Mediolateral Balance    10-22-04     Pete Ramey    with 2018 edits

When I was first learning the farrier trade, I was fortunate enough to be taken under the wing of an old shoer right before time caught up with his wrecked body enough to put him out of business. He had been taught decades before by another old shoer, and I doubt very seriously that either of them had ever read a paragraph of a farrier text and definitely not a veterinary paper. My mentor's methods were very simple. Keep the horses barefoot and routinely trimmed during the off season to drive up the sole, keep the heels low and the shoe way back under the horse. “Cheat” the toes back if you need to so he doesn’t trip on them, leave the frog alone and most of all, leave the sole alone and let it tell you where the foot wants to be. In fact, I am pretty sure I never really used a hoof knife until I was on my own – at least I know I never needed to sharpen a knife under his watch. We just scraped away any loose flakes of exfoliating sole and leveled off the walls above the remaining sole plane in prep for the shoe.

His nutritional knowledge was apparently limited to a strong distaste for fat on a horse – he liked muscle and ribs. “You’d better back off on that horse’s feed or he won’t be able to carry you anywhere.” That is pretty much all I remember, as far as the horses and their hooves go; the rest was all about the metal work.

As I later studied deeper into corrective shoeing and worked hard to educate myself, I became obsessed with the world of hoof gauges, measurements, T-squares, formulas, dots, bridges, COAs, HPAs, ratios and mapping. I came to think my old teacher as a “cowboy shoer”— incompetent even. I failed to notice the fact that the people in the fancy barns who used the more-expensive educated farriers with the high-dollar rigs (and 100 reasons to cut sole from the horse) had horses and hooves that were wrecked with problems. I also conveniently forgot for a while that very few of the horses in my teacher’s care ever had a problem at all. When they did it was usually from some injury and not sore feet. Which came first, the chicken or the egg? My answer at that time would have been wrong.

Since then, I have systematically had to unlearn many of the things I learned to do to the horse that once made me feel superior to my old mentor and at the same time developed a deep respect for the pure, raw effectiveness of his simple, "uneducated" ways passed down through the generations.

He balanced trims and shoes using the horse’s natural sole plane. I never saw him cut into the sole on one side to achieve some mediolateral balance goal. After a short trip into other methods, I have realized that more often than not, his method works the best. But I have seen the sole plane be wrong, so as always, the truth is not quite so simple – it depends.

First, what is my idea of correct mediolateral balance? In over 99% of hooves, I believe that the best you can do is leave the same amount of sole covering both sides of the coffin bone and both sides of the lateral cartilages. Then leave the same amount of quarter, heel wall and bar standing above that sole on each side. Even in most horses with angular deformities, the limb can torque towards straightness when the ground-balanced foot is loaded, providing the best chance of adapting the joints toward straightness.

But… I have seen horses with malformed or remodeled coffin bones that were thicker on one side and joint spacing up the limb correct only when the ground plane of P3 is tilted up out of a parallel orientation to the ground. I have seen joints seized in positions that would not let the bottom of the foot reach the ground on one side. And I have seen arthritis cases that show pain reaction to a balanced foot and move better when the internal foot is out of balance with the ground. I do believe that most of these cases were caused by long-term balancing with the hairline or by T-squaring to the limb. Regardless of the cause, once this damage occurs, it is often best to do whatever you can to provide comfort. This can mean intentionally imbalancing the foot to provide pain relief and to support permanent imbalances in the limbs. Understand, though, that in these cases you are in salvage mode, not rehab mode. These cases are best identified and treated with radiographs, by studying the movement of the horse, and through experimentation.

Those exceptions aside, the vast majority of the time it is best to balance the internal structures of the foot to the ground. To accomplish this in the field, I combine four very flawed indicators:

1)    Radiographs

Looking at a quality zero degree DP radiograph, it is easy to measure and compare exactly how much sole is on each side, thus to determine if the mediolateral ground plane of P3 is parallel with the ground. This is a very useful tool for sorting through imbalance issues, but it has a big flaw – you can really only see the mediolateral balance in one spot near the widest part of the foot on a radiograph. You can’t see heel or toe balance.

