small animal spinal disorders: diagnosis and surgery

Cervical disc disease is a frequent disorder of dogs.Small dogs are affected commonly, particularly thosewith chondrodystrophoid characteristics although thecondition can occur in any breed (Gage, 1975; Dallman

et al., 1992). Dachshunds, Beagles, Poodles, Spaniels,Shih Tzus, Pekingese and Chihuahuas are affectedmost often. Large-breed dogs also suffer from cervicaldisc disease, usually as part of the syndrome of cervicalspondylomyelopathy (see Chapter 11). Most small dogssuffer signs after 2 years of age, with a mean onset at 6 years (Goggin et al., 1970; Gage, 1975).

CLINICAL SIGNSThe predominant clinical sign is severe neck pain (7.1and Box 7.1), which may be acute or chronic (Fry et al., 1991; Smith et al., 1997). In making a diagnosis,it is usually adequate to palpate the spine and musclesof the neck rather than flex and extend the neck toconfirm pain (2.13). This is one of the few conditionsthat cause dogs to scream spontaneously. Often thepain is unremitting and not responsive to medicationalthough dogs with more marked neurological deficitsoften show less pain. Affected dogs may be reluctant toeat unless the food is raised off the floor.

Nerve root signature (pain on traction of the limb)is another frequent finding (Seim and Prata, 1982; Fry et al., 1991; Morgan et al., 1993). It may present as

Chapter

7

Clinical signs 93

Diagnosis 94Survey radiography 94CSF analysis 94Myelography 95CT and MRI 95

Treatment options 96Non-surgical treatment 96Surgical treatment 96Fenestration 96Ventral decompression 96Ventral decompression and fixation 97Dorsal decompression 98

Complications 98Intraoperative 98Early postoperative 99

Postoperative care 102

Prognosis 102

Cervical disc disease in cats 103

Key issues for future investigation 103

References 104

Procedures 106Approach to the ventral neck 106Fenestration 109Ventral decompression 111Ventral decompression with

distraction-stabilization 117Dorsal hemilaminectomy 119Dorsal laminectomy 120

Cervical disc disease

7.1 Dachshund with neck pain caused by a cervical disc extrusion. Note low head position and thoracic limb held up dueto root signature. The hunched posture can be mistaken forthoracolumbar pain; history and physical examinationdifferentiates the two.

an apparent orthopedic lameness but nerve root paincan usually be elicited by neck palpation or limb trac-tion. This sign usually indicates that more caudal discsare affected but can also be seen with C2/3 discs(Morgan et al., 1993). Neurological deficits may berestricted to one thoracic limb or the dog may show

hemiparesis, tetraparesis or even tetraplegia withhypoventilation (6.1, 7.11). Neurological deficits aremore common with lesions at C4/5 to C6/7 inclusive,while neck pain without deficits is more common withlesions at C2/3 and C3/4 (Lemarie et al., 2000). Thismay reflect the greater degree of space in the cranialvertebral canal compared to more caudally.

Most dogs have Hansen type I extrusions. Hansentype II herniations do occur, generally in larger breeddogs (7.56). The C2/3 disc is involved most frequently,with the incidence decreasing caudally (Seim and Prata,1982; Fry et al., 1991). Lesions at C6/7 are the leastcommon, with the exception of large-breed dogs as partof cervical spondylomyelopathy and also in Pekingese(Fry et al., 1991). The C7/T1 disc herniates occasionally(7.56). Intracranial lesions can cause neck pain on rareoccasions and should be considered under differentialdiagnosis (Coates and Dewey, 1998) (Box 7.2).

DIAGNOSISSurvey radiographyDiagnosis is based on the clinical signs described above.Survey radiographic features of chronic disc disease arecommon incidental findings in older dogs. Narrowingof the intervertebral space or dorsal displacement ofmineralized disc material is suggestive of disc extrusion(Morgan et al., 1993) (7.2). Discography may be usefulfor non-mineralized, lateral extrusions (Felts and Prata,1983; Wrigley and Reuter, 1984). Myelography oradvanced imaging is necessary for definitive diagnosis(Somerville et al., 2001).

CSF analysisAnalysis of CSF is useful to eliminate inflammatoryCNS disease. Results of CSF analysis may be abnormalin disc disease, but elevations of protein and cells areusually mild (Thomson et al., 1989). Conditions otherthan disc disease are more common in dogs less than 2 years old or in aged animals (Box 7.2).

Small Animal Spinal Disorders94

Box 7.1 Clinical signs of cervical disc disease

Neck pain

Spontaneous screaming

Low head carriage

Thoracic limb lameness or paresis

Thoracic limb nerve root signature

Hemiparesis

Tetraparesis

A B

7.2 A: Lateral myelogram from a 10-year-old Shih Tzu that presented withneck pain and no neurological deficits.There is a narrow intervertebral space at C5/6 with extruded, mineralized discmaterial and splitting of the ventralcontrast column at this level (4.234.25).B: Dorsoventral myelogram. Furtherimages from the same dog are shown in 7.3, 7.9 and 7.37.

Box 7.2 Differential diagnoses for neck pain

Schmorls node

Facet joint pain

Synovial cyst

Bicipital bursitis

Temporomandibular joint (TMJ) lesion or oropharyngeal pain

Otitis media

Cervical spondylomyelopathy

Atlantoaxial subluxation

Syringohydromyelia

Osteoporotic pathological fracture

Soft tissue tumor in the neck or bone tumor

Intracranial lesion

Mid-thoracic lesion, e.g. T5/6 discospondylitis

Thoracic lesion, e.g. pleuritic pain

Meningomyelitis

Polyarthritis

Polymyositis

Spinal cord hematoma or hemorrhage

MyelographyMyelography or advanced imaging is necessary to confirm the diagnosis and because multiple discs aresometimes involved. In some lateral or intraforaminalextrusions the myelogram is normal but oblique viewsmay reveal the offending disc (Felts and Prata, 1983).Oblique views are also useful in determining the sideon which an asymmetrical extrusion lies, although CTor MRI are better.

CT and MRIDepending on the scanner, CT is usually much faster to perform than myelography and is also more accuratefor surgical planning (Olby et al., 1999). When available,CT is the imaging modality of choice for chondro-dystrophoid dogs with suspected cervical disc disease(4.39B, 7.4, 7.5). The cross-sectional image helps the surgeon to plan the ventral slot and is also useful to identify lateralized or foraminal lesions (Hara et al., 1994;

Cervical disc disease 95

C3C4 C5

C6

A B

7.3 A: CT scan through C5/6 made after myelography (same dog as shown in 7.2). The connection between the discextrusion and the rest of the nucleuspulposus is seen clearly. B: T2-weighted,sagittal MRI to show a disc extrusion atC4/5 (transverse image, 4.44A). The C3/4and C5/6 discs are of relatively normalsignal intensity but C2/3 and especiallyC4/5 and C6/7 discs are degenerate withlow signal intensity (Sether et al., 1990;Levitski et al., 1999).

