Steppin' Out: Hooves From An Artistic Perspective Part VI: Ongoing Debates

Hi there, we're back again with this twelve-part series exploring the equine foot as it relates to sculpture. All the "backstory" in the previous Parts I-V was necessary to understand why we need to shape our sculpture's feet a certain way. When we fall back on his evolutionary biology, it's more likely we'll create responsible depictions of our admired subject rather than unwittingly validating harm.

So let's explore some of the ongoing debates about the equine foot in order to stuff our heads with even more curiosities to ponder. Let's go!…

Debates

While the study of the equine foot could be said as ongoing since the past 200 years, it's only been relatively recently that modern science has turned its eye onto it. So despite our long relationship with this animal, we aren’t anywhere near a thorough understanding of his complex, absolutely unique, variable, and enigmatic feet. As a result, a multitude of conflicting theories and methodologies swarm the subject, sometimes overlapping and sometimes contradicting each other into a bewildering arena of study…and sometimes making our artistic choices difficult.

But because of the current science, the nature of equine podiatry is changing, and it seems for the better. Fresh ideas and surprising results are forcing a re-examination of the equine foot, and it's currently an exciting field of study as a result.

But we have to be careful, too. There are some involved who have a vested financial interest in their concepts and related products, creating a conflict of interest that begs objectivity. And sometimes “new” theories are really a skew of an older one so that the “discoverer” can claim credit without infringing on patent or copyright laws (Duckett, 1997). Sadly, too, some of the methods endorsed by these proponents can actually cause harm. For example many of David Duckett’s FWCF principles have been  plagiarized. While most of his concepts have been confirmed by science or practical experience, they’ve also been misinterpreted or misapplied in the stampede to “brand” a variation. Some of these misinterpretations focus on his “Duckett’s Dot,” which has been confirmed in studies to be the center of weight-bearing in the equine foot; it’s a point of reference for the foot that never changes, which his method uses to balance the hoof from the middle of the foot to the periphery. Yet some have renamed this "Dot" and claimed it as their own.

Other misinterpreted Duckett principles relate to the bridge, the pillars, his center of rotation and mass, and his conceptualization of four-point weight-bearing areas of the foot. However, nearly all the variations spun off from his concepts fail in application because the information isn’t being applied correctly due misinterpretation. Dr. Strasser is also plagued by the same effect because unqualified or irresponsible people inappropriately apply her methods (Simons), usually resulting in lame horses. Her methods are published only in German journals and seldom are translated into English, except for two books that are too generalized to be considered professional references, yet are used by untrained individuals with inadequate or absent training. In short, it’s rather a mess out there as theories and individuals jockey for position in the rapidly evolving understanding of the equine foot. So artist—beware.

Even some of the incoming data is confusing and subject to sharply contrasting interpretations. One such issue is the ongoing debate over the role of the lamellae. While data consistently demonstrates that forces from the limb or from the ground do not completely pass from the coffin bone to the wall, just how that happens is subject to differing opinion.

For example, one hypothesis asserts that forces from the ground do not pass directly from the coffin bone to the sole, which isn’t equipped to deal with loading by itself. Rather, the posterior part of the foot strikes the ground first, dissipating much of the initial energies through expansion and through the participation of the digital cushion, frog and bars. The quarters and sole around the toe area transmit forces to the wall, which compresses along its tubules, as energies are transferred again from inside the wall to the lamellae and then to the coffin bone. The coffin joint then flexes, initiating the tendons and ligaments, resulting in a coffin bone that doesn’t exert undue pressures on the sole, meaning that the sole should support very little weight or impact (Pollitt). However, this concept cannot account for the thick soles and other structural and functional differences inside the foot found in feral or barefoot horses. Indeed, why does the toe callus exist on healthy barefoot? The study also doesn't adequately account for the soundness of its test subjects.

In contrast, an opposing proposition maintains that the only purpose of the lamellae is simply to function as a protective “gel cushion” during impact and to produce wall, and it’s the other mechanisms in the foot that are more intended to bear the forces of weight and impact, specifically the posterior and palmar foot (Bowker, Ramey). Even so, this concept doesn’t account for the profound difference between equine lamellae and that of other hooved species. Shouldn’t there be a mechanical reason for the secondary lamellae found only in equines?  And how does the idea explain the devastating “sinker” effects of laminitis?

Altogether, however, the current ideas on this can agree on two things—(1) the lamellae should not bear the full brunt of weight-bearing, and (2) the posterior part of the foot is a key component in impact management.

An additional debate is whether feral or wild foot physiology can, or should, apply to domestic hooves. Indeed, both kinds of horses exist under very different conditions, essentially defined by the presence of a fence. Also, natural selection favors strong-footed horses in the wild whereas the domestic population is largely bred for “conformation,” an arbitrary set of standards created by people, not nature. And if our conception of foot function has been wrong or incomplete all this time, then we haven't been properly selecting for quality feet all this time either. Indeed, quality feet aren't often on the "wish list" for breeding decisions as a specific requirement.

There’s also the question of whether wild and feral principles that seem to depend on hard feet and desert conditions can be applied to all the breeds, particularly those evolved on soft terrain (like northern breeds) or those that are completely man-made (like drafts), since the genetics to produce a “desert-type hard foot” may simply not be within the gene pool. Then again, if we've been misunderstanding the foot all this time, how much of this is nature and how much is nurture? How could our management of these breeds be changed to create a better foot? Management that would have to begin Day One as a foal, too.

