Canine-managing Mandibular Fractures In Dogs

Vol.18, No. 5

May 1996

Continuing Education Article

FOCAL POINT ★ Each of the approaches to the management of canine mandibular fractures has advantages and disadvantages; the technique to be used will vary from case to case.

KEY FACTS ■ Vehicular trauma—usually, being hit by a car—is the most common cause of canine mandibular fractures. ■ Mandibular fractures constitute a small percentage of all fractures in dogs (1.5% to 2.5%). ■ The endotracheal tube is ideally placed through a pharyngostomy opening in order to enable optimum assessment of dental occlusion. ■ Dental bonding, which is a relatively new technique, has been successfully used to manage various fractures in several regions of the mandible.

Managing Mandibular Fractures in Dogs Rapperswil, Switzerland

Ulrich A. Goeggerle, DrMedVet

Noah’s Ark Pet Hospital Rensselaer, Indiana

Greg A. Inskeep, DVM

Purdue University

James P. Toombs, DVM, MS

I

n dogs, the incidence of mandibular fractures is 1.5% to 2.5% of all fractures.1 The most common causes of these fractures in dogs are vehicular trauma, fights, unknown trauma, iatrogenic trauma, and gunshots. The most frequently affected areas are the premolar, molar, and symphyseal regions and the vertical ramus. The canines, the incisors, and the condylar and coronoid regions are less commonly affected (Figure 1). Nearly 50% of dogs that sustain mandibular fractures are younger than 1 year of age1 (see the box). This article reviews the common types of mandibular fractures in dogs and discusses several management techniques.

ANATOMY AND BIOMECHANICAL PRINCIPLES Appropriate management of fractures of the mandible depends on a knowledge of the exact anatomy and the biomechanical principles of this dynamic structure (Figure 2). The mandibular canal is a very important structure that contains the alveolar artery, vein, and nerve. It marks the border between the upper two thirds and the lower third of the mandibular body. Proper decision-making in fracture repair depends on an appreciation of the tension side of the bone and the various forces that act on it. The tension side of the mandible is on the alveolar margin (Figure 3). MANAGEMENT Anesthesia in Fracture Repair Because dental occlusion is used as a guide in fixation of most mandibular fractures, normal placement of an endotracheal tube interferes with proper surgical technique. Placement of the tube through a pharyngostomy opening is recommended in all cases in which dental occlusion is used to assess functional positive or negative anatomic reduction of mandibular fractures.2 A recommended technique for translocation of the endotracheal tube3 is illustrated in Figure 4. Repair Techniques Tape Muzzle A tape muzzle is indicated for fractures with healthy soft tissue and high

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first, passed caudal to the ears, brought back to the opposite side, and again attached to the first piece. A third piece is placed to exactly cover the second piece, this time sticky side down. The same is done with the last piece of tape, which covers the first piece3 (Figure 5). The tape muzzle technique is inexpensive, easy to perform, and noninvasive. It is usually well tolerated by dogs and provides maximum Figure 1—Distribution of mandibular fractures in dogs. (From Evans preservation of the existing blood supply in the HE, Umphlet RC: Miller’s Anatomy of the Dog, ed 3. Ithaca, NY, Cor- fractured region. Development of contact dernell University Press, 1993. Reprinted with permission.) matitis is a common complication3; this can be minimized by keeping the region under the Data Concerning muzzle clean and well ventilated. Aspiration Mandibular pneumonia is rare but Fractures1 can occur if the patient vomits.5,6

