Article by Breanne Hill
Navicular is a bone, not a lameness disorder.
This is the message veterinarians are trying to communicate to owners who have horses that are suffering from pain and lameness in the back of the foot and leg.
The tiny navicular bone is the lowest bone located in the back of a horse’s foot. It touches—is almost wedged between—the short pastern bone, which is above it, and the coffin bone, which is in front of it (see diagram).
Due to this small bone’s location and because it is the recipient of a lot of weight and force, the navicular bone has long been pinpointed as the source of pain when a horse comes up lame in the back of the foot and leg. However, with the advent of new medical technology, veterinarians have changed the way they evaluate “navicular” and the role its namesake bone plays in lameness. In fact, doctors no longer officially refer to the issue as navicular, but rather as palmar (in the back) foot pain.
Dr. Britt Conklin, DVM, CF, is a veterinarian, certified farrier and co-owner of Reata Equine Hospital and Podiatry Center in Weatherford, Texas. He explains that the change in name from navicular to palmar foot pain was due in no small part to what veterinarians have seen thanks to sources such as MRI imaging, which allows doctors to see deep into the internal structures of the body.
“Navicular was a name we used as a sort of catchall for pain in the back of the foot,” Conklin says. “What we were saying, essentially, is that everything had to do with that bone. Now, through imaging, we see that it’s not just about the bone. It could be a tendon. It could be a ligament. It could be any number of soft tissue structures associated with the back of the foot.”
So, should we just throw everything we ever thought we knew about navicular aside? Not at all. According to Conklin, the science behind this type of lameness is not about what we haven’t known in the past, but about what we’ve learned and how researchers are planning to build on that knowledge in the future.
Doctors can only go as far as their diagnostic capabilities allow them to go. This means that for any doctor, not being able to see an internal problem can keep him from prescribing an accurate treatment.
Once upon a time, when a horse was brought in with lameness issues, a veterinarian’s only tool for viewing the problem internally was x-ray. Although useful for bone analysis, x-ray was hardly any help when trying to view tendons and tissues.
“With the x-ray,” Conklin says, “we could look at the navicular bone and say, ‘Oh, this horse is sore,’ or ‘I’m concerned about how the bone looks on the x-ray, so it must be the bone.’ We didn’t have the ability to know what else might be going on in there until maybe the horse was euthanized. Then we could dissect the limb to see where the problem really was. But other than that, we were limited.”
The advent of ultrasound imaging, which uses sound waves to produce pictures inside the body, gave veterinarians a little more insight into the leg and hoof, although, Conklin says, not enough to produce an accurate diagnosis of the structures of the foot.
“Ultrasound is still very objective,” he explains. “It’s hard to evaluate the deep structures in the foot using an ultrasound.”
Nevertheless, through x-ray and ultrasound, veterinarians diagnosed horses as having “navicular” and set out to prescribe treatments.
According to Conklin, vets have traditionally gone with one or more of three main options to treat navicular. The first option was corrective shoeing, which usually involved elevating a horse’s heel to cut down on pressure in the back of the hoof. Then an injection that promoted joint lubrication and healing or cartilage regeneration, such as steroids, hyaluronic acid, Adequan or Legend, was added in conjunction with the shoeing.
Where the horse was injected with these products was as limited as the science behind the navicular diagnosis.
“We had the capabilities to inject in two areas,” Conklin says. “The coffin joint, which connects to the navicular bone, or the bursa, which is behind the navicular bone.”
The coffin joint and the bursa contain natural lubricants, and their objective is to keep movement free and easy in their area.
“We’d inject them and see if we could get a healing response,” Conklin says. “That helped some cases out. Then, the frequency of when we’d have to inject again depended on the horse.
“Again, I couldn’t tell you specifically what was wrong with the horse, so if it were something besides the navicular bone, I might be injecting, and it would only last two weeks because we’re not treating the right thing.”
After corrective shoeing and injection treatements, the horse was generally sent on his way and back to his job. If, however, the horse came up lame again, he would be brought back in for the third treatment option: cutting the nerves leading to the foot.
“Cutting the nerves works pretty well,” Conklin says. “The horses got along well. The unfortunate thing was that those nerves grow back all the time. We may only have gotten two or three years out of it.
“There were also a lot of secondary concerns that came with it, including the development of more pain in other areas, so we tried to reserve the nerve cutting for the more nagging cases.”
Today, the treatment of navicular, or rather palmar foot pain, is much more accurate due to the wide range of knowledge veterinarians and farriers have acquired through MRI imaging and other new medical advancements, such as stem cell research.
When patients are brought to Conklin now, they are evaluated, treated, given a precise recovery plan and then monitored during that recovery.
As in the past, Conklin’s first offensive measure in fighting foot pain is often corrective shoeing. In order to get the most from corrective shoeing measures, Conklin looks for indicators, such as undesirable conformation, to help him make the right shoeing choices for each horse.