Until we know more objective facts about the equine foot, these debates will continue. Happily, technologies are advancing, giving scientists better insights and means to gauge function and effect to tease out the spectrum of possibilities and consequences to this compact and complicated biological mechanism.

This brings us to the debate on what exactly constitutes a good foot (which will be discussed in greater detail starting with Part VII), not only because there are so few objective examples in the domestic population, but because we don't know enough to rigidly define its parameters into a single operating paradigm. For example, the issue of a contracted foot can be ambiguous because it’s endemic in the domestic population, implying that nearly all the “good” domestic feet used as idyllic examples may actually be exhibiting a degree of contraction (Strasser). In other words, what most consider to be a normal, healthy shape in the domestic foot may actually be pathological. Indeed, the feet depicted in the popular Ellenberger anatomy book, An Atlas of Animal Anatomy For Artists are contracted. What's more, if the assertion that soft terrain accelerates heel contraction since it cannot stimulate the foot through expansion like a hard surface (Strasser), then domestic feet may be far more contracted than ever imagined. 

A further debate examines whether the coffin bone should be ground level at stance, or have an elevated posterior of about 3˚- 5˚, meaning the horse literally walks on tiptoe (Ramey, 2006). Interestingly, neither feral, wild nor domestic feet offer clear answers, since outwardly sound individuals from all these groups appear to exhibit a spectrum of coffin bone orientations within those parameters. It’s also unclear if the debates are talking about the same thing—the solar surface of the coffin bone, or the outer rim of the coffin bone? Remember, the coffin is shaped like an upside-down bowl with a pyramid on top, but only contacts a flat surface along its distal rim. Are the discussions referring to the solar vault in relation to the dorsal plane, or to the orientation of the distal rim to the dorsal plane (Cook)? 

Insufficient imaging technologies cloud our view, as well. For example, the distal rim is often lost in x-ray, leaving only the thick middle portion to be seen, while sagittal sections of the leg in dissection only reveal this middle aspect. But these middle-section views (which are so common in anatomy books) only tell half the story since the orientation of the distal rim isn't depicted. Nonetheless, those who support an angled coffin bone at stance claim this elevation is necessary for the proper arch of the foot so that when the arch is loaded, the coffin bone has room to become ground level under the forces of impact, spreading support over the entire distal foot and optimizing all the mechanisms that absorb and transform those energies (Ramey).

On the other hand, those who believe the coffin should be ground level at stance point to the anatomy of the coffin bone itself, which naturally sits flush with a flat surface (Strasser). They also suggest that a ground-parallel orientation aligns the bones properly and balances the pulling forces of the laminar corium and the deep digital flexor tendon, minimizing the pulling effects of the latter on the toe's laminar corium, arguing that a pointed coffin bone compels this tendon to pull upward, stretching and traumatizing the lamellae, particularly at impact. It’s also thought to maximize solar support and frog ground contact. Further study is necessary in this area to shed some definitive light on what the optimum conditions truly are, or if perhaps there’s a spectrum of acceptable circumstances for the coffin bone’s orientation within the foot. 

But one wonders if these two camps are saying the same thing, only in different ways because if we miss the coffin's distal rim, which is flat, in lieu of its central mass, which is angled, we won't see that the coffin bone is both level and angled at the same time! Hopefully better imaging technologies will become available to resolve this confusion.

This brings us to the debate over the hoof wall’s optimum angle, an argument that has existed since Xenophon’s time (Heymering). Essentially, while everyone agrees the coffin bone should parallel the dorsal wall, there’s no agreement as to the correct orientation of the coffin bone itself, thus there’s no agreement as to the proper angle of the wall. Indeed, very different numbers are produced whether the coffin bone is ground-parallel or tipped. For instance, the fore coffin bone is angled at about 45˚ and the hind coffin bone is angled at about 55˚, so if it’s ground-parallel, then the wall must match these angles as well. However, if the coffin is tipped, this means the wall’s angle must be altered in kind, placing the fore feet angle up to about 50˚ and the hind foot angle up to about 60˚. Added into the mix are the steep angles on mules, donkeys and half-asses, and some zebras, and since we know even less about their mechanics, we aren’t able to compare horse foot function to theirs.

Also clouding this issue is that many studies on wall angles have been surveyed incompletely, with no regard for horsemanship or management, or how weight-bearing and balance changes at stance alter the orientation of the bony digits inside the hoof. There’s no agreement on how different hoof angles alter the function and structure of the foot either. If we can’t define what a healthy foot looks like or how it functions, how can we begin to create a comparative baseline? We also have no idea as to the discomfort level any given horse may be experiencing due to foot structure, so what may be assumed to be normal and good might be considered subjective. Indeed, it seems that domestic feet have appeared sound within a wide range of wall angles and foot development, which begs the question of "sound." So, again, artist—beware. Keep an open mind because the hoof wall debates and related discussion clearly illustrate just how much we really don't know. 

Still, we artists still need some idea on how to sculpt the feet! To that end, here are some tentative ideas to ponder for our sculptures, bearing in mind that further study may change these concepts over time.

For starters, regarding the coffin bone debates, some argue the correct foot has a 45˚- 50˚ front wall angle and a 55˚- 60˚ rear wall angle, as well as a very low heel, a comparatively long toe, and a straight coronet 30˚ to the ground, which is claimed to automatically orient the coffin bone on a ground-parallel alignment, based on x-rays of “healthy” domestic feet (Strasser). However, traditional farriery favors a front foot angle of about 54˚ and a hind foot angle of about 57˚, based on a long history of conflicting studies (Heymering, Simons, Clayton). On the other hand, data collected from feral and wild studies seem to place the front foot angle at about 50˚- 54˚ (sometimes as high as 60˚) and the hind foot angle at about 60˚- 65˚, though there’s variation based on individual differences and lifestyle (Jackson, Ramey).

