Steppin' Out: Hooves From An Artistic Perspective Part IX: The Good Foot Part 3

Welcome back! This twelve part series explores the equine foot as it relates to realistic equine sculpture. We've explored quite a bit so far, and we're continuing our detailed analysis of the foot in order to render them correctly in our sculptures. There's a lot to consider, but it's all learnable and applicable, so let's go!…

Lateral Cartilages

Science is discovering the unexpected and crucial role the lateral cartilages play in a quality foot. Indeed, they are unique to soliopeds for a reason! 

As we've already learned, there are two general ideas about how the lateral cartilages play their essential role in foot mechanics: The hemodynamic flow theory (Bowker, et al, 1998) and the Suspension Theory of Hoof Dynamics™ (La Pierre, 2001). Because the lateral cartilages appear to play such a pivotal role in foot mechanics, artists are advised to sculpt them with care.

Good 

A quality set of lateral cartilages are described as follows:

• Lateral cartilages are thick, large, fibrous, resilient and riddled with dense arterio-venus capillary complexes (which also are encased completely in the cartilage). They are thicker and larger on the forefeet than those of the hindfeet, and should be smooth, firm, even, and symmetrical. However, their levelness can change for the positive (remember, the foot adapts) if a habitual gait causes a foot naturally to land unevenly, such as with trotters and pacers, who tend to land along the outside wall first. This is why many trotters and pacers often have uneven lateral cartilages at stance because this actually allows their feet to land and wear level when moving. In short, not all uneven lateral cartilages are sheared heels.
• Lateral cartilages should be open, broad, smooth, “pulled down” and widely spaced. 

Bad 

A poor quality set of lateral cartilages are described as follows:

• Lateral cartilages that are small, atrophied, thin, and fatty with sparse arterio-venus capillary complexes that lie outside the body of the cartilages. 
• Cartilages with bumps, creases, cuts, sidebone, dips or other deformities that indicate injury or disease. 
• Cartilages that are “pinched,” or “crunched up,” indicating a mechanical sinker in which the extensor process of the coffin bone has sunk below the coronet. 

Artistic mistakes 

Uneven, asymmetrical, atrophied, or even nonexistent lateral cartilages are common in sculpture. Sometimes the lateral cartilages are skewed off their proper alignment, or often are too bulbous around the coronet, as well. Sinker cartilages are very common in artwork as well. Also, when the pastern is flexed, an artist can misinterpret the tight area between the pastern and lateral cartilages, misshaping them to fit into the area.

Coronet

The coronet has proven to have some fascinating and potentially important biomechanical functions, as described in the Suspension Theory of Hoof Dynamics™ (LaPierre, 2001). Therefore, the coronet cannot be sculpted as an afterthought. 

Good 

A quality coronet can be described as follows:

• Even, symmetrical and continuous.
• Slightly rounded in front to flatten at the heel bulbs. 
• Lying at, or just below, the extensor process of the coffin bone.

Bad 

An inferior coronet is easy to identify and is described as follows:

• Possessing swelling, bumps, knobs or other signs of injury or infection. For example, low ringbone is caused by torn ligaments surrounding the pastern and coffin joint, with a subsequent formation of new bone in these areas. Where bone formation extends across the joint, the condition is called “true low ringbone” and movement is painfully inhibited. “False low ringbone” is the same condition, but the bony formation lies along the long and short pastern bones and doesn’t involve a joint space. Lameness from low false ringbone usually is created by inflammations of the overlaying affected fleshy areas. In addition, a “false quarter” indicates a defect or injury to the coronet, and is a permanent condition. However, it rarely causes lameness if therapeutically trimmed to maintain ML Balance. In addition, injuries or distortions to the coronet often are accompanied by vertical sandcracks, or sometimes horizontal “blow-out” cracks.  
• A coronet that lies above the extensor process of the coffin bone, indicating a sinking of the coffin bone within the hoof capsule. 
• A coronet that’s wavy or displaced, indicating injury or ML imbalance in which a portion of the wall is too long, thereby pushing up against the corresponding portion of the coronet (often seen at the quarters in feet with a level rim or shod, opposed to the “scooped out” quarters of the “four-point” or barefoot hoof).