Loop Cerclage with Stainless Steel Symphyseal fractures are the main indication for loop cerclage, especially if incisors are loose or Figure 2—Anatomy of the canine mandible. (From Evans HE, Umphlet incomplete and interRC: Miller’s Anatomy of the Dog, ed 3. Ithaca, NY, Cornell University dental wiring cannot Press, 1993. Reprinted with permission.) be performed. When one or two lower canine teeth are missing, loop cerclage is contraindicathealing potential (e.g., in young animals)3 that involve ed.7–9 In some cases, sedation minimal or no displacement, such as midbody unilater3,4 combined with local anestheal fractures. Further indications are vertical ramus sia is sufficient for the procefractures4 and comminuted fractures, if they are unilatdure. In areas that are more eral and good occlusion can be achieved.4 Use of a tape difficult to approach and in muzzle is a helpful adjunctive treatment with other nervous dogs, a short-duration techniques (e.g., internal reduction or dental bonding). injectable anesthetic or gas Tape muzzles are not effective in brachycephalic anesthesia is recommended. breeds.3 They are also contraindicated in fractures of The technique is illustrated in the rostral mandibular region.3 Figure 6. Modified versions General anesthesia is seldom required for tape muzzle have been described.8 application. In most cases, sedation is sufficient. A 0.5Loop cerclage is an inexto 2-inch wide nonelastic tape is used. The first piece of pensive and easy procedure; tape is placed (sticky side up) around the caudal part of in many cases, it can be perthe muzzle. A gap of 0.5 to 1.5 centimeters is left beformed via sedation. If the certween the upper and lower incisors to allow vomiting clage is tightened too much, and sufficient movement of the tongue for alimentabone necrosis can occur. tion. This gap can be maintained by inserting a pencil or pen between the upper and lower incisor teeth while Interdental Wiring the initial portion of the muzzle is applied. A second Indications for interdental piece of tape (again, sticky side up) is attached to the VERTICAL RAMUS FRACTURES ■ TAPE MUZZLE TECHNIQUE

■ Frequency: 1.5%–2.5% of all fractures in dogs

■ Age of affected dogs: Approximately 43% younger than 1 year old ■ Causes: —Vehicular trauma (52.3%) —Fights (19.1%) —Unknown trauma (12.4%) —Iatrogenic trauma (11.4%) —Gunshots (4.8%) ■ Affected regions: —Premolars (31%) —Molars (18%) —Symphysis (15%) —Vertical ramus (12%) —Canines (9%) —Incisors —Condyle (5%) —Coronoid process

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3— External forces (medium arrows) and internal forces (large arrows) that act on the mandible. The result is a continuum of tensile and compressive stresses from one side of the bone to the other (small arrows). In an intact mandible (A) and in a fractured mandible (B), the only area of compressive stresses is the point of fragment contact (C). P = pterygoid muscle, T = temporalis muscle, M = masseter muscle, D = digastric muscle. (From Rudy RL, Boudrieau RJ: Maxillofacial and mandibular fractures. Semin Vet Med Surg Small Anim 7(1):20, 1992. Reprinted with permission.) Figure

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tary wiring include simple transverse fractures,3 short oblique fractures,3 comminuted fractures,2 and bilateral rostral body fractures.9 Significant comminution and bone loss3 are contraindications. General anesthesia is necessary. The mandibular body is approached from a ventral direction.2 If fractures are in the condylar region, the approach is lateral. The fractured area is exposed, and the direction of displacement of the fracture parts is determined. A Kirschner wire is used to make a hole in the two fracture fragments to enable placement of a hemicerclage wire. The mandibular canal and the tooth roots should be avoided. One or preferably two 18- to 20-gauge wires are placed perpendicular to the fracture line. One wire should be placed as close as possible to the tension side of the mandible. After reduction of the fracture, the ends of the wires are twisted, cut, and bent down (Figure 8). Advantages of this technique are that the implants are small and few in number and that no special equipment is required for their application. The major disadvantage is that slight inaccuracy leads to displacement and instability.9

