CHAPTER 17
FRACTURES OF THE SKULL
CHARLES D. NEWTON
- Surgical Anatomy
Premaxilla Fractures
Maxillary Fractures
Fractures of thr Hard Palate
Fracture of the Zygomatic Arch
Cranial Fractures
Fracture of the Occipital Condyle
Prior to the discovery of Roentgen, skull fractures in dogs and cats were treated conservatively. While radiography probably could have aided early veterinarians in arriving at a definitive diagnosis, the technique of "wait and see," manifested as bandaging of the head and maxilla for fractures, was the treatment of choice.
Of greater importance in the treatment of skull fractures was the advent of sterile technique and the application of human neurosurgical techniques to dogs. In 1938, Dandy and Reichert(7,8) demonstrated surgical approaches to the skull and craniotomy techniques in the dog. Although their intent was the development of an animal model of hypophysectomy, it marked the beginning of major extracranial and intracranial surgery in the dog.
In 1946, Burr(4) reported the use of a leather muzzle to treat multiple maxillary fractures in a fox terrier, representing perhaps the first such case in veterinary literature. Since that time the literature has been greatly expanded by major contributors such as Hoerlein(16) and Oliver,(20,21)who extensively described cranial and intracranial surgical techniques in the dog.
SURGICAL ANATOMY
Before contemplating the management of any type of skull fracture or interpreting the radiographs of a skull, the surgeon must be knowledgeable about its anatomy.(9,13,19) While most long bones are relatively simple to study and prominences and foramina are remembered easily, the skull is far more complex. The skull of the dog and cat is a complicated structure (Fig. 17-1) formed by fourteen paired and seven unpaired bones (Figs. 17-2 through 17-4). These interlock via undulating fissure lines to form maxilla or domed portion of the nose, palate (ventral horizontal plate beneath the nasal cavity), and the domed calvarium, which protects the brain. Through these 35 major separate bones run over 40 major foramina, through which course the cranial nerves, major arteries, veins, and lymphatics. A thorough knowledge of the location of these structures or review of anatomy is necessary for radiographic interpretation or surgical management.(9) Seemingly innocuous fractures that course through the foramina of major nerves can easily result in occlusive callus and subsequent neural dysfunction. Such fractures will greatly affect the prognosis of fracture repair.
When dealing with the skull, specifically the calvarium, an understanding of the anatomy of the brain and meninges is crucial. Because cranial fractures often depress and injure these structures, familiarity with the major venous sinuses of the meninges and the anatomical location of cerebral cortical functions is imperative. One anatomical variation of note is the large, dome-shaped skull usually associated with open frontanelles, which characterizes hydrocephalus (Fig. 17-5), accompanied by a thin radiographic appearance of the calvarium.(24) The open sutures must not be mistaken for fracture lines. The age and breed of the animal, plus a slow progressive history of dullness and cerebral dysfunction, simplify differentiation from acute fracture.
SURGICAL APPROACHES
APPROACH TO THE PREMAXILLA, MAXILLA, AND HARD PALATE
The premaxilla, maxilla, and hard palate can be exposed surgically by direct incision over the affected area. The incision must reflect knowledge of the normal location of nerves, arteries, and veins exiting the infraorbital foramina. Careful surgical dissection will expose the area of fracture. Fractures of the premaxilla or maxilla involving fractures of alveolae can be approached more directly via gum incision through the buccal surface.
APPROACHES TO THE CALVARIUM
The most descriptive calvarial approaches are described by Oliver.(20,21) Lateral or bilateral exposure of the dorsal calvarium can be made by a dorsal midline incision over the skull. After incision of the superficial temporal fossa, the temporalis muscle can be elevated and moved ventrally to expose the calvarium. Further retraction allows for complete visualization of the entire parietal bone, the caudal portion of the frontal bone, and the dorsal edge of the temporal bone.