Therefore, at this time, the basic range of hoof angles that can be thought of as “generally acceptable” is 45˚- 60˚ for the forefoot and 55˚- 65˚ for the hindfoot. However, hoof angle also can be a function of age, since foals often have steep wall angles (and upright pasterns) from as steep as 70˚ in the fore foot at about three months (Redden) to 60˚- 65˚ in the fore foot at sixteen months (Heymering, 1990). 

And artists also should know that determining the correct hoof angle based on the pastern, shoulder or bony alignment of the digits has proven to be unreliable due to their inconsistency at any given moment or circumstance (Heymering). However, if the foot and digits appear to be optimal (as best we can judge), most professionals agree that using the pastern angle (the angle of the 1st and 2nd phalanxes from the middle of the pastern joint, through the middle of the coffin bone, which the wall should parallel) currently is the best means to determine the optimum wall angle, regardless of the proximity of the frog to the ground (Heymering). According to repeated data (Clayton, 2001), trimming the foot to lower angles (long toe-low heel, or LT-LH) doesn't achieve a smooth, springy and long, low “grass clipping” stride. Quite the opposite, in fact. The idea that hoof angles regulate the gaits may also be false, since they seem more prone to control breakover than landing (Clayton, 2001). Plus, the concept of aligning the 1st and 2nd phalanxes to the coffin bone has been called into question, as desirable or even possible, since some reports claim this bony alignment rarely is straight, and actually should not be straight (Strasser).

This brings us to the conflict over the bony alignment of the 1st and 2nd phalanxes to the coffin bone. Conventional theory using x-rays claims this alignment should be based on an angled coffin bone to create a straight line through the three digits from the center of the pastern joint to the center of the coffin bone (and the wall should match this angle). However, others claim that since the equine foot was meant to absorb shock, a straight-line alignment is far less effective (and prone to injury) compared to a slightly curved alignment that acts as a leaf-spring (but what traditional thought regards as broken-back axis)(Strasser). This line of thinking believes the steep and straight-lined angle of the digits actually is a pathological structure born from a tipped coffin bone and overly high heels. The issue is unclear since none of these alignment studies using x-rays seem to have accounted for the shifts in weight-bearing that are characteristic of the horse, even in stance. Indeed, a horse simply raising his head, or lifting a foot, or standing on non-deformable surfaces, squirming because of a fly, or shifting his weight to the hindquarter or forequarter can create vastly different results in the alignments and angles of the foot bones. A horse rarely stands stock still, with even balance on all four feet! This seriously compromises the studies regarding foot bone angulation, which means many of the underpinnings of equine podiatry as suggested by current research could be incomplete. It’s hoped that future studies will seek to standardize the horse’s stance and balance before taking images and making deductions based on them.

There’s also debate about the role of the frog. Some assert that the frog isn’t a factor in hoof expansion and weight-bearing and so it never should contact the ground (Klimesh). On the other hand, others claim it’s an essential component of those mechanisms and should have ground contact at all times (Strasser). However, it’s hard to tell if these two camps are talking about the same thing, since the “no contact’ argument doesn’t seem to clarify if that claim applies to stance or loading, or what type of footing is involved, nor does it seem to define adequately what a healthy frog looks like, either. Adding to the confusion is that domestic, feral, and wild hooves seem to provide equally sound feet with different frog configurations. The frog also figures into the debate about the orientation of the coffin bone insofar as those who support a tipped coffin bone claim this allows room for a well-developed frog. Subsequently, the frog has found its way into the discussions of the wall. Those who believe in a hoof with a high wall angle and a frog that doesn’t contact the ground argue that the foot must be made “pathological” (low-heeled and less than 53˚) in order to achieve ground contact with the frog. Another controversy is the practice of trimming to the widest point in the frog as a therapy for collapsed underrun heels, which advocates applying heel wedges to recreate correct bony alignment. However, the application of this approach is not only ambiguous, but also most cases will result in bruising and a broken-back axis to the bony alignment of the foot.

Similarly, debate exists regarding proper heel height, with feral and wild feet providing conflicting examples: some having very low heels, some having practically no heel at all, others having much higher heels, and everything in between (Ramey, 2005, 2006). Regardless, the commonality seems to be very strong and well-developed heel buttresses and bars with a fully developed posterior foot, indicating heel-first landings and a mature circulatory, sensory, and energy management system inside the foot (Ramey). Nevertheless, traditional applications use toe angles to determine proper balance and foot orientation, whereas unconventional methods use heel height for these applications, which creates its own set of debates (Ramey, 2005, 2006)(Strasser). In this case, heels are lowered to be about 1 inch or with the bulbs directly on the ground with no concern about the dorsal wall’s angle. Supporters claim this reinstates the proper function and expansion of the posterior foot because too much horn in the heel area (wall, buttress and bars) will inhibit it. In this paradigm, there’s a difference between a pathologically low heel and a correct low heel, in that the heels on a diseased foot will be underrun and contracted, whereas the heels on a correct foot will be low and oriented straight down (Simons) or match the front angle of the wall. It may be that heel length is dependent on the lifestyle and peculiarities of the individual’s situation and, hopefully, further study will provide more definitive information.