Artistic mistakes 

Many sculptures have low ringbone, or bulbous, protruding coronets. Displaced coronets also are common, as seen in coronets imprecisely sculpted in a wavy or uneven line. Bumps, pits and divots are typical, too. Many sculptures also have a coronet placed above the extensor process of the coffin bone with the accompanying long hoof capsule, “crunched up” lateral cartilages and flat foot with shallow collateral grooves characteristic of mechanical sinkers. [Note: Uneven coronets are common in paintwork, too, because the artist painted them hastily without precision.]

Frog 

As discussed, the frog plays a major role in weight bearing, dissipation of impact, and traction. Therefore, they require great care in sculpting.

Good 

A quality frog is easy to identify and can be described as follows:

• Being symmetrical and straight, pointing to the toe without deviation. 
• Be long, extending more than half the distance from the heels to the toe, with the apex ideally ending about one inch from the white line at the toe. 
• Be wide, being no less than two-thirds of its total length, measured from the heel to the apex, and measured at the widest point at the heel. 
• Be slightly enlarged at the buttress, and densely calloused. The ideal buttress is thought to be approximately 1/4 inch beyond the distal plane of the heels, though this can vary with lifestyle.
• Naturally exfoliates constantly. In natural conditions, this tends to happen at the frog apex first, then progresses back to the middle portion. In contrast, the posterior portion, or buttress, appears not to exfoliate, but rather callouses substantially. 
• There's still debate as to whether it’s desirable for a frog to be bulbous and protruding out the back of the heel, since some feral specimens possess such a frog, while others don’t.
• Be one of the elements to touch down first at landing, not only because it’s meant to participate in impact, but also because the frog’s buttress contains a high concentration of proprioceptors (Bowker, et al., 1995), or “feelers” that provide information on limb orientation, pressure, and tension in relation to the ground (which may be why it’s quick to regrow if trimmed). It’s believed that when the foot lands heel-first, these proprioceptors provide sensory awareness of the ground, along with pressures and tensions for the horse to coordinate motion. 
• Whether or not the frog should touch the ground in stance is dependent on the horse’s lifestyle and performance requirements—static structure is quite different in motion. 
• Be flanked on either side by prominent bars. How they meet the ground surface in stance also appears to be dependent on the horse’s lifestyle and performance demands.

Bad 

In contrast, poor quality frogs are obvious and can be described as:

• Lacking the proper frog proportions being narrow and/or short.
• “Sucked up” too deeply into the heel, inhibiting them from participating in impact.
• Abnormally too large or protruding, which can indicate disease or injury.
• Misshapen or crooked, which can mean deformity, disease, imbalance, or injury to the frog.
• Stretched forwards as the foot becomes increasingly unbalanced, which is typical of the LT-LH foot.

Artistic mistakes 

Problem frogs are typical in sculpture, usually being too small, too narrow and/or too short. However, they also can be too too large, misshapen, and often crooked. 

Bars

Like the lateral cartilages, the bars have taken on a more prominent role in foot mechanics, being instrumental in the support, function, and development of the foot. 

Essentially, the bars are the wall itself inverted inwards to flank either side of the frog. The heels have the thinnest wall, but it thickens as it becomes the bars, effectively increasing the surface area of the palmar foot for loading. It was thought the bars were the same cellular composition of the wall, but upon microscopic inspection, their structure is significantly different from that of the wall, having more keratinized layers, a different kind of laminae and an additional third layer (Bowker, 2003). In short, they’re built for impact and loading more than the rest of the wall. 

The bars also help the posterior of the foot expand at impact due to their unique structure and location, which implies that nature intended impact forces to be directed into the internal foot (and onto the digital cushion) at the posterior of the foot, rather than onto the hoof wall (Bowker, 2003). Along these lines, the bars may play a critical role in the cyclical stimulation of the foot that encourages maturation of the digital cushion, the lateral cartilages, and the vascular networks which typify a quality foot. 

A healthy set of bars also is believed to protect the frog from bruises, corns and injuries by shouldering most of the burden of impact. 

