Ch 33 degenerative lumbosacral stenosis Flashcards
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
Distraction and Fixation (4 goals)
There is ongoing controversy about how to best surgically manage degenerative lumbosacral stenosis in the dog
The goal of distraction:
1. restore the width of intervertebral disc space and foramina by distracting the articulation
2. relieve the pressure on neural tissues;
3. revents further development of degenerative changes via stability
4. bony fusion of the lumbosacral articulation
maintenance of the distracted necessitates stabilization, which is achieved with pins, screws, and polymethylmethacrylate, and interbody devices
Excessive mobility of the lumbosacral articulation is thought to cause degenerative changes (proliferation of ligament + IVD degen)
guidelines whether or not to distract do not exist. Often the decision based on the surgeon’s impressions
Fusion is promoted by placing a cancellous bone graft or osteoconductive or osteoinductive materials (e.g., rhBMP-2
List some techniques of LS stabilisation
combined +/- dorasal laminectomy/disectomy
Pins/screws and PMMA
Dorsal cross-pinning
Lag screws across zygapophyseal joint (placed ina ventrolateral direction at 30-45 degree angle in relation to sagittal plane, 25% diameter joint)
SOP
Pedicle screw rod fixation (nserted under fluoroscopic guidance)
interbody device (aimed at maintaining the width of the IVD)
3D printed titanium implants
complications
laminectomy
- seroma formation
- instability
- acute worsening of clinical signs
- need for revision due to excessive scar formation
distraction/stabilisaion
- incorrect placement of implants can cause trauma/compression to the neural structures.
breakage
migration
infection
fracture of an articular process
bony fusion, it is difficult to achieve
adjacent segment disease L6-7
Titanium implants create less imaging artifact than steel
What is the prognosis with surgery?
What is the main known poor prognostic indicator?
Good to excellent outcome in 73 - 93%
Recurrence in 18% (3 - 54.5%)
Presence of urinary or faecal incontinence and duration of urinary incontinence (over 1m) associated with a poor prognosis
Only 41% military dogs returned to normal function. 38% improved and 20% never returned to work.
recurrence
3% to 54.5%.
18% of the dogs between 6 and 36 months (mean, 22 months)
potential reasons can be put forth to explain the rates of recurrence. New bone formation following dorsal laminectomy or scar tissue formation over the laminectomy site could impinge on the cauda equina. The authors advocate the use of a free fat graft to prevent development of scar tissue overlying the laminectomy
Continued mobility and instability of the lumbosacral articulation
Evaluation of the rostral projection of the sacral lamina as a
component of degenerative lumbosacral stenosis in German
shepherd dogs
Saunders 2018
rostral projection of sacral lamina (telescoping) in DLSS
- not associated with diagnosis of DLSS – less projection observed in affected dogs
- cannot be used to predict cauda equina syndrome
- may be relevant in individual dog pathology
Medium-Term Outcome and CT Assessment of
Lateral Foraminotomy at the Lumbosacral
Junction in Dogs with Degenerative
Lumbosacral Stenosis
Andrew John Worth 2018
LS lateral foraminotomy for DLSS
- 5/6 alleviation of pain, increased levels of activity; recurrence 1/6 (1/2 working dogs)
- volumetric analysis (2/6): 650-800% volume increase in extension immediately post-op
- bone regrowth at follow-up → mean 335% increase at 24m post-op
- 4/6 dogs increased volume vs pre-surgical
Evaluation of L7-S1 nerve root pathology with low-field
MRI in dogs with lumbosacral foraminal stenosis
Lichtenhahn 2020
Study design: Retrospective study.
Animals: Client-owned dogs (n = 240
Conclusion: A loss of foraminal fat signal (seen in 87.9%) was likely to be associated with L7
radiculopathy and foraminal stenosis. Unilateral lesions were generally associated
with clinical signs on the ipsilateral limb.
The effects of foraminotomy and intervertebral distraction on the
volume of the lumbosacral intervertebral neurovascular foramen: An
ex vivo study
Smolders 2020
Vet J
to compare the effect of foraminotomy and
intervertebral distraction on the total, cranial, and caudal compartmental volumes of the L7-S1
intervertebral neurovascular foramen (NF).
CT images were obtained from eight canine lumbosacral (L5-CD1) specimens in the following sequential conditions: native spine (1), after dorsal laminectomy and partial discectomy of L7-S1 (2), after L7-S1 foraminotomy (3), after distraction with an interbody cage
between L7 and S1 (4), after cage distraction stabilized with pedicle screw-rod
fixation in neutral (5) and flexed position (6).
Foraminotomy induced a significantly larger increase in total NF volume compared to
distraction. Foraminotomy, but not distraction, induced a significant increase in volume of the cranial subcompartment
Foraminotomy is more effective in increasing the foraminal volume and especially the cranial subcompartment, which is where the L7 nerve root traverses the NF.
Hence, foraminotomy may be more effective in decompressing the L7 nerve root.
