What can be done for wobblers?

WOBBLERS?
Y
Neurological
injuries caused
by pressure
on the spinal
cord can be
devastating, but
many horses
can recover and
return to active
lives. The key is
early diagnosis
and treatment.
V E T; A R N D B R O N K H O R S T
By Heather Smith Thomas
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our old horse had
always been reliable
as a rock, carrying
your kids smoothly
and steadily through
every lesson. Recently,
though, he’s started resisting a bit.
You can’t find anything obviously
wrong---he just doesn’t seem to want
to go. Then one day you notice his left
hind leg swinging wide as he walks in
from the pasture….
At a farm down the road, this year’s
weanlings are roughhousing. Two colts
rear, paw and knock each other over in
the soft grass. One leaps to his feet and
streaks away. The other stumbles as he
rises, “bunny hops” to sort his feet, then
gallops off.
As different as they are, the aging
campaigner and the young colt are experiencing a similar problem. Both are
wobblers. That is, both are beginning
to experience mild neurological signs
resulting from spinal cord damage.
In the past, the term “wobbles” has
been used generally to describe any
neurological dysfunction resulting
from a wide range of sources, including diseases such as equine protozoal
myeloencephalitis (EPM). Now, though,
“wobbler syndrome” usually carries
a more specific meaning: a physical
pinching of the spinal cord caused
by malformation or overgrowth of
vertebrae in the neck. The condition
occurs, for different reasons, in young,
fast-growing colts and also in horses
old enough to be developing arthritis.
The good news is that, with appropriate treatment, many wobblers can
return to comfortable, and many times
active, lives. Barrie Grant, DVM, DACVS,
MRCVS, who has decades of experience
treating wobblers at his consulting
practice in Bonsall, California, reports
that 80 percent of horses with the condition improve, and a third return to
athletic activities, including jumping
and racing.
But to be effective, treatment needs
to start early. And that means catching
the problem as soon as the horse begins
to show the first subtle signs of trouble.
Here’s what you need to know.
WHERE THE
TROUBLE STARTS
The focal point in wobbler syndrome
is the spinal canal of the neck, the
cylindrical chamber where the spinal
cord runs down through the center of
each of the seven cervical vertebrae.
Normally, the vertebrae protect the
spinal cord from external trauma.
But if bone or cartilage encroaches on
the canal, it can become more like a
trap, squeezing the delicate nerve
tissue and damaging the individual
neurons that run along the surface
of the cord.
In wobbles, the spinal cord may be
affected in two ways. Dynamic compression occurs when a malformation of the
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HORSE:DARLENE WOHLART
WHAT
CAN BE
DONE
FOR
spinal canal
NORMAL
ANATOMY
The focal point in wobbler syndrome
is the spinal canal of the neck, the
cylindrical chamber where the spinal
cord runs down through the center of
each of the seven cervical vertebrae.
Normally, the vertebrae protect the
spinal cord from external trauma. But
if bone or cartilage encroaches on the
canal, it can become more like a trap,
compressing the delicate nerve tissue
and damaging the neurons that run
along the surface of the cord.
neck
vertebrae
COMPRESSED
narrowing
of spinal
canal
cervical vertebrae causes the bones to
press inward when the neck is flexed,
but the pressure is relieved when the
horse straightens his neck. This condition is more likely to occur in the more
mobile region of the upper neck.
Static compression results when
excess growth of bone or cartilage
presses constantly against the cord and
affects the horse even when he is standing still. Static compression can occur
anywhere along the neck but is more
common in the lower cervical vertebrae,
near the shoulder.
Wobbles may also be caused by
trauma to the spinal column or a tumor
that impinges on the spinal cord, but
most cases are the result of developmental abnormalities or wear-related
vertebral changes. In young, growing
horses, wobbles is usually caused by a
developmental disorder called cervical
vertebral myelopathy (CVM), which
causes instability in the vertebrae. “These horses are not
necessarily born neurologic, but over time
spinal
cord
I L L U S T R AT I O N S B Y C E L I A S T R A I N
atlas
spinal
canal
cervical
vertebrae
axis
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C1
C2 C3 C4 C5 C6 C7
(atlas) (axis)
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the development of their bones causes a
narrowing of the spinal canal and cord
compression,” says Steve Trostle, DVM,
DACVS, of Blue Ridge Equine Clinic
in Earlysville, Virginia. “The faster
growing young horses are the ones that
develop this problem.”
