Spinal Fracture or Luxation

COMMON NEUROLOGIC PROBLEMS

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SPINAL FRACTURE OR LUXATION Rodney S. Bagley, DVM

Spinal trauma is a common cause of spinal cord dysfunction in dogs and cats.U· 30• 44• 46• 50• 63 Spinal trauma can occur either from exogenous or endogenous spinal injury. Automobile-related injury (i.e., being hit by a car) is the most common exogenous cause of trauma to the spine in small animals; however, falls, trauma from falling objects, and projectile missile damage are also possible. Depending on the position of the animal, the type of force, the area of impact, and the inherent strengths and weaknesses of the vertebral column, exogenous spinal injury often results in vertebral fracture, subluxation, or luxation.B An understanding of these factors may aid in retrospective evaluation of the injury but is often not necessary for clinical management of animals with vertebral fractures. This article focuses on clinical management and treatment of small animals suffering exogenous spinal injury resulting in vertebral fracture or luxation. The major pathophysiologic changes that occur in the spinal cord have been previously reviewed. 3• 11• 30• 44. 46• 50• 63 The experimental literature pertaining to spinal trauma is voluminous and constantly evolving. Because the spinal cord is encircled by a rigid inelastic bony encasement (vertebrae) and because of the relatively soft texture of spinal parenchyma, any decrease in canal diameter may result in spinal cord injury. Mechanical injury to nervous tissue (especially axons) results in physiologic or morphologic disruption of nervous impulses. Ultimately, numerous pathophysiologic consequences may result, including ischemia, hemorrhage, alterations in spinal cord blood flow, and edema.3• 11• 30• 44• 46• 50• 63 These secondary events lead to a self-perpetuating process of damage

From the Department of Clinical Sciences, Washington State University, College of Veterinary Medicine, Pullman, Washington

VETERINARY CLINICS OF NORTH AMERICA: SMALL ANIMAL PRACTICE VOLUME 30 • NUMBER 1 • JANUARY 2000

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to the spinal cord that is often equally if not more detrimental to the spinal cord as the initial mechanical injury (second injury theory). 3' n 30, 44, 46, so, 63 Putative mediators of this self-perpetuating process include excitatory neurotransmitters, endorphins, catecholamines, and free radicals released after the initial insult. Current therapeutic efforts are directed at counterbalancing or neutralizing the effects of these byproducts of trauma. Based on this information, two considerations become paramount when treating a spinal fracture or luxation. One is to prevent further mechanical damage to the spinal cord. This is accomplished primarily by realigning and stabilizing the vertebral column. The second aspect of treating spinal injury is to stop or hinder the development of these secondary pathophysiologic events that perpetuate the magnitude of spinal damage. CLINICAL ASSESSMENT OF ANIMALS WITH SUSPECTED SPINAL TRAUMA

It is not uncommon for owners to have witnessed the animal being traumatized, and they may contact the veterinarian for advice prior to transporting the animal to the hospital. Owners should be advised to be cautious when dealing with traumatized animals as they can have severe pain and may become uncharacteristically aggressive. Placing the animal on a rigid movable surface such as a board is ideal. If a rigid surface is not available, placing the animal in a blanket or other sling-like apparatus can be used for moving the animal. Multiple persons to help with moving the animal may decrease the chance of additional injury to the animal during transport. On presentation to the hospital, an animal with suspected vertebral column instability should be immobilized as soon as possible after admission. It is important to obtain a rapid but complete history of the current problem. Information that may be significant includes whether or not the owner witnessed the traumatic event and the relevant circumstances such as how long ago the accident occurred and what movement the animal was capable of immediately after the trauma. For example, was the dog able to walk at some point? Has it been able to urinate on its own? Was the animal normal before the trauma? As spinal injury frequently occurs in association with multiple organ trauma, it is imperative to determine the presence of other life-threatening injuries as quickly as possible. The animal should be expeditiously evaluated and treated using basic emergency procedures. Specific assessments include respiratory and heart rate, heart rhythm, degree of peripheral perfusion (capillary refill times, coolness of limbs), ability to voluntarily move, and level of consciousness. The degree of general health may influence subsequent neurologic evaluations. If, for example, the animal is poorly responsive because of poor perfusion to the brain, assessments for deep pain recognition are difficult to accurately assess.