A secondary flaw is that we often don’t have radiographs available. Even if we do, if they are a month old or more, they generally aren’t of use in the field for making balance decisions. All that said, the first thing I do when I am in doubt about a balance decision is order zero degree DP radiographs – they can be very enlightening.

2)   Collateral Groove Heights off the Ground

As discussed in http://www.hoofrehab.com/HorsesSole.html, the collateral grooves provide a very important window into the internal foot, because very consistently, it is 7/16” (9mm) from the bottom of each groove to the corium. So you can use the collateral grooves to locate the coffin bone and the lateral cartilages. If you measure the collateral groove depths on each side of the foot and find that both sides are balanced with each other, P3 and the lateral cartilages are probably balanced with the ground. I generally compare the depths on each side an inch behind the apex of the frog and at the deepest point, usually at mid-bar. When you measure, try to hold the gauge either vertically, or on the same angle on each side (sometimes difficult or impossible at the back of the foot, but do try).

Figures 1, 2 and 3

There are two scenarios I know of that cause the information provided by the collateral grooves to be wrong. First, when there has been simultaneous abscessing of the frog and solar coriums, the sole and frog can disconnect creating a false sole and frog, including a false collateral groove. Hopefully there are new soles, frogs and accurate collateral grooves growing in underneath, and eventually the false material will shed off (hopefully after the new growth is approaching full thickness). Until then, the information provided by the collateral grooves is pretty useless.

The second scenario that alters normal collateral groove distances to the corium is fungal or bacterial infection. These are common in the central sulci of the frogs (in fact I consider central sulcus infection to be one of the most important lamenesses in horses – not just because of how common they are or the pain they cause, but because of the effects of the resulting toe-first compensation that then thins soles at the toe, causes navicular damage, destroys lamellar attachment and damages joints, ligaments, tendons…). These infections are considerably less common in the collateral grooves, but it does happen. Collateral groove infections can eat their way to (even into) the corium, making collateral groove measurements unusable. Be suspicious of collateral groove measurements if you find pain response, cottage cheese-like residue, or find the distinct smell of fungal infection in the collateral grooves.

Even with these two occasional exceptions, comparing collateral groove balance is by-far the most accurate and reliable of the four indicators. The biggest problem is that at the back of the foot, we don’t always have access to the information hiding there – some collateral grooves are too tight to accurately measure – you sometimes don’t really know if you are measuring to the true bottom or not. This fact alone makes these measurements just one more useful indicator, rather than a solid stand-alone method of balancing the lateral cartilages and P3 to the ground.

Critical Note: The flexible lateral cartilages tend to adjust to a preloaded position that is prepared for the most common way that foot hits the ground (for instance, lateral side higher in a hind foot of a horse that is worked a lot at speed and reaches underneath the midline at each stride). So it is okay if one lateral cartilage resides higher on one side when the foot is at rest, dangling in your hand. The caudal foot twists and distorts vertically at impact to accommodate moving through turns and uneven terrain – you still need to balance the sole, bar and heel wall the same thicknesses covering each lateral cartilage, even if it appears you are leaving the foot imbalanced because of this resting or neutral position of the lateral cartilages.

3)    The Hairline

If a horse has been well-maintained, has been moving correctly and has been continually in balance, long-term, the coronet/hairline will be ground parallel at the toe (when viewed from the front from ground level) and also at the heels (when viewed from the back from ground level). So it is common for people to use the coronet as a stand-alone method. This is a mistake, because the coronet lies and it lies often. If either excess load or excess wall length (usually caused by less load/use/wear occurring on that side) has been common on any area of the hoof wall, the coronet migrates proximally (moves up the limb). If an area of the wall has commonly been unloaded, the hairline migrates distally (moves down the limb). This range of motion – where the hairline might be currently residing relative to P3 and the lateral cartilages – can vary by an inch or more.

