EXTERNAL SKELETAL FIXATION
0195-5616/92 $0.00 + .20
FRACTURES OF THE MANDIBLE AND MAXILLA Jacqueline R. Davidson, DVM, MS, and Michael S. Bauer, DVM
Mandibular and maxillary fractures are common injuries requiring veterinary care. Mandibular fractures account for 11.4% to 14.5% of all fractures in catsll, 16 and 2.5% of all fractures in dogs. 11 Maxillary fractures occur less frequently than mandibular fractures. Most mandibular and maxillary fractures result from automobile trauma,lI although falls, gunshot wounds, kicks, and animal fights also result in facial fractures. Mandibular fractures usually necessitate surgical intervention, whereas many maxillary fractures may not require fixation .3 Indications for surgical repair of maxillary fractures include malocclusion, oronasal communication, facial deformity, or obstructed upper airways.14, 18 A variety of techniques have been used to stabilize facial fractures, including tape muzzles; intraoral splinting; aluminum rod splinting; interdental wiring; internal fixation with bone plates, screws, and orthopedic wires; and external fixation devices. External fixation can be used for many mandibular fractures and is especially applicable for comminuted fractures,fractures with bone loss, and fractures with extensive soft tissue damage. External fixation may also be used in cases of simple mandibular fractures, multiple or bilateral fractures, infected fractures, and delayed union or nonunions. Repair of mandibular fractures using external fixation is somewhat restricted to fractures in the mandibular body. If the fracture is too caudal, an inadequate amount of bone for pin placement will be present in the caudal fracture segment. External fixators can be used to stabilize maxillary fractures, ls but since this is an infrequent application, this discussion concentrates on mandibular fractures. From the Department of Veterinary Clinical Sciences, Purdue University School of Veterinary Medicine, West Lafayette, Indiana
VETERINARY CLINICS OF NORTH AMERICA: SMALL ANIMAL PRACTICE VOLUME 22 • NUMBER 1 • JANUARY 1992
109
110
DAVIDSON & BAUER
INITIAL EVALUATION
A thorough physical examination should be performed on animals with mandibular or maxillary fractures because concurrent injuries are common. Cardiovascular compromise, neurologic injuries, or respiratory embarrassment may be life-threatening. The cardiovascular system should be evaluated for shock, which may be complicated by dehydration. An electrocardiogram should also be performed to rule out traumatic myocarditis. The neurologic system should be examined, paying particular attention to the central nervous system. Thoracic auscultation and radiography are needed to rule out pulmonary contusions, pneumothorax, diaphragmatic hernia, or other manifestations of thoracic trauma. Respiratory distress may develop if the upper airways are compromised by hemorrhage, damaged soft tissue, edema, or bone fragments. The animal's mouth should not be manually or surgically closed unless the upper airways are patent. If the upper airways are occluded, an emergency tracheostomy may be required. Once the patient is stable, sedation or general anesthesia can be used to permit full evaluation of the fractures. The mandible and maxilla should be examined both intraorally and externally. Intraoral examination may reveal malocclusion, loose teeth, open fractures, hard palate injuries, and concurrent soft tissue damage. During external examination, particular attention should be given to facial asymmetry, dental malocclusion, and soft tissue damage. The mandible and maxilla should be palpated and the temporomandibular joints manipulated to identify all injuries. Radiographs should be made while the animal is anesthetized. Lateral, ventrodorsal, oblique, and intraoral views are usually necessary to evaluate the bone structures fully. PRINCIPLES OF ORAL FRACTURE MANAGEMENT
General inhalant anesthesia is normally used for repair of mandibular and maxillary fractures . Anesthetic induction is most easily accomplished using an intravenous, ultra-short-acting barbiturate. Mask induction is usually avoided in cases of facial injuries because of patient discomfort as well as the possibility of concurrent partial upper airway obstruction interfering with rapid induction. Reduction of mandibular and maxillary fractures and restoration of proper dental occlusion require frequent, complete closure of the animal's mouth during surgery. Therefore in most instances, the endotracheal tube should bypass the oral cavity via a pharyngotomy. Following standard intubation, a pharyngotomy is performed similar to that used for placement of a pharyngostomy tube for esophageal feeding. 7 Preparation is made to disconnect the endotracheal tube from the anesthesia machine and pull the tube through the pharyngotomy. A curved hemostat is inserted through the pharyngotomy into the oropharynx. The endotracheal tube adapter is removed, the cuff de-
FRACTURES OF THE MANDIBLE AND MAXILLA
111
flated, and the end of the tube advanced into the oropharynx. The tube is grasped with the hemostats, pulled through the pharyngotomy, and reconnected to the anesthesia machine. Once the animal has been anesthetized, the oral cavity should be wiped or flushed using a dilute antiseptic such as povodine iodine or chlorhexidine. Although a true aseptic field is nearly impossible to preserve during most surgeries of the maxilla or mandible, the skin in the surgical field should still be prepared for standard invasive surgery. The majority of mandibular fractures are most easily repaired with the animal in dorsal recumbency. The anesthetist and anesthesia equipment should be placed to one side of the animal to allow the surgeon freedom to work at the end and on one side of the surgery table. The surgical field is usually quarter draped to prevent gross contamination of the surgeon or equipment. Perioperative prophylactic antibiotics are recommended for most mandibular or maxillary fracture repairs. Cefazolin (22 mglkg intravenously) is the authors' choice because it may be given intravenously; is effective against staphylococcal species, most anaerobes, and commonly encountered gram-negative bacilli; and has a relatively long serum and tissue half-life. Cefazolin should be repeated every 2% hours when used as a perioperative, prophylactic antibiotic. Prolonged use of antibiotics is usually not needed but may be indicated if gross infection is present. In such cases, choice of antibiotics should be based on bacterial culture and antibiotic sensitivity results. The primary objectives of fracture fixation of the mandible or maxilla are to restore normal occlusion and masticatory function . Restoration of normal occlusion is more important than perfect reduction of bone fragments. 12 Malocclusion may result in complications such as temporomandibular arthritis,S impaired mastication, abnormal tooth wear, plaque and tartar accumulation, periodontal disease, or unacceptable cosmetics. IS Because the teeth have a constant relationship to the structures of the maxilla and mandible, establishing normal occlusion will often result in relatively normal fracture reduction. 6 In fact, for severely comminuted fractures or fractures with significant bone loss, restoration of normal occlusion may be the only guideline for alignment. To achieve normal occlusion, the mandibular canine tooth should be positioned in the middle of the space between the maxillary lateral incisor and canine tooth. Also, the cusp of the mandibular fourth premolar should be positioned between the maxillary third and fourth premolars. 13 Loose teeth or teeth involved in the fracture should be removed unless they are important for reduction.12, 14 These teeth are probably devitalized and may interfere with bone healing. Once normal occlusion is achieved, it is usually not necessary to approach the fracture site. If the fracture is open or if an approach is made, however, soft tissue attachments to bone fragments should be preserved, especially in comminuted fractures .12 Small, unstable, avascular bone fragments have a high probability of sequestration that may delay or prevent fracture healint and should usually be removed. If
