Breakover   2-15-05     Pete Ramey     with 2018 edits

Note: If you are new to hooves and the terminology used here, as a prerequisite, read the 12-article series http://www.hoofrehab.com/HorsebackMagazineArticles..html . Written for lay horse owners, they provide a good introduction to hoof care and rehab.

The breakover point on the horse’s foot is the area at the toe that the horse pivots on and pushes from as the heels leave the ground. It is not necessarily the farthest-forward part of the foot – think of the ball of your own foot, which bears the brunt of pushing into the next stride, vs. your toes, which are actually farther forward, but doing little-to-no work as you pivot, leap or run.

As with your own foot, the horse’s natural breakover point is comprised of hard-callused sole, backed up by bone. This does not mean the horse’s hoof wall does not do hard work – but the wall is typically worn or trimmed/rolled back from the breakover point so that it does not become engaged until a little later in the stride after initial breakover of the foot.

Many people think of breakover as occurring only at the center of the toe, but actually it can occur anywhere around the foot as the horse turns or navigates uneven terrain. Therefore, the shape of the breakover point on the horse is round – a projection of the shape of the coffin bone (P3).

The sole at the outer periphery of P3 should be allowed to callus into dense material 5/8”to 3/4" (15-18mm)-thick to accommodate the incredible forces that occur to the region. Special care must be taken by the farrier or trimmer not to rob the horses of this necessary armor during maintenance trims (a true epidemic in the farrier world), and if a horse has 1/2" (12mm) or less sole thickness covering the outer periphery of P3, then hoof protection (my personal favorites are hoof boots with padded insoles) must be provided when riding, particularly on firm terrain.

correct breakover point

Figure 1 

In a healthy hoof with perfect lamellar connection [Figure 1] setting the correct breakover point is easy. If you were to project the line of the dorsal aspect of P3 to the ground (orange line) around the perimeter of P3, you are simply outlining the sole. In front feet, measuring from the sole, allow for 1/8” (3mm) of white line width (the white line – never white in color – is made of 50% epidermal laminae, 50% sole. Thus it is the bond between the hoof wall and the sole in healthy situations). Allow another 1/8” (3mm) of hoof wall to bear active ground pressure (blue lines) around the outer perimeter, then roll the wall on a 45-60 degree angle (red line). In other words, with tight lamellar connection, you simply roll/bevel the walls to achieve natural breakover for the horse. The densely callused sole around the outer periphery of P3 (green shading) will still bear the brunt of the ground force at the toe in most terrain, even though in these healthy, well-connected feet the wall is technically sticking out a bit longer and more forward of this rim of callused sole backed up by the cushioned design of the solar corium and by bone.

On hind feet with adequate sole thickness, I generally place breakover all the way back to, or only 1/8” (3mm) outside the perimeter of this true sole supported by P3.

This healthy, natural breakover point allows the horse to move correctly. The foot can stay on the ground longer (than if the breakover were farther forward), thus fly lower, farther in a long, efficient arc. The resulting long stride allows time and extension for the horse to load the heels at impact, taking premium advantage of the energy dissipating features built into the foot and each limb.

Finding and applying this correct breakover point gets much more complicated, though, when the hoof walls have become flared or rotated away from the bone [Figure 2]. The limbs, muscles, ligaments and tendons still have the same breakover needs for optimal movement and efficiency. When the toe wall migrates forward of its normal position around P3, it creates a biomechanical nightmare for the horse.

The typical result is that the horse has to step (breakover) a little earlier in the stride, lifting the foot more steeply to allow time to step over the longer toe (think of yourself walking in swim fins) and to avoid the pain involved in this now-increased stress and lever forces on the laminae. This generally alters the whole stride into a higher, shorter arc causing the foot to land toe-first because there is not enough stride extension for the horse to load the heels. Toe-first impact is one of the primary causes of toe flare and hoof capsule rotation – so a viscous cycle is created. The flip side of this is that the number one trick to growing out wall flare and hoof capsule rotation is achieving flat impacts at the walk and heel-first impacts at faster gaits. This means you will have to optimize breakover on these horses to eventually grow in well-connected walls.

Alternately, as the pain of separating laminae becomes more severe, the horse might start to avoid breakover completely, keeping the feet out front at all times, exaggerating the heel load. This is a defense mechanism that takes stress off the separating toe wall and thus the laminae. Again, in this case, the same trim relieves lever forces on the toe wall, usually eliminating the need for the horse to stretch back in this “founder stance” or move in this pattern. This is also helpful for growing in well-connected new laminae.

