Ch 31 - Cervical Vertebral Column and Spinal Cord Flashcards
What CN deficits can be seen with a C1-C5 lesion?
Positional strabysmus and/or facial hyperaesthesia with C1-C3
v. rare!
Damage to what nerve roots can cause Horners syndrome?
T1-T3
What does paresis or paralysis indicated?
- A disease process affecting the descending UMN tracts
- Or a diffuse neuromuscular disease
Why do dogs with cervical lesions often present with more pronounced motor dysfunction in the pelvic limbs?
The descending UMN tracts to the pelvic limbs are more peripherally located within the spinal cord
What percentage of tetraparetic dogs are incorrectly localaised based on the FL withdrawal?
34%
How quickly does neurogenic atrophy become clinically obvious? Disuse atrophy?
- Neurogenic wtihin 7 days
- Disuse will take several weeks
What is a transverse myelopathy?
No transmission of ascending or descending impulses across the site of the lesion
What is Horners Syndrome?
What spinal cord segment can cause this?
What is the path of the sympathetic nerves?
- Horners syndrome is loos of sympathetic innervation to the eye causing miosis, ptosis, enophthalmos and elevation of the third eyelid
- T1-T3
- Hypothalamus -> descends sp. cord in lateral tectotegmental tracts
What are the advantages of the modified ventral approach to the cervical spine?
- Helps to protect the trachea, right recurrent laryngeal nerve and right carotid sheath
- Provided increased exposure of the caudal cervical vertebrae
- Decreases risk of haemorrhage from right caudal thyroid artery
What are the benefits of the right parasagittal approach for the ventral approach to the AA joint?
- Improved exposure of the joint
- Avoids dissection around the thyroid gland, trachea and recurrent laryngeal nerve
What surgical landmark can be used for ventral C1-C2
Pointed ventral prominence (ventral tubercle) on the caudal aspect of C1. This indicates the ventral midline of C1-C2 joint space
What is a lateral approach to the cervical spine good for?
Lateral or foraminal IVD herniation and nerve sheath neoplasms
What muscles required dissection for the lateral approach to C1-C4?
How does this differ for C5-C7?
- Platysma
- Blunt seperation through brachiocephalicus
- Splenius
- Serratus vantralis
- Plane of dissection between longissimus capitus and complexus muscles to expose articular facet
- Dorsal branch of the spinal nerve needs to be sacrificed, the tendinous attachments of the complexus and multifidus are then detached from the articular process
- Longissimus capitus sharply dissected from transverse process and reflected ventrally to fully expose the joints
C5-C7 requires seperation of brachiocephalicus from trapezium (not dissection through). The superficial cervical artery and vein will be located between these muscles and is ligated
What retractor can be used to retract the scapula on approach to the brachial plexus?
Farabeuf retractor
What muscle do the spinal nerves of the brachial plexus lie deep to?
Scalenus muscle
What joint is considered the yes joint?
And the no joint?
- Yes joint - occipitoatlas joint
- No joint - atlantoaxial joint
How many pairs of foramina does the atlas have?
Two
- Transverse foramen - passes obliquely through transverse process
- Lateral vertebral foramen - perforates the craniodorsal part of the vertebral dorsal arch. First cervical spinal nerve and its associated vasculature run through here
What are the atlantal fossae?
Depressions ventral to the wings on each side where the vertebral vein and artery run
How many bony elements for the atlas and axis develop from?
How long does it take for fusion?
- Atlas - 3 boney elements
- Axis - 7 boney elements (pair of arches, 3 parts of the body, the dens, apical elements of the dens)
- Fusion of dorsal atlas by 106d, ventral suture by 115d
- Fusion of all parts of axis from 30 - 396d
What is another name for the dens?
Odontoid process
List the stabilising ligaments of the AA joint
- Transverse ligament - holds the dens within the ventral aspect of the vertebral foramen. Prevents dorsal movement which allowing rotation
- Apical ligament - attachs dens to basioccipital bone
- Bilateral alar ligaments - Attach dens to the occipital condyles
- Dorsal atlantoaxial ligament - Joins dorsal arch of atlas to craniodorsal spine of axis
Alar ligaments provide the most important stabilisation against VD shearing forces
List possible congenital or developmental abnormalities of the AA joint
- Dysplasia (34%)
- Hypoplasia or aplasia (46%)
- Dorsal angulation of the dens
- Seperation of the dens
- Absense of the transverse ligament
- Incomplete ossification of the atlas
- Block vertebrae
What percentage of dogs with AA sublux will have a normal dens?
24%
What breeds are predisposed to congenital abnormalities predisposing to AA instability?
- Yorkies
- Chihuahuas
- Min Poodles
- Poms
- Pekingese
Standard Poodles! - inherited ansense/hypoplasia of the dens
What is predictive of AA instability on a plain lateral radiograph?
An angle between the atlas and axis of less than 162 degrees
What is a contraindication for dorsal stabilisation of AA sublux?
What are the advantages of ventral stabilisation?