112
DAVIDSON & BAUER
an avascular bone fragment is considered necessary for reduction or fracture stability, it may be left; clinical suspicion of sequestration, however, should remain high. Most mandibular fractures are open to the oral cavity,4, 14, 16, 17 allowing bacterial contamination to occur, so they should be treated in a manner similar to a contaminated wound. Soft tissue wounds should be debrided and copiously lavaged with sterile saline. Removal of devitalized tissue will help prevent infection. Although large mucosal defects may be sutured, oral wounds are usually left open to drain and heal by second intention. Initial debridement and fracture stabilization can be performed concurrently, Grossly infected wounds, however, may be treated for several days before implant placement for fracture stabilization. In such instances, management of concurrent oral soft tissue wounds should be continued after the fracture has been stabilized. If the achievement of normal occlusion results in incomplete reduction, healing may still occur. Regardless of the precision of reduction, most facial fractures heal by secondary bone healing, which is characterized by callus production and subsequent remodeling. Secondary bone healing is acceptable for fracture healing, especially in the mandibular body where callus formation usually does not interfere with function . In the presence of incomplete reduction, large bone defects, or severely comminuted fractures, healing may be promoted by the use of a cancellous bone graft. Healthy soft tissues must be available, however, to close over the grafted region to prevent loss of the graft. In some cases, placing the cancellous bone graft at the fracture site may be postponed until the oral mucosa has healed. In these cases, the graft may be placed through a ventral approach to the mandible. EXTERNAL FIXATION
External fixation provides rigid stability with rapid return to masticatory function. It requires minimal dissection and disruption of local blood supply, providing an environment that promotes bone healing. It has an advantage over internal fixation in that implants are not located at the fracture site. This may be important in contaminated or infected fractures . Additionally, if closed reduction and stabilization are performed, blood supply is preserved. External fixators are relatively easy to apply and are generally well tolerated by animals. External fixation of the mandible can be achieved with conventional pins, clamps, and connecting rods; with pins or screws and acrylic; or with the biphasic method using screws and acrylic. Kirschner-Ehmer Splint
A Kirschner-Ehmer splint involves the use of pins, clamps, and connecting bars, To apply a Kirschner-Ehmer splint, the pins are placed
FRACTURES OF THE MANDIBLE AND MAXILLA
113
percutaneously within the body of the mandible, avoiding the tooth roots and the mandibular canal, which contains the mandibular alveolar artery, vein, and nerve. 12 These structures can usually be avoided by inserting the pins in the ventral third of the mandibular body.9 A minimum of two pins penetrating both cortices should be placed in each major fragment. The pins may be placed transmandibularly; this is especially true for those in the more rostral aspect of the mandible. Pins must be in the same plane so one connecting bar can be used. Smooth pins should be placed at divergent angles. Since threaded pins have greater pullout strength, they may be placed perpendicular to the long axis of the mandible, which will allow more pins to be placed in a given length of bone. It is preferable to place the pins with a slowspeed drill (150 rpm) rather than a high-speed drill or hand chuck. Pre drilling may be done, but it is sometimes difficult to locate the predrilled hole when placing the pin, especially when the pin is placed transmandibularly. The small Kirschner clamps will fit smooth pin sizes from V16" to 3/32" in diameter and fully threaded %0" pins. The medium Kirschner clamps will fit smooth pin sizes from %4" to VB" in diameter and fully threaded Vs" pins. The small Kirschner-Ehmer splint may be used in the mandibular fractures of small dogs weighing up to 10 to 12 Kg, and the medium Kirschner-Ehmer splint may be used in the mandibular fractures of large dogs. The large Kirschner-Ehmer splint is too large and heavy for most canine mandibles. Smooth, partially threaded or fully threaded pins may be used. Studies in long bones have elucidated the advantages of using threaded versus smooth pins. Threaded pins grip the bone more securely than smooth pins and prolong the stability of the pin-bone interface.1, 2 A minor disadvantage of end-threaded pins is the potential for pin breakage at the threaded and nonthreaded shaft junction. This is relatively uncommon in mandibular fractures because the forces placed on the mandible are minimized by appropriate postoperative care. Therefore the authors prefer threaded pins, especially in cases in which there is not adequate room in the bone to place divergent pins. To apply a Kirschner-Ehmer splint, a small skin incision is made before placing each pin. The most rostral and caudal pins are placed first. The connecting bar is attached to the pins with the anticipated number of empty clamps on the connecting bar between the two end pins. The occlusion is aligned, and end clamps are tightened before placing the middle pins through clamps on the connecting bar and into the mandible. Fine adjustments in alignment may still be made after the Kirschner-Ehmer splint has been placed. Acrylic Splint
The use of dental acrylic (polymethyl methacrylate) for pin stabilization provides rigid, strong fixation and is an alternative to a Kirschner-
114
DAVIDSON & BAUER
Ehmer splint with connecting bars and clamps (Fig. 1). A %" acrylic rod is stiffer and stronger than a medium-sized Kirschner-Ehmer connecting bar.8 The dental acrylic fixator has several advantages Over the Kirschner-Ehmer splint. An acrylic splint is lighter than a comparable Kirschner-Ehmer fixator, the acrylic splint may curve around the jaw rostrally and incorporate transmandibular or bilateral pins, and fixation pins may be in different planes and of different sizes. Pins or cortical screws may be used for purchase in the mandible if one follows the same principles for placement as for the KirschnerEhmer splint pins. If pins are used for fixation, they may be bent over to lie parallel with the skin so the acrylic has more surface to grip (Fig. 2). If screws are used, wire may be wrapped around the screw heads to act as a scaffold for the acrylic. 1O Once the pins or screws are in place, aseptic surgical technique is not required. The acrylic bar can be made from commercial grade dental acrylic by mixing 3 parts powder (polymer) to 1 part liquid (monomer). If soft tissue repair is needed beneath the area of the acrylic bar, sterile bone cement may be used. The bar can be formed by molding it by hand over the pin or screw ends. An alternative is to use plastic tubing as a mold by impaling it over the pins and injecting the acrylic into it with a syringeY The acrylic should be positioned at least 1 cm from the skin surface to prevent irritation. 19 Soft tissues should be packed off by wet sponges to protect them from the heat generated by the exothermic reaction as the acrylic cures. To maintain alignment until the acrylic sets (about 10 minutes), the fracture must be manually held in reduction, or several
Figure 1. A mandibular external fixator placed using pins and a hand molded acrylic bar. (Courtesy of Dr. Sean W. Aiken, Purdue University, West Lafayette, IN.)
