October 31, 2013
Flexural limb deformities of the coffin joint are not career-ending horse health concerns if they are managed early.
Hopes and dreams are pinned inside the foaling stall. But a foal that stands on its tiptoes, its front legs unable to function well enough for a proper walk, can dash the dreams of a breeder set on a performance career.
The good news is that flexural limb deformities – which can occur in the knee, fetlock and coffin joint – won’t necessarily end an athletic career before it can even begin. Experts say they can be treated successfully, especially if addressed early.
There are two conditions that may develop to cause deformities in the coffin bone.
The coffin bone attaches to the deep digital flexor tendon, which in turn is attached to the inferior check ligament, which attaches to the back of the cannon bone, just below the knee. There’s a bone-to-bone connection that is part of the horse’s stay apparatus – the mechanism that allows the horse to stand for long periods of time and even sleep on his feet.
For elaborations on this deformity, we went to Dr. Nathaniel White, who is a Professor Emeritus of Equine Surgery at Virginia Tech’s Marion DuPont Scott Equine Medical Center. White has a master’s degree in pathology and is a diplomat with the American College of Veterinary Surgeons.
Congenital Flexural Deformity
In some foals, the condition is a congenital defect; they’re born with tendons and ligaments that don’t allow the normal extension of the coffin joint. Occurring in in-utero positioning, the fetus situates so that the tendons in its legs don’t elongate properly as they grow, White said.
Often a veterinarian’s first course of action is to administer a high intravenous dose of the antibiotic oxytetracycline. The drug allows the tendon-ligament unit to relax, but it’s most effective when used on neonatal foals.
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“They are more likely to respond in that first month of age. As they get older, there’s less success. If you get that clubfoot conformation, and it’s there for a month or more, I’ve not seen success with this,” Dr. White says.
Casts or splints – such as those made from a section of PVC pipe, heated and bent to accommodate the fetlock – are also commonly used on newborns.
The first few days of a foal’s life “the ligaments and tendons are malleable and just getting them support will let them stretch,” Dr. White says.
Acquired Flexural Deformity
For other foals, the problem develops at about 2 to 3 months of age.
Foals who grow rapidly may experience pain at their growth plates, and “the nervous system responds by retracting and pulling on the flexor tendons,” Dr. White says.
There are cells, called myofibrocytes or myofibroblasts, in the ligaments of young animals that function much like muscle cells. These cells have been found in the inferior check ligament, and as that ligament is shortened, pressure is applied to the deep digital flexor tendon, and the coffin bone is pulled backward. Outwardly, this shows up as a clubfoot, with steeper angles of the front hoof wall and an excessive amount of heel.
Horse owners whose foals are born normally will want to be on the lookout for any signs of hoof abnormalities. They’ll first notice a hoof – or both front hooves – that seem to be suddenly upright. (The process is gradual, but the discovery may be “overnight.”)
“Their foot will grow with a longer heel than normal. You trim that heel down, and they still will stand on their toe with a little bit of space underneath the heel, or it just continues to grow, and the front of the hoof wall is much straighter than normal,” Dr. White says.
A normal hoof angle (the angle between the ground and the front of the hoof wall) is between 45 and 55 degrees. In foals with flexural deformities, the angle is usually between 65 and 70 degrees (known as a Type I deformity). The most severe cases can be 90 degrees, where the hoof wall is perpendicular to the ground, or even beyond that axis, so the hoof wall is angled the opposite way (a Type II deformity).
Radiographs, coupled with an evaluation of the horse’s conformation, will confirm the diagnosis of a flexural deformity.
Correct the Problem
“Once you know that you have a deformity, the next thing is to decide whether this is one of those growth problems or whether you have an injury or a pain response elsewhere,” Dr. White says.
If the abnormal hoof growth is due to an injury elsewhere, say, an injured shoulder that caused the foal to quit using that limb, addressing the primary injury will take care of the hoof abnormality. But if the foal has a conformational defect, “Those need to be resolved either through shoeing or surgery.”
A veterinarian should be called early to address the problem, and “the first thing I’d recommend would be to raise the angle of the foot dramatically up on wedges,” Dr. White says.
This can be done with glue-on shoes. By wedging up the heel, tension is released on the deep digital flexor tendon and the inferior check ligament, potentially relieving the pain that’s caused by their pressure.
“That allows the horse to step and create a little bit more of a displacement of the fetlock, and then over about three or four weeks, you gradually let the foot or the feet down to a normal angle,” Dr. White says. In that amount of time, the tendon-ligament unit has relaxed and is able to stretch out without contractures.
It might seem more intuitive to lower the heel and pull everything back into its proper place, Dr. White says, but that simply adds more pressure and pain.
Another shoeing technique involves applying a shoe with an extended toe. That extension acts like a lever, delaying the horse’s break over and forcing his heel down. But it’s not a favorite of Dr. White’s because, he says, it addresses the mechanics of the problem but not the pain that’s present.
The Next Option
For horses who are severely affected, or for whom shoeing hasn’t worked after a couple of months, surgery is the next step.
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The procedure called an inferior check ligament desmotomy consists of cutting the ligament, thus allowing the deep digital flexor tendon to stretch out and put the coffin bone back in its rightful position.
“It’s highly successful in very young animals (foals 3 to 6 months of age), not as successful as the horse gets older,” Dr. White says. The procedure is still effective enough in older horses that he doesn’t hesitate to recommend it when necessary to relieve pain or lameness, though it is not as effective.
In older horses, the surgery can be done standing, under local anesthesia. For foals, Dr. White prefers to use general anesthesia.
Vets use ultrasounds for the procedure. “You can actually watch yourself make the cut, so it helps us to know what we’re cutting, because obviously, you don’t want to cut anything else.” The precision also allows for a smaller incision – usually about ¾ of an inch – made on the outside of the cannon bone.
Farrier services are invaluable thereafter. “We want to trim the foot to normal,” Dr. White says. “We may even want to put a shoe on it with a slight extended toe to make sure the foot stays flat on the ground so the new growth will be normal conformation.”
“In about six weeks to three months, that check ligament will be healed back together because it’s needed for part of the mechanism for locomotion.”
The normal recovery protocol is three months confined to a stall or small pen with bandages for the first four weeks to reduce swelling and scarring. This is followed by three months of turnout.
Foals, which heal more quickly, are generally recovered in six months. Older horses might take up to a year.
An examination with ultrasound is essential before a horse is put back to work to make sure inferior check ligament has fully healed and is at full strength, but there is no reason why, if treated early, a horse cannot then go on to become a performance animal.
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