Reading Your Horse's Inner Hoof Structures
What's going on inside your horse's hooves during injury or disease? Our sources reveal what they've learned when dealing with sheared heels, white line disease, abscesses, and other common hoof conditions.
Posted by Diane E. Rice | Jan 12, 2022 | Abscesses, Diagnostics and Technology, Hoof Care, Hoof Problems, Horse Care, Lameness, Lower Limb, Navicular Problems, Sheared & Contracted Heels, Thrush, White Line Disease
What's going on inside your horse's hooves during injury and disease?
Your horse's hooves are amazingly complex structures designed to communicate with the central nervous system, carry weight, and absorb concussion. Each hoof's intricate parts and their corresponding functions normally work together to support and propel him, pain-free.
But what's happening inside the hoof when pain, resulting from injury and/or disease, sets in? Our sources—Ann-Marie Hancock, DVM, EDO, and Tim Rogers, DVM, of True North Equine Veterinary Services, in Warrenton, Virginia; and Paige Poss, partner in Anatomy of the Equine LLC, in Tucson, Arizona; presenter at the Northeast Association of Equine Practitioners (NEAEP) symposium; and a longtime hoof trimmer whose hoof dissection photographs have helped shed light on hoof pathology (disease or damage)—reveal what they've learned dealing with six common hoof conditions.
Sheared Heels
What are they?The two heel bulbs at the back of the horse's foot can become unbalanced due to conformation faults or improper trimming, causing either the inner or outer heel bulb to be higher than the other. This can lead to pain and lame- ness along with hoof wall injuries such as cracks and thrush.
How can I spot them? When viewed from the rear, one heel bulb is noticeably higher than the other.
What's going on? The hoof capsule (the hoof wall, sole, frog, and heel bulbs, which form a casing that protects the soft tissues and bony structures within) is moving, shifting from its original, correct placement, says Poss.
"Some think that sheared heels are more from improper landing and are more a motion problem than a static problem and try to trim them to get both heels (of the affected hoof) to land at the same time," Rogers says.
Poss cautions, however, that balancing the hoof capsule can unbalance the bony column (the bones up the leg): "For example, think of walking with a wedge under the inside of your shoe's heel; you'd have to bow your knee out and adjust through your hip and all the way up your body.
"At some point," she continues, "I absolutely want veterinary involvement to get radiographs (X rays) so I can really see if the bony column is unbalanced or if it's just distortion in the hoof capsule."
"Paige and I have found that if we can change the body mechanics so the horse is lifting through the shoulder and he's more base-wide, instead of tightrope-walking with his feet close together, his landing pattern is more normal," Hancock says.
They accomplish this through body-work such as osteopathy and chiropractic. She adds that changing the horse's body posture/movement also changes his stance, so if loading during stance phase (when the foot is in contact with the ground) or even normal weight-bearing while walking around the paddock is causing sheared heels, changing the horse's basic posture and conformation could be key to changing sheared heels in a more permanent way than farriery alone.
"Some people are starting to look at thermography of the sole to determine the horse's load-bearing pattern," adds Poss. "If they're only load-bearing on one side of the foot, you might address that as part of the capsular distortion."
Sidebone
What is it? Lateral cartilages (which slope up and back from the wings of the coffin bone), most often in the forefeet, become calcified due to excessive concussion or how the hoof is landing due to conformation and/or shoeing.
How can I spot it? Horses with sidebone are either asymptomatic and diagnosed on radiographs or have mild to moderate lameness that has been localized to that region of the foot, and other lameness causes have been ruled out.
What's going on? Although most cases of sidebone occur in draft breeds due to the concussion caused by their sheer weight, Hancock says when she does see sidebone in light breeds, it occurs on the side of the foot the horse lands on—the side that receives the most concussion.
Most of the time, says Hancock, this has more to do with a rolling, lateral-to-medial (outer to inner) landing pattern and a horse that stands base-narrow, maybe toed in with a shorter lateral wall and a higher, upright medial wall.
"The medial side takes the concussion and landing, as the lateral side lands first, rolls, and then the medial side will slap down last," she says. "The concussion is what stimulates the wall growth and can also irritate the area of the lateral cartilage, causing it to try to lay down bone for stability."
