Technology is vastly improving veterinarians' ability to diagnose equine lameness

VETERINARIANS have many tools to diagnose lameness problems. Robert K. Schneider, D.V.M., M.S., a professor of equine orthopedic surgery and the 2005 recipient of the Robert B. McEachern Distinguished Professorship in Equine Medicine at Washington State University, said many lamenesses can be diagnosed from observing abnormalities in the horse's leg, but there are many cases in which lamenesses are more difficult to pinpoint.

Various new techniques such as bone scans can be employed to locate the problem. Even some of the more obvious lamenesses also might benefit from modern technology to help determine the cause or to identify the structure that is injured and the extent of the damage.

"After we have identified the lame leg, the next step is to figure out where the problem is located," Schneider said. "Sometimes that's possible with examination and the signs the horse is showing. For example, increased fluid in a joint [and] swelling around a tendon or ligament give obvious clues. Sometimes just examination of the patient enables you to localize the source of the lameness."

Nerve blocks

When an examination fails to locate the source of lameness, Schneider said, "The next thing we try to do is localize it by using diagnostic blocks.

"We inject local anesthesia over nerves [to desensitize an area completely] or inject local anesthetic into joints or tendon sheaths to desensitize structures that we suspect might be the problem," he said. "When we do that, we are looking for an improvement in the degree of lameness once the block takes effect."

Some problems cannot be localized by either method. "There are no signs that tell you where the problem is, and after you do a series of blocks on the horse's leg, you still have not changed the horse's lameness," Schneider said. "In those horses, a procedure that is commonly performed is a nuclear bone scan."

Nuclear bone scan

When a nuclear bone scan is performed on a horse, the animal is injected with a radioactive substance that is taken up by the skeleton, and the clinician looks for abnormal areas of uptake that would tell where the cause of the lameness is located. As a result, the bone scan shows areas of abnormal bone activity or "hot spots."

One advantage of a bone scan, or nuclear scintigraphy, is that you can scan the entire horse, including areas that are difficult to X-ray, not just the legs.

"It can help identify horses with chronic back problems, for instance, that may show up as a lameness and be hard to localize by blocking," Schneider said. "A bone scan may also help in diagnosis of leg problems that could be blocked out but for some reason are not definitive. Nerve blocks are not 100% effective."

Schneider said the two most common instances in which a veterinarian would perform a bone scan is to examine a horse with a lameness that cannot be localized and to uncover why a horse has a vague change in attitude, gait, and willingness to work. The horse may be just a little "off" and you know the animal is hurting, but you are not sure where.

Even when the veterinarian has located the area of injury, sometimes a bone scan will be performed to see if there is abnormal activity in the area.

"This could help with diagnosis," Schneider said. "There is also a soft-tissue phase of scintigraphy that some people use, and sometimes it's also used to determine areas of increased or decreased circulation.

"Even though a veterinarian knows where the problem is [and may have used X-rays and did not see anything], he might perform scintigraphy to look for any abnormality that might help determine the cause of lameness. There are some bone injuries that cannot be detected with radiographs [stress fractures, stress reactions in bones, and bone contusions]. Scintigraphy lets you see the area of increased activity, so we know the bone is damaged, even though we can't see it on our X-ray.

"Those three methods [observation and clinical examination, nerve blocks, and bone scan] are what most veterinarians use to localize lameness issues to determine the where and the why. It's a bit like putting together the pieces of a puzzle. You have to consider everything: what type of athlete the horse is, what he does as an athlete, etc. Certain types of horses tend to have certain types of lameness more commonly.

"So you use every piece of the puzzle: the history of the horse, how long the horse has been lame, etc. Once you have it localized, either by examination or nerve blocks or by scintigraphy, it may need to be imaged to try to determine the why."

Radiographs

Several imaging modalities, starting with X-rays (radiographs), help determine why the horse is lame.

"Still, to this day, the gold standard for most equine veterinarians is radiographs," Schneider said. "These are valuable and in many instances allow you to make an accurate diagnosis. There are all kinds of abnormalities that can be seen on radiographs. Bone problems like fractures, chip fractures, and OCD [osteochondritis dissecans] cartilage abnormalities are easily seen.

"In addition to those, we can see proliferation of bone around a joint, showing there is inflammation--arthritis--in the joint. Proliferation of bone in a ligament or tendon insertion tells you the insertion has been injured. If the fibers of the ligament or the tendon, where they insert on the bone, have been pulled out, the bone will react at that site. You may not see this in an acute injury, but there will be bone proliferation on a radiograph in a chronic situation."