A B

7.4 A: Transverse CT and B: 3Dreconstruction of CT scan from a 5-year-old Lhasa Apso that had neckpain and was unable to walk. The scanrevealed a large mineralized extrusion atthe C4/5 disc space. The postoperativescan is shown in 7.5.

A B

7.5 A: Transverse and B: 3Dreconstruction of the post-surgical CTscan from the same dog as shown in 7.4. A ventral slot was performed,which permitted the surgeon to removethe majority of the extruded material.Note the small amount of residualmaterial present to one side of the slot(arrowhead and arrow). The width of thisslot is 39% of the vertebral body width.

Bagley et al., 1996) (7.6). The scanner can also be used toshow the exact location and extent of disc material on ascout image (4.39A). A heterogenous, hyperattenuating,extradural mass with loss of epidural fat is a characteristicfeature of a mineralized disc extrusion (Olby et al., 2000).If CT is not diagnostic it can be followed by a myelogramor a CT myelogram (Hara et al., 1994). For more infor-mation on performing and interpreting CT images in discdisease, see Chapter 4, page 5557. MRI may be betterthan CT, particularly when the disc material is not miner-alized, but scan times are usually longer and the cost ishigher (Levitski et al., 1999) (4.42, 4.44A, 7.3B).

TREATMENT OPTIONSTreatment may be non-surgical or surgical.

Non-surgical treatmentThis entails cage rest and use of anti-inflammatory medi-cations. It can be tried in any patient unless markedneurological deficits are present. Either non-steroidalanti-inflammatory drugs (NSAIDs), low-dose pred-nisolone, or narcotics may be used, sometimes com-bined with diazepam or methocarbamol (Tables 15.1,15.2). Acupuncture may also be of benefit (Janssens,1985). The catastrophic worsening of neurological sta-tus that can occur with medical treatment of thoraco-lumbar discs is rare with cervical disc disease. However,the neck pain in cervical disc disease seems to be lessresponsive to non-surgical treatment than does the painfrom thoracolumbar disc disease. Progression of signs orlack of response in 12 weeks indicates treatment fail-ure. A dog that is responding well to non-surgical treat-ment should be kept rested for at least 6 weeks after clinical signs have resolved. Recurrence of clinicalsigns after non-surgical treatment has been reported in over 30% of patients (Russell and Griffiths, 1968;Janssens, 1985). The role of chemonucleolysis is unclearand cervical discs must first be exposed surgically if thisprocedure is planned (Atilola et al., 1993).

Surgical treatmentIndications for surgical treatment include: Failure of non-surgical treatment. Unremitting pain. Severe or progressive neurological deficits.Ventral decompression is the preferred procedure. Itmay need to be combined with stabilization for caudaldisc extrusions. Dorsal or dorsolateral decompressionmay be required in extrusions that cannot be reachedvia ventral slot or if there is doubt about the diagnosis.

Fenestration (7.307.36)Although the value and desirability of fenestration hasbeen questioned (Fingeroth, 1989), it should preventfurther extrusion of disc material into the vertebral canaland so reduce the recurrence rate (Russell and Griffiths,1968). It also appears effective for dogs with discogenicpain (Morgan et al., 1993 (Algorithm 7.1)). It is usual tofenestrate the discs from C2/3 to C5/6 inclusive; C6/7is fenestrated if there is evidence of disease. Advantagesand disadvantages of fenestration compared to ventralslot decompression are shown in Table 7.1. Fenestrationis only recommended as a primary procedure for dogswith discogenic pain and as a prophylactic procedure incombination with ventral decompression. In small breeddogs that develop signs suggestive of Wobbler syn-drome, fenestration is probably contraindicated as itmay exacerbate bulging of the dorsal anulus (7.15A).

Ventral decompression (7.377.52)General indications for decompression include: Presence of neurological deficits. Spinal cord compression on neuroimaging. Failure of fenestration.

Removal of disc material by ventral slot decompres-sion provides the most rapid resolution of clinical signsand it is therefore the treatment of choice. Accurate


A B

7.6 Dog with severe neck pain and rootsignature but no neurological deficits.A: Transverse CT scan and B: 3Dreconstruction reveals disc materialwithin the intervertebral foramen atC5/6 (arrowheads). The disc materialwas removed using a blunt probe aftera standard ventral approach withelevation of the longus colli musclesfrom the ventral and lateral aspects ofthe anulus fibrosus. Fenestration wasalso performed. The dog was pain freewithin 2 days.

identification of the disc involved is an obvious prerequi-site. The width of the slot should be about one third thewidth of the vertebral body and certainly no more than50% (7.10, 7.16). These parameters are especiallyimportant for the C4/5 to C6/7 discs inclusive (Fitch et al., 2000; Lemarie et al., 2000). The inverted conetechnique can be used to improve access while minimiz-ing any potential instability (Goring et al., 1991) (7.50).

Postoperative fusion occurs in a proportion of dogsfollowing ventral decompression but how well maydepend on the width of the slot (11.12); narrow slotsare less likely to fuse than wide slots (Gilpin, 1976;Seim and Prata, 1982). If osseous fusion does occuracross the slot it can then predispose even small breeddogs to domino lesions, although probably to a lesserdegree than it does in large-breed dogs (Prata and Stoll,1973; Bagley et al., 1993) (7.14).

Ventral decompression and fixation (7.537.55)Postoperative instability or subluxation are importantpotential complications that can be prevented by fixation of the interspace at the time of ventral decom-pression (Fitch et al., 2000; Lemarie et al., 2000).Fixation is not usually necessary for cranial disc lesions(C2/3 and C3/4) but should be considered for caudallesions (C4/5C6/7) when the slot width is nearing50% of the vertebral body width (Lemarie et al., 2000)(7.10, 7.16). Fixation is probably not necessary forcaudal lesions if the slot dimensions are less than 50%of the vertebral body width. When subluxation doesoccur following ventral decompression the rescue technique of choice is distraction-stabilization. Severalmethods can be used for fixation after ventral slot (see also pages 118, 220). Cement plugs are very diffi-cult to use in small dogs (7.13, 7.54). Bone autografts


Neuroimaging

No spinal cordcompression

Tractionresponsive

(small dogs*)

Reassessdiagnosis

Tractionnon-responsive

Singlelesions

Dorsallaminectomy

Caudal discsC4/5 to C6/7

Cranial discsC2/3 to C3/4

Fenestratefor

discogenicpain

C7/T1 or verylateral extrusion Ventral

slot

Dorsolateralhemilaminectomy

or dorsallaminectomy

Ventral slot andstabilize if width

close to 50%

Distraction(7.55)

*less than 10 kg body weight

Multiplelesions

Algorithm 7.1 Surgical decision-making in cervical disc disease.

Fenestration Slot

Technically Easy Difficult

Accurate identification Not required Requiredof disc involved

Special equipment No Yesrequired

Potential for iatrogenic Unlikely Possibledamage

Removal of disc material No Yesfrom vertebral canal

Resolution of neck pain Slow in Usually within many dogs a few days

Table 7.1 Comparison of ventral fenestration and slot

from the ilium are effective but necessitate two surgi-cal approaches (Prata and Stoll, 1973). A more recentstudy preferred a bone allograft block placed in theinterspace without use of additional implants (Lemarieet al., 2000). Autografts give better radiographic fusionthan allografts but other factors such as graft site morbidity also affect final outcome in humans (Floydand Ohnmeiss, 2000). Whatever method is used, bonyfusion should be encouraged so that long-term fixationdoes not depend solely on the implant(s). The progno-sis is good for dogs that subluxate after a ventral slot provided that the site can be stabilized (Lemarie et al., 2000).