CVM is most common in
Thoroughbreds, but it has also been
documented in most breeds of riding
horses and is also occasionally seen
in draft breeds. Males are three times
more likely to be wobblers than females,
possibly because colts tend to grow
faster than fillies.
Researchers
One of the early signs of wobbles
are still looking into is a loss of proprioception–the sense of
why some horses
where the body and limbs are–which can
become wobblers
lead a horse to stand with his feet in
while others do not:
unusual positions or swing his legs
“No one has done
oddly as he moves.
many genetic studies but we know
there are families of horses that produce more wobblers than average,” says
Regardless of the cause, in horses
John Madigan, DVM, of the University
young and old, the effects of wobbles
of California–Davis.
are the same: The pinching of the spinal
A different type of wobbles, one
cord impairs neurological communicaresulting from arthritic changes in
tions between the brain and the rest of
the neck vertebrae, is most often
the body.
seen in older horses. “Bone response
One of the most noticeable early
to injury is to create more bone,” exsigns
is a loss of proprioception---the
plains Trostle. “With arthritis you get
sense of where the body and limbs are
loss of cartilage and the development
---which can lead a horse to stand with
of more bone. Sometimes that bony
enlargement can impinge on the spinal his feet in unusual positions or swing
his legs oddly as he moves. Left uncord. These cases have not been given
treated, the impingement on the spinal
a specific name.”
cord will cause further neural damage
This form of wobbles can develop
over time, and the horse will lose more
in any breed, but it’s most often seen
control over his legs, becoming more
in equine athletes. “These cases are
incoordinated. Because the nerves that
increasing in number,” says Madigan.
serve the hindquarters are located on
“It may be a performance horse, such
the surface of the spinal cord, the hind
as a jumper, and the rider notices that
legs are usually affected first.
the horse is becoming a little stumbly.
The severity of wobbles is graded on
When checked, we notice there’s a big
a scale of 0 to 5:
bony lesion in the lower cervical area.”
RED FLAGS
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P A U L A D A S I LV A / A R N D B R O N K H O R S T P H O T O G R A P H Y
spinal
cord
Grade 0: The horse is normal.
Grade 1: The horse has a very mild
deficit that can be detected only with
manipulation and a trained observer.
Grade 2: The horse has deficits that
most people would notice with special
maneuvers.
Grade 3: The horse has prominent
deficits anyone can see.
Grade 4: The horse may be affected
enough to fall during the exam or when
at liberty.
Grade 5: The horse is unable to rise
on his own.
Some early signs of wobbles are
so subtle that they are easily mistaken
for behavioral issues. “Many horses
today have mild clinical signs, poor
performance in the show ring, and
personality changes because they don’t
want to jump anymore,” says Grant.
“They are probably frustrated because
they no longer know exactly where
their legs are or where their feet are
landing. Their agility is compromised.
Eventually, jumpers start refusing, and
dressage horses start shying at objects
in the ring.”
Often, he says, “they become sour
and don’t want to do their job anymore,
and you can’t blame them when you see
what their problem actually is. Most
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C O U R T E S Y, S T E V E T R O S T L E , D V M , D A C V S
INVESTIGATION:
If wobbles is suspected, a
veterinarian will first conduct
a neurological examination
(above) and test the horse
for lameness. Then he or she
will take radiographs of the
neck vertebrae (right).
horses try very hard, and when they
decide they don’t want to do something,
there’s usually a reason.”
As neurological dysfunction progresses, clues that a horse has wobbles
become increasingly apparent and
may include:
• Gait abnormalities. Wobbles may
cause a horse with a normally level trot
to begin to move with a high, animated
gait or step out unevenly, taking long
and short strides. A horse developing
wobbles may also have difficulty cantering, even at liberty, or may insert “bunny
hops” into the gait. Also, wobblers
sometimes have difficulty establishing
the correct lead.
