Degenerative lumbosacral stenosis

What it is

Degenerative lumbosacral stenosis (DLSS) is the most common cause of cauda equina syndrome in the dog. Several degenerative changes at the L7–S1 junction add up: Hansen type II protrusion of the L7–S1 disc, thickening of the ligamentum flavum and of the joint capsules, osteophytes of the articular processes and instability of the joint. Together they narrow the vertebral canal and the intervertebral foramina through which the L7 nerve roots leave. Transitional lumbosacral vertebrae and osteochondrosis of the sacral endplate predispose to it.

Who it affects

Middle-aged to older dogs of medium and large breeds, especially the German shepherd and active working dogs. Males are affected more often.

Anatomy involved

In the dog the spinal cord ends at about the level of L6–L7, so the canal of the last lumbar vertebra and the sacrum contains no cord, only the cauda equina: the nerve roots of L7, the sacral and the caudal segments, which leave through the L7–S1 intervertebral foramina and the sacral foramina. The lumbosacral joint is the most mobile joint of the caudal spine, and it transmits the thrust of the pelvic limbs to the trunk, which explains its tendency to degenerate. The L7 root, which contributes to the sciatic nerve, is the one most often trapped in the foramen.

Clinical signs

• Lumbosacral pain, reproduced by pressing on the lumbosacral area and by hyperextending the joint (lordosis test) or lifting the tail.
• Reluctance to jump, climb stairs or sit; stiffness on rising.
• Pelvic limb lameness from compression of a nerve root, sometimes with weakness of hock flexion and reduced withdrawal reflex.
• In advanced cases: low tail carriage or weak tail, and urinary or faecal incontinence.

Diagnosis

• Neurological and orthopaedic examination; hip dysplasia and cranial cruciate ligament disease often coexist and must be ruled out.
• Radiographs show spondylosis, endplate sclerosis or a step between L7 and the sacrum, but these findings are common in healthy dogs and are not diagnostic.
• MRI (the method of choice) or CT to show the compression of the cauda equina and the foramina.

Treatment

Conservative: weight loss, restricted and controlled exercise, NSAIDs and analgesics, physiotherapy and, in some cases, epidural corticosteroid injections. Surgical for dogs with persistent pain or neurological deficits: dorsal laminectomy with or without partial discectomy, foraminotomy for root entrapment, and distraction-fusion techniques when instability predominates. Working dogs may not return to their previous level of work.