Lameness: Getting to the Bottom of It
Your horse is favoring his left front leg, but you're not sure if the problem is in his foot or higher up the limb. Or, he may be just a little "off" in his performance and won't stay in the proper lead at a canter. Pinpointing lameness is crucial before proper treatment can be prescribed.
Stuart Shoemaker, DVM, Dipl. ACVS, of Idaho Equine Hospital, in Nampa, says there are several approaches to lameness examinations and diagnostic methods. "What we do will be partly determined by the age of the horse and what it does for living," he explains. "For example, very young horses (especially Western performance horses that are only 2 or 3 years old) will have a different group of lamenesses, associated with the type of exercise they are doing, compared with older horses that have different reasons for lameness."
As the body ages, the tissues become less elastic. "Though the traditional lameness examination involved X rays, and X rays were the gold standard, in reality the majority of lamenesses we see in upper-end athletes are soft tissue injuries--some of which cannot be identified with radiographs," he adds.
"Our patients cannot talk, so we must do a series of exams to identify the source of pain," says Shoemaker. "This starts with the history--what the horse does, how old he is, whether there was a specific event that occurred before he became lame. Was the lameness acute or a slow onset? The type of horse and how it is ridden can also give clues. Certain disciplines have higher incidence of certain kinds of lameness. Thus, the history gives you lots of insight when trying to discover what's wrong."
Kent Allen, DVM, is the owner of Virginia Equine Imaging, a practice that specializes in lameness issues. He says some lame horses have long, complex histories. "They've been to multiple veterinarians and arrive at our referral practice with images (ultrasound or X rays), or in some cases (the owners) just tell us the trainer said the horse was lame and they want us to look at it," says Allen. "No matter what the situation, the veterinarian needs to listen to the history. Sometimes this means just sitting there and letting the owner talk."
Some clients provide written histories. "Parts of a history may be pertinent and some may not be," he says. "If they go back two or three years and describe how the horse trotted around the pasture as a yearling, this may not be relevant. Conversely, if two years ago the horse had stifle OCD (osteochondritis dissecans) surgery, this could be relevant to the current situation. Even if he isn't lame in that leg, it could be a factor.
"We need to sort through the history and glean what's pertinent, particularly what the horse has been doing for the last six months, and when the owner first noticed the lameness or felt a problem," he says.
"The second-most important thing, and the one that's overlooked the most, is that you have to put your hands on the patient to do a good physical examination," says Shoemaker. "This aspect has been lost a little in recent years as more diagnostic tools have become available. People are jumping quickly to use ultrasound, digital X rays, etc., and miss the opportunity to do a good physical exam. Often the diagnosis is right there, if you simply put your hands on the horse."
Allen says, "What we are looking for are soft tissue swellings, or bony areas that might have swelling. These may have relevance later when we're trying to put all this together. The veterinarian will palpate the limbs and feel for heat, swelling, or evidence of pain. We'll also use a hoof tester to make sure the problem is not in the foot. This is a standard part of the exam, particularly in the front limb. But just because a horse is sensitive to the hoof tester doesn't mean he's lame on that foot."
Watch the Horse Move
The next step is observing the horse in motion--walked out and back--to observe cadence of footfalls, stride, range of motion, etc. "Then we'll have the horse trotted, to see if we can detect any lameness on the straightaway," says Allen. "After that, we longe the horse in a circle, often on a variety of surfaces.
"The primary test would be on a firm surface with good traction," he says. "If you do it on slippery asphalt, the horse won't move naturally. He'll be hesitant or slipping and you won't see his natural gait."
The vet might want to see the horse ridden, which can sometimes show aspects of the gait not seen otherwise. "But remember that a rider can mask or disguise certain lameness aspects," Allen adds.
His favorite surface is a stone dust round pen that's kept watered and rolled. "It's firm, but has some grip," he explains. "There's no way a horse could slip and fall. Sometimes the horse will be asked to trot circles in an arena-type surface. Other vets use a gravel base. But at some point you have to see the horse on a firm surface."
Often, such a surface accentuates some types of lamenesses due to the concussion it causes. The vet might use a soft, deep surface to see if there's a difference in the horse's gaits. A horse might be less lame on the soft surface if concussion is the issue, but a tendon injury could be more painful on the soft, loose surface because the tendons have to work harder in this footing.
After watching the horse move Allen usually flexes the limbs. (Note: Veterinarians might do these steps in a different order, doing flexion tests before exercise, for example.) "We generally hold the leg up for 30 seconds to a minute, then immediately trot the horse," says Allen. "This won't diagnose the problem, but it gives a determination of how lame the horse moves off, in comparison to what he does after the opposite limb is flexed."