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• Excessive wear on the toes.
Repetitive stumbling or foot dragging
may cause a horse to “square off” the
leading edges of his hooves.
• Sores on the heels and coronary
areas. Stepping on his own feet may
leave a horse with wounds, most commonly on the front heels from overreaching with his hind feet.
• Knuckling. The pastern joints in
the hind legs may bend forward unnaturally, causing the toes to dig into
the ground. This may happen only at
certain times, such as when going
downhill or stopping. This gives a rider
the impression that the leg has given
way or dropped out.
Identifying wobbles quickly is critical. The longer the compression on the
cord continues, the more severe the
neural injury will become and the less
likely the horse will be able to achieve
a full recovery. “Spinal tissue does not
heal quickly, and it can suffer permanent damage,” says Trostle. “The cord
will heal some, after the compression
is relieved, but all of the damage may
not be resolved. The longer the problem
exists, the greater the likelihood that
some of it will not recover.”
If wobbles is suspected, a veterinarian will first conduct a complete
neurological examination as well as a
lameness exam. He’ll also rule out diseases and conditions other than wobbles that can cause incoordination: “It
doesn’t really matter whether it’s pinching or destruction, lack of vitamin E or
lack of myelin---an important part of the
cell membrane---you end up with the
same kind of appearance in the horse,”
says Grant. “It’s easy to take blood samples and check these things at the same
time a neurologic and lameness exam
is being done.”
The next step is to take radiographs
of the neck vertebrae. But because of
the heavy musculature of the horse’s
neck, the bones cannot be viewed from
every angle. “The thing that’s difficult
in doing radiographs of the horse’s
neck is that we can really only take
them from the side---what we call lateral to medial,” explains Trostle. “We are
usually taught to take x-rays from the
front-to-back plane as well, so that if we
put them together with the x-rays from
the side they would make a 90-degree
angle. But the horse’s neck is so big
and thick that we can’t take that top-tobottom view, so this is a limiting factor
in diagnostics.”
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X-rays alone are not conclusive evidence of wobbles. Even if images show
evidence of injury or malformation in
the neck bones, that doesn’t necessarily
mean that compression is occurring.
Likewise, “if the
INSIDE LOOK:
x-rays are normal
An x-ray that shows
this doesn’t mean
arthritic changes
the horse doesn’t
in a horse’s neck
have wobbler
vertebrae (top) is not
syndrome,” says
necessarily
evidence
Trostle, noting
of wobbles. But a
that an abnormalmyelogram,
which
ity may not be
uses contrast dye to
visible from the
highlight the spinal
angle depicted on
canal, can clearly
the x-ray.
Trostle also
reveal spinal cord
uses the x-rays to
compression (right).
make measurements that compare the height of the
spinal canal to the size of the vertebrae.
This calculation determines whether
an individual’s spinal canal is smaller
than average, which might make him
a more likely candidate for wobbles.
“People look at some of the measurement ratios to see if these might have a
positive predictive value for the horse
actually having spinal cord compression,” says Trostle. “This is an area
currently being investigated and is
somewhat controversial.”
If compression on the spinal cord
is still suspected, the next step is myelography. For this procedure, the horse
is anesthetized and a contrast dye is
injected into the cerebral spinal fluid
(CSF), which fills the space around the
spinal cord. Then x-rays are taken with
the neck in neutral, extended and fully
flexed positions. In the resulting images, the dye highlights any narrowing
of the spinal channel and thus pinching
of the spinal cord.
The myelogram is important because
it shows at exactly what point or points
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the vertebrae are impinging on the
spinal cord and to what extent. “Then
you can determine whether it’s a mild,
moderate or severe case and what the
horse’s chances are,” says Grant. “The
most important thing is to get an accurate diagnosis rather than just shooting
in the dark.”
