Ch 31 Cervical vertebral column Flashcards
What CN deficits can be seen with a C1-C5 lesion?
Positional strabysmus and/or facial hyperaesthesia with C1-C3
v. rare!
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
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
C1-C5 CS
C6-T2
difference in stride length between the thoracic and pelvic limbs is sometimes called a two-engine gait.
Ventral Approach to the Cervical Vertebral Column
paramedian
right sternocephalicus muscle is separated from the right sternohyoideus muscle (Figure 31.3). The sternohyoideus muscles are then retracted to the left with the trachea, esophagus, and carotid sheath.
protect the trachea, right recurrent laryngeal nerve, and the contents of the right carotid sheath
decreasing the likelihood of hemorrhage from the right caudal thyroid artery.
exposure of the longus colli muscles (D) and the longus capitis muscles
right carotid sheath
he vagosympathetic trunk, carotid artery, and internal jugular vein
Ventral Approach to the Atlantoaxial Articulation
What are the benefits of the right parasagittal?
What surgical landmark can be used for ventral C1-C2
right-sided parasagittal approach
advantages: improved exposure of the joint avoidance of dissection thyroid gland, trachea, and recurrent laryngeal nerve.
improved ability to drill or drive a Kirschner wire across the right C1-C2 articulation without the larynx and trachea directly adjacent
mandible to a point at least 5 cm caudal to the caudal edge of the thyroid cartilage
right sternothyroideus and sternocephalicus muscles and the right carotid sheath are then exposed and separated, exposing the paired longus colli muscles and cervical vertebrae
retraction of the right carotid sheath to the left side
locating a pointed ventral prominence, the ventral tubercle, on the caudal aspect of C1
Lateral Approach to the Cervical Vertebral Column
lateral or foraminal IVDE, as well as nerve sheath neoplasms
Articular processes of C3-C6 are palpated to serve as a landmark
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
Lateral Approach to the Brachial Plexus
What muscle do the spinal nerves of the brachial plexus lie deep to?
Scalenus muscle
Atlantoaxial Instability
leads to compression and contusion of the cervical spinal cord, resulting from displacement of the vertebrae (subluxation) into the vertebral canal;
atlantoaxial subluxation results from a ligamentous and/or osseous abnormality
AA anatomy
neurovascular paths?
Movement at this joint is mainly rotational,
First cervical spinal nerve and its associated vasculature pass through the lateral vertebral foramen
he vertebral artery enters the vertebral canal through the lateral vertebral foramen, after first having run through the transverse foramen of the atlas
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
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
List the stabilising ligaments of the AA joint
dens = Odontoid process
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
Traumatic atlantoaxial subluxation can occur in dogs of any breed
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
Spinal cord trauma secondary to an acute episode of subluxation has the same underlying pathophysiology as that related to acute disc extrusion and acute vertebral fracture-luxation.
tear ligaments of fracture dens
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
CT and MRI
CT can assist with identification of dens conformation or the presence of a fracture of the dens or vertebra, as well as with deciding on appropriate size of implants and surgical implant placement
MRI can provide additional information regarding spinal cord pathology such as hemorrhage or edema and syringohydromyelia, which might be important for prognosis . Additionally, MRI enables visualization of the ligamentous and supporting structures
AA Tx: conservative
what?
how long?
how sccessful?
abilize the atlantoaxial articulation while the ligamentous structures heal
strict cage confinement for 6 weeks, analgesia
external coaptation ideally using a rigid cervical brace.
splint must immobilize the occipitoatlantoaxial articulation > must come over the head rostral to the ears and extend caudal to the level of the cranial aspect of the thorax.
Complications
recurrence of disease
corneal ulcers,
migration of the splint
moist dermatitis and decubital ulcers, hyperthermia,
respiratory compromise
otitis externa,
nonsurgical or conservative approaches are likely to result in recurrent or progressive clinical signs.
AA surgery
dorsal - what not achieved
ventral -advanatges?
goal = align and stabilize AA, prevent further spinal cord damage
Dorsal
Osseous fusion generally is not achieved > cannot resist movement in directions other than flexion
continuous movement, more likely failure of implants is associated with recurrence of clinical signs
Ventral
advantage of creating a bony ankylosis providing permanent joint fusion
odontoidectomy can be performed if required
What is a contraindication for dorsal stabilisation of AA sublux?
