Hoof Balance Made Easy
Gene Ovnicek, RMF
The topic we will be discussing is how to more easily achieve hoof balance through a better understanding of hoof form and function. We will also be talking about how these principles apply to Navicular syndrome, as well some natural principles and guidelines for hoof care that are tools farriers can use which are complimentary to good conventional trimming and shoeing practices. Duckett’s references, Savoldi’s ideas, and the information gleaned from feral hoof studies can aid farriers in evaluating and treating various types of feet, healthy and pathologic. The latest scientific and practical information that has evolved over the last 15 years, as well as sound principles revisited from the past, serve as a basis for these simple hoof trimming and shoeing guidelines. The studies of feral horse hoof patterns and anatomy fit well with the research and studies that are ongoing, with emphasis on where the domestic horse fits in with feral horse information, and visa versa.
I will show you information that will simplify many issues that pertained to lateral medial hoof balance, anterior posterior hoof balance, as well as establishing a reliable formula for detecting and treating hoof deformities and distortions before they affect the performance and soundness of horses. The part that makes this information easy to apply is that finding the widest part of the foot offers the most reliable reference to the distal phalanx. This will help to recognize hoof distortions long before they become irreversible.
The purpose for studying the feet of feral horses was to find consistencies with naturally worn feet that might be valuable in treating lameness in domestic horses, as well as preventing lameness. This information opened the door to research expanding in a slightly different direction. For one, the sole and frog seemed to be an active part of weight-bearing, which was a completely new thought for most farriers and veterinarians. It has also been shown that domestic feet wear exactly the same when the environment and lifestyle will maintain the feet optimally. The most interesting and important part of the feral hoof information was, what sole structures of the foot stopped the wear from occurring closer to the apex of the frog and into the distal phalanx. Dr. Bob Bowker's research on lamina density with barefooted horses helps to understand what Dave Duckett talked about in the early 1990’s regarding “pillars”. These appeared to be stronger portions of the sole seen in the medial and lateral toe quarters of the foot. It is also shown that the lamina is more dense in the areas of the medial and lateral toe quarters on barefooted horses according to lamina counting done by Dr. Bowker. The more dense lamina is consistent with the imprint marks made on the foot from the study of the feral horses. It was also noted by Bowker that feral horses had no secondary lamina between the two pillar points on the dorsal aspect of the distal phalanx. This seemed to suggest that the wall forward of the pillars was not as necessary for weight-bearing when the foot was loaded on the pillars and flat to the ground. Moreover, the friction that occurs at the time of breakover is what wore the foot to this rolled, rounded form. The friction was obviously less stressful than the impact in normal movement because the wear was always maintained close the distal border of the distal phalanx. The part that is still difficult for many horsemen to accept is that the wear that occurs on the front of the foot is a normal event. Dave Duckett's work in the early 90’s suggests that breakover occurs at the same spot that the imprint marks were found, and at the same position that we see naturally worn domestic horse’s feet. However, many of our conventional ideas of breakover are based on domestic feet that have distortions. Because hoof distortion was, and is something that we commonly see, I believe it is considered normal and used by many as the optimal model. My goal is to offer ways to recognize distortions, and get a clearer picture of what is "NORMAL", as opposed to what is COMMON.
The Widest Part of the Foot
The first and primary tool I use to evaluate the balance of the foot is what Duckett calls the Bridge, or more commonly known today as the widest part of the foot. If you can learn to quickly and accurately identify the widest part of the foot at the sole, you will consistently be able to find the tip of the distal phalanx (coffin bone) and balance the foot around the boney column. A combination of 3 approaches are used to accurately identify the widest part of the foot. The quickest, but not always the most reliable is to measure back from the true frog apex about 1”. A line perpendicular to the frog at that point is generally the widest part. However, if the frog apex appears to be stretched and pulled forward, you must employ the other methods to get a more accurate assessment. The second method is to find the place where the bars terminate into the frog commissures. If you run a pick up the commissures, you will feel a bulge or swell where the bars seem to terminate. A line across the foot at that point should be the widest part. Third, and probably most accurate, is to exfoliate the sole from the toe quarters to the heels on each side (meaning remove the chalky material until the waxy appearing surface is revealed). Then, using a marker draw a line at the wall/sole junction from the toe quarters to the heel. Mark a line at the apex or peak of the arc you’ve just drawn. Connect the mark from one side to the other. This line is essentially the widest part of the sole. If through the use of all 3 methods you find the lines you have drawn all fall on top of each other, you can rest assure that you are quite accurate with you assessment of the widest part of the foot. From this line, you can measure forward approximately 1” (on a #0 - #1size foot), to find the true frog apex. From there, you can measure another 1” forward to find the tip of the coffin bone (give or take 1/8” or so).