“I might look at a patient’s foot conformation and say, ‘He’s got a very under-slung foot. He’s got low heels. The toes are very long. The heels are crushed and under run,’” he says. “That puts pressure on the navicular bone. So maybe if we just manipulate with shoeing it will help. We’ll look at the conformation first and adjust the shoeing.”
Low heels and long toes are just two examples of faults that might cause navicular bone pain and require corrective shoeing. But nine times out of 10, Conklin says, the purpose of corrective shoeing is to relieve the tension placed on the flexor tendon, not the navicular bone. The flexor tendon, the tendon that runs down the back of a horse’s leg, has been found to play a large role in palmar foot pain.
“It often has a tear in it or is strained because of its close association with the navicular bone itself,” Conklin says. “The lower the horse’s heel, the tighter that tendon is. So, we’ll wedge the horse’s heel, or elevate it, to give relief.”
Wedging a horse’s heal is a precise science. Simply putting on wedged shoes can further crush the structure of the foot and cause more pain. For that reason, wedging is not the only corrective shoeing technique that is used on palmar foot pain patients, and if it is used, a sole support is also inserted with the shoe to give extra cushion.
“It’s just all about taking that strain off of the injured areas,” Conklin says.
Injections also are still used to treat palmar foot pain, both with and without corrective shoeing. However, the specifics of where the injections are given—and what those injections are—has changed slightly.
“Before we give injections, I’d probably recommend having an MRI,” Conklin says, “and then we’d be able to say, ‘Gosh, we’ve got a tear in this tendon and some swelling in the bone and inflammation in the bursa and a little bit of inflammation in the coffin joint.’
“Then, I could recommend that we inject here and here and put some treatment modality inside the tendon to make it heal better.”
While injections, such as Adequan and Legend, are still regularly used to treat palmar foot pain, there are some new options available in today’s market. The two most groundbreaking of these options are stem cell injections and platelet rich plasma injections. The namesake ingredients in these formulas are taken from the patient itself through drawn blood. That blood is then packaged with modifying agents to improve the healing of the diseased or damaged area.
“We can take a stem cell, a cell that has the ability to differentiate into anything—an eyeball, hair, anything—and inject it into an environment, such as a messed-up tendon or ligament, and speed up that healing time,” Conklin says. “It’s all in an effort to get back to what normal was for this horse. We want to take that torn tendon and get all those fibers back to where they were again.”
Steroids are no longer a popular option for injections, according to Conklin, but there is another agent taken directly from the horse that acts as a pain preventative—IRAP.
“IRAP comes from the blood of the patient,” Conklin says. “It stops or blocks part of the inflammatory cascade within a joint and reduces pain. It’s often used to treat osteoarthritis.
“The difference between IRAP and steroids is that IRAP will not affect cartilage. We found that steroids can be detrimental to cartilage.”
MRIs have helped veterinarians estimate how often a horse should have injections, as well as enabled them to develop a workable rest period and monitoring system after treatment.
“Tendons, for example, are like cables,” Conklin says. “They are made up of fibers, and we can see those fibers in an MRI. Injections and down time can be determined by the number of fibers that are broken. A horse with four or five torn fibers will have a longer recovery than one with two torn fibers.
“We can also determine if we need to inject stem cells in there one or more times, depending on what we see with the MRI.”
Nerve cutting is still an option in horses that are just not recovering, but more often than not, a prescribed cycle of rest and limited exercise does the trick.
“We will tell you exactly how long your horse should be on rest, depending upon his injuries,” Conklin says. “If we’re dealing with a minor injury, we’ll set the patient up on a shoeing and injection schedule, and they might be back to work within a week or 10 days.
“On the other hand, if a horse is having nagging palmar foot pain, we may be looking at a torn tendon, and then he may need, like, eight months off.”
Rest doesn’t mean a horse just stands in his stall until his recovery is over. Palmar foot pain horses are usually subjected to “controlled exercise,” or daily walks, and even swimming therapy.
“We’ll set up an entire time line,” Conklin says, “with a shoeing protocol and owner responsibility sheet for each patient.
“We used to just shoe them, inject them and say, ‘Go on and tell us what happens.’ But now that we have specific ideas about what the problem is, I can tell you how long your horse needs to be off and exactly what we need to treat.”
Despite these advancements in diagnoses and medical care, Conklin believes there remains room for improvement in the treatment of palmar foot pain.
“We have these new ways of viewing the inside of the leg and hoof, but we’re still limited in our treatments, I think,” Conklin says. “What we would like to see is the treatment catch up to our technology.”
What this means is that although veterinarians have, in general, the ability to treat structures such as tendons, they don’t have remedies that specifically improve the healing of tendons and each of the other parts of the leg.
