Horses that are lame in the hindquarters might swing out their hind legs, have side-slipping saddles, or resist certain movements or directions. In more severe cases they avoid placing pressure on the affected limb. The cause might be a stifle injury, a tendon issue, hock problems, or a variety of other sources of pain. But new research suggests some hind-limb lamenesses might be associated with imbalances in the hind hooves.

Specifically, when a hoof or its internal structures (i.e., distal phalanx, better known as the coffin bone) tilt the wrong direction, it could cause foot pain leading to lameness. Perhaps more importantly, such imbalances can also lead to issues higher up in the limb, creating problems across the bones, joints, and soft tissues. These pathologies occurring secondarily to the primary foot problem can create hind-limb lameness that often looks like it has nothing to do with the feet, even though the foot is the origin of the problem, says Tracy Turner, DVM, MS, Dipl. ACVS, ACVSMR, of Turner Equine Sports Medicine and Surgery, in Big Lake, Minnesota.

The Distal Phalanx Angle and the Broken-Back Hoof Axis

Shaped like a mini-hoof and suspended in space behind the hoof wall by lamellar tissues, the coffin bone should—in theory—have a front surface that runs parallel to the hoof wall. Its bottom surface, meanwhile, should slant slightly downward (toward the front tip of the bone) compared to the ground. In other words, the healthy position of the coffin bone includes a very mild ­positive angle of about 2 to 5 degrees, explains Lynn Pezzanite, DVM, MS, a postdoctoral scholar at the Colorado State University (CSU) College of Veterinary Medicine & Biomedical Sciences, in Fort Collins.

The foot’s external shape doesn’t always reflect what’s going on with the coffin bone, she says. To get a better view, veterinarians can use X rays to visualize and calculate the relationship between the bottom surface of the coffin bone and the ground, known as the plantar angle of the distal phalanx (PADP).

If the bottom surface of the coffin bone is parallel to the ground, it’s a neutral PADP. If it’s tilted back—the tip of the coffin bone is higher than the back end, like it’s lifting up at the toe—that’s a negative PADP. Neutral PADPs have an angle of 0 degrees; negative PADPs have increasingly higher numbers depending on the severity of the angle.

Horses with negative or neutral PADPs have what’s known as a broken-back hoof axis, Turner says. That’s problematic because it causes the hoof to stay on the ground longer than normal during a step. As a result the deep digital flexor tendon (DDFT) experiences far greater strain than it should before the heel finally lifts.

“I mean, the foot’s backward,” he says. “So instead of tilting down, the bone’s tilting up, which puts tremendous strain on the flexor tendon. It just lengthens the whole leg so it doesn’t move quite as nicely as it should.”

Mediolateral Imbalances

In the front hooves, outside walls tend to grow higher than the inside walls, says Turner. “But on the back foot, what we saw was just the opposite,” he says.

Ideally, hoof wall growth should be even on both sides of the hoof, he says. When the inside wall grows higher than the outside wall on hind feet, horses generally rotate their legs inward and place them more under themselves during a step. This can create pressure on the inner side of all the joints along that leg and cause pain, inflammation, and damage.

Upper Hind-Limb Lamenesses Arising From Foot Imbalances

Historically, horse people have focused on the localized site of hind-limb lameness without necessarily looking into other potential sources of that pain, Turner says.

Owners and veterinarians began considering the “whole horse” effect as they realized certain performance issues throughout the body were rooted in previously overlooked areas, such as dental problems, he says.

Eventually, people began making the connection between front foot imbalances and pain higher up the forelimbs, he says. But they still weren’t investigating such a link in the hind limbs, possibly because they’re so different from the forelimbs, with distinct anatomy and loading patterns.

It was only about 25 years ago that ­scientists—including Turner—started ­making the connection between hind foot problems and hind-limb lameness. “I’d spent a lot of time looking at front feet, but then I started seeing more and more hind-limb lamenesses, and I thought, ‘There have to be other predisposing factors,’ ” he recalls. “So I started taking a critical look at horses’ rear feet, and it was like, ‘Wow, how come we haven’t paid any attention to this?’ ”

Inspired, Turner carried out a retrospective study in which he noted many of the horses that required therapeutic hock injections also had negative PADPs, he says. Today he recognizes the most common lameness caused by hoof imbalance is tarsitis, or hock inflammation.

While less common, the most serious type of lameness related to hind-limb hoof imbalance is tenosynovitis of the distal (lower) DDFT sheath, characterized by swelling, pain, and sometimes reduced blood supply to the tendon, he says.

Pezzanite’s research has also led her to pinpoint pain in the hock and proximal metatarsus (the upper part of the hind cannon bone), including the flexor tendons and proximal suspensory ligament, as being associated with neutral or negative PADPs, she says. Researchers on other studies have linked lumbar (in the loin—vertebrae L1-6 or L1-5 in some horses) and stifle pain to such hoof imbalances. “That isn’t surprising,” she adds. “These horses with negative hoof angles tend to stand more under themselves in the hind limbs, which I would imagine would change the loading of those muscles in the lumbar region and higher in the limb.”

