By Dr. Alicia Nolfi
Everything that we see externally in the equine foot is a direct result of what is happening internally. The foot is a dynamic organ that has suspension and support components working together to achieve stability and movement. When all components of the foot are healthy and have total recall, the foot has optimal equilibrium. When one component is unhealthy, for whatever reason, adjacent and possibly non-adjacent components will assume excessive load or tension, leading to further breakdown. Preventive equine podiatry, striving to recognize unhealthy characteristics of the foot before they become a career- or life-threatening problem, is invaluable for this reason. The foot will tell you what is breaking down, often long before a clinical problem is obvious. We just need to understand what we are seeing.
We must leave behind the concept of perfect, asymmetrical feet that match. Those feet do not exist nor are they truly healthy. Focusing on what is healthy, as determined by optimal perfusion to, growth of and function of all components, is vital.
The hoof wall is a support component that should be strong, thick, glistening and durable. Horn wall cracks happen for a reason – the horn is not strong or durable anymore. Why? Something is causing the horn to break down.
With toe cracks – there is excessive pull or stretch on the inner and outer horn tubules – towards the inside of the foot. Toe cracks initiate because of unhealthy internal mechanics, but also because of external influences. Or a combination of both. Importantly, what continues to happen inside perpetuates the problem – whether it starred due to internal or external factors.
The action of the deep digital flexor tendon, which is attached to the bottom and back half of the coffin bone, pulls the front half of the coffