Spinal conditions affecting small animals The most commonly encountered spinal conditions

affect-ing small animals are:

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Vertebral body abnormalities

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IVDD types I & II

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Spinal fractures

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Atlantoaxial luxation/subluxation

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Caudal cervical spondylomyelopthy (wobbler syndrome)

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Lumbosacral conditions

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Fibrocartilaginous embolism

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Discospondylitis

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Chronic degenerative radiculomyelopathy Vertebral body abnormalities

The most common vertebral body abnormalities seen in small animals are:

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Hemivertebrae

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Transitional vertebrae

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Block vertebrae

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Spina bifida

Hemivertebrae are most commonly seen in the screw tail breeds, i.e. Boston Terrier, Pug (Figure 7.12), English and French Bulldogs. This is the most clinically significant ver-tebral anomaly in the dog. There is a failure of ossification of part of the vertebral body, unilateral, dorsal or ventral.

Clinical signs are usually secondary to cord compression and may be chronic or acute in onset. Decompressive

Firstly, and very importantly the animal’s collar should be removed and not replaced. Use of a harness for the remainder of the animal’s life is advised.

Medical management of cervical disc disease may be attempted. Absolute rest and the judicious use of anti-inflammatories may be beneficial. However, in the author’s experience, because of the pain associated with cervical disc disease, this condition is best treated surgically.

The most common site for cervical disc disease is C2– C3 and the frequency appears to diminish caudally.

Cervical IVDD in large breed dogs is usually Hansen type II and most commonly occurs between C5 and C7. This may be associated with caudal cervical spondylomyelo-pathy and is discussed later.

Surgical options

The common surgical treatments are:

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Ventral slot

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Dorsal laminectomy

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Dorsolateral hemilaminectomy

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Facetectomy

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Cervical disc fenestration Ventral slot

A ventral slot is the most commonly performed technique for surgical management of cervical IVDD. The advantages include minimal muscle dissection and easy access to adja-cent intervertebral discs for fenestration.

A ventral approach is made to the cervical spine, the relevant disc space identified and a ventral fenestration performed. A slot-shaped laminectomy is performed com-mencing ventrally and extending into the neural canal. Disc material is removed from the canal. Closure is then under-taken. Fusion between vertebral bodies occurs approxim-ately 8 –12 weeks postoperatively.

Disadvantages include, occasional severe intraoperative haemorrhage due to laceration of the venous sinus, incom-plete removal of disc material, inability to perform the pro-cedure on more than one vertebra owing to instability and post-operative vertebral body fracture or collapse.

Prognosis is dependent on the degree of sensory and motor loss as well as location of IVDD. The prognosis is improved if there are no thoracic limb sensory deficits in C2– C3 or C3 – C4 lesions and if the animal is ambulatory within 96 hours of surgery. Complete recovery appears more likely with cranial cervical lesions than caudal cervical lesions. Long-standing tetraparetic animals have a signific-antly worse prognosis. Occasionally a C2–3 lesion will cause progression of neurological signs leading to brainstem swell-ing and respiratory and cardiac arrest. Followswell-ing surgery the author expects 95–100% of dogs to be either normal or have mild cervical pain within 2 weeks of surgery. Recurrence of severe pain occasionally occurs within 1–2 weeks, usually because of incomplete disc removal or vertebral collapse surgery may be indicated in some cases. Animals with

verte-bral body abnormalities should not be used for breeding.

Transitional vertebrae may be seen at any level of the spinal column. The main area of clinical significance is at the lumbosacral junction where transitional vertebrae may result in instability and spinal cord compression.

Block vertebrae result from improper separation of the vertebrae during development. Block vertebrae are inher-ently stable and are not usually clinically significant.

Spina bifida is characterised by an incomplete dorsal lamina and may not be of clinical significance in mild cases, however, in more severe cases with meningeal involvement (spinal bifida cystica)neurological abnormalities are often evident and corrective surgery may be required. Spina bifida is more commonly seen in the screw tail breeds and in Manx cats.

IVDD types I & II

Due to the blurring between Type I and II IVDD these will be discussed together and within spinal cord regions.