"With the history, physical examination, and observation, you have several pieces of information," says Shoemaker. "These may lead you to determine that the foot is the source of pain. We can then use analgesia--nerve blocks, or blocks of joints and tendon sheaths--to give us the source of lameness. We're asking the horse, 'Does your foot hurt?' by numbing the foot. If he then goes sound, he's saying, 'Yes, it was my foot, and now it feels better.'
"A lameness exam is like a whodunit crime investigation," continues Shoemaker. "You put together a series of pieces of information. The history, and putting your hands on the patient (finding a certain area is hot or swollen), then asking if the foot hurts or the tendon sheath hurts (by using a block) gives clues. If the patient goes sound, you've localized the region."
Allen says, "If we've palpated the limb and a tendon is sore, we may go straight to ultrasound" or use nerve blocks to pinpoint a more elusive area, starting at the lowest point. "We work progressively up the leg until we find the point at which he goes sound after that area is blocked."
Diagnosis is a step-by-step process, and sometimes the answer is elusive. "Let's say you've done two or three nerve blocks on the right front, and it blocks (the horse goes sound) at the right fetlock," says Allen. Next you would X ray the fetlock.
"If the X rays are negative, you'd start wondering if it could be a soft-tissue lesion, so you'd next ultrasound the fetlock and look at the collateral ligaments and cartilagefor any soft tissue lesions," he says.
Some cases are not straightforward and can't be readily diagnosed with blocks, ultrasound, or X rays. "There may be multiple limbs involved or some other situation that's not simple," says Allen. "Multiple veterinarians may have looked at the horse multiple times, with different answers."
Some of these horses require a bone scan (nuclear scintigraphy, which shows areas of metabolic activity, indicating bone remodeling) because the entire body can be imaged. If the problem is in the hip or back (areas that are difficult to X ray), the vet could locate it with this method.
"The vast majority of problems are bony when dealing with a lameness that's persisted for a month or more, or a multilimb lameness," says Allen. "Based on a bone scan, we'll launch into a more specifically directed block, X ray, or ultrasound. "
How extensive the diagnostic effort becomes will depend on the horse. "If he's mildly off behind and won't hold leads, you could just inject the hocks and see how he does," notes Allen. "But if a horse has had a right front limb lameness no one can successfully block, and he has been lame for 30 to 60 days, that horse doesn't need another drug; it needs a diagnosis."
Further complicating the process, a horse might start out with a lameness in one area (i.e., stifles or hocks) and exhibit a more prominent lameness in a forelimb. This makes diagnosis a two-step process.
Shoemaker adds, "Today, equine orthopedics is headed toward MRI. In the very near future the standard for looking at extremities (from knees and hocks down) will be MRI, because you can look at tissues three-dimensionally and at the interface between bone and tendon, and bone and ligament. These interfaces are where many injuries occur. The MRI is far more sensitive than ultrasound or radiographs. X rays are very effective for seeing certain kinds of bone changes, however, and will not be replaced by MRI for these diagnoses.
"I tell my interns and veterinarians who work for me that therapy is always more effective with a diagnosis," he says. "It is difficult to choose a treatment for your patient if you don't have an accurate diagnosis. Without an accurate diagnosis we are merely treating symptoms and making assumptions as to what's wrong with the horse, and oftentimes we are incorrect.
"Many people are treating injuries, such as sacroiliac problems, with no concrete data to support what they're doing," says Shoemaker. "They might be injecting into an area that's uncomfortable, but the sacroiliac ligament may have nothing to do with the lameness. This is currently a popular diagnosis in hind limb lamenesses in horses that are suddenly off."
Allen has a saying that gets quoted a lot: "Absent a diagnosis, medicine is poison, surgery is trauma, and alternative therapy is witchcraft," he notes. "This is true every day in our practice. If you can get to the diagnosis quicker, you save a lot of money, and start the horse toward recovery a lot sooner."
About the Author
Heather Smith Thomas ranches with her husband near Salmon, Idaho, raising cattle and a few horses. She has a B.A. in English and history from University of Puget Sound (1966). She has raised and trained horses for 50 years, and has been writing freelance articles and books nearly that long, publishing 20 books and more than 9,000 articles for horse and livestock publications. Some of her books include Understanding Equine Hoof Care, The Horse Conformation Handbook, Care and Management of Horses, Storey's Guide to Raising Horses and Storey's Guide to Training Horses. Besides having her own blog, www.heathersmiththomas.blogspot.com, she writes a biweekly blog at http://insidestorey.blogspot.com that comes out on Tuesdays.
POLL: University Equine Hospitals