Interarcade Wiring wiring are symphyseal fractures (if the incisors are inInterarcade wiring can be used for simple, nondistact and firm7) and simple transverse mandibular body placed fractures of the mandibular body and ramus10 fractures.3 Oblique and complicated fractures of the and even for severely comminuted fractures that body of the mandible are contraindications. The techinvolve the vertical ramus. Other indications include nique should be avoided if teeth next to the fracture those described for the tape muzzle technique. Signifiline are loose or broken. Short-duration injectable anescantly displaced fractures and fractures with bone loss thetics (e.g., propofol) or gas anesthesia are appropriate are contraindications for interarcade wiring. for this procedure. The wire is General anesthesia is necessary tightened on the buccal side just to perform the technique. The enough to maintain reduction3 last upper premolar (P4) and the (Figure 7). If the wire is tightfirst lower molar (M1) are idenened too much, distraction of tified bilaterally. The gingiva the ventral part of the fracture around these teeth is elevated can result. If this occurs, addi- A subperiosteally on the lingual tional interfragmentary wiring and buccal surfaces and retracted will be necessary.9 so that the adjacent bone beThe major advantage of this comes visible. Holes are drilled technique is that there are no in the maxilla and mandible, in a implants in the fractured region. buccal-to-lingual direction, beD In addition, the technique is in- Figure 4— Placement of an endotracheal tube tween the roots immediately adexpensive and easy to perform. through a pharyngostomy opening. (A) Palpation jacent to the body of the tooth. Indications for this technique are of the piriform fossa through the mouth. (B) Skin The holes are drilled perpendiclimited. It should only be used if incision over the piriform fossa. (C) Guiding ular to the tooth axis. Placement the teeth next to the fracture line the endotracheal tube from the pharynx through of the wire is depicted in Figure are firm and intact and if the re- the incision. (D) The endotracheal tube placed 9. The ends of the wire are through the pharyngostomy opening. (From Slat- twisted next to the hole in the gion is easily accessible. ter DJ: Textbook of Small Animal Surgery, ed 2. mandible. Normal occlusion is Philadelphia, WB Saunders Co, 1993, p 1921. obtained by holding the jaws Interfragmentary Wiring Reprinted with permission.) Indications for interfragmenmanually together, and the final TRANSVERSE MANDIBULAR BODY FRACTURES ■ SEVERELY COMMINUTED FRACTURES

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is probably the only advantage of this technique. Major disadvantages are that damage of tooth roots, vasculature, and nerves in the mandibular canal is likely9 (Figure 10) and that exact positioning of the pin is difficult.11 It is also difficult to determine the best size of pin. Such complications as malocclusion and nonunion 3 are common.

Plate Fixation Plate fixation is indicated in managFigure 5—Tape muzzle applied to a dog with a mandibular ing complex and bilatfracture. eral fractures of the mandibular body 7 tightening of the wire is done. The twisted end is shortand fractures of the ened and placed in the space between the two rows of ramus. Contraindicaupper and lower teeth10 (Figure 9). If the wire is placed tions are infected Figure 7—Interdental wiring. (A) correctly, direct pressure is applied only to the teeth; fractures and fractures Correct application of wire. (B) 10 bone necrosis thus is minimal. with bone loss. Gen- Distraction of the ventral part of the fracture line caused by excesThe procedure is inexpensive, easy to maintain, and eral anesthesia is resive wire tension. (From Slatter 10 well tolerated. Aspiration of ingesta is rare but may quired. For fractures DJ: Textbook of Small Animal occur if the animal vomits. This is the major potential of the mandibular Surgery, ed 2. Philadelphia, WB disadvantage of the technique. Stretching and breaking body, a ventral ap- Saunders Co, 1993, p 1915. Reof the wire 10 and subproach is performed.2 printed with permission.) For fractures in the sequent loss of fracture region of the ramus, a reduction is another polateral approach is preferred. Ideally, the plate is placed tential complication. next to the alveolar border of the mandibular body, which Intramedullary is the tension side of this bone; however, plates are often Pinning placed near the ventral border of the mandibular body to Unilateral and bilateral avoid tooth roots and the mandibular canal. After reductransverse or oblique tion of the fracture, the plate is contoured to the bone (the fractures of the mandibumost important step in this procedure). Placement of the lar body (especially in the plate follows the general principles of plate fixation in otharea from PM2 to M111) er bones3,5 (Figure 11). can be managed via inAn advantage of plate fixation is that the technique tramedullary pinning. provides good rigidity,7 allowing unrestricted use of the mandible immediately after surgery.7 Disadvantages are Contraindications are that the procedure is expensive and difficult to percomminuted fractures form. Direct contact of the implant with the fracture and fractures with bone Figure 6— Loop cerclage with loss as well as fractures stainless steel. After placement of disturbs circulation to the healing bone. Because of the rostral to the second pre- two hypodermic needles (1 and anatomy of the mandible, it is hard to place a bone molar and caudal to the 2), a stainless-steel wire is inserted plate at the location that is biomechanically ideal. first molar. General anes- using the needles as a guide. The thesia is necessary to per- wire is twisted outside the skin. External Skeletal Fixation Indications for external skeletal fixation include form the procedure. The (From Brinker WO, Piermattei technique has been de- DL, Flo GS: Handbook of Small mandibular fractures that are complex,3 highly comscribed in the literature.11 Animal Orthopedics and Fracture minuted,3 or open3 and those that involve bone loss.12 The fact that intra- Treatment. Philadelphia, WB Generalized bone disease is a contraindication for this medullary pinning is Saunders Co, 1990. Reprinted technique.13,14 Dogs with mandibular fractures have with permission.) been successfully treated via several external fixation relatively inexpensive FRACTURES WITH BONE LOSS ■ PRINCIPLES OF PLATE FIXATION