Cervical disc disease

Clinical signs are related to location of lesion. Cervical disc extrusion causes severe pain occasionally with the absence of other clinical signs. Nerve root signs are common with more caudal lesions and Horner’s syndrome may also be seen.

Diagnosis is based on signalment, clinical signs and imaging. Plain spinal films and myelography are essential prior to treatment.

Figure 7.12 (a) A 6-month-old Pug with congenital hemivertebrae. (b) Lateral thoracolumbar radiographs of the same dog.

(a)

(b)

and should be investigated. Physiotherapy plays a vital role in recovery following spinal surgery and is increasingly becoming an invaluable component of therapy.

Thoracolumbar disc disease

This is the most common form of disc disease in small animals accounting for 66 – 86% of all cases.

Two forms are recognised:

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Type I disc disease – an acute, often explosive extrusion of disc material into the neural canal. Type I IVDD usu-ally occurs in chondrodysplastic breeds of young age.

T12–T13 is the most common site with incidence decreasing caudally in chondrodystrophic breeds (Figure 7.13).

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Type II disc disease – a chronic slow and insidious disc protrusion usually in older non-chondrodysplastic animals. L1–L2 is the most common site in non-chondrodystrophic.

Grading of these cases is important in deciding treatment options and prognosis.

The following grades are used by the author although other systems are available:

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Grade I – Single episode of mild, moderate or severe back pain with slight to no conscious proprioception deficits and no motor weakness. Prognosis is good with medical management and fenestration.

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Grade II – Recurrent back pain or persistent severe back pain with conscious proprioception deficits and ambula-tory paraparesis. Prognosis is guarded to good with fenestration and conservative management but excellent with decompressive surgery.

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Grade III – Uncontrolled severe back pain with con-scious proprioception deficits and ambulatory parapare-sis. Prognosis is excellent with decompressive surgery.

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Grade IV – weakly or non-ambulatory paraparesis with back pain. Prognosis is good to excellent with decom-pressive surgery.

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Grade VA – Paraplegia less than 48 hours duration but with deep pain present. Prognosis is guarded to poor with decompressive surgery.

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Grade VB – Paraplegia greater than 48 hours duration but with deep pain absent. Prognosis is poor to grave, with decompressive surgery.

Treatment options – conservative or surgical

Many animals will respond to conservative management, however, recurrence at the same site is likely (up to 80%).

Conservative management involves absolute cage rest and pain relief. Some authors advocate the use of corticosteroids in these animals but there is little scientific evidence that corticosteroids are of benefit and considerable evidence of deleterious side effects, care must also be exercised with the use of non-steroidal anti-inflammatory drugs (NSAIDs). A large number of human patients with spinal cord injury will develop gastrointestinal side effects, regardless of therapy;

the situation is thought to be similar in animals.

Which animals are good candidates for medical manage-ment? Grade I and II animals have a similar prognosis with medical vs. surgical management, however, the recurrence rate is very high for medically managed animals. Some authors advise Grade VB animals have a similar recovery rate (albeit very low) for medical vs. surgical management;

however, this author finds even severely affected animals have a better prognosis if treated surgically.

Surgical options

The commonly practised surgical options include:

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Disc fenestration

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Hemilaminectomy

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Pediculectomy

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Dorsal laminectomy

Dorsolateral hemilaminectomy

The author prefers to perform this procedure under mag-nification. With the animal positioned in sternal recum-bency and rotated slightly away from the surgeon, a dorsal incision is made. The facsial attachments in the midline are incised and the epaxial musculature elevated from the dorsal spinous process. The muscular attachments onto the articu-lar facets are sharply dissected. The articuarticu-lar facets are removed with rongeurs and the dorsolateral pedicles removed with a high-speed bur. Once the spinal cord is exposed the underlying disc material can be removed and the canal lavaged to remove remaining debris. The underlying disc and often, adjacent discs, may be fenestrated at this time. An

Figure 7.13 CT scan of the L2 of 4-year-old Dachshund, a large type I inter-vertebral disc extrusion is evident on the left side of the neural canal.

Surgical management

Surgical management is indicated in unstable fracture–

luxations, if the animal is weakly ambulatory or tetraparetic, or if conservative therapy is unsuccessful. Surgical manage-ment allows for decompression of the spinal cord as well as vertebral stabilisation. A variety of techniques have been described. The most common are the ventral and dorsal stabilisation techniques.