In general, adherence to the recommendation tolimit the width of the slot to near 33% is preferable tomanaging potential or subsequent complications.

Dorsal decompression (7.567.59)Dorsal laminectomy is much easier technically in smalldogs than large dogs and short-term morbidity is less ofa problem (Gill et al., 1996; De Risio et al., 2002).Dorsal laminectomy has been proposed as an alterna-tive to ventral decompression for small dogs but ventralslot has the advantage of permitting removal of discmaterial (Gill et al., 1996; Fitch et al., 2000). Dorsallaminectomy is therefore best reserved for lesions atC7/T1, where there is doubt regarding the diagnosis, orfor dogs with multiple lesions (7.15, 7.59).

Hemilaminectomy can be performed in the cervicalregion using a lateral approach but a dorsolateralapproach is easier (Lipsitz and Bailey, 1995) (7.567.58,12.1512.29). Hemilaminectomy is indicated wheredisc material is situated too laterally to access via ventralslot, for some lesions at C7/T1 (7.56), or if there is doubt about the diagnosis (Seim and Prata, 1982).Intraforaminal extrusions approached in this way orlaterally (Lipsity & Bailey, 1995) may occasionally beaccessible without entering the vertebral canal (Prataand Stoll, 1973; Felts and Prata, 1983) (7.6).

COMPLICATIONSIntraoperativeThe ventral surgical approach itself has few complica-tions unless the surgeon does not identify the midlinecorrectly and damages the vertebral artery. It is also pos-sible to damage vital structures such as the recurrentlaryngeal nerve (7.25, 7.54); the esophagus can be per-forated if mistaken for the longus colli muscle andpleura or other vital structures may be damaged at thelevel of the thoracic inlet (Funkquist and Svalastoga,1979). Spinal cord damage during fenestration can

occur if the intervertebral space is explored recklessly.Other technical errors can occur during fenestration,ventral decompression (7.7, 7.8), or implant placement(Box 7.3).

Hemorrhage can be problematical at various stages.Dorsal laminectomy can damage vessels in the epiduralspace, especially at the level of a foramen (Hurov,1979) (7.59, 11.51, 11.52). During a ventral approachthe longus colli muscles tend to bleed when removed


C5

C4

7.7 This dog presented with neck pain and no neurologicaldeficits. Myelography revealed a mineralized extrusion at theC4/5 space. A ventral slot was performed with fenestrationbetween C2/3 and C6/7 inclusive. There was considerablehemorrhage from the vertebral venous plexus and no discmaterial was retrieved from the vertebral canal. It was assumedthat the response would be at least equivalent to a fenestration;re-examination was scheduled in 2 weeks.

C5

C4

7.8 Two weeks after surgery the dog was tetraparetic andunable to stand. The ventral slot had been performed at thecorrect interspace; the cranial margin is just visible in the caudal portion of C4 (arrowhead). However, the degree of spinal cord compression is now worse than before. The slot was re-explored; it was noted to have been directed to one side. The slot was redirected to the midline and a large amount of disc material was removed; hemorrhage was minimal. The dog made a good recovery and was able to walk 2 weeks later.

from their insertion on the ventral process. Muscledissection should be restricted to the midline to avoidbleeding from the vertebral artery or its branches. Thevertebral arteries may also be damaged during removalof lateral or foraminal disc material from either a ven-tral or a lateral approach (Felts and Prata, 1983) (7.6).Bleeding from the bone during drilling can be con-trolled with bone wax. The vertebral venous plexus(7.43, 7.44, 11.29B) is damaged easily and hemor-rhage can be so severe that it is impossible to continueto explore the vertebral canal (7.7); it may occasionallyeven be fatal (Clark, 1986). Severe hemorrhage mayoccur in as many as one quarter of dogs undergoingventral slot, even without pre-existing coagulopathy(Smith et al., 1997). Concurrent use of aspirin or thepresence of any coagulopathy increases the risk (15.2).Steps recommended in case of severe venous plexushemorrhage are outlined in Table 7.2. Venous plexushemorrhage can lead on rare occasions to complicationsin the early postoperative period. Two dogs that hadvenous plexus hemorrhage during ventral decompres-sion developed acute, progressive tetraparesis within12 h. Both had large blood clots compressing the spinalcord but recovered well after evacuation combinedwith hemostasis using thrombin (Seim and Prata,1982) (Table 7.2).

Early postoperativeThese relate mainly to continued pain; neurologicaldeterioration (7.8); or respiratory complications (Box7.4). After fenestration neck pain can persist in a sig-nificant number of dogs and may take 12 months toresolve completely (Denny, 1978) (see Prognosis,page 102). Neurological deterioration after fenestra-tion can also occur, probably when incorrect fenestra-tion technique leads to disc material being forced intothe vertebral canal (Tomlinson, 1985).

After ventral slot decompression neck pain shouldimprove within a few days. Moderate or severe pain has been reported 3 days after surgery in up to 65% ofdogs although this could have been due to excessiveslot width in some of these dogs (Fitch et al., 2000).Persistence of severe pain beyond 72 h, or progressiveneurological deficits, warrant repeat imaging (Seim and


Box 7.3 Intraoperative complications

Iatrogenic injury

Cardiopulmonary arrest

Implant complications

Hemorrhage (7.7)

Disc extrusion due to fenestration

Ventral slot too wide (7.16)

Surgery performed at the wrong site

Redistribution of disc material

Inadequate decompression (7.8)

Box 7.4 Early postoperative complications

Residual or increased compression at the site (7.8)

Residual material within a foramen

Subluxation or instability at the surgical site (7.10, 7.16, 7.52)

Extradural hematoma

Implant complications (7.13, 7.54)

New extrusion at another site

Hyperflexion injury

Dyspnea (7.12)

Infection or sepsis

Vascular decompensation of spinal cord

Hypoventilation (6.1, 7.11)

Edema (7.12)

Seroma or hematoma of wound

Horners syndrome

Megaesophagus

Laryngeal paralysis

Aspiration

Pneumonia

Preoperative Intraoperative Postoperative

Evaluate for coagulopathy Place finger over the slot if severe Check for neurological deteriorationCross-match for high-risk patients Relieve retraction pressure on jugular veins

Plug slot with macerated muscle tissuePack slot with GelfoamOcclude plexus with direct pressure (11.29B)Avoid long-term continuous suction of hemorrhageIncrease fluid rate, consider plasma or blood product

Table 7.2 Hemorrhage from vertebral venous plexus

Prata, 1982; Smith et al., 1997). This may mean thatsome dogs are imaged unnecessarily (7.9) but will alsoidentify quickly any dogs that need further surgery.