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If the animal is mentally alert but unable to move, immediate concerns should be directed toward the neurologic and musculoskeletal systems. Initial observations of posture can be helpful in determining if a neurologic abnormality exists. Schiff-Sherrington posture is characterized by thoracic limb extension with normal to sometimes decreased tone and reflexes in the pelvic limb. 18 This results from a lesion affecting the thoracolumbar spinal segments and interrupting the ascending inhibitory impulses from the border cells in the lumbar gray matter. These cell are present in the dorsolateral part of the ventral gray matter from L1 to L7, with a maximal population from L2 to L4. Axons from these cells cross to ascend in the contralateral fasciculus proprius of the lateral funiculus to terminate in the cervical intumescence. These border cells are responsible for tonic inhibition to extensor muscle alpha motor neurons in the cervical intumescence. This loss of ascending inhibition to the thoracic limbs results in extension. The thoracic limbs, however, are otherwise neurologically normal. Although Schiff-Sherrington posture is usually seen with severe spinal cord injuries, this posture alone does not indicate that the spinal lesion is irreversible. The presence or absence of deep pain sensation is a more important prognostic indicator. If the animal is calm and quiet, it should be further examined in the position it was in when admitted. Usually, this is a lateral or sternal recumbent position. If the animal is struggling to move, it should be immediately restrained. This can be accomplished by firmly taping the animal to a rigid back board or similar structure (Fig. 1). If thoracolumbar vertebral trauma is suspected, the animal can be secured w ith white

Figure 1. Dog shown immobilized by being taped to a back board.

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tape placed over the scapula and femoral trochanter regions. If cervical injury is suspected, the head should also be secured. Any rigid surface that is movable can be used to support the spine during manipulations and movement. A board 8 to 10 inches wide, 4 to 5 ft long, and 0.75 to 1 inch thick works well. Handles can be attached to make it easier to move the board from flat surfaces such as floors. It is also helpful to record the weight of the board directly on the board. With this information, an accurate body weight can then be recorded for the animal even after it has been immobilized. When a nervous system injury is suspected, a complete neurologic assessment is mandatory. This examination should allow one to determine the location of a lesion(s) and the severity of nervous tissue damage. Allowances must be made for the fact that these animals may have unstable vertebral fractures and it should be realized that the normal manipulations necessary for a complete neurologic examination may be detrimental. The examination and diagnostic sequence need to be modified to accommodate for a possible unstable vertebral segment and the immobilization method used. Observation of any voluntary movement is noted. It is important, however, to differentiate voluntary from reflex movements. Reflex movements often occur when the animal is touched or physically stimulated, whereas voluntary movements are made without external stimulation. Talking to the animal or calling its name may result in attempts by the animal to move the limbs or wag the tail. Until definitively proven, voluntary movement should be assumed to be absent. Cranial nerves, spinal reflexes (assessed on the uppermost limbs), spinal palpation for hyperesthesia, cutaneous trunci reflex, and assessment for deep pain can be performed with an animal in a lateral recumbent position. For evaluation of the opposite (down) side, a second backboard is used to "sandwich" the animal between, facilitating the flipping of the animal. The second backboard is placed on the uppermost side of the animal. These boards are firmly held together with the animal being trapped between them. If necessary, the boards can be secured together with tape. The animal and board configuration is then flipped over so that the board previously on the uppermost side of the animal is now below the animal. The animal can then be secured to this bottom board as previously described using a single board. It is important to determine the severity of neurologic injury, as this allows for establishment of a management strategy and a realistic prognosis for the owner. In our hospital, the severity of a spinal cord injury is graded using the following scale: Grading scale used at Washington State University to assess the degree of spinal injury. Least severely affected 10 Normal 8 Pain only 6 Paresis (walking) 5 Paresis (not walking)

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4 Plegia (urination, deep pain intact) 3 Plegia (urination absent, deep pain intact) 2 Plegia (deep pain absent < 48 hours) 1 Plegia (deep pain absent > 48 hours) 0 Myelomalacia Most severely affected General guidelines for management of spinal trauma often center around the severity of the injury. Animals that are less severely affected (pain only or mildly paretic) are more often managed without surgical intervention. Animals that are more severely neurologically impaired (nonambulatory paretic or paralyzed) are often evaluated for possible surgical stabilization. Animals that have no deep pain have a grave prognosis for retum to function. Animals that lose deep pain secondary to intervertebral disc disease and have decompressive surgery within 48 hours have approximately a 50% or greater chance of eventually walking. 1 In the author's experience, animals that have no deep pain after suffering spinal trauma have a less than 50% chance of recovery. If deep pain sensation following trauma is lost for 48 hours or longer prior to therapy, the chance of functional recovery is virtual nil. Additionally, if deep pain sensation is absent in an animal with 100% or greater displacement of the vertebral canal, the prognosis for walking is hopeless. Based on these initial neurologic parameters, if a vertebral injury is suspected, it is reasonable to take survey radiographs of the affected area prior to additional manipulation of the animal (Fig. 2). As some

Figure 2. Survey radiograph from a dog that was hit by a car and had no deep pain sensation in the pelvic limbs. There is greater than 100% displacement of the vertebral canal at L4-5 (arrows).