Good 

A good set of bars is important and described as follows:

• Angled rather than upright. However, there’s ongoing debate regarding the preferred angle of the bars, since feral and sound domestic feet appear to present a spectrum of viable possibilities. At present, it’s thought quality bars should angle approximately 45˚(Welz, 2007) - 60˚ (Seely, 2008), rather than be upright. 
• Long in length, ending about 3/4 inch behind the apex of the frog. 
• “Short” in height, insofar as they aren’t so long as to become overlaid (folded over onto the sole), but protrude beyond the surface of the sole. However, it’s debated whether the bars should be level with the wall or with the frog, particularly on domestic feet. The prevailing thought is that while the bars are supposed to be a load-bearing feature, they are supposed to do so passively, i.e. they shouldn’t be level with the hoof wall in most situations. Specifically, for hufmechanismus (hoof mechanism) to function, the sole should descend and flatten to expand the walls, but this cannot happen when the bars are level with the walls. On the other hand, it appears that some feral feet provide sound examples of various bar lengths, depending on lifestyle. Perhaps the bars are highly adaptable like the rest of the foot. (For some good examples of variation, visit www.hoofrehab.com/thebars.htm.) For example, feral feet existing in rocky habitats tend to have bars that are worn down to about 1/16^th above a concave sole (which is considered the “general rule” of bar height), whereas those feet existing in sandy or silty soft habitats tend to have more pronounced bars, conceivably for more traction in softer soils (and perhaps the “packing” effect of the soft footing triggers hufmechanismus). Because it appears the bars adapt to the animal’s lifestyle, an artist needs to consider the imagined habitat of a sculpture before sculpting them.
• Be tough, well-kerantinized and without bends or kinks.
• Be widely spaced at the heel to the apex, to accommodate a well-developed frog.

Bad 

Inferior bars are common in the domestic population and usually typified by:

• Being below or flush with the sole, often due to overzealous trimming.
• Being too short in length, usually due to overzealous trimming. 
• Being too long in height, so they overlay the sole and lose their supportive qualities. 
• Having an angle to the ground other than 45˚- 60˚, making them either too upright or too sloping.
• Have bends or kinks rather than being straight. 

Artistic mistakes 

In sculpture, the bars are typically ignored, implying they're either overly trimmed or entirely nonexistent. If they are present, they're typically too close together (to create contracted heels), too short (not extending 3/4 from the apex of the frog), or more rarely, laid over to blend with the sole. 

Sole

One of the big paradigm shifts has been the function of the sole. Previously it was considered more of an incidental structure than something essential for sound foot development and function. In the past, too, the sole often was blamed for general tenderness or inhibited foot function. 

Yet modern research has found none of this to be the case, and that it’s usually an overly trimmed sole, coupled with an underdeveloped digital cushion and frog that often are the culprits (Ramey, 2005). In reality, the sole plays a prominent role in what creates and constitutes a “good foot” because the coffin bone moves within the hoof capsule under the force of loading with each step (discovered in radiographs of horses standing and moving on various surfaces). With an unsupported sole, such as standing on a hard surface that won’t “fill in” to support the sole cavity, or the sole is trimmed away that would otherwise “fill in” this space, or the presence of a shoe that lifts the sole away from ground contact, the coffin sinks inside the hoof structure more extremely than nature intended…with each step. This suggests that the quality of the sole may mediate this effect, regulating its internal motion within normal parameters. 

Similarly, this may explain the dynamics of road founder which is common with shod domestic horses, but seemingly absent in feral horses living on hard, caked terrain (but who often have mud-packed solar surfaces). It also could explain why domestic barefeet adapted to hard surfaces (such as asphalt) will grow additional sole to “fill in” the gap between the vault and the road surface.  

Because the sole seems to be such an important structure for a sound foot, it could explain why it regrows so quickly and adapts almost immediately to lifestyle changes, often within a few days (Lamm, 1998). Interestingly, the bars largely are responsible for growing sole material by producing its keratinized horn, meaning that the sole grows forward, mostly from the bars to the toe (which suggests that overly trimming the bars may comprise the sole) (Bowker, 2003). 

As discussed earlier, a useful way to gauge the proper thickness of the sole is using the collateral grooves along the frog as a measure, because their depth is consistent among individuals or breeds. Dissections of healthy feet show that the deepest part of the collateral grooves is about 7/16” - 1/2” away from the laminar corium on the bottom of the coffin bone. When the sole is the correct thickness and concavity, the anterior depth (around the apex of the frog) of these collateral grooves is lifted upwards 5/8” - 3/4” from the ground and a posterior depth (at the heels and along the bars) lifted about 1” off the ground (Ramey, 2005) (the higher posterior area is thought to allow for the necessary flattening of the sole and expansion of the foot during peak loading).