What are the advantages of ventral stabilisation?
Dorsal deviation of the dens
Dorsal techniques for AA stabilisation (5) and their associated long term success rates
Atlantoaxial wiring/dorsal loop wiring - 52%
loop needs to be folded back toward the axis, and at this time risk for iatrogenic trauma to the spinal cord
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 (4)
articular cartilage can be scarified. This can encourage bony ankylosis
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
Fracture of the Atlas or Axis
The dorsal arch of the atlas can fracture following a dorsal stabilization techniqu
Episodic pain has been reported in dogs for several months to life postoperatively
Improper pin placement with inadequate bone purchase is the main cause of implant migration. Implant failure can be an incidental finding at recheck
post-op
nsaid, monitor, restrict 4-8wks
another surgery may not be necessary, > strong fibrous or osseous union.
What are the known risk factors effecting surgical outcome for AA stabilisation
Ageof onset: Dogs under 24m had greater odds of successful outcome
Durationand severity of clinical signs: Under 10m associated with greater odds of successful outcome
AA Px
conservative?
mortality rate?
conservative: good long-term outcome has been documented in 10 of 26 (38%) cases
perioperative mortality rate: 4% and 30% of dogs
Biomechanical evaluation of two dorsal and two ventral stabilization techniques for atlantoaxial joint instability in toy-breed dogs
Progin 2021
4 techniques (dorsal wire, modified dorsal clamp kishigami, ventral transarticular pin, and augmented ventral transarticular pin fixation). experimental (13 skull)
The AAJs with dorsal wire, ventral transarticular pin, and augmented ventral transarticular pin fixations had similar biomechanical properties, but not clamp.
load cycling and clinical studies are needed
Atlanto-axial ventral stabilisation using 3D-printed patient-specific drill guides for placement of bicortical screws in dogs
Toni 2020
To report outcome and complications following atlanto-axial stabilisation by polymethylmethacrylate applied to screws placed using 3D-printed patient-specific drill guides.
Materials and Methods: Case series
Of 61 bicortical screws placed, 57 (93%) were fully contained
rate of vertebral canal screw penetration of 7% in this
study compares favourably to previously reported values of 21%
and 9% using similar patient-specific guides
stainless steel screws resulting in greater CT artefact then would have occurred with titanium screws
Computed Tomography and Biomechanical
Comparison between Trans-Articular Screw
Fixation and 2 Polymethylmethacrylate Cemented
Constructs for Ventral Atlantoaxial Stabilization
Guillaume Leblond 2018
cadavers
The CT data revealed that TSF achieved significantly better apposition than
cemented constructs
4.4% were graded as dangerous and
86.8% as optimal.
Determination of cutoff values on computed tomography
and magnetic resonance images for the diagnosis of
atlantoaxial instability in small-breed dogs
Bastien Planchamp 2022
Study design: Retrospective multicenter study.
Sample population: Client-owned dogs (n = 123) and 28 cadavers.
ventral compression index (VCI f ≥0.16 in extended and ≥0.2 in flexed
head positions were diagnostic for AAI (sensitivity of 100% and 100%, specificity of 94.54% and 96.67%, respectively).
The location of the endotracheal tube tie can influence interpretation of MR images of the craniocervical region of small breed dogs
Dorsal compression of the cervical spinal cord can be identified by examining the cervical subarachnoid space at the atlantoaxial (AA) or atlantooccipital region using MRI. Dorsal compressive lesions have been described with various terms, such as AA constrictive lesions, dural fibrous bands, or AA bands,
These dorsal compressive lesions, identified
with MRI, are a significant predictor of craniocervical junction
abnormalities, such as atlantooccipital and AA instability,
atlantooccipital overlap,
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? (8)
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
neurotmesis: Full recovery usually not seen and accompanied by scar.
nerve roots lack an epineurium, traction of the thoracic limb or severe abduction of the scapula can result in stretching or avulsion of these nerve roots, usually within the dura
dorsal root = sensory input into the spinal cord
ventral root = motor function and autonomic innervation.
myelin sheath for each myelinated axon is formed by Schwann cell plasma membranes wrapping around the axon like an “onion peel.”
The Schwann cells are separated by junctions called nodes of Ranvier, which assist in the rapid conduction of action potentials along the axon.
Endoneurium surrounds each axon
Groups of axons are surrounded by perineurium
tissue around the entire nerve, called the epineurium
What are the 3 forms of brachial plexua injury and their common associated signs?
