Though proper repair techniques can be an integral part of the process, long-term resolution of most quarter cracks requires a close look at the primary cause of the defect—foot dysfunction….

Thanks to his wins in two legs of the Triple Crown, Big Brown and his hooves frequented media headlines, introducing legions of lay people to the term “quarter crack” as his team worked to address the hoof issues affecting the horse.

While quarter cracks are not uncommon in performance horses, few horse owners have the resources to fly in a hoof repair specialist like Big Brown’s Ian McKinlay. But take heart—the most important factor in healing most quarter cracks isn’t fancy stitching and patch work—it’s identifying and fixing its underlying causative agents in the structure of the hoof.

Quarter cracks can result from a variety of issues related to hoof conformation, management practices or injury, including: long toes and underrun heels; short shoeing; upright feet with high stacked heels; or an injury to the coronary band or infection beneath the hoof wall. 

“The main cause of quarter cracks is dysfunctional heel structure. When the heel position is underrun, it pushes the hoof wall up proximally and interferes with the collateral cartilage, which is probably how quarter cracks occur [mechanically],” explained Dr. Scott Morrison, equine podiatrist and co-owner of Rood & Riddle Equine Hospital in Lexington, Ky. “In a normal foot, every time it hits the ground and bears weight, the collateral cartilages, which are right above the hoof in the quarter region, adduct or open up.

There’s normally clearance between the top of the hoof wall and the collateral cartilage, but when the hoof wall is pushed up, the coronary band gets shoved up, and when the collateral cartilage doesn’t have enough room to adduct and open up, that blows out the quarter and you get cracks.”

Often on a horse with low, underrun heels, there can be a side-to-side (lateral-medial) imbalance where one heel is lower than the other, as a result of conformation or improper trimming. The horse will tend to load the lower side more heavily, which can add additional stress to that quarter and increase the likelihood of a crack.

“Most of the time we see quarter cracks on the medial [inside] side up front and laterally [outside] behind because most horses load medially up front and laterally behind,” noted Morrison. “When you see it laterally on a front foot, it’s usually because it’s a wide-chested horse that stands base narrow. A lot of hunter-jumpers are base narrow behind and twist their hocks when they walk, so we typically see cracks on the lateral side on hind feet.”

While medial/lateral unbalance can contribute to a quarter crack on one side of the foot, what about those unfortunate souls with cracks on both sides of their feet?

“Low-heeled horses don’t land really hard on the heels; a lot actually land toe first. You look at the horses with the upright, stacked, high heel, or a clubby footed horse, a lot of them often land really hard on the heels, which can overload the quarters,” said Morrison. “Combine that with a little bit of anunderrun heel, and they can get quarter cracks pretty easily, often both medially and laterally.”

Unlike most hoof cracks, quarter cracks usually start to form inside the hoof and eventually become apparent when they “pop” through the hoof wall. Because of this inside-out development, a true quarter crack extends through the full thickness of the hoof wall, down to the underlying sensitive tissues, which can lead to pain and unsoundness due to various manifestations of inflammation, infection and instability. Even before a crack propagates through the hoof wall, when it’s still a “blind” crack, it’s common to see the characteristic upward bulge in the coronary band in the affected quarter of the hoof.

Quarter cracks aren’t always painful; lameness usually is a result of infection or instability in a particularly bad crack. “Blind cracks tend to be more painful because then you have serum leaking out of the damaged tissue with nowhere to go,” said Morrison, who led a hoof wall crack and repair techniques workshop with fellow podiatrist Stephen O’Grady at last year’s American Association of Equine Practitioners Annual Convention in Orlando, Fla. “They can be mistaken for abscesses. Sometimes the serum pocket can blow out of the coronary band like an abscess would.”

Stop—Drop, Then Repair

The first step in resolving a quarter crack is to fix what’s causing it. Sounds like a no-brainer, but while the ugly, gaping crack is leering at you from your beloved steed’s hoof, the first instinct might be to fix’er right up with a nice smooth patch of acrylic. Such a repair can be a valuable tool in recovering from a quarter crack, particularly if the horse is expected to continue performing while it grows out, but first and foremost, you need to relieve the damaging forces at play and let that telltale hump in the coronary band drop.

