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EQUINE HEALTH
Sidewinder is a term describing a neurologi- cal or musculosketal symptom in older horse that has an unusual clinical presen- tation. These horses have a sudden alteration in gait that makes the hindquarters list to one side or the other when the horse walks.
Amy Johnson DVM, DACVIM, of Large Animal Internal Medicine at New Bolton Center in Pennsylvania, says there is not much about this syndrome in the literature. “It’s been around for a long time, but we still don’t know much about it. I have seen horses with this problem since I was in veterinary school (20 years ago), but it’s challenging to diagnose the cause. Therefore, there has not been a lot of research, so it’s not widely published in the literature,” she explains.
There are other conditions and diseases that can cause a horse to walk abnormally. “This syndrome is just a description, a symptom, not a disease in itself or a diagnosis. There are many different things that could result in a horse hav- ing this type of gait.” If a horse owner observes the odd movement, it’s important to get their veterinarian involved and try to figure out the actual cause.
“In my experience, this syndrome is much more common in older horses than it is in young horses. It’s usually seen in horses that are
in their late teens or in their 20’s or older. It’s very uncommon in horses below the age of 15, and most of the time there is a sudden onset. The horse seems normal one day and the next day is walking abnormally.”
There are different terms for this. Some people call these horses sidewinders, some
call them crab walkers or side walkers. “The way I describe the gait is that the hind legs
are moving on a different track than the front legs—offset to one side or the other. When you watch the horse from behind, the front legs are moving straight forward, and the horse is al- most walking on three tracks. If you look at the horse from behind and the hind end is drifting to the left, the left hind foot will be moving way out to the side and the right hind will be in line with the left front. The right front will be on a third track,” says Johnson.
“This is pretty consistent and that’s another thing that’s interesting about these horses. The hind end is not following the front but sticking out to one side or the other, consistently to one side. When the horse is standing, it tends to weight one hind leg more than the other. If the hind end is offset to the left, the left hind leg would be held to the left, away from the body and resting when the horse is standing still, with most of the weight
on the right hind—which is positioned more centrally,” she explains.
“Sometimes these older horses end up just traveling/spinning in a circle when they try
to walk, and they may want to lean against a wall to support that weak side. It’s not really a whole-body balance problem; the hind end just keeps listing to one side and the front legs step in place to compensate for that drifting move- ment of the hind legs. The old horses get smart and lean up against a fence or the stall wall to stop the spinning movement,” she says.
The hind leg locomotion is what’s affected, which is different from some of the other situ- ations that might cause ataxia in a horse (like a neck problem that affects all four legs). EPM is a disease that the veterinarian will check for because it is one of the causes of this side- walking syndrome.
“EPM is one of those bizarre diseases that can cause several different signs because it can affect the brain, or the spinal cord, or different areas of the spinal cord. When it affects the spi- nal cord in the thoracolumbar region (between the front legs and the back legs) it would not affect the front legs but could cause this abnor- mal gait in the hind legs,” she explains.
It’s important to have some tests to rule in or rule out some of the possibilities. “The
SIDEWINDER
SYNDROME
IN HORSES
by Heather Smith Thomas
“This syndrome is just a description, a symptom, not a disease in itself or a diagnosis. There are many different things that could result in a horse having this type of gait.”
60 SPEEDHORSE October 2020