"You can try to reduce concussion by getting a proper heel-first landing using the back of the foot, but I've never seen anyone reverse sidebones," Rogers says."
"White Line Disease, aka Seedy Toe
What is it? Degradation of the white line (between the sole and hoof wall).
How can I spot it? It's a crumbly, mealy condition of the white line that you might notice while picking your horse's hooves."
What's going on? Poss says that from her observations, both white line disease and chronic hoof cracks (read a summary of her NEAEP presentation here) are accompanied by changes to the internal structures supporting the wall, white line, and sole and, behind that, the coffin bone.
"You can think of the coffin bone as a trellis that the laminae (the tissues that connect the hoof wall to the coffin bone) and sole corium (composed of the hairlike papillae over the entire inner surface of the sole) rest on, and now part of that lattice is gone," she says. "You still have the laminae, the sole corium, and the tissues that are growing the white line, but they no longer have a good place to sit so they end up melding together."
While the body develops ways to repair damage, the repaired structure might not be as good as the original. "When the hoof wall begins to peel away from the coffin bone, or if the laminae and coffin bone are damaged, the body is going to fill in any space," explains Rogers. "The hoof wall is tubular horn and intertubular horn, and what you end up with is only the intertubular horn excreted to fill in that space. It's like fiberglass being made up of mesh and glue, and it's the two ingredients that make it strong. With white line disease, the gap is filling in with just the glue, so it's weaker and porous and a great place for bacteria and yeast to get into. When resected, the wall looks more like coral than wax."
Treatment for white line disease should address the mechanical problem and build a healthier connection between the inner (reaching out from the coffin bone) and outer (reaching out from the hoof wall) laminae, says Hancock. "This would include decreasing stretch at the toe and opening up any crumbly, infected areas, as well as balancing the foot for the long term," she explains.
Thrush that happens in the center of the frog can get surprisingly deep and erode down to soft tissue and the corium.
What is it? An opportunistic bacterial infection of the frog (the collateral grooves you pick out when cleaning your horse's feet or the central sulcus—the single groove at the center of the frog).
How can I spot it? Sometimes you'll smell it before you see it, though thrush in the central sulcus can be odorless.
What's going on? While thrush in the grooves at the side of the frog can cause discomfort, Poss says thrush in the center of the frog tends to be most painful.
FREE DOWNLOAD | Fact Sheet: Thrush in Horses
"Thrush that happens in the center of the frog can get surprisingly deep and erode down to soft tissue and the corium," she says.
Hancock says horses with these deep, narrow cracks between the heel bulbs often don't have discharge or, again, smell, but if you try to palpate between the heel bulbs, the horse is acutely sensitive. These horses need medical treatment—often topical antibiotics or antifungals—to help heal the area before the horse is willing to bear weight on it and to improve circulation in the digital cushion (the soft tissue beneath the sole that separates the frog and heel bulb from the underlying tendons and bones) and caudal (back) heel structures.
"When I look at the bottom of the foot, if I see a nice, wide frog with a central sulcus that's open, that's a healthy foot," says Rogers. "But when I see a long, skinny frog that's stretched and the central sulcus is a tiny slit, that tells me the foot isn't using that frog properly. The real problem is that we have an unhealthy frog, probably with poor circulation, and that invites bacteria to come live there."
Poss says immunosuppressed horses can be at particular risk of poor circulation in the limbs and feet because of inflammation in their body. "It's the health issue that caused the problem (rather than wet conditions), and the thrush is just eating the dead tissue," she says. "If you're not treating what's causing the issue, you're just treading water."
In these cases consulting with a veterinarian to look at hoof health, sole thickness, and bone status using radiographs can be incredibly helpful, says Hancock.
"Using a venogram (an X ray taken of the foot after contrast media has been injected into its blood vessels) can also help answer some questions about the overall health of the foot," she says. "Diagnosis and treatment of other underlying diseases can be critical to changing poor circulation and poor hoof growth."
Abscesses
What are they? Pockets of infection between the inner and outer laminae.