In both life and the studio, a straight edge can be laid across the walls to measure the depth of these anterior and posterior points in the collateral grooves (assuming the wall is of correct length and structure). The sole is too thin and/or of inadequate concavity if the measurement is less than 5/8”, whereas the sole can be safely trimmed if the measurement is more than 3/4” (Ramey, 2005). For sculpture, these measurements would have to be scaled down of course, but they are helpful for gauging if the coffin bones in a sculpture have “sunk” or if the sole has been “trimmed” too thin.

Good 

Because the sole is integral to foot function, it has a rather distinct appearance when healthy, as follows:

• Its firm and heavily calloused, with densely packed, cornified layers. It either can be “slicked out” and shiny like smooth, polished leather, or exhibit its natural exfoliation process, depending on lifestyle.  
• In most cases, it mirrors the vault on the distal surface of the coffin bone and the distal edge of the lateral cartilages. This vaulted surface is created by a coffin bone suspended high within the hoof capsule, at or above the coronet, “sucking up” the solar surface of the sole. This vault should emanate as a smooth dome from the frog and bars, flowing to the edge of the toe callus, or wall (depending on lifestyle) like an inverted salad bowl, with the frog at the bottom of the “bowl,” about 1/4” deep from the walls (the 1/4” vault is thought to allow for the typical 1/4” expansion at the heels, at peak loading) (Ramey, 2005). Keep in mind, however, that different lifestyles often customize the sole, so pay attention to an individual’s biology when sculpting. For example, a vaulted foot can be disguised through adaptation to hard, flat surfaces by “filling in” the perimeter. 
• Its thickest under the coffin bone since the dense, thick sole may contribute to coffin bone support, as seen on the sole as the “toe callus” (Bowker, 2003, Ramey, 2003). 
• In a self-maintaining healthy foot, the sole sloughs off to maintain optimum thickness, and toughens quickly to provide a protective, supportive pad. Sole thickness is dependent on the lifestyle and mass of the animal, with recent research suggesting it should range from at least 1/2” to 3/4”. In many feral feet living on rocky, abrasive terrain, this toe callus is 1” thick and actually follows the white line all around the hoof wall, from bar to bar (Ramey, 2003). This directly challenges the concept that a sole which is “too thick” inhibits foot function. Indeed, in contrast, conventional theory maintains that the sole should be no thicker than about 3/8” at the toe and 1/4” at the heels, far thinner than what nature appears to have intended!
• Bears weight and fully participates in impact and loading. In fact, research suggests that it may be the sole that’s meant to bear most of the horse’s weight at loading (which makes the issue of peripheral loading especially worrisome—discussed later). Its surface area is far greater than that of the distal rim of the wall, and under natural conditions, it becomes far thicker and denser than previously understood, thus becoming a superior material to withstand physical and abrasive forces than the wall. 
• As for color, the sole can be various shades of tan, brown or grey, and have dark pigmentation in splotchy patches. It often is stained or dirtied by the habitat, such as the ground, grass, or manure. 

Bad 

Poor soles are common in the domestic population and can be described as:

• Has punctures or other such injuries. 
• Too thin, which can cause an unnatural and extreme downward migration of the internal structures (usually the coffin bone and the lateral cartilages) since sole support is compromised or nonexistent. Over time as the internal foot repeatedly sinks below normal parameters, this pushes the entire hoof capsule up at the coronet, placing the capsule higher on the bony column (or above the extensor process of coffin bone, and sometimes halfway up the 2^nd phalanx). The end result is a characteristic type of foot with a long hoof capsule, shallow collateral grooves (flat foot) and “crunched up” lateral cartilages, otherwise known as a “mechanical sinker.” Incidentally, this kind of “flat foot” often is associated with the LT-LH structure, and besides mechanical failure, is prone to corns, bruises, abscesses, laminitis, and other impaction injuries. However, the flat foot associated with a sinker shouldn’t be confused with a sole that’s grown in to “fill in” the gap between its vaulted surface and the ground (which can be determined by measuring the depth of the collateral grooves). Interestingly, the sinker foot doesn’t appear to exist in feral populations, but is common, almost typical, in domestic populations, particularly in shod horses. The culprits usually are aggressive trimming or “cleaning up” of the sole with each farrier appointment, or shortening an overly long hoof capsule too quickly, both of which produce an unnaturally thin sole. [Note: It appears the solution may be allowing the sole to grow, thicken and callous to push up the coffin bone back up to its proper orientation with the coronet, allowing the hoof capsule to “drop,” and with therapeutic footing and exercise, natural wear will shorten the hoof capsule (Ramey, 2006).] Unfortunately, a common “correction” for flat "sinker" feet is to pare out the sole even more to artificially create a concave vaulted surface! What this boils down to is that artists should understand both the relationship between the coffin bone and the coronet, and the relationship between the coffin bone and the wall and sole in order to avoid duplicating this kind of foot. 
• Being uneven, with ridges, lumps or bumps, and made of crumbly, soft tissue. This kind of sole is typical of domestic horses (and characteristic of shod horses), in sharp contrast to the soles of feral or barefooted horses. This condition is probably the result of over-zealous trimming of the sole, and which the palmar foot is trying to regrow the sole quickly. It’s been observed that when the sole is desperate to restore its proper structure and function, it prioritizes where pressures are most extreme, building up callous material in those areas first, resulting in an uneven surface and texture. If untouched and allowed to grow, it will even out into the smooth, thick, dense surface typical of a feral foot. However, if these bumps are trimmed repeatedly to “clean up” the sole, this reverses what the foot is trying to fix and keeps it in a perpetual state of crisis. 