FRACTURES OF THE MANDIBLE AND MAXILLA
115
Figure 2. Lateral radiograph of a mandibular pin and acrylic fixator. The pins have been bent to provide more surface for the acrylic to grip. (Courtesy of Dr. Jonathan N. Chambers, University of Georgia, Athens, GA, and Dr. James P. Toombs, Purdue University, West Lafayette, IN.)
of the pins may be left long and temporarily clamped with KirschnerEhmer clamps and a connecting bar.s When the acrylic has hardened, the clamps and bar are removed and the projecting pins are cut. Biphase Splint
The biphase splint (Walter Lorenz Surgical Instruments, Inc., Jacksonville, FL) is so named because it is applied in two steps or phases. In phase I, special bone screws are placed percutaneously in the mandible and left protruding through the skin by approximately 2 cm. External clamps and bars are secured to the screws to reduce and maintain fracture fixation temporarily. In phase II, an acrylic bar is placed across the ends of the screws and allowed to set. Once the acrylic is rigid, the clamps and bars of phase I are removed. The biphase external skeletal fixation splint has been used in humans since 1949 to repair severe facial fractures and to stabilize mandibular defects bridged by bone grafts. 19 Of the seven cases reported in the veterinary literature, no major complications were associated with the use of the biphase splint. 9, 19 The biphase splint has s.everal advantages over a KirschnerEhmer splint. Rigid fixation can generally be maintained for a longer period of time, and the biphase splint is less bulky and more lightweight than a conventional Kirschner-Ehmer splint. A potential disadvantage
116
DAVIDSON & BAUER
of the biphase splint is the cost of the necessary equipment and instrumentation. 19 Another limitation of the biphase splint is that the animal must be of at least medium size (12 to 15 kg) so the mandible is large enough to accept the screws. 9 The biphase splint uses special Vitallium screws, which have fine, narrow-spaced machine threads on one end that accept a washerfaced nut. The other end of the screw has coarse, wide-spaced, self-tapping threads for use in bone. A hexagonal table is located at the junction of the shaft and the machine-threaded region (Fig. 3). This allows the screw to be tightened into the bone by the use of a wrench. Just below the hexagonal table the shaft is flanged to provide a place to secure the clamps involved in phase I. 9, 19 The mandibular body has two distinct cortices with the medullary cavity between them. In the ramus, however, the two cortices are usually fused. 9 Therefore two different types of bone screws are available for use in these regions. The screw for use in the ramus is thicker, has a shorter threaded region (6.3 mm), and has a shoulder at the junction of the threads and the shaft. 9,19 This shoulder rests against the outer cortex of the mandible when the screw is properly seated. 19 Screws for use in the mandibular body have a longer threaded region (12.7 mm) and are nonshouldered. 9 Symphyseal screws are also available that have a threaded region of intermediate length (9.5 mm). To apply a biphase splint, a l-cm stab incision is made in the skin over the intended screw site, and the soft tissues are bluntly dissected. A drill guide is inserted to drill a %4" hole perpendicularly through the mandibular body or ramus. 9 At least two screws should be placed in • each major bone fragment. 9, 19 Although tooth roots should be avoided, it is possible to place a screw through a tooth root if there is no available bone. The tooth may need to be extracted later, however, if a root abscess develops.9 Once all the screws have been placed, the phase I clamps and connecting bars can be attached. At least one screw from each fracture segment is attached to a clamp at the hexagonal region of the screw. The connecting bars are placed through the clamps, and the clamps are tightened to maintain the fracture in reduction. The appa-
.
B
c
o
Figure 3. A Richards 1% inch mandibular screw with nut. A, One-half inch long region of self-tapping bone threads. B, Flanged area for phase I clamp attachment. C, Hexagonal table, which is gripped by wrench to tighten screw into the bone. 0, Machine-threaded region with washerfaced nut.
FRACTURES OF THE MANDIBLE AND MAXILLA
117
Figure 4. A bilateral biphase splint in place after surgery. (Courtesy of Dr. Jonathan N. Chambers, University of Georgia, Athens, GA, and Dr. James P. Toombs, Purdue University, West Lafayette, IN.)