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fractures and subluxations can be subtle, good quality and w ell-positioned radiographs are usually most helpful (Fig. 3).12· 20 This may be accomplished with the animal awake and immobilized. Poor radiographic technique resulting in rotation of the spine (especially in the cervical area) can make an assessment for unstable and malaligned vertebral segments difficult. Sedation may be necessary to achieve accurate positioning for radiographs in some animals. This should not be

Figure 3. A, Lateral survey radiograph taken in an awake dog that was hit by a car and had cervical pain. B, Lateral survey radiograph from the same dog as in (A) under anesthesia. Note the significant amount of displacement of C2 compared with C1. Illustration continued on following page

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Figure 3 (Continued). C, Transverse computed tomographic (CT) image of the C1-2 joint space. Note the fracture of the cranioventral aspect of C2 (arrow). D, Lateral survey radiograph showing the surgical repair using cortical bone screws, Steinmann pins, and polymethylmethacrylate.

performed, however, if the examiner is unsure of the physical diagnosis, as sedation often influences the results of the neurologic examination. Additionally, sedation or anesthesia results in the loss of voluntary paraspinal muscle contraction, and unstable vertebral segments may be more likely to subluxate (see Fig. 3). Intuitively, survey radiographs provide a static record of the location of the vertebrae at the time of study; however, they do not allow for assessment of how extensive the displacement of the vertebrae was at the time of injury and prior to radiology. The neurologic assessment of the severity of spinal injury is most important in establishing the prognosis, in many instances, regardless of the radiographic features. As a

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result of the strong paraspinal musculature, vertebrae can be significantly displaced acutely at the time of injury but then subsequently pulled back into a more normal position. This is especially true with lumbar vertebral trauma in cats. Clinical signs in these animals appear worse than the radiographs would suggest. Disturbances to adjacent soft tissue such as paraspinal muscle disruption or hematoma may also be an additional radiographic clue to the site of injury. Serial radiographs may indicate instability; however, the degree of instability is often difficult to predict. A scheme has been devised for predicting spinal instability in human patients based on the degree of vertebral damage, which has been modified for use in animals. 49 In this model, the vertebrae are divided into three compartments. The ventral compartment is composed of the ventral longitudinal ligament and ventral portion of the annulus. The middle compartment includes the dorsal portion of the annulus, dorsal vertebral body, and dorsal longitudinal ligament. The dorsal compartment includes the articular facets and joint capsules, ligamentum flavum, vertebral arch and pedicle, and spinous processes and interspinous ligaments. Damage to two or more components would indicate the need for surgical stabilization. Myelography or other advanced imaging such as computed tomography (CT) or magnetic resonance (MR) imaging is needed to establish spinal compression and to ensure that additional lesions not seen on survey radiography are not present (Fig. 3 and 4). CT is helpful in determining abnormalities of bone that may not be apparent with survey radiography. Three-dimensional reconstruction from CT images may provide additional anatomic information regarding bone contour. MR imaging has the distinct advantage of showing information regarding intramedullary spinal disease. Bone detail is not as apparent on MR imaging as with CT. CORTICOSTEROID THERAPY

Prior to or during radiographic evaluation, and if the animal is not severely hypotensive, corticosteroids should be administered. Although medical treatments for spinal trauma are numerous, experimental studies in small animals have suggested that only soluble corticosteroids (methylprednisolone sodium succinate) given within 1 hour of the trauma are beneficial.6-lo, 23• 24, 29, 36, 37 A multicenter study in human beings also suggested that methylprednisolone sodium succinate given within the first 8 hours after spinal trauma was beneficial. 8 In this study, methylprednisolone sodium succinate was given at 30 mg/kg intravenously (IV) as a slow bolus and then at 5.4 mg/kg/h IV for the next 23 hours as a constant infusion in an attempt to keep a high level of this corticosteroid in the injured cord for a longer period. An abstracted report on the use of this same treatment regimen in dogs with intervertebral disk disease suggested a benefit but provided less objective data. 54 This protocol requires intensive monitoring for this 24-hour period. To

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Figure 4. A, Sagittal T2-weighted MR image from a dog with a fracture of L6 (arrow). B, Sagittal T2-weighted MR image from a dog with a fracture of T12 (arrow) .. P refers to "posterior. " used as a marker and taken from human positioning in the MR umt.

avoid continual monitoring, it has been suggested that the methylprednisolone sodium succinate be given as an initial bolus (time 0) at a dose of 30 mg/kg IV, with additional doses of 15 mg / kg IV given at 2 and 6 hours after the initial dose. An experimental study simulating ventral spinal trauma in dogs did not show significant benefit from the administration of methylprednisolone sodium succinate used in this way; however, the degree of spinal trauma produced may not have been severe enough to allow for separation of the treatment and control groups.15 The benefits of numerous other medical treatments for spinal trauma have either not been proved or are uncertain. 28• 29 All clinical studies must be viewed with some degree of skepticism, however, as the type and degree of injury in individual clinical cases vary, and rarely is there a control population. If methylprednisolone sodium succinate is given too quickly in an awake animal, vomiting often occurs. If the medication is given too rapidly with the animal under general anesthesia, hypoten-