Dispute also exists over whether it’s normal or not for a horse to be sore after a trim (particularly to lower high contracted heels or transitioning from shod to barefoot). Those who assert soreness is normal claim that a foot “dulled” by shoes, or unhealthy structure has an impaired circulatory and sensory system, making it numb to the pain it should be experiencing. In essence, the soreness after a corrective trim is simply the “awake” foot feeling the healing forces of the trim, which is only a transitional period as it heals itself and reforms (which may take up to a year)(Strasser). On the other hand, others believe a horse never should experience post-trim soreness since this not only indicates harm done to the animal, but also is a reversal of any positive steps that could fix the condition (Ramey). For example, if heel contraction can be interpreted as the foot’s defense mechanism to protect the underdeveloped systems within the posterior foot, overzealous trimming of the heels to lower or “open them up” actually causes more posterior pain, exacerbating the pre-existing condition (Ramey).

Annoyingly, this is a classic example of multiple treatments working on some horses some of the time, leaving each camp to believe their approach is the correct one in every situation. Add to this discussion on how to achieve the desired length of the hoof capsule, and things really compound. While most ideas agree that a short hoof capsule with short toes is the ideal structure of the wall, attaining this result has polarized the industry. On one hand, some promote the aggressive trimming of the foot to achieve those dimensions immediately, regardless of the internal situation (such as coffin sinking and thin soles)(Strasser). On the other hand, others support a gradual modification of the foot to those specifications so that the horse is never sore and can continually move to promote healing (Ramey). More research is needed on this subject, because a working paradigm may remain elusive unless we have clarity on these issues only because they speak to almost all we know about the equine foot.

In a nutshell, all these debates basically stem from the fundamental differences between what’s known as the “Strasser trim” and the “feral trim,” two dominant views of the equine foot that lie outside of conventional thought, which brings conventional theory into the mix. Dr. Strasser developed her approach specifically for rehabilitation of unsound domestic hooves, which entailed trimming away damaged or undesirable material to reinstate proper blood circulation and weight-bearing so that the foot could heal itself. Special footing usually is involved, such as rubber mats and submersion in water to soak and soften the hoof wall to allow it to expand more readily. To reinstate quickly or even amplify the “hoof mechanism,” the Strasser trim pares the sole to create a concave solar surface (often aggressively), in the belief that a thin sole provides less resistance to the wall’s necessary alternating expansion and contraction to increase circulation. The bars also are shortened to end halfway down the frog and to a height of about 7/16 inch, with the “seat of the corn” sloped to meet the bars. “Opening cuts” or notches also are made if the heels are contracted to help them expand, while the heels are trimmed to about 1 3/8 inch to angle immediately the coffin bone to a ground parallel orientation. The hooves are trimmed flat on the bottom so that the coronet is at a 30˚ angle to the ground and the front hoof angle is about 45˚ and the rear hooves are about 55˚, to orient the coffin bones on a ground-parallel orientation, also forcing the pastern into a lower angle to create a long breakover. If there’s a flare at the toe, it usually is “backed up” vertically until the outside aspect of the wall meets the ground. The Strasser trim also can be implemented on sound feet to a lesser degree. 

In contrast, the feral trim is intended to transform a shod hoof into a barefoot hoof, trimming the foot so that it gradually develops into those forms seen on feral feet, yet striving to keep the horse comfortable at all times. The sole is untouched and encouraged to grow into a thick, dense and calloused shield since it’s believed to be an important weight-bearing and supportive structure for the internal foot. It also is believed that solar concavity will naturally occur over time as the sole grows, shortening the wall, elevating the coffin bone, and removing peripheral loading. The bars are either left alone or trimmed to the level of the sole or slightly higher, but rarely in ground contact, and are considered an important component for circulation and weight-bearing. The heels usually are not trimmed aggressively to reorient the foot quickly, but are allowed to gradually reform themselves as the foot reforms itself, with increased motion and deformable footing playing integral parts in rehabilitation. The hoof isn’t trimmed to a 30˚ hairline or to 45˚ or 55˚ angles, but allowed to reform itself over time and with exercise. Instead of paring down or notching the heels to reverse contracted heels, a “mustang roll” is used to remove the long toe lever to ease and shorten breakover so that the stride can lengthen to automatically initiate heel-first landings, which naturally will “open up” the heel over time.

Ultimately, one thing everyone can agree on in almost all cases is that motion is the key to the equine foot. Even so, what the debates really appear to be orbiting around is the concept of how to achieve that proper foot function, by either carving the foot into the proper form to create proper motion, or that proper motion is what creates a proper foot. In short, it's a literal “which came first, the chicken or the egg” dilemma. And what makes things particularly difficult is the persistent bad state of domestic feet, which fails to provide us with an objective view of cause and effect. Even the study of feral or wild feet doesn’t shed light on this quandary since we’re unable to track a foot’s development over time, under different situations. Some comprehensive and scientific methods may be necessary to illuminate this problem; until that happens, we may simply never know which came first, the pain or the poor shape.

Sum Up

After all this, it’s clear that while the horse’s foot may seem simple on the outside, there’s a whole lot more than what meets the eye! And because scientific equine podiatry is still relatively new, we have seen only the tip of the proverbial toe. We can learn a valuable lesson from the horse’s foot—strength is not achieved through rigidity, but through flexibility, symbiotic function, and adaptability. Continued research will shed more light on the equine foot to help us distinguish which are positive interpretations and which are negative. 

