Navicular syndrome—now often referred to by veterinarians as caudal heel pain—is a diagnosis many horse owners dread. But advances in imaging technology, like magnetic resonance imaging, have made diagnosing and treating navicular-related lameness more precise, and, in many cases, a diagnosis of caudal heel pain isn’t career-ending.
Here are some things to keep in mind about caudal heel pain, according to Dr. Liz Barrett of the Hagyard Equine Medical Institute in Lexington, Ky.
1. The problem isn’t necessarily in the navicular bone.
A horse that becomes sound after a veterinarian blocks the palmar digital nerve—which stops nerves from sending pain signals from the back two-thirds of the foot and the entire sole of the foot—is likely to receive a diagnosis of caudal heel pain. But a number of different problems might be causing that pain, from changes in the navicular bone to soft-tissue injury, and the cause will dictate the treatment. A horse who becomes sound with a palmar digital nerve block is telling you the pain comes from that area, but that’s just the first clue. “There is a lot in there: the navicular bone, parts of the deep digital flexor tendon, the suspensory ligament of the navicular bone, the T ligament, the back of the coffin joint, the sole of the foot—all kinds of things are down there,” explained Barrett. “So there are a lot of things that could be causing the pain.”
Possible causes of heel pain include bursitis, synovitis, pain in the navicular bone, soft-tissue tears (e.g., in the deep digital flexor tendon or in the structures that hold the navicular bone in place).
“Soft-tissue injuries are tough,” said Barrett. “If it’s a tendon injury up higher, we can use stem cells or shock wave therapy, but when the soft-tissue injury is down in the foot and in the bursa, they’re more difficult; they’re also at increased risk of getting adhesions. It can be tough to rehab a horse from that.”
But Barrett also cautions that there are limits to imaging the hoof, too. “There’s a lot that a vet can’t see, so you can’t always say for sure that this is what’s going on versus something else,” she said.
2. There are a lot of potential treatments.
So many potential causes mean a number of potential treatments, too. Thanks to advanced imaging techniques, veterinarians can now see soft-tissue injuries as well as bone problems, which means they can target treatments more effectively. For example, horses with soft-tissue injuries typically do not respond well to treatments for navicular or coffin bone problems, and in the past those horses might simply have been labeled “poor responders.” Now, depending on the nature and severity of the injury, those horses might improve on treatments for soft-tissue problems.”
Treatments can range from a shoeing change to more delicate procedures, like injecting the navicular bursa (the fluid-filled sac that cushions the navicular bone from the deep digital flexor tendon). Relatively new treatments include injection with drugs from the bisphosphonate class (iike Osphos®), a group of drugs used to treat osteoporosis in people.
“It’s meant to help with bone pain,” Barrett said. “It’s an intramuscular injection, and it’s not meant to be given any more often than every six months. This should be given only with veterinary guidance. You have to make sure the horse has good kidney function, because kidney issues can be a side-effect.”
Isoxsuprine and aspirin can also help increase blood flow to the foot, and Previcox (firocoxib) and phenylbutazone (bute) can help relieve discomfort—but be sure to consult your veterinarian. Horses should not take bute, for example, if they are on OsPhos.
3. Conformation and shoeing can play a role.
Podiatry issues are a common cause of heel pain, Barrett said. “If a horse has poor angles, they can overload that area and there’s more weight and pressure in the heel, which results in a mechanical lameness,” she said. “Every time they step they put more pressure on the heel.”
For some cases, there are shoeing changes that can help. “Round the toe, bring the break-over back, and elevate the heel a bit or support their heel,” Barrett said. “Those things can help, and if a horse responds to that without needing any other treatment, that’s the best-case scenario.”
4. Any horse can be affected by it.
“Big-bodied horses with little feet are probably over-represented, but you can definitely see it in warmbloods, Thoroughbreds, and other breeds,” Barrett said.
5. Schedule a thorough veterinary evaluation.
Given the many potential causes for caudal heel pain, it’s worth it to get a detailed veterinary exam, including nerve-blocking. “Heel pain can be a bit tricky,” cautioned Barrett. “The horses don’t always look lame. They don’t necessarily have a head-bob, because so often the lameness is bilateral—it’s in both feet. Sometimes I’ll look at a horse who looks short or choppy up front, so I’ll block one foot, and then the horse will be very lame on the other foot. That can be shocking for the owners, because they don’t realize the horse is that sore until you take away the pain in one foot.”
6. A good relationship between veterinarian and farrier is key.
Tackling heel problems requires open, collegial communication between veterinarian and farrier. A horse owner can help by facilitating conversations between the two and making sure each party is informed.
7. Don’t jump to the worst-case conclusion.
“I would say that of 10 horses that are positive after that palmar digital nerve block, probably eight of them get better with shoeing changes, one will need injections, and that last one will be the frustrating one that you find a tear in the soft-tissue structure that has a pretty poor prognosis,” said Barrett. “So it’s not that the majority of horses have that problem.”
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