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sion often is noted. Acute death has also been noted experimentally with bolus injections of methylprednisolone; however, this is rare in clinical practice. 35 For these reasons, it is advisable to administer the methylprednisolone sodium succinate IV over approximately 5 to 10 minutes. Other side effects of corticosteroid administration with spinal disease, primarily those involving the gastrointestinal tract, have been established. 21, 27, 38, 62

NONSURGICAL TREATMENT OF SPINAL TRAUMA

Treatments of spinal trauma can be separated into surgical and nonsurgical categories. In many instances, these modalities are combined. Whether to use either or both of these categories depends on numerous factors and is often heavily dependent on anecdotal experiences of the examiner and nonmedical factors such as owner finances. These factors make objective comparisons of the two treatment modalities difficult, as the populations of affected animals are different. Some studies have shown equal long-term outcomes for recovery from spinal trauma in nonsurgically treated patients. 14• 26• 39• 47 Regardless of the additional therapies administered, confinement is the initial mandatory treatment of any unstable vertebral problem. Cage confinement may be necessary for 4 to 6 weeks in animals with nonsurgically managed spinal fractures. External support bandages or casts have been used successfully by some. 43 The goals of external support are immobilization of the vertebral segments cranial and caudal to the damaged area. After the damaged area has been identified, a soft wrap is placed over the body above and below the injured segment. Cast padding covered by cling gauze and Vetrap (3-M Animal Care Products, St Paul, MN) works well. Next, a rigid external support is applied. A plaster or fiberglass cast molded to the shape of the spine can be used. The author has had good success using aluminum rods bent in a rectangular shape and contoured to the curvature of the spine (Fig. 5). The ends of the rectangular configuration can be bent outward and used as handles, which aids during manipulation, physical therapy, and support when walking. Additional handles can be fashioned with the bandage to serve the same purpose. The casting material or aluminum rods are secured to the soft wrap using bandage material. White porous tape works well for this purpose. If a cranial cervical fracture is present, the underlying bandage should be placed up over the head to the level of the eyes (see Fig. 5). Holes can be cut in the bandage to allow the ears to protrude normally. If an external support is applied after surgery, the bandage material immediately overlying the incision can be cut open and the incision monitored for problems. With lower lumbar and lumbosacral fractures, especially in male dogs, the penis or vulva must not be incorporated in the bandage. This may prevent securing the bandage effectively. To

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Figure 5. A, A dog with a T13 fracture that has had a external spinal splint applied. 8 , A dog with a C3 fracture that has had a external spinal splint applied.

prevent urination onto the b andage in male animals, a plastic shield cut from a used intravenous fluid bag or waterproof pads (Val-U-Sorb Underpad, Professional Medical Products, Greenwood, SC) can be secured to the bandage ventrally. If more protection from moisture d amage to the entire bandage is needed, a trash bag or suitable barrier can be placed over the bandage with the ends tucked into the ends of the bandage. The layers of bandage and covering material may result in an increase in the animal's body temperature, especially if the ambient environment is warm. Therefore, the animal's body temperature should be monitored often after placing the bandage to prevent overheating.

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SURGICAL TREATMENT OF SPINAL TRAUMA

Indications for surgical treatment of spinal trauma are numerous and often inconsistent among clinicians. Some authors suggest that similar results are obtained with both surgical and nonsurgical treatments for spinal fracture, irrespective of the severity of clinical signs14' 26' 47; however, improvements in diagnosis and surgical techniques may affect these outcomes. Additionally, surgical treatments are often used in more severely affected animals, lending an inherent bias to previous reports in which comparisons have been made. Also, the surgeon's experience with spinal fracture fixation and management is an important variable that is difficult to quantify. Therefore, the role of surgery for spinal trauma is somewhat unclear. Historical indications for surgical treatment include spinal instability and spinal cord compression. If radiographs show damage of two or more components of the spine, stabilization is indicated. External fixation with splints and bandages may be helpful if applied correctly. Internal fixation and stabilization, however, are often necessary. A variety of techniques have been used and have been previously reviewed.4, 5, 13, 22, 33, 34, 41, 48, 5o, 5I-s3, 56, 58, 6~ Each technique has advantages and disadvantages, with the success of each depending on the surgeon's experience with that particular technique. In our hospital, internal fixation using a combination of bone screws, Kirschner wires, Steinmann pins, and polymethylmethacrylate (PMMA) cement is most often chosen for stabilization (Figs. 3 and 6). 2' 4, 5, 19, 22, 48, 55, 65, 66 Screws and pins are used to anchor the PMMA to the bone. Similar fixation devices have been shown to provide adequate protection against excessive spinal rotation in canine cadaver spine preparations. Rigid spinal fixation increases the chances of fracture healing in canine spinesY Although stiffer implants may result in more bypassed bone mineral loss initially (6-12 weeks) during healing, ultimate bone mineral density becomes equal at 24 weeks. The principles of vertebral screw placement have been reviewed. 31 Preventing disruption to as much normal bone and joint space as possible and increasing the amount of bone contacted with the screw are important considerations. In dogs and cats, screws are usually placed in the vertebral bodies because of the relatively larger amount of bone present there. Screws holes are directed from a dorsolateral to ventromedial direction in the vertebral body to increase the amount of bone contacted. To avoid entering the spinal canal, the screws should enter the vertebral body no more dorsally than the accessory processes and directly ventrally. In the lumbar area, a screw can safely be placed at the level where the transverse process connects with the vertebral body and then directed ventrally. In the thoracic area, ventral exposure is more difficult to achieve without entering the thoracic cavity. Here, screw holes are drilled in a more dorsal to ventral direction as compared to a lateral to medial direction. To allow room for drilling, muscles over the unstable vertebral

