radiographs can be made and evaluated. Computed tomography (CT) with three‐dimensional reconstruction provides excellent detail of injuries present, especially in complex cases with fractures of multiple bones of the skull and the mandible [4, 5]. Results of the diagnostics will help shape the final treatment plan.

13.4 Surgical Principles

Surgical approaches for treatment of maxillofacial and mandibular injuries will vary by the particular injury and can be intraoral, extraoral, or both. Patients should be anesthetized safely, carefully monitored, and positioned to allow for the best approach to the fracture repair. The naturally contaminated environment of the oral cavity provides an additional challenge not always present in appendicular skeletal fracture repair. The presence of advanced periodontal disease also further complicates treatment and healing by perpetuating a contaminated environment if left untreated. Infection and persistent periodontal disease can lead to osteomyelitis and non‐union of fracture fragments. Extractions, judicious debridement of tissues, and systemic antimicrobial therapy may be indicated under these conditions. The use of antimicrobials is controversial as to time of administration and duration of use. Some advocate only peri‐operative use of intravenous antibiotics based on human and canine studies showing minimal benefit for post‐operative usage [6–8]. Other studies indicate that post‐operative antimicrobial usage is justified in cases of open fractures that communicate with the oral cavity or the paranasal sinuses in humans [8, 9]. The main concern for generalized usage of antimicrobials is resistance. Amoxicillin‐clavulanic acid, clindamycin, doxycycline, and metronidazole are common choices for treatment of the anaerobic types of bacteria often present in periodontitis in humans [8, 10, 11]. Clipping of the hair and preparation of skin for sterile surgery is advised for an extraoral approach. Decontamination of the oral cavity with antiseptic agents can reduce the bacterial load present in the mouth to foster a clean‐contaminated environment [8, 12].

When utilizing normal occlusion as a way to gauge successful fracture reduction, steps must be taken to allow for evaluation of the occlusion at any time throughout the surgery. Removing as many obstructions from the oral cavity will greatly increase exposure and reduce the difficulty of repair. Esophageal monitoring equipment or temperature probes should be replaced by external electrocardiogram monitoring, auscultation by stethoscope, and rectal temperature probes. The endotracheal tube will also reduce access and visibility in the oral cavity. Extubation–reintubation practices are not a great option as the chance of malocclusion occurring is increased and maintaining reduction of fracture fragments is much more difficult. A better alternative would be to place the endotracheal tube via pharyngotomy or through a transmylohyoidal approach [13–16]. The patient is initially intubated through an oral approach and attached to the anesthesia delivery system. Reintubation or repositioning of the endotracheal tube through one of the aforementioned approaches is performed. For the pharyngotomy approach, the caudal mandible and lateral cervical area is clipped and prepped for aseptic surgery. A long‐handled angled forcep is placed into the mouth and directed just caudal to the angle of the mandible. This approach avoids several vital structures in this area such as the hypoglossal nerve, external carotid artery, external jugular vein, the lingual artery, and the linguofacial vein [15, 17]. A skin incision is made over the tip of the angled forcep. The tip of the forcep is protruded through the sphincter colli muscle and through the skin incision. The tissues are stretched by repeated opening of the forceps to allow for passage of a second appropriately sized endotracheal tube [13–15]. The tip of the second endotracheal tube is grasped and advanced through the pharyngotomy and into the oral cavity. The per os endotracheal tube is removed and the pharyngotomy endotracheal tube is placed into the trachea. The tube is secured with a finger trap suture to prevent dislodgement [14]. Once surgery is completed the pharyngotomy tube is removed and the per os endotracheal tube is replaced for recovery of the patient. For the transmylohyoid approach, the patient is placed in dorsal recumbency and the ventral aspect of the mandible is clipped and prepared aseptically for surgery. A skin incision is made medial to the ventral border of the mandible at the level of the mandibular first molar tooth. Blunt dissection of the subcutaneous tissues and the mylohyoideus muscle along the lingual cortex of the mandible is performed to allow for passage of the endotracheal tube that has been previously placed per os. A hemostat is placed into the incision directed toward the oral cavity and an intraoral mucosal incision is made over the tip of the instrument. The tissue is again stretched to allow for passage of the endotracheal tube. The anesthesia circuit is disconnected, the connector of the endotracheal tube is removed, and the hemostat placed into the incision is used to grasp the end of the endotracheal tube passing it through the incision into an extraoral position (Figure 13.1). The tube is secured with a finger trap suture or gauze tie as preferred [16]. The connector is replaced and the anesthesia circuit is reconnected. With this approach it is possible to direct a single endotracheal tube into an oral or extraoral position through the same incision, thus avoiding the extra step of reintubation. After a final check of the occlusion post‐fracture repair, the patient’s per os endotracheal tube is removed and the patient is again intubated through an oral approach for recovery from anesthesia. The incision made for pharyngotomy or the transmylohyoid approach should not be closed and is left to heal by second intention [13–16].