Potential causes of severe postoperative pain areshown in Box 7.4. One common cause is when some ofthe disc material has simply been moved to a new loca-tion during attempts at retrieval, which sets up a newarea of irritation. A poorly executed slot is actually nobetter than a fenestration and can be worse (Chamberset al., 1986) (4.25, 7.8, 11.21).

Vertebral instability is another important cause ofpersistent pain after surgery and can occur if the slot is made too wide (Seim and Prata, 1982). Range ofmotion increases in cadaver spines by 3040% afterfenestration and by 66% after a ventral slot, even if the slot is only one third of the vertebral width (Macy

et al., 1999; Wolf and Roe, personal communication).Subluxation leads to severe pain or marked deteriora-tion in neurological status due to nerve root, meningealor spinal cord compression (7.10, 7.16, 7.52). Signsassociated with this usually occur within a week of sur-gery but can be delayed for up to 3 months (Lemarie et al., 2000). If subluxation does occur, the lesion shouldbe managed by distraction-stabilization, as for a trau-matic fracture or subluxation. It is likely that instabilityis under-recognized as a cause of continued pain after surgery (Macy et al., 1999; Fitch et al., 2000, Lemarieet al., 2000).

Infection at the surgical site may cause either inci-sional drainage or systemic signs (Chambers et al., 1982;Fry et al., 1991; Lipsitz and Bailey, 1995). It can occurfollowing dorsal or ventral decompression, especially if the dog becomes bacteremic for any reason (see page84). Discospondylitis (14.11) or even epidural abscessa-tion (14.14) may also develop.

Respiratory arrest during or after surgery has beenreported in several studies (Clark, 1986; Waters, 1989;Smith et al., 1997; Beal et al., 2001). This can be due toeither cardiopulmonary or neurological abnormalities(see Chapter 6, page 82). Some dogs develop moresevere neurological deficits following surgery so that


7.10 Ventrodorsal radiograph of a dog where subluxation hadoccurred following a very wide ventral slot (59%). The dog hadsevere neck pain for a week after surgery, which promptedrepeat radiography. Treatment by distraction-stabilization wasattempted but the dog died (7.16, 7.52).

A

B

R

R

7.9 Residual disc material does not always cause persistentpain. A: Preoperative 3D reconstruction of the CT myelogramshown in 7.3B. There is a large mass of mineralized material on the left side of the floor of the vertebral canal. B: 3Dreconstruction made immediately following surgery. A ventralslot has been performed but removal of disc material wassuboptimal. Despite this, the dog was almost pain free the dayafter surgery and was normal within a few days. The slot widthin this dog is approximately 38%.

they are unable to breathe spontaneously. In these ani-mals the only option is to put them on a mechanicalventilator. Ventilation should be considered once thepaCO2 exceeds 50 mmHg and the dog should either beventilated or euthanized on humane grounds if thepaCO2 is greater than 70 mmHg (7.11).

Swelling or edema in the ventral neck can also causeproblems after surgery (Fry et al., 1991; Smith et al.,1997) (7.12). Care with hemostasis and wound closurehelps to avoid this. Seroma is a particular risk after dor-sal decompression (15.34).

Technical problems may occur when trying to placeimplants in small dogs (7.13, 7.54). Other potential

complications include trauma during recovery (11.22);megaesophagus (15.40) and Horners syndrome(Boydell, 1995); seizures after myelography; urinarytract infection; diarrhea and sepsis (Fry et al., 1991).

Any dog that has undergone ventral decompres-sion in the past, or that has congenitally fused vertebrae,could go on to develop a domino lesion. The incidenceis much lower than in Wobbler syndrome but it doesoccur (Prata and Stoll, 1973; Bagley et al., 1996) (7.14).

The overall risks of serious complications or mor-tality with cervical surgery are higher than in thoraco-lumbar surgery. The highest mortality rate is for dogsthat are unable to walk prior to surgery, especially thosewith pre-existing disease. Nine of 37 such dogs (25%)in one study died or were euthanized. Causes of death


7.11 Some dogs only need to be ventilated for a day or two but others require ventilation for 12 weeks before they can beweaned off mechanical support (Beal et al., 2001) (6.1).

7.12 This dog shows profound swelling 2 days after a ventralslot; the base of the tongue was also affected. It caused thisdog no problems but can cause dysphagia or dyspnea in someanimals. Hot packing and anti-inflammatory medications areindicated (Jerram et al., 1997) (see page 357). The possibility ofinfection should be investigated.

A

B

C7

C7

7.13 Nine-year-old pug with chronic tetraparesis localizing toC6T2 spinal cord. A: There is severe spinal cord compressionat C5/6 and C6/7, which was reduced partially by traction.Cement plugs were placed at C5/6 and C6/7 using anchorholes in the end plates and the dog was put in a splint (Dixon et al., 1996) (11.39). B: It developed severe neck pain 5 days later; neurological status was unchanged. A myelogramshowed the lesion at C6/7 had improved but C5/6 was worse.Disc material could have extruded spontaneously, been forcedinto the canal during plug placement, or the distraction hadfailed. There was no evidence of cement in the canal. The dogwas euthanized; no necropsy was performed.

included cardiac arrest, pulmonary thromboembolismand respiratory dysfunction (Waters, 1989). Recumbentdogs are also at high risk of developing pneumonia, asare those that develop laryngeal paralysis (Prata andStoll, 1973; Lemarie et al., 2000) (see Chapter 15).Three of 52 dogs in another study died after ventraldecompression for cervical disc herniation: one fromuncontrollable venous plexus hemorrhage and twofrom acute bradycardia and hypotension (Clark, 1986).Two of these dogs presented with only neck pain.Dysrhythmias are common during cervical disc surgery.They were reported in 15 of 48 dogs (31%), two ofwhich died, emphasizing the importance of good anes-thetic monitoring (Stauffer et al., 1988). Hypotensionis also common during ventral decompression and mayinfluence outcome (Griffiths, 1973; Cybulski, 1988;Smith et al., 1997) (see page 86).

In summary, a high index of suspicion for complica-tions must be maintained if the surgery does not go asplanned, if the response to surgery is poor and certainlyif the animals neurological status worsens after surgery(7.7). In such cases, repeat imaging is strongly recom-mended (7.77.9).

POSTOPERATIVE CARE (see Chapter 15)Most patients should be much less painful within a dayor two of ventral slot surgery. Two weeks of restrictedexercise should be enforced, even if improvement hasbeen marked. Leash exercise for urination and defeca-tion is allowed, but a harness should be used ratherthan a collar. If discomfort persists, anti-inflammatorydrugs may be needed (Table 15.2) along withdiazepam, methocarbamol, ultrasound (15.13B), laser(15.14A), or acupuncture. Severe pain beyond 48 hwarrants repeat imaging (see Complications, page 99).

Dogs with preoperative neurological deficits benefitfrom physiotherapy once the pain has subsided. Large-breed dogs are prone to problems related to recumbency,

and strict attention to bedding and cleanliness isrequired (see Chapter 15).