Dorsal deviation of the dens
Ventral advantages:
- odontoidectomy can be performed if required
- Provides a means for bony ankylosis for permanent joint fusion (approach of choice for AA fractures)
List the dorsal techniques for AA stabilisation and their associated long term success rates
- Atlantoaxial wiring/dorsal loop wiring - 52%
- Double stranded cross-suturing (less than 2kg) - 50%
- nuchal ligament technique - 75%
- Dorsal cross-pinning
- Kishigami AA tension band - 75%
What is this device?
What are its advantages?
- Kishigami tension band for dorsal stabilisation of AA sublux
- Reduced risk of damaging the spinal cord as it does not need to be passed under the dorsal arch
List the ventral stabilisation techniques for AA subluxation and their associated long-term success rates
- Transarticular screws or pins - 47%
- Pins and PMMA - 94% (long-term complications 34%)
- Screws and PMMA (placed 30-40 degrees)
- Ventral plating (mini H-plate 2.0mm, 5-hole butterfly plate 1.5mm)
What is the mean optimal AA insertion angle of transarticular screw/pin insertions?
What was the mean corridor length and width?
- 40+/-1 degree in medial to lateral direction
- 20+/-1 degree in VD direction from ventral aspect of vertebral foramen of the axis
Mean corridor length 7mm, width 3-5mm
AIming in a craniolateral direction
What is the overall rate of complications for dorsal and vental stabilisation of AA sublux?
- Dorsal 71%
- Ventral 53%
Implant failure of the transarticular pins most common complications. Implant failure 48% dorsal vs 44% ventral, may or may not require re-op
What are the known risk factors effecting surgical outcome for AA stabilisation
- Age of onset: Dogs under 24m had greater odds of successful outcome
- Duration and severity of clinical signs: Under 10m associated with greater odds of successful outcome
In what percentage of dogs does the C5 spinal cord segment contribute to the brachial plexus?
24%
What nerves are branches of the brachial plexus?
- Brachiocephalic
- Suprascapular
- Subscapular
- Axillary
- Musculocutaneous
- Radial
- Median
- Ulnar
- Dorsal thoracic
- Lateral thoracic
- Long thoracic
- Pectoral
- Muscular branches
List the 6 classes of nerve trauma
- Class 1: Neurapraxia - interruption of the function and conduction of a nerve without structural changes. Reversible, up to 6 weeks to improve
- Class 2: Axonotmesis - crush or percussion injuries causing Wallerian degeneration. Internal architecture of the nerve, including the endoneurium and Schwann sheath is well preserved. Recovery expected but can take several weeks
- Class 3: Neurotmesis - Disruption of axons and endoneurium but fascicular orientation is maintained by intact perineurium
- Class 4: Neurotmesis - Disrupted perineurium
- Class 5: Neurotmesis - Entire nerve severed
- Class 6: COmbines several of the previouse degree of injury per fascicle
What are the 3 forms of brachial plexua injury and their common associated signs?
- Injury of the cranial portion (C5-C7) - Effects musculocutaneous, axillary, subscapular and suprascapular nerves. Loss of shoulder movement and elbow flexion, shoulder atrophy
- Injury to the caudal potion (C8-T2) - Radial, median and ulnar nerves. Cannot extened elbow and thererfore cannot weight bear. Radial nerve involved in 92% of dogs. Can sometimes see Horners syndrome and loss of cutaneous trunci
- Complete injury (C6-T2) - Drags leg knuckles, shoulder more ventral, hypotonic and atrophy
WHat is indicative of a poor prognosis on EMG?
Early decreased radial nerve conduction velocity indicates a poor prognosis
List the surgical techniques for brachial plexus repair
- Neurotization (nerve transfer) - Can be neuroneural or neuromuscular using 9-0 monofilament nylon
- Reimplantation via hemilaminectomy, durotomy, incision into pia mater and spinal cord
Successful neurotization in cats using right lateral thoracic and thoracodorsal nerve to reinnervate the left transected musculocutaneous nerve
What percentage of IVDH are cervical?
14-25%
What are the most common sites of cervical disc herniation in chondrodystrophic dogs?
- 80% C2-C4
- 44-59% C2-C3
Caudal disc spaces are mosre common in Yorkies and Chihuahuas as well as large breeds
What CSF protein may serve as a prognostic indicator?
Microtuble-associated protein tau (positively associated with the severity of spinal cord damage)
What is chemonucleolysis?
Intradiscal injection of chondroitinase ABC to treat disc herniation. 92% of dogs improved with 77% having excellent improvement
What are the maximum sizes of a ventral slot window?
- 33% length of vertebral body
- 50% width (but preferably 33%)
What are the advantages of a slanted slot?
What are the recommened window sizes?
- Provides access at the site of herniation without removing a large portion of the annulus, thereby preserving more stability
- Window: 20% width and 20-25% length
What are the reported complication rates of v-slot?
- 9.9% complications, 6.4% of which are major
- Mean mortality 3-8%
- Respiratory compromise (phrenic nerve C5-C7)
- Cardiac dysrhythmmias
- Haemorrhage (18.9%)
- Neuro deterioration
- Instability (8% when width 50%)
What has been shown to be associated with prognosis for cervical IVDH?