To then use that information for trimming or for applying shoes, we then draw a line approximately ¼” ahead of the line at the tip of the coffin bone to mark where we would like to place breakover. The breakover point of the shoe or the role of the toe (if barefoot) should fall over this location. The most caudal bearing point should be the back of the frog if the horse is barefoot, as the frog will typically take precedence over the heel once the heels are trimmed. If the horse is shod, the heels of the shoe should be located at the most palmer aspect of the frog. The anterior/posterior ratio is generally 50/50 around the widest part of the foot. From that we know the foot is equally proportioned around the articulation of the Distal Interphalangeal (DIP) joint. On most horses, having the ratios equal around the widest part of the foot is usually sufficient. However, in many horses it is seen to be more beneficial to have more support behind the widest part than in front, since the back of the foot is better designed for support and weight bearing. If you see a horse with more mass ahead of the widest part of the foot than behind, then you are dealing with hoof distortion. It’s that simple!
Shoe Wear, Hoof Wear, & Breakover
There has been divided controversy on shoe wear, particularly that which occurs at the toe. Some feel that shoe wear should be prevented and others feel that the shoe wear should be allowed to occur in light of the way the natural foot wears without shoes, in a natural environment. I feel that shoe wear is an indication that something important is happening. It appears that the toe is being worn to the same part of the foot relative to the distal border of the distal phalanx. However, with shoes placed at the perimeter of the wall, the wear does not occur quickly enough to find the optimal place for breakover before the next shoeing period, do to the resistance of the metal. Therefore, the excessive wear that is commonly seen can be a good thing, in that it acts as an indication that moving the breakover back might assist in relieving the excess leverage, especially if some lameness is present. Adjusting the breakover has for some time been shown to be of some assistance to helping those horses that have Navicular related problems, as well as ligament and tendon issues of the DIP joint. Perhaps if we read the warnings in the shoe wear, we could address those needs before these Navicular related issues and soft tissue damages occur.
A closer look at shoe wear makes it easy to understand why the toe wears in the manner that it does, and particularly why there is more wear when the dorsal wall has become a greater distance ahead of the widest part of the foot. It appears as though the excessive leverage that is necessary to pivot over the front of the foot creates extra wear and friction in order to get over the front of the foot. It is common knowledge that the inferior check ligament controls the tension on the deep digital flexor tendon, and that there is very little-to-no stretching that occurs below the knee. This is the same mechanism that allows the horse to stand while sleeping without falling down. With the knee locked in place through the weight-bearing phase of the stride, the leverage creates friction as the limb passes over the toe. Wear then occurs on the distal end of the dorsal wall. This fits very well with the position of Duckett’s Pillars and the findings of the wear seen on the feral horses, as well as the naturally maintained feet of domestic horses and worn shoes from everyday horses.
It appears that the natural wear terminates at the top edge of the sole callus, which is the ridge of horn that is formed around the distal border of the distal phalanx. This sole structure that protects the tip of the coffin bone seems to establish the equilibrium regarding breakover. The sole callus is a product of the terminal papillae, which are similar to the papillae of the dorsal hoof wall, and produce the horn tubules that are directly oriented to the distal border of the distal phalanx. You will see a 30° sagital section show that the sole material generated from the terminal papillae in this region is wider and thicker than the areas anterior and posterior to this region of the foot. The imprint marks shown on the feral horses feet, as well as the pattern duplicated by naturally worn domestic feet, parallel these histological findings as well, particularly when complemented by the lamina density being located in that same region of the wall and sole. Looking at the coffin bone we see other complementary anatomy that makes the concept of pillar bearing points and a place for breakover more realistic. The largest percentage of coffin bones will show bearing points near the dorsal, distal aspect. This will vary some from one horse to the other. The non-weight-bearing portion in the anterior aspect of the bone strongly represents the roll or the rocker that is seen on all horses that are allowed to wear their feet naturally. On the ventral aspect of the coffin bone we see corresponding ridges that radiate from the attachment position of the impar ligament and deep digital flexor tendon. These ridges radiate to the contact point seen on the distal border of the distal phalanx that also correspond with the higher density of lamina in that same region as well as the imprint findings of feral horses.
