A quarter crack in a horse’s hoof can put an end to an owner’s riding plans and take months to resolve, even in the competent hands of a qualified hoof care professional and veterinarian. And, in the most severe cases, they can lead to lifelong lameness.

These cracks are so named because they occur in the heel quarter (back half, a quarter of the foot on each side of the frog) of the horse’s hoof wall. They typically originate at the hairline and are positioned vertically.

They form in response to various problems and hoof imbalances and often require a multimodal approach to resolve, said Stuart Muir, NZCEF, CJF, Dipl. WCF, APF, who serves as resident farrier at Rood & Riddle Equine Hospital in Lexington, Kentucky, where he works closely with podiatrist Scott Morrison, DVM, and other veterinarians on the team. Muir addressed the causes of quarter cracks and the challenges they present during the 2020 American Association of Equine Practitioners’ Annual Convention, held virtually.

What Causes Quarter Cracks?

Quarter cracks vary in severity. They can lead to mild lameness, or they can penetrate beyond the hoof wall, going so deep they bleed. These more severe cases can cause a 3- to 5-point lameness on the AAEP’s 5-point lameness scale, with 5 being non-weight-bearing.

Quarter cracks also expose the hoof’s interior structures to infection risk and related scarring. Deeply penetrating cracks can negatively affect the fragile laminae (the tissues that attach the coffin bone to the hoof capsule) and lateral cartilages (which slope up and back from the wings of the coffin bone and cause sidebone when ossified) and lead to demineralization of the coffin bone.

“When we think about horses’ feet, we know that there’s a certain amount of expansion and contraction,” Muir said. “As long as this (contraction and expansion) stays within the threshold of the physiological range that the hoof capsule can withstand, there’s never a problem. But I think quarter cracks are really just evidence of capsule dysfunction.”

Muir offered several reasons for capsule dysfunction, including:

• Hoof capsule health and function. Inadequate nutrition, poor sanitization, lack of exercise, and living in bedded stalls can all lead to poor hoof quality and growth. Any combination of these factors can make a horse prone to bacterial and/or fungal hoof infections (i.e., thrush, white line disease), further damaging the hoof capsule and making it vulnerable to dysfunction.
• Exposure to moisture can soften the hoof wall. For horses with a history of quarter cracks, moisture might be enough to cause reoccurrence, Muir said.
• Limb conformation. Imbalances caused by a horse’s conformation can result in force with the ground, stressing, distorting, and ultimately damaging the hoof capsule. Imbalances can be axial (e.g., offset knees), contractual (e.g., a contracted deep digital flexor tendon, club foot), and rotational deviations within the bony column (e.g., limbs rotating in or out due to muscular deformity).The distorted hoof capsule becomes weak and is more likely to break down.
• Limb position during loading and gait abnormalities related to conformational issues can cause hoof distortion. Blunt force trauma from interference between legs or feet can also create cracks.
• Imbalanced trimming or shoeing. This can result from the previously mentioned conformational issues, infrequent or irregular hoof care, or poor trimming/shoeing technique.

Shoeing Strategies

Because various hoof imbalances can lead to quarter cracks, veterinarians and farriers must address each case individually, Muir said. “I think it’s important that we always try to find the primary reason why these horses are cracking, and try to create a healthy, functional foot around that issue,” he said.

For example, a hoof with a negative palmar angle (formed by the bottom of the coffin bone and the ground) and underslung heels requires a different approach than a horse with a clubby (upright) foot. The previous might need more heel support, while the latter might benefit from a composite and/or glue-on shoe to allow the hoof capsule to relax, he said.

Hoof perfusion (growth) is the farrier’s friend when dealing with quarter cracks, Muir said. Healthy growth, often tied to blood flow in the foot as well as genetics, gives the farrier more foot to work with and helps the crack grow out. Muir showed venograms (foot X rays taken after contrast media has been injected into the blood vessels) indicating wedging can impede circulation, which in time could reduce hoof growth and make the problem worse. “,” he said. Shoeing prescriptions should change as the hoof capsule responds to treatment or if other pathologies (disease or damage) arise, he added.

Muir also shared the importance of shoeing around the center of rotation, creating a 50:50 balance between the toe and the heel of the shoe to ensure the horse’s heels are well-supported. This can help reduce leverage that would otherwise continue to split the crack.

For years veterinarians and farriers relied on heart bar shoes to address quarter cracks, Muir said. These shoes have a bar across the heel with an attached plate covering the frog, allowing the structure to share the force of loading the foot and reducing stress on the cracking area. Muir said the market now offers more options, such as fillers, impression materials, pads, plates, and various bar shoes, that can serve the same purpose. Choosing an approach depends on the farrier’s comfort level with the various available products, he said.

Crack Repair

Veterinarians and farriers also have more choices of materials with which to repair cracks, Muir said. These include fillers, Kevlar or other woven fabric patches, adhesives, and stainless stitches that are usually applied in conjunction with shoeing to help support hoof wall. Patching involves using an adhesive to impregnate and attach fabric over the crack to reinforce the wall. Stainless steel sutures zipper the crack to achieve a similar result.

Deciding to use patching or stitching depends on hoof quality and the crack’s depth and location, he said. The hoof wall around quarter cracks is often thin or weak, otherwise a crack wouldn’t have formed there. For that reason, “stitching through the wall is quite risky,” Muir said. He noted that he uses acrylic glue filler to build pillars to allow stitching into hoof, placing the stitches through the filler rather than the hoof wall on thin-walled horses.

Don’t Discount a Barefoot Approach

Many horses Muir works on are sport horses, and their owners want to keep them both in training and shoes. However, resting the horse, pulling the shoes, and managing the quarter crack barefoot might be a better or even necessary approach to allow the hoof capsule to heal. He shared a case study of a hunter who, after months of specialized shoeing with limited results, showed significant monthly improvement after going barefoot.

Take-Home Message

Quarter cracks are serious and can cause long-term internal damage in addition to acute lameness. Because quarter cracks result from a variety of factors—ranging from hoof health to conformational abnormalities—veterinarians and farriers must take an individualized approach to treating them.