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fast-growing colts and also in horses old enough to be developing arthritis.

The good news is that, with appro-priate 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 con-dition 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 compres-sion occurs when a malformation of the

Your 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 ex-periencing 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, includ-ing 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,

By Heather Smith Thomas

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.

WHAT CAN BE

DONE FOR WOBBLERS?

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 condi-tion 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 stand-ing 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 develop-mental 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 verte-

brae. “These horses are not necessarily born neuro-

logic, but over time

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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.

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 are still looking into why some horses become wobblers while others do not: “No one has done many genetic stud-ies but we know there are families of horses that pro-duce more wobblers than average,” says John Madigan, DVM, of the University of California–Davis.

A different type of wobbles, one resulting from arthritic changes in the neck vertebrae, is most often seen in older horses. “Bone response to injury is to create more bone,” ex-plains Trostle. “With arthritis you get loss of cartilage and the development of more bone. Sometimes that bony enlargement can impinge on the spinal cord. These cases have not been given a specific name.”

This form of wobbles can develop in any breed, but it’s most often seen in equine athletes. “These cases are increasing in number,” says Madigan. “It may be a performance horse, such as a jumper, and the rider notices that the horse is becoming a little stumbly. When checked, we notice there’s a big bony lesion in the lower cervical area.”

E Q U U S 4 1 7 53

ANATOMY

RED FLAGSRegardless of the cause, in horses

young and old, the effects of wobbles are the same: The pinching of the spinal cord impairs neurological communica-tions between the brain and the rest of the body.

One of the most noticeable early signs is a loss of proprioception---the sense of where the body and limbs are ---which can lead a horse to stand with his feet in unusual positions or swing his legs oddly as he moves. Left un-treated, the impingement on the spinal cord will cause further neural damage over time, and the horse will lose more control over his legs, becoming more incoordinated. Because the nerves that serve the hindquarters are located on the surface of the spinal cord, the hind legs are usually affected first.

The severity of wobbles is graded on a scale of 0 to 5:

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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

One of the early signs of wobbles is a loss of proprioception–the sense of

where the body and limbs are–which can lead a horse to stand with his feet in unusual positions or swing his legs

oddly as he moves.

NORMAL

COMPRESSED

spinal cord

neck vertebrae

spinal cord

spinal canal

narrowing of spinal canal

spinal canal

cervical C1 C2 C3 C4 C5 C6 C7 vertebrae (atlas) (axis)

atlas

axis

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types of wobblers and the paths usu-ally chosen to treat them.

For older horses with mild arthri-tis in the cervical vertebrae: Rest and drug therapy

If the problem is caught early, when the degree of compression and impair-ment is still mild, a horse may be able to live comfortably with the same basic treatments used to manage other arthritic joints: nonsteroidal anti-inflammatory drugs (NSAIDs), supple-ments 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

horses try very hard, and when they decide they don’t want to do something, there’s usually a reason.”

As neurological dysfunction pro-gresses, 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 canter-ing, even at liberty, or may insert “bunny hops” into the gait. Also, wobblers sometimes have difficulty establishing the correct lead.

A TRICKY DIAGNOSISIdentifying wobbles quickly is criti-

cal. 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 perma-nent 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 veteri-narian will first conduct a complete neurological examination as well as a lameness exam. He’ll also rule out dis-eases and conditions other than wob-bles that can cause incoordination: “It doesn’t really matter whether it’s pinch-ing 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 sam-ples 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 later-al 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-to-bottom view, so this is a limiting factor in diagnostics.”

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).

• 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 com-monly on the front heels from over-reaching with his hind feet.

• Knuckling. The pastern joints in the hind legs may bend forward un-naturally, 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.

X-rays alone are not conclusive evi-dence 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 x-rays are normal this doesn’t mean the horse doesn’t have wobbler syndrome,” says Trostle, noting that an abnormal-ity may not be visible from the angle depicted on the x-ray.

Trostle also uses the x-rays to make measure-ments 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 measure-ment ratios to see if these might have a positive predictive value for the horse actually having spinal cord compres-sion,” 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 my-elography. 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 im-ages, 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

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 accu-rate diagnosis rather than just shooting in the dark.”

TREATMENT OPTIONSThe 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

INSIDE LOOK: An x-ray that shows

arthritic changes

in a horse’s neck

vertebrae (top) is not

necessarily evidence

of wobbles. But a

myelogram, which

uses contrast dye to

highlight the spinal

canal, can clearly

reveal spinal cord

compression (right).

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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 con-tinue 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

with their peers as far as weight and growth and become healthy adults.

“For this approach to work, the horse must be young enough that there is still growth occurring,” says Trostle. “Once a horse gets past a year of age, this paced diet is not as effective be-cause the bones have done most of their enlarging. The horse isn’t done growing yet, but the neck bones are, for all practical purposes. In the true wobblers with developmental issues, surgery is still probably the preferred method of treatment.”

For horses with significant com-pression, especially young equine athletes: Surgery to relieve the pres-sure on the spinal cord and/or stabilize the vertebral joints

The primary surgical remedy for CVM involves fusing the affected cervical joint by implanting a titanium cylindrical threaded basket-shaped device, now called a “Seattle Slew im-plant” (see “The Most Famous Wobbler,” at left), into the affected vertebrae. As the surgical site heals, new bone tissue fuses to the implant and prevents joint movement.

This technique can eliminate dy-namic instability that causes compres-sion, and it can also help diminish cord impingement from bony overgrowth: “The bone above that articular facet--- which has become enlarged either from the horse’s growth/development,

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 nec-essarily have a significant impact on a horse’s athletic ability. “Many horses

have gone on to race well, or go on to grand prix dres-sage or jumping, after surgical treat-

ment,” says Grant. But if more than one joint must be immobilized, neck mobil-ity will be affected. “We can do what’s called a single level or a double level, or sometimes a triple or quadruple level,” says Trostle. “But the more levels we do, the greater the decrease in mobility or movement of the neck. A single level has very little clinical impact or signifi-cance on the horse’s mobility. A double level has some, but a triple level will definitely impact the horse.”

A horse’s prognosis depends in part on how seriously he had been impaired. The more incoordinated he was, the greater the likelihood he will experience setbacks as he convalesces and the lower his chances of returning to normal. Nevertheless, says Trostle, “We generally consider that 80 percent of the horses will improve about one grade after the surgery.” In addition, Grant reports that 54 percent of his patients improve two or more grades after surgery.

But it can take time. Neural tissue heals slowly, and horses may require at least one year and maybe up to two to reach maximum recovery, according to Grant. For that reason, the surgery is most successful when it is per- formed early, before too much damage has occurred. One study from Ohio State University tracked 73 horses after surgery to fuse their cervical vertebrae and found that the best

THE MOST FAMOUS WOBBLERresults were achieved in those who underwent the procedure within 30 days or less after the first signs of im-pairment 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 com-pression. “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 myelo-grams 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 com-pression 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.”

Vigilance--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 neurologi-

cal status, see “Just Clumsy or Something

Worse?” EQUUS 403. In addition, Barrie

Grant, DVM, maintains this informative

website: www.equinewobblers.com.

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

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.

For many youngsters with CVM the best therapy is a

“paced diet.”

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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