Navicular Disease and Treatments
October 11, 2011
By Heather Smith Thomas
In earlier years, a diagnosis of navicular disease was often considered career-ending for a horse. Chronic lameness was typical, in spite of therapeutic shoeing, medication, etc. and sometimes the only option to enable the horse to travel sound was neurectomy—so he would no longer feel pain in the foot. Success rate for neurectomy is only about 50% however, because the nerves may regrow, and this procedure is not without risk.
Today we realize that what was earlier called navicular disease (with the horse showing pain in the rear part of the foot, often positive to hoof testers over the navicular area and going sound after a posterior digital nerve block) includes a host of different problems within the foot, some of which are unrelated to the navicular bone and/or its bursa. The term navicular syndrome is now used instead unless the condition actually affects the bone and bursa specifically.
Mike Pownall, DVM (veterinarian/farrier, McKee-Pownall Equine Services, Rockwood, Ontario) says the biggest difference today in diagnosing and treating heel pain, compared to 10 or 20 years ago, is the advent of MRI. This diagnostic technique enables us to know what is actually going on with the foot.
“It gives us an accurate diagnosis, and more accurate and effective treatment options, and also gives us a prognosis. Without using MRI, a person is usually trying to deal with the condition with shoeing, shockwave treatment, injecting the bursa or coffin joint, or resting the horse,” he says. You are just shooting in the dark as to what might be the best treatment for that particular horse.
Joe Bracamonte, DVM, DVSc, Diplomate ACVS (Assistant Professor, Large Animal Surgery, Western College of Veterinary Medicine, University of Saskatchewan) says our way of looking at horses with navicular disease has changed. “Radiography, for a long time, served as the gold standard for looking at horses with lameness localized to the foot. Radiographs provided excellent evaluation of bony structures but minimal information on soft tissue structures. We can’t assess very much soft tissue injury with radiography,” he explains.
“With MRI we can visualize so much more—not just the navicular bone. We can also identify lesions involving the deep digital flexor tendon. This is a common finding in horses that present with caudal heel pain, that cannot be assessed with plain radiographs,” says Bracamonte.
Other diagnostic methods that may be more helpful than radiographs include contrast CT scans, if a person doesn’t have access to MRI. Bone scan (nuclear scintigraphy) may also be helpful in some situations. “With accurate diagnosis we are able to help more horses with proper treatment and provide owners with a more realistic prognosis,” he says.
NEW TREATMENTS
“We are also having good luck now using a drug called Tildren for treating navicular disease,” says Pownall. “This drug is licensed in Europe for treating women with osteoporosis. Veterinarians started using it for horses with navicular disease. This drug is very effective in treating navicular cases that involve the bone,” says Pownall.
When the bone is traumatized it begins to remodel. “If you can slow down that process, this can head off severe changes, and also helps with pain regulation. Thus this new drug is very helpful. It’s available now in both the U.S. and Canada via an emergency drug release,” he says. If your veterinarian thinks this drug might help a specific horse, it can be obtained for use in that particular horse.
Tildren (tiludronic acid or tiludronate) is a biphosphate that has been shown to inhibit bone resorption and slows down bone turnover. This drug is usually given to the horse via a large intravenous dose (usually with a catheter and IV drip for about an hour) and has a beneficial effect on any sites in the body affected by osteoarthritis, including the navicular bone. It affects bone metabolism and reduces bone resorption by inhibiting the activity of osteoclasts. Benefits (including relief of pain) can usually be seen within 2 to 4 weeks and the effects generally last about 6 months or longer. Some horses are given monthly booster doses to prolong the beneficial effects of this drug.
“Another thing that’s helpful in dealing with these horses, when we can use MRI to see what’s going on in the foot, is that we are having better luck treating the navicular bursa as opposed to treating the coffin joint. Injecting the bursa is tricky. It helps to use digital x-ray so you can see instantly if the needle placement is correct, but with the better diagnosis we can treat the bursa this way if needed, and have a better success rate,” explains Pownall.