That pivot point seen through radiographs of naturally worn feet and reported by Dr. Barbara Page in 1999 at the AAEP, show that from the anterior distal border of the distal phalanx, approximately one quarter of an inch or 6 mm, is where breakover occurs. When you see a horse that has an obvious long toe and a broken back pastern axis, conventional standards for hoof trimming are to remove the toe portion of the foot from the bottom and leave the heel in order to align the distal phalanges. Serious complications can be derived from trimming the hoof aggressively (which happen occasionally) in order to achieve alignment, especially with feet that have a severe condition of poor pastern alignment. It's been noted that trimming close to the sensitive area of the sole can be responsible for causing dorsal wall hoof distortion. The tissue that surrounds the distal border of the distal phalanx (in light of the terminal papillae) seems to be as much of a bonding structure as it is protective sole material for the internal structures of the distal phalanx. When the foot is trimmed too close, the dorsal wall seems to detach at the distal end of the distal phalanx in the toe area between the two medial and lateral toe pillars. This can be easily noticed by the frog being deformed and stretched forward at the same proportions as the dorsal wall. The stretched frog can be noticed long before pathology has occurred. There seems to be a scar tissue forming between the distal border of the distal phalanx and the interface of the dorsal wall. We’ve demonstrated this by driving nails through the sole behind the lamina on feet that have major hoof distortions occurring in the anterior wall, similar to laminitic feet but no seen to be pathologic. This phenomena in of itself should alert us that hoof balance looked at primarily from using the external hoof wall, should be revisited. I believe hoof balance needs to include references that are more consistent with the distal phalanx. What's even more apparent now is that we've been able to see the damage that occurs around the distal Interphalangeal joint with the collateral ligaments, the flexor tendon lesions, and damage to the impar ligament as a result of the distortion that creates the longer toe that we thought was normal. This may be part of the reason for an increase in cases of Navicular related issues associated with soft tissue injuries where no significant changes to the Navicular Bone are noted.
It is a common practice to fit the shoe with plenty of width in order to provide a wide base of support. However, in light of new information regarding collateral ligaments issues as well as coffin joint problems, we need to rethink the concept of a wide base of support and perimeter fit. A shorter toe and medial/lateral breakover positioned inside the wall perimeter (much like a naturally worn foot), becomes even more important as a horse hyper extends prior to liftoff, especially while turning a corner at the same time. If you increase leverages beyond what is normal or practical, and then ask the horse to do maneuvers and circles in a non-yielding or even partially yielding surface, the DIP joint is going to suffer.
Pastern alignment in a static state is important. However, the alignment of the distal phalanges at the time of ground contact and foot loading is even more important. Simply engaging the back of the foot first through a heel-first landing, with the frog in close proximity to the ground, will align the DIP joint upon ground contact. The ability of the horse to land slightly heel-first is influenced by the freedom it has to move over the toe. In other words, if the horse cannot get its foot off the ground in a reasonable amount of time, it is unlikely that the foot will land heel-first. Therefore, alignment of the distal phalanges upon ground contact is less likely when the forces are the greatest, which is when the alignment is needed.
It is also seen that if there is a delay in breakover, the horse is more likely to engage the ground toe-first, causing a caudal movement of the pastern upon ground contact and initial load. You can actually see this occur with your naked eye on horses that have a short stride and land toe-first. If you watch above the coronary band and you can see the pastern move to the rear. According to MRI and ultrasound pathology findings, damage to the soft tissue in the DIP joint is likely occurring as a result of increased effort at the time of breakover.
Distortions of the Back of the Foot
Heels that run forward often develop corns, and usually belong to those horses that fail to land heel-first because of the pain from the heel distortion. Early recognition of this condition will enable the farrier an opportunity to alter this distortion before pain occurs. Occasionally you'll see bruising that occurs at the place where the bars terminate, which is ventral to the Navicular bone. The distortion of the heels growing forward and bending inward, forces the tissue of the bars and sole into the static region of the foot at its widest part. This condition can be altered by simply trimming the extra height from the heel to the level of the sole. This not only changes the curvature of the heel but also lengthens the base of support. The heel is positioned more caudal to the rest of the foot and the heel curvature is much straighter. The foundation in the heel buttress is more stable and suitable for loading, and the frog is in closer proximity to the ground so that normal hoof biomechanics are likely to resume. Do keep in mind that you will probably need to address distortions in the front half of the foot as well, as they seem to go hand-in-hand.
One more helpful hint when dealing with distortions in the back of the foot has to do with evaluating the curvature of the heels and bars from one side of the foot to the other. The heel that curves the most is always the tallest heel, and the wall will be a greater distance (or height) from the sole. This information is especially helpful when evaluating lateral/medial balance, thanks to Mike Savoldi.
