There is a disorder (it may actually be two or three) in
the canine similar to the “wobbles” in thoroughbred
horses. Much has been written on this, with various
descriptions such as cervical vertebral instability (CVI),
cervical spondylopathy, stenosis of the cervical
vertebral canal, caudal cervical spondylomyelopathy, and
even the mouthful, caudal cervical vertebral
malformation/malarticulation. It was once referred to
(incorrectly, perhaps?) as spondylolisthesis. However,
no term is more used, more succinct, more descriptive,
or even perhaps more accurate, than “wobbler syndrome”.
In the horse, about 12% of this syndrome can be blamed
on osteochondrosis and here, too, there may be some
parallels with the dog.
Cervical Vertebral Instability (CVI or “Wobbler
Syndrome”)
That we may be dealing with two very similar disorders
or two variations of a disorder is indicated by the
differences seen in early studies on middle-aged and
older Doberman Pinschers, Basset Hounds, and later work
with Great Danes. The earlier work pointed at
instability, subluxation of the vertebrae, and a
tendency for one of the vertebral bodies (the actual
bone segments of the spine, not including the material
between) to lose bone, ride up onto the one in front of
it, and thus compress the spinal cord from the bottom.
See the figure provided. This would be a little like a
car with an angled bumper running into another car ahead
of it, its front bumper sliding up and over the rear
bumper of the other vehicle and smashing into its trunk
and taillights, although in slow motion. Mostly large
breeds have been involved such as those named above,
plus Saints, Old English Sheepdogs, and Rhodesian
Ridgebacks, though infrequently in smaller breeds, also.
Another abnormality is seen in the spinal column of dogs
with Wobbler Syndrome: a partial closing or narrowing of
the canal by abnormal thickening of the vertebral body
surrounding it. Stenosis is a squeezing or partial
closing of a tubular structure such as an artery, heart
arch, or, as in this context, the spinal canal (where
the spinal cord runs through the vertebrae). It is
congenital (found at birth), developmental (gets worse),
and degenerative (has destructive effects) in man and
probably so in dogs as well. Stenosis has been seen in
the cervical and lumbar vertebral canal and the
intervertebral foramina (spaces between the vertebrae),
and may be “silent” not giving rise to complaint, in
many individuals unless accompanied by other factors
such as protrusion of a disc, spinal instability, or
movement such as the extreme flexion or extension of the
neck or other part of the spine.
Most of the lesions in early studies were between the
sixth and seventh cervical (neck) vertebrae, which are
designated C6 and C7. It has been thought that there was
an inherited malformation of these spinal segments
(vertebrae) with possibly a simple recessive trait but
more recent evidence indicates more genes are involved
in somewhat more complex ways. We know a little more
about osteochondrosis and the etiology of osteophyte
formation now.
Clinical Signs
At the point of greatest cord compression, the damaged
ascending sensory neurons (those nerve cell carrying
electrical impulses to the brain) begin to die. Their
myelin sheaths deteriorate, and confusing impulses cross
over from one axon to another, in effect making the
brain and cord “think” they are coming from someplace
else, and thus the return messages to contract certain
muscle fibers may be sent to some of the wrong places.
This gives rise to much of the missteps and poor
movement. Many of the axons (main conductors) also die,
and loss of sensation results.
Simultaneously, descending motor neurons are affected
the same way, so fewer of them function from that part
back to the muscles. Therefore, the dog may seem not to
know where its limbs are, drags its toes in a manner
similar to those with GSD myelopathy or stands on the
top surface of one of its rear paws, has poor
coordination especially in the pelvic limbs, may stand
wide and, if the thoracic limbs are affected, may have a
prancing gait. In severe cases, the dog falls down
easily and has a hard time getting up on its feet. The
syndrome affects both sides of the body equally.
The next figure represents a neuron (nerve cell), which
can be very long as in some peripheral nerves or very
short as in some brain cells. Most have myelin
“insulation” covering the axons that conduct
electrochemical messages much the way electrical wires
conduct electricity in your house or appliances. Sensory
nerves have different endings than do motor nerves, and
one sensory ending may vary from another way.