ratus can then be adjusted until proper dental occlusion is achieved. At this point, reduction may be evaluated radiographically if desired. In phase II of biphase splint application, the acrylic bar is applied. A long, rectangular mold may be prelubricated with K-Y jelly and used to form the bar. As the acrylic bar begins to harden, it is removed from the mold and placed over the machine-threaded end of the screws. The nuts are tightened down on top of the acrylic bar after the acrylic is set. The phase I clamps and bars can then be removed, leaving the screws and acrylic bar as permanent stabilization9• 19 (Fig. 4). The screws may remain indefinitely as long as they are stable. Screw loosening is a problem in some cases. 19 If local infection develops around a screw, it can usually be controlled by daily cleaning and topical antibiotic ointment. 9 If a screw needs removal, the phase I apparatus is reapplied and the acrylic bar is cut on either side of the screw. After the scr~w has been removed, the acrylic bar is patched using fresh acrylic. 9 POSTOPERATIVE CARE
Postoperative care of external fjxators is minimal and can easily be performed by owners. The skin around the pins or screws should be cleaned daily using hydrogen peroxide on a cotton-tipped swab. Oral hygiene may also be maintained by flushing the mouth with water or
118
DAVIDSON & BAUER
dilute hydrogen peroxide solution twice daily until any oral mucosal wounds have healed. 9 If a Kirschner-Ehmer splint is used, it may be desirable to keep the connecting bar and clamps wrapped to prevent self-trauma and to prevent it from catching on objects in the environment. An Elizabethan collar or leg hobbles may also be used to prevent the animal from pawing the fixator. A soft food diet should be fed until the fractures have healed. The fracture may be evaluated radiographically in 3 to 5 weeks. If the fracture appears to be healed, stability can be palpated after loosening the metal connecting bar of a Kirschner-Ehmer splint or cutting the bar of an acrylic splint with an air drill or cast cutter. If the fracture is still unstable, the metal connecting bar of a Kirschner-Ehmer splint can be retightened. In the case of an acrylic bar, it can be patched with fresh acrylic. 19 If the fracture is stable, the fixator may be completely removed. To remove a fixator that has pins and an acrylic bar, the pins can be cut between the skin and the acrylic. The pins may then be pulled with a hand chuck. To remove a biphase splint, the nuts are removed and the acrylic bar is cut next to each screw. A periosteal elevator can then be used to crack the acrylic off the screw, allowing the screw to be removed. 9 The resulting skin wounds are allowed to heal by second intention. Removal of external fixation may not require general anesthesia, but sedation is usually necessary. SUMMARY
External fixation is an effective method for stabilization of many mandibular fractures. Thorough physical examination and patient stabilization should be instituted before attending to the fractures and associated soft tissue trauma. Normal occlusion rather than perfect reduction is the goal of oral fracture repair. Loose teeth or teeth in the fracture should be removed, as should any avascular bone fragments. Soft tissue wounds should be treated as for any contaminated wound. Mucosal wounds are allowed to heal by second intention. Although prophylactic perioperative antibiotics are indicated, they are usually not needed postoperatively. The three basic types of external fixators described include the Kirschner-Ehmer splint, pins or screws and acrylic, and the biphase splint. All three types are relatively easy to apply, and the principles of their application are similar. A minimum of two pins or screws are placed percutaneously in each fragment, avoiding the mandibular canal. The Kirschner-Ehmer splint is more easily adjustable than the biphase splint or the pin-acrylic splint, which use acrylic connecting bars. The advantages of fixators that use acrylic bars are that the pins or screws need not all be in the same plane and that they are more lightweight than the Kirschner-Ehmer splint. The disadvantages of the biphase splint are its increased expense and its use being limited to larger dogs. External fixators are well tolerated by the animals, and postoperative care is minimal. Mandibular fractures
FRACTURES OF THE MANDIBLE AND MAXILLA
119
are usually healed in 3 to 5 weeks, and the fixators can be removed with the animal under sedation.
References JP, Hollingsworth SC: Primary treatment of severe fractures by external skeletal fixation: Threaded pins compared with smooth pins. J Am Anim Hosp Assoc 22:659-670, 1986 Bennet RA, Egger EL, Histand M, et al: Comparison of the strength and holding power of 4 pin designs for use with half pin (type I) external skeletal fixation. Vet Surg 16:207-211, 1987 Bone DL: Maxillary fractures. In Bojrab MJ (ed): Current Techniques in Small Animal Surgery, ed 3. Philadelphia, Lea & Febiger, 1990, pp 883-890 Brinker WO, Piermattei DL, Flo GL: Handbook of Small Animal Orthopedics and Fracture Treatment, ed 2. Philadelphia, WB Saunders, 1990, pp 230-243 Chambers IN: Principles of management of mandibular fractures in the dog and cat. J Vet Orthop 2:26-36, 1981 Cooper MD, Roger CL, Rosenfeld PA, et al: Management of mandibular fractures using biphasic pins and mandibular splints. Laryngoscope 92:1042-1048, 1982 Crow DT, Downs MO: Pharyngostomy complications in dogs and cats and recommended technical modifications: Experimental and clinical investigations. J Am Anim Hosp Assoc 22:493-503, 1986 Egger EL: Management of mandibular fractures with acrylic-pin external fixation splints. In Proceedings 15th Annual Veterinary Orthopedic Society Meeting, Breckenridge, CO, 1988, P 6 Greenwood KM, Creagh GB: Bi-phase external skeletal splint fixation of mandibular fractures in dogs. Vet Surg 9:128-134, 1980 Nunamaker DM: Fractures and dislocations of the mandible. In Newton CD, Nunamaker DM (eds): Textbook of Small Animal Orthopaedics. Philadelphia, JB Lippincott, 1985, pp 297-305 Phillips IR: A survey of bone fractures in the dog and cat. J Small Anim Pract 20:661674,1979 Pope ER: Oral trauma-orthopedic considerations. ACVS 18th Ann Vet Surg Forum:389-391, 1990 Ross DL: Evaluation of oral abnormalities. In Proceedings American Animal Hospital Association 45th Annual Meeting, Salt Lake City, UT 1978, pp 79-83 Schrader SC: Dental orthopedics. In Bojrab MJ, Tholen M (eds): Small Animal Oral Medicine and Surgery. Philadelphia, Lea & Febiger, 1990, pp 241-264 Stambaugh JE, Nunamaker DM: External skeletal fixation of comminuted maxillary fractures in dogs. Vet Surg 11:72-76, 1982 Umphlet RC, Johnson AL: Mandibular fractures in the cat A retrospective study. Vet Surg 17:333-337, 1988 Umphlet RC, Johnson AL: Mandibular fractures in the dog. A retrospective study of 157 cases (abstr.). In Proceedings 16th Annual Veterinary Orthopedic Society Meeting, Park City, UT, 1989, P 37 Weigel JP: Trauma to oral structures. In Harvey CE (ed): Veterinary Dentistry. Philadelphia, WB Saunders, 1985, pp 140-155 Weigel JP, Dorn AS, Chase DC, et al: The use of the biphase external fixation splint for repair of canine mandibular fractures. J Am Anim Hosp Assoc 17:547-554, 1981
1. Aron DN, Toombs
2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
Address reprint requests to Jacqueline R. Davidson, DVM, MS Surgical Referral Service, Ltd Veterinary Specialty Clinic 1105 Milwaukee Avenue Riverwoods, IL 60015
0195-5616/92 $0.00 + .20
FRACTURES OF THE MANDIBLE AND MAXILLA Jacqueline R. Davidson, DVM, MS, and Michael S. Bauer, DVM