Surgical approach to the occipital bones is accomplished via a dorsal midline incision extending from midcalvarium to midcervical spine or a transverse incision over the nuchal crest(22) After appropriate subcutaneous dissection, the rhomboideus muscle, splenius muscle, and other neck muscles attaching to the caudal aspect of the occipital bone are incised, leaving sufficient tendon for suturing at the end of the operation. Other deeper neck muscles are elevated from the occipital bones with a periosteal elevator. This allows exposure of the entire occipital surface of the skull, the foramen magnum, and dorsal edge of the occipital condyles.(12)
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FIG. 17-1 (A) A dog skull. (B) A cat skull. |
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FIG. 17-2 Bones of the skull, lateral aspect. (Zygomatic arch and mandible removed). (Evans HE, Christensen GC: Miller's Anatomy of the Dog, pp 113-161. Philadelphia, WB Saunders, 1979) |
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FIG. 17-3 Bones of the skull, dorsal aspect. (Evans HE, Christensen GC: Miller's Anatomy of the Dog, pp 113-161. Philadelphia, WB Saunders, 1979) |
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FIG. 17-4 Bones of the skull, ventral aspect. (Evans HE, Christensen GC: Miller's Anatomy of the Dog, pp 11:3 161. Philadelphia, 1979) |
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FIG. 17-5 Lateral radiograph of the skull demonstrates open fontanelles in a dog with hydrocephalus. |
CLASSIFICATION OF FRACTURE TYPES
PREMAXILLARY FRACTURES
Premaxillary fractures may be unilateral or bilateral, may involve any number of incisors, and usually result from direct trauma. Complications include tooth impaction, tooth and alveolar avulsions, and fracture of the entire premaxillary region.
At presentation, dogs demonstrate epistaxis, bleeding from the oral cavity, and oral dysfunction. Many animals will not exhibit a great deal of discomfort. The diagnosis is easily made by palpation and oral inspection; however, radiography will better delineate the extent of the injury (Fig 17-6, A).
It is common for the oral mucosa to be torn in association with this fracture; damage to or hemorrhage from the nasal mucosa or turbinates should also be expected.
Reduction consists of general anesthesia and careful manipulation of fracture fragments back into anatomical alignment. Alignment is ensured by checking occlusion to the lower arcade. If alveolar walls have been avulsed by individual teeth, they generally cannot be repaired and the teeth are extracted. Larger fragments, once reduced, are poorly immobilized if only closed techniques are used.
The best results are accomplished with surgical fixation by wiring major fragments together with orthopaedic wire, wiring teeth back to firmly anchored teeth, or pinning the premaxilla or fragments into alignment with Kirschner wires (Fig. 17-6, B and C). Pinning can be very difficult owing to fragment size and the presence of tooth roots.
Postoperative management must include either a period of muzzling or a diet of soft food until union occurs. Chewing of hard objects, including food, can cause fixation failure, If immobilization is adequate, the prognosis for success and return to normal function is very good.
Common complications result from inadequate fixation, early chewing, or loss of teeth. Infection of the bony fragments may also result in gradual Iysis of the entire body fragment or at least of teeth as a result of alveolar infection and subsequent loosening.
Similar fractures occur to the premaxilla and maxilla, resulting in a bone fragment containing the canine tooth and one or more incisors. Their clinical presentation and methods of management mimic those previously mentioned for premaxillary fractures. There is one advantage: the canine tooth and associated avulsed bone permit better fixation. Closed methods of fixation using acrylic templates can be employed to hold the canine tooth in alignment by anchoring it to the opposite canine tooth.(23) Similarly, orthopaedic wire between the two canine teeth will firmly anchor the bony fragment. The use of ancillary wire sutures or Kirschner wires may give added stability. This fracture, because of its large fragments and more stable fixation, rarely requires additional muzzling during healing. Attendant soft tissue tears of mucosa should be sutured to lessen the likelihood of food impacting into the fracture site.
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FIG. 17-6 Radiographs of the maxilla of a dog demonstrate fracture of the premaxilla (A). (B, C) The fracture after fixation with pins and wire. |
MAXILLARY FRACTURES
Maxillary fractures include any fracture affecting the maxillary bone or nasal bones. While the fractures can be simple fissures, they are more often multiple fractures; fracture fragments may remain in alignment or may be depressed. Individual teeth or groups of teeth may avulse as separate fractures or in association with multiple maxillary and nasal bone fractures.
At presentation, most animals demonstrate epistaxis, swelling over the maxillary region, or deformity of the entire head and nasal region. Palpation will reveal crepitus beneath the skin. Although radiographs are helpful, there may be such a large number of fracture lines that no definitive assessment can be made. Owing to the amount of trauma that usually causes these fractures, accompanying complications such as eye trauma, cerebral trauma resulting in depression, or frontal sinus fracture resulting in subcutaneous emphysema may occur. Coughing or choking on blood from damaged mucosa can also be expected.