The descriptive terms “ataxia” and “spastic paresis” in
this disorder refer to weakness and partial paralysis
with incoordinate motion, and these are seen principally
in the rear. When cervical spinal cord damage is further
toward the head, the forelimbs and even perhaps the
diaphragm may be involved, but in canine Wobblers, the
lesion is usually found in the caudal (rearmost)
cervical vertebral spaces such as C6-7, rarely C5-6,
although in Basset Hounds the same or a similar syndrome
is associated with the cord pinching occurring around
C2-3. Wherever it exists, it may cause an abducted
(limbs move away from each other) and sometimes
fast-beat gait with stumbling especially when turning.
The ataxia, of course, is due to the damage to the
ascending neurons and the jerky movement and paresis to
damage to the descending neurons, both at the point of
cord compression.
Cause
It was discovered very early in man and described in the
dog by 1967 that vertebral canal stenosis is a cause of
spinal cord compression and these researchers considered
deformation of the vertebral bodies to be the cause of
that stenosis. Others have looked at this and similar
problems in a variety of breeds.
About the same time as the above work and a little
later, another cause of spinal canal stenosis was
proposed: a deformation of the vertebral arches (that
part of the segments covering the canal), as well as the
discs, the processes, and articulations in the joints
between the bone segments. Other things happening at the
same time and possibly contributing to stenosis or
associated with it otherwise include hypertrophy
(overgrowth or thickening) of the flavum ligament or of
the dorsal longitudinal ligament or of the dorsal
annulus. Simple poor alignment and malarticulation have
also been blamed or implicated. Another cause of
compression of the cord is the CVI (cervical vertebral
instability) mentioned earlier, and identified by
various names such as spondylolisthesis and vertebral
subluxation.
In the earlier work on CVI, instability was the
diagnosis when greater flexion between two vertebrae
than “normal” was evident. When we speak of flexion, we
mean the bending of joints so that the limb or extremity
is “folded” toward the centerline of the torso, while
extension is a straightening-out away from the rest of
the body. In speaking of the neck, flexion is the
bending of the head downward toward the sternum, and
extension is the bending up as if stretching to reach
over the back. How valid is the diagnosis of neck
instability as “shown” in flexion, was brought into
question in 1977 by Wright who found the abnormal
angulation (one bone starting to slip or ride up on
another) in many dogs who had no clinical signs of
cervical spinal problems. It had been standard practice
to bend the neck down fully and see if there were any
irregularities or subluxation on the radiograph. These
pictures were compared to the neck in a neutral position
(same as it would be carried in standing). These
pictures were almost invariably taken in a lateral view
(from the “side”; with the dog in lateral recumbency),
although some people showed how useful a ventrodorsal
view could be in demonstrating lateral compression of
the cord.
In 1982 Olsson, Stavenborn, and Hoppe in Sweden studied
Great Danes and found that the ones with wobbler
syndrome had radiographically demonstrable lesions only
when the neck was in extension, which ran counter to the
experiences previously reported. They did not find any
CVI or vertebral body deformation, except for a slight
deformation in the vertebrae of one dog, and guessed at
a number of possible reasons. Their work was only with
Great Danes, and previous studies had also included
Bassets and Dobes, so perhaps there is a different
genetic pathway for some breeds than for others. The
syndrome in Danes occurs mostly in young dogs and in
Dobes they occur mainly in older dogs. The 1982 Swedish
study involved “wobbler” dogs from 4½ to 24 months. Both
plain radiographs and some made after the injection of a
dye for myelography were studied, with the necks in all
positions. The euthanized dogs’ spinal systems were then
studied for comparison.
Even normal Danes have relatively smaller ventrodorsal
height to the spinal canal, and larger prominent
intervertebral joints compared to many other breeds.
When they looked at a dog without wobbler signs and
increased C3-4 flexion as seen on a regular film, the
myelogram didn’t indicate any pinching of the cord, even
though it looked as if the bone could have done so. The
wobbler dogs with increased flexion between two
vertebrae showed no pinching, either. The picture that
came out of this work in Sweden is that compression of
the cord is most severe when the neck is extended. It
also appeared that the compression and stenosis took
place at the cranial end of the vertebral canal, where
the height was less and the “roof” was pushed down onto
the cord when the neck was lifted (extended). This is
probably why many wobblers will hold their heads down,
by the way, but that is not the best diagnostic sign.
Often, Danes with wobbler syndrome have an abnormal
vertebral arch (between the “neckbones ”) that is plump
and longer, and frequently it is seen in association
with deformed and asymmetrical articular processes. Many
also have considerable osteophytic deposits that may
contribute to further compression. Compression was more
dynamic than static, meaning other forces combined with
the malformation to produce the compression, such as
disc protrusion and even the normal movement of the head
and neck. Possibly the most important finding of this
research, beyond the hint of breed and genetic
differences, is that cord pinching might not be
demonstrated in wobblers unless myelography is used in
conjunction with radiography and pictures are taken with
the neck in different positions.
