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The diagnosis of pain

By Daniel H. Grove, DVM - November 1st, 2017 - Ask the Vet

AskTheVetLameness in horses is one of the most common issues for which an ambulatory practitioner is called. Horses are athletes that work hard and use four limbs to get that work done. Just as with human athletes, horses get injured. One thing that makes diagnosing the problem more challenging is that they do not tell us exactly where it hurts. This month, let us go through the basics of the lameness exam and some of the more common tools available to us to diagnose the problem.

The lameness exam usually involves first determining which limb(s) is/are sore. This usually involves jogging the horse, as this a symmetrical two-beat gait. Once the limb is identified, now we have to determine where the pain is coming from. Commonly, practitioners start with the hoof and work their way up. The hoof can be visually examined, palpated, and pain can be elicited with hoof testers. Next, you can move up the limb checking for swelling or heat. Often times in the back of the pastern or fetlock, you can feel for an increased digital pulse. This can be an indicator of inflammation in the hoof.

Next, flexion tests are often employed. In the front, you can flex the fetlock and lower joints, then the carpus, then the elbow, and finally the shoulder. The hind limb is a little different. You can do the fetlock and below just like in the front, but the hock and stifle are tied together (in a normal animal) so you have to flex the entire upper limb together. The limb is held up for a predetermined amount of time and then the animal is watched as it jogs off. If the lameness increases, it can help localize the area of discomfort.

After this initial clinical exam, nerve blocks may be indicated to determine the location of the pain. Local anesthetic is injected adjacent to nerves in the limb or directly in a joint. If the lameness goes away, you have an area to focus on. In some cases, you never are able to get a response to a block. It can be very difficult sometimes. After this step, often your next move is to imaging diagnostics to attempt to identify the problem.

Imaging in equine medicine has grown by leaps and bounds in the last few decades. Modalities have improved tremendously as well as the introduction of new modalities. One of the most common is radiography or “x-rays”. Radiographs are excellent at looking at bone problems and not so good at soft-tissue problems. They allow us to look for problems in the bone with very good detail. Sonography is also very common. It uses ultrasound waves that pass through the tissues and bounce back to give an image. Ultrasound is very good at looking at soft-tissue injuries and not so good on bone. These two imaging techniques can often times be done right at your horse’s barn.

If by the time your veterinarian has gone through these things and cannot find an answer, often times it is time for a specialist or referral hospital. Here, they usually have some more advanced imaging devices at their disposal. First, let’s talk about nuclear scintigraphy. A “nuke scan” uses a radioactive dye that is injected into a vein. Then images are taken via a gamma camera to look for concentration of the dye where there is increased blood flow. The horse if often imaged twice, first to look for soft tissue areas of increased uptake which show up quickly, then second to look for bone lesions that take up the dye more slowly.

An additional device than can be used is an MRI. An MRI machine uses a big magnet that spins around the body part being imaged. The magnetic field causes the water molecules to line up. When the field is discontinued the water molecules drop back down at different rates. This allows the MRI machine to gather images with great detail.

A final device I will discuss is a CT or computed topography machine. This machine uses x-ray light just like in radiography, but the duration is longer and from various angles. This allows for more detailed images than with traditional radiography.

Lameness can be one of the most challenging things an equine practitioner does. No two veterinarians probably go about it in exactly same way. Also, different experiences and training can give one practitioner a different view of what is going on versus the other. I tried in this column to go over a general view of the order and some of the tools I employ in my lameness diagnosis. As with most things, prevention is much better than trying to treat lameness after it has occurred. Use a good quality joint supplement, good support wraps or boot, and have a good farrier to do your best to keep your athlete healthy and pain free!

–Dan

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