Exogenous Spinal Trauma-surgical Therapy And Aftercare

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Vol. 22, No. 3 March 2000

Refereed Peer Review

FOCAL POINT ★ Surgical treatment of vertebral injury can help decrease spinal instability and realign spinal structures.

Exogenous Spinal Trauma: Surgical Therapy and Aftercare* Washington State University

KEY FACTS ■ Knowledge of normal vertebral anatomy is important before surgical repair of vertebral fractures or luxations is undertaken. ■ Cortical bone screws, pins, and polymethylmethacrylate are often useful as internal spinal fracture apparatus. ■ Decompression is indicated if myelography confirms spinal cord compression from intervertebral disk rupture or hematoma. ■ Because spinal injury and surgery are associated with considerable postoperative pain, opiate analgesics are commonly administered. ■ Several simple but effective methods of physical therapy can be used for patients recovering from spinal surgery.

Rodney S. Bagley, DVM Gena M. Silver, DVM, MS Rebecca L. Connors, LVT

Michael L. Harrington, DVM, MS Anthony J. Cambridge, BVMS Michael P. Moore, DVM, MS

ABSTRACT: Surgical treatment should be considered in animals with spinal cord instability and/or compression related to exogenous injury. This article reviews some techniques for manual reduction, internal fixation, and stabilization of spinal injuries and discusses such aftercare issues as pain control, complications associated with prolonged recumbency, and physical therapy.

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pinal trauma is a common cause of spinal cord dysfunction in dogs and cats. When the spine is subjected to exogenous injury, the impact often causes vertebral fracture or luxation. Because each spinal injury is unique, treatment guidelines need to be individualized. The indications for surgical treatment of spinal trauma are numerous but controversial. Some authors suggest that similar results are obtained with both surgical and nonsurgical treatment of spinal fractures, regardless of the severity.1,2 Intuitively, however, surgical stabilization of spinal instability seems reasonable when the chance of increasing instability is likely. No prospective case-controlled studies definitively show the best treatment for animals with spinal fracture or luxation. Surgical treatment, however, should be considered for animals with spinal cord instability and/or compression related to exogenous injury. Serial radiographs and cautious palpation may confirm instability. However, myelography or other advanced imaging (e.g., computed tomography, magnetic resonance imaging) may be needed to establish spinal cord compression or damage. Instability of a vertebral segment can be difficult to predict from a single radiograph. Thus a scheme for predicting spinal instability based on the degree of vertebral damage was devised for humans and adapted to dogs.3 In this model, the vertebrae are divided into three compartments: ventral, middle, and dorsal. The ventral (anterior) compartment is composed of the ventral vertebral body, ventral ligament, and anulus. The middle compartment includes the dorsal anu*A companion article entitled “Exogenous Spinal Trauma: Clinical Assessment and Initial Management” appeared in the December 1999 (Vol. 21, No. 12) issue of Compendium.

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lus, dorsal vertebral body, and dorsal longitudinal ligament; and the dorsal compartment includes the articular facets and joint capsules, ligamentum flavum, dorsal vertebral arch and pedicle, and dorsal spinous processes and interspinous ligaments. Damage to two or more components would indicate the need for surgical stabilization because the chance of clinically significant spinal instability is high.3 When instability is documented, external fixation with splints and bandages may be helpful if they are applied correctly.4 Internal fixation and stabilization, however, are often necessary. Various techniques have been reviewed in the literature5–17; each technique has advantages and disadvantages.

SURGICAL THERAPY Alignment and Reduction To begin spinal stabilization, the skin over the affected area is incised and the paraspinal muscles are removed from affected vertebrae. However, veterinarians are advised to use caution when removing muscle because the animal’s normal anatomy may have been disrupted by the trauma; removal of supporting muscle, tendons, and ligaments during surgery could aggravate existing vertebral instability. The vertebral segments should be aligned either before or after placement of screws or pins. More normal anatomic alignment can decrease compression of associated dura mater and nerve roots. Excessive spinal manipulation, however, should be avoided to minimize additional cord damage. Manual reduction of vertebral fractures can be difficult. Surgical tools can provide counterbalancing forces or torque to aid in realignment. Because most vertebral fractures are associated with collapsed vertebral segments, lamina spreaders are useful. By slowly increasing the degree of distraction of the vertebral segments, veterinarians can avoid some of the paraspinal muscle spasms and contracture that result in vertebral segment collapse. Manipulations may also be aided by neuromuscular blockage during anesthesia. If achieving a solid purchase point at the vertebrae on either side of the fracture becomes difficult, the lamina spreader can be positioned in previously placed screws or pins. The jaws of the lamina spreader should be positioned as close to the screw–bone interface as possible to minimize the potential of screws becoming loose when distraction force is applied. When the vertebral segments are distracted, they are easier to realign manually or using surgical instruments. Realignment is typically required for lumbosacral fractures. Because the body of L-7 is generally displaced in a dorsocaudal direction and the lumbosacral articular facets are luxated, elevation of the sacrum or depression