Mandibular and maxillary fractures are common injuries requiring veterinary care. Mandibular fractures account for 11.4% to 14.5% of all fractures in catsll, 16 and 2.5% of all fractures in dogs. 11 Maxillary fractures occur less frequently than mandibular fractures. Most mandibular and maxillary fractures result from automobile trauma,lI although falls, gunshot wounds, kicks, and animal fights also result in facial fractures. Mandibular fractures usually necessitate surgical intervention, whereas many maxillary fractures may not require fixation .3 Indications for surgical repair of maxillary fractures include malocclusion, oronasal communication, facial deformity, or obstructed upper airways.14, 18 A variety of techniques have been used to stabilize facial fractures, including tape muzzles; intraoral splinting; aluminum rod splinting; interdental wiring; internal fixation with bone plates, screws, and orthopedic wires; and external fixation devices. External fixation can be used for many mandibular fractures and is especially applicable for comminuted fractures,fractures with bone loss, and fractures with extensive soft tissue damage. External fixation may also be used in cases of simple mandibular fractures, multiple or bilateral fractures, infected fractures, and delayed union or nonunions. Repair of mandibular fractures using external fixation is somewhat restricted to fractures in the mandibular body. If the fracture is too caudal, an inadequate amount of bone for pin placement will be present in the caudal fracture segment. External fixators can be used to stabilize maxillary fractures, ls but since this is an infrequent application, this discussion concentrates on mandibular fractures. From the Department of Veterinary Clinical Sciences, Purdue University School of Veterinary Medicine, West Lafayette, Indiana
VETERINARY CLINICS OF NORTH AMERICA: SMALL ANIMAL PRACTICE VOLUME 22 • NUMBER 1 • JANUARY 1992
109
110
DAVIDSON & BAUER
INITIAL EVALUATION
A thorough physical examination should be performed on animals with mandibular or maxillary fractures because concurrent injuries are common. Cardiovascular compromise, neurologic injuries, or respiratory embarrassment may be life-threatening. The cardiovascular system should be evaluated for shock, which may be complicated by dehydration. An electrocardiogram should also be performed to rule out traumatic myocarditis. The neurologic system should be examined, paying particular attention to the central nervous system. Thoracic auscultation and radiography are needed to rule out pulmonary contusions, pneumothorax, diaphragmatic hernia, or other manifestations of thoracic trauma. Respiratory distress may develop if the upper airways are compromised by hemorrhage, damaged soft tissue, edema, or bone fragments. The animal's mouth should not be manually or surgically closed unless the upper airways are patent. If the upper airways are occluded, an emergency tracheostomy may be required. Once the patient is stable, sedation or general anesthesia can be used to permit full evaluation of the fractures. The mandible and maxilla should be examined both intraorally and externally. Intraoral examination may reveal malocclusion, loose teeth, open fractures, hard palate injuries, and concurrent soft tissue damage. During external examination, particular attention should be given to facial asymmetry, dental malocclusion, and soft tissue damage. The mandible and maxilla should be palpated and the temporomandibular joints manipulated to identify all injuries. Radiographs should be made while the animal is anesthetized. Lateral, ventrodorsal, oblique, and intraoral views are usually necessary to evaluate the bone structures fully. PRINCIPLES OF ORAL FRACTURE MANAGEMENT
General inhalant anesthesia is normally used for repair of mandibular and maxillary fractures . Anesthetic induction is most easily accomplished using an intravenous, ultra-short-acting barbiturate. Mask induction is usually avoided in cases of facial injuries because of patient discomfort as well as the possibility of concurrent partial upper airway obstruction interfering with rapid induction. Reduction of mandibular and maxillary fractures and restoration of proper dental occlusion require frequent, complete closure of the animal's mouth during surgery. Therefore in most instances, the endotracheal tube should bypass the oral cavity via a pharyngotomy. Following standard intubation, a pharyngotomy is performed similar to that used for placement of a pharyngostomy tube for esophageal feeding. 7 Preparation is made to disconnect the endotracheal tube from the anesthesia machine and pull the tube through the pharyngotomy. A curved hemostat is inserted through the pharyngotomy into the oropharynx. The endotracheal tube adapter is removed, the cuff de-
FRACTURES OF THE MANDIBLE AND MAXILLA
111
flated, and the end of the tube advanced into the oropharynx. The tube is grasped with the hemostats, pulled through the pharyngotomy, and reconnected to the anesthesia machine. Once the animal has been anesthetized, the oral cavity should be wiped or flushed using a dilute antiseptic such as povodine iodine or chlorhexidine. Although a true aseptic field is nearly impossible to preserve during most surgeries of the maxilla or mandible, the skin in the surgical field should still be prepared for standard invasive surgery. The majority of mandibular fractures are most easily repaired with the animal in dorsal recumbency. The anesthetist and anesthesia equipment should be placed to one side of the animal to allow the surgeon freedom to work at the end and on one side of the surgery table. The surgical field is usually quarter draped to prevent gross contamination of the surgeon or equipment. Perioperative prophylactic antibiotics are recommended for most mandibular or maxillary fracture repairs. Cefazolin (22 mglkg intravenously) is the authors' choice because it may be given intravenously; is effective against staphylococcal species, most anaerobes, and commonly encountered gram-negative bacilli; and has a relatively long serum and tissue half-life. Cefazolin should be repeated every 2% hours when used as a perioperative, prophylactic antibiotic. Prolonged use of antibiotics is usually not needed but may be indicated if gross infection is present. In such cases, choice of antibiotics should be based on bacterial culture and antibiotic sensitivity results. The primary objectives of fracture fixation of the mandible or maxilla are to restore normal occlusion and masticatory function . Restoration of normal occlusion is more important than perfect reduction of bone fragments. 12 Malocclusion may result in complications such as temporomandibular arthritis,S impaired mastication, abnormal tooth wear, plaque and tartar accumulation, periodontal disease, or unacceptable cosmetics. IS Because the teeth have a constant relationship to the structures of the maxilla and mandible, establishing normal occlusion will often result in relatively normal fracture reduction. 6 In fact, for severely comminuted fractures or fractures with significant bone loss, restoration of normal occlusion may be the only guideline for alignment. To achieve normal occlusion, the mandibular canine tooth should be positioned in the middle of the space between the maxillary lateral incisor and canine tooth. Also, the cusp of the mandibular fourth premolar should be positioned between the maxillary third and fourth premolars. 13 Loose teeth or teeth involved in the fracture should be removed unless they are important for reduction.12, 14 These teeth are probably devitalized and may interfere with bone healing. Once normal occlusion is achieved, it is usually not necessary to approach the fracture site. If the fracture is open or if an approach is made, however, soft tissue attachments to bone fragments should be preserved, especially in comminuted fractures .12 Small, unstable, avascular bone fragments have a high probability of sequestration that may delay or prevent fracture healint and should usually be removed. If