Fracture repair principles apply to treatment of maxillofacial trauma in the same manner as for appendicular fractures. Determining the best method of repair depends on knowledge of not only the anatomy but also of the forces that are applied to the bones during physiologic movement. Appliances or implants used to repair fractures must be placed appropriately to counteract these forces. Excessive strain placed on the implant will lead to failure of the device, and improper stabilization and alignment of a fracture may lead to non‐union. The tension band principle states that all fixation devices are strongest in tension. As long as all stresses are acting parallel to the long axis of the implant it should be able to neutralize the normal physiologic forces after fixation [18, 19]. In the mandible the tension band surface is the alveolar border, and, as such, implants or appliances should be placed in this location whenever possible. The maxilla also has lines of stress and areas of buttressed support that should be considered during repair. Anatomic reduction and compression of fracture fragments along with maintenance of occlusion are the cornerstones of successful maxillofacial fracture repair.

13.5 Treatment Planning

In this section, the different types of fractures that may be encountered will be addressed, with brief discussions of recommended treatments. The specific treatments themselves will be covered later in the chapter. Each location has specific anatomic features that will influence fracture repair type.

13.5.1 Rostral Mandibular Fractures

The rostral mandible is typically defined as the incisor and canine teeth and the bone surrounding these teeth. The mandibular symphysis is the fibrous joining of the right and left mandibles in this rostral location. Unlike in humans where the mandibles eventually fuse at the midline, the symphysis in dogs and cats is a fibrous joint and can have varying degrees of physiologic movement [20]. Therefore mandibular symphyseal fracture is not a true “fracture” but a disruption of this fibrous union between the mandibles. This is one of the most common mandibular injuries in the cat [21, 22]. The degree of trauma in this region will determine the extent of treatment necessary [21]. In type I injuries, there will be a separation with no break in the soft tissues, while type II injuries have soft tissue disruption. A type III lesion will also have comminution of the bone fragments, often together with broken teeth [21]. Stabilization of a straightforward symphyseal separation is relatively simple to achieve with circumferential osseous wiring around the rostral mandibles just distal to the canine teeth. Care must be taken to ensure the incisor teeth remain in alignment, as step defects can be easy to create. Interdental wiring can also be used in these types of injuries and may allow for more precise maintenance of tooth alignment. Parasymphyseal fractures are a common iatrogenic injury during extraction of the mandibular canine tooth. Osseous circumferential wiring may still be successful in this type of fracture or, if the canines and incisors are missing, intraosseous wiring or use of a heavy grade suture can provide appropriate stabilization, especially in smaller patients.

13.5.2 Mandibular Body Fractures

Fractures of the body of the mandible are the most frequent oral fractures seen in the dog [23, 24]. A unilateral fracture may cause the jaw to be deviated toward the side of the injury, the same as with a caudoventral luxation of the TMJ, while rostroventral luxation of the TMJ will deviate away from the injured side [25, 26]. With minimal displacement, particularly with a unilateral defect and intact symphysis, a conservative approach with a gauze or tape muzzle may be sufficient. One way to determine the feasibility of a muzzle would be to see if the mouth closes easily while maintaining proper occlusion [24]. With the mandible, however, there are a few factors that determine what treatment is best, particularly the considerations of the biomechanical effects the muscles of mastication have on the mandible and any fracture segments. The bulk of the muscles, the masseter, temporal and pterygoid, work to swing the mandible dorsally as in closing the mouth, with their insertion on the caudal end of the body of the mandible [24, 27]. This movement can lift the caudal mandible in a rostrodorsal direction [28]. The digastricus muscle works in opposition to these muscles, tending to pull the rostral portion of the mandible caudoventrally, as in opening the mouth.