of L-7 is required to anatomically reduce the fracture. Reduction can be accomplished using the L-shaped end of a Senn retractor.18 The blade end of the retractor should be positioned in a caudal direction in the vertebral canal. The retractor shaft should then be pushed cranially and dorsally to elevate the sacrum and depress L-7. Use of a lamina spreader to distract the vertebrae after realignment with the Senn retractor may result in better anatomic reduction.

Internal Fixation and Stabilization After reasonable alignment of most vertebral segments is obtained 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. The articular facets should be positioned in as normal a configuration as possible to avoid fixation of the vertebral segments in a collapsed to excessively distracted position. Screws or pins should then be inserted on either side of the vertebrae and in vertebral bodies cranial and caudal to the fracture site. At Washington State University, internal fixation involves a combination of bone screws, Kirschner wires, Steinmann pins, and polymethylmethacrylate (PMMA) (Figures 1, 2, 3, and 4). The methods used to insert fixation devices are modifications of previously described techniques.19–23 Screws and pins can be used to anchor the PMMA to bone. Similar fixation devices have been shown to provide adequate protection against excessive spinal rotation in canine cadaver spine preparations.3,7,8 In dogs, rigid spinal fixation can improve the likelihood of the fracture healing.24 Whereas stiffer implants may initially (i.e., 6 to 12 weeks after reduction) result in more mineral loss, the ultimate bone mineral density equalizes 24 weeks after reduction. The principles of vertebral screw placement have been reviewed.25 Preventing disruption to as much normal bone and joint space as possible and increasing the amount of bone contact with the screws are important considerations. In dogs and cats, screws can usually be placed in the vertebral bodies because of the presence of relatively larger amounts of bone volume. Screw holes should be drilled from a dorsolateral to ventromedial direction at an approximate 45° to 60° angle to the dorsal sagittal plane into the vertebral body to increase the amount of contact with bone. To avoid entering the spinal canal, the screws should be placed no more dorsal than are the accessory processes. In the lumbar area, a screw can safely be placed in a ventral direction at the level where the transverse process connects with the vertebral body. In the thoracic area, ventral exposure may be more difficult to achieve without entering the thoracic cavity. Thus screw holes are usually drilled into the

MANUAL REDUCTION ■ LAMINA SPREADER ■ FIXATION DEVICES

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transverse processes in a more nerves. Screw size depends on dorsal to ventral rather than the amount of bone available lateral to medial direction. for screw placement. The bone at the articular and In the cervical area, screws dorsal spinous processes of the can similarly be placed in the vertebrae can be used for screw vertebral bodies using a venplacement. tral approach rather than dorTo allow room for drilling, sal or lateral approach (Figure muscles over the unstable ver4). The ventral convex surface tebral segments should be biof the cervical vertebrae can laterally retracted. However, reprovide an estimate of the potraction should be attempted sition of the underlying spinal cautiously because excessive record. Screw holes should inimoval of paraspinal ligament Figure 1A tially begin slightly lateral to and bone may exacerbate midline and angled more latspinal instability. The necessary erally to avoid iatrogenic penorientation of the screw holes etration of the spinal cord. often requires veterinarians to Because this angulation can drill on a slanted part of the damage paraspinal vascular vertebrae. Thus it may be helpstructures (e.g., the vertebral ful to make a small divot in the artery), brisk bleeding may bone using a bone curette occur when the drill bit is re(House curette) that accommoved. Bleeding can usually modates an initial drill purbe controlled by quickly tapchase. Because of the angle of ping and placing the screw the drill, the bit can be placed into the drill hole. Bone wax close to and possibly entwine placed at the interface of the Figure 1B overlying musculature. bone and screw can also minTo avoid tissue damage, an imize bleeding. For fractures aluminum suture packet can involving C1-2, the wings of be used to cover underlying C-1 can be used for screw musculature during drilling. purchase (Figure 4). Drilling screw holes with a Fixation using cortical drill bit does not evidently bone screws and PMMA decrease pullout strength or may fail more often than uscause weaker fixation.25 Taping Steinmann pins and ping screw holes before inPMMA.26 According to one study,26 cortical screws bent serting the screws, however, at the screw–bone interface may weaken the fixation beduring experimental manipcause of a substantial amount ulations of isolated canine of associated cancellous bone spinal cadaver preparations. in vertebrae.25 A screw hole should be Figure 1C We have, however, not endrilled through the vertebral Figure 1—(A) Preoperative lateral myelographic view of a dog countered this situation clinbody to the ventral cortical with a subluxation at L1-2. (B) Postoperative lateral radio- ically when using cortical level. The drill hole often ex- graphic view of the same area after surgical repair using corti- bone screws and PMMA to tends ventrally through the cal bone screws and polymethylmethacrylate. (C) Schematic fix in vivo spinal fractures. ventral cortical surface of the showing the approximate angle for placing a vertebral body Bending is most likely the screw in the lumbar spinal area. vertebral body. This cortical result of the associated parasurface should be penetrated spinal ligament and muscucautiously to avoid damage to underlying structures, lar support in the intact animal, additional apparatus such as the aorta. Screws should be directed away from incorporated in the fixation, and decreased likelihood the intervertebral disk area to avoid damage to exiting of intact spinal segments withstanding the excessive ORIENTATION OF SCREW HOLES ■ SCREW PLACEMENT ■ SCREW–BONE INTERFACE