How can I spot them? Sometimes lameness will be your only indication, but you might also spot a black area at the white line or the coronary band where the infection has broken through.
What's going on? Abscesses vary widely in how they appear in different hoof types and conditions, says Poss.
"The way horses blow out abscesses in the heel, sole, and frog is different in different environments," says Poss. "In dry areas where the hooves are super, super hard, the horse tends to stay lame for months (if left untreated). Where it's wetter and moisture gets retained, abscesses seem to follow the path of least resistance and blow out quickly."
"In sandy, wet soil, the feet stay soft but wet, splayed, and flat," adds Hancock. "There, most abscesses don't come out at the sole; rather, they erupt at the coronary band after a few weeks."
Both of the veterinarians and Poss agree that thin-soled horses are more prone to abscesses. "I've been shocked when I go out and do radiographs here (in Virginia) at how many horses I see with one-third inch or less of sole depth," says Rogers. "And when you consider that probably 6 millimeters of that is blood vessels, that means the sole is actually paper thin."
Podotrochlosis, aka Navicular Syndrome
What is it? Lameness involving any part of the podotrochlear apparatus, which includes the navicular bone, the navicular bursa, the coffin joint, the impar ligament, the suspensory ligament of the navicular bone, and the deep digital flexor tendon (DDFT).
The soft tissue structures surrounding the navicular bone support it during standing and movement. If one or more of these structures become compromised, excessive strain on the bone can lead to degeneration or remodeling.
Special Feature | Podotrochlosis: 'Navicular' is No Longer the End of the Road for Horses
How can I spot it? Your horse will "walk on eggshells," short-stride in front, and be more lame on hard ground than on soft ground. "When you watch them move on a circle," says Hancock, "they'll be lame on whichever foot is on the inside of the circle. If the veterinarian does a nerve block of the heel bulbs on one front leg, then the horse will look lame on the opposite front leg."
What's going on? "Navicular syndrome can be only painful (due to pathology in the) soft tissue, like the frog, digital cushion, and nerve, or it can include damage to the DDFT, the navicular bursa, or the navicular bone," says Hancock. "For more degenerative cases, good frog support may not be enough. Some veterinarians will use wedge shoes or pads or rail systems to take the strain off the deep digital flexor tendon. They may also treat using bisphosphonates, navicular bursal injections, shock wave, or laser therapy to decrease inflammation, improve tissue health, and restore function."
Hancock and Rogers agree that discouraging toe-first landings is critical for caudal heel health. "When horses land toe-first, the coffin joint has to go into extension—which is completely backward," Rogers says. "It has to do it very quickly, and that quick reverse movement puts a lot of tension on all the soft tissues of the caudal foot. That's how you get damage.
"But you have to remember that some horses land toe-first because their heels already hurt," he adds. "Since their heels already hurt and landing toe-first makes the horse worse, now you have to experiment with how to encourage a heel-first landing without causing him pain."
Poss likens it to having a splinter in your heel and someone saying, "I don't care what you've got in your heel; you need to walk on it."
"The message I try to give my clients," she says, "is that you need to build a good team that can work through these issues. It's not a matter of just looking at X rays and doing what the X rays say; sometimes there are mitigating factors (e.g., other health issues) that complicate things. Sometimes the horse just can't load the foot the way the X rays say he should. The bottom line is having patience to allow your hoof care team to work through the experimentation it sometimes takes."
Take-Home Message
Understanding the physical processes involved with your horse's hoof condition will help your veterinarian and farrier design the optimal course of treatment. As with all illnesses and injuries, maintaining a working relationship with your hoof care team is the best way to achieve a healthy, happy, pain-free horse.
Diane E. Rice
Diane Rice earned her bachelor's degree in agricultural journalism from the University of Wisconsin, then married her education with her lifelong passion for horses by working in editorial positions at Appaloosa Journal for 12 years. She has also served on the American Horse Publications' board of directors. She now freelances in writing, editing, and proofreading. She lives in Middleton, Idaho, and spends her spare time gardening, reading, serving in her church, and spending time with her daughters, their families, and a myriad of her own and other people's pets.
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