Monday, March 30, 2015

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 artiststoo 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 artis 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

Related Posts with Thumbnails