Athletic trainers, orthopedic surgeons, and all the various other professionals involved in human sports medicine have it easy. Waaaay easy. When a person has pain when they are doing an activity (running, jumping, etc), they can go into the doctor or trainer and “Here’s where it hurts” and “It hurts whenever I do X activity”. The doctor can get essential information from the patient in less than 10 minutes simply by asking the right questions and getting detailed, honest answers.
Now lets talk about the difference a veterinarian faces when performing a lameness exam on a horse. The horse can not tell us which leg hurts, where on the leg it hurts, what activity makes it worse, how long it has been happening, etc, etc, etc. A veterinarian relies on the owner or horse trainer to gather some of this information, but often the information is vague or conflicting depending on whom you are talking with. Many times I get some variation of the following history:
“My horse has been ‘off’ for a couple of months now. It feels like it is in the hind leg but my trainer said she is short striding in the front. I gave the horse some ‘bute’ but I ran out so I stopped a couple of weeks ago. My farrier put on shoes last week.”
This type of history is very vague and really does not tell the vet much except this is a chronic mild to moderate lameness. Now it is up to the vet to figure out what is really going on and how to fix it.
Which leg or legs are lame?
This is the first question the vet attempts to answer when performing a lameness exam. Sometimes it is very obvious, other times it can hard to tell. In order to determine which leg or legs are lame, the vet will watch the horse perform different gaits, starting with a basic walk. If not obvious at a walk the vet will move on to a trot in a straight line. If it is still not obvious the vet may lunge the horse in different directions and on different surfaces. Basically the idea is to visualize the lameness or gait abnormality that the owner or rider has noticed.
Several things can come up that make finding the lame limb difficult or impossible:
1. The horse is not lame the day of the examination. This situation happens very often and is a major frustration for owners. You can have a horse that has been consistently lame for three months but the day the vet examines it the horse will suddenly be sound. An important piece of advice is to exercise your horse before the vet appointment and make sure his is actually still lame!
2. Multiple legs are lame. It is extremely hard to make an accurate diagnosis when a horse has multiple limbs that are making his gait abnormal. One leg may be compensating for another or the legs may have two completely different issues.
Where in the limb or body is the lameness coming from?
Once the vet determines which limb is lame, the next step is to find where in that limb the lameness is coming from. Again, sometimes this can be quite obvious. For instance, if the right front leg is lame and the fetlock is swollen, hot, and painful your vet probably will be confident that the lameness is coming from the fetlock region. If it is not obvious, your vet can perform certain tests to help localize the lameness.
One simple test is called a “flexion test”. Your vet will hold certain joints in flexion for various periods of time and then watch the horse trot. If flexing a joint makes the lameness worse, it is highly likely that the lameness is coming from that joint. Another way to help localize a lameness is to test the hoof for sensitivity to pressure. A hoof tester is a device that puts pressure on certain regions of the foot. A reaction or pulling the foot away from the examiner tells the vet that the horse is sore at that particular location in the foot.
If after performing flexion tests, palpating the limb, and manipulating the limb, the location of the lameness is still not obvious your vet make begin “blocking” the limb/joints. “Blocking” refers to numbing portions of the limb and watching the horse trot. If the lameness disappears after a nerve “block”, then the vet can be confident that the problem area is within the portion of the leg that was numb. This test does not always pinpoint the exact location of the lameness, and sometimes the results can be questionable – for instance, the lameness might improve by only 50%. If this is the case your vet may repeat the block on a different day or use a combination of tests to localize the lameness within the leg.
What pathology or abnormality is causing the lameness?
After your vet is confident that they have pinpointed the lame leg and localized the lameness to a region of the leg, they can begin to look for an abnormality in that region that is responsible for the lameness. The most common way to detect the abnormality is by using diagnostic imaging (x-rays, ultrasound, MRI, etc). Depending on the case and the experience of the vet, they will usually start with either x-rays or ultrasound to image the leg. X-rays are used to visualize bones and joints, whereas ultrasound is better for looking at tendons and ligaments. Sometimes a defect or abnormality may be very small and impossible to see with x-rays or an ultrasound. At that point your vet may refer your horse for an MRI or a nuclear scan. Diagnostic imaging often is the most costly part of the lameness exam.
What can an owner do prepare for a lameness exam?
If a horse owner has never had the experience of dealing with lameness issues, there are several things that I think they should know before having a lameness exam done on their horse.
– Do not give your horse any pain medication (bute, Banamine, etc) at least 48 hours before a lameness exam. The vet wants to see your horse when it is as lame as possible. This make localizing the lameness much easier.
– Bring your tack with you and be prepared to ride. Sometimes a gait abnormality is only visible under saddle. The vet needs to see the lameness in order to make a diagnosis, so you will need to recreate the situation in which the lameness occurs.
– The examination may take several hours, maybe even days. The more difficult it is to determine where the lameness is coming from, the longer the exam will take. If blocking the leg doesn’t show >80% improvement then it may need to be blocked a different way (for example a joint blocked instead of a region of the leg) to narrow down the source of the pain. The numbing effect of a block can last hours and the vet needs to be sure that the first block has completely worn off before trying a second one in the same region.
– Lameness examinations can be expensive. A subtle lameness with a hard-to-visualize abnormality can be very difficult and time-consuming to correctly diagnose. An owner needs to be prepared that in order to get definitive answers, they may be spending thousands of dollars. On the other hand, an obvious lameness that is easy to diagnose (example: hoof abscess) will not be so costly.
In order for a veterinarian to be proficient in lameness diagnostics, they must be experienced in the observation of gaits, recognition of subtle abnormalities, interpretation of test results and diagnostic imaging. The lameness exam is an exercise of both the art and science of veterinary medicine.