Degenerative lumbosacral stenosis

Question 1

What are the different caudal locations of spinal cord termination based on size?

Answer 1

Large/giant breed: L4
Dogs < 10 kg: L6
Toy breeds and cats: L7

The dural sac extends a further 1 to 2cm beyond the terminal portion of the conus medullaris.

Question 2

What are the specific nerves that make up the cauda equine?

Answer 2

S1, S2, S3 (sometimes extended to include L7)

Question 3

What is cauda equina syndrome?

Answer 3

The term used to describe the clinical signs resulting from disease processes that involve the lumbosacral articulation that affect the nerve roots and/or the spinal nerves of the cauda equina.

Question 4

What is the most common cause of cauda equina syndrome?

Answer 4

Lumbosacral stenosis

Question 5

What abnormalities occur alone or in combination with degenerative lumbosacral stenosis?

Answer 5

IVDH (normally type 2), transitional vertebrae, congenital osseous stenosis of the vertebral canal or intervertebral foramina, sacral osteochondrosis, proliferation of the joint capsule or ligaments, osteophytosis of the articular processes, epidural fibrosis, instabilitiy or malalignment/subluxation of L7-S1.

Question 6

Describe the pathophysiology of degenerative lumbosacral stenosis

Answer 6

Abnormal motion pattern predisposes to degeneration of the IVD. Degeneration of the IVD shifts loading to the zygaphophyseal joints and ventral vertebral bodies), Surrounding anatomic structures respond by proliferation and hypertrophy. Additional disc degeneration results in IVDH (type 2). A combination of these factors results in compression of nerve roots, with demyelination, axonal loss and inflammation.

Question 7

Is degenerative lumbosacral stenosis more common in male or female dogs?

Answer 7

Male dogs. Mainly large breed.

Question 8

Describe the nerves originating from the lumbar intumescence and the possible neurologic findings related to these nerves in cases of degenerative lumbosacral stenosis

Answer 8

Question 9

What examination techniques may elicit pain responses at the lumbosacral articulation?

Answer 9

1. Traction or extension of the tail.
2. Direct digital pressure per rectum.
3. Pressure on the articulation while elevating the thoracic limbs.
4. As above but elevating the pelvic limbs and extending the hips (lordosis test).
5. As above but hyperextending one pelvic limb at a time.
6. Swinging the pelvic limbs side to side

Question 10

Is severe neurologic dysfunction frequently seen in patients with degenerative lumbosacral stenosis?

Answer 10

No, generally mild. Often deficits relate to dysfunction of the fibular branch of the sciatic nerve (absent hock flexion during withdrawal testing)

Question 11

What is associated with a significantly worse prognosis in instances of degenerative lumbosacral stenosis?

Answer 11

Urinary and faecal incontinence

Question 12

Is there a correlation between the severity of clinical signs and degree of cauda equina compression as seen on MRI?

Answer 12

No - severity is ultimately based on neurologic examination.

Question 13

What diagnostics could be considered in the work-up of degenerative lumbosacral stenosis?

Answer 13

Electrophysiologic testing, radiographs, CT/MRI

Question 14

What are some differential diagnoses for degenerative lumbosacral stenosis?

Answer 14

Question 15

In the pelvic limbs electromyography should only be abnormal in muscles innervated by which nerve?

Answer 15

The sciatic. F-wave latencies would be prolonged with compressive radiculopathy.

Question 16

Is myelography or epidurography more likely to be diagnostic in a patient with degenerative lumbosacral stenosis?

Answer 16

Epidurography as the dural sac is likely terminated prior to the lumbosacral articulation. Discography is now considered outdates as may cause in itself degeneration of the disc space.

Question 17

Describe some typical CT findings associated with degenerative lumbosacral stenosis

Answer 17

Question 18

What is the most likely location of sacral osteochondrosis?

Answer 18

Dorsal aspect

Question 19

Does CT imaging of the lumbosacral articulation in flexion or extension accentuate foraminal compression and IVD protrusion?

Answer 19

Extension

Question 20

In what percentage of dogs might medical management with NSAIDS and gabapentin be successful?

Answer 20

55%

Question 21

When might medical management of lumbosacral stenosis be considered?

Answer 21

First episode, older/inactive dogs

Question 22

Name the 5 surgical procedures that may be considered in the treatment of degenerative lumbosacral stenosis?

Answer 22

1. Dorsal laminectomy is the mainstay of surgical therapy +/- partial discectomy, foraminotomy, removal of the zygapophyseal joint.
2. Stabilization by fusion may be required after removal of the joints, when ventral subluxation of S1 is present, or to prevent further development of lumbosacral instability.

Question 23

Describe the surgical landmarks for dorsal laminectomy of the lumbosacral joint

Answer 23

Question 24

Describe access to the lumbosacral disc space for annulectomy and nucleus pulpectomy

Answer 24

Question 25

If performing a lateral approach for foraminotomy of the lumbosacral articulation, which structures impede physical and visual access to the foramen?

Answer 25

The wing of the ilium and the ilicostalis lumborum musculature. A technique has been described where an osteotomy is created in the wing of the ilium.

Question 26

What are the guidelines for when to perform distraction and fixation on a patient with degenerative lumbosacral stenosis?

Answer 26

Specific guidelines don’t exist

Question 27

What are the goals of distraction/fixation in the treatment of degenerative lumbosacral stenosis

Answer 27

Restore the width of the intervertebral disc space and the cross sectional area of the intervertebral foramina. It is believed that distraction/stabilization prevents the development of further bony changes.

Question 28

What techniques are described for distraction/fixation?

Answer 28

Pins/screws and PMMA, dorsal cross pinning (relies on the integrity of the dorsal spinous process of L7), lag screws placed across the zygapophyseal joints, SOP plating, pedicle screw and rod fixation +/- use of interbody device.

Question 29

When using an interbody device should the bony endplates of the vertebrae be broached with osteostixis or preserved?

Answer 29

Preserved to prevent subsidence, however the cartilagenous end plates need to be removed

Question 30

When placing cortical screws to fuse the zyagophyseal joints, what size should the screws be?

Answer 30

25% of the diameter of the articular process

Question 31

What are the general rates of improvement/return to normal function in dogs undergoing dorsal laminectomy and discectomy for degenerative lumbosacral stenosis?

Answer 31

70 - 80%

Question 32

What factors have been associated with a worsened prognosis following distraction/fixation for degenerative lumbosacral stenosis?

Answer 32

The presence of urinary and fecal incontinence, duration of urinary incontinence (the probability of a poor outcome was 5.88 times higher for dogs with urinary incontinence >1 month duration), age and severity of clinical signs.

Question 33

What are reported rates of recurrence following distraction/fixation techniques for degenerative lumbosacral stenosis?

Answer 33

3 - 55%

Question 34

What are some complications associated with surgical intervention for degenerative lumbosacral stenosis?

Answer 34

Seroma formation, instability, acute worsening of clinical signs, need for revision surgery, implant failure, fracture of articular processes, infection.

Question 35

According to Lichtenhahn 2020 in Vet Surg, what sign on MRI is associated with L7 radiculopathy and foraminal stenosis?

Answer 35

Loss of foraminal fat signal (generally associated with clinical signs on the ipsilateral limb).

Question 36

In a study by Tanoue 2022 in JAVMA, what were the 4 complications reported for dorsal laminectomy with screws and PMMA for treatment of degenerative lumbosacral stenosis?

Answer 36

Implant failure, delayed healing of surgical wounds, seroma, swelling of the affected area (all minor, no major complications).