Artistic mistakes 

The sinker type of foot is common in sculpture, perhaps because it’s so common in the domestic population. But it's also because many artists equate a desirable large foot with a long hoof capsule, not understanding this is exactly the wrong way to measure hoof size (more on that later). Also sometimes the sculpting of the lateral cartilages can be a bit clumsy, suggesting they're "crunched up" rather than smoothly "pulled down."

Soles with bumps and lumps are common in sculpture, too, as well as soles that are too thin, as indicated by shallow collateral grooves. Furthermore, the soles don’t match the implied lifestyle of the sculpture. [

[Note: With painting, the soles often don’t reflect the habitat depicted in a base. For example, if the base is painted like red clay dirt, the sole should also be tinted by the red clay. Or if the base is grassy, then the palmar foot should be stained with green. The sole often darkens when damp, so a piece depicted in such a habitat should have a "wet" colored sole, i.e. dark.]

White Line

The white line is the junction between the inner wall and the sole, and is about 1/8” wide. “White line” is an inaccurate term, however, because its actual color is tan, and in life, it appears as a dark line because of dirt staining. Only when it’s scraped clean does it show up as a pale line. 

It lies along the circumference of the sole and inverts to continue along the bars, almost to the apex of the frog. It grows with the hoof wall, but because it wears slightly faster than either the sole or wall, it creates a subtle and shallow discreet groove (which helps to indicate how “tight” the junction is between the wall and laminae). Functionally, it’s thought to act as a buffer zone for the necessary give-and-take movements between the rigid wall and fleshy internal structures. 

An interesting new, and rather radical, conceptualization about an additional role of the white line has been proposed. It’s suggested that as hooves get too long, they’re supposed to flare and it’s the comparatively weaker white line at the level of the sole that allows the wall to chip away naturally (Ramey, 2005). If the walls didn’t chip away, they quickly would overgrow and become dangerously long (because the equine sole doesn’t keep growing to keep up with the wall). This mechanism is particularly important for horses living in soft, marshy habitats because their hooves aren’t subjected to an abrasive surface. Perhaps not incidentally, their hooves are typified by flatter soles and flared walls with ample chips that break away. The fungal infections that usually would cause white line disease may indeed be necessary to weaken the wall enough at the white line at sole level so it can break off and maintain optimum hoof length. However, since the rest of the foot is typically healthy and properly formed in a feral horse, these fungal infections don’t present the problem they do for domestic horses (Ramey, 2005).

Curiously, this hypothesis also seems to explain how a herd can transition between multiple habitats and how their feet adapt quickly. For example, consider a herd migrating from a more arid region into a lush valley for seasonal grazing. Their arid region hooves quickly will overgrow in the softer pasture unless nature devised a way for the hooves to maintain a normal length under these conditions. Then when they migrate back to the abrasive environment, their hooves again change to fit that habitat, eroding away the “raggedness” of the pasture hoof. Pete Ramey goes on to to say in his article, The End of White Line Disease (2005):

Recent research from Michigan State University (Bowker) shows that the epidermal laminae in domestic horses go through startling changes where flares are present. They actually become forked, and then the fork spreads back to the base until the lamina has divided into two weaker ones. This is the body’s reaction to stress and an attempt to “hang on” to the flared walls. In contrast, flared wild hooves that come to the University don’t show this division. In other words, in spite of the fact that the wild horses are moving twenty miles a day on very rocky terrain, the hooves are not stressed. Why? Only in domestication do we try to force flared walls into a support role. In the wild, a flared wall is moved out of an active support role, and the body makes no attempt to hold onto it.