Medial/Lateral Balance
It's been shown by Mike Savoldi that the thickness of the functional sole is the same under the ventral border of the distal phalanx. Therefore, trimming each side of the hoof wall the same distance from the exfoliated, functional sole will insure that lateral/medial balance is easily attained. It should be noted however, that you must be very specific about accurately identifying the live, functional sole in order to use it as a guide. If you cut into the sole too aggressively and go through the plane of the live sole/dead sole junction, you have seriously jeopardized your ability to use the sole as a guide. So, tread lightly.
The live or functional sole is seen as the waxy appearing surface just below the chalky or exfoliating sole material. If you can identify the live sole, primarily in the region close to the wall/sole junction, you can be assured that by trimming the hoof wall an equal height from that live sole on each side, you will have the ventral border of the distal phalanx parallel to the ground from side to side. Whether you leave ¼”, 1/8” or zero wall above the level of the sole, balance is achieved as long as you leave the same amount on the opposite side. This method is extremely helpful and much more accurate on those horses that are pigeon-toed or base narrow, because frequently the hoof capsule has been shifted and lost its relationship to the coffin bone, and therefore is unreliable when sited in a more conventional way. In short, the live sole is proving to be a much more reliable and less subjective means of evaluating and achieving medial/lateral balance.
Lameness Detection & Prevention
Hoof distortions, as mentioned earlier, are the primary reason for lameness issues of the Navicular bone, impar ligament, deep digital flexor tendon, and collateral ligaments. Gait faults associated with hoof distortions are the early indicators that lameness is likely to occur. Stumbling is one of the more subtle conditions that is easy to recognize and is often mentioned by the horse owner. Forging is another gait fault that is often justified by breed type, rider’s ability or discipline the horse is asked to perform. These are not justifiable excuses now that we understand hoof distortions by mapping out the bottom of the foot using Duckett’s Dot, the Bridge or widest part of the foot, and the Pillars.
Horses that land toe-first are those that are closer to lameness and considered by some veterinarians to be a grade one lame. Hoof conditions that are associated with lower limb lameness are generally those with heels that grow forward much like the dorsal wall, and when they are left taller than they should be, they start to crush, become underrun, and become painful. As a result of this condition, the horse will often land toe-first because of the pain that is incurred from the distorted heels, and the longer toe slows the breakover which discourages the heel-first landing. It is easy to see this condition in the early stages of distortion. Simply using the true frog apex, termination of the bars, and exfoliate sole in the quarters (as described earlier) will give you the information you need to evaluate hoof distortion. If the front portion, from the widest part to where breakover occurs, is greater than the back portion, there is hoof balance disparity. Keep in mind that if the foot is longer in front of the widest part, there will be a delay in breakover. When the toe is longer than normal, and once the pastern moves beyond its normal range, the flexor tendon loses a portion of its tension and support to the distal interphalangeal joint. At that moment, forces are diverted towards the impar ligament, suspensory ligament to the Navicular bone, and the collateral ligaments of the distal interphalangeal joint.
A potential for lameness exists with horses that are shod with a flat plate fitted slightly wider than the prepared foot so that there a visible portion of the shoe around the perimeter of the hoof wall. The extra width and length is perceived as support; however the stress on the collateral ligaments and deep digital flexor tendon at the time of breakover increases when the perimeters are lengthened. The stresses to the DIP Joint are compounded even greater when horses are engaged in circles and turning. It becomes easy to see how the natural wear that occurs may be beneficial to relieving some of the discomforts to the distal interphalangeal joint. With the new technology that we have available to us today, deep flexor lesions, collateral ligament damage, impar ligament strain, and DIP joint disease appear to have a fairly common cause.
Summary
Mike Savoldi and Dave Duckett’s work, plus the information from the naturally worn foot of the feral horse as well as the naturally worn foot of the domestic horse, appear to offer a commonsense approach to a possible solution, or at least a direction for resolving the issues regarding pathology seen in-and-around the DIP joint. Many critics contend that the naturally worn foot is not valuable for domestic horse hoof maintenance. Keep in mind that horses were not intended to be ridden and the foot, in its natural state, has been worn consistently to relieve strain on the distal interphalangeal joint. If we add extra strain and stress to the animal and their feet with a rider, a saddle, and disciplines that are challenging to the whole horse, why would we add extra length and width to the foot that only increases the leverage forces around the distal interphalangeal joint? Nearly all horseshoe manufacturers that have become aware of the needs of the industry, are producing shoe styles and types to accommodate these excessive leverage forces in their newer products, and the benefits are being seen in the horses.
Keep in mind that the most valuable tool that can easily be used, is mapping out the foot to determine distortions of early and a potential lameness situation. These same guidelines can be used in normal, everyday shoeing, and maintenance practices as a means of preventing lameness.
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