TREATMENT OPTIONS
The best treatment for a horse with
wobbles depends on several factors,
including the cause and severity of the
spinal compression as well as the age
of the horse, his current occupation and
his owner’s expectations for his future
use. Here are the three most common
types of wobblers and the paths usually chosen to treat them.
For older horses with mild arthritis in the cervical vertebrae: Rest and
drug therapy
If the problem is caught early, when
the degree of compression and impairment is still mild, a horse may be able
to live comfortably with the same
basic treatments used to manage other
arthritic joints: nonsteroidal antiinflammatory drugs (NSAIDs), supplements containing chondroitin sulfate
and/or other joint-support agents, and
possibly steroid injections for slightly
more advanced cases. “In the older
horses, you could inject the articular
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C O U R T E S Y, S T E V E T R O S T L E , D V M , D A C V S
A TRICKY DIAGNOSIS
therapeutic option for Seattle Slew.
With the assistance of another wobbler
surgery pioneer, George Bagby, MD, Grant
adapted a basketlike implant used to fuse
vertebrae in people for use in Seattle
Slew’s neck vertebrae. In April 2000, he
and a team of surgeons inserted the new
device, now dubbed the “Seattle Slew
implant,” into the neck of the famous
stallion. The vertebrae fused and Seattle
Slew recovered, going on to breed 60
mares in 2001.
The stallion later experienced a
recurrence of wobbles and had further
surgery, before he died in his sleep in May
2002 at the age of 28.
INNOVATION:
After Seattle Slew (inset)
developed wobbles, surgeons adapted
an implant from human medicine to
stabilize the stallion’s neck vertebrae.
The “Seattle Slew implant,” shown here in
another horse’s x-ray, is now frequently used
to treat horses with significant spinal compression.
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facets with steroids to try to relieve
some of the discomfort,” says Trostle.
“For some horses, this has a benefit but
for others it does not. It’s hard to predict
which ones will be helped.”
Retirement or a change of career may
also be in order. Strenuous activities
such as jumping or galloping up and
down hills increase pressure on the
bones in the neck. Some horses may be
able to handle less intense exercise over
safe, flat surfaces; others may need to
be retired from all work.
The goal of this approach is simply
to let the horse live comfortably. These
treatments may relieve pain, but they
won’t reverse the arthritic process in
the neck. “If there are bony
changes compressing the
cord, injecting the facet joint
will help with the pain but
won’t produce regression or
modification of the bone that
is impacting on the spinal
cord,” says Trostle. “It may be
a short-term relief.”
For foals or younger
weanlings with CVM:
Restricted diet to
slow growth
For many youngsters with CVM
the best therapy is a “paced diet,”
which provides only 60 percent of the
carbohydrates and proteins usually
recommended for growing horses.
The colt will lose weight but will continue to grow. The goal is to slow the
overgrowth of the cervical vertebrae
and prevent them from impinging on
the spinal cord.
The timing may vary, but foals
who are diagnosed with CVM at around
6 months of age would typically remain
on the regimen for eight to 10 months.
Once they’ve achieved their adult
height, they go back on full nutrition.
Thereafter they generally catch up
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or from arthritis---tends to atrophy or
melt back a bit and takes the pressure
off the spine,” says Trostle.
Fusing only one joint will not necessarily have a significant impact on a
horse’s athletic ability. “Many horses
have gone on to
race well, or go on
to grand prix dressage or jumping,
after surgical treatment,” says Grant. But if more than one
with their peers as far as weight and
joint must be immobilized, neck mobilgrowth and become healthy adults.
ity will be affected. “We can do what’s
“For this approach to work, the
horse must be young enough that there called a single level or a double level, or
sometimes a triple or quadruple level,”
is still growth occurring,” says Trostle.
says Trostle. “But the more levels we do,
“Once a horse gets past a year of age,
the greater the decrease in mobility or
this paced diet is not as effective bemovement of the neck. A single level
cause the bones have done most of
has very little clinical impact or signifitheir enlarging. The horse isn’t done
cance on the horse’s mobility. A double
growing yet, but the neck bones are,
level has some, but a triple level will
for all practical purposes. In the true
definitely impact the horse.”