We recently found wild horse hooves in the Great Basin of northern California. The horse was killed in a cattle grate. She was mature and had beautiful hooves, but some flaring was present after a winter in the snow. She has approximately 410 laminae per hoof, opposed to the “normal” 550-600 we see in domestic hooves (not under natural care). In spite of the fact she had lived most of her life on a solid bed of baseball sized lava rocks, her feet had been subject to far less stress than her domestic brothers standing in soft pastures! The flaring she had was simply the natural way getting rid of the excess growth she had during the snowy months. 

Moreover, it’s been observed that there’s a mechanical progression, or logical pattern, to the breaking of the wall, which appears to be dependent on the lifestyle of the animal (Love, 1998). For instance, on abrasive, rocky ground, the wall wears level and smooth, while on softer ground (such as grass covered clay), the lateral walls flare and break away just in front of the bars, leaving heel points that extend downwards to form natural heel caulks. In contrast, in soft soils or sand, the walls flare and break away, especially at the quarters, not only to create heel caulks, but also to keep the frog and bars in contact with the ground.

Apparently, what also makes the white line vulnerable to infection is a diet overly rich in sugars, which systemically weakens the bond between the hoof capsule and the coffin bone. However, toe-first landings are implicated, too, by placing impact energies onto an area poorly designed to mediate them, unlike the posterior foot.

Therefore, if living conditions of a horse have a direct impact on the white line, this is a detail important for sculpture. It also means that the nature of a sculpted hoof’s white line can reveal much about the health of the portrayed foot.

Good 

A healthy white line clearly is evident and described as:

• Being distinct, “tight,” and regular.
• Being consistent to the lifestyle of the animal.

Bad 

A poor quality white line is common and can be described as:

• Being wide, flared, torn, stretched or otherwise irregular, which would indicate disease or injury. A common condition in the domestic population (but rare in feral populations) is “white line disease,” which actually is a misnomer—it’s not a disease, but an infection or syndrome (Ramey, 2005). It can be identified by a stretching of the white line which then is invaded by infection, causing rotted, weak tissue, and other symptoms. The result is a wall that becomes detached from the laminae, allowing the white line to stretch and distort, and infection to invade further underneath the hoof capsule.

Artistic mistakes 

White line problems are typical of sculpture, usually being misshapen, irregular, or stretched because of imprecise sculpting (or painting).

Digital Cushion

Once disregarded, recent studies have found that the digital cushion is crucial to foot function, Indeed, it can be thought of as the “canary in a cage” when it comes to the equine foot. 

It seems that when a developing foot is deprived of the necessary stimulation from adequate motion and footing, the digital cushion remains in its juvenile state, as a thin sheet of fatty, spongy material. This juvenile consistency in the mature horse transfers impact energies onto the navicular area, and up the bony column, which may explain why under-developed digital cushions have been linked to so many lameness problems, including navicular. In contrast, when the foot is properly stimulated from birth, the digital cushion matures from fatty tissue into a thick pad of firm, dense fibro-cartilage, a hallmark of a healthy foot. 

Good 

Although unable to be seen from the outside, a quality digital cushion is described as:

• Being made of thick and dense fibro-cartilage.
• Large and lying over the bars and between the lateral cartilages.

Bad 

Though we can’t see it, an inferior digital cushion is described as:

• Thin, small, and made of fatty, spongy material, i.e. remaining in its juvenile state.

Artistic mistakes 

While not directly implicated, since the digital cushion lies within the foot, a poorly constructed foot in sculpture can be assumed to have a poor quality digital cushion, especially if the foot is of the LT-LH variety, or has contracted heels, or a poor quality frog. 

Heels

An artist should pay careful attention to the heels on a sculpture because they are an important factor in a good foot. Feral horses on abrasive surfaces usually wear their heels back to the widest part of the frog to maximize the energy absorption mechanics of the posterior foot. However, feral feet also exhibit higher heels on occasion, dependent on the habitat. 