Reduction of a simple maxillary fracture is rarely necessary, since single fissures generally remain in alignment. Multiple fractures may be so severely fragmented that anatomical reduction is impossible. In the latter instance, it is common to mold the bones into a cosmetic shape without opening the skin. Open reduction of multiple fractures rarely allows one to achieve better alignment and may result in loss of blood supply to individual bony fragments and subsequent sequestration. Severely depressed maxillary fragments must be opened for reduction and subsequent fragment elevation. Single or multiple tooth avulsion can be reduced as previously described without open reduction.
METHODS OF CLOSED REDUCTION
Simple fractures heal without fixation. If alignment of the dental arcades is in question or if the maxillary region is so unstable that it is painful, the mouth should be muzzled to prevent fragment motion and subsequent pain to the animal.
Half-pin fixation is an excellent method of closed fixation. Under general anesthesia, multiple small Kirschner wires are placed into as many fragments as possible. Following adequate alignment of fragments, the pins are attached to one another for solid fixation. Plaster of Paris '5 can be used, but my experience indicates a higher success rate using dental or hoof acrylic (Fig. 17-7).
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FIG. 17-7 An oblique radiograph of a young Great Dane shows multiple fractures of the maxilla and hard palate, with a fracture of a rostral mandible and a vertical ramus fracture on the same side (A). The vertical ramus fracture was reduced and stabilized using two small Steinmann pins (B,C). The rostral mandibular fracture was treated with a plate and screws and the maxillary fracture was treated with external skeletal fixation using Kirschner wires and an acrylic bridge around the perimeter connecting the pins together. (Stambaugh JE, Nunamaker DM: External skeletal fixation of comminuted maxillary fractures in dogs. Vet Surg 2:72- 76, 1982) |
METHODS OF OPEN REDUCTION AND FIXATION
Open reduction and fixation usually requires a minimum amount of metal; therefore, single sutures of orthopaedic wire to fasten bony fragments are sufficient. In the rare instance in which a severely depressed fragment will not remain in alignment, tiny properly contoured plates can be used to elevate and secure the fragment in place.(18) This usually results in better cosmetic result than leaving a deeply depressed area in the dog's maxilla. Other methods of placing multiple screws into fragments and then lacing them together with orthopaedic wire have been used successfully. In instances in which comminution is severe and fragments must be discarded, the resulting cosmetic defect may be corrected by covering the defect with silicone sheeting or stainless steel gauze.
Single or multiple tooth avulsions are repaired as previously discussed, using small Kirschner wires or orthopaedic wire sutures. Intraoral acrylic splints connecting teeth from the left to right side have been described as successful, while wiring from the left to right side over the palate accomplishes the same end result and requires less equipment.
Postoperatively, most dogs and cats require soft food; occasionally muzzling will lessen the discomfort of the fractures. Once fracture healing has been documented radiographically, external fixation, half-pin fixation, or external wires can be removed. For most animals with maxillary fracture, the prognosis of complete return to normal function is good. The cosmetic result may not always be perfect, however.
A common complication is loss of teeth or loosening of metal due to early and excessive chewing of hard objects. Severe maxillary fractures may result in loss of nasal turbinates or damage to the infraorbital nerve in the canal or where it exits the infraorbital foramen.
FRACTURES OF THE HARD PALATE
Palatine fractures may be the result of automobile trauma and may be found in association with maxillary fractures; however, the classic cause is the "high rise" syndrome in cats. These fractures result when cats jump or fall from a height and land on their forelimbs and chin. The hard palate will commonly fracture on its midline.
At presentation most animals appear relatively normal; they may or may not have epistaxis or blood on their tongue. Examination will reveal crepitus on palpation of the hard palate and usually a complete tear in the mucosa covering the palate. If the fracture is due to automobile trauma, the animal's eyes or cerebrum must be inspected carefully for trauma. One must be aware of the potential for fracture of the mandibular symphysis, forelimb trauma, or pneumothorax when examining cats who have fallen from heights.
Closed reduction can be accomplished in many fashions. One of the simplest methods is to wire the canine teeth together, left to right, and the fourth pre-molars together, left to right. This should result in complete alignment and fixation of the palatine fracture. The mucosa should be sutured over the repair. Another technique that is successful with cats is to wire the canine teeth together and make the orthopaedic wire to exit through the upper lips and tighten over the maxilla: this ensures good fixation. The wire over the maxilla should be in a rubber tube to prevent migration through the skin.
Open reduction and fixation can be accomplished by lacing the palatine halves together with wire sutures(25) This technique requires the drilling of many holes in each fragment, which is often difficult and time-consuming.