Schneider said if the lameness can be localized by examination with nerve blocks, the veterinarian will X-ray the area.

"Let's say the veterinarian blocked the foot and it didn't change the lameness, but when the horse's leg was blocked above the fetlock joint, the lameness disappeared," he said. "Then the next step the veterinarian would take would be to X-ray the fetlock-joint area to determine what problem is present."

Radiographs have become more useful today because of recent developments such as digital radiography. "This has improved the image quality," Schneider said. "My personal opinion is that digital radiography doesn't find anything that can't be found with high-quality films using standard, routine radiographs. But it has improved the quality of the image to where subtle things are more easily seen."

Ultrasound

"If radiographs are normal and don't allow you to make a definitive diagnosis, other imaging techniques such as ultrasound can be employed," Schneider said. "This primarily looks at soft tissues but can look at bone in some limited ways.

Schneider said ultrasound is frequently used, even when the veterinarian knows the location of the problem.

"For example, if a horse has a bowed tendon, most veterinarians find that with their fingers," he said. "They know the horse has injured the tendon. But the ultrasound is useful because it allows you to assess the severity and nature of the injury. It enables you to quantify how much damage there is, which is impossible to tell by feeling with your fingers."

Schneider said the two types of horses that receive an ultrasound evaluation of their limbs are those with tendon injuries where the severity of the damage needs to be determined and those that may have an undiagnosed tendon or ligament injury.

MRI

Magnetic resonance imaging (MRI) is proving to be extremely valuable for lameness diagnosis, especially when high-field magnets are used. High-field magnets are currently necessary to obtain clear images of the horse's leg.

"MRI looks at the chemical change within the leg," Schneider said. "Ultrasound looks at fibrous structure by bouncing a sound wave back into the scan head. MRI is looking at chemistry, at the molecular level, which allows it to find small areas of inflammation that can't be found other ways."

Washington State's equine hospital offers scintigraphy and MRI. "We would perform MRI when we know where the problem is, rather than scintigraphy," Schneider said. "MRI is not a very good scanning technique because it involves general anesthesia and you have a coil you must move over the horse's various anatomic areas. To keep anesthesia to a reasonable length of time, we usually want to know where we are looking. Although we are frequently looking at the feet or the fetlock, in high-field magnets the horse's leg can be imaged from the hock and the carpus [knee] to the foot.

"We do MRI almost daily, for horses in which we know where the lameness problem is but we don't know what is causing it. We know the where, but not the why. The MRI is an extremely valuable tool because it lets you see both bone and soft tissue, and lets you look in sectional anatomy. We can look into the leg in different view planes that can't be done any other way."

Schneider believes MRI will continue to be a useful imaging modality for making specific diagnoses as it becomes more available.

"It lets us make an accurate diagnosis of the problem," he said. "We were the first to use it, here, and now it's available [with the high-field magnets necessary to get quality images] in several other hospitals. This is an evolutionary process as the technology develops and becomes cheaper and more available. It has proven its ability to make an accurate diagnosis."

CT scan

Computed tomography, better known as a CT scan, is another tool sometimes used in equine medicine.

"CT is basically sectional X-rays," Schneider said. "It allows us to look at the structures in sections, similar to MRI, but, unfortunately, it's not very good for viewing soft tissues.

"I mention it because it's another imagining modality that some people use on lame horses, trying to determine the cause. For us, we mostly use it for viewing complicated fractures. We might use it when looking at multiple fractures in a carpus in unusual planes or in a comminuted fracture in a cannon bone [where part of the bone is crushed or broken into small pieces], where we are trying to determine the exact plane of the fracture--the main fracture planes."

These are not diagnosis issues, but it does let you look at a cross-section of the leg to assess the damage, he said.

Overall, technology has significantly improved the ability to diagnose lameness in a horse, Schneider said.

"We are making diagnoses now that were unheard of 20 years ago," he said. "It's an area where veterinary medicine has made leaps and bounds forward and will continue to do so as we gain more experience with technologies like MRI. Now that we can make more specific and accurate diagnoses of what the problem is, this allows us to prescribe accurate treatment protocols that increase the horse's chance for successful recovery."

And as a result, a high percentage of equine athletes will be coming back sound and continuing their careers.