Good 

A good set of heels is important to a healthy foot and appear as:

• Symmetrical, open and broad. 
• Having the toe-heel tubules matching, i.e. the angle of the heel should equal the angle of the wall. [Note: Hoof striping follows the tubules and therefore also follows this alignment.] 
• Consistent with lifestyle. While heel length is generally preferred to be quite low, it also can be dependent on lifestyle because feral feet provide sound examples of relatively high-heeled horses. Additionally, ponies also are thought to be naturally high-heeled, as are asses and mules, as are many hemiones and zebras. 

Bad 

The heels are subject to many problems, all usually due to typical domestic management, such as:

• Contracted heels: Usually defined as a frog width less than 67% of the frog length (Turner, 2003) (i.e. narrow frog), causing the hoof to become more oval shaped rather than round, and usually with underrun heels. This structure places weight-bearing farther forward than the intended center of weight-bearing and leaves the heel unsupported. On the other hand, Strasser is more extreme in her definition: A foot is contracted if the heels lie inside a region from the point-of-frog to the outside of the bulbs. The bars on a contracted foot are typically upright rather than obliquely angled, which causes the frog and sole to have reduced contact with the ground and thus increasing peripheral loading along the wall. When loaded, a contracted foot is forced to become narrower, rather than expanded, unnaturally constricting the blood supply and internal structures within the foot, which can result in bruising, shearing and other compression-induced damage (which can induce navicular syndrome), along with leg pain and injury. In addition, a contracted foot also has lateral cartilages that are pinched together, creating a characteristic “Y” configuration when viewed from behind. Furthermore, the frog develops a very deep sulcus, inviting thrush and other infections. In short, a contracted foot is a very painful and debilitating condition. Often are associated with toe-first landings and the LT-LH structure, they can also be paired with a clubfoot or navicular syndrome. (In some cases, a clubfoot is thought to be created by contracted heels as the horse attempts to escape the pain in his heel by shifting his weight more onto his toe, which can also induce laminitis.) Contracted heels also can be an indicator of poor management (such as a sedentary lifestyle), disease, neglect, injury or problematic trimming, such as overzealous trimming of the bars or excessive hoof length (many farriers have been trained to leave the heels long to mediate the lingering soreness in the posterior foot caused by underdevelopment of the internal foot in domestic horses, which also can lead to underrun heels and folded-over bars in addition to contraction). Predictably, the condition usually causes a spectrum of lameness problems which can be difficult to reverse. 
• Too long: Heels that are too long, usually defined as 1/2” beyond the sole, are implicated in shortened stride and impaired breakover (Ovnicek, 2002). 
• Underrun heels: Defined as a heel angle 5˚ less than the dorsal angle of the wall. This condition renders the heels unable to support the posterior foot, and therefore compromises the foot’s expansion and contraction cycle. This often leads to interference problems, gait faults and stumbling, probably due to the pathological changes it causes in the navicular area and its placement of the weight-bearing surface too far forward, circumventing the mechanisms designed to absorb and dissipate impact. Predictably, this condition leads to many lameness problems, such as quartercracks, navicular syndrome, bruises, abscesses, corium damage, etc. Underrun heels are associated with the LT – LH structure, too, since the heels tend to follow the toe (i.e. a long toe tends to “pull” the heels forward). Curiously, if there’s a flare on one side of the toe, the opposite diagonal heel often will be underrun, as well. Underrun heels are rare in feral hooves because the heels often are worn back to the widest part of the frog and the posterior foot plays an active role in foot mechanics. In contrast, underrun heels are ubiquitous in the domestic population due to customary management practices and problematic trimming. Alarmingly, a lameness study found that underrun heels occurred in 77% of domestic horses while another found that this condition was in 52% of performance horses (Turner, 2003).

Artistic mistakes 

Contracted heels are pervasive in sculpture because the artist wasn’t generous with the frogs, or didn't understand the proper structure of the heels. This is understandable, however, since foot contraction is pervasive in the domestic population, too. Underrun heels are common in sculpture, too, because the artist has placed the hoof capsule too far forward on the imagined bony column or was overzealous in smoothing the back of the hoof. 

Sum Up

Lots to think about, isn't it? But oh  no, we aren't done yet! In the next installment we'll begin our inspection of the hoof wall, so there's lots more to cover. Until then, keep steppin' out in style!

"When the student is ready, the teacher will appear." ~ Buddhist proverb