Chapter 33 Degenerative LS Stenosis Flashcards
Define the cauda equine
The sacral and caudal nerve roots
What is the embyologic origin of the SC?
And the vertebral column?
Neuroectoderm –> SC
Mesoderm –> Vertebral column
At what level does the SC typically terminate in:
Large breed dogs
Dogs <15kg
Cats and small dogs
Large breed dogs L4
Dogs <15kg L6
Cats and small dogs L7
How far does the dural sac extend in relation to the SC?
1-2cm further caudally
Which nerves (specifically) form the cauda equina
S1, S2, S3 and caudal nerves
(but L7 spinal nerve often included when LS discussed)
From which spinal cord segments do the following nerves arise, and what is their function?
Femoral n.
Sciatic n.
Pelvic n.
Pudendal n.
Caudal n.
Femoral n.: L4-L6. Hip flexion and stifle extension
Sciatic n.: L6-S1 (sometimes S2), Hipe extension, stifle flexion
Pelvic n.: S1-S3. Parasymathetic innervation to bladder (i.e. detrusor m)
Pudendal n.: S1-S3. Motor to urinary and anal sphincters
Caudal n.: Cd1-Cd5. Tail tone
How many formaina are present in the canine (and feline) sacrum?
2 on each side (for S1 and S2 nerves)
+ vertebral canal
What passes through intervertebral foramen?
Spinal nerve and accompanying spinl branch of dorsal intercostal arteries (thoracic vertebrae) or lumbar arteries (lumbar vertebrae)
What are the regions of the intervertebral foramen?
Entrance, middle and exit zones
List 5 breeds at greater risk of DLSS
- GSD
- Doberman
- Rottweiler
- Bernese
- Boxer
- Dalmatian
- Irish Setter
- Lab
Sex predispositioon for DLSS?
Male
Name a risk facotr for DLSS aside from breed, male and increasing age
Heavy work or training
List 5 clinical signs that may be seen with DLSS
- Crouched posture
- PL lameness/nerve root signature
- Reluctance to jump
- PL weakness
- Reduced flexor-withdrawal, cranial tibial, gastroc, perineal reflexes
- Urinary and faecal incontinence
- (Possible mild proprioceptive deficits - postural reaction deficits not usually seen in DLSS)
List 5 ddx for DLSS
Disco, fracture, neoplasia, SAD, CDM, ortho condition, ATE, prostatic/anorectal disease, polyarthritis, polyneuropathy, polymyositis, meningomyelitis
List 3 diseases that could cause coindidental T3-S3 myelopathy
IVDD, DISH, CDM
List 3 electrophysiologic tests that could be used to assess functional integrity of cauda equina
- EMG
- Motor nerve assessment (direct evoked potentials, motor nerve conduction velocity, F-waves)
- Somatosensory evoked potentials/sensory nerve testing (sensory nerve conduction velocity, cord dorsum potentials)
When performog rads for cauda equina syndrom, which anatomic regions shoudl be included (i.e. to ensure inclusion of relevant SC segments)
From L4 vertebra to Cd vertebra
List radiographic/CT findings taht may be seens with DLSS
- IVD space narrowing
- Vacuum disc phenomenon
- End plate sclerosis
- Spondylosis deformans
- Telescoping of cranial sacral lamina into vertebral canal
- Sacral subluxation/LS step formation
- Transitional vertebrae
- Sacral OCD
And on CT specifically:
- Loss of epidural fat withing vertebral canal/intervertebral foramina
- IVDP
- Zygapophyseal joint osteophytosis
- (Extradural synovial/ganglion cysts)
A, Lateral radiograph of the L6 and L7 vertebrae and the sacrum of a dog with degenerative lumbosacral stenosis. There is incomplete fusion of the sacral body suggestive of a transitional vertebra (*), telescoping of the cranial laminae of the sacrum (arrow) into the caudal aperture of L7 foramen, and vacuum disc phenomenon of the lumbosacral intervertebral disc (arrowhead).
B, Midline sagittal plane computed tomographic reconstruction of the lumbosacral articulation in a dog with degenerative lumbosacral stenosis. Typical findings are collapse of the intervertebral disc space, end plate sclerosis, vacuum disc phenomenon (arrowhead), ventral spondylosis, ventral subluxation of the sacrum (dotted line), and elongation of the sacral laminae (arrow) into the caudal aperture of the L7 foramen.
Decribe imaging findings
Midline sagittal plane computed tomographic reconstruction of the lumbosacral articulation in a dog demonstrating osteochondrosis lesion of the dorsal aspect of the sacrum (arrow). This is the most common area for osteochondrosis lesions to be seen in the lumbosacral articulation.
List 6 anatomical changes that can contribute to DLSS
A: bulging of the annulus fibrosus and nucleus pulposus
B: thickening of the dorsal aspect of the annulus fibrosus
C: spondylosis deformans
D: osteophyte formation within the caudal aspect of the vertebral foramen and surrounding the caudal articular process of L7 vertebra
E: thickening of the joint capsule of the zygapophyseal joints
F: thickening of the yellow ligament
List Mr sequences that should be run for DLSS
T1W (pre and post-contrast)
T2W
Transverse and sagittal
When might medical management of DLSS be indicated?
First episode
Inactive, older dogs with only episodic pain
What was reported sucess rate of medical management of LDSS with NSAIDS and gabapentin and 6 weeks rest?
What other medical protocol has been used? What was success rate?