Figure 2

The lamellar wedge – the area between the now separated hoof wall and P3 varies dramatically in its texture and integrity. Sometimes it is an air space or bacteria-infested mush, sometimes it is made of harder material than the sole, sometimes it is anywhere in-between those extremes. Occasionally, all or part of the lamellar wedge is covered over by old sole material which has been distorted forward of proper support by P3. But the callused outer periphery of the sole – the tough “extension” of P3 (green shading) is generally still in the same spot relative to P3. Using radiographs, or often you can simply see the difference between the textures and colors of the true sole and the lamellar wedge, try to locate the border between the true sole and the lamellar wedge material. If you can find it, biomechanically, this should be the breakover point, with the roll beginning 1/4" outside that perimeter (blue lines) to protect the corium. Assuming the sole is of adequate thickness (over 1/2"- or 12mm-thick), the wall and lamellar wedge should be trimmed from this point with the nipper or rasp held on the angle of a normally rolled wall (red line in Figure 2).

BUT… If the sole is thin, I cheat the breakover forward by 1/2”-5/8” (12-15mm) simply to leave extra padding out front. Optimizing breakover on a thin-soled horse often leads to overexposure of the dermis, then bruising, then abscessing and P3 remodeling… not worth the potential gain. If an appliance is being added, whether a boot or shoe, then go ahead and optimize breakover on that appliance – but don’t do so on the foot until the sole is 5/8” (15mm)-thick or more.

The reasons behind optimizing breakover in a case like this are, 1) improve overall stride to get the horse loading flat/heel-first so that well-connected walls/laminae can be grown, and 2) to relieve the lever forces prying away at the lamellar connection so that well-connected walls/laminae can be grown. If you manage to get the breakover back far enough to achieve those two goals, it is back far enough – no need to increase risk to the corium by bringing it back farther when the soles are thin.

Trim more often, rather than taking the risks associated with over-trimming. Trim just enough to keep the new growth at the coronet from levering away from the bone during the next 3-4 weeks. Then come back 3-4 weeks later and do it again. If, instead, you trim so much wall that lever forces will be relieved for 8 or more weeks, the likelihood of increased pain and corium damage increases.

Figure 3

Eventually, this is the goal: [Figure 3] to grow in a normal wall/lamellar connection around the existing P3 (dashed line). There will, of course, need to be very careful heel work done and probably sweeping nutritional changes needed to achieve this, but keeping the breakover trimmed correctly along the way is a big part of success with these cases.

See the articles http://www.hoofrehab.com/HeelHeight.html and http://www.hoofrehab.com/Diet.html

Important note: In a rotated or severely flared hoof, do not trim the dorsal wall to the dotted line in Figure 3 – wait for the new well-connected growth. Instead, top dress the dorsal wall similar to the purple line in Figure 2. In order for the generally weaker lamellar wedge material to protect the dermis as well as a healthy hoof wall would, it needs to be about twice the thickness of normal hoof wall. Trimming the lamellar wedge down to normal wall thickness (1/2”-5/8” or 12-15mm) overexposes the dermis to damage.

Figures 4 and 5

On rotated, flared or exceptionally low angled hooves, any boots or shoes applied should have the breakover modified to optimize movement and efficiency. With hoof boots, in some cases this can be achieved by rasping a more aggressive breakover into the boot tread. In more severe cases, heat-fitting and/or toe-slotting Easyboot Gloves may be required. See http://hoofrehab.com/GloveMod.html

 

Finding the True Sole and Lamellar Wedge Visually

Looking for texture and color differences on the bottom of the foot is often effective for locating the true sole supported by P3. Careful though, some soles have striped pigmentation. Don’t make breakover decisions based on color alone – look for the texture and prominence as well. Some lamellar wedges are tougher than the sole and will be protruding past it. Other lamellar wedges are softer than the sole and will have worn off passive to the sole. Use lateral radiographs, as well, to help you determine where each tissue grew from. If you draw a line down the dorsal aspect of P3, generally the tissue behind the line is true sole and the tissue between the line and the wall is lamellar wedge material.

Figures 6 and 7

Figures 8 and 9

In Figures 6, 7 and 8, it is easy to see the boundary between the true sole and the lamellar wedge (yellow line). If the sole is over 1/2” (12mm)-thick, breakover should be brought back to 1/4" (6mm) in front of the true sole, well into the lamellar wedge material (Figure 9). Warning: this horse will need 24/7 boots with padded insoles and/or soft terrain until well-connected wall has been grown.

Figures 10 and 11

Five months later (Figure10 and 11), the walls have grown in much better-connected. Now getting breakover right only involves rolling the wall – the lamellar wedge is almost gone.