“I need a drug that’s going to treat the tendon,” he says. “I need a drug that’s going to treat the cartilage inside the joint.
“We can see what’s going on now, which is a great step, better than we had five years ago, but now we need to know exactly how to treat the specific areas that are involved.”
The only drug that has been developed with a specific area in mind focuses on bone healing, but according to Conklin, even this drug has yet to be proven.
“It’s still under the table as to whether it is doing what it’s supposed to be doing,” he says.
With the success of stem cell injections, however, Conklin is confident that structure specific drugs will be available for use in the future, which will make palmar foot pain even less of a threat to a horse’s health and athletic career.
“It’s going to take some time to figure out the research, but there are people working on developing these drugs,” he says. “It’s not as simple as finding mold on penicillin and figuring out that it kills a lot of bacteria. We have to understand so many more details about how molecules interact and about how genes are turned on, what this drug would do to a whole cascade of inflammatory events. It’s very intricate.”
In the meantime, Conklin offers a ray of hope to owners whose valuable riding partners are suffering from palmar foot pain.
“A palmar foot pain diagnosis is not the end of an athletic career,” Conklin says. “There are a lot of horses that have been treated and are still performing at high levels. After treatment, most horses go back to competing at the level they have always been. The key is to get treatment before the issue develops into a bigger problem.”
What Causes Palmar Foot Pain?
Palmar foot pain, which in the past has been known as navicular, is a common malady that develops toward the back and bottom of a horse’s legs and foot.
According to Dr. Britt Conklin of Reata Equine Hospital and Podiatry Center in Weatherford, Texas, these are some of the primary causes of the disorder: – – Genetics
“From what we know, it can be genetic,” Conklin says. “In other words, a horse can have a predisposition for it. This doesn’t mean they’re born with the foot pain. It means that if a parent had some weakness in the navicular bone, it can get passed on. Then, when the horse gets old enough to have a job, you can see some problems develop.”
“If your horse is badly conformed, say, with a long toe, low heal and very thin digital cushion [a structure in the back of the hoof that protects the region around the navicular bone], then he can’t absorb the amount of concussion that a horse with an upright hoof structure, a lot of frog and a lot of digital cushion can,” Conklin says. “So after a while, if you’re running on a lot of hard ground, and you get exaggerated concussion in that area, you could end up with a damaged bone.”
– Bad Shoeing
“A horse that has been shod wrong, especially if his conformation isn’t ideal, is going to have a lot of stress put on his tendons and ligaments,” Conklin says. “The foot isn’t landing symmetrically. They aren’t landing flat. Imagine landing wrong on your foot and slapping the same area over and over again. Over time, that can cause strain and even tear tendons and ligaments.”
– Traumatic Events
“There’s no way an owner can control this, but horses can be running out in the pasture and step in a hole and tear part of the deep flexor tendon,” Conklin says. “These traumatic events happen all the time with horses.”
– Wear and Tear
“Barrel horses, and rodeo horses in general, are susceptible to palmar foot pain, more so than cutting horses and reining horses and race horses,” Conklin says. “They have jobs that require short bursts of energy and hard stops and turns. That all contributes to stress on the legs and feet.”
– Poor Management
“As an owner, you have to keep up with what you control,” Conklin says. “You can’t control wear and tear except by not running your horse in arenas that are rock hard. You can control early detection. Don’t let your horse keep running if something is wrong. Don’t try to bute your way through it. Get a diagnosis. You can also control foot management. Get yourself a good competent farrier who really pays attention to your horse’s needs.”
Symptoms of Palmar Foot Pain
While it’s tempting to diagnose your horse at home, you should take animals that appear to be in pain for more than three days to a veterinarian for an official diagnosis and treatment.
You can, however, watch out for these warning signs that your barrel horse might be developing palmar foot pain.
-Slower performance times, accompanied by a hint of lameness toward the back of the foot
– Refusal to turn barrels or running past barrels, accompanied by a hint of lameness toward the back of the foot
– Suddenly running stronger in one direction than in the other
– A distinctive head bob when running, as if the horse is struggling to get along
– Walking or running on the toe of the hoof instead of the whole hoof
REMEMBER: Palmar foot pain has only been reported on a limited basis in the back legs. It is primarily found in the front legs.
Reata Equine Hospital’s Podiatry Center is a state-of-the-art, 3,000 square foot facility that caters to hoof problems in horses. Headed by Dr. Britt Conklin, the center has its own blacksmith shop, two climate controlled treatment areas, sling capabilities to accommodate patients with severe hoof and leg problems and an apartment with a viewing window for around-the-clock observation and treatment.
For more information, go to reataequinehospital.com.
Breanne Hill is managing editor of Barrel Horse News. E-mail comments on this article to [email protected].
This article originally appeared in the August 2009 issue of Barrel Horse News.