Ch 33 degenerative lumbosacral stenosis Flashcards
(41 cards)
Anatomy
L7 vertebra and the sacrum is composed of an amphiarthrosis (cartilaginous joint) that includes the intervertebral disc and bilateral synovial joints
The cauda equina courses obliquely and caudally within the vertebral canal, residing within the ventrolateral aspect of the vertebral foramen, which is formed by the articular processes and pedicles, immediately before exiting their respective intervertebral foramina.
The intervertebral foramina are defined and bordered by?
The intervertebral foramina:
- articular processes and joint capsule of the zygapophyseal joints
- the pedicles
- vertebral body
- dorsolateral portion of IVD
On the sagittal reconstruction images, note the large amount of hypoattenuating intraforaminal fat
What are the embryological origins of the vertebral column and the spinal cord?
How does this contribute to the formation of the cauda equina?
spinal cord is neuroectodermal origin, vertebral column is mesodermal origin.
They grow at different rates with the vertebral column outgrowing the spinal cord. As a result, the nerve roots of the terminal portion of the spinal cord have to course a longer distance to exit their respective intervertebral foramina
What does the spinal cord terminate in various sized dogs?
Large/giant breeds - L4
Dogs under 15kg - L6
Toy breeds and cats - L7
Dural sac extends 1-2cm further caudally than the terminal conus medullaris and may extend into the sacrum in over 80% of dogs
Define cauda equine syndrome
clinical signs resulting from a disease process which involves the LS articulation and effects the nerve roots and/or spinal nerves of the cauda equina
DLSS is common natural cause of CES characterized by an acquired narrowing of the vertebral canal at the lumbosacral (LS) junction, lateral intervertebral neurovascular foramina, or a combination of the 2, resulting in compressive
radiculopathy of 1 or more nerve roots of the cauda equina
multifactorial degenerative disorder (8)
result in neural or vascular compression of the cauda equina (compressive radiculopathy of 1 or more nerve roots of the cauda equina)
- Hansen type II (less common type I) IVD
- transitional vertebrae ( Estimations indicated a moderate heritability of lumbosacral transitional vertebrae)
- congenital osseous stenosis of the vertebral canal or intervertebral foramina,
- sacral osteochondrosis,
- proliferation of the joint capsules or ligaments
- osteophytosis of the articular processes
- epidural fibrosis
- instability or malalignment/subluxation of L7-S1
Synovial and ganglion cysts, epidural lipomatosis,49 as well as congenital malformations associated with tethered cord syndrome
DLS associated with type II IVDD, osseous stenosis, malformations, and transitional vertebrae has also been reported in cats.
What percentage of LS disc cultures are positive?
23%
pathophys of DLSS (5)
risk factors: in GSD include transitional vertebral anomalies (TVA) and sacral osteochondrosis
- altered and abnormal motion of LS articulation predispose to degeneration of the IVD > set in motion a slowly progressive degeneration LS joint.
- As the IVD degenerates > shifts the load bearing from the central IVD to peripheral parts (zygapophyseal joints and vertebral bodies).
- resulting altered biomechanical loading/ instability > surrounding anatomic structures respond by proliferation and hypertrophy : yellow ligament, epidural fibrosis, osteophyte formation, and ventral spondylosis.
- Further degen of IVD leads to bulging of the annulus fibrosus and Hansen type II protrusion
- Ultimately, physical deformation or compression of the nerve roots followed by demyelination, axonal loss, and inflammation.
What proinflammatory cytokines and growth factors are released with compressive radiculopathy?
TNFalpha
IL-6
IL-beta
Perpetuates the disease locally and within neural tissue and is an important mechanism in the induction of neuropathic pain
also compromise nerve root microcirculation
CS of DLSS
What is intermittent claudication?
male than in female dogs. Degenerative lumbosacral stenosis affects mainly large-breed dogs, and German Shepherd Dogs are predisposed
static or intermittent, root signature, reluctant to jump or work.
Paroxysmal manifestations consistant with caudal lumbar pain or pelvic limb cramping, or weakness as a result of vascular compromise or compression of nerve roots in the cauda equina. Signs are exacerbated by activity
Occasionally, urinary and fecal incontinence
What nerves are effected by degenerative LS stenosis?
What reflex is most reliable?
Cranial tibial
Gastrocnemium
Perineal reflex and flexor-withdrawal reflex may be normal or depressed
Often, deficitis relate to sciatic dysfunction, causing a failure of hock flexion on withdrawal reflex.
May also be a pseudohyperreflexia of the patellar reflex due to loss of antigonistic muscle tone from the caudal muscle musculature
Dx of DLSS
pelvic limb neurologic dysfunction is usually not seen (consdier other ddx)
ddx
(1) applying traction or extension to the tail,
(2) applying direct digital pressure per rectum to the lumbosacral disc
(3) percutaneously applying direct pressure overlying the dorsal lumbosacral articulation while standing
(4) percutaneously applying direct pressure overlying the dorsal lumbosacral articulation while elevating and supporting the pelvic limbs a few centimeters off the ground and extending the hip joints (termed the lordosis test)
(5) rotating the lumbosacral articulation by swinging the pelvic limbs from side to side.