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Figure 6. A, Postoperative ventrodorsal radiographs showing repair of a T12-13 fracture/ luxation in a dog. The fracture has been stabilized using cortical bone screws, Steinmann pins, and polymethylmethacrylate. 8 , Postoperative ventrodorsal radiographs showing repair of an L7 fracture/luxation in a dog. The fracture has been stabilized using cortical bone screws, K-wires, Steinmann pins, and polymethylmethacrylate.

segments are retracted bilaterally. This should be performed cautiously, however, as excessive removal of paraspinal ligaments may result in increased instability. Because the orientation of the screw holes often results in drilling the screw holes on a slanted part of the vertebra, it may be necessary to make a small divot in the bone with a bone curette (House curette) or burr to allow firm drill purchase. Because of the angulation of the drill, the bit may be placed close to and possibly entwine the overlying musculature. To avoid damage to this tissue by the drill bit, an aluminum suture packet can be used to cover the underlying musculature during drilling. Drilling screw holes with a drill bit does not appear to decrease pullout strength or cause weaker fixation.31 Tapping of the holes prior to screw insertion, however, may weaken fixation strength because of the significant amount of associated cancellous bone in vertebrae.31 The screw hole is drilled through the vertebral body to the ventral cortical level. Often, the drill hole extends ventrally through the ventral cortical surface of the vertebral body. This cortical surface should be penetrated cautiously to avoid damage to structures such as the aorta.

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Screws should be directed away from the intervertebral disk area to avoid damage to exiting nerves. The screw size chosen depends on the size of the vertebrae to be fused. One study has suggested that cortical bone screw and PMMA fixation may have a greater failure rate than similar fixation with Steinmann pins and PMMA. 22 Cortical screws have bent at the screw-bone interface during experimental manipulations of isolated canine spinal cadaver preparations. We and others, however, have not encountered this situation clinically when cortical bone screws and PMMA are used to fix spinal fractures. 48 This is most likely a result of the associated paraspinal ligament and muscular support in the intact animal, the additional apparatus incorporated in the fixation, and the failure of the intact spinal segments to undergo the excessive forces used experimentally. Advantages to the use of bone screws over Steinmann pins for spinal fixation include ease of placement and possibly more secure anchoring of the vertebral bone and PMMA. Increased resistance to Steinmann pin placement is encountered at the vertebral endplate. This may increase pin wobble during placement, possibly contributing to pin loosening. Predrilling of the pin path with a smaller pin may decrease this pin wobble. An attempt should be made to realign the vertebral segments. Knowledge of normal vertebral and spinal anatomy is important so as to recognize when more normal alignment is achieved. Alignment should be performed cautiously and slowly, providing time for overcoming muscle contracture. Lamina spreaders are useful to distract collapsed vertebral segments. If it is difficult to get purchase on the vertebrae because of their smooth contour, the bone screws are placed prior to realignment. The lamina spreader can then be purchased on the bone screws, and the manipulations can be performed. Manipulations may also be aided by neuromuscular blockage during anesthesia. Excessive and coarse spinal manipulation should be avoided, as additional spinal cord damage can result. Instrumentation that can be placed strategically to create forces that counterbalance the forces keeping the vertebrae in malalignment can be beneficial during surgical realignment of vertebral displacement. This is especially true for fractures in the lumbosacral area. The body of L7 generally is displaced dorsocaudally relative to the lumbosacral intervertebral disk space, and the lumbosacral articular facets are luxated. Therefore, elevation of the sacrum or depression of L7 is necessary to anatomically reduce the fracture. As the L-shaped end of the Senn retractor is blunt, it can be slipped further under the sacral arch without damaging the underlying cauda equina. 25 This is important to avoid slippage as the fracture is reduced. Additionally, the tip of the retractor is bent upward, which further limits slippage. The relatively thin shaft of the Senn retractor does not obstruct the placement of implants (e.g., screws or wires), which is helpful, because the fracture must be held in reduction during the stabilization procedure. A final benefit of the retractor is the flat surface that lies over the dorsal lamina of L7. The handle of the retractor can be moved cranially to