Fractures of the palate that do not affect the midline can be neglected, wired, or pinned into alignment or discarded. One must beware of discarding large pieces, since a hard object may penetrate the palate and cause development of an oral nasal fistula. Such defects have been repaired using metal implants to occlude the opening.(5) Most animals do very well following palate fracture. If food impacts into the fracture, steps must be taken to avoid contamination or osteomyelitis. Occasionally, food will be forced into the nasal cavity through the palatine fracture and result in an acute or chronic nasal discharge.
FRACTURE OF THE ZYGOMATIC ARCH
The zygomatic arch is formed cranially by the zygomatic bone and caudally by the zygomatic process of the temporal bone. As a unit, they form the arch that gives lateral contour to the face. Cranially, the zygomatic arch contributes to the ventral and lateral rim of the orbit. Fracture in this region may result in damage to the eye or associated structures. The central arch passes lateral to the vertical ramus of the mandible and if fractured may depress into the mandible and alter mastication. The caudal extent of the arch contains the temporal component of the temporomandibular joint. Masticatory dysfunction can result from fracture.
Surgical exposure to the zygomatic arch is made by incision directly over the bone. Care must be taken to avoid the zygomaticotemporal and zygomaticofacial nerves, which course medial to the arch. Periosteal elevation should result in total exposure of the bone.
Examination of animals with fractures of the zygomatic arch reveals crepitus on palpation of the arch or obvious cosmetic deformity. Animals may have associated evidence of trauma to the eye or central nervous system or obvious discomfort when opening or closing the mouth. Radiographs will confirm the presence or absence of fracture.(11,26) Simple fractures rarely depress and result in deformity; multiple fractures routinely depress, however. In young animals, the zygomatic suture line may cause confusion.
Fracture reduction is rarely necessary unless fragments are sufficiently depressed to cause mastication problems or cosmetic deformity. Benign neglect is the accepted treatment.
Depressed fragments involving the orbit, midarea, or caudal region require surgical exposure and elevation. Usually, a periosteal elevator will facilitate reduction, and fixation can be accomplished using orthopaedic wire to secure fragments together. In extreme or rare cases of comminution or if cosmetic perfection is required, tiny plates may be used.
Most animals do not require special aftercare following open or closed fixation; bandaging is contraindicated, since it may depress the fragments. Complications may arise as a result of excessive callus formation. If the callus forms medially, it can result in bony union to the vertical ramus of the mandible or at least impingement sufficient to cause pain.(7) Fractures through or contiguous to the temporomandibular joint may result in degenerative joint disease or bony ankylosis. Should this complication occur, surgical resection of the excess bone is usually successful. If such treatment is unsuccessful and the callus reforms, the entire segment of affected zygomatic arch may be resected.
CRANIAL FRACTURES
The cranial bones form the dorsum of the skull and the encasement for the brain. The brain is encased primarily within the frontal bones, parietal bones, temporal bones, and occipital bones. While some of this encasement is extracranial, namely, the frontal sinus of the frontal bone, most lies directly over the brain. Such encasing bones are known collectively as the calvarium. The calvarium differs from other bones in its diploic construction. Diploic bone possesses two distinct cortices with an interstitial layer of honey-combed bone and vessels. This reinforcement gives added protection to the brain from trauma.
Anatomically palpable prominences can be found in skulls of well-muscled dogs. The dorsal sagittal crest runs cranial-caudal over the dorsum of the calvarium, and the nuchal crest runs mediallateral over the caudal edge of the skull. Although most brachycephalic dogs lack these prominences, they are present in most cats.
EXTRACRANIAL FRACTURES
Extracranial fractures involve bones of the brain case but are not penetrating fractures. Such fractures generally involve the nuchal or sagittal crest, the zygomatic process of the frontal bone, or the frontal sinus. Most of these fractures, by their proximity to the brain, will be associated with concussion; however, bony fragments never approach the brain. Dogs or cats may present with signs as minimal as skin bruising or contusion or as severe as unconsciousness, depending on the amount of trauma to the brain. (16,17) All efforts in examination should be directed toward a thorough evaluation of the central nervous system. The use of mannitol or cortisone may be necessary to prevent or lessen central edema.(6)
Fracture of the crests results in palpable crepitus and slight deformity. Fractures of the frontal sinus are more severe. If complete penetration occurs, the animal will appear with subcutaneous emphysema over the face and skull. Following a complete physical examination, the head should be wrapped in a compressive dressing until final disposition of the fractured sinus is determined.
Final disposition of extracranial fractures rarely requires surgery. Most fractures are seated firmly in place, eliminating the need for internal fixation. If fixation is needed to prevent avulsion by a muscle or for cosmetic reasons, orthopaedic wire sutures are sufficient.