112
DAVIDSON & BAUER
an avascular bone fragment is considered necessary for reduction or fracture stability, it may be left; clinical suspicion of sequestration, however, should remain high. Most mandibular fractures are open to the oral cavity,4, 14, 16, 17 allowing bacterial contamination to occur, so they should be treated in a manner similar to a contaminated wound. Soft tissue wounds should be debrided and copiously lavaged with sterile saline. Removal of devitalized tissue will help prevent infection. Although large mucosal defects may be sutured, oral wounds are usually left open to drain and heal by second intention. Initial debridement and fracture stabilization can be performed concurrently, Grossly infected wounds, however, may be treated for several days before implant placement for fracture stabilization. In such instances, management of concurrent oral soft tissue wounds should be continued after the fracture has been stabilized. If the achievement of normal occlusion results in incomplete reduction, healing may still occur. Regardless of the precision of reduction, most facial fractures heal by secondary bone healing, which is characterized by callus production and subsequent remodeling. Secondary bone healing is acceptable for fracture healing, especially in the mandibular body where callus formation usually does not interfere with function . In the presence of incomplete reduction, large bone defects, or severely comminuted fractures, healing may be promoted by the use of a cancellous bone graft. Healthy soft tissues must be available, however, to close over the grafted region to prevent loss of the graft. In some cases, placing the cancellous bone graft at the fracture site may be postponed until the oral mucosa has healed. In these cases, the graft may be placed through a ventral approach to the mandible. EXTERNAL FIXATION
External fixation provides rigid stability with rapid return to masticatory function. It requires minimal dissection and disruption of local blood supply, providing an environment that promotes bone healing. It has an advantage over internal fixation in that implants are not located at the fracture site. This may be important in contaminated or infected fractures . Additionally, if closed reduction and stabilization are performed, blood supply is preserved. External fixators are relatively easy to apply and are generally well tolerated by animals. External fixation of the mandible can be achieved with conventional pins, clamps, and connecting rods; with pins or screws and acrylic; or with the biphasic method using screws and acrylic. Kirschner-Ehmer Splint
A Kirschner-Ehmer splint involves the use of pins, clamps, and connecting bars, To apply a Kirschner-Ehmer splint, the pins are placed
FRACTURES OF THE MANDIBLE AND MAXILLA
113
percutaneously within the body of the mandible, avoiding the tooth roots and the mandibular canal, which contains the mandibular alveolar artery, vein, and nerve. 12 These structures can usually be avoided by inserting the pins in the ventral third of the mandibular body.9 A minimum of two pins penetrating both cortices should be placed in each major fragment. The pins may be placed transmandibularly; this is especially true for those in the more rostral aspect of the mandible. Pins must be in the same plane so one connecting bar can be used. Smooth pins should be placed at divergent angles. Since threaded pins have greater pullout strength, they may be placed perpendicular to the long axis of the mandible, which will allow more pins to be placed in a given length of bone. It is preferable to place the pins with a slowspeed drill (150 rpm) rather than a high-speed drill or hand chuck. Pre drilling may be done, but it is sometimes difficult to locate the predrilled hole when placing the pin, especially when the pin is placed transmandibularly. The small Kirschner clamps will fit smooth pin sizes from V16" to 3/32" in diameter and fully threaded %0" pins. The medium Kirschner clamps will fit smooth pin sizes from %4" to VB" in diameter and fully threaded Vs" pins. The small Kirschner-Ehmer splint may be used in the mandibular fractures of small dogs weighing up to 10 to 12 Kg, and the medium Kirschner-Ehmer splint may be used in the mandibular fractures of large dogs. The large Kirschner-Ehmer splint is too large and heavy for most canine mandibles. Smooth, partially threaded or fully threaded pins may be used. Studies in long bones have elucidated the advantages of using threaded versus smooth pins. Threaded pins grip the bone more securely than smooth pins and prolong the stability of the pin-bone interface.1, 2 A minor disadvantage of end-threaded pins is the potential for pin breakage at the threaded and nonthreaded shaft junction. This is relatively uncommon in mandibular fractures because the forces placed on the mandible are minimized by appropriate postoperative care. Therefore the authors prefer threaded pins, especially in cases in which there is not adequate room in the bone to place divergent pins. To apply a Kirschner-Ehmer splint, a small skin incision is made before placing each pin. The most rostral and caudal pins are placed first. The connecting bar is attached to the pins with the anticipated number of empty clamps on the connecting bar between the two end pins. The occlusion is aligned, and end clamps are tightened before placing the middle pins through clamps on the connecting bar and into the mandible. Fine adjustments in alignment may still be made after the Kirschner-Ehmer splint has been placed. Acrylic Splint
The use of dental acrylic (polymethyl methacrylate) for pin stabilization provides rigid, strong fixation and is an alternative to a Kirschner-
114
DAVIDSON & BAUER
Ehmer splint with connecting bars and clamps (Fig. 1). A %" acrylic rod is stiffer and stronger than a medium-sized Kirschner-Ehmer connecting bar.8 The dental acrylic fixator has several advantages Over the Kirschner-Ehmer splint. An acrylic splint is lighter than a comparable Kirschner-Ehmer fixator, the acrylic splint may curve around the jaw rostrally and incorporate transmandibular or bilateral pins, and fixation pins may be in different planes and of different sizes. Pins or cortical screws may be used for purchase in the mandible if one follows the same principles for placement as for the KirschnerEhmer splint pins. If pins are used for fixation, they may be bent over to lie parallel with the skin so the acrylic has more surface to grip (Fig. 2). If screws are used, wire may be wrapped around the screw heads to act as a scaffold for the acrylic. 1O Once the pins or screws are in place, aseptic surgical technique is not required. The acrylic bar can be made from commercial grade dental acrylic by mixing 3 parts powder (polymer) to 1 part liquid (monomer). If soft tissue repair is needed beneath the area of the acrylic bar, sterile bone cement may be used. The bar can be formed by molding it by hand over the pin or screw ends. An alternative is to use plastic tubing as a mold by impaling it over the pins and injecting the acrylic into it with a syringeY The acrylic should be positioned at least 1 cm from the skin surface to prevent irritation. 19 Soft tissues should be packed off by wet sponges to protect them from the heat generated by the exothermic reaction as the acrylic cures. To maintain alignment until the acrylic sets (about 10 minutes), the fracture must be manually held in reduction, or several
Figure 1. A mandibular external fixator placed using pins and a hand molded acrylic bar. (Courtesy of Dr. Sean W. Aiken, Purdue University, West Lafayette, IN.)