But it seems like an overwhelming goal! We can’t even explain why feral feet don’t exhibit flares, contraction, cracks or laminitis, or any of the pathologies that are typical of the domestic foot. We don’t even know why wild or feral horses rarely suffer many of the maladies domestic horses do, such as colic, nutritional deficiencies, worms, foaling problems, etc. Is this because weakened horses are selected out so we never see them, or are they trying to tell us something important? Undeniably, what little we’ve learned from wild and feral horses so far has proven provocative and ground-breaking. But the habitat for them is rapidly diminishing, and feral horses as well as the Takh and other wild equines are threatened. Unless we work aggressively to save them in their natural state or learn what we can now, what information will be lost when they’re gone? Will our domestic friends be forever suffering within our fences? 

Personally, I believe each camp holds a piece of the puzzle, though I believe the feral foot has more to teach us about soundness than we may currently realize. And practically speaking, I suspect the equine foot functions much like a DanskoTM clog shoe. Thick, shaped soles and developed posterior foot with the protective "wall" of dense "leather" in front, with all the bony and squishy fleshy structures nestled inside, all working together to reinforce and buffer. So quite literally, equines are wearing clogs! *clop clop clop*

I also believe all the components in the hoof are there for an evolutionary reason, and therefore all are equally important. Subsequently, no one part serves one function, nor does so in isolation, but all parts serve multiple, interdependent functions at different times, forcing our empirical methods to take a more holistic approach. We have to remember that 65 million years of evolution created something efficient and absolutely unique for a reason, something the sum of its parts. Finally, I believe the equine foot has secrets about its function that have yet to be revealed, simply because scientific equine podiatry is still developing technologies to peer into the foot with greater clarity. 

Truly, the equine foot is a marvel of biological design and is unique in the animal kingdom. No other animal has a foot like an equine. This brings into sharper focus why an equine artist should give it the conscientious attention it deserves. In the next installment then, we’ll evaluate what's believed to constitute a quality foot as it's currently conceived so we can make more informed choices in the studio. Until then, put your best foot forward!

"Education is the most powerful weapon which you can use to change the world." ~ Nelson Mandela

Steppin' Out: Hooves From An Artistic Perspective Part VI: Ongoing Debates

Steppin' Out: Hooves From An Artistic Perspective Part V: Mechanics Cont'd

Hello again! We're back in this twelve-part series exploring the equine foot as it relates to sculpture. We're in the thick of mechanics in this Part V, so let's just dive back in…

A New Interpretation of the Lamellae

The weight-bearing ability of the lamellae has long been debated and while new data is providing more insightful information, its interpretation is still being considered. But while the exact meaning of this new research is still being researched, what is clear is that it’s challenging conventional practices to the point of requiring a rather significant paradigm shift in the management practices of domestic equines. The good thing is that it’s certain that research will continue in this area, and new information may prove pivotal to improved husbandry of the domestic foot. Nonetheless, let’s first consider the lamellae of feral or wild hooves so we can gain a basic perspective.

To start, the lamellae are thicker in the feral foot and often less in number (Ramey, 2005). Their microscopic fiber orientation also isn’t “pulled down,” as is often the case with domestic feet, but is at right angles to the coffin bone and hoof capsule (Pollitt), largely due to the thick soles that support the coffin bones high in the hoof capsule that orient the coronets at the top of or just below the apex of the coffin bone. This creates unrestrained motion of the coffin joint, freed up lateral cartilages, and short hoof capsules with quick breakover. The lamellae also are closely meshed in feral feet, tightly attaching the wall to the coffin bone down the entire length of the wall, so flares, distortions or cracks are rare. 

While the study of feral and wild feet as it applies to domestic feet is debatable, one thing it clearly and consistently has demonstrated is that the lamellae were never intended to manage or mediate impact, or suspend the entire weight of the horse by itself (Bowker, Ramey, Pollitt). This is a direct contradiction of the conventional belief that the lamellae act as a "leaf-spring" for the bony column and so should bear the majority of weight and impact. Granted, the lamellae are tough and uniquely designed in comparison to other hooved mammals and, yes, they do play a key role in foot function, clearly seen when they fail (such as with founder). Yet we have to remember that equines are unlike any other hooved mammal—they are solipeds that are large, heavy cecal-digesting herbivores dependent on extended speed on varied terrain for escape, a unique niche in the animal kingdom. This may be why their lamellae are unique.

It’s becoming apparent that the lamellae may play multiple roles in foot function (as suggested by the hemodyanmic theory and the Suspension Theory of Hoof Dynamics™, discussed later) and therefore are to be assisted in the support of the coffin by other (and better) weight-bearing mechanisms within the foot. One of these primary assistants may be the sole, especially the toe callus, since its texture and location make it a far better design for the task than the lamellae (Ramey, Bowker). Even better than the hoof wall. Coincidentally, it’s been reported that a well-developed toe callus is denser and tougher than the wall’s horn (Ramey). And any corium “crushing” a thick sole has been accused of causing has not been exhibited in feral or wild feet, even in those specimens with soles an inch thick (Ramey, 2005).

Other assisting components that feral and wild feet seem to exhibit are the bars, frog, digital cushion and lateral cartilages, as well as the foot’s internal and external arches, all of which are activated by loading. Overall, it may be this communal support that allows the foot to function properly, and not by the single actions of the lamellae.