What is the only means of providing functional data about the cauda equina?
Electrophysiologic testing
What are the most consistent radiographic signs suggestive of LS stenosis?
Sacral osteochondrosis
Transitional vertebrae (incomplete fusion of the sacral body)
telescoping of the cranial laminae of the sacrum (arrow) into the caudal aperture of L7 foramen
LS step formation
LS disc vacuum phenomenon
An epidurogram in dogs with degenerative lumbosacral stenosis may show narrowing
What are the main CT findings consistent with LS stenosis?
flexion/extension?
cT good for Sx planning
changes can be seen in neurologically normal dogs
Loss of epidural fat
Abnormal soft tissue density in intervertebral foramina
Buldging of LS disc
Displacement of dural sac
Subluxation and osteophytosis of zygapophyseal joints
Compressed and inflammed tissue will often contrast enhance
flexion and extension increase the sensitivity of detection
extended position accentuates foraminal compression, as well as intervertebral disc protrusion
degree of cauda equina compression correlates poorly w clinical severity
MRI findings
pro’s: can ID other pathology
MRI findings are similar with the high signal fat getting replaced by hypointense material (disc vs fibrosis vs bony proliferation)
T1-weighted with contrast enable visualization of vertebrae and help differentiating degenerative changes of the vertebra with DLSS from other pathologies such as discospondylitis.
HASTE - MR myelogram
What is the success rate of medical management?
55%
neuropathic pain–modifying agents (gabapentin, amantadine, pregabalin)
In one study, 55% of dogs were successfully managed with NSAID and gabapentin, alone or in conjunction, as well as a 4- to 6-week period of restricted activity.
79% improvement with 1mg/kg methypred epidural. 3 injections (1st injection, 2 weeks and 6 weeks later)
> may predispose to bacterial infections in the intervertebral disc. As mentioned previously, positive bacterial cultures
What are the indications for surgical stabilisation?
Removal of the zygapophyseal joints
Ventral subluxation of S1
To prevent further development of instability
Surgerical aims
laminectomy + what? (3)
moderate to severe pain, and when dogs display neurologic deficits
primary aim = decompress the cauda equina and free entrapped nerve roots.
Dorsal laminectomy
can be supplemented with additional procedures:
(1) partial discectomy consisting of dorsal fenestration (or dorsal annulectomy) and nuclear pulpectomy
(2) foraminotomy,9,11,17,40 and rarely (3) removal of the zygapophyseal joint
How is the S1 nerve root identified?
Large spinal ganglion at the level if the LS IVD
dorsal laminectomy
compression of the nerve roots due to bony proliferation, soft tissue hypertrophy, or both
dorsal laminectomy alleviates dorsal compression + allows access for removal of the herniated intervertebral disc material.
magnification with surgical loupes
position: hips, stifles, and hocks flexed
caudal two-thirds of the L7 laminae is removed. Only in rare cases should the spinous process of L7 and the cranial portion of the median sacral crest be left in place.
if herniation at L6-L7 articulation, the dorsal laminectomy may be extended cranial
from lateral to medial coursing dorsally over the lumbosacral intervertebral disc are the S1, S2, and S3 nerve roots with the dural sac (if present) or terminal filaments being located on the midline
If the intervertebral disc herniation is situated laterally in the vertebral canal, the caudal articular process of L7 must be partially removed to decompress the L7 nerve roots.
Complete removal of the zygapophyseal joint(s) carries a risk for destabilization
Removal of the epidural fat > to view the cauda equina and dural sac. If adhesions are identified
Partial discectomy > started with a dorsal fenestration (also called annulectomy)
avoid damaging the internal vertebral venous plexus
free fat grafts >rotect the ventral aspect of the cauda equina from postoperative adhesions and tissue proliferation due to scar formation
69-93% improved, ~15-18% relapse
submit a sample of the disc for aerobic bacteria
What are the 2 approach options for a foraminotomy?
What can be used to enhance visualisation?
Dorsally through a dorsal laminectomy
Laterally without a laminectomy
Can use endoscopy to improve visualisation.
A osteotomy of the wing of the ilium has been described
foraminotomy
compression of L7 spinal nerve(s) as it exits its respective intervertebral foramen/foramina
- via a dorsal laminectomy (L7 nreve as easily visaulised)
Visual access can be improved by removing the medial aspect of the caudal articular process of L7. The use of an endoscope - foraminotomy (no direct vision of cauda equina) can be performed from a lateral approach
llows access to all aspects of the foramen and lateral portion of the intervertebral disc
routine craniolateral approach to the ilium
What options are available for physical distraction of the LS joint prior to stabilisation?
Modified Gelpi retractors
Distractor on preplaced screws
T-handle distractor
Distracted until correct anatomical position of the zygapophyseal joints is attained