“Regarding some of the medications that can be injected into the navicular bursa, we’ve typically used some type of cortisone and hyaluronic acid, but now I think veterinarians are using newer treatments more often such as stem cells and IRAP (interleuken receptor antagonist protein) which are both showing a lot of promise in treating this area. Research in treatment is still in its infancy, so we don’t have a lot of evidence yet, but I think as time goes on we will get a better idea of the efficacy of various treatments and medications,” he says.
Bracamonte says that back in the 1990s a lot of people were using isoxsuprine for navicular disease but most veterinarians no longer use this. “Tildren is looking more promising,” he says.
“I still think the hallmark of treating any kind of navicular area of pain is excellent trimming and shoeing,” says Pownall. “You can do all the modern treatments in the world, but if the foot is out of balance or shod improperly you are going one step forward and two steps backward in trying to resolve the problem.” If the foot is not balanced there will be stress on areas that shouldn’t be undergoing extra stress and strain.
Thus it helps to have a good farrier working with the veterinarian on a navicular case. A team effort is crucial with many types of foot lameness. “If you don’t have that team working together to help the horse, you are missing the benefit that both the farrier and the veterinarian can provide,” he says.
ANOTHER POTENTIAL TREATMENT OPTION
Dr. Carl Kirker-Head (Tufts University’s Cummings School of Veterinary Medicine) has been working on several research studies involving navicular disease. “The treatments for classic navicular disease, which shows clinically as lameness caused by pain emanating from the bone, bursa and/or adjacent deep digital flexor tendon, have had only limited success. Historically, we were trying corrective farriery, blood thinners, blood vessel dilators, etc. The end stage treatment has often been neurectomy, cutting the nerves to that area, which has also met with poor success. In our experience, about half of the horses receiving neurectomy have regrowth of the nerve within 2 years, and re-sensitization—which means they start to feel the pain again,” he says.
“There have been a couple of studies looking at horses with navicular disease, identifying the fact that the pressure of the fluid inside the navicular bone (intraosseous pressure) is elevated above normal in affected horses. In our study, we looked at this and made a correlation with human bone diseases, some of which also result in increased intraosseous pressure. In several of the human conditions, the standard of care has been to drill decompression channels into the affected bone—to essentially relieve the pain by reducing the pressure within the bone and possibly to facilitate a more balanced remodeling of the bone,” says Kirker-Head
This core decompression is currently used for treating human patients with osteonecrosis (bone death due to poor blood supply to that area). The procedure has had moderately good success in human patients. Kirker-Head simply took that concept and applied it to the horse to see if it might be a way to ease a horse’s pain by relieving the abnormally high fluid pressure within the navicular bone, and to see if it might help stimulate new bone growth in a way that would be more favorable to the bone.
In horses with navicular disease, one feature is that the constant extra pressure on the navicular bone from the deep digital flexor tendon (which is often due to poor conformation) results in abnormal remodeling of the navicular bone. As part of that process, the bone begins to degenerate and fill with fluid creating pain from the increased pressure. Kirker-Head decided to try the decompression drilling to see if it might ease the pain, first doing the procedure experimentally on normal, healthy horses.
“Here at Tufts the research has been done by myself and my associate, Dr. Florien Jenner, who was my research fellow at the time. We designed a minimally invasive surgical procedure that would allow us to access the navicular bone safely and repeatedly. We drilled three decompression channels into the bone from the back of the pastern. Thus we were able to get down into the bone safely without having to approach the bone through the hoof capsule,” he explains.
“We had good visualization of the proximal (top) border of the navicular bone, within the coffin joint, using fluoroscopic visualization which is like an x-ray video. We created the three decompression channels into the bone,” he says. This was done with six healthy horses that had no sign of any problems to make sure this procedure could be performed successfully and repeatedly without complications.