PROGNOSISResolution of clinical signs may be slow after fenestra-tion. Of 12 dogs with neck pain, six recovered rapidlybut five continued to have intermittent pain for 14weeks. Of a further 16 dogs with thoracic limb paresis,12 (75%) recovered in an average of 38 weeks. Ofnine with severe deficits (tetraparesis or tetraplegia),five (56%) recovered in 16 weeks (Denny, 1978).Fenestration has been compared to ventral slot decom-pression in 111 dogs that were able to walk prior tosurgery. Intraoperative and postoperative complications,other than simple incisional swelling, were more com-mon after ventral decompression (30% vs 12%), resultingin longer hospital stays (7.12). However, neurologicalrecovery was slower following fenestration. Fenestrateddogs were three times more likely to have static signs at discharge and twice as likely to be unchanged at their last hospital visit (Fry et al., 1991). Ventral slot decom-pression gives much better results overall (Table 7.3).This is probably because even dogs with no neuro-logical deficits usually have substantial amounts of disc material in the vertebral canal.

The prognosis for dogs with pain or moderate neurological deficits is usually good after a ventral slot(Table 7.3). The prognosis for dogs that cannot walk ismore guarded. Complete recoveries are reported in5560% of such dogs, a further 1520% recover withresidual deficits and 2025% die or are euthanized.Dogs that do not walk within 2 weeks are likely to continue to have residual deficits (Waters, 1989; Smithet al., 1997). Others have reported better recoveryrates for severely affected dogs (Seim and Prata, 1982).

The outcome after ventral slot decompression insmall-breed dogs appears to be better for dogs with cranial cervical lesions (C2/3 or C3/4) than for those


A B

T1

T1

7.14 A: Eight-year-old Silky terrier(5 kg) with a disc extrusion at C5/6. A ventral slot was performed and the dog made a good recovery. B: Eighteen months later the dogshowed recurrence of neck pain, rootsignature, mild tetraparesis and ataxia.A repeat myelogram revealed noresidual compression at C5/6 butextrusion of disc material at C4/5 andC6/7. Note the fusion at C5/6 (7.53,7.54).

with caudal cervical lesions (C4/5C6/7 inclusive)(Waters, 1989; Fitch et al., 2000). Long-term resolu-tion of signs after ventral slot decompression was seenin 31 of 47 dogs with cranial lesions (66%) compared toonly 10 of 48 with caudal lesions (21%). The poor outcome for dogs with caudal lesions undergoing a ventral slot contrasts with the long-term resolutionseen in 12 of 15 dogs (80%) that were also stabilizedand distracted intraoperatively at the ventral slot site(Fitch et al., 2000).

One of the main reasons for failure to improve, or forrecurrence of signs after ventral slot decompression, ispostoperative instability or subluxation. These prob-lems have only been reported in dogs with caudallesions (Seim and Prata, 1982; Wheeler and Sharp,1994; Smith et al., 1997; Fitch et al., 2000; Lemarie et al., 2000). One factor that increases the risk consid-erably is the width of the slot. In dogs that suffer sub-luxation the slot is usually too wide; reported as3980% of the vertebral width and a median of 50%

(Fitch et al., 2000; Lemarie et al., 2000) (7.10, 7.16).Subluxation does appear to be a significant risk when awide slot is performed for caudal lesions. It is not clearif this is also true for small dogs when the slot width is kept to about one third of vertebral body width(Lemarie et al., 2000). If ventral slot decompression isto be performed in dogs with caudal lesions, the slotproportions should be close to 33% or an inverted coneshould be considered (Goring et al., 1991). If the widthof a caudal slot is nearing 50% then the site should alsobe stabilized (Lemarie et al., 2000).

CERVICAL DISC DISEASE IN CATSDisc herniation is not uncommon in cats, particularly inthe cervical region, but clinical signs related to theselesions are rare (Heavner, 1971; Littlewood et al., 1984;Kathmann et al., 2000; Knipe et al., 2001; Muana et al.,2001). The principles of diagnosis and treatment are discussed above.


Neurological No. of No. recovered* No. recovered* No. recovered* No. recovered*status dogs by 2 days (%) by 7 days (%) by 28 days (%) by 365 days (%) No recovery

Pain / RS1 33 16 (48) 24 (73) 30 (91) 33 (100) 0

Can walk1 14 6 (43) 10 (71) 12 (86) 14 (100) 0

Can not walk1,2 18 5 (28) 10 (56) 14 (78) 15 (83) 3 (17)

1Seim and Prata (1982); 2Waters (1989).* Recovered defined as no neck pain; ability to walk for dogs unable to walk before surgery.RS, Root signature.

Table 7.3 Results of ventral slot decompression for cervical disc

Key issues for future investigation

1. How to manage dogs with multiple extrusions of mineralized disc material (7.15A)? Options include dorsal laminectomy (Gillet al., 1996), or several ventral slot(s) with bone graft distraction. For the latter procedure it would help to be able to decidewhich lesion(s) is most significant (4.43).

2. How to deal with multiple, dynamic lesions in small dogs (7.15B)? Options include dorsal laminectomy, fusion using cementplugs (but see 7.13), or possibly several ventral slots, each with bone graft or cement wedges (page 118).

3. What is the maximum recommended width for a slot and what are the risks of instability (7.16)?

4. Is there a need for routine fixation to prevent luxation in dogs with caudal lesions or is this only necessary when the slot widthis 50% (Lemarie et al., 2000)?

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Chambers, J.N., Oliver, J.E., Jr, Bjorling, D.E. (1986) Update on ventraldecompression for caudal cervical disk herniation in Doberman Pinschers.Journal of the American Animal Hospital Association 22, 775778.

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5. Are cranial lesions more resistant to subluxation (Lemarie et al., 2000) (7.16B)?

6. What is the best way to fuse interspaces in small-breed dogs? Options include metal and bone cement (page 118) or boneallografts combined with ventral slot (Fitch et al., 2000). Non-biological materials that permit bone in-growth may becomeavailable in the future (Cook et al., 1994; Emery et al., 1996).

A B

7.16 A: Ventrodorsal survey radiograph from a 6-year-old Yorkshire terrier that suffered a vertebral subluxation at the site of aprevious ventral slot at C4/5 (arrow). The width of the slot is 55% (same dog as in 7.52). B: Seven-year-old Dachshund withneck pain and root signature that was unable to walk after ventral slot at C3/4; slot width is 66%. An external splint was applied;the dog could walk within 2 weeks.

A B

7.15 A: Multiple herniations in a Pomeranian with neck pain, mild tetraparesis and a disconnected gait (see page 28). Extraduralcompression is evident from C2/3 to C7/T1 inclusive; several lesions were of mineralized material. Fenestration of these disc spacesled to recurrence of signs within a year. B: Miniature pinscher with neck pain and thoracic limb root signature. Traction-responsive,ventral extradural compression is present from C2/3 to C6/7 inclusive.

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Denny, H.R. (1978) The surgical treatment of cervical disc protrusions inthe dog: a review of 40 cases. Journal of Small Animal Practice 19,251257.

Dixon, B.C., Tomlinson, J.L., Kraus, K.H. (1996) Modified distraction-stabilization technique using an interbody polymethyl methacrylate plug in dogs with caudal cervical spondylomyelopathy. Journal of theAmerican Veterinary Medical Association 208, 6168.