Another reinterpretation of the lamellae is a visa-versa switch, in that it’s not the wall that assists the lamellae in weight-bearing, it’s the lamellae that assist the wall. To illustrate, the wall works best when attached firmly to the entire length of the coffin bone and sole, but it can only do that when the lamellae are strong, healthy and tight. If this essential adhesion is amiss, one result may be cracks and flares. Put another way, without the assistance of a strong lamellae layer, the wall is simply unable to bear forces properly or to hold its conical shape, and so it fails (Ramey, 2005).

This also means the lamellae require correct breakover to maintain their adhesion and function at the toe, which undoubtedly sustains enormous pressures at the moment of loading and breakover. Without proper lamellar adhesion, the wall at the toe can be stretched, producing flares, infection, and lamellar wedges rather quickly (Ramey, 2005).

A possible confirmation of this reinterpreted perspective is the high percentage of mechanical lamellar failure, or "mechanical sinker," the gradual sinking of the bony column within the hoof capsule paired with the misplaced point of breakover in almost all domestic feet. This effect is typically due to the presence of a shoe, a "peripheral loading" device (Bowker), and aggressively paring down the sole. 

Laminitis is often cited as the second biggest killer of domestic horses. While its causes are still ambiguous and may have multiple triggers, implicated in its onset may be traditional trimming practices that pare down the sole, bars and frog, forcing the wall and lamellae to sustain forces they were never meant to bear. Alarmingly, conservative data collected in studies of low-grade laminitis suggest that as many as 46%-50% of domestic horses suffer constant unnatural trauma to their lamellae (Vialls, 2007). Some researchers claim that every domestic horse will experience at least one bout of low-grade laminitis during his/her lifetime, but because the symptoms are so generalized, it won’t be recognized as a laminitic attack. Studies as early as 1910 have shown that diseased structural changes can occur in the lamellae without exhibiting pathology on the hoof for some time, or at all. Indeed, low-grade laminitis can masquerade as a number of common ailments in domestic feet, to include foot tenderness, gait abnormalities, choppy stride, flares, bruising, thrush, white line disease, lamellar wedges, abscesses, underrun heels, flat footedness, and even an altered resting stance and behavior problems (sometimes it can be misdiagnosed as navicular syndrome).

Low-grade laminitis also tends to bruise the coronary corium during each bout, which grows downward to form orange or ochre colored bands encircling the wall, or in patches on the wall, which most easily are seen on pale hooves (thought this effect can be seen on dark hooves in extreme cases)(Vialls, 2007). This bruised portion of the wall may compromise lamellae adhesion, which may explain why shod hooves that suffer chronic low-grade laminitis have the most bruising and flaring right above the nails on the wall. 

Painters, beware!

Horses suffering from foot pain, either caused by low-grade laminitis or palmar tenderness, tend to adopt typical resting postures and footfalls. In an effort to relieve foot pain, typically on the forefeet, a horse will bring his hindlegs underneath his belly, much like during a laminitic attack, and also bring his forelegs under his belly, often bending at the knee slightly (to produce an artificial over-at-the-knee stance) to relieve pressure on the posterior part of the front foot. As the condition worsens, this stance becomes more obvious and begins to influence footfall and movement. Symptoms include stifle malfunctions, tightness in the hamstrings (the Semitendinosus and Semimembranosus muscles), hock unsoundness, spine and hindquarter soreness, girthiness (from nerve dysfunction), saddle fit problems, malfunction of the Stay Apparatus, and arthritis in the legs. 

As the syndrome amplifies, the horse adopts a "box stance," as though he was standing on a circus pedestal, creating reversed angles in the front feet and hind feet (high front angles and low rear angles in both pastern and hoof)(Ware). In terms of motion, such horses typically exhibit a resistance to forward motion as well as chronic tension throughout the body, along with stumbling, running-out when jumping or bucking when landing, or a resistance going downhill, or doing so sideways (Ware). 

Another symptom is toe-first landing, which is common in the domestic population (Ware, Bowker, Ramey). This may explain the reputation of bad feet in the Thoroughbred population. Aside from a paradigm that selects only for one trait (speed), the  management practices of racing Thoroughbreds sets them up for a lifetime of foot problems. Specifically, at too young an age these horses undergo extreme levels of performance and nutrition along with shoeing and trimming (usually for a low heel-long toe structure in an effort to increase leverage, i.e. speed), which are biologically inappropriate for their age. Many yearlings already are shod, even when their feet and their coffin bones aren’t past the foal stage of growth (Ware).

Additionally, toe-first induced foot pain may be implicated in the common occurrence of tendon and ligament breakdown in racing Thoroughbreds through the “whip lash” effect this type of footfall creates (Ware). Since toe-first landings bypass all the biological mechanisms of impact management and proprioception (Bowker, Ramey), footfalls are uncoordinated and more forceful than normal, causing a “snapping” action with each step that traumatizes the leg’s tendons and ligaments unnaturally (Ware). 

But this does present a quandary for artists—too often design considerations can force the creation of sculptures with implied toe-first landings, either for aesthetic or logistical reasons. Admittedly,  it does create a more graceful composition. But it cannot be ignored that perfectly sound horses can temporarily assume such postures and footfalls during “the moment,” which a sculpture could capture. Perhaps a better understanding of a healthy foot structure and recreating that in our sculptures can compensate for such design demands.

For these reasons, road founder may not be caused by the road itself, but by the peripheral loading caused by a trim or shoe that makes the wall the primary weight-bearer by lifting the sole, bars and frog off the ground surface, forcing the lamellae to shoulder loading and breakover almost exclusively (Ramey). Add to this the persistent underdevelopment of the foot, sedentary stalling, the high levels of performance and nutritional deviations, and it shouldn't be surprising that foot problems are pervasive in domestic populations.