Fracture biomechanics indicate that the tension side of the mandible is the dorsal or alveolar border of the mandible where the teeth are [18]. Stabilization on this border will provide for a natural compressive force on the ventral surface. This can be provided with methods such as interdental wires and splints. Plate placement at the tension side of the mandible is much more difficult due to presence of the teeth and roots. Use of miniplates or larger plates in buttress fashion on the ventral border of the mandible is possible and can be used in combination with interdental or interfragmentary wire to counteract distractive and bending forces [19].

13.5.2.1 Favorable/Unfavorable Fractures

Biomechanical muscular forces have a particular influence on the type of stabilization needed for fractures in the region. If the fracture line is perpendicular to the long axis of the mandible, some dorsal distraction may occur [29]. With a fracture line that runs caudodorsally, the forces tend to keep the segments compressed together, classifying it as a favorable fracture (Figure 13.2). While some of these can be adequately treated with conservative methods such as a tape muzzle, often a single interosseous wire placed perpendicular to the fracture line will provide sufficient reduction and resistance to displacement forces. This is often true when the fracture is unilateral, there is no symphyseal mobility, and the intact opposite mandible provides both a good basis for reduction as well as stability [24].

When the fracture line runs in a caudoventral direction, however, the larger muscles of mastication exert force upward on the distal segment and the digastricus tends to pull the rostral segment down and caudally, with subsequent displacement and classification as an unfavorable fracture (Figure 13.3). Two intraosseous wires can be placed, one dorsally and one ventrally, or just one ventrally with acrylic splint stabilization to compensate for any dorsal gap should be sufficient [24]. Alternatively, two wires may be placed with a common placement site in the rostral segment and two sites in the distal segment to approximate a perpendicular relationship of the two wires. This triangular method helps to provide additional stabilization against the muscular forces. A good indication for use of miniplates in the mandible would be the presence of an unfavorable fracture. This more rigid type of fixation can adequately counteract the muscular forces pulling the fracture fragments apart [19].

Acrylic splints may be used, alone or in combination with wire placement. The combination of interdental wire and acrylic together is significantly stronger than either material alone [30]. Incorporating wires into acrylic in edentulous areas can be one means of fixation of pathologic fractures due to periodontal disease at the lower first molars. Similarly, a direct acrylic splint can be secured to the mandible with cerclage wires when interdental wiring is not an option [31]. Maxillomandibular fixation (MMF), immobilizing the mouth in partial occlusion, prevents excessive movement while still allowing some ability to drink and eat is another less invasive method of fracture repair [32].

Severely comminuted fractures that have gaps or non‐viable tissues often require more complicated means of fixation. While some appendicular skeletal fixation means do not translate as well to the oral cavity, such as intramedullary pinning, plating and screws, some forms of external fixation have been successfully employed [28, 33]. The combination of using Kirschner wires or Steinmann pins on either side of the fracture site, even bilaterally, with an acrylic‐filled tube to engage the pin ends can provide immediate stabilization. Areas of substantial bone loss, either due to fragmentation or necrosis, can be held in position with this method to allow the defect to eventually fill in, though this can be a long‐term solution (several months if more than 4–6 cm). Alternately, grafts of cancellous bone chips or even ribs can be used to facilitate bone regrowth [24]. If the area is grossly contaminated, delaying implantation until the epithelial surfaces have healed, then placing the material through a sterile, ventral approach may be the optimum method [34]. More recently other treatment options have been attempted such as the use of bone morphogenic proteins to regenerate bone in a large defect. Recombinant human bone morphogenic protein 2 (rhBMP‐2) is infused into a compression‐resistant matrix and placed into a large mandibular defect, followed by placement of a large plate or plates in buttress fashion [35–39].

Fractures of this region that become a non‐union may be manageable as a fibrous union if unilateral with a stable opposite mandible. Bilateral lesions, particularly ones instigated by severe periodontal disease are often nearly impossible to manage, and while long‐term mouth closure methods (muzzle, interarcade fixation, commissuroplasty) may eventually provide a functional “bite,” the management and possible complications are often challenging [28]. Continuing research into methods utilizing rhBMP‐2 has the potential to provide new treatments in cases of non‐union, malunion, repair of large defects from osteomyelitis, or severe trauma in addition to immediate reconstruction after a mandibulectomy procedure.