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Felts, J.F., Prata, R.G. (1983) Cervical disk disease in the dog: intraforam-inal and lateral extrusions. Journal of the American Animal HospitalAssociation 19, 755760.

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Fitch, R.B., Kerwin, S.C., Hosgood, G. (2000) Caudal cervical interverte-bral disk disease in the small dog: role of distraction and stabilization inventral slot decompression. Journal of the American Animal HospitalAssociation 36, 6874.

Floyd, T., Ohnmeiss, D. (2000) A meta-analysis of autograft versus allo-graft in anterior cervical fusion. European Spine Journal 9, 398403.

Fry, T.R., Johnson, A.L., Hungerford, L., Toombs, J. (1991) Surgical treatment of cervical disc herniations in ambulatory dogs. Ventraldecompression vs. fenestration, 111 cases (19801988). Progress inVeterinary Neurology 2, 165173.

Funkquist, B., Svalastoga, E. (1979) A simplified surgical approach to the lasttwo cervical discs of the dog. Journal of Small Animal Practice 20, 593601.

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Gill, P.J., Lippincott, C.L., Anderson, S.M. (1996) Dorsal laminectomy in the treatment of cervical intervertebral disk disease in small dogs: aretrospective study of 30 cases. Journal of the American Animal Hospital Association 32, 7780.

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Griffiths, I.R. (1973) Spinal cord blood flow in dogs: the effect of bloodpressure. Journal of Neurology, Neurosurgery and Psychiatry 36, 914.

Hara, Y., Tagawa, M., Ejima, H., Orima, H., Fujita, M. (1994) Usefulnessof computed tomography after myelography for surgery on dogs withcervical intervertebral disc protrusion. Journal of Veterinary MedicalScience 56, 791794.

Heavner, J.E. (1971) Intervertebral disc syndrome in the cat. Journal of theAmerican Veterinary Medical Association 159, 425427.

Hurov, L. (1979) Dorsal decompressive cervical laminectomy in the dog:surgical considerations and clinical cases. Journal of the American AnimalHospital Association 15, 301309.

Janssens, L.A.A. (1985) The treatment of canine cervical disc disease byacupuncture: a review of 32 cases. Journal of Small Animal Practice 26,203212.

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Knipe, M.F., Vernau, K.M., Hornof, W.J., LeCouteur, R.A. (2001)Intervertebral disc extrusion in six cats. Journal of Feline Medicine andSurgery 3, 161168.

Lemarie, R.J., Kerwin, S.C., Partington, B.P., Hosgood, G. (2000) Vertebralsubluxation following ventral cervical decompression in the dog. Journal ofthe American Animal Hospital Association 36, 348358.

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7.18 Landmarks are (a) larynx; (b) wing of atlas; and (c) manubrium of sternum. Incision site is depictedon the midline. a

b

c

7.19 Landmarks can be palpated; in this illustrationthe surgeon is palpating the wings of the atlas(left hand) and the prominent transverseprocess of C6 (4.6, 7.37B).

7.18

7.19

7.17 Positioning of dog for ventral approach to theneck. Excessive extension will close the dorsaldisc space; mild traction may be preferable(11.24A).

7.17

PROCEDURES

Approach to the ventral neck (7.177.29)The cervical spine is extended over a sandbag; the thoracic limbs are pulled in a caudal direction, and tape is used toimmobilize the head and thorax (7.17). It is important to have the dog straight to insure that the neck is aligned correctly.Note that extension of the caudal portion of the neck as shown here will tend to close the dorsal intervertebral space ofC5/6 and C6/7 spaces. Ventral slot decompression at these sites is easier to perform if the neck is put in a more neutralposition. If access needs to be improved to C6/7, it is preferable to put the neck in gentle traction using a weight on themaxilla (11.24), or consider a dorsal (11.4411.55, 7.59) or dorsolateral laminectomy (7.567.58, 12.1512.29).

Deep anatomy includes the carotid sheaths, recurrent laryngeal nerves and esophagus (7.257.27). Careful dissectionof the loose fascial layers in a longitudinal direction will expose these structures. Finger dissection here is safe and effective. Further dissection of the deep fascia reveals the longus colli muscles, which lie ventral to the cervical vertebrae(7.28). If preferred, the paramedian approach to the ventral neck can be used instead of the approach described herein order to provide greater protection for blood vessels, nerves, trachea and esophagus (11.2511.27).

Blunt-jawed self-retaining retractors (5.8) are used initially to maintain exposure (7.29). The retractors must not interferewith gas flow in the airway. Palpate the end of the endotracheal tube and insure that it is positioned distal to the retractors.Moist towels or sponges are used to protect the tissues. The longus colli muscles join in the midline and insert on the ventralprocess of the vertebra, thus overlying the intervertebral discs (7.29). Accurate identification of the intervertebral discs at thisstage is crucial. The ventral process of C5 vertebral body lies in the midline between the cranial borders of the large C6 trans-verse processes (4.6, 7.37B); the C5/6 intervertebral disc lies immediately behind this ventral process. The ventral processof C1 is particularly prominent and sharp (7.19); this also can or may be palpated. There is no intervertebral disc at C1/2.


7.20 Superficial anatomyseealso 7.21. The skin andsuperficial fascia havebeen divided to reveal thesternocephalicus muscles(a), and sternohyoidmuscles (b). The cervicalvertebrae C1 through C7are seen in thebackground.

a

b

7.21 The skin and superficial fascia have beendivided. This reveals the sternocephalicusmuscles (a), and the sternohyoid muscles (b).The sternocephalicus muscles should be dividedto the manubrium, particularly if access to thecaudal cervical vertebrae is required.

a

b

7.22 The sternohyoid muscles are divided in themidline. If the median raphe is not apparent, applyfinger pressure to the muscles over the tracheaand the raphe will become visible.

7.22

7.23 Making a small incision in the fascia and thendissecting the fascia bluntly usually preventsbleeding. The caudal thyroid vein lies in theconnective tissue with small branches on eachside. This vein should be preserved if possible;the branches may be cauterized. The trachea isimmediately under the fascia.

7.23

7.20

7.21


7.26 There are several layers of loose fascia that mustbe penetrated before reaching the longus collimuscles. The esophagus is identified by its pinkcolor compared to the darker red of the longuscolli muscles; differentiation is aided by having anesophageal stethoscope in place (see 7.27 forlabels). The recurrent laryngeal nerve has beenseparated from the trachea. This is for illustrationonly and is not done normally.

b

a

7.27 Note the recurrent laryngeal nerve (a),and the carotid sheath containing thecarotid artery along with the moreprominent, white vagosympathetictrunk (b). The trachea and esophagushave been retracted away from thesurgeon; they should be kept togetheron the same side of the incision.

b

a

7.27

7.24 Once the sternohyoid muscles have beendivided the trachea is visible. Here the separationis made with fingers.

7.24

7.25 Close up view of the trachea (a); recurrentlaryngeal nerve (b); and carotid sheath (c). Theapproach is between the recurrent laryngealnerve (which remains associated with thetrachea) and the carotid sheath at the levelindicated by the arrow. At this stage theesophagus must be identified or the surgeoncould damage it inadvertently (7.26).

a

b

c

7.25

7.26


7.28 Retraction of the vital structures exposes thelongus colli muscles. The transverse processes ofC6 are large and are directed ventrally; they arepalpated readily as shown here (4.6, 7.37B).