55%
Epidural methyl pred acetet (1 mg/kg) at 0, 2 weeks and 6 weeks –> 79% success
What % of dogs with DLSS hasd +ve bacterial culture from disc material?
23%
When is surgery indicated for DLSS
Moderate-severe pain
Neuro defecits
What 4 procedures might be performed in additon to dorsal laminectomy for management of DLSS
- Partial discectomy (i.e. dorsal annulectomy)
- Foraminotomy
- Zygapophyseal joint removal
- Distraction and fixation
What are the lateral, cranial and caudal landmarks for dorsal laminectomy.
Describe shape of laminectomy hole
Lateral margins = medial to zygapophyseal joints
Cranial limit = leave cranial 1/3 of L7 dorsal laminal intact usually (can extend to include whole L7 dorsal lamina if need to reach L6-L7 disc)
Sacral laminectomy should be wider –> “keyhole” shape
An intraoperative dorsal view at the start of burring to create the dorsal laminectomy. The laminectomy should include the caudal two-thirds of the L7 laminae and the cranial sacral laminae. The cranial sacral laminae should be removed farther laterally than the L7 laminae, giving the laminectomy a keyhole-shaped appearance.
What precedured have/are being performed in image?
Dorsal laminectomy + partial discectomy
The dorsal annulus fibrosus is excised in a two-step procedure with a #65 Beaver knife. While the cauda equina is being retracted (like a curtain) to one side, exposure of the dorsal annulus allows for the first incisions to be made, which creates one-half (lateral) of the dorsal fenestration. The procedure is repeated on the other side to make a complete dorsal fenestration. After incisions are made in the dorsal annulus fibrosus the dorsal part of the annulus fibrosus can be removed relatively easily using grasping forceps.
How will L7 - S3 nerve roots be located anatomically, at level of LS disc?
L7 nerve roots located laterally, within intervertebral foramen. Then from lateral to medial, S1, S2, S3 nerve roots (in dural sac if present)
A, Exposure with dorsal laminectomy. The cauda equina is gently retracted to the right side. A, L7 nerve root; B, bulging annulus fibrosus and proliferation of fibrous tissue (dotted line indicates incision in annulus fibrosus for first part of dorsal fenestration); C, S1 dorsal nerve root and ganglion.
B, The cauda equina and dural sac (arrowhead) are gently retracted, exposing the disc protrusion (*). Care should be taken not to damage the internal vertebral venous plexus (arrow).
List 3 approaches for foraminotomy
What is the limitation of each
- Dorsal, via dorsal laminectomy. Cant view lateral annulous fibrosus or exit zone of intervertebral foramen
- Lateral. Cant view cauda equina and difficult to view entry zone of foramen. Advantage = dont affect articular processes.
- (Lateral via transiliac approach. Not assessed clinically)
List steps in post dorsal laminectomy distraction + stabilization
- Distract
- Debride cartilage from zygapophyeal joints
- Partial discectomy
- Remove vertebral end plate cartilage (+- forage. Make sure to preserve bony end plate if using an interbody device - need to prevent subsidence)
- Bone graft or rhBMP-2 in intervertebral space, zygapophysela joints, over laminae
- Stabilize
List 6 techniques for stabilizing LS
- Pins/screws + PMMA
- Dorsal cross pinning (Pins from base of L7 spinoud process into zygapophyseal joint and ilial wings. Have to preserve L7 so could only do a caudal dorsal laminenctomy)
- Zygapophyseal lag screws (lag screws, directed 30-45º ventrolaterally)
- SOP plate
- Pedicle screw rod fixation (titanium - better for MRI)
- (+- interbody device/cage - fill with cancellous bone if being used)
- (MTVB: Minimally-invasive transilial vertebral blocking)
What is max screw diameter for zygapophyseal lag screws in LS stabilization?
Approx 25% of diameter of articular process
What angle should LS zygapophyseal lag screws be directed at
30-45º in ventrolateral direction
What procedures have been performed?
What feauture of implant affects post-op imaging and how?
Dorsal laminectomy + stabilization using pedicle screw-rod fixation technique + intervertebral cage device
Titanium –> fewer imaging artefacts
A, After dorsal laminectomy the lumbosacral articulation can be distracted and stabilized using a pedicle screw-rod fixation construct. The pedicle screws are inserted into the L7 (left on image) and S1 pedicles and connected with two titanium rods.
B, Postoperative lateral radiograph after distraction and stabilization with a pedicle screw-rod construct. With distraction the width of the lumbosacral intervertebral disc space has been a restored and is maintained through the use of an intervertebral cage device. *Dural sac.
What factors have been associated with poor prognosis in DLSS cases
- Presence of urinary and faeceal incontinence
- Duration of urinary incontinence (x6 higher if urinary incontinence >1 month, vs <1 month)
What is overall success rate (clinical improvement) following dorsal laminectomy?
79%
N.B. No studies compare just dorsal laminectomy vs distraction-stabilization
List 4 possible complications following surgery for DLSS
- Seroma
- Instability
- Worsening of clinical signs
- Excessive scar formation
And if implants:
- Implant bending/breakage/migration
- Articular process fracture
- Infection
Name a novel technique for management of DLSS.
MTVB: Minimally-invasive transilial vertebral blocking
(Müller, VetSurg, 2017) –> all 59 dogs improved by at least 1 neuro grade (grades detailed in paper)
Device placed with LS join in flexed positon –> distraction and widening of foramen