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should be removed before the technique is applied.15 Postoperative care includes daily cleaning of screw–skin junctions and feeding of a soft diet until healing is complete. To remove the splint, the central portion of the bar is cut and the stability of the fracture site is assessed. If instability is evident, the bar is repaired with an acrylic patch. Sedation is usually sufficient to remove the splint.15 For the acrylic and pin (or Kirschner-wire) fixation technique, the same principle is used as in the biphase splint technique. The former technique is less expensive and can be used in smaller dogs. Stiff, threaded pins or Kirschner wires are used instead of the cobalt-chromium screws. The Kirschner–Ehmer splint is not described here because its indications are limited and it has no major advantages when compared with the biphase external fixation splint or the acrylic and pin splint. Figure 9—Interarcade wiring. The ends of the wire Advantages of external fixation are passed, in a buccal-to-lingual direction, through for treatment of mandibular fracpredrilled holes. One end (a) is passed, in a lingualimto-buccal direction, through the hole in the man- tures include exclusion of 12 and plants in the healing area dible. The other end (b) is bent over the posterior notch of the crown of the first lower molar. (From avoidance of surgical dissection at 12,16 Good anLantz GC: Interarcade wiring as a method of fixa- the fracture site. tion for selected mandibular injuries. JAAHA chorage in the bone is provided 17:599, 1981. Reprinted with permission.) by screws or threaded pins. 12,16 The biphase mandibular splint and the acrylic and pin splint are lightweight 16 and formable. 14 Possible loosening of the screws14 and the high cost (because of the special equipment required14) are disadvantages of the biphase splint. The convincing advantages of acrylic and pin fixation make this technique our first choice. Figure 8—Interfragmentary wiring.

(A through C) Use of interfragmentary wires in fractures of various regions. (D) Supplementation of interfragmentary wire with pin. (E and F) Combination of interfragmentary wires and interdental wires in a simple rostral bilateral fracture. (From Brinker WO, Piermattei DL, Flo GS: Handbook of Small Animal Orthopedics and Fracture Treatment. Philadelphia, WB Saunders Co, 1990. Reprinted with permission.)

systems, including the biphase mandibular splint (designed for humans), the Kirschner–Ehmer splint (with small or mediumsized clamps), and the acrylic and pin splint. Patient size, and thus mandible size, dictates which system can be used in a given case. The biphase mandibular splint is contraindicated in dogs that weigh less than 10 kilograms; the mandibular fixation screws are too large to enable safe placement in dogs that have small mandibles. The Kirschner–Ehmer splint can be used in small patients; the acrylic and pin splint is less bulky and is probably the external fixation technique that is best suited to treating mandibular fractures in very small patients. General anesthesia is necessary for fixator application regardless of the technique used. The biphase mandibular splint uses special cobaltchromium transfixation screws and dental acrylic to form the primary splint. Swivel clamps, screw-holding blocks, and metal rods are used as a temporary mechanical splint to maintain reduction of the fracture until the acrylic splint hardens (Figure 12). Teeth with exposed roots in the fracture gap may interfere with bony union and