FRACTURES OF THE MANDIBLE AND MAXILLA
115
Figure 2. Lateral radiograph of a mandibular pin and acrylic fixator. The pins have been bent to provide more surface for the acrylic to grip. (Courtesy of Dr. Jonathan N. Chambers, University of Georgia, Athens, GA, and Dr. James P. Toombs, Purdue University, West Lafayette, IN.)
of the pins may be left long and temporarily clamped with KirschnerEhmer clamps and a connecting bar.s When the acrylic has hardened, the clamps and bar are removed and the projecting pins are cut. Biphase Splint
The biphase splint (Walter Lorenz Surgical Instruments, Inc., Jacksonville, FL) is so named because it is applied in two steps or phases. In phase I, special bone screws are placed percutaneously in the mandible and left protruding through the skin by approximately 2 cm. External clamps and bars are secured to the screws to reduce and maintain fracture fixation temporarily. In phase II, an acrylic bar is placed across the ends of the screws and allowed to set. Once the acrylic is rigid, the clamps and bars of phase I are removed. The biphase external skeletal fixation splint has been used in humans since 1949 to repair severe facial fractures and to stabilize mandibular defects bridged by bone grafts. 19 Of the seven cases reported in the veterinary literature, no major complications were associated with the use of the biphase splint. 9, 19 The biphase splint has s.everal advantages over a KirschnerEhmer splint. Rigid fixation can generally be maintained for a longer period of time, and the biphase splint is less bulky and more lightweight than a conventional Kirschner-Ehmer splint. A potential disadvantage
116
DAVIDSON & BAUER
of the biphase splint is the cost of the necessary equipment and instrumentation. 19 Another limitation of the biphase splint is that the animal must be of at least medium size (12 to 15 kg) so the mandible is large enough to accept the screws. 9 The biphase splint uses special Vitallium screws, which have fine, narrow-spaced machine threads on one end that accept a washerfaced nut. The other end of the screw has coarse, wide-spaced, self-tapping threads for use in bone. A hexagonal table is located at the junction of the shaft and the machine-threaded region (Fig. 3). This allows the screw to be tightened into the bone by the use of a wrench. Just below the hexagonal table the shaft is flanged to provide a place to secure the clamps involved in phase I. 9, 19 The mandibular body has two distinct cortices with the medullary cavity between them. In the ramus, however, the two cortices are usually fused. 9 Therefore two different types of bone screws are available for use in these regions. The screw for use in the ramus is thicker, has a shorter threaded region (6.3 mm), and has a shoulder at the junction of the threads and the shaft. 9,19 This shoulder rests against the outer cortex of the mandible when the screw is properly seated. 19 Screws for use in the mandibular body have a longer threaded region (12.7 mm) and are nonshouldered. 9 Symphyseal screws are also available that have a threaded region of intermediate length (9.5 mm). To apply a biphase splint, a l-cm stab incision is made in the skin over the intended screw site, and the soft tissues are bluntly dissected. A drill guide is inserted to drill a %4" hole perpendicularly through the mandibular body or ramus. 9 At least two screws should be placed in • each major bone fragment. 9, 19 Although tooth roots should be avoided, it is possible to place a screw through a tooth root if there is no available bone. The tooth may need to be extracted later, however, if a root abscess develops.9 Once all the screws have been placed, the phase I clamps and connecting bars can be attached. At least one screw from each fracture segment is attached to a clamp at the hexagonal region of the screw. The connecting bars are placed through the clamps, and the clamps are tightened to maintain the fracture in reduction. The appa-
.
B
c
o
Figure 3. A Richards 1% inch mandibular screw with nut. A, One-half inch long region of self-tapping bone threads. B, Flanged area for phase I clamp attachment. C, Hexagonal table, which is gripped by wrench to tighten screw into the bone. 0, Machine-threaded region with washerfaced nut.
FRACTURES OF THE MANDIBLE AND MAXILLA
117
Figure 4. A bilateral biphase splint in place after surgery. (Courtesy of Dr. Jonathan N. Chambers, University of Georgia, Athens, GA, and Dr. James P. Toombs, Purdue University, West Lafayette, IN.)