7.28

7.29 Deep anatomy. Note the pattern oflongus colli muscle bellies runningcranially. Once landmarks have beenidentified and any fenestrationscompleted, pressure on the jugularveins should be relieved bysubstituting smaller Gelpi retractorsover the space of interest if a ventralslot is to be performed.

7.29

7.30 To gain access to the disc, the longus collimuscles are divided in the midline, immediatelycaudal to the ventral process. They may be cutor division may be achieved with a pair of small,curved hemostats.

7.30

Fenestration (7.307.36)During fenestration it is important not to confuse the ventral process of C2C5 vertebrae with the transverse processes(see under Approach, page 106). The longus colli muscles run cranially to insert on the ventral process in the midline.The transverse processes can be palpated on each side of the ventral process. The three rows of structures (ventralprocesses in the midline, transverse processes laterally on each side) should be identified before proceeding.


7.31 Method of fenestration. The anulus fibrosus is cutin the form of a window to allow access to thenucleus pulposus (7.34).

7.31

7.32 The nuclear material is removed (7.35). It isimportant not to push the instrument deeplythrough the dorsal anulus fibrosus into thevertebral canal. Radiographs provide some guideto the depth of the intervertebral space as long asmagnification is taken into account. The window inthe anulus must be larger than the instrument toavoid creating a piston effect, which could forcedisc material dorsally into the vertebral canal.

7.32

7.33 If greater exposure of the disc is required, themuscle separation is maintained by self-retainingretractors. The longus colli tendons may also becut. The ventral surface of the vertebra (a), andthe ventral anulus fibrosus (b), can be seen. Thesurgeons finger is on the ventral process of thevertebra cranial to the disc.

b a

7.33

7.34 Fenestration is done by cutting a hole in theanulus fibrosus; this should be made as large aspossible to allow complete evacuation of thenucleus pulposus. A fresh #11 scalpel blade isused to make the opening, either by making fourcuts in a rectangular pattern in the anulusfibrosus, or by using a sawing motion in an ovalpattern until the piece of anulus is free. Thesurgeons finger is on the ventral process in thispicture.

7.34


7.35 Disc fenestrated. Nucleus pulposus is oozingfrom the intervertebral space. The removed pieceof anulus fibrosus lies cranial to the disc space(arrow). A small curette or blunt instrument isused to remove the nucleus pulposus by enteringthe space, dragging towards the surgeon andthen lifting the material out. This maneuver should be repeated until there is a reasonablecertainty that all the nuclear material has been removed. Care must be taken to avoid penetrating thevertebral canal dorsally (7.32).

7.35

7.36 Sagittal diagram shows that fenestration onlyallows access to disc material in theintervertebral space. Disc material lying in thevertebral canal cannot be removed byfenestration.

7.36

Ventral decompression (7.377.52)Sometimes the dorsal longitudinal ligament remains after removal of the anulus fibrosus. The ventral surface (the sidenearest the surgeon) of the ligament is slightly roughened and has longitudinal fibers; the dorsal surface is smooth andshiny. The identity of any tissue exposed in the vertebral canal must be established before further manipulations or inci-sions are made. It is often necessary to complete bone removal before tissue can be identified clearly.

If hemorrhage from the venous plexus does occur, it may be possible to control it with Gelfoam, direct pressure(11.29), or a small piece of muscle (Table 7.2). Pressure on the jugular veins should be relieved. Work should then con-tinue at the other end of the slot. Suction may be maintained while disc material is being removed, but careful note mustbe taken of the amount of blood aspirated. If hemorrhage is severe, the slot is packed and time allowed for it to stopbefore re-exploration.


7.37 A: View of cervical vertebrae showing ventral slotdecompression. The procedure allows access to thevertebral canal through the vertebral body. Correctidentification of the intended space is crucial (seeApproach, page 106). Where concomitant fenestrationis to be performed this should be done first in order toverify landmarks. B: 3D reconstruction of a ventral slot(same dog as shown in 7.9) to illustrate the appearancefrom a ventral aspect at C5/6. The overall width of thisslot is 38%. Note the prominent wings of C6(arrowheads).

7.37

7.38 The site for the ventral slot is prepared byremoving the musculature from the vertebrae onboth sides of the midline. The longus collimuscles are separated from the ventral process.Hemostasis at this stage is important, asexcessive bleeding will obscure the site of theslot. Muscle separation is maintained with self-retaining retractors and tissues are protectedwith moist sponges. 7.38

A

B


7.39 Sagittal section shows that the slot should bestarted more in the vertebra cranial to the discthan the one caudal, because of the angulationof the disc space relative to the vertebral canal.This will also allow room for screws or pins tobe placed should the slot collapse or subluxate(7.10, 7.16, 7.52, 11.21).

7.39

7.40 The slot is commenced in the position describedin 7.39. Initially drilling is only into the cranialvertebra. The cortical bone has been penetratedto reveal purple cancellous bone; theintervertebral disc is caudal to this. The aim is tocreate a slot approximately one third of the widthof the vertebra and one third of its length, withthe disc space at its center once the vertebralcanal is reached (7.39, 7.41). This size of slotshould not result in instability and if kept on midline should avoid the internal vertebral venous plexus (7.8, 7.43, 7.44).

7.40

7.41 Partially completed slot. Somewhat moreadvanced than in the previous illustration.Hemorrhage from the bone is controlled withbone wax. It is important to keep the burirrigated and the site free of debris. It is useful tostop drilling periodically to clean the site and toassess progress.

7.41

7.42 The floor of the slot is shown. It is important tojudge the depth of the slot accurately. Corticalbone is white and hard (a), in contrast to the darkcancellous bone (b). The cancellous bone isremoved over the whole slot area, using a smallbur. The remaining cortical bone is then thinnedto allow easy removal; it is best to thin the wholearea before entering the vertebral canal (8.36,10.34). The dorsal anulus fibrosus is visible (c).The shape of the opening into the vertebral canalmust take into account the location of the venousplexus (7.43, 7.44).

a cb

7.42


7.43 Latex-infused preparation to demonstrate thelocation of vertebral venous plexus on the floor ofthe vertebral canal. The dorsal lamina has beenremoved for this view from above the spine. Thediscs are represented in orange. Note how thevenous plexus converges in the mid-portion ofthe vertebra and diverges over the disc (1.36, 7.44).

7.43

7.44 This series of CT scans was made after intravenous contrast tohighlight the vertebral venous plexus (arrows). A: Middle of C6vertebra. B: At the C6/7 disc space. C: Middle of C7. Note howthe vessels diverge at the level of the disc space but convergeagain over the vertebral bodies.

