In normal dogs, motion of the vertebral column in flexion and extension progressively increases caudally in the lumbar vertebral
column, with the L7-S1 articulation demonstrating the greatest amount of mobility.11 Instability of the L7-sacral articulation has been identified in dogs with degenerative lumbosacral stenosis.2,12 Other studies have found reduced mobility of the lumbosacral junction.13 Objective radiographic evidence of instability has also been identified.13,14 Often the caudal articular processes and facets of the L7 vertebra are displaced caudally in relation to the sacrum. As a
result, the L7-S1 intervertebral foramen is narrowed, compressing the L7 spinal nerve. This may lead to the chronic pain.
Compression at the cauda equina can also be exacerbated with extension of the pelvic limbs.13,14
A surgical technique for internal fixation of the L7-S1 articulation has been defined.15 Often this technique is combined with decompressive surgery (see below). Some neurologists have advocated internal fixation for all dogs with degenerative lumbosacral stenosis.16 A direct comparison between the outcome of dogs treated by decompression alone vs. decompression and stabilization has not
been made. Consequently, despite evidence of instability in some dogs with degenerative lumbosacral stenosis, the role of
instability at the L7-sacral articulation and its effect on the pathophysiology of degenerative lumbosacral stenosis remains
Vascular compromise may also play a role in the pathophysiology of degenerative lumbosacral stenosis. In people, intermittent
claudication, numbness, pain, and weakness of the legs with exercise that resolves with rest is thought to be the result of
nerve root ischemia from compression of radicular arteries.17 Experimentally, compression within the vertebral canal of the cauda equina or within the L7-sacral foramen of the L7 spinal
nerve results in vascular compromise, leading to ischemia of the L7 dorsal root ganglia.17 Although not documented, ischemia may play a role in clinical cases, given the similarity between clinical signs of degenerative
lumbosacral stenosis and intermittent claudication in people.2
Affected dogs are often large-breed older dogs, with German shepherds being overrepresented.8,12,18-20 Other more commonly affected breeds include Great Danes, Airedale terriers, Irish setters, English springer spaniels, boxers,
and Labrador and golden retrievers.19 Affected dogs are usually between 6 and 7 years of age at presentation.12,18 There is also a male predisposition.10,12,20,21
HISTORY AND CLINICAL SIGNS
In general, affected dogs have a long-term history of pelvic limb weakness that may be intermittent. Typically, dogs progressively
worsen over time.
Clinical signs are referable to dysfunction of the L7, S1-S3, or caudal spinal nerve roots. Abnormalities in any one part
of the lower motor neuron unit, the cell body within the spinal cord, spinal nerve roots, peripheral nerves, neuromuscular
junction, or muscle, are clinically indistinguishable from a lesion in another part of the lower motor neuron unit.22 So be sure to consider the entire lower motor neuron unit when evaluating patients with signs consistent with degenerative
The most common clinical sign associated with degenerative lumbosacral stenosis is pain at the lumbosacral articulation.8,12,18,21,23 Other clinical signs may be present in various combinations depending on severity and which nerve roots are affected. In
general, varying degrees of paraparesis may also be present. Patients may assume a crouched stance with overflexion of the
hip, stifle, and hock joints. Occasionally, dogs may hold a pelvic limb off the ground; this is known as a root signature.
Gait analysis reveals a shortened, choppy stride. Occasionally, the paresis results in knuckling over and subsequently ambulating
on the dorsum of the paw. In extreme cases, the severity of the paresis is great enough to give the impression of proprioceptive
ataxia. However, true incoordination, or ataxia, is usually not seen. Affected dogs often have difficulty rising, jumping,
and climbing stairs. Exercise intolerance is sometimes noted.
Urinary incontinence, ranging from occasional overflow of urine during sleep to constant dribbling of urine, can be observed.
Urethral sphincter dyssynergia can also be occasionally seen. In this case, the patient can initiate urination, but voiding
ceases abruptly and prematurely with continued straining. Likewise, defecation can be affected. Abnormalities include an inability
to posture or a change in posture, straining to defecate, and fecal incontinence.