This fact makes the hairline the least accurate of the four indicators. That said, it does provide useful information about how the horse has been moving and how the horse has agreed with previous balance decisions. It is the most common way I first notice balance issues when a horse walks up to me. You just have to take the information provided with suspicion and then look to the other indicators for confirmation.

4)   The Sole Plane

Horses have a very strong tendency to callus the sole in a very uniform sole thickness on each side of the foot. Additionally, even if you are removing excess sole, if you exfoliate a sole down to the same texture/moisture content on each side, the thickness on each side will generally be in balance. In a vast majority of cases, you can simply use the sole plane to balance the foot, leaving the same amount of heel, wall and bar standing above the sole on each side, as in the before and after trim pictures below.

The flaw to this method is that sometimes the sole does lie. Excess wear can occur on one side, retained false sole can look exactly like good callused sole on the other side of the foot. Donkeys, mini horses (commonly) and sone normal-sized horses (rarely) can grow excess sole that fails to callus or change textures as it moves away from the corium. Given the limitations of the other three indicators, even with these exceptions at play, day in and day out, the sole plane is our best indicator of mediolateral balance. You just need to consider the other three so you don’t get fooled when one of these exceptions occurs.

 

Putting It All Together

When I start a new horse, on each individual foot, I consider all of the information I have available from each of the four indicators. I watch the horse move, looking for feet that land out of balance – ideally, I want both heels on each foot to impact the ground simultaneously when the horse is trotting in a straight line. I want the entire foot to land flat to the ground when the horse is walking in a straight line. This provides important information, but be cautious with this indicator as well – some horses avoid pain on the bottom of the foot by voluntarily side-loading. These horses need treatment for whatever is causing the pain, but they still have the same mediolateral balance needs as discussed above.

Once I get to know a horse – if all of the indicators seem to agree with each other and there is no evidence of imbalanced movement (excess wear on one side, one bar or heel trying to flare, crush or roll under, etc.) – I tend to shift to only using the sole plane for balance during maintenance trims. If I do ever see any suspicious wear patterns, distortion or movement, I immediately shift back to gathering all of the information I can from the other indicators.

In a nutshell, I am processing the information from four very flawed sources (five if you count the footfalls) and then guessing at mediolateral balance. That sounds bad, I know, but it works much better than considering any one of them alone. After all is said and done, I seem to be good at sorting through imbalance issues, so I suppose standing on shaky ground while thinking can be better than being solidly and mindlessly entrenched in any one method that can fail you.

 

Considering the Steep and More Sloping Sides of the Foot 

When viewed from the front or back, many coffin bones have a steeper side and a more sloping side opposite of each other. Likewise, the quarter walls will also have steeper and more sloping sides. Generally speaking, when these horses were born, the coffin bones and walls were at the same angle on each side. This asymmetry is a product of the way the individual horse moves – a remodeling, perhaps an adaption. The side of the foot that has been continually used more/loaded more by the horse will remodel into the steep side of the foot. The side of the foot that is used less/loaded less will remodel into the more sloping side of the foot. The frog will generally reside off center, with less foot width on the steep/more used side of the foot.

Most commonly, the steep/more-used side of the front feet is the medial side, unless the horse has angular deformity (toes in) at the lower limb joints. In these cases, the steep/more-used side will tend to be the lateral side. On hind feet, the steep/more-used side will more commonly be the lateral side, as horses tend to reach the hind limbs underneath the midline during normal movement, placing more load on the lateral wall. Various problems, usually hip or back problems can prevent the horse from moving this way, usually causing the steeper/more-used side of the foot to be on the medial side.

These steep and flared sides of the foot need to be recognized and treated very differently than each other. Horses are very good at slowing down or speeding up the growth rate of the walls to accommodate the current demand. They are not very good at growing different amounts of wall on each side – high wear/demand in one spot of the wall tends to accelerate the wall growth everywhere.