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rotate the vertebral body into position if necessary. The width of the blade is 6 mm. This width may be too large to be inserted between L7 and Sl in small dogs unless the dorsal intervertebral space is enlarged via a dorsal laminectomy prior to placement of the retractor. The use of the lamina spreader to distract the vertebrae after realignment with the Senn retractor results in more appropriate anatomic reduction. Once reasonable alignment is achieved, and if at least one pair of articular facets remains intact, a small Kirschner wire can be driven across the facets to maintain alignment during subsequent screw placement. Screws are placed on either side of the fracture site in the vertebral bodies or articular facets. These screws are incorporated with PMMA either in a "donut-shaped" or bilateral "cigar-shaped" configuration. Bone wax is placed within the screw heads to prevent plugging with PMMA. This becomes important if the screws need to be removed at a future date. The area should be lavaged with saline during the time that the PMMA is curing, as this process creates heat that could damage adjacent tissues. This is most critical when a laminectomy has been performed, as heat damage to the spinal cord is possible even if Gelfoam (Pharmacia & Upjohn Company, Kalamazoo, MI) is placed over the laminectomy defect. The PMMA is formed to encompass the metal apparatus without damaging exiting peripheral nerves. If it is necessary to form the PMMA close to the laminectomy defect, the spinal cord can be covered using an aluminum suture packet which encloses many varieties of suture material. After initial curing of the cement, the packet can be removed, as the cement does not bond to this substance. If additional implant rigidity is required, Steinmann pins can be placed in a longitudinal fashion along the spinous processes. These pins can be bent to approximate the angulation of the vertebral column and wired to the implanted screws to secure them in place. PMMA is placed over these pins and screws as described previously. Any wires used should be totally encased with PMMA to increase wire strength. 19 Small Kirschner wires can also be placed perpendicularly through the spinous processes and incorporated into the fixation. Decompression is indicated if myelography indicates spinal cord compression as a result of intervertebral disk rupture or hematoma. Often with fractures and luxations, spinal compression is the result of bony instability, and realignment of the spine is all that is needed. Removing additional bone from the damaged area during laminectomy may decrease stability and make internal fixation more difficult. Removal of the articular facets and diskectomy significantly increase rotational instability in canine cadaver spinal preparations. 49, 65 A hemilaminectomy is preferable if decompression is needed, as this results in the least amount of instability of all decompressive procedures.57 If no compression is seen other than that occurring as a result of displaced vertebrae, it is preferable to realign the vertebrae and not to perform a laminectomy to preserve as much bone integrity as possible. Durotomy and myelotomy may also be indicated in severely affected animals to afford further decompression and to assess the severity of

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spinal cord damage. 29, 42, 61 Myelomalacia can be accurately assessed only after durotomy. POSTOPERATIVE MANAGEMENT

As spinal surgery is potentially associated with a significant amount of postoperative pain, opiate analgesics are commonly used to alleviate pain. Fentanyl, a synthetic opioid, is available in a dermal patch (Duragesic, Fentanyl Transdermal System; Janssen Pharmaceutica, Titusville, NJ), allowing a convenient way to manage postoperative pain for up to 72 hours. 45 Adequate blood levels may take up to 12 to 24 hours to be reached; therefore, initial pain management should be supplemented with injectable agents (morphine 0.3 mg/kg administered intramuscularly every 4 hours for first 12 hours at least). Patches are applied as soon as possible after the initial physical assessment. The patch is applied to the dorsal neck or rump area away from any possible surgical site. In order for the drug delivery system to make adequate contact with the skin, an area 3 sq in should be shaved prior to adhering the patch. An elevated body temperature may increase the amount of drug administered through the patch; thus, the animal should be checked for the presence of fever on a daily basis. Occasionally, an animal develops dermatitis at the patch site, necessitating removal of the patch and alternative pain therapy. If animals are recumbent for a time, special attention to prevent recumbency complications is necessary. 16, 40, 60 The recumbent animal should be turned at least every 1 to 4 hours to prevent decubital ulcers from developing on bony protuberances such as hips or shoulders. 58 Extra padding under the dog with foam rubber or thick fleece material is necessary. Small soft-sided waterbeds are helpful in preventing bed sores. Frequent turning is also important in preventing atelectasis, which may lead to pneumonia. Ideally, the animal should be kept in a sternal or sternal oblique position to allow for chest expansion. The recumbent animal is often unable to move itself from an area it has soiled. Absorbent waterproof pads such as the Val-U-Sorb Underpad can be useful in soaking up urine and preventing the saturation of bedding material with urine or feces. Frequent bathing may be necessary to prevent urine scald. This may be accomplished during hydrotherapy. Long-term recumbency can lead to limb edema and muscle atrophy. Massage of the affected limbs and other forms of physical therapy can prevent or help to treat these complications. It is important to encourage the recumbent animal to begin walking again. To prevent slipping, a textured nonslip surface such as concrete or soil is helpful for this exercise. When the dog has deficits in its rear limbs only (paraparesis), it can be supported by a number of simple methods. The dog can be grasped by the base of the tail (when minimal support is needed) or supported by a towel under the abdomen and assisted to walk. Commercially made supports (Walkabout; Santa Cruz,