“We then monitored those horses post-operatively for 12 weeks to make sure there were no adverse complications. We were able to show that we could perform the surgery and that drilling the holes did provide a reduced spike in pressure in a stress test—in which we injected a small volume of fluid into the navicular bone—to simulate the elevated pressure you might encounter in horses with actual navicular disease,” he says.
“We were able to substantially reduce the pressure spike,” says Kirker-Head. The next logical step was to try this on navicular horses.
“We have not done very many yet. At this point, between myself and a colleague in the UK (Dr. Andy Bathe), we have only done five horses. So far, this procedure has provided improvement in soundness in the trial horses, but not necessarily lasting improvement. In one of the five horses, we had a return of clinical lameness several months later. So at this point we are just collecting more cases,” he says. Kirker-Head hopes to try this procedure in more horses and evaluate the results.
It’s increasingly difficult to find horses with actual navicular disease, however. “With the advent of MRI, we now realize that many of what we thought were classical navicular disease cases are actually not, and their lameness issues are more complicated. So we have to be quite selective and make sure that horses having the surgery are 1) in the earlier stages of the disease process and 2) are not showing pain because of other conditions within the hoof,” he says.
If navicular horses can be treated with core decompression drilling in the early phases of this degenerative disease, they might have more chance to respond positively and become sound again. “We hope to treat horses within the first 6-12 months of this disease,” he explains.
The blanket term “navicular syndrome” covers a lot of issues within the foot, and many of these cases result in complications that would not respond to simply drilling the bone. “But we have now done enough of these surgeries that we are comfortable with our ability to get there and do it, and we have shown that we can do it without endangering the horse. So now we just need to get a clinical series to show how the short-term and long-term outcome plays out,” says Kirker-Head.
“This will be an ongoing study and we encourage people who are interested in enrolling their horses to contact me,” he says. Horse owners can participate in this program and possibly help their own horse in the process.
Anyone who has a horse that has been diagnosed in early stages of navicular disease can get in touch with him by e-mail at carl.kirker-head@tufts.edu
ABOUT TILDREN RESEARCH
A study was done in 2003, in France, evaluating use of Tildren in horses with navicular disease. “This was a double-blind, placebo-controlled clinical trial,” says Bracamonte.
The objective of this study was to determine if the bone remodeling changes in navicular disease could be corrected with this drug. Two different doses of tiludronate were evaluated. Horses with navicular disease were split into two groups—recent and chronic cases—and then followed over 6 months after receiving the drug. Some of the horses were given 0.5 mg/kg and the others were given 1 mg/kg. The drug was administered daily for 10 days via IV injections.
The horses receiving the higher dose showed the most improvement and returned to normal levels of activity within two to six months after the treatment. Horses with recent onset of navicular disease showed the best improvement. The lower dose of the drug failed to significantly improve the condition.
“We are finally able to get Tildren in Canada and the U.S. Success in treatment depends partly on how severe the pathology is; it’s always better to catch it early before there are significant changes in the bone. Horses that have recent onset of clinical signs are the best candidates for this treatment,” says Bracamonte.
At this point it’s still an “emergency release” drug and can only be used on a case-by-case basis with the veterinarian requesting its use. “We are now working on licensing so we can offer it to our clients,” he says.
“Some veterinarians are using Tildren in regional limb perfusions. This is the same way we treat horses with joint infections, using antibiotics,” he says. A tourniquet is used temporarily on the affected limb—to help make sure the drug stays in that area awhile—to deliver high levels of the antibiotic into the affected area.
“Giving a drug systemically doesn’t get enough of it into the joint. The dose we’d have to give, to have high enough concentration at the site of infection, would be bad for the horse’s health and might damage the kidneys,” he explains.
“So we isolate the area of the problem, apply a tourniquet (to restrict blood in and out of that area), and with a catheter we inject a certain volume of antibiotic to deliver a high concentration to that area. We only leave the tourniquet on for about 30 minutes.” This procedure is now being used for administering Tildren. It is normally given IV, but some people are trying it via regional limb perfusion and feel it gives even better results.
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