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forces used experimentally. Rebe placed perpendicularly through gardless, pins may be used as althe dorsal spinous processes and ternatives to screws for obtaining incorporated into the fixation (Figpurchase into the vertebrae. ure 2). The advantages of using bone Decompression screws over Steinmann pins for Decompression is indicated if spinal fixation include ease of myelography confirms spinal cord placement and possibly more secompression from intervertebral cure anchoring of vertebral bone disk rupture or hematoma. With and PMMA. Increased resistance fractures and luxations, spinal comto Steinmann pin placement is pression often results from bony inencountered at the vertebral end stability, thus requiring realignment plate, which can cause the pins to and stabilization of the vertebrae. wobble during placement, possiAdditional bone removed from the bly contributing to pin loosening. damaged area during laminectomy Predrilling the pin path with a may increase the degree of instabilismaller pin can prevent this probty and make internal fixation more lem. difficult. Removal of the articular Bone screws can be incorporated facets and diskectomy have substanwith PMMA in either a donut- or tially increased spinal rotation instabilateral cigar-shaped configurability in canine cadaver spinal preption. Bone wax should be placed inarations.3,8 side the screw heads to prevent Figure 2A Of the decompressive procethem from being plugged with dures, hemilaminectomy is preferPMMA. This becomes important if able because it causes the least the screws need to be removed later. amount of instability.3,8 If no comThe area should be lavaged with pression other than that occurring saline while the PMMA is curing from displaced vertebrae is evident, because the heat that is generated we recommend realigning the vercould damage adjacent tissues. This tebrae and not performing a lamstep is most critical when a inectomy in order to preserve as laminectomy has been concurrently much bone integrity as possible. performed because of potential heat Durotomy and myelotomy may damage to the spinal cord. The also be indicated in severely affectPMMA should be formed to ened animals to afford further decompass the metal apparatus withcompression and to assess the seout damaging exiting peripheral verity of spinal cord damage.28–30 nerves. If it is necessary to form the Figure 2B PMMA close to the laminectomy Figure 2—(A) Postoperative ventrodorsal radio- Myelomalacia can be accurately defect, the spinal cord can be cov- graphic view of a dog showing a repaired spinal assessed only after durotomy. ered with an aluminum suture fracture/luxation using cortical bone screws, packet. After the cement has cured, Kirschner wires, Steinmann pins, and polymethyl- AFTERCARE the packet can be removed. methacrylate. (B) Schematic showing the place- Pain Control Because spinal injury and surIf additional implant rigidity is ment of vertebral body screws and connecting required, Steinmann pins can be Steinmann pins on either side of a lumbar fracture. gery are associated with considerable postoperative pain, opiate analplaced dorsally in a longitudinal gesics are commonly administered. fashion along the dorsal spinous Although some veterinarians may prefer administering processes (Figure 2). These pins can be bent to approxiNSAIDs either alone or in conjunction with opiate mate the angle of the vertebral column and wired to the analgesics, NSAIDs and corticosteroids administered implanted screws to secure them in place. PMMA concurrently can increase the risk of gastrointestinal ulshould be put on the pins and screws as described preceration. Fentanyl, a synthetic opioid, is available in a viously. Any wires should be totally encased with PMMA dermal patch that conveniently manages postoperative to increase wire strength.27 Small Kirschner wires can also BONE SCREWS ■ STEINMANN PINS ■ SPINAL COMPRESSION