As for mediolateral imbalances, Turner says he’s noticed that higher inside walls are associated with a higher incidence of lameness related to hock and/or stifle pain.

“In Western medicine, we have a tendency to diagnose the problem and treat that problem, but there are almost always underlying issues,” he says. “Take a step back, and look at these feet, because there is an association here.”

Checking for Imbalances

Pezzanite’s work has revealed that hind-limb lameness is “very prevalent, even in young animals,” she says. For example, in one of her recent studies, 60% of Western performance horses experienced at least low-grade hind-limb lameness within six months of starting training.

If diagnostic nerve-blocking confirms a horse has hind-limb pain causing lameness, she says she recommends the horse undergo radiographic imaging of the hind feet to see if imbalances might be playing a role.

While certain visual clues might point to imbalances, the only way to gauge such deformities is through radiographs, our sources say. X rays not only permit proper diagnoses but can also guide effective treatment by providing an accurate view of angles.

“A picture’s worth a thousand words,” Turner says. “You can see it; you can measure it; you can even tell how much to take off.”

He recommends taking lateromedial (from the side) and dorsoplantar (by lining up the radiographic beam perpendicularly to the frontal plane of the hoof) views of each hind foot to provide vets and farriers with a solid basis for therapeutic planning.

Viewing the Imbalanced Hoof

While the best way to confirm a hoof imbalance is to view the hoof from multiple angles on X ray, imbalanced hooves often give clues through their outward appearance, our sources say.

One telltale sign is the “bull-nose” shape of the front of the hoof wall as it curves over its internal structures in a clearly rounded form, explains Turner. From a back view, the frog can be seen protruding down past the sides of the hoof wall or the shoe, and it’s usually bigger than usual from getting so much stimulation against the ground. Meanwhile, the coronary band takes on an acute angle of 40-45 degrees from toe to heel, and the heel bulbs have a bended shape. The hoof wall at the heel is usually thin, he says.

Many horses with this imbalance are reluctant to lift a hind limb because of the pain it creates on the foot that’s still standing, Turner adds. They often show signs of pain when a farrier applies a hoof tester on either side at the angle of the sole at the heels.

As for mediolateral imbalances, hooves generally appear asymmetrical when viewed from behind, he says. The inner wall is usually more upright, and the outward wall appears more slanted toward the outside.

Treating Hind Hoof Imbalances

Therapeutic trimming and shoeing to correct hoof imbalances should aim to gradually realign the foot while providing support as long as the horse needs it, our sources say. Importantly, farriers should use the horse’s foot X rays as a guide. “Having those images to help make decisions is really critical,” Pezzanite says.

With negative PADPs, farriers should aim to shorten and round the toe to reduce strain on the DDFT and pressure on the heels and frogs, our sources say. 

The best treatment for hind hoof imbalance is often just letting the horse go ­barefoot—ideally at rest at pasture—for one or two months while benefiting from regular, skilled trims, says Turner.

For mild cases, therapeutic shoeing can allow horses to continue working as they regain foot balance, he says. Farriers should temporarily remove the shoes and apply a specific trim to reshape the foot while applying a frog wedge and keeping the foot moist for 24 to 48 hours using a poultice. Afterward, the horse can be reshod according to his X rays, with heel-elevating wedges if needed, says Turner.

It can take several trimming/shoeing cycles to get a horse’s foot back in balance because the farrier might only be able to adjust by a single degree per cycle, Pezzanite says. However, more frequent cycles can speed up the process, she adds. “If six weeks is typical, then reducing that to a really consistent, tight, four-week schedule can benefit a lot of these horses and help them make more rapid progress,” she says.

Meanwhile, horses can benefit from multimodal therapy designed to reduce inflammation and pain, she adds. Such therapy might include joint injections, oral or injectable medications for back pain such as corticosteroids, non-steroidal anti-inflammatories, and muscle relaxants, and physical rehabilitation exercises following consultation with a veterinarian and tailored to the horse’s individual disease processes.

Over time and with proper therapy, says Turner, horses should need fewer therapeutic joint injections. In fact, therapeutic interventions of the hind feet seem to have faster and more lasting effects than those in the forelimbs—probably because of their reduced weight-bearing, he adds.

“In my opinion, if you start correcting those issues in the foot, the other issues sort of correct themselves,” Turner says.

Follow-up should include hoof X rays every six to 12 months to keep an eye on the foot angles. “You just want to make sure you’re staying on target,” he says.

Take-Home Message

Hock, proximal metatarsal (tendon, ligament), and even lumbar pain sometimes result from imbalances in the hind feet, our sources say. While frequently overlooked, front-to-back and side-to-side hind foot imbalances can upset healthy biomechanics and lead to excessive pressure in various hind-end structures and, consequently, lameness. With X-ray-guided farriery to correct such imbalances, horses can gradually become balanced, sound, and less dependent on therapeutic joint or soft tissue treatments.