Single dose epidural methylprednisolone as a treatment and predictor
of outcome following subsequent decompressive surgery in
degenerative lumbosacral stenosis with foraminal stenosis
Gomes 2020
Epidural steroid injection
has a role in the management of DLSS dogs, particularly when surgery is not an option
prospectively recruited
- epidural steroid: 27/32 (84.4%) improvement → 17/22 (77.2%) relapse within 6m
- 5/32 (15.6%) persistent improvement up to mean 9.4m f/u
- not useful as a predictor for post-surgical outcome
- sx → improvement in all dogs, outcome improved with decompression
Lumbosacral IVDE in dogs
Conclusion: was characterized by acute/subacute
onset of lumbosacral pain and nerve root signature and lateralized and often
dispersed extradural material over a degenerated L7-S1 intervertebral disk on
MRI. Early decompressive dorsal laminectomy generally resulted in excellent clinical outcome.
Distraction Stabilization of Degenerative
Lumbosacral Stenosis: Technique and Mid- to
Long-Term Outcome in 30 Cases
Inness 2021
presence of telescoping of S1 (dynamic narrowing of the intervertebral foramen during lumbosacral extension)
retrospective (30). Pins+ PMMA + laminectomy + annulectomy
outcome: 18/21 (85.7%) clinical improvement, 16/18 normal (remain active >1 year following surgery.), 21/21 improved pain scores
- complications: catastrophic 3/21 – 2/3 iliac artery laceration (excessive pin insertion)
major 5/21 → 3/5 revision – implant failure, seroma, SSI
Catastrophic complications occurred in 3 dogs
- sx → mean LS step reduction 60%, foraminal width increase 50% up to 2y post-op
- distraction-stabilisation may maintain foraminal enlargement longer than foraminotomy
Clinical Significance Dorsal laminectomy, annulectomy and distraction stabilization
is a complex procedure which can significantly increase foraminal width, reduce pain
and improve gait characteristics in dogs in the short- to long-term, and should be
performed by surgeons experienced in lumbosacral pin placement.
Postoperative outcomes of combined surgery comprising dorsal laminectomy, transarticular screws, pedicle screws and polymethylmethacrylate for dorsal fixation in 21 dogs with degenerative lumbosacral stenosis
Hirofumi Tanoue 2022
potential for underreporting of complications in records
potential for underreporting of complications in records
restrospective, dorsal laminectomy, transarticular screws, pedicle screws +PMMA for DLSS
- outcome: 21/21 resolution of clinical signs, improvement of proprioception at 3m post-op
no recurrence of clinical signs up to 36m post-op (66% <1y)
- complications: minor: 6/21 (28.6%) - implant failure, delayed wound healing, seroma
no major
only 66% of the cases could be followed for 12 months
Accuracy of Lumbosacral Pedicle Screw
Placement in Dogs: A Novel 3D Printed Patient-
Specific Drill Guide versus Freehand Technique
in Novice and Expert Surgeons
Bonger 2022
Pozzi study: Conclusion: The use of a customized 3D-printed guide generally improved the accuracy of PSI in canine lumbosacral vertebrae, although statistical significance was reached only at L5.
A novice and an expert surgeon each placed 3.5mm cortical screws in 10 cadavers;
3D-printed drill guide vs free-hand for placement LS pedicle screw placement
- unilateral 3DPG did not improve accuracy of screw placement
- increased variability in expert surgeon – potential suboptimal design
Congenitalmalformations of the lumbosacral vertebral column are common in neurologically normal French Bulldogs, English Bulldogs, and Pugs, with breed-specific differences
In 76 (51.0%) of the 149 included dogs
Effects
of intervertebral distraction screw fixation
of the lumbosacral joint on the adjacent lumbar segments in Beagles
Tanoue 2020
Insertion of a Fitz intervertebral traction screw, developed by Solano et al,18 between the cervical vertebrae can lengthen the distance between the vertebral end plates while maintaining correct positioning of vertebrae.
7 healthy Beagles.
PROCEDURES
Dorsal laminectomy was performed at the LSJ in each dog to expose the intervertebral disk. The IDS was then inserted into the L7-S1 disk
Results suggested that IDS fixation of the LSJ restricted lumbosacral ROM and prevented decreases in lumbosacral ID and IFA in healthy dogs. There were no changes at L6-7 and L5-6.
it appears that IDS insertion as performed in the present study could sufficiently restrict the degree of extension and thus serve as an effective method for treating nerve root compression.
Biomechanical evaluation of the lumbosacral portion of the vertebral column in canine cadavers has revealed increased stability of the LSJ after pedicle screw-rod fixation following dorsal laminectomy.16,17 The disadvantages of this technique include the risk of complications such as implant breakage and fracture of the articular processes of L7, which may be partially due to the lack of stabilized structures on the ventral aspect of the intervertebral joint, such as the intervertebral disk.1
Harris 2019 – LS transitional vertebrae potential risk factor for LS stenosis
- clinical signs: LS pain, low tail carriage, difficulty jumping, urinary/faecal incontinence
- neuro signs: proprioceptive deficits, ambulatory paraparesis, pelvic limb ataxia,
reduced spinal and perianal reflexes
- 7/13 (53.8%) cats with LS stenosis had LS transitional vertebrae
- prevalence of transitional vertebrae 24/405 (5.9%)
JFMS