Figures 12 and 13

Combining Radiographs and Visual Indicators to find the True Sole, Supported by P3

The foot in Figures 12 and 13 has an obvious line between the true sole (outlined by orange dots in photo) and the lamellar wedge (black, weak, infected). The radiograph confirms the presence of the lamellar wedge to erase any doubt about the hoof capsule rotation present here.

By projecting the dorsal aspect of P3 to the ground (orange line on radiograph, orange dots in photo), then moving forward 1/2" (6mm) (red dotted line), the natural breakover around P3 can be created (red line in radiograph and photo).

Figures 14 and 15

Five months later, as the well-connected walls and laminae grow in, breakover can be optimized by simply rolling the wall. The “right” breakover point has not changed at all throughout treatment, though the application of it has changed dramatically.

Figure 16

Remember that when the sole is thin it is a mistake to optimize breakover when trimming the foot. Whether by projecting the dorsal aspect of P3 to the ground (blue line) or by seeing the boundary between the true sole and the lamellar wedge, if you move forward 1/4" (6mm) from the true sole line and place breakover (yellow line), the corium (red line) will be overexposed to impact trauma. Instead, cheat the breakover 1/2"-5/8” (12-15mm) farther forward (green line) until the sole thickens. During this time, of course, be sure no one is trimming the sole – this is too common.

Alternate Methods for Finding the Natural Breakover Point

In horses, the apex (front of) of the frog consistently grows/originates from a point 1/2" (12mm) or so behind the tip of P3 (not true in donkeys and some mules). So – to an extent – in horses, the apex of the frog and overall frog length can be helpful in finding the natural breakover point when there are no fresh radiographs and when you cannot see a distinct line between the sole and the lamellar wedge (which is an indicator of P3 remodeling). Note: when measuring to the apex of the frog, be sure to measure to the bottom of the collateral groove (the tight seam between the frog and sole), ignoring any overhanging flap of frog material.

If you measure the overall frog length (including the bulbs) in most horses, then divide that number by three, the resulting measurement is approximately the distance from the leading edge of the true sole to the apex of the frog, so very close to where the breakover should be located. There are exceptions to this:

·        Healthy development of the lateral cartilages and digital cushions makes the frog larger/longer in proportion to the size of P3.

·        There is some individual variance from horse to horse of where on P3 the frog corium originates.

·        Distal descent of P3 can elongate the frog.

·        Horses with P3 remodeling (bone loss at the outer periphery and/or ski-tipping) generally have the tissue of the frog apex originating closer to the forward edge of (or even in front of) P3.

·        Under-run distortion of the hoof capsule and heel bulbs can artificially elongate the back of the frog, thus the overall frog length.

Each of these exceptions makes setting breakover 1/3 of the frog length in front of the frog too conservative or too far forward. But this means, at least, that this ratio is a good place to start when you have no other indicators. Again, when the soles are thin [collateral groove height less than 1/2" (12mm) off the ground], don’t optimize the breakover. Instead set breakover at half the total frog length in front of the apex of the frog as a very safe starting point.

Figures 17 and 18

Another useful tool to help find this same breakover point is to project (not cut!) the upper 1” (25mm) of new wall growth to the ground, then add the typical 45-60 degree roll to the lower portion, simulating the dimensions of a normal “mustang roll” on the wall. In Figures 17 and 18, using the same hooves previously discussed, if you project the angle of the upper 1” (or more) of new growth to the ground (blue lines) it will approximate the same breakover point, unless that upper growth is also rotated. Even then, it will get you closer than if you simply rolled the existing rotated wall at ground level.

Don’t use less than 1” of growth for this projection! The coronet can bend, distort, and thus trick you into being too aggressive if you try to do this with a shorter length of new hoof growth.

Figure 19

Using all of the above indicators in unison is considerably more accurate than using any one of them alone. In the foot in Figure 19, I set breakover at 1/3 of the frog length in front of the apex of the frog (blue vs. yellow lines). This helped me notice a very subtle sole/lamellar wedge line (red dashed line) I might otherwise have overlooked.

Figure 20

Be willing to go outside the box, rather than blindly following methodology. The Thoroughbred above has a thin sole and is getting much of its vertical depth/height off the ground from a proud rim of lamellar wedge around the outer periphery. Don’t bring breakover back so far that you would lose vertical height/depth. Remember that the reason for optimizing the breakover is correct and comfortable movement. This trim achieved these for the horse, while also providing more protection for the corium than it would have if I had brought breakover back farther.

