The Top 5 Causes of Equine Lameness
If you're trying to solve your horse's mystery lameness, take a look at these likely culprits.
By Joan Norton, VMD
Lameness is one of the most prevalent veterinary complaints in the horse. While there are a multitude of ways horses can go lame, some conditions occur more frequently.
Lameness in the horse can range from an obvious non-weight-bearing gait to more subtle signs of discomfort that may only be displayed as poor performance. The goals of a lameness examination are to identify the affected leg and the exact part of it that is causing the lameness.
Before watching the horse move, your vet may want to know about his recent activity. The horse should be examined from a distance and up close, with a thorough palpation of the legs. As the vast majority (up to 90 percent) of all lamenesses originate in the foot, the hoof, sole and heels should be carefully assessed; applying pressure around the foot with hoof testers can help to detect any pain. Finally, the horse can be observed at the walk and trot, both in a straight line and on a circle, to look for signs of lameness.
The area of origin can be more closely isolated with flexion tests, placing pressure on a joint in the leg by flexing it; lameness often worsens after flexion.
To further pinpoint where the pain is coming from, a diagnostic nerve block can be used, where a local anesthetic is injected to numb a portion of the leg. The horse is then jogged again to see if the lameness has improved or resolved. These procedures are started at the heel/hoof and progress up the leg until the area of pain is identified.
Next, diagnostics such as radiographs (X-rays), ultrasound and even more detailed scans, including computed tomography (CT) or magnetic resonance imaging (MRI), can be employed to determine the exact cause of the lameness.
Here are the top five causes of lameness.
Subsolar abscesses, localized infections just beneath the sole of the hoof, are one of the most widespread causes of foot pain. As an abscess develops, it exerts pressure on the sensitive structures of the foot.
The navicular bone is a small canoe-shaped bone that lies within the hoof behind the coffin and short pastern bones. Navicular syndrome is a term used to describe the heel pain and pathology of navicular disease.
While heel pain is a component of navicular syndrome, it is very important to point out that there are a multitude of other structures in the hoof that can cause heel pain, such as the suspensory ligament of the navicular bone, the impar ligament that connects the navicular bone to the back of the coffin bone, and other collateral ligaments.
Degenerative Joint Disease
Degenerative joint disease (DJD) is a common occurrence in older, and sometimes not so old, equine athletes. The body is designed to maintain the cartilage in the joints, repairing damage after normal wear and tear. In athletic horses, however, excessive wear can overwhelm the repair process.
Tendon and Ligament Injury
There are several important tendons and ligaments in the lower leg. The superficial digital flexor tendon, the deep digital flexor tendon, and the suspensory ligament are the most prominent and often prone to injury.
While it is impossible to list all the ways why horses can go lame, it’s useful to understand some of the top causes. Knowing how these injuries and diseases present will allow you to better recognize a problem and start appropriate treatment sooner so that you can get back in the saddle.
The Lameness Scale
The American Association of Equine Practitioners has developed a grading scale (0-5) so that all horsemen and veterinarians can use the same criteria for describing a lameness.
Grade 0: A sound horse .
Grade 1: Lameness that is difficult to observe and is not consistently apparent.
Grade 2: Lameness that is difficult to observe at a walk or when trotting in a straight line, but consistently apparent under certain circumstances.
Grade 3: Lameness that is consistently observable at a trot under all circumstances.
Grade 4: Lameness that is obvious at the walk.
Grade 5: Lameness that produces minimal weight bearing in motion and/or at rest, or a complete inability to move.
Hoof Care and Lameness
JOAN NORTON, VMD, DACVIM, is the founder of Norton Veterinary Consulting and Education Resources, a firm dedicated to the education of horsemen and equine veterinarians through internal medicine consultations, lectures, webinars and writing. More information on her services and courses can be found at www.nortonveterinaryconsulting.com
The Lameness Exam: What to Expect After You’ve Called the Vet
Among the many things that a horse owner dreads is going out to the barn and seeing your horse not moving right. It can be as simple as an occasional irregular stride on the lunge line or as dramatic as head-bobbing, hip-hiking lameness (or worse), but in either case, the next step is contacting the veterinarian and scheduling a lameness exam. Although there are some typical components to nearly every lameness exam—such as use of hoof testers and flexion tests--there is no one, standard “lameness exam” because every horse and every situation is different. For example, the tools and tests used for a horse who has taken some uneven steps competing at the highest levels of his sport may be very different from the way a vet approaches the diagnosis of a young horse that comes in from the pasture limping.
