GAINING PERSPECTIVE. Getting the most accurate reading of what’s happening in the hoof can require taking X-rays from numerous angles, including dorsopalmar (left), lateral (middle) and dorsal views. Farriers should be prepard to ask equine veterinarians for radiographs.
Farriers working with equine veterinarians should be willing and able to gain insights into ailing hooves through the use of radiographs and other diagnostic imagining techniques.
“Imaging provides necessary information for a diagnosis and prognosis. It gives the information we need to proceed,” says Tracy Turner, a member of the International Equine Veterinarians Hall Of Fame.
He adds, “Without a diagnosis, any medicine given to the horse is poison. Antibiotics can create all sorts of problems, so it’s not a good idea to give them unless you have a reason. If you do surgery without a diagnosis, you’re only creating trauma. And if you’re doing any other therapy without a diagnosis, it’s witchcraft as far as I’m concerned. If you don’t know what you’re dealing with, then you’re wasting your time.”
As an example of the usefulness of diagnostic imaging, Turner, based in Elk River, Minn., notes the many potential causes of palmar foot pain or navicular syndrome, including: navicular osteitis, deep flexor tendonitis, insertional tenothapy, navicular bursitis, coffin joint problems, navicular bone fractures, injuries to the proximal ligament, injuries to the impar ligament and sole bruising.
“If you have trouble differentiating these, imaging is the way to get the best idea of what’s wrong with an ailing hoof,” Turner says. “What we can do from a diagnostic standpoint is narrow things down to a region and take some images.”
However, Turner cautions that diagnostic images should be interpreted in the context of clinical signs found through a physical examination of the horse. “We want to make sure the puzzle fits. If I have a bone spur in a joint, but I can’t make the joint painful, the bone spur is not a problem,” he says.
In addition, comparing new images with images of the same foot taken previously can help make sense of the problems, he adds.
THE BIG PICTURE. Tracy Turner combines clinical input with imaging.
Farriers need a basic understanding of diagnostic imaging to know what they are looking at when vets share such images. It is no longer as simple as looking for cracks in a bone on an old-fashioned X-ray. Science has taken diagnostic imaging far beyond those X-rays, which can now be taken with traditional film or with a digital camera and computerized plates, to numerous other methods.
Turner breaks the various imaging techniques into two categories:
- Anatomic — Anatomic imaging reveals the anatomy, the physical structure, of the hoof. Anatomic technology includes X-rays that shows bones; ultrasounds that reveal soft tissues such as tendons and ligaments; and CAT scans (computer-aided tomography), which Turner describes as “a fancy radiograph that looks at just a slice of the bone.”
Anatomic imaging methods reveal structural change. “There has to be disruption in the anatomy, or it won’t be detected by the imaging,” Turner says, adding that anatomic imaging is considered “static,” meaning it captures a moment in time.
- Physiologic — Physiologic imaging provides images that are a function of metabolism, the ongoing processes within the body. Physiologic methods include bone scans, thermography and MRIs (magnetic resonance imaging). Physiologic imaging is temporal, meaning it changes from minute to minute and hour to hour because of physiology changes, according to Turner.
Thermography, which detects the different temperature levels within the body part being imaged, reveals blood flow. “Essentially, it provides a picture of the circulation through the leg,” he says. A bone scan reveals the bone metabolism and shows how the bones are changing shape, while MRIs indicate how much fluid is moving in and out of tissue.
Physiologic imaging offers the advantage of early detection, Turner notes.
“You will see changes in physiologic imaging before anatomic disruption,” he says. “The majority of injuries a horse will experience are really an accumulation of injuries. If a bone is stressed, the bone will gradually start to change its shape, and imaging will reveal the metabolic change in the bone. If there is inflammation in the tissues, we can see inflammation in the tendons and joints 2 weeks before the actual anatomic disruption, when the horse actually feels the injury.”
Another difference between the two imaging categories is that anatomic imaging doesn’t address the viability of the tissue being examined. With an X-ray, for example, “I can get the same image from a dead animal as I can from a live one,” Turner says, because it simply takes a picture of the anatomical structure.
Combining anatomical and physiologic imaging provides the most definitive diagnosis, he says.
Film Versus Digital
SHARING INFORMATION. It is the vet’s responsibility to diagnose, but many appreciate farrier input.
X-rays remain the most common of the diagnostic imaging methods. Though they have been in use for a long time, farriers should remember some principles when working with X-rays, Turner says.
“The hoof is a complex object, so we need sufficient X-rays to get the picture and draw conclusions,” he says. He recommends a minimum of five shots from different angles, including the front, sides, solar and rear. “I’m looking at the foot from every angle to get an appreciation of what’s been changing,” he says.
“Essentially, what you can see on an X-ray is one of two things: you either get new bone or you lose bone. You have to figure out what each of those means. New bone takes time to form, so you’d be looking at an older lesion. If the horse has lost bone, that means there’s been inflammation and that’s a more active condition within the hoof,” he says.
Turner also notes differences between traditional film X-rays and increasingly common digital radiographs, some of which are more important to the vet creating the images. A film X-ray is similar to taking photographs, he says, with different types of films available for detecting different things.
Both film and digital radiographs require the hoof and the machine to be positioned correctly, but the digital method provides results immediately, allowing for quick reshooting, if needed, and thus a higher likelihood of clear, definitive images, Turner says.
Also, digital radiographs can also be expanded in size to show more detail, and the contrast and density of the images can be manipulated with a computer to further increase their clarity. Furthermore, digital radiographs don’t require potentially dangerous radiation, and the images can be stored in less space than film images, which can be a concern for vets who are generally required by law to keep the images for 7 years.
On the down side, digital radiograph equipment is more expensive and so has not completely replaced film radiographs.