13.5.3 Fractures of the Mandibular Ramus

Mandibular ramus fractures are less common than ones of the mandibular body or symphysis [23]. In the far caudal region of the mandibular body and even up in the ramus, internal fixation may not be needed if displacement is minimal due to the supportive effect of the surrounding musculature [25, 28]. Unilateral fractures dorsal to the condylar process may respond well to a tape muzzle over a two to three week period, but fractures below that level may take additional time, up to four to five weeks. If unstable, the flatter bones, without associated teeth, make it somewhat amenable to plate fixation, with the caveat that substantial muscle masses can make exposure more challenging. Fixation of the ramus using miniplates would utilize a tension band plate along the coronoid crest and a stabilizing plate along the condyloid crest [19]. Intraosseous wiring is also a potential repair method. External fixation is not likely to be successful given the thin nature of the bone for pin placement [25]. If there is significant malocclusion associated with a suspected ramus fracture, the TMJs should be closely examined for any signs of concurrent fracture or luxation [24]. Future problems may occur with larger callus formation during conservative management if there is any interference with normal oral movements. Zygomaticomandibular ankylosis occurs when there is fusion of the coronoid process to the zygomatic arch, which can also restrict movement of the TMJ [26]. If restricted TMJ movement and morbidity exists after treatment for a caudal mandibular fracture then excision arthroplasty can be considered to alleviate discomfort. Mandibular condylectomy can be performed to prevent contact of the mandible with the temporal bone. Fibrous tissue formation will occur to create a false joint [25].

13.5.4 Fractures of the Temporomandibular Joint

As with other portions of the vertical ramus, fractures in this region are uncommon and usually the result of trauma [22, 23, 26, 40] (Figure 13.4). The most common clinical finding with TMJ fracture or luxation is a malocclusion, which may present as the inability to open or close the mouth, or lateral shifting of the mandible [26]. Complete oral examination is performed under anesthesia and should also include diagnostic imaging for comprehensive evaluation of the TMJ and concurrent maxillofacial injuries. If any structures of the TMJ are affected, complete evaluation with radiographs and/or CT is indicated for diagnosis and treatment planning [41]. In a recent study utilizing a CT scan for evaluation of TMJ disorders, TMJ fractures were the most common TMJ disorder identified in cats and the second most common TMJ disorder identified in dogs. Cats in this study were all noted to have fractured the condylar process of the mandible. Dogs were found to have fractures of either the condylar process or the temporal bone. It was suggested that differences in skull anatomy between dogs and cats resulted in the variance of fracture types [41].

Subluxation of the TMJ may not result in significant clinical signs and usually is managed conservatively by feeding a soft diet and pain medications [26]. Joint luxations most commonly occur in a rostrodorsal direction. Caudoventral luxations occur less frequently and are usually accompanied by fracture of the retroarticular process. Unilateral rostrodorsal luxations usually result in shifting of the mandible toward the contralateral side. Unilateral caudoventral luxations tend to shift the mandible toward the ipsilateral (affected) side [26]. Fractures of the TMJ may result in crepitus when the mandible is manipulated, but usually the mandible can be easily placed into occlusion, whereas the mandible may be resistant to reduction in the case of a luxation injury. Fractures of the caudal mandible and condyle may cause displacement of the mandible caudally, resulting in a shifting of the mandible toward the affected side. Luxation injuries can be seen radiographically with ventrodorsal, dorsoventral, or laterodorsal oblique projections. Radiographs may also reveal fractures of the retroarticular process, condylar neck, or condyle [42, 43]. Computed tomography is particularly useful for visualization of fractures with multiple fragments or condylar fractures that may not be appreciated on radiographs, given its ability to isolate the regional anatomy without superimposition of other structures and to provide three‐dimensional reconstruction [41, 44].