Ventral techniques involve identification of the affected site via a ventral approach. Stabilisation or fusion of the affected vertebrae and support until fusion is complete – usually 6 –8 weeks. Dorsal techniques rely on restoring ver-tebral alignment and assisting with fixation of facet joints, fusion is unlikely, the dorsal spinous process does not allow plating to be undertaken.

Prognosis

Prognosis depends on neurological status before surgery as well as radiographic classification, method of repair and response to post-operative management. There is a poor correlation between degree of vertebral displacement and neurological condition. There appears to be a high peri-operative mortality rate (approaching 40%) with cervical fractures, however, if the animal survives the peri-operative period the recovery rate is excellent, with 97–100% of cases having a complete recovery. Poor prognostic factors include severe neurological status, deteriorating neurolo-gical status and an interval of more than 5 days before treatment.

In general, animals managed with conservative manage-ment tend to have milder neurological injury, a slower improvement but reduced hospital stay times, while those managed with surgery tend to have more severe neurologi-cal injury, more rapid improvement but increased hospital stay times.

Thoracolumbar fractures

The thoracolumbar spine is the most common site of spinal fracture–luxation in the dog and cat. Most are traumatic, usually with severe concurrent injuries both soft tissue and orthopaedic. It is important to remember that radiographic findings are not consistent with neurological findings. Up to 20% of animals have a second spinal fracture–luxation!

Functionally, the spine is made up of three connected units, the dorsal lamina and facet joints, the pedicles and vertebral body / intervertebral disc. This is the three-compartment theory.A disruption of the ventral compart-ment is most significant in destabilising the spinal column.

Treatment options are non-surgical management or surgical management.

Non-surgical management

Non-surgical management is best reserved for animals with stable fractures and minimal neurological deficits.

Non-surgical management includes, strict cage rest, use of autogenous fat graft is usually placed over the spinal cord

before closure to help prevent scar tissue causing narrowing of the neural canal. Closure is routine. Procedure for a dorsal approach is similar.

Advantages of hemilaminectomy are removal of the majority of the intervertebral disc, retrieval of disc material with minimal spinal cord trauma, ability to extend laminec-tomy cranially and caudally to improve retrieval of disc material and minimal effect of hemilaminectomy on torsional stability of the thoracolumbar spine.

Prognosis is very good, the success rates for non-ambulatory dogs, following hemilaminectomy is 79–95%.

Physiotherapy plays a vital role in recovery following spinal surgery and is increasingly becoming an invaluable com-ponent of therapy.

Factors affecting neurological recovery

The time interval between the onset of neurological disease and surgical decompression is a major influencing factor.

The recovery rate is far more rapid in dogs undergoing decompressive surgery within 48 hours of onset of clinical signs than those surgically treated after 48 hours. This delay has more profound effect on the prognosis of more severely affected animals.

The severity of neurological disease is also very import-ant; the prognosis for recovery deteriorates with increasing neurological grade. Grade I recovery rate 95–99% – Grade V 45 –65%.

The presence or absence of deep pain sensation is a major prognostic factor. The deep pain fibres are located in the dorsal aspect of the ventral commissure of the spinal cord.

Severe spinal cord injury is required for animals to lose deep pain sensation. There are several studies (Duvalet al. 1996;

Scott & McKee 1999) with slightly differing outcomes but universal agreement that the absence of deep pain severely worsens prognosis. Addition of physiotherapy post surgery hastens neurological recovery.

Spinal fractures Cervical fractures

Cervical fractures are uncommon. They can be associated with trauma or developmental weakness of a pathological nature. Overall, 80% of cervical fractures occur at C1–C2.

Any animals with severe neck pain following trauma must be managed very carefully – especially if anaesthetised for radiography.

Non-surgical management

Conservative management may be attempted for mini-mally displaced fractures in the absence of severe neurolo-gical signs. Conservative management involves strict cage confinement, use of a neck brace and appropriate analgesia.

Cage rest should be considered for 4– 6 weeks. If there is any deterioration in neurological status the animal should immediately be reassessed.

a back splint and appropriate analgesia. If there is no improvement or there is neurological deterioration then the animal should be re-appraised.