- Site: caudal to C3-C4 have poorer prognosis (likely included Wobblers)
- Degree of injury: LMN dysfunction.
- Duration of disease: Able to walk within 96hr are likely to make a full recovery, dogs that do not walk within 2 weeks are likely to have residual deficits
- Type of Tx: 36% recurrency with conservative vs 5-10% surgical, v-slot 90% full recovery 1m and 98% vs 78% hemilam at 12m, higher complication with v-slot but longer recovery wtih slanted slot, Hansen type II good and excellent in 47% and 32%
What anatomical differences explain the predisposition of wobblers in large dogs?
- The vertebral foramen is proportionately smaller in lare dogs
- The vertebral height of the cranial aspect of the foramen in significantly smaller than small dogs, resulting in a funnel shaped vertebral foramen
What three factors explain the pathophysiology of cervicospondylomyelopathy?
- Vertebral canal stenosis
- Pornounced torsion of the caudal cervical column leading to IVD degeneration (caudal cervical spine has three times more torsion than cranial)
- Protrusion of larger volume intervertebral discs
What causes osseous compression in CSM?
- Proliferation of the laminae dorsally
- Articular processes dorsolaterally
- Pedicles laterally
What molecular mechanisms play a role in CSM?
- Apoptosis of oligodendrocytes interfering with remyelination
- Upregulation of alpha-2-HS and SPRAC as well as complement C3, all assoc with osteoarthritis change
- Significant reduction in monocyte chemoattractant protein/chemokine ligand 2 (MCP-1/CCL2) concentrations - monocytes are needed for clearance of axonal and myelin debris for clearance and recovery
- Elevation of IL6 - implicated in generation and propagation of chronic inflammation
What are the rates of single lesions vs multiple lesions in CSM?
- Large breeds: 50/50
- Giant breeds: 20% single site, 80% multiple
What is the rate of post-myelogram seizures in Dobermans?
25-27%
What additional tests should be performed in a presurgical evaluation of a Wobblers patient, esp. if a Doberman
- Thyroid function
- von Willebrand status
- Cardiac function
What is the rate of improvement in conservative vs surgical treatment of CSM
Conservative:
- 54% improved
- 27% static
Surgery
- 81% improvement
How are corticosteroids helpful in conservative management of CSM?
- Decrease vasogenic oedema
- Protection from glutamate toxicity
- Reduction of apoptosis
List the direct decompressive techniques for treatment of CSM
- Ventral slot (72%)
- Inverted cone
- Dorsal laminectomy (79-95%, 30% recurrence)
- Hemilaminectomy
List the indirect decompression-distraction techniques for treatment of CSM
- Pins and PMMA (73%)
- Screw Bar-PMMA
- PMMA plug (82%, long term 62%)
- Locking plate (73%)
- Distractible titanium cage
- polyetheretherketone (PEEK) cage with locking plates
- Traction screw with locking plates
What is a motion-preserving technique for treating CSM?
What are the benefits?
Cervical Disc Arthroplasy: a technique to distract the spine while preserving moton
- Allows direct decompression
- Allows reestabishment of normal disc space with preserved motion to decrease risk of domino effect (adjacent segment disease)
What is the recommened width of an inverted cone v-slot?
What are the proposed benefits?
- 20% width of vertebral body
- Allows more complete removal of the protruded disc
- Less risk of haemorrhage
- Minimised risk of IVDS collapse
What distractors can be used for IVDS?
- Caspar distractor
- modified Gelpi distractor
What is the recommended angle of insertion for pins when treating CSM?
-C5-C6 - 30-35 degrees
C7 - 45 degrees
Monocortical screws perform similarly to bicortical positive profile pins
What are some key points in the application of a PMMA plug?
How can you reduce the rates of migration?
- Discectomy, leaving approx 3-5mm of dorsal annulus intact
- Anchor holes in the adjacent vertebral end plates
- Bone graft into ventral disc space once PMMA has hardened
- A retention screw can help to prevent migration
What complications are possible with CSM treatment?
14.9% complication rate
- Neuro deterioration (70% after continuous dorsal laminectomy, up to 42% with ventral techniques)
- Improper implant placement (25-57%)
- Domino effect (20%)
- Laminectomy membrane?
- Implant failure (7.5-30%)
- Collapse
- Insufficient decompression
- Recurrence 24%
What MRI findins are associated with a poorer outcome for CSM?
Spinal cord hyperintensity on T2W with concurrent hypointensity on T1W images
What are extradural synovial cysts?
Cysts originating from the zygapophyseal joints of the vertebral articulations and are located extradurally. Divided histologically into synovial cysts (epithelial lining) and ganglion cysts (mucinous degeneration or articular cartilage)
What is the main predisposing factor of extradural synovial cysts?
Degenerative changes of the zygapophyseal joint
What are the treatment options for extradural synovial cysts?
- Dorsal laminectomy
- Hemilaminectomy
- Percutaneous cyst rupture with corticosteroid injection (humans)
Must remove enture cyst and periarticular soft tissues to minimize risk of recurrence