The breeder/owner can make a tentative diagnosis based
on symptoms before taking the dog in for myelograms. But
you want to remember that there are other problems, and
you should differentiate between them. If the dog has no
pain, but the unstable gait described, it is very
possibly wobbler syndrome. If pain and hypersensitivity
are present, your dog may instead have cervical disc
protrusion syndrome. The pain probably comes more from
the secondary inflammation that results when the disc’s
nucleus pulposus tissue extrudes into the epidural space
in the canal and calcifies with this “hardened
cement-like” material acting much the way osteophytes do
in irritating and abrading the surrounding soft tissues.
In the wobbler, inflammation is not much of a problem if
at all.
In the important 1974 work at Cornell on Great Danes,
joint problems, and nutrition, evidence indicated that
vertebral body deformation is a manifestation of
osteochondrosis brought on by rapid growth and
overnutrition. Olsson and colleagues commented that some
of the changes seen in the cartilage between the
vertebrae have similarities to osteochondritic changes
seen in other joints, and implies that high-energy,
high-calorie “rich” diets may, in certain dogs and
breeds genetically predisposed to these disorders, bring
on the osteochondrosis responsible for the stenotic
myelopathy (pinching and disease of the spinal cord)
seen in animals.
Other environmental factors may worsen a congenital or
hereditary problem. It has been theorized that the very
heavy head of a Thoroughbred horse, a Great Dane, or a
Basset Hound put great stress on certain vertebrae
during early growth, but there are too many questions to
give much credence to that. Dobes certainly don’t have
heavy heads, and different vertebrae are involved in
different breeds. Separate genes and locations may be
involved in Bassets compared to other breeds. A
cooperative pedigree and clinical study program between
breeders and some veterinary school teams could provide
more accuracy in detection and improve some breeds of
dogs through prevention of disease.
Treatment of Wobbler Syndrome
Earlier treatments have included fusion of adjacent
vertebrae with bone grafts and bone cements, or simply
the use of anti-inflammatory drugs, but improvements
were needed. A technique developed at the U. of TN in
1983 calls for drilling a slot between the two segments
and filling the gap with about ½ to 1-inch of bone cut
from the pelvis. What makes it different is the use of
stainless alloy rods with hooked ends attached to other
vertebrae, and a threaded section with nuts that can be
tightened to adjust tension. About 75% of the dogs
treated this way at the U. of Florida vet school regain
at least partial use of their legs, a much better
prognosis than has previously been had. Fewer dogs now
face euthanasia.
Fenestration is an operation in which a hole or channel
is cut (usually in a disc) so that the spinal cord or
large nerve at the ganglia has more room. But unless
something is done to prevent continued or repeated cord
compression, it is rarely successful. If the two bones
that squeeze the nerve are spread apart (distracted) and
the space and relationship of the bones stabilized,
there is much greater chance of success. A technique
developed at Tufts involves a plug of polymethyl
methacrylate — in effect, a wad of “super glue”. Anchor
holes are drilled in opposing faces of adjacent
vertebrae where most of the disc has been cut out (but
some left to bridge and cushion the bones). After the
glue plug hardens, the distraction device is removed,
and some cancellous bone (harvested from the greater
tubercles of one or each humerus) is grafted onto the
bottom, causing what would appear to be a man-made
spondylosis (bridge) on the ventral surfaces. Of course,
there is no flexibility between these two “fused”
segments, but no misalignment and consequent repeat of
the cord compression, either.
Fred Lanting is an internationally respected show judge,
approved by many registries as an all-breed judge, has
judged numerous countries’ Sieger Shows and
Landesgruppen events, and has many years experience with
SV. He presents seminars and consults worldwide on such
topics as Gait-&-Structure, HD and Other Orthopedic
Disorders, Anatomy, Training Techniques, and The GSD. He
conducts annual non-profit sightseeing tours of Europe,
centered on the Sieger Show (biggest breed show in the
world) and BSP. Check out his website: www.MrGSD.com
All Things Canine -- consulting division, Willow Wood
Services Phone: 256-498-3319 Fax: 256-498-3311 E-mail
mrgsd@hiwaay.net
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