Figure 21

With bare feet, from 10:00 to 2:00 around the toe, horses seem to care very little about whether hoof wall is standing longer than the sole. In this region, if the soles are of healthy thickness, it is generally safe to bring breakover back so that the walls appear unloaded when the horse is standing on a hard, flat surface. I believe this is because horses don’t actually need a toe wall for standing still on a hard surface – they need a toe wall when they are propelling themselves along through their home and work terrain. So a foot with the breakover trimmed as in Figure 21 has a very active hoof wall engaged after breakover when the foot is tilted up higher and the horse is pushing off the toes.

But from 10:00 to 2:00, back, horses do seem to care more about whether wall is sticking up past the sole. It is much more likely that you will make a horse tenderfooted if you don’t leave 1/8”-1/4” (3-6mm) of wall standing past the sole at the quarters and heels.

There is a time and place to unload big quarter flares – this is just to say that it cannot be done nearly as routinely as at the toe.

Important note: When hooves are bare, booted, have tape-on pads, epoxies and with some thoughtful glue-on applications, the solar corium receives huge loads from impact through breakover, and a 100% release of that load when the foot is in flight – this is the natural way the sole should be loaded and does not seem to cause a lot of problems. But beware of shoeing with sole pressure, as this pressure is “clamped on,” so is not fully released during hoof flight. The solar corium, like all living tissue is quickly damaged by constant pressure without release.

Figures 22 and 23

Another variance I commonly need to do occurs when a foot has wholesale wall flare all the way around the foot, or at least one big quarter flare along with a toe flare or hoof capsule rotation. In the foot in the Figures 22 and 23, if you trimmed aggressively to try to grow out the rotation, and both quarter flares during the same visit, the horse would almost certainly be lamed and in danger of bruising of the corium, particularly if any of the horse’s terrain was firm or rocky. Even worse, the resulting compensative movement would probably make growing in well-connected walls impossible, anyway. So instead of trying to do it all at once, I find it important to “pick my battles.” In this case, I felt that toe-first impact and discomfort caused by the rotated toe wall was causing the primary problems. So from 10:00 to 2:00 around the toe, I optimized the breakover.

At the quarter walls and heels, I took a more passive approach – I left the walls standing well past the sole and just rolled/beveled their entire width. Remember the real secret to growing out wall flare is flat and/or heel-first impact, anyway.

The result of being aggressive with the toe wall and more conservative with the quarter walls is a “squared off” look that I am generally not a fan of. In this case, though, it is the right thing to do. At some future trim, when I am not making a big breakover change, I might “pick another battle” and go more aggressively after one or both of the wall flares. Eventually, when well-connected walls/laminae have been grown in everywhere, the foot will be round – following the shape of P3. But this method is often a very important means to that end.

Figure 24

In this foot, the border between the true sole and the lamellar wedge is marked by the blue dashed line – this horse has about a 10 degree hoof capsule rotation. Everything between the blue line and the wall (green line) is lamellar wedge material. This photo shows a variation to trimming I commonly use when soles are moderately thin – 3/8” (9mm). To leave adequate protection for the corium while simultaneously optimizing breakover, I place a slight bevel on the entire width of the lamellar wedge (10-30 degrees, depending on how close the solar corium is to the outdoors). Then the wall is rolled normally. Notice the sole was not touched, but was allowed to keep all callusing and thickness. This horse is comfortable barefoot in the turnout environment and ridden in boots with padded insoles while I grow out the rotation and wall cracks. The breakover point is back at the supported sole (blue line), while adequate armor is left out front.

Alterations

Aside from normal or natural breakover discussed here, there is a long list of issues – really any injury or biomechanical problem a horse might have – in which altering or exaggerating the breakover farther back might help the horse move better. These generally warrant experimentation and careful scrutiny of the horse’s movement to find the “right spot” for breakover. I caution you again, though, to do these alterations on the appliances you use, whether nail-on, glue-on, epoxies, urethanes, or boots. It is important that you not over-trim the foot itself in the name of some other issue the horse has. Don’t trim sole unless, perhaps, it is over 5/8"(15mm)-thick and leave at least 1/2" (12mm) thickness of good, solid hoof wall or 1” (25mm) of lamellar wedge out front to simply pad the corium from impact trauma. And if you find less material than this already present upon your initial visit, be sure to treat the horse as compromised – provide protection in some form, and/or make sure the terrain is soft, until the protective tissue has reached these adequate thicknesses.

 

All photos are from Pete Ramey’s files or from the book Care and Rehabilitation of the Equine Foot. Black and white line drawings by Karen Sullivan – color graffiti added to them by Pete.