Unless avulsion confirmed, traction trauma to this region is appropriate
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
If the injury is severe > damage the spinal cord
- ipsilateral pelvic limb general proprioceptive ataxia
- UMN paresis or plegia.
WHat is indicative of a poor prognosis on EMG?
Early decreased radial nerve conduction velocity indicates a poor prognosis
Electromyography allows detection of abnormal spontaneous electrical activity indicative of denervated muscles 1 week to 10 days after injury
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
adult dog, this axonal regrowth can reach at least 10 to 15 cm within a 4-month period
Brachial avulsion Px
grave if radial nerve avulsion occurs
Carpal arthrodesis or tendon transposition > triceps innervation is required to be able to bear weight through the elbow
given at least 4 to 6 weeks before a grave prognosis
Limb amputation should be discussed if self-mutilation becomes apparent and is not responsive
What percentage of IVDH are cervical?
What type?
breed?
pathophysiology of spinal cord concussion and compression
14-25%
most type I extrusion
smll.chondrodys breeds
or
Labs, doberman, dalmation
cervical IVD dx
- CSF
- rads: rule out disco/#/malformation. Narrow IVd/mineralisation (25% accuracy)
- myelogram CT: heterogenous, hyperattenuating extradural mass with loss of epidural fat. possible compression inversely proprtional to ppst-op neuro status
- MRI: nonivasive, high res image with increase localisation accuracy compared to CT. degree of compresion not prognostic. Hypointense on T2W
ID hydrated IVD (hyperintense, seagull)
Accuracy of a patient-specific 3D printed drill guide for placement
of cervical transpedicular screws
Sinead E. Hamilton-Bennet
Prospective case-series.
Sample Population: Thirty-two cervical pedicle screws (CPS) placed in 3 large
breed dogs.
The majority (29/32) of these screws were
placed without evidence of vertebral canal breach (grade 0), whereas a vertebral canal
breach <2 mm (grade 1) was detected in 3/32 screws.
In a cadaveric study comparing the biomechanics of
bicortical pins and monocortical screws with PMMA placed
free-hand in the canine cervical vertebral column, 100% of
bicortical pins violated the vertebral canal compared with a
much lower incidence after monocortical screw fixation.32
The angles for ideal screw insertion are of limited use in
dogs, because of conflicting reports, inter- and intra-breed
anatomical variations, and rotational effects of both surgical
positioning and intraoperative probing or screwing on vertebral
alignment.14,33,34 Consequently, free-hand CPS placement
in dogs is not recommended.14,33
Accuracy of a 3-dimensionally printed custom endoscopy
port for minimally invasive ventral slot decompression in
dogs: A cadaveric study
Kang 2022
Cadaveric study.
Animals: Fifteen
Conclusion: Screw positioning and creation of ventral slots were accurately
performed using the 3DEP by both inexperienced and experienced surgeons.
Clinical significance: The use of a 3DEP for minimally invasive cervical ventral
slot decompression may be an alternative to the conventional ventral slot
in dogs. Additional studies are needed to evaluate efficacy and safety.
Recurrence of signs consistent with
cervical intervertebral disc extrusion in
dogs
Argent 2022
Objectives: Report the rate of recurrent clinical signs following successful treatment of cervical IVDD, and explore the association between treatment method and recurrence.
Materials and Methods: Medical records of dogs with MRI- or CT-confirmed
Recurrence was considered
presumed if based on clinical signs or confirmed if based on repeat cross-sectional imaging
Clinical Significance: Following successful initial medical or surgical treatment, clinical signs consistent
with recurrent cervical disc extrusion occurred with similar frequency. Medically treated cases tended
to have recurrence at the same site as initial presentation, whereas surgical treatment prevented this.
Recurrence usually occurred within 2 years. The retrospective study design, small number of recurrences
and lack of imaging confirmation of every recurrence should be considered when interpreting
the results.
Direct decompression (4)
single static ventral +/- dynmaic
review short term uscess 80%, recurrenc2 20%
difference between tehcnique outcomes??