Figure 10—Intramedullary pinning of a mandibu-

lar fracture. An intramedullary pin that is large enough for stable fixation often damages tooth roots or the neurovascular structures in the mandibular canal. (From Chambers JN: Principles of management of mandibular fractures in the dog and cat. J Vet Orthop 2(2):26, 1981. Reprinted with permission.)

Partial Mandibulectomy Partial mandibulectomy is indicated (1) if chronic mandibular osteomyelitis is present and (2) in all cases in which primary fixation is impossible. 17 General anesthesia is required. The technique is detailed in the liter-

BIPHASE MANDIBULAR SPLINT ■ TRANSFIXATION SCREWS

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ature. 17 If a combined ventral and oral approach is performed, enough gingival and buccal tissue must be preserved to guarantee closure without tension. Skin closure is accomplished via nonabsorbable suture material in a simple interrupted pattern. For intraoral soft tissue closure, polyglactin 910 or polydioxanone is recommended.17 Excision of the infected area allows primary healing of the chronically inflamed region; this healing is the main goal of the procedure. Wound dehiscence is the most common complication. 17

Figure 11—Bone plate fixation of a mandibular

fracture. The plate is placed in the lower half of the mandible to avoid tooth roots and the mandibular canal. To avoid damaging the roots, screws must be placed at an angle. (From Chambers JN: Principles of management of mandibular fractures in the dog and cat. J Vet Orthop 2(2):26, 1981. Reprinted with permission.)

Figure 12A Figure 12B Figure 12—Biphase external fixation splinting of a mandibular fracture. (A) Ventrodor-

sal radiograph demonstrating placement of cobalt-chromium screws. (B) The patient after placement of the splint.

General anesthesia is required. A tape muzzle can be applied as an additional support for the dental bonding, especially in large dogs. After complete healing of the fracture, the dental composite is removed with dental burrs. General anesthesia is usually necessary. Physiologic inability to open the jaw is caused by muscle contracture and the development of fibrous tissue near the fracture site. To break down part of this fibrous tissue, the mouth is opened with gentle force during anesthesia. Muscle contracture should resolve as soon as the patient is eating normally again.6 Major advantages of this technique are that it does not damage the blood supply or the teeth, it can be used in brachycephalic breeds, and it allows maintenance of peroral alimentation.6 Because injuries in which more then two canine teeth are missing are rare, the disadvantage of requiring two intact canine teeth is minimal. The possibility of overheating (related to disturbed thermoregulation) in a warm environment can be minimized by thorough instruction of the owners concerning patient care.6 Another possible complication, aspiration pneumonia if the

Partial mandibulectomy is a salvage procedure and should only be considered if other fixation techniques have failed or severe chronic osteomyelitis is present.

Dental Bonding Dental bonding involves the use of dental composite to connect opposing canine teeth of the maxilla and mandible (Figure 13). The goals are to neutralize internal and external forces that act on the mandible and to stabilize mandibular fractures in three dimensions. Single or multiple fractures in any region of the mandible can be managed by dental bonding.6 Dental bonding is contraindicated if more than two canines are unstable or missing6 or if bilateral rostral fractures are present. INTRAORAL SOFT TISSUE CLOSURE ■ DENTAL COMPOSITE

Figure 13—Dental bonding. Frontal view of the mouth of a dog with dental acrylic in place (crosshatched area), connecting the upper and the lower canine teeth. (From Wallace BJ, Kapatkin AS, Manfra Maretta S: Dental composite for the fixation of mandibular fractures and luxations in 11 cats and 6 dogs. Vet Surg 23:190, 1994. Reprinted with permission.)