A back brace aims to immobilise the vertebral segments cranial and caudal to fracture–luxation. The splint may be constructed from aluminium sheeting, thermosetting plastic or casting material. The splint may be best applied to an anaesthetised animal and then modified after recov-ery. In the author’s experience, cats are intolerant of back splints.

Surgical management

Surgical management should be considered in animals with unstable fracture–luxation, weakly ambulatory or non-ambulatory tetraparesis, severe pain, or if conservative management is unsuccessful. The aim is to decompress the spinal cord and stabilise the fracture–luxation. Pathological fractures secondary to neoplasia are not usually treated sur-gically. In other cases of pathological fracture the underly-ing pathology must be diagnosed and treated.

A variety of surgical techniques have been described including: Steinmann or threaded pins and polymethyl methacrylate (PMMA) (Waldron et al. 1991), vertebral body plating, clamp rod internal fixator (CRIF) system, plastic dorsal spinous process plates, modified segmental spinal fixation (spinal stapling), external skeletal fixation (ESF) – both traditional ESF or circular ESF.

Post-operative management involves analgesia, cage rest and usually external support with cage rest for 4–6 weeks.

Serial neurological examination is advised and any deterio-ration in neurological status should be thoroughly assessed.

Prognosis

Prognosis is dependent on neurological status, success of repair and response to repair. There is poor correlation between degree of vertebral displacement and neurological condition. In general, animals with presence of deep pain whose fractures are stabilised quickly have a good prognosis while those without deep pain have a poor prognosis.

Physiotherapy plays a vital role in recovery following spinal surgery and is increasingly becoming an invaluable component of therapy.

Lumbosacral and coccygeal fractures

Lumbosacral and coccygeal fractures are not uncommon in small animals. Animals subject to trauma from behind, usually in car accidents, often have fractures in this area. A major problem, along with loss of locomotion, is the loss of bladder control and anal tone. Bladder management in particular is vital both short and long term.

Non-surgical management

Non-surgical management can be considered for animals with stable fractures and minimal neurological deficits.

Cage rest, application of a back brace and analgesia are

advised. Repeated neurological examinations are essential to determine response to therapy. Cage rest is advised for 6 weeks. Bladder management, if the animal is not urinat-ing voluntarily, is vital.

Surgical management

Surgical management is advised for animals with unstable fracture–luxations, or that are poorly ambulatory or have non-ambulatory tetraparesis, or if conservative manage-ment is unsuccessful. The aim is to decompress the cauda equina and stabilise the vertebral bodies.

A dorsal approach is made and the fracture reduced.

The most common method of maintaining reduction is the use of transilial pin fixation. A pin is placed between the ilial wings over the dorsal lamina of L7 to prevent dorsal luxation, the facet joints may be screwed or pinned as well.

The use of pins or screws and PMMA bone cement has also been described. Most animals are too small for dorsal plating or stapling techniques. More recently, the use of transilial pins with an ESF has been described, as has use of the CRIF system.

Prognosis

In general, the prognosis depends on severity of cauda equina damage. The cauda equina nerve roots appear more resistant to compression than the spinal cord. The progno-sis is good for animals with retained neurological function of the pelvic limbs, anus, urinary bladder, perineum and tail regardless of degree of compression; however, the pro-gnosis is poor with loss of motor function and deep pain perception.

Atlantoaxial luxation

Atlantoaxial luxation may be either congenital or acquired.

Congenital luxations occur with little or no trauma and are secondary to failure of normal development of the dens (most common) or failure of normal development of the alar, apical and or transverse ligaments of the dens. This condition has been reported in many different breeds.

Neurological signs tend to be less severe than with trau-matic locations.

Acquired atlantioaxial luxation

This condition is most commonly seen in the toy breeds.

Yorkshire Terrier, Lhasa Apso, Chihuahua, Pekinese, Toy Poodle and Pomeranian all appear predisposed. Clinical signs include abnormal low head carriage, progressive tetraparesis and ataxia associated with neck pain. There may be an acute presentation with very minor trauma and the animal may dislike its head being touched. Usually it occurs in young animals, less than 12 months of age.