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CA) can be helpful and are available in a wide variety of sizes. These devices can be used on both the thoracic and pelvic limbs to provide a sling effect. Because of possible binding in the axial and groin areas, these should not be used for extended walking exercises. For the animal that is reluctant to walk or has deficits in all four limbs a supportive sling, preferably on wheels, may be necessary. Although not practical in all hospital settings, hydrotherapy can also be an effective method of physical therapy. Swimming provides a buoyant environment for the animal to attempt movement of its limbs without having to support its full weight. The warm water also promotes adequate circulation and muscle relaxation. A nonslip surface such as a cage mat should be placed on the bottom of the tub or deep sink. Sterile petrolatum ointment should be applied over the surgical incision. Rarely are wound complications such as infection noted if clean water is used at each therapy. The water can be filled to a depth that provides enough support for the animal to attempt to stand on its own and encourages the animal to swim. An animal should never be left unattended in water. The therapist should keep his or her hands on the animal at all times to prevent slipping or attempts at jumping out. A variety of children's flotation devices can be helpful in supporting the animal in the water. 16 These range from simple inflatable toys available from a local discount or department store to specially adapted canine life vests which can be purchased from water-ski or diving equipment stores. Another popular toy that can be found near pool accessories is a long foam-rubber tube. This can be useful as a support under the abdomen of a swimming dog, and several of these can also be assembled into a raft-like device to support a heavy or tetraparetic animal. The animal's ability to urinate following spinal trauma is another important factor in determining the prognosis for recovery and quality of life. Inability to control bladder function can have a greater influence on the dog's quality of life than the return of limb function. Assessing the animal's bladder function both prior to and following spinal surgery is crucial. The presence or absence of urine on the animal's bedding or in the cage, voluntary or involuntary urination, and the ease or difficulty with which the bladder is expressed should be determined. The bladder should be gently palpated regularly (at least every 6 hours and more frequently in animals that are polyuric) to determine the volume of urine it contains and to establish whether or not the animal is fully emptying its bladder each time it urinates. Urine left in the bladder because of inadequate bladder emptying can lead to cystitis. Manual expression may be necessary every 6 hours if the animal is not able to urinate on its own. FOLLOW-UP MANAGEMENT If the animal has been managed nonsurgically, follow-up evaluations can be scheduled as necessary based on clinical course. It is ideal

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to evaluate animals at 3 and 6 weeks after injury to critically assess neurologic progress. If an external support bandage has been applied, more frequent evaluations may be performed to provide an opportunity to change soiled bandages. Radiographic assessment of fracture healing may also be used to determine when cage confinement or external support can be terminated. If healing is suspected to be complete, a gradual return to exercise should be initiated. Short leash-controlled walks are begun (10-15 minutes, 1-3 times per day for the first 1-2 weeks) on flat surfaces with good footing, and the animal is monitored for any pain or decline in neurologic status. If leash walks are tolerated, the duration and number of walks during the day can be increased over the next 2 to 4 weeks. If the animal tolerates this exercise, it may have free activity after this time, provided that the activity area is enclosed (e.g., fenced yard) and there is good footing. The animal that has had surgical fixation is treated similarly. Appropriate wound management is undertaken for the first 2 weeks. If clinical improvement is noted, the aforementioned exercise scheme can be followed. Radiographs can be taken at least 6 weeks after surgery to assess the alignment, surgical implants, and fracture healing but are not consistently needed unless complications arise. Postoperative infection of implants can result in systemic illness or draining tracts in the area of the surgery. If infection is present but localized, appropriate antibiotics are prescribed until fracture healing is thought to be complete. In human patients, deep wound infections after spinal instrumentation are treated with local debridement, intravenous and oral antibiotics, and insertion of an antibiotic-containing irrigation-suction system with maintenance of the instrumentation within the infected wound. 32 If, however, the wound remains despite aggressive local and systemic treatment, the fixation apparatus can be removed surgically after the fracture has healed and definitive cultures have been taken of the surgical area. If screws have been implanted, a high-speed air drill is used to remove the PMMA from over the screw heads. A screwdriver is used to back out the screws. Once the screws are removed, the PMMA can usually be removed easily. If pins have been incorporated in the fixation device, the air drill is used to remove the PMMA over the pins, and these can then be removed with pliers or a similar device. If healing occurs normally and the apparatus does not become infected, it may remain in the animal indefinitely.