What very commonly happens to these feet with distinct steep and more sloping sides is that the wall’s growth rate will be perfect for the higher demand at the steeper/more-used side of the foot – this side of the foot will often self-maintain if given a chance, with little or no trimming needed. But this almost always translates to excess wall growth on the more sloping/less used/less wear side of the foot. The result of this constant excess growth is wall flare that is very difficult to grow out.

These less-used walls seem to overgrow and flare overnight because they are growing at the same rate required by the more-used side of the foot. It is difficult (and expensive) for a hoof professional to get to a horse often enough to trim the walls before they overgrow and flare, spreading separation into the new well-attached growth. A useful trick is to teach the horse owner to trim only that overgrowing, flared side of the foot on a weekly basis. This stops you from wheel-spinning, when trying to grow out the wall flare while working the rest of the foot on a 5-week trim cycle.

The most useful trick for growing out these flares, though, is being careful not to artificially accelerate the growth rate of the walls. This is done by never trimming any part of the wall (this applies to bars as well) that is not overgrown. Sounds easy – but it is the hardest thing in the world for a professional to do – we tend to want to leave it all pretty, shiny and clean. But any part of the foot that is not overgrown should be left dirty. Only trim those parts of the wall that are overgrown, or you will artificially accelerate the growth everywhere.

I learned this from teaching horse owners to trim their own hooves by doing weekly light trims. If they were trimming the entire wall, they would get the walls growing so fast they had to do big trims on a weekly basis or the walls would overgrow and flare between trims. Weekly trimming is great, and is the very best way to grow well-connected walls – but you must only trim the parts of the wall that overgrow, using the parts of the foot that self-maintain as a guide for determining how much wall the individual horse needs standing above sole in a given terrain. In the before and after trim pictures below, the [right in photo] side of the foot self-maintained perfectly during a six-week trim cycle. It was left alone. The overgrown [left in photo] side of the foot was trimmed to match the height above the sole and the angle of the roll on the wall. This slows the growth rate down, making it possible to grow out the wall flare using a reasonable trim cycle.

Figures 4 and 5

For heel height discussion, read http://www.hoofrehab.com/HeelHeight.html

 

Now to the Tricky Part - Balancing Asymmetrical Feet

Very often these feet with distinct more- and less-used sides of the foot will have good wall connection on the steep side of the foot because this side of the foot has never overgrown. In contrast the less-used side of the foot will have big wall flares because they have constantly overgrown. Growing out these big wall flares requires big trims to relieve the lever forces on the walls (by the way, once you have identified a side of the foot the horse doesn’t use, you can get away with very aggressive trimming on that side without making the horse tender-footed or particularly at risk of bruising the sole - that tidbit was worth the price of admission).

The trim required to grow out the flares (generally, trim the walls to the level of the sole and bevel/roll the full thickness of the wall) leaves the sole with no wall protruding past it (or commonly, the wall is already flared out level with the sole when you arrive). This leaves many practitioners (including me, for many years) to automatically over-trim the well-connected side of the foot in the name of mediolateral balance. You may know the well-connected side needs 1/4" of hoof wall standing above the sole, but you trim it off anyway, because you need to balance to the lack of wall height on the flared side of the foot, right? This artificially accelerates the growth rate on both sides of the foot, making the flare difficult-to-impossible to grow out.

To break out of this trap, treat each side of these feet independently. This sounds really wrong, I know, but this foot is not loading in a balanced way no matter how you balance it. Plus, it turns out that in most horse terrain that the foot can sink into a bit, this does not imbalance the load or movement. The horse is balancing on greater surface area of the sole and frog. That 1/4" of wall standing longer than the sole just sinks into the dirt, offering little-to-no resistance. Think of a snowshoe with a 1/4" thicker frame on one side – it wouldn’t affect your movement through snow.

Note: This does not apply to hard, flat terrain. Hooves adapted for this type of environment tend to need walls that are trimmed to or worn to the level of the sole so that the wall and sole can share the load.

Once you succeed in growing well-connected walls on both sides of these asymmetrical feet, start balancing them normally, allowing the same amount of wall to stand longer than the sole on each side. This was a temporary measure to break out of a trap.