7.44

C

A

B


7.45 The dorsal anulus fibrosus is incised on eachside of the slot using a fresh #11 blade. Oneincision can be seen uppermost in the picture(arrow). The near-side incision is being made.The incision is then extended to where thecortical bone has been removed.

7.45

7.46 The anulus fibrosus is lifted with a suitableinstrument (in this case, a pointed tartar scraper)and dissected free. Removal can be facilitated bypreserving a small knub of anulus to grasp withfine rongeurs (11.29A).

7.46

7.47 The dorsal anulus has been removed, allowing aview into the vertebral canal. Here the glossydura mater is visible. When extruded discmaterial is present, it is wise to remove it fromthe midline first to avoid damaging the venousplexus early in the procedure.

7.47

7.48 The slot is almost complete. The floor of the slot isexcised with fine rongeurs or a small curette afterbone has been removed and ligamentous tissuecut with a scalpel. Great patience is requiredwhen removing herniated disc material;magnification and additional lighting are preferred(5.15.3). Once all material has been removed,the spinal cord will lie adjacent to the edges of theslot as shown. If the disc is asymmetricallypositioned, it is possible to shape the base of theslot to allow more exposure on one side althoughthis may increase the risk of bleeding (7.50B).

7.48


7.49 Removal of mineralized disc material is generallystraightforward although patience is required. Asin the thoracolumbar region, additional discmaterial usually remains in the vertebral canalunless the dura returns to lie level with the bone.

7.49

7.51 Access to disc material in the vertebral canal viaa ventral slot. A: Sagittal diagram. Note thestarting position of the slot relative to the disc.B: Inverted preoperative (left) and postoperative(right) 3D reconstruction of the dog shown in7.50. The extrusion at C2/3 is indicated in theleft-hand panel (*). The margins of the slot areoutlined in the right-hand panel by arrowheads.

7.51

*

7.50 In small dogs or dogswith very largeextrusions the invertedcone technique canimprove access to thevertebral canal A: This5-year-old Dachshundhad severe neck painand mild tetraparesis. The 3D reconstruction of the preoperative CT shows a huge extrusion at C2/3,viewed looking caudally. B: 3D reconstruction made from the immediate postoperative CT scan lookingcranially to C1. The slot has been extended to one side (arrowhead) as an inverted cone in order to givegreater access without causing instability (Goring et al., 1991). Nearly all of the material has beenremoved. The width is approximately 33%.

7.50

A B

A

B


7.53 A: This 8-kg Silky terrierhad undergone a ventralslot at C5/6 and thensuffered domino lesions atC4/5 and C6/7 some18months later (same dog as7.14). B: Both lesions weretraction-responsive.

T1

7.54 A: Cement plugs at C4/5 andC6/7 using anchor holes in theend plates (11.38) withcancellous grafting from C4 toC7 (Dixon et al., 1996). Anexternal splint was not used. B:Six-week follow-up shows end-plate fracture at C4/5 andventral displacement of theimplant at C6/7 (7.13). The dog was doing well clinically but had developed iatrogenic laryngeal paralysis.

Ventral decompression with distraction-stabilization (7.537.55) (see also Chapter 11)Preferred methods of distraction-stabilization use a corticocancellous autograft, allograft (Veterinary Transplant Services,Seattle, WA), or metal and bone cement (Fitch et al., 2000); cement plugs are difficult to use in small dogs (7.13, 7.54).Initial distraction can be accomplished as shown in 11.3111.34, by K-wires (page 235), or by a rope around the dogsupper canine teeth and tied to the surgical table (7.55, 11.24). After distraction a bone allograft (Veterinary TransplantServices, Seattle, WA), cement (page 118), or an autograft from the wing of C6, sternum or ilium, can be wedged intothe slot to maintain distraction (Fitch et al., 2000). Metal and cement implants may also be used (7.55).

C6

T1

A

A

A

B

B

B

7.53

7.52 A: Postoperative radiograph of adog that had a subluxation afterventral slot at C4/5. The width ofthe slot was 55% of the vertebralbody (7.16). B: Stabilization wasperformed using pins and cement.The dog suffered respiratory arrestand did not recover from surgery.

C6

7.52

T1T1

7.54


7.55 Miniature pinscher with severe neck pain and left thoracic limb rootsignature. A: Preoperative myelogram shows collapse andmineralized material at C6/7. B: CT myelogram shows mineralizedextrusion or osteophytes within the left foramen also (arrowhead)(Prata and Stoll, 1973). C: Postoperative radiograph of stabilizationusing 2.7-mm screws and bone cement following traction on themaxilla as the cement hardened (compare disc space to A). Thecaudal screw is positioned poorly but the dog has shown noclinical signs for 6 years.

7.55

L

A

B

C

Distraction can be maintained with a small amount of bone cement wedged into a partial ventral slot. The edges ofthe slot are undercut to prevent slippage of the cement. This method can also be used to rescue a wide orsubluxated ventral slot, as the main goal here is to prevent excessive collapse or subluxation as seen in 7.10.Gelfoam (Pharmacia, Kalamazoo, MI) should be used to insulate the spinal cord (page 235 and 239). The cementwedge should be kept to the ventral half of the interspace.


7.57 A: Preoperativemyelogram and B: 3Dreconstruction of thepostoperative CT scan to show thehemilaminectomy(arrowheads) used toaccess the mass. The gapbetween C6 and C7(arrow) is an artefact ofreconstruction. Head is tothe right in these images.

7.57

7.58 Postoperative A:Transverse and B: 3Dreconstruction of a CTscan from the same dog asshown in 7.567.57. Themass was confirmed to bea large, fibrous discherniation; about 75% of itwas removed using acombination of scalpel androngeurs. A pocket of gas is visible at the surgical site in A. The extent of the hemilaminectomy is shownclearly in B. The dog made a rapid recovery.

7.58

7.56 A: Transverse and B: 3Dreconstruction of a CTscan from a 12-year-oldLabrador retriever withparaparesis, worse on theright side. Neurologicalexamination revealed adisconnected thoraciclimb gait (see page 28)and guarding of the neck.These findings suggesteda caudal cervical lesion; a C7/T1 ventral, extradural compression was confirmed by myelography. CTscan revealed the mass to be mainly right-sided. Differential diagnoses were a disc, nerve root tumor ormeningioma.

L7.56

Dorsal hemilaminectomy (7.567.58) (see also page 266)

L

A

A

A B

B

B


7.59 A: Ventrodorsal myelogram from a dog with hemiparesis and neckpain shows left-sided, extradural compression over C7 vertebra. B: CT myelogram shows mineralized material to the left of the duraltube over mid-C7 vertebral body. C: Intraoperative photograph showsmineralized disc material to one side of the dural tube (arrowheads).The dura was retracted using stay sutures to improve access.Fenestration was performed using a ventral approach after thelaminectomy. The dogs neurological status was improved the next dayand it was almost normal 1 month later.

R7.59

Dorsal laminectomy (7.59)The surgical approach is described in Chapter 11 (11.4411.55). Large veins may be encountered in the dorsal epiduralspace, especially close to the intervertebral foramen (Hurov, 1979) (11.51, 11.52).

L

A

B

C

small animal spinal disorders: diagnosis and surgery

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