Contracted and Sheared Heels
Common challenges farriers face include contracted heels and sheared heels. Scott Morrison, DVM, head of the equine podiatry service at Rood & Riddle Equine Hospital, in Lexington, Ky., says both of these conditions often result from less-than-ideal conformation.
"If a foot is too upright it tends to load the toe more and underload the heel portion," explains Morrison. "When the heel is underloaded it becomes contracted. Clubfeet may lead to contraction, just because the heel area is not loaded adequately. Horses lame in the heel area may become contracted because they are not putting enough weight on the heels (the most elastic part of the foot). If a horse favors a foot for a long time, the entire foot can become contracted."
Steve Norman, a Midway, Ky., farrier who shoes many of America's top Thoroughbred racehorses, says that once a foot con-tracts it might be difficult to get it back to normal. "If the problem is due to an injury that resolves to full recovery, there's more chance to get the contracted heels back to normal (the foot has a chance to return to normal shape). But you may still end up with one foot smaller than the other one," says Norman.
Contraction is usually a sign of something else going on in the foot that hinders normal use. Morrison says, "Some horses with severe pain become contracted."
Horses with navicular problems, for instance, do not generally load the heel; they land toe first and travel in a way that they do not load their heels as a sound horse would. Rather than make a long stride by throwing the foot out in front and landing on the heel, these horses' strides are short and choppy as they try to land on the toe instead. They might have normal conformation, but if they have chronic heel pain, they might develop a contracted heel.
"Once the heels become contracted, however, they also act as a source of pain," says Morrison. "This becomes a vicious cycle. These horses may have had mild lameness in the heel, which sets them up for heel contraction, which in turn creates more pain, and more contracture."
How you address contracted heels will depend on the cause. "If it's a clubfoot, there are several very effective shoeing methods," says Morrison. "Clubfeet are a result of a contracted tendon." Heels become long to accommodate the contracted tendon.
Some people try to correct this by trimming the heels to make the foot look more normal. "But this puts more tension on the tendon, which will just make the foot more clubby," says Morrison. "For treating clubfeet, we often make a shoe that takes tension off the deep digital flexor tendon. If you need to trim some of the heel, which will put more tension on the tendon, you do something to counterbalance that--such as changing the breakover. That's the other half of the formula. The deep digital flexor tendon pulls tightest and has the most tension at the caudal phase of the stride, during breakover.
"Once you get a clubfoot rebalanced, often the heel contracture resolves," Morrison notes. "So we trim the heels down to normal height, rocker the toe of the shoe to ease breakover, and use a soft sole support. Not all sole supports are the same. Some are very hard and firm, and not very elastic. I like to use supports that are about the same consistency as a freshly trimmed, well-hydrated frog."
With most contracted heels and clubfeet, frogs atrophy from disuse and harden. In a healthy foot the central sulcus of the frog is open, but when heels contract there's a very narrow cleft, which creates a favorable environment for thrush and infections--debris can be trapped here and there's very little air.
"You need to load those structures, to break that heel pain cycle," states Morrison. "It sounds almost opposite of every other thing we do in therapeutic shoeing. This is one instance you need to load the structure that's sore. We load it by using soft sole support material to engage those structures into weight bearing."
If the foot can take weight in a way the horse can tolerate it, this starts to reverse the destructive process of contracted heels.
"Contracted heels may have multiple sources of pain, from the contracture itself and sometimes infection, and there may be deeper heel pain in the navicular region that needs to be addressed," he explains. "Sometimes you need to prioritize and treat one thing at a time."
Some horses with contracted heels require surgery, says Morrison, such as cases where the frog is almost nonexistent and the hoof walls have grown into the base of the frog "like an ingrown toenail," he notes.
"For severe contracted heels we often make a spring shoe with a hinge in the toe," describes Morrison. "We also use frog springs, like they use in gaited horses, but we put these right into the shoe rather than under the foot. The shoe has a hinge in the toe, and there's a spring at the end of the branch of the shoe. That's the most effective way to open up a contracted heel. It will open up about 4 to 5 millimeters immediately after you put it in, then the spring continues to push on the branches of the shoe so they get wider apart over time."
Morrison says he uses a lot of these shoes, especially on feet that have been in a cast for a leg injury or lame for a long period of time. "The primary problem is resolved--whether it was a fracture or some other injury that healed--but they end up with a contracted heel and heel pain," he says. "Young, growing horses may get a clubfoot secondary to heel pain."
He says that when foals or yearlings get coffin bone fractures, veterinarians use casts or therapeutic glue-on shoes to immobilize affected hooves so the fractures can heal. "After the fracture resolves, the horse may be lame because of the contracted heel," says Morrison. "So then you are trying to find ways to spread the heel back out again."
