Using Self-Adjusting Palmar Angles to Treat Heel Pain

"How do we use the palmar angle (the angle the wings of the coffin bone make with the ground) to influence the mechanics (of the foot)?" asked Ric Redden, DVM, host of the 16th annual Bluegrass Laminitis Symposium and founder of the International Equine Podiatry Center in Versailles, Ky.

First, you have to define which palmar angle you are discussing--the one between the coffin bone and the ground surface of the foot, and/or the one between the coffin bone and the ground. On a barefoot horse, or one with a flat shoe, they will be the same; however, on a horse with a wedge pad or other non-flat shoe, they could be very different.

Next, consider the mechanics already at work inside the hoof. "Let's consider the support sling of the digit,” Redden began. “The deep flexor tendon cradles the navicular bone, pushing it against the articular (joint) surfaces of P2 and P3," he continued. "(The navicular bone) is attached by a very secure anchor to the semilunar crest of the coffin bone, which in turn is anchored to the wall with a very vascular, sensitive laminar network. The pressure exerted on all these structures is influenced by body weight, speed, footing, conformation, and the unique way in which each foot lands, torques, and loads.”

The foot’s equilibrium “is based on the fact that all members or structures of the support mechanism perform as a healthy, fully functional unit, he added. “When one member fails, the next one is challenged, and soon a cascading series of events is well on its way.

"When the palmar angle is lowered, pressure is applied to the tendon, bursa, apex, sole corium, laminae, and horn wall. The slightest adjustment greatly affects the circulation as well as sensitivity of the digit. The digital cushion, frog, sole, heel bulbs, and horn wall all function as an energy sink (dissipating the force, up to 2,000 pounds per square inch or psi, and heat of up to 110ºF generated by hoof impact with the ground) while protecting the sensitive structures."

Traditional Treatment

Most horses with heel pain don't like to move down hills or turn in tight circles, especially on hard ground, Redden said. He recommended treating these heel-sore horses with a "mechanical solution that simply takes the pressure or load away from the heel area, significantly improving the healing environment.

"You want to be able to let the horse shift his weight away from the hot spot," he explained. "It's amazing how fast they can heal if you relieve the hot spots and increase perfusion (blood supply). If you can get blood to the hot spots quick, Mother Nature runs in and does the rest.

"The traditional method of treating heel pain has been egg bars with slight heel elevation and a pad of some sort, all of which have merit but are very low on the mechanical scale," he went on. "The egg bar supports the tendon apparatus, not the heel, as it actually increases load on the heel--that's how it supports the tendon--but this slight benefit reduces load over the bursa (the cushioning sac between the navicular bone and deep digital flexor tendon) and bone. The flat surface that is extended past the heel locks the heel on the ground longer, increasing the length of the stance phase, and thus the toe is locked down too, especially with a long toe. The breakover is thus delayed as well.

“A wedge pad can act to decrease pressure over the bursa area also, depending on the relationship of toe angle, navicular bone angle, sole depth, and palmar angle,” he added. “However, the payback is a crushed heel.

"The reasons egg bars are so popular are that they are inexpensive, easy to apply, and most always offer immediate relief of pain to some degree--a horseman's dream. Unfortunately, they seldom if ever improve the quality and mass of foot, and most often slowly crush the heel tubules, reducing mass of cushion and wall strength. Sole depth remains constant (normally thin); therefore, the mechanics are not sufficient to offer a better healing environment (an increase in sole depth indicates increased tissue growth from increased circulation)."

New Theories

"Significantly raising the palmar angle of P3 shifts load away from the apex of P3, navicular bone, and laminar zone toward the heel and can have a profound effect on the hot spots," Redden explained of his therapeutic shoeing paradigm. This method of modifying stresses starting with the bony column and the inner hoof environment--not just the outer hoof capsule--has yielded improvement in many of his tough cases, he said.

"The goal is to have a self-adjusting palmar angle; the horse will be able to raise his palmar angle several degrees above the normal palmar zone of a healthy foot with similar conformation," he stated. "The palmar angle (angle with the ground) on a large majority of normal, strong feet will fall in the range of three to five degrees on front feet and five to eight degrees on hind feet. Unfortunately, a large number of performance athletes have various degrees of heel compression, which can be seen as a diminishing palmar angle." However, he added, what is normally seen and what is healthy aren't necessarily the same thing.

The shoeing system Redden developed for improving the heel environment is one in which the standing horse can adjust his hoof angle to a comfortable spot. "When the horse stands still, his heel is locked into position when shod with a traditional flat shoe," he said. "The palmar angle is locked in place with this shoe, therefore the healing environment and perfusion are severely limited, so you have hours and hours of standing still and not healing. My theory is that inactivity, the hours of compression, and no movement takes the heels away--not the farrier. If a shoe is designed so that it only works when the horse is moving, and movement is the greater part of his day, then great--things will happen. But if he doesn't spend most of his day moving, then things won't change. Whatever the shoe is, it has got to give the horse adequate perfusion, otherwise any healing is limited.”

However, if you shoe the horse so that breakover is moved back to directly beneath the center of articulation of the coffin joint (which will be farther back for horses with a broken-back hoof-pastern axis, and farther forward for those with a broken-forward axis such as moderate to severe club feet), he said that the horse can sleep standing up all day without moving and still provide a better healing environment. The little movements of balancing and conscious weight shifting change the load on the inner structures, effectively massaging the circulation within the foot that is necessary for healing and tissue growth.

“The venograms show clear evidence to support this concept; it’s not just a theory,” Redden said. "Instead of pushing the heel into place with a wedge, we're letting him pull his foot into place with the rock and roll shoe. It's 24-hour healing."

This shoe is one Redden developed to ease breakover for laminitic horses, and he has broadened and tailored it for horses with various hoof problems. The bone angles with a properly tailored shoe might be the same as those with a wedge pad, but they are created by the horse using his body weight and balance to influence the tendons, and not compressive force on the heels brought on by static shoes. This, along with the air space beneath the heels of the shoe, spares the blood vessels and digital cushion in this area and thus allows heel growth to improve.

See a before/after correction with this shoe here.

He noted that this shoeing style is useful in horses with crushed heels, long-toe/low-heel conformation, heel pain, sole pain from internal bruising (such as crushing of the sole under P3), pedal osteitis, laminitis, toe cracks, thin soles, and quarter cracks. "You need film (X rays) before and after shoeing these horses; otherwise, you don't know what you've done," he cautioned.

"Give Mother Nature a chance to do her thing simply by removing the handicaps, and things start to happen," he concluded. "I like to think of healing with the hope of a cure; many horses can heal sufficiently to relieve the hot spots, but are never fully cured of the original problem."

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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