ratus can then be adjusted until proper dental occlusion is achieved. At this point, reduction may be evaluated radiographically if desired. In phase II of biphase splint application, the acrylic bar is applied. A long, rectangular mold may be prelubricated with K-Y jelly and used to form the bar. As the acrylic bar begins to harden, it is removed from the mold and placed over the machine-threaded end of the screws. The nuts are tightened down on top of the acrylic bar after the acrylic is set. The phase I clamps and bars can then be removed, leaving the screws and acrylic bar as permanent stabilization9• 19 (Fig. 4). The screws may remain indefinitely as long as they are stable. Screw loosening is a problem in some cases. 19 If local infection develops around a screw, it can usually be controlled by daily cleaning and topical antibiotic ointment. 9 If a screw needs removal, the phase I apparatus is reapplied and the acrylic bar is cut on either side of the screw. After the scr~w has been removed, the acrylic bar is patched using fresh acrylic. 9 POSTOPERATIVE CARE
Postoperative care of external fjxators is minimal and can easily be performed by owners. The skin around the pins or screws should be cleaned daily using hydrogen peroxide on a cotton-tipped swab. Oral hygiene may also be maintained by flushing the mouth with water or
118
DAVIDSON & BAUER
dilute hydrogen peroxide solution twice daily until any oral mucosal wounds have healed. 9 If a Kirschner-Ehmer splint is used, it may be desirable to keep the connecting bar and clamps wrapped to prevent self-trauma and to prevent it from catching on objects in the environment. An Elizabethan collar or leg hobbles may also be used to prevent the animal from pawing the fixator. A soft food diet should be fed until the fractures have healed. The fracture may be evaluated radiographically in 3 to 5 weeks. If the fracture appears to be healed, stability can be palpated after loosening the metal connecting bar of a Kirschner-Ehmer splint or cutting the bar of an acrylic splint with an air drill or cast cutter. If the fracture is still unstable, the metal connecting bar of a Kirschner-Ehmer splint can be retightened. In the case of an acrylic bar, it can be patched with fresh acrylic. 19 If the fracture is stable, the fixator may be completely removed. To remove a fixator that has pins and an acrylic bar, the pins can be cut between the skin and the acrylic. The pins may then be pulled with a hand chuck. To remove a biphase splint, the nuts are removed and the acrylic bar is cut next to each screw. A periosteal elevator can then be used to crack the acrylic off the screw, allowing the screw to be removed. 9 The resulting skin wounds are allowed to heal by second intention. Removal of external fixation may not require general anesthesia, but sedation is usually necessary. SUMMARY
External fixation is an effective method for stabilization of many mandibular fractures. Thorough physical examination and patient stabilization should be instituted before attending to the fractures and associated soft tissue trauma. Normal occlusion rather than perfect reduction is the goal of oral fracture repair. Loose teeth or teeth in the fracture should be removed, as should any avascular bone fragments. Soft tissue wounds should be treated as for any contaminated wound. Mucosal wounds are allowed to heal by second intention. Although prophylactic perioperative antibiotics are indicated, they are usually not needed postoperatively. The three basic types of external fixators described include the Kirschner-Ehmer splint, pins or screws and acrylic, and the biphase splint. All three types are relatively easy to apply, and the principles of their application are similar. A minimum of two pins or screws are placed percutaneously in each fragment, avoiding the mandibular canal. The Kirschner-Ehmer splint is more easily adjustable than the biphase splint or the pin-acrylic splint, which use acrylic connecting bars. The advantages of fixators that use acrylic bars are that the pins or screws need not all be in the same plane and that they are more lightweight than the Kirschner-Ehmer splint. The disadvantages of the biphase splint are its increased expense and its use being limited to larger dogs. External fixators are well tolerated by the animals, and postoperative care is minimal. Mandibular fractures
FRACTURES OF THE MANDIBLE AND MAXILLA
119
are usually healed in 3 to 5 weeks, and the fixators can be removed with the animal under sedation.
References JP, Hollingsworth SC: Primary treatment of severe fractures by external skeletal fixation: Threaded pins compared with smooth pins. J Am Anim Hosp Assoc 22:659-670, 1986 Bennet RA, Egger EL, Histand M, et al: Comparison of the strength and holding power of 4 pin designs for use with half pin (type I) external skeletal fixation. Vet Surg 16:207-211, 1987 Bone DL: Maxillary fractures. In Bojrab MJ (ed): Current Techniques in Small Animal Surgery, ed 3. Philadelphia, Lea & Febiger, 1990, pp 883-890 Brinker WO, Piermattei DL, Flo GL: Handbook of Small Animal Orthopedics and Fracture Treatment, ed 2. Philadelphia, WB Saunders, 1990, pp 230-243 Chambers IN: Principles of management of mandibular fractures in the dog and cat. J Vet Orthop 2:26-36, 1981 Cooper MD, Roger CL, Rosenfeld PA, et al: Management of mandibular fractures using biphasic pins and mandibular splints. Laryngoscope 92:1042-1048, 1982 Crow DT, Downs MO: Pharyngostomy complications in dogs and cats and recommended technical modifications: Experimental and clinical investigations. J Am Anim Hosp Assoc 22:493-503, 1986 Egger EL: Management of mandibular fractures with acrylic-pin external fixation splints. In Proceedings 15th Annual Veterinary Orthopedic Society Meeting, Breckenridge, CO, 1988, P 6 Greenwood KM, Creagh GB: Bi-phase external skeletal splint fixation of mandibular fractures in dogs. Vet Surg 9:128-134, 1980 Nunamaker DM: Fractures and dislocations of the mandible. In Newton CD, Nunamaker DM (eds): Textbook of Small Animal Orthopaedics. Philadelphia, JB Lippincott, 1985, pp 297-305 Phillips IR: A survey of bone fractures in the dog and cat. J Small Anim Pract 20:661674,1979 Pope ER: Oral trauma-orthopedic considerations. ACVS 18th Ann Vet Surg Forum:389-391, 1990 Ross DL: Evaluation of oral abnormalities. In Proceedings American Animal Hospital Association 45th Annual Meeting, Salt Lake City, UT 1978, pp 79-83 Schrader SC: Dental orthopedics. In Bojrab MJ, Tholen M (eds): Small Animal Oral Medicine and Surgery. Philadelphia, Lea & Febiger, 1990, pp 241-264 Stambaugh JE, Nunamaker DM: External skeletal fixation of comminuted maxillary fractures in dogs. Vet Surg 11:72-76, 1982 Umphlet RC, Johnson AL: Mandibular fractures in the cat A retrospective study. Vet Surg 17:333-337, 1988 Umphlet RC, Johnson AL: Mandibular fractures in the dog. A retrospective study of 157 cases (abstr.). In Proceedings 16th Annual Veterinary Orthopedic Society Meeting, Park City, UT, 1989, P 37 Weigel JP: Trauma to oral structures. In Harvey CE (ed): Veterinary Dentistry. Philadelphia, WB Saunders, 1985, pp 140-155 Weigel JP, Dorn AS, Chase DC, et al: The use of the biphase external fixation splint for repair of canine mandibular fractures. J Am Anim Hosp Assoc 17:547-554, 1981
1. Aron DN, Toombs
2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
Address reprint requests to Jacqueline R. Davidson, DVM, MS Surgical Referral Service, Ltd Veterinary Specialty Clinic 1105 Milwaukee Avenue Riverwoods, IL 60015