Turner advises vets and farriers to let a thorough analysis of the radiographs serve as input for determining what’s happening inside the hoof, rather than considering the image to be a diagnosis in itself.
“You need to look at the X-rays and let them tell you what is going on,” he says. “As you look at these things, interpret the different information. If you find lost bone due to chronic inflammation, you have to figure out what predisposed it to that inflammation.”
A dorsal view provides a good view of the joints. “Look at the joint surfaces and for anything that might indicate joint disease. Look for joint alignment, but be careful because alignment will change with the horse’s posture as the horse moves around and shifts its weight.” he says.
In lateral to medial images, Turner adds, “Look at joint surfaces for signs of arthritis and bony changes where they are most likely to occur, where tendons and ligaments insert.
“If you see changes in the distal bone, that is the insertion of the deep digital flexor tendon. Underneath the navicular bone, it’s the impar ligament. At the top of the navicular bone, that’s the suspensory ligament. The back of the pastern joint, that’s the straight sesmoidian ligament. These are all places where you can start to see calcification. If we see calcification, it means there was some sort of stress on the bone,” he says.
Active calcification will not be as dense as the rest of the bone. The area is calcifying because of stress or injury, and it is very active, Turner says, and the denser the calcified area is, the older it is.
Another common check on radiographs is the distance from the top of the hoof capsule to the top of P3, he says. In most horses, that distance will range from zero to 5 millimeters, a quarter of an inch at most, he says, except with gaited horses, in which the distance tends to be larger.
“More distance means there’s been shifting inside the hoof capsule; the foot has been jamming somehow, or there’s been damage to the laminae, which has caused a mild amount of sinking,” according to Turner.
Radiographs can also be useful for assessing the vascular channels and their size to detect chronic inflammation, he adds, and the top and bottom of the navicular bone can be checked for changes. Look at the bony column in the hoof capsule to check for medial-lateral balance, he says.
Don’t Be Misled
Also, he says, “You can look at the hoof-pastern axis. But before you say, ‘Wow, he’s really broken back,’ remember that it’s highly dependent on how much weight it’s bearing. Where’s the position of the cannon bone? Radiographs can lie to you.”
He also cautions about a radiographic discovery of sidebone, a common finding often associated with horses with high body mass. “Lateral cartilage is most commonly affected,” Turner says. “It’s not associated with any specific lameness, it’s just there. Some people associate it with chronic hoof imbalance, but we know that there’s an inheritable nature to these in certain breeds.
“However, if it’s a large medial one, that’s more important. If there’s asymmetry between the left and right legs, that’s important. It means some sort of trauma has occurred to create that asymmetry.”
Turner warns that radiographs magnify the image a little because of the space between the foot and the film or digital plate, meaning measurements on the image are slightly exaggerated. “If somebody says the measurement is a half-inch, cheat a little bit and don’t go quite that far, even on the digital radiographs,” he says, “because it hasn’t compensated for the magnified image. The farther the plate was away from the object, the bigger the measurement will be.”
Other Imaging Methods
Turner says thermography, or heat images, can be useful for looking at laminitis and palmar foot pain because of the dynamic information available. In laminitis, thermography can provide information during the developmental phase, the acute phase, the chronic phase and post-chronic phase.
In a healthy hoof, he notes, thermography will show the coronary band as a fine line of higher temperature, but as laminitis inflames the foot it becomes as hot as the coronary band.
As P3 begins to displace in chronic laminitis, Turner says, “Usually you’ll see a decrease in temperature at the coronary band because as the bone sinks inside the capsule, it pulls the coronary band underneath it, and the heat is blocked by the hoof capsule. It looks cold in thermography. If it gets real cold, that means it’s cutting off the blood supply.”
In the post-chronic stage, he says, “When the laminae might be stabilized and the horse might be walking around, thermography will reveal a cold spot in the hoof indicating a loss of the blood supply.”
Thermography can also be useful for differentiating a horse with sore feet and one with laminitis, according to Turner. The sore-footed horse will show heat coming from the circumflex vessel, not from the laminae, he says.
Thermography is commonly used to assess blood flow. A standard testing procedure is to take thermographs of the hooves both before and after a horse if exercised for 15 minutes. “We should see at least a half a degree increase in temperature in the second test,” Turner says. “If the temperature doesn’t increase, it means there is poor circulation, which means something has to be done to improve the circulation.”
Also, while other imaging techniques might show whether cartilage has calcified, thermography can reveal whether the involved ligaments and tendons are inflamed. And the method can look at weight bearing in the feet. Hot spots in the shoe or hoof will show if the horse is landing harder on one side or the other, thus creating uneven friction and heat. “The question is,” Turner says, “is that a hoof imbalance, or is the horse staying away from some other painful area.”
Bone scans involve injecting radio isotope into the horse’s body, where it circulates. The isotope first passes through the vascular system, then into the soft tissues, followed by the bones. Once it’s into the bones, which takes about 2 hours, a “camera” reads the gamma radiation emitted by the radio isotopes, Turner says. Bones that are under stress and metabolically active will appear blacker in the bone scan images.
A CAT scan is essentially an X-ray that looks at just a slice of the foot and avoids interference from nearby hoof structures that would also appear in traditional or digital X-rays. An X-ray is essentially a two-dimensional picture of a three-dimensional object, while a CAT scan produces a two-dimensional picture of a two-dimensional object, he says.
MRIs use large magnets to magnetize the tissue, forcing electrons in the body to flow in one direction. Turning the magnets off allows the electrons to return to their normal direction, and the differences in flow are measured, Turner says.
The MRI images provide the best anatomic detail of any imaging method, including the soft tissues, and it also measures physiologic changes, he says. It also can take images of slices. “It takes pictures from 360 degrees around, and then we can tell the computer we want to see a certain section of it all,” he says.