wobblers with developmental issues,
A horse’s prognosis depends in
surgery is still probably the preferred
part on how seriously he had been
method of treatment.”
impaired. The more incoordinated he
For horses with significant comwas, the greater the likelihood he will
pression, especially young equine
experience setbacks as he convalesces
athletes: Surgery to relieve the pressure on the spinal cord and/or stabilize and the lower his chances of returning
to normal. Nevertheless, says Trostle,
the vertebral joints
“We generally consider that 80 percent
The primary surgical remedy for
of the horses will improve about one
CVM involves fusing the affected
grade after the surgery.” In addition,
cervical joint by implanting a titanium
Grant reports that 54 percent of his
cylindrical threaded basket-shaped
patients improve two or more grades
device, now called a “Seattle Slew implant” (see “The Most Famous Wobbler,” after surgery.
But it can take time. Neural tissue
at left), into the affected vertebrae.
heals slowly, and horses may require
As the surgical site heals, new bone
tissue fuses to the implant and prevents at least one year and maybe up to two
to reach maximum recovery, according
joint movement.
to Grant. For that reason, the surgery
This technique can eliminate dyis most successful when it is pernamic instability that causes compression, and it can also help diminish cord formed early, before too much damage
has occurred. One study from Ohio
impingement from bony overgrowth:
State University tracked 73 horses
“The bone above that articular facet--after surgery to fuse their cervical
which has become enlarged either
vertebrae and found that the best
from the horse’s growth/development,
For many youngsters with
CVM the best therapy is a
“paced diet.”
BOB LANGRISH
C O U R T E S Y, S T E V E T R O S T L E , D V M , D A C V S
In 2000, Seattle Slew, winner of the
1977 Triple Crown, was one of the world’s
leading Thoroughbred sires, with progeny
including Landaluce, Slew o’ Gold, A.P. Indy
and several other champions. But it looked
like his stud career might be over.
The 26-year-old stallion had suddenly
developed incoordination in his hind legs,
affecting his gaits and making breeding
dangerous if not impossible. A neurologic
examination along with x-rays and other
imaging procedures eventually pinpointed
the source of the problem: arthritic
changes in the neck vertebrae resulting
in impingement on the spinal cord.
Intravertebral steroid injections brought
some improvement, but eventually a
myelogram revealed severe narrowing
of the spinal canal at the sixth and
seventh vertebrae.
Barrie Grant, DVM, who had helped
to develop a surgical technique for
stabilizing the cervical vertebrae in
wobblers back in the 1970s at Washington
State University, was part of the team
called in to confer on the case. Surgery,
the veterinarians decided, was the best
BARBARA LIVINGSTON
THE MOST FAMOUS WOBBLER
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results were achieved in those who
underwent the procedure within 30
days or less after the first signs of impairment appeared.
In some cases, that may mean that
it’s best to proceed with the surgery
even if the myelogram does not show
distinct and obvious evidence of compression. “People who are doing the
surgery now are realizing that we’ve
been interpreting the myelograms too
harshly,” says Grant. “Some horses
with only mild changes on the myelograms are actually the cases we
can help the best. Some of these
horses go better when their hocks or
stifles are injected, because they have
steroids in the system that also help the
spinal cord. Or they may act like they
have a weak or sore back, which may be
due to not enough nerve function going
to the muscles.”
In the past, he says, “We may not
have been operating on those horses,
because we wanted to first have a
really distinct compression that anyone
could see, regarding how bad the compression is.”
But, Grant adds, “When these mild
cases are properly diagnosed and we do
surgery, they may go back to the top of
their career again---such as jumping big
fences---and are happy doing their job.”
V
igilance--to catch the first signs
of trouble---is the key to getting a
case of wobbles under control before it
becomes catastrophic. But the chances
are good that with appropriate care a
wobbler can go on to live an active,
comfortable life.
For more on assessing a horse’s neurological status, see “Just Clumsy or Something
Worse?” EQUUS 403. In addition, Barrie
Grant, DVM, maintains this informative
website: www.equinewobblers.com.
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