Surprisingly, the first thing a vet will do when called out to examine a horse for lameness does not involve palpating the limbs or watching the horse jog — it’s gather a history. This means asking the owner, and possibly trainer, questions about the problem and encouraging them to describe what they are seeing and feeling, including when it first started, how it has changed and if any treatment has already been given.
Once the vet has these basic facts, the actual lameness exam itself can begin. Step one is a visual inspection at rest, before the horse is even asked to move. Here the vet is assessing conformation, balance and symmetry left to right as well as back to front, plus the horse’s overall posture and comfort level.
The next step is palpation, or feeling the various body parts by hand. Don’t be surprised if the vet palpates the normal limb first then moves to the abnormal limb. This is because it is helpful to be able to compare one leg to the other and to know what it is supposed to feel like for that particular horse before trying to decide if the way a specific structure looks or feels is not normal. Digital pulses (the intensity of the heart rate in the blood vessels of the lower limbs) may also be assessed. At this point, the vet may apply hoof testers to the feet, to determine if there’s any pain or discomfort when certain areas of the hoof are squeezed or pressed on. Armed with this preliminary data, it may now be time to observe the horse on the move.
Some veterinarians prefer to have the horse jog in-hand while others prefer to see the horse jog at the end of a lunge line. After watching the horse in motion, perhaps on both straight lines and circles, and on both hard and soft ground, the vet may wish to perform flexion texts.
In this procedure, additional stress is placed on specific joints such as the knee, fetlock (ankle), stifle, and hock by holding one leg off the ground in a bent position for a minute or two then putting it down and immediately trotting the horse off. Flexion tests are helpful to localize soundness issues by temporarily accentuating pain. So a horse that was a Grade 1 on the right front at first might demonstrate a Grade 2 or 3 lameness after the knee is flexed, indicating that may be where the problem is (see sidebar for more information on grading a lameness).
Additional Diagnostic Tests
Depending on the results so far, the vet may decide it is time to numb a limb, usually beginning at the bottom with the hoof and working up the leg. “Nerve blocks” are performed by injecting topical anesthetic agents just under the skin and over the top of nerves. Within a few minutes, structures served by these nerves become temporarily deadened and if pain was originating from that particular area of the leg, the horse may now jog out sound. However, if that area was NOT the source of the lameness, then the horse will jog the same as before and another area may then be blocked against pain. Entire joints can be numbed with a “joint block” in which the anesthetic agent is sterilely injected into the joint itself and, after waiting for the agent to take effect, the horse is jogged to see if there is any difference in his way of going.
The next service the vet may offer is imaging. Today’s veterinarians have a wide array of visualization tools at their disposal to aid in the diagnosis of lameness but these modalities do not take the place of a thorough lameness exam, they are complementary to it. Once a lameness has been localized to a specific area, the best tool for the job will be selected, such as radiographs (X-rays) for bones and joints or ultrasound for soft tissues like tendons and ligaments. Advanced imaging choices include scintigraphy (nuclear scan), MRI and/or CT scans. Sometimes images of specific structures can be used to rule in a cause for lameness—such as an OCD cyst in the stifle or a core lesion in the suspensory—and sometimes images can be used to rule out a cause for lameness—such as properly aligned fibers in the superficial digital flexor tendon or pristine articular cartilage surfaces in the hock joint.
From a horse that feels uneven in the reins or won’t pick up a certain canter lead to a non-weight bearing lameness (an emergency!), your vet is your best resource to get to the bottom of the issue quickly so that appropriate treatment can be started right away and you can get back to enjoying your horse!
Lameness Grading System
A lameness grading system has been developed by the American Association of Equine Practitioners (AAEP) to standardize the degree of a horse’s unsoundness:
0: Lameness not perceptible under any circumstances.
1: Lameness is difficult to observe and is not consistently apparent, regardless of circumstances (e.g. under saddle, circling, inclines, hard surface, etc.).
2: Lameness is difficult to observe at a walk or when trotting in a straight line but consistently apparent under certain circumstances (e.g. weight-carrying, circling, inclines, hard surface, etc.).
3: Lameness is consistently observable at a trot under all circumstances.
4: Lameness is obvious at a walk.
5: Lameness produces minimal weight bearing in motion and/or at rest or a complete inability to move.