13.5.5 Fractures of the Maxilla

Discussion of maxillary trauma for the purpose of this section will include fractures of the incisive, palatine, zygomatic, lacrimal, frontal, nasal bones, and the maxillary bone proper [45, 46]. Maxillary fractures are less common than mandibular lesions and may be more difficult to detect and evaluate fully with skull and dental radiographs due to overlapping structures. Epistaxis, swelling, discomfort, and malocclusion may be indications of damage, but displacement at times can be minimal. If such is the case, and the occlusion is still correct, little may need to be done. Occasionally the simple act of suturing any soft tissue defects after digital realignment will provide sufficient stabilization [24, 34], though some cases benefit from other methods such as tape muzzles or acrylic splints, with or without interdental wiring. For more complex fractures and obvious facial deformity, computed tomography is indicated to fully evaluate the injuries present. Three‐dimensional reconstruction provides added information [46]. Miniplates have been utilized for comminuted and depressed fractures of the maxillofacial bones. Depression fractures of the bones that make up the borders of the nasal cavity can cause significant impairment of airflow and can result in long‐term morbidity with chronic nasal obstruction [47]. Most of the maxillary bones are relatively thin and surround larger areas of space such as the nasal cavity and paranasal sinuses [48]. The bones of the maxilla can be thought of as a frame surrounding these voids. This strong and lightweight frame connects the base of the skull to the occlusal surfaces [46, 49]. The human skull was found to have buttresses of projecting support and similar buttresses are noted in the dog and cat skulls [49, 50]. Damage to these buttressed areas of support will cause the frame to collapse. Understanding the anatomy and support of the maxillofacial frame will facilitate proper management of fractures to this area. Three primary buttresses exist: medial, lateral, and caudal. Generally, repair of two of the three main buttresses will restore the position of the maxilla in relation to the skull and mandible [46, 50, 51].

13.6 Treatment Modalities

Repair techniques of maxillofacial injuries can be generally described as non/less‐invasive or invasive. Non‐invasive techniques may include tape muzzle, MMF/immobilization, interdental wiring, acrylic splinting, or combination of interdental wiring and acrylic splinting. External fixation is another minimally invasive technique for fracture stabilization. In general non‐invasive techniques allow for preservation of vital structures such as the teeth and neurovascular anatomy. Minimal disruption of the periosteum is also beneficial for encouraging bony healing [52]. The location of the injury often dictates which type of repair is likely to be most successful. Some areas such as the ramus of the mandible and certain areas of the maxilla can be repaired with an invasive technique such as plating with fewer concerns of interfering with structures such as teeth or neurovascular anatomy. The mandible provides a challenge for use of traditional plating techniques due to the volume occupied by tooth roots and the structures within the mandibular canal.

13.6.2 Maxillomandibular Fixation

There are other means of limiting oral movements while maintaining occlusion, such as MMF [21, 29, 33]. Many methods of immobilizing the movement of the mandible exist and the goal of treatment is similar to a tape muzzle – immobilize the movement of the jaws to allow healing of the fracture. However, the success rate with MMF would be expected to be higher because complete immobilization can be achieved. Invasive methods of immobilizing the mandible can include placing circumferential wires around both the maxilla and mandible or with transosseous placement of wires or screws with stabilization between the two arcades [29, 55]. Less invasive methods are also quite successful and with less potential side effects. The patient should be properly anesthetized and positioned for oral surgery. Placement of an endotracheal tube via pharyngotomy or a transmylohyoid approach is performed to facilitate application of the chosen technique and allow for simple extubation on recovery. With the mouth held in proper occlusion and a slight space between the incisors, the canines can be joined together with a composite bridge (Figure 13.5). Various techniques and materials for joining the canines have been reported. The canine teeth are scaled, polished with flour pumice, and acid etched in preparation for placement of an acrylic dental composite material. The canine teeth are placed in occlusion and a normal caudal dentition relationship should be confirmed. The maxillary and mandibular canines should overlap about one‐third of the crown height, enough to allow for the patient to drink water and lap up gruel‐consistency food. Self‐curing acrylic or composite is applied on the canine teeth to create two pillars of material. Syringe cases can also be placed on the canines to act as a mold for the composite and are left in place until the appliance is removed [54, 56]. A feeding tube should be placed to ensure nutritional needs can be met if the patient will not aliment voluntarily while the appliance is in place. The same factors of concern with respiratory distress or vomiting apply as with the tape muzzle.

13.6.3 Wiring Techniques

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