References 1. Anderson SM, Lippincott CL, Gill PJ: Hemilaminectomy in dogs without deep pain perception. California Veterinarian 45:24, 1991 2. Benzel EC, Baldwin NG: Crossed-screw fixation of the unstable thoracic and lumbar spine. J Neurosurg 82:11, 1995 3. Berg RJ, Rucker NC: Pathophysiology and medical management of acute spinal cord injury. Compend Contin Educ Pract Vet 7:646, 1985

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4. Blass CE, Seim HB III: Spinal fixation in dogs using Steinmann pins and methylmethacrylate. Vet Surg 13:203, 1984 5. Blass CE, Waldron DR, van Ee RT: Cervical stabilization in three dogs using Steinmann pins and methylmethacrylate. J Am Anim Hosp Assoc 24:61, 1988 6. Bracken MB, Holford TR: Effects of timing of methylprednisolone or naloxone administration on recovery of segmental and long-tract neurological function in NASCIS 2. J Neurosurg 79:500, 1993 7. Bracken MB, Shepard MJ, Collins WF Jr, et a!: Methylprednisolone or naloxone treatment after acute spinal cord injury: 1-year follow-up data. J Neurosurg 76:23, 1992 8. Bracken MB, Shepard MJ, Collins WF, et a!: A randomized controlled study of methylprednisolone or naloxone in the treatment of acute spinal-cord injury. N Eng! J Med 322:1045, 1990 9. Braughler JM, Hall ED: Lactate and pyruvate metabolism in injured cat spinal cord before and after a single large intravenous dose of methylprednisolone. J Neurosurg 59:256, 1983 10. Braughler JM, Hall ED: Uptake and elimination of methylprednisolone from contused cat spinal cord following intravenous injection of the sodium succinate ester. J Neurosurg 58:538, 1983 11. Braund KG, Shores A, Brawner WR: The etiology, pathology and pathophysiology of acute spinal trauma. Vet Med (Praha) 85:684, 1990 12. Brawner WR Jr, Braund KG, Shores A: Radiographic evaluation of dogs and cats with acute spinal cord trauma. Vet Med (Praha) 85:703, 1990 13. Broecker KA, Seim HB III: Spinal fractures and luxations. In Slatter D (ed): Textbook of Small Animal Surgery, ed 2. Philadelphia, WB Saunders, 1993, p 1110 14. Carberry CA, Flanders JA, Dietz AE, et a!: Nonsurgical management of thoracic and lumbar spinal fractures and fracture/luxations in the dog and cat: A review of 17 cases. J Am Anim Hosp Assoc 25:43, 1989 15. Coates JR Sorjonen DC Simpson ST, et a!: Clinicopathologic effects of a 21-aminosteroid compound (U74389G) and high-dose methylprednisolone on spinal cord function after simulated spinal cord trauma. Vet Surg 24:128, 1995 16. Connors RL, Bagley RS, Silver GM, et a!: Exogenous spinal trauma in dogs and cats: Recognition and management. Veterinary Technician 18:301, 1997 17. Craven TG, Carson WL, Asher MA, et a!: The effects of implant stiffness on the bypassed bone mineral density and facet fusion stiffness of the canine spine. Spine 19:1664, 1994 18. deLahanta A: Veterinary Neuroanatomy and Clinical Neurology, ed 2. Philadelphia, WB Saunders, 1983 19. Duff TA, Khan A, Corbett JE: Surgical stabilization of cervical fractures using methyl methacrylate. J Neurosurg 76:440, 1992 20. Feeney DA, Oliver JE: Blunt spinal trauma in the dog and cat: Insight into radiographic lesions. JAm Anim Hosp Assoc 16:885, 1980 21. Galandiuk S, Raque G, Appel S, et a!: The two-edged sword of large-dose steroids for spinal cord trauma. Ann Surg 218:419, 1993 22. Garcia JNP, Milthorpe BK, Russell D, et a!: Biomechanical study of canine spinal fixation using pins or bone screws with polymethacrylate. Vet Surg 23:322, 1994 23. Hall ED: The neuroprotective pharmacology of methylprednisolone. J Neurosurg 76:13, 1992 24. Hall ED, Braughler JM: Effects of intravenous methylprednisolone on spinal cord lipid peroxidation and (Na+ + K+)-ATPase activity. J Neurosurg 57:247, 1982 25. Harrington ML, Bagley RS: Realignment of a seventh lumbar vertebral fracture/ luxation using a Senn retractor in two puppies. J Am Anim Hosp Assoc 34:377, 1998 26. Hawthorne JC Blevins WE, Wallace LJ, et a!: Cervical vertebral fractures in 56 dogs: A retrospective study. JAm Anim Hosp Assoc 35:135, 1999 27. Hoerlein BF, Spano JS: Non-neurological complications following decompressive spinal cord surgery. Arch Am Coli Vet Surg 4:11, 1975 28. Hoerlein BF, Redding RW, Hoff EJ, et a!: Evaluation of dexamethasone, DMSO, mannitol and solcoseryl in acute spinal cord trauma. JAm Anim Hosp Assoc 19:216, 1983 29. Hoerlein BF, Redding RW, Hoff EJ, eta!: Evaluation of naloxone, crocetin, thyrotropin

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Address reprint requests to Rodney S. Bagley, DVM Department of Oinical Sciences Washington State University College of Veterinary Medicine Pullman, WA 99164-7060