When a horse develops sheared heels, hoof symmetry becomes distorted and one heel bears most of the weight. Norman says this is one of the more common problems in racehorses.
"It often starts at an early age--due to conformation," Norman says. "Most cases it's because the foal toes out, putting too much pressure on the inside (medial, or toward the midline) quarter, shoving (displacing) that heel up. A lot of toed-out horses have a straight wall on the inside of the foot and a flared wall on the outside (the lateral side)."
This can also happen on a toed-in horse, where there is too much weight on the outside of the foot, shoving that heel upward.
Morrison says the problem also occurs in horses whose feet and pasterns are not in a straight line. "If you look at them from the front, it looks like the hoof is offset to the outside," he says. "The pastern comes into the hoof capsule a little to the inside." This conformation puts extra stress on the inside heel.
"Wherever the most force is, it creates trauma," says Norman. "It starts early in life, and if not dealt with at yearling stage, it gets worse after the horse goes into training, carrying (more) weight and working at speed. Then you are dealing with sheared heels and sometimes quarter cracks. If the laminae (which serve to attach the coffin bone to the hoof wall) start tearing, this creates hemorrhaging, and a quarter crack blows out. The crack has already been forming in the laminae. We call this a blind quarter crack because it hasn't surfaced yet.
"When the digital cushion becomes compressed on one side it hinders the natural shock absorption in the back of the heel and there's even more concussion in that area," explains Norman. "You try to support the foot to relieve the pressure, and it's hard to do that and still keep the horse racing."
The earlier you catch sheared heels and deal with them, the better. "The first sign is the hairline around the bulbs of the heel changes," Norman says. "Hair over the stressed heel sticks straight up while the hairline over the normal heel bulb will be lying down. When you feel heat in the heel bulb or see the hair standing up, this is the first sign of inflammation. You'll also see a red ridge around the hairline due to heat and concussion."
If he sees this clue, he tries to figure out how to shoe that horse differently so the horse won't place so much pressure on that heel.
"Most sheared heels are like a unilateral contracture (just one side)," says Morrison. "A normal foot should have sloping hoof walls. As one heel gets more contracted and that wall becomes vertical, it begins to be displaced upward. My theory on sheared heels is that the part of the foot that's under the most vertical load tends to develop a straight wall. The side with a more horizontal load develops a flare. I see a lot of normal horses develop a straight medial wall and more flared lateral wall, but when this becomes exaggerated--with more hoof capsule distortion--the inside heel becomes aligned directly beneath the bony column (the vertical line of force) and gets pushed upward, creating the sheared heel.
"It's very important to radiograph those feet for balance," stresses Morrison. "There are a couple common ways to deal with sheared heels. Some people trim the sheared heel side lower, and some people trim the opposite side lower. Those who trim the sheared heel lower are trying to match wall length, since the inside wall is shoved upward and if you measure the actual length of the wall it is longer, while the outside (flared side) is shorter. The same school of thought looks at the coronary band and tries to trim the hoof so the coronary band will be parallel to the ground.
"But trimming them this way is probably the opposite of what you want, since radiographs show the coffin bone is tipped lower on the medial side," he stresses.
Length of wall and alignment of coronary band can't be used as guides for trimming because the foot is distorted: this type of trimming can add more stress, tipping the coffin bone even lower on that side.
"How to trim these feet is often a subject of debate, but one way to settle this is to have good-quality radiographs taken, and show these to the farrier," says Morrison. "Then it starts to make sense on how to trim. You can easily be making the problem worse, otherwise."
While conformation often is to blame for contracted and sheared heels, there are other causes, such as heel pain and casts that hold the hoof capsule rigid. Noticing and treating contracted and sheared heels early can prevent or shorten lamenesses caused by the horse compensating for improper hoof wall support.
About the Author
Heather Smith Thomas ranches with her husband near Salmon, Idaho, raising cattle and a few horses. She has a B.A. in English and history from University of Puget Sound (1966). She has raised and trained horses for 50 years, and has been writing freelance articles and books nearly that long, publishing 20 books and more than 9,000 articles for horse and livestock publications. Some of her books include Understanding Equine Hoof Care, The Horse Conformation Handbook, Care and Management of Horses, Storey's Guide to Raising Horses and Storey's Guide to Training Horses. Besides having her own blog, www.heathersmiththomas.blogspot.com, she writes a biweekly blog at http://insidestorey.blogspot.com that comes out on Tuesdays.
POLL: Rehabbing the Injured Horse