The frontal sinus may require open fixation if major fragments have been depressed. They should be elevated and wired in place. If comminution is severe or elevation impossible, the defect may be covered with silicone sheeting or stainless steel gauze.(10) Most minor fractures of the frontal sinus heal spontaneously without surgery.
Complications associated with extracranial fracture usually relate to problems with the central nervous system. Although most fractures heal uneventfully, central nervous system complications may be severe or remain unrecognized.
INTRACRANIAL FRACTURES
Intracranial fractures involve the calvarium and potentially the brain. Fractures may be linear cracks, depressed bony fragments, or comminuted separate bony fragments; most intracranial fractures are closed fractures.(3,14,28)
An animal with an intracranial fracture will present with primary signs relating to the central nervous system. Thorough neurologic examination must precede a definitive fracture workup. Cerebral edema or the effects of concussion must be minimized before a more thorough radiographic evaluation.
Linear fractures are palpable only in poorly muscled animals or when the fracture line opening is severe. Diagnosis is made from radiographs (Fig. 17-8).(1,11) Assuming the linear fracture is not depressed or comminuted, no definitive treatment is needed. Supportive care, aimed specifically at the central nervous system, is of greater concern.
Depression fractures result when multiple linear fractures occur in a small area and the fragments depress into the brain (Fig. 17-9). Because of the underlying periosteum and the thick meninges, the undersurface is usually smooth. The signs at presentation do not relate to brain laceration or penetration but rather to concussion or the presence of a space-occupying mass. Care of the central nervous system is paramount. In instances of minor depressive fractures, surgical intervention is unnecessary. Where greater depression exists, the cerebral loss is extensive and the calvarium must be elevated.
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FIG. 17-8 Lateral radiograph of the skull of a dog demonstrates a linear fracture. |
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FIG. 17-9 Oblique radiograph of the skull of a dog demonstrates a depression fracture. |
It is difficult to lift a depressed area of the calvarium. A better approach is to push the fragments up from beneath (Fig. 17-10). To accomplish elevation, multiple large burr holes are drilled around the periphery of the lesion. A small, curved, blunt elevator may then be inserted through the holes, beneath the depressed area to elevate the bone fragments. Attempts to complete removal of the crushed area are difficult because lifting the edge of any fragment tends to further depress its opposite side. The result may be more severe than if left untreated.
Comminuted calvarial fractures are the most severe (Fig. 17-11). Sharp fragment edges can easily lacerate the meninges, venous sinuses, or the cerebral cortex. Such severely comminuted fractures should be approached surgically, and individual fragments should be removed. Despite cortical laceration, dogs and cats can recover if the fragments are removed to prevent further laceration. Large calvarial defects may result if the comminuted area is large. While the temporalis muscle is ample protection in most cases, onlay grafts of rib or iliac crest may be necessary in some animals.
As with all intracranial fractures, care of the central nervous system, prevention of edema, and, if the central nervous system is healthy, removal of hematoma, take precedence. The prognosis for repair of the cranial fracture is good.
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FIG. 17-10 Placement of burr holes adjacent to fracture fragments and elevation of fragments. (Redrawn after Oliver JE: Craniotomy, craniectomy and skull fractures. In Bojrab MJ (ed): Current Techniques in Small Animal Surgery, p 362. Philadelphia, Lea & Febiger, 1975) |
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FIG. 17-11 Lateral radiograph of the skull of a dog demonstrates a comminuted fracture. |
FRACTURE OF THE OCCIPITAL CONDYLE
The occipital condyles are very ventral on the occipital bone and lie on either side of the foramen magnum. They form the occipital half of the articulation of the atlas. In rare instances of severe head or neck trauma, fractures may occur through a condyle, or an entire condyle may fracture free of the occipital bone. The potential for severe brain stem laceration or vascular laceration and immediate death is great. If the lacerations are not severe, the presenting sign is cervical pain, similar to that in a dog with cervical disk disease. Physical examination will probably not assist in the diagnosis but will localize the problem to the cervical region.
Radiographs of the cervical spine, lateral and dorsoventral, will suggest fracture if displacement of a condyle is present. Open-mouth positioning to project the foramen magnum will be definitive in most instances.
Management should be conservative. I know of no adequate method of internal fixation, and surgical exposure is difficult. Most cases will heal uneventfully if the animal is placed in a cervical collar to provide support until union is complete. During the first 24 hours post-trauma, the dog must be continuously reexamined for signs referrable to brain stem injury.
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