Luxation may be due to axial fracture at synostosis between dens and body of the axis or luxation with an intact dens. The transverse ligaments ± apical ligaments must rupture for atlantoaxial luxation.

4. Hypertrophy of the ligamentum flavum

5. Vertebral arch abnormality and hourglass compression C5–C6 is the most common site for non-IVDD-associated caudal cervical spondylomyelopathy, while C6 – C7 is the most common site for IVDD-associated caudal cervical spondylomyelopathy. CCSM causes chronic spinal cord compression.

Clinical signs

Regardless of aetiology and classification type CCSM may be divided by functional appearance into static or dynamic compressive lesions. This is based on the myelographic appearance of the compression under traction and is important, as the treatment modality is dependent on this differentiation. Routine myelography of the caudal cervical spine is undertaken, mild traction is then applied and if the compression is unchanged the lesion is termed a static lesion, however, if the lesion resolves with traction it is termed a dynamic lesion.

About 80% of cases occur in the Great Dane and Doberman Pinscher, the author sees an increasing number of Labrador Retrievers as well as other breeds. Dogs may be seen at a young age (<2 years) with congenital compression of the spinal cord. Older animals presenting with progres-sive deterioration of neurological signs are most common.

The usual history is of progressive ataxia over a period of months to years. The thoracic and pelvic limbs are affected but signs begin earlier and are more pronounced in the pelvic limbs. Animal may also present acutely after minor trauma. There is cervical pain in only 40% of cases.

Neurological examination reveals stiff, short and choppy gait with straight legs, marked muscular atrophy and neck pain may be noted with manipulation in some cases. UMN reflexes are noted to the pelvic limbs and may include crossed extensor reflex if chronic.

Diagnosis

Diagnosis is based on clinical and neurological examination and plain and myelographic findings. Advanced imaging is not usually considered necessary in CCSM, as myelography is the best diagnostic modality for differentiating between static and dynamic lesions.

Treatment options may be divided into conservative or surgical.

Conservative management

Conservative management is not a good option. CCSM is a chronic progressive disease and conservative management is not effective for static lesions. Conservative management may provide short-term relief for dynamic lesions although underlying instability and malformation are not corrected and neurological deterioration will continue. Some authors state that use of a neck brace will lead to muscle atrophy resulting in a deterioration of neurological status.

Diagnosis

Diagnosis is by clinical signs and usually plain radiography;

although CT may be of benefit in planning surgical reconstruction.

Treatment may be conservative management or surgical.

Conservative management

Conservative management includes strict cage rest, a neck brace and appropriate analgesia. Cage rest should be for 6–8 weeks. Although conservative management may result in clinical improvement recurrence is common, as only limited soft tissue fibrosis appears to occur between the atlas and the axis.

Surgical management

Surgical management is more common. Indications include severe neck pain, severe neurological signs or if conservative management is not successful.

Either ventral stabilisation or dorsal stabilisation may be undertaken. Ventral stabilisation involves reduction of lux-ation and fusion of the articular joints with bone graft and screws, while dorsal stabilisation involves replacement or augmentation of the dorsal atlantoaxial ligament with wire, nylon or a fascial strip.

Prognosis

The prognosis depends on the severity of neurological signs and therapeutic management. Conservative management has a guarded prognosis due to recurrence. Surgical man-agement has a good to excellent prognosis for ventral approach but a slightly reduced prognosis for the dorsal approach. Physiotherapy plays a vital role in recovery fol-lowing spinal surgery and is increasingly becoming an invaluable component of therapy.

Caudal cervical spondylomyelopathy

It should be noted at this point that the author does not like the term ‘wobbler syndrome’ for this condition and instead uses the acronym CCSM.

CCSM is an abnormality of caudal cervical vertebrae or intervertebral discs causing spinal cord compression.

Synonyms include:

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Canine caudal cervical spondylomyelopathy

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Cervical vertebral instability

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Spondylolisthesis

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Cervical spondylopathy

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Cervical malformation or malarticulation syndrome The causes may be hereditary, nutritional, traumatic and acquired or a combination of these aetiologies.

There are five recognised different classifications:

1. Chronic degenerative disc disease 2. Congenital osseous malformation 3. Vertebral tipping

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