Indirect (6)
all have problems
goals = adeute distraction and maintian longterm wit osseous fusion
most coomon complications = implant fail before fusion
ideally use distractor rather than manual
1. PMMA + Pins
single, increased failure if 2
v-slot then threaded positive profile pins, bone graft
angles: 35 C5-6, 45 C7
monocoruical screw performed similar biomehcnically
> reduced PMMA amount to reduce oeisiohageal irritation
> modifications: corticcancellous bone to distract + u-shape wire spacer
71% sucess long term
penetration risk 25-57%
6. disc arthroplasty
in humans no consensus
aim to preserve all motion to reduce ASS (no fusion)
probs:
long-term lacking, high subsidence rate + still reduce IVD mobility
Surgical management and long-term outcome of dogs with cervical
spondylomyelopathy with an anchored intervertebral titanium device
King 2020
50% subsidence
90% initially, but then 70% longer term, with 2 euthed
10 dogs with (DACSM) and 1 dog with osseous-associated
Design Retrospective case series.
myelography with or without advanced imaging , Sx with C-LOX implant.
Long-term follow-up was available in 8/11 with owner questionnaire. 2 euth.
Seven (70%) dogs with DACSM
improved neurologically but had persistent neurological dysfunction
Postoperative radiographs revealed cage subsidence in
5 (50%) dogs, and loosening of a single cranial or caudal vertebral
body screw in 4 (40%) dogs with DACSM.
Five major complications occurred in 4 (40%) patients
Adjacent segment disease
occurred in three dogs (30%) with DACSM
conclusion: comparable to previously
described distraction–stabilisation techniques.
Association of neurologic signs with high-field MRI findings
in 100 dogs with osseous-associated cervical spondylomyelopathy
Marília de Albuquerque Bonelli 2021
prospective study found durastion/worsneing over 1.9 months > not confirmed in this study
retrosepctive study
weremale (75%) with chronic presentation (89%), more than one site
of spinal cord compression (78%) and foraminal stenosis (91%).
Dogs with multiples sites of spinal cord compression were more likely to have severe spinal cord compression
There was correlation (weak) between neurologic grade and severity of spinal cord compression
disc degeneration was seen in 80%
of dogs.
extradural intraspinal cysts (25%) > partially responsible for spinal cord
and/or nerve root compression
majority of dogs with severe spinal cord compression and T2Wspinal cord hyperintensity were younger than 3 years of age.
> older dogs not have more severe imaging changes or clinical signs
Comparison of Cervical Stabilization with
Transpedicular Pins and Polymethylmethacrylate
versus Transvertebral Body Polyaxial Screws with or
without an Interbody Distractor in Dogs
Marinho 2022
compare the biomechanical properties of
caudal cervical vertebral stabilization using bicortical transpedicular pins with polymethylmethacrylate
(PMMA) versus transvertebral body polyaxial screws and connecting
rods with or without an interbody distractor.
Study Design Ten canine cervical vertebral columns
Stabilization obtained with transvertebral body polyaxial screws was
comparable to that from the well-established bicortical pins/PMMA construct. Association
of an intervertebral distractor did not change AROM of the polyaxial screw
constructs.
Instrumented cervical fusion in nine dogs with caudal
cervical spondylomyelopathy
Bok 2019
Dogs have a
natural lordotic position that increases the risk of ventral extrusion
of intervertebral implants from shearing forces, and ventral
fixation and stabilization are often required to prevent
ventral dislodging of the intervertebral implants.
Study design: Short case series.
Animals: Nine large-breed dogs.
Methods: Medical records of dogs treated
surgery objective was spinal distraction by implantation of a
SynCage and fixation with two Unilock plates
According to CT, the volume of bone (mean ± SD) through the cage was 79.5% ± 14.3% Subsidence was seen in one of nine dogs.
Implant failure was evident in four dogs, and plates were removed in two dogs.
In seven of nine dogs, infraclinical pathology was observed in adjacent segment
survival 9-51 months (average 27mths) > several dies from other dz
Biomechanical effects of a titanium intervertebral cage as a
stand-alone device, and in combination with locking plates
in the canine caudal cervical spine
Rick Beishuizen
evaluate the change in ex vivo biomechanical properties of the
canine cervical spine, due to an intervertebral cage, both as a stand-alone
device and in combination with plates
Although the anchorless stand-alone device has
successfully and safely been used in vivo in a limited
number of clinical cases, more research is necessary
regarding the in vivo biomechanical consequences in the
long term, the risk of cage migration, non-union and subsidence
in the long term, and the biomechanical effects
of bony ingrowth through the cage.