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pain for up to 72 hours. Because 12 to 24 hours may be required to reach adequate blood levels of fentanyl, initial pain management can be supplemented with injectable agents (e.g., 0.3 mg/kg of intramuscular morphine every 4 hours for at least the first 12 hours). After shaving a 3-square-inch area, the Figure 3A fentanyl patch should be applied to the dorsal neck or rump area away from the surgical site. Because an elevated body temperature may increase the amount of drug administered through the patch, patients should be checked daily for fevers. If a patient develops dermatitis at the patch site, the patch should be removed and alternative Figure 3B pain therapy initiated.

can effectively prevent limb edema and muscle atrophy and improve general circulation to the limbs. Passive range-of-motion exercises (e.g., extending and flexing each joint in the thoracic and pelvic limbs) can also thwart joint stiffness, edema, and muscle atrophy. It can also be helpful to mimic an exaggerated walking motion by moving limbs in a circular fashion. These exercises should be done daily for 10 to 20 minutes.

Support Devices During recovery, patients should be encouraged to begin walking, preferably on a textured, nonslip surface such as concrete or soil. Several techniques and support devices can be used for patients Figure 3—(A) Preoperative lateral radiographic view of a dog with paraparesis. For examwith a fracture of L-6. (B) Postoperative lateral radiographic ple, dogs can be grasped by Recumbency view of the same area after surgical repair using cortical bone the base of the tail or supComplications To prevent complications screws, Kirschner wires, Steinmann pins, and polymethyl- ported by placing a towel unassociated with prolonged re- methacrylate. der the abdomen. Commercumbency, special attention cial support devices are also should be given to patients following spinal trauma or available in a variety of sizes. These devices can be used surgery.31,32 Recumbent patients should be turned every 1 on both thoracic and pelvic limbs to provide stability; to 4 hours to prevent decubital ulcers from developing however, because they can bind the axial and groin areas, on bony protuberances (e.g., the hips or shoulders).3 Exsupport devices should not be used for extended walking tra padding of foam rubber or thick fleece and small exercises. For patients that are reluctant to walk or have soft-sided waterbeds may also help prevent the developtetraparesis, a supportive sling, preferably on wheels, may ment of bed sores. Frequent turning also prevents atelecbe required. tasis, which can lead to pneumonia. Ideally, these paWe do not encourage using specially manufactured tients should remain in a sternal or sternal oblique carts that support the pelvic limbs and rump of animals position to allow chest expansion. recovering from spinal trauma unless the prognosis for Because recumbent animals are often unable to avoid return to function is hopeless. If an animal is confined soiling their bedding, absorbent waterproof pads can be to a cart, it becomes less motivated to exercise the pelused to soak up urine and prevent urine or fecal saturavic limbs. However, after sufficient recovery time has passed tion of bedding material. Frequent bathing, preferably (at least 1 month), a custom-sized cart may benefit the during hydrotherapy, may be needed to protect patients quality of life of animals that are unable to regain limb from urine scald. function. Physical Therapy Massage and Passive Exercise Several simple, effective methods of physical therapy that do not require expensive equipment can be used for postsurgical spinal patients.32,34 For example, massages

Hydrotherapy Although not practical in all hospital settings, hydrotherapy can be effective. Swimming provides a buoyant environment that allows patients to move their limbs without supporting their full weight. Warm water also