Minimally, to allow the coronary band to drop into its regular straight orientation, Morrison will apply a heart bar shoe, which increases the load bearing surface of the foot, and will float the bottom of the affected quarter of the hoof. This floating creates a gap between the hoof and the shoe, which unloads the crack and provides room for the hoof wall and coronary band to drop down into a more normal position.

“If you patched the crack right away, you’d stick the hoof wall in that displaced position. You could develop a chronic problem where it won’t drop and it’ll scar in that position and will be prone to reoccur,” he said. “If they’ll let us, we’ll have them go barefoot for a week and let it drop that way and come back for shoes and patching. Shoeing is 80 percent of the formula—if you don’t have the shoeing right, the best quarter crack patch will fail.”

If the horse can take the time off and can handle it, Morrison advocates allowing it to go barefoot as an alternative. “If the sole is strong enough and it’s not going to screw the heck out of their foot going barefoot, a lot of times I’ll do that. Some of the race horses that come to me, I’ll strip everything off and have them go barefoot for 60 days,” he said. “The quarter crack is a secondary problem. Pulling the shoe and having them go barefoot is the quickest way to strengthen and change the morphology of the heel—it’s addressing the primary problem.”

Another immediate concern before any repair work can commence is addressing any underlying infection in the hoof. A minor infection can typically be handled by cleaning up the crack with a Dremel and packing it with a mild antiseptic, but more aggressive tactics may be required for more pervasive infection. In the worst cases, in which the underlying bones and collateral cartilage can be infected, Morrison will often send in the troops to do the dirty work for him via “larval therapy,” i.e. using sterile, medical-grade maggots to wriggle and nibble their way around the wound to clean things up.

“I don’t like to debride too much on the laminae because anytime you scrape away tissue, you’re probably damaging healthy tissue, and the horse will respond by laying down scar tissue, which is weak and not as elastic,” he explained. “If you get scar tissue in the bed of a quarter crack, it can be a source of another crack in the future. I like to use the larval therapy [in these advanced cases] because they’re only going to debride the infected tissue.”

Patching Things Up

There are many methods that can be employed to repair the actual hoof defect once the coronary band has been allowed to drop and steps have been taken to address any hoof conformation that contributed to the formation of the crack. If the horse is comfortable with the shoeing situation and the crack is stable, it may not require a physical repair at all, but if the horse needs to perform or if the hoof is still sensitive or unstable around the crack, it likely needs further intervention.

“There are a lot of different forces you’re trying to counteract when you patch them: sheering forces, the up-and-down motion on either side of the crack; tension; and compression. You need a patch to address all the forces,” explained Morrison, who typically stitches them together using stainless steel wire.

Big Brown’s repair featured a single-stitch method that uses long, staple-like, U-shaped wires fed through tiny holes drilled in opposing sides of the crack. The tails of the wire from the opposite sides are twisted together inside the body of the crack to create tension and draw the edges of the crack together.  Before they’re inserted into the holes in the hoof, the wires are laced through protective metal buttons that sit on the outside of the hoof wall to dissipate the force and prevent the wire from cutting through the hoof wall when it’s twisted.

While this single layer works well to provide the necessary tension across the crack, a second layer of stitching, performed “shoelace” style between small screws on either side, helps to mitigate the up-and-down sheering forces for cases requiring more stability, such as in the foot of a jumper or a heavy warmblood. On top of whatever stitchery is employed, Morrison typically applies a Kevlar/fiberglass/acrylic mesh to stabilize and reinforce the repair.

“On some horses that are really thin-walled in the quarters where you want to avoid drilling into the hoof wall, you can just use fiberglass and acrylic patches or you can build up either side with acrylic and stitch through that,” he noted.

A good patch can last for three months, which is a plus, considering how expensive and time-consuming they are to perform. Because moisture can compromise the acrylic’s ability to adhere to the hoof, Morrison recommends that clients rub beeswax around the margin of the patch to seal out moisture or duct tape a plastic bag, such as an empty I.V. fluid bag, over the hoof when bathing a patched horse.