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dog vomits, can also be avoided by good instruction of owners.6

SUMMARY Each of the techniques described here has advantages and disadvantages, and each has distinct indications. The decision of which technique to use should be made on a case-by-case basis. Intramedullary pinning in mandibular fractures has numerous disadvantages and thus cannot be recommended. Dental bonding is a relatively new technique that has been successfully used to manage various fractures in several regions of the mandible. We recommend this technique as a fairly easy to perform, inexpensive, and effective method for managing mandibular fractures. With the exception of the tape muzzle (a basic and commonly used technique), this article has not described the procedures in detail.

4. 5. 6. 7.

8. 9. 10. 11.

About the Authors Dr. Goeggerle is in private practice in a small animal clinic in Rapperswil, Switzerland. Dr. Inskeep is affiliated with Noah’s Ark Pet Hospital in Rensselaer, Indiana. Dr. Toombs, who is a Diplomate of the American College of Veterinary Surgeons, is affiliated with the Department of Clinical Sciences, School of Veterinary Medicine, Purdue University, West Lafayette, Indiana.

12. 13. 14. 15.

REFERENCES

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1. Umphlet RC, Johnson AL: Mandibular fractures in the dog. A retrospective study. Vet Surg 19(4):272–275, 1990. 2. Rudy RL, Boudrieau RJ: Maxillofacial and mandibular fractures. Semin Vet Med Surg Small Anim 7(1):3–20, 1992. 3. Egger EL: Skull and mandibular fractures, in Slatter DJ:

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Textbook of Small Animal Surgery, ed 2. Philadelphia, WB Saunders Co, 1993, pp 1910–1921. Withrow SJ: Taping of the mandible in treatment of mandibular fractures. JAAHA 11:27–31, 1981. Taylor RA: Mandibular fractures, in Bojrab MJ (ed): Current Techniques in Small Animal Surgery, ed 3. Philadelphia, Lea & Febiger, 1990, pp 890–894. Wallace BJ, Kapatkin AS, Manfra Maretta S: Dental composite for the fixation of mandibular fractures and luxations in 11 cats and 6 dogs. Vet Surg 23:190–194, 1994. Brinker WO, Piermattei DL, Flo GS: Fractures and dislocations of the upper and lower jaw, in Handbook of Small Animal Orthopedics and Fracture Treatment. Philadelphia, WB Saunders Co, 1990, pp 230–243. Hinko PJ: A method for reduction and fixation of symphyseal fractures of the mandible. JAAHA 12:98–100, 1976. Chambers JN: Principles of management of mandibular fractures in the dog and cat. J Vet Orthop 2(2):26–36, 1981. Lantz GC: Interarcade wiring as a method of fixation for selected mandibular injuries. JAAHA 17:599–603, 1981. Cechner PE: Malocclusion in the dog caused by intramedullary pin fixation of mandibular fractures: Two case reports. JAAHA 16:79–85, 1980. Greenwood KM, Creagh JR: Bi-phase external skeletal splint fixation of mandibular fractures in dogs. J Am Coll Vet Surg 9:128–134, 1980. Stampley AR, Lawrence D: Acrylic external fixation in the treatment of complex mandibular fractures. Canine Pract 18(6):15–19, 1993. Weigl JP, Dorn AS, Chase DC, Jaffrey B: The use of the biphase external fixation splint for repair of canine mandibular fractures. JAAHA 17:547–554, 1981. Toombs JP: Treatment of mandibular fractures with the bi-phase external fixation splint. Proc 16th Annu Vet Surg Forum:257–258, 1988. Davidson JR, Bauer MS: Fractures of the mandible and the maxilla. Vet Clin North Am Small Anim Pract 22(1):109– 119, 1992. Lantz GC, Salisbury SK: Partial mandibulectomy for treatment of mandibular fractures in dogs: Eight cases (1981– 1984). JAVMA 191(2):243–245, 1987.