PAIN MANAGEMENT ■ PROLONGED RECUMBENCY ■ POSTSURGICAL EXERCISE

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promotes adequate circulaurinating. Because retained tion and muscle relaxation. urine can lead to cystitis, A nonslip surface (e.g., a cage manual expression may be mat) should be placed on the necessary every 6 hours if bottom of the tub or deep the animal cannot urinate sink. Although wound infecon its own. tions rarely occur if clean waThe color and smell of ter is used, sterile petrolatum urine should be evaluated at ointment should be applied each voiding. Urinalysis using over the surgical incision. The a urine dipstick and sediment tub or sink should be suffievaluation should be done ciently filled to support the daily to detect any infection animal while it attempts to Figure 4A and appropriate cultures substand or swim. An animal mitted if pyuria, bacteriuria, should never be left unattendor hematuria is noted. ed while it is in water. The If expression is difficult, therapist should keep his or the bladder can be drained her hands on the animal at all using a sterile urinary cathetimes to prevent slipping or atter. Indwelling urinary cathtempts to jump out. eters are not recommended Various flotation devices, because they increase the risk ranging from simple inflatof bladder infection.35 Depending on the nature of the able children’s toys available at neurologic lesion and the department stores to specially cause of abnormal bladder adapted canine life vests sold function, several pharmacoat water ski or dive equiplogic agents that assist in bladment stores, can help support Figure 4B der management are availanimals in the water.32 Popular swim toys available from Figure 4—(A) Pre- and (B) postoperative lateral radiographs able. Phenoxybenzamine can pool accessory outlets include of a dog with a C-2 fracture. The fracture has been stabilized reduce the tone of the interusing cortical bone screws, Steinmann pins, and polymethyllong, foam rubber tubes. nal urethral sphincter, wheremethacrylate. These can be used to support as diazepam or dantrolene the abdomen of swimming can increase the tone. Detrudogs and can be assembled into raftlike devices that supsor contractility can be enhanced with administration of port heavy or tetraparetic animals. bethanechol. The actions of these agents, however, are highly specific; and veterinarians should pay strict attenBladder Management tion to labeled contraindications. An animal’s ability to urinate after spinal trauma is Animals unable to voluntarily urinate often require an important factor in determining the prognosis for continued hospitalization, although some owners are recovery and quality of life. Because an incontinent dog comfortable with at-home bladder management while sometimes presents overwhelming nursing care detheir pets are recovering from spinal surgery. Commumands for owners, inability to control bladder function nication between veterinarians and clients on the postmay affect an animal’s quality of life more than does operative care of animals with spinal trauma is critical the return of limb function. Thus assessing an animal’s to a successful outcome. bladder function both before and after spinal surgery is Follow-Up crucial. The presence or absence of urine on the aniAppropriate wound management should be followed mal’s bedding or in the cage, voluntary or involuntary until the skin at the surgical site has healed. When clinurination, and the ease or difficulty with which the ical improvement in limb function is noted, an exercise bladder can be expressed are important determinants. scheme can be initiated. Radiographs should be taken The bladder should be gently palpated regularly (i.e., at at least 6 weeks after surgery to assess alignment, surgileast every 6 hours and more frequently for animals cal implants, and fracture healing. Postoperative infecwith polyuria) to determine urine volume and establish tion of implants can result in systemic illness or the dewhether the animal is fully emptying its bladder when FLOTATION DEVICES ■ INCONTINENCE ■ MANUAL EXPRESSION

Small Animal/Exotics

The Rapid Publication Veterinary Research Quarterly

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velopment of draining tracts at or near the surgical site. If localized infection develops, appropriate antibiotics should be administered until fracture healing is complete. In humans, deep wound infections of the spine have been treated with local debridement, intravenous and oral antibiotics, and insertion of an antibiotic-containing irrigation–suction system without removing the surgical implants.36 If aggressive local and systemic treatment fail to resolve the infection, the fixation apparatus can be removed after the fracture has healed and definitive cultures of the surgical area have been taken. If screws have been implanted, the PMMA cement can be removed from the screw heads by using a high-speed air drill with a burr and then the screws removed using a screwdriver. The remaining PMMA cement can usually be cleared with ease. Similarly, if pins have been used for fixation, pliers or a similar tool can be used to remove the pins after the PMMA cement has been cleared from the pinheads. If healing occurs normally and the apparatus does not become infected, it may remain in animals indefinitely.

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About the Authors Drs. Bagley, Harrington, Silver, Cambridge, and Moore and Ms. Connors are associated with the Department of Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman, Washington. Drs. Bagley (Neurology and Internal Medicine), Harrington (Neurology), and Moore are Diplomates of the American College of Veterinary Internal Medicine. Dr. Silver is a neurology and neurosurgery resident. Dr. Cambridge is a resident in surgery. Ms. Connors is the neurology veterinary technician.

REFERENCES 1. Selcer RR, Bubb WJ, Walker TL: Management of vertebral column fractures in dogs and cats: 211 cases (1977–1985). JAVMA 198:1965–1968, 1991. 2. Carberry CA, Flanders JA, Dietz AE, et al: Nonsurgical management of thoracic and lumbar spinal fractures and fracture/luxations in the dog and cat: A review of 17 cases. JAAHA 25:43–54, 1989. 3. Shires PK, Waldron DR, Hedlund CS, et al: A biomechanical study of rotational instability in unaltered and surgically altered canine thoracolumbar vertebral motion units. Prog Vet Neurol 2:6–14, 1991. 4. Patterson RH, Smith GK: Back splinting for treatment of thoracic and lumbar fracture/luxation in the dog: Principles of application and case series. VCOT 5:179–187, 1992. 5. Matthiesen DT: Thoracolumbar spinal fracture/luxations: Surgical management. Compend Contin Educ Pract Vet 5(10):867–878, 1983.

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