3.1 Principles of Lumbosacral Disease

Question 1

What is the anatomy of the lumbosacral region?

Answer 1

The VERTEBRAL column contains 7-13-7-3, while the SPINAL CORD SEGMENTS contains 8-13-7-3. They do not closely align.

there is NO spinal cord present within the lumbosacral region (the tapered end, the conium, sits at vertebra L5 or L6 in most dogs)

• the lumbosacral vertical canal is occupied by the caudal equina instead (L7 to coccygeal nerve roots)
• L7-S1 contribute to the sciatic nerve
• S1-S3 are the pelvic, pudendal, and coccygeal/caudal nerves

the tapering end of the spinal cord is called the conus medullaris, and the filium terminale is the filamentous attachment from the conus medullaris to the sacral certebral column

Question 2

What is the innervation to the bladder?

Answer 2

there are 3 main nerves that affect the bladder:

(1) hypogastric
- originates from the thoracolumbar region: T3-L3 SC segments
- relaxes the bladder and contracts the internal sphincter

(2) pelvic
- originates from S1-S3 SC segments
- contracts the bladder

(3) pudendal
- originates from S1-S3 SC segments
-contracts the external sphincter

Question 3

Which lesions lead to “UMN” and “LMN” bladder?

Answer 3

thoracolumbar lesions lead to UMN bladder (most common)
- large and full, firm/turgid
- risistant to manual expression
- inconsistent leakage

S1-S3 lesion leads to LMN bladder
- flaccid/atonic
- easily expressed
- can leak urine spontaneously (urine scald)
- persistent UTIs

UTIs are the most common complication of bladder dysfunction; occurs with both UMN and LMN disease

Question 4

How do you manage urinary incontinence?

Answer 4

1. manual bladder expression
2. repeated aseptic catheterization
3. if animal is completely paralyzed: indwelling foley catheter with closed collection system

note: if an animal is non-ambulatory, assume that they have lost bladder function; these functions prevent UTIs, urine scald, and overstretching of the bladder

Question 5

What is sacrocaudal luxation?

Answer 5

a “tail pull injury”: trauma to the sacral spinal cord segments (common in HBC patients)
- flaccid tail
- present with or without paresis (may be transient)
- anal sphincter and bladder dysfunction (guarded prognosis)

while owners do not know if it is necessary to come in (as it is ‘only’ a flaccid tail and the animal is still moving/jumping as normal), permanent urinary/fecal incontenance is a massive risk, and very dangerous

prognostic indicators:
- sensation at tail base
- presence of perianal sensation and tone

if present: very common to recover within 7-14 days; if absent about 50%; if absent for 30 days, very unlikely

Question 6

What is cauda equina syndrome (CES)?

Answer 6

“Lumbosacral disease”

multiple disorders with clincial signs of cauda equina dysfunction (traumatic, infectious, degenerative, neoplestic, etc)

• vague, unspecific clinical signs associated with general lumbosacral pain and weakness, as well as specific hindlimb, tail, perianal, and bladder nerve dysfunction (most common is sciatic nerve dysfunction: e.g., dropped hock)
• often “unwillingness” to jump or run up the stairs
• unilateral/bilateral pelvic limb lameness very common (can be difficult to differentiate from orthopedic disease)
• spinal hyperesthesia can be present
• often pain on extension of the hips and dorsal extension of the tail (stretching of affected nerves)
• other signs: flaccid tail, urinary/fecal incontinance

other differentials to consider: orthopedic lameness (arthritis, hip dysplasia, etc.)

Question 7

What is the sciatic nerve?

Answer 7

mixed motor and sensory nerve that inenrvates the hindlimb: exits L7-S1 intervertebral foramen and splits into the peroneal nerve and the tibial nerve

• peroneal nerve innervates the dorsal side of the distal limb
• tibial nerve innervates the plantar side of the distal limb

tibial nerve dysfunction is very characteristic of lumbosacral disease

• dropped hock (plantigrade stance in cats): overflexion of the tarsus due to decreased innervation
• leads to atrophy and loss of hock flexion during withdrawal reflex
• uncommon but may see patellar pseudohyperreflexia upon patellar reflex

Question 8

What is degenerative lumbosacral stenosis?

definition, causes, diagnosis, prognosis, treatment

Answer 8

the MOST COMMON cause of cauda equina syndrome in dogs

a multifactorial disorder which results in the progressive stenosis of the lumbosacral vertebral canal due to degenerative changes of adjacent bony and soft tissue structures:

• interverterbral disc protrustion type II (most common cause)
• migamentum flavum hypertrophy
• articular process hypertrophy
• telescoping lamina S1 into vertebral canal L7
• vertebral misalignment, synovial cysts, transitional vertebrae, osteochondrosis, etc.

usually occurs in older, large breed dogs (GSDs overrepresented)

diagnosis by CT or MRI:

• radiographic change is NOT always associated with clinical signs and is often used to overdiagnose
• spondylosis has poor clinical correlation

prognosis:

• the main prognostic indicator of degenerative lumbosacral stenosis is urinary incontentace
• incontinent by one month (or for one month) recovery is not likely

treatment:
1. mild cases treated medically (50% success): NSAIDs, gabapentin, exercise restriction
2. advanced medical management: epidural injections (local anesthetic + corticostroids) every 4-6 weeks
3. surgical treatment (80% success): decompressive surgery, lateral foraminotomy, or distraction-stabilization