In addition to low-grade laminitis, another chronic problem in domestic feet—and therefore in art—is the gradual sinking of the limb’s bony column in the hoof capsule, causing the coronet band to rise up onto the 2nd phalanx (Ramey, 2006). Mimicking a laminitic attack which has caused the coffin to sink towards the ground, this "mechanical sinker" encases the coffin joint within the hoof, flattens the thin soft soles (flat feet) and causes the hoof capsule to become abnormally long (often with a long toe and underrun heels) while "crunching" the lateral cartilages together. Caused by overzealous paring down of the sole (and frog), often to "clean it up" at every trim, this practice removes the depth of dense callous the foot requires (Ramey, 2006), keeping the sole chronically too thin and soft. Pair this with peripheral loading and there's nothing to stop the bony column from sinking into the hoof capsule. Even so, this sinking effect is a gradual process that can take years to develop and largely goes unnoticed until the horse actually exhibits overt unsoundness (Ramey, 2006). Unfortunately, this means that most people regard such feet as sound and thus put these horses through regular performance demands when, in actuality, their feet are hampered by an ongoing syndrome that compromises their comfort and athleticism.

Likewise, many sculptures exhibit this kind of foot, only because the artist mimicked what was commonly seen in references. In this way, an artist can inadvertently portray pathology, illustrating the importance of knowing what a quality foot is all about. 

In contrast, when the coffin bone is oriented high in the hoof capsule, with its peak at or just above the coronet, the sole can be thick and the frog fully developed, resulting in a short and “dropped” hoof capsule, one far shorter than most domestic feet. Just because tissue is dead and cornified doesn’t mean it’s unnecessary.

Indeed, conventional thought of yesteryear perhaps recognized this syndrome, as old-time farriers advised the pulling of shoes for part of the year so that the foot could fix itself during the off-season (Ramey, 2006). Ironically in our modern age, that idea somehow got lost in general practice, perhaps because the animal shifted from being one of utility to that of leisure or sport, with an impetus to keep shoes on year 'round. As a result, most domestic feet possess this problem to some degree, and it’s reported to be especially chronic in sport horses (Ramey, 2006). It’s also the reason why hooves appear to get longer as the horse ages, with old horses being “long in the tooth and hoof” (Ramey, 2006) since it can take years for this syndrome to manifest fully.

Thankfully, we artists can avoid recreating this situation by paying attention to the length of our sculpted hoof capsules and the depth of the collateral grooves and solar concavity, and to where the coronet bands are oriented on our sculptures’ imagined bony columns. Remember, the sole should be vaulted, and the frog and bars at the base of the vault, with the collateral grooves about 5/8 inch to 3/4 inch from the ground at the apex of the frog and about 1 inch at the heels, and the coronet should be level with, or just below, the coffin bone (Ramey, 2006). If we can “see” where the coffin bone is within the sculpted feet, using all these aspects as guides, we can evaluate the proper foot structure for our sculptures.

Furthermore, if our sculptures’ internal anatomy is correct, then hoof capsule lengths should be scaled to match what’s seen in life: between 3 inches and 3 1/2 inches at the toe for an average horse, with heel heights about 1 inch (Ramey, 2006) (though it should be said that heels vary quite a bit among individuals and lifestyles). And don't forget the beveled toe!

However, it should be mentioned as a caution that the exact orientation of the hoof capsule in feral or wild feet is subject to debate, since the specimens were not x-rayed alive and standing up, but often alive and lying down or dead and dissected. Hopefully, a new kind of technology will allow us to peer inside such feet when the animal is bearing weight and moving freely.

Heel-First Landing

Research indicates the equine foot is designed for heel-first landing rather than toe-first landing (flat-footed landing is thought to be acceptable occasionally or at slow paces, such as the walk)(Bowker, 2003, Drossman, 2006, Ramey, 2005, 2007). Think about it—all the support structures at the back of the foot are far more suited for impact than the front half, plus all those sensory and circulatory bundles that lie to the rear of the coffin are best initiated when impact occurs first at the heel. The heel area may also serve different functions at different stages of stride, such as mediating the initial impact and high frequency energies at the first stage of landing, then helping to expand the foot at peak loading and then helping the horse to place his foot for the next stride with its rich sensory bundles. Heel-first landings may also factor into foot development, since data shows that those horses who grew up with heel-first impact on variable terrain, with different movements, at variable speeds, tend to develop fully mature feet. 

On the other hand, heel-first landing can only continue to happen if the foot has developed properly and is maintained to support that development. Regrettably, research is indicating that many domestic feet are undeveloped due to management practices (Bowker, 2003), resulting in feet with insufficient weight-bearing and energy management systems, particularly at the back of the foot. Frog, lateral cartilage, digital cushion, bar, heel buttress, vascular and sensory systems are habitually inadequate or misshapen, typically causing sensitivity and pain at the posterior of the foot. In turn, this sensitivity usually forces the horse to land flat-footed or toe-first, circumventing all the mechanisms nature intended for impact (Bowker 2003, Ware, Trotter, 1999, Ramey). Over time, the result can be a cavalcade of problems, such as contracted heels, navicular syndrome, leg and body pain, mechanical sinking, cracks, separation of the wall at the toe (seedy toe, lamellar wedges and flares) and generalized unidentifiable foot pain.

Heel-first landing is also linked to breakover, insofar as the more breakover is “backed up” the way nature intended, the stride is lengthened to compel the foot to land heel-first automatically (Ramey). Agility and balance are also associated with heel-first landings, as the act of turning or movement on uneven terrain causes the posterior foot to sheer and distort to adjust, since the heels and bars can move independently, ensuring nimbleness and maneuverability (Ramey). On the other hand, this essential aspect of footfall cannot happen if the foot doesn’t land heel-first, which is why flat-footed or toe-first landings tend to cause a choppy gait as well as stumbling, interference and injury.

Different Ideas

Besides all we’ve learned so far, there are currently two dominant concepts regarding foot function, the depression theory and the pressure theory. While both agree that the expansion of the lateral cartilages is essential to foot function, and that the digital cushion and the surrounding vasculature participate in energy dissipation, they disagree on how it's achieved. On one hand, the depression theory maintains that downward force of the leg onto the digital cushion forces the lateral cartilages outward for energy dissipation and circulation. On the other hand, the pressure theory claims that compression of the frog from the ground pushes the digital cushion upward to force the lateral cartilages outward. However, neither theory can account for the data found in biomechanical studies that indicate negative pressures occur within the digital cushion during stance and impact. To explain, studies using accelerometers have shown that the pressure on the digital cushion when the foot is in the air is zero, but when the foot lands it actually goes into negative numbers rather than the expected positive numbers (Bowker, et al, 1998). Which begs more questions, doesn't it?

The hoof mechanism theory, or hufmechanismus, relies on motion and is defined by the reversible distortion of the hoof capsule upon impact, which alternately expands and contracts the foot (Strasser). As the hoof expands, the laminar corium is stretched, sucking up blood into the foot and then when it contracts, blood is pumped out, assisting the heart as an essential blood pump. Hoof mechanism also is thought to dissipate about 70%-80% of impact and act as a “suction cup” effect to provide traction and sure-footedness.

To continue along those lines, the hemodyanmic flow theory (Bowker, et al, 1998) (sometimes referred to as hydraulic theory) suggests the anatomical relationship between the lateral cartilages, digital cushion and the surrounding vascular plexuses (solar plexus, laminal plexus and the coronary plexuses) creates a hydraulic system that dissipates and transfers the initial impact energy and high frequency vibrations to the fluid and cartilaginous elements within the foot, and away from the bones and other structures vulnerable to these energies. Specifically, the thick microvessel plexuses surrounding the digital cushion and the lateral cartilages are thought to function together at peak loading, much like a gel-filled cushion in a sneaker. In this way, during the landing phase the lateral cartilages expand outward, creating a vacuum within the foot that draws the blood quickly out from under the coffin bone into these microvessels and the rear portion of the foot, where the digital cushion rests. Then as blood rapidly moves through these narrow microvessels, a low-pressure system is produced within the foot, thereby sucking more blood into the whole system. In turn, this sudden rush of blood into the foot lowers the pressure on the internal structures of the foot, efficiently dissipating concussion, vibrations and impact in what physicists refer to as "Helatious Sucking Force." Evidence has continued to suggest that those horses with fibro-cartilaginous digital cushions, thick lateral cartilages and extensive vascular plexuses have the soundest feet due to a maximized hemodynamic flow system.

Still, another idea claims to account for these negative numbers, as well, that being the Suspension Theory of Hoof Dynamics™ (La Pierre, 2001). This concept takes the coronary band into account as a primary mechanism of foot function, suggesting that as the leg descends during impact, it causes the 2nd phalanx to expand the lateral cartilages outward due to the ligamentary, fibrous and tissue attachments between them (as opposed to the digital cushion). The pressures placed on the foot vasculature from this outward expansion of the cartilages and the downward decent of the 2nd phalanx, coupled with the resistance provided by the coronary band (like a tourniquet), restricts and highly pressurizes the venous blood flow in the foot. Then right before mid-stance, when the leg begins to lift weight off the foot, the tourniquet-like restriction of the coronet is relieved, releasing the pressurized venous blood within the foot. It’s this rapid exchange of blood from the lateral cartilages and the coronary vasculature to the digital vein that’s proposed to create negative pressures within the foot. Also, the system has perpetual equilibrium because the more force it experiences, the more the pastern descends, thus the greater the resistance the coronary band will present the blood flow. Basically, this hypothesis dispenses with the assertion that the expansion of the foot creates the negative pressures, and favors instead the idea that it’s the timed constriction of the coronary band that’s responsible for this effect. It has it’s own unconventional spin to offer as well, such as dismissing the idea that the frog’s primary job is to pump blood or to act as a stabilizer for the digital cushion against the descending bony column. Another interesting twist is that, while shoeing can work within the pressure, depression and hemodynamic flow theory, it can’t work within the Suspension Theory of Hoof Dynamics™. In contrast to the former ideas that only require expansion and contraction of the posterior of the foot, the Suspension theory requires multi-dimensional distortion of the lateral cartilages as well (which is canceled out by a rigid shoe).

Any which way, it's clear that the expansion, contraction, and distortion cycle of the foot is necessary for creating and maintaining a heathy foot. Again, the more movement the foot experiences under nature's design, the better it becomes. Absolutely, the equine is a creature of movement, right down to his feet!

Sum Up

Now that we have all this swimming around in our noggins, let's take a look at some ongoing debates about the equine foot, which we'll do in Part VI. So until then, may "you tip toe through the tulips!"

"Art hath an enemy called ignorance." ~ Ben Jonson

Steppin' Out: Hooves From An Artistic Perspective Part V: Mechanics Cont'd