Chapter 33 Degenerative LS Stenosis

Question 1

Define the cauda equine

Answer 1

The sacral and caudal nerve roots

Question 2

What is the embyologic origin of the SC?

And the vertebral column?

Answer 2

Neuroectoderm –> SC

Mesoderm –> Vertebral column

Question 3

At what level does the SC typically terminate in:

Large breed dogs

Dogs <15kg

Cats and small dogs

Answer 3

Large breed dogs L4

Dogs <15kg L6

Cats and small dogs L7

Question 4

How far does the dural sac extend in relation to the SC?

Answer 4

1-2cm further caudally

Question 5

Which nerves (specifically) form the cauda equina

Answer 5

S1, S2, S3 and caudal nerves

(but L7 spinal nerve often included when LS discussed)

Question 6

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.

Answer 6

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

Question 7

How many formaina are present in the canine (and feline) sacrum?

Answer 7

2 on each side (for S1 and S2 nerves)

+ vertebral canal

Question 8

What passes through intervertebral foramen?

Answer 8

Spinal nerve and accompanying spinl branch of dorsal intercostal arteries (thoracic vertebrae) or lumbar arteries (lumbar vertebrae)

Question 9

What are the regions of the intervertebral foramen?

Answer 9

Entrance, middle and exit zones

Question 10

List 5 breeds at greater risk of DLSS

Answer 10

• GSD
• Doberman
• Rottweiler
• Bernese
• Boxer
• Dalmatian
• Irish Setter
• Lab

Question 11

Sex predispositioon for DLSS?

Answer 11

Male

Question 12

Name a risk facotr for DLSS aside from breed, male and increasing age

Answer 12

Heavy work or training

Question 13

List 5 clinical signs that may be seen with DLSS

Answer 13

1. Crouched posture
2. PL lameness/nerve root signature
3. Reluctance to jump
4. PL weakness
5. Reduced flexor-withdrawal, cranial tibial, gastroc, perineal reflexes
6. Urinary and faecal incontinence
7. (Possible mild proprioceptive deficits - postural reaction deficits not usually seen in DLSS)

Question 14

List 5 ddx for DLSS

Answer 14

Disco, fracture, neoplasia, SAD, CDM, ortho condition, ATE, prostatic/anorectal disease, polyarthritis, polyneuropathy, polymyositis, meningomyelitis

Question 15

List 3 diseases that could cause coindidental T3-S3 myelopathy

Answer 15

IVDD, DISH, CDM

Question 16

List 3 electrophysiologic tests that could be used to assess functional integrity of cauda equina

Answer 16

• 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)

Question 17

When performog rads for cauda equina syndrom, which anatomic regions shoudl be included (i.e. to ensure inclusion of relevant SC segments)

Answer 17

From L4 vertebra to Cd vertebra

Question 18

List radiographic/CT findings taht may be seens with DLSS

Answer 18

• 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.

Question 19

Decribe imaging findings

Answer 19

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.

Question 20

List 6 anatomical changes that can contribute to DLSS

Answer 20

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

Question 21

List Mr sequences that should be run for DLSS

Answer 21

T1W (pre and post-contrast)

T2W

Transverse and sagittal

Question 22

When might medical management of DLSS be indicated?

Answer 22

First episode

Inactive, older dogs with only episodic pain

Question 23

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?

Answer 23

55%

Epidural methyl pred acetet (1 mg/kg) at 0, 2 weeks and 6 weeks –> 79% success

Question 24

What % of dogs with DLSS hasd +ve bacterial culture from disc material?

Answer 24

23%

Question 25

When is surgery indicated for DLSS

Answer 25

Moderate-severe pain Neuro defecits

Question 26

What 4 procedures might be performed in additon to dorsal laminectomy for management of DLSS

Answer 26

1. Partial discectomy (i.e. dorsal annulectomy) 2. Foraminotomy 3. Zygapophyseal joint removal 4. Distraction and fixation

Question 27

What are the lateral, cranial and caudal landmarks for dorsal laminectomy. Describe shape of laminectomy hole

Answer 27

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.

Question 28

What precedured have/are being performed in image?

Answer 28

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.

Question 29

How will L7 - S3 nerve roots be located anatomically, at level of LS disc?

Answer 29

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).

Question 30

List 3 approaches for foraminotomy What is the limitation of each

Answer 30

* 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)

Question 31

List steps in post dorsal laminectomy distraction + stabilization

Answer 31

1. Distract 2. Debride cartilage from zygapophyeal joints 3. Partial discectomy 4. Remove vertebral end plate cartilage (+- forage. Make sure to preserve *bony* end plate if using an interbody device - need to prevent subsidence) 5. Bone graft or rhBMP-2 in intervertebral space, zygapophysela joints, over laminae 6. Stabilize

Question 32

List 6 techniques for stabilizing LS

Answer 32

1. Pins/screws + PMMA 2. 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) 3. Zygapophyseal lag screws (lag screws, directed 30-45º ventrolaterally) 4. SOP plate 5. Pedicle screw rod fixation (titanium - better for MRI) 6. (+- interbody device/cage - fill with cancellous bone if being used) 7. (MTVB: Minimally-invasive transilial vertebral blocking)

Question 33

What is max screw diameter for zygapophyseal lag screws in LS stabilization?

Answer 33

Approx 25% of diameter of articular process

Question 34

What angle should LS zygapophyseal lag screws be directed at

Answer 34

30-45º in ventrolateral direction

Question 35

What procedures have been performed? What feauture of implant affects post-op imaging and how?

Answer 35

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.

Question 36

What factors have been associated with poor prognosis in DLSS cases

Answer 36

* Presence of urinary and faeceal incontinence * Duration of urinary incontinence (x6 higher if urinary incontinence \>1 month, vs \<1 month)

Question 37

What is overall success rate (clinical improvement) following dorsal laminectomy?

Answer 37

79% N.B. No studies compare just dorsal laminectomy vs distraction-stabilization

Question 38

List 4 possible complications following surgery for DLSS

Answer 38

* Seroma * Instability * Worsening of clinical signs * Excessive scar formation And if implants: * Implant bending/breakage/migration * Articular process fracture * Infection

Question 39

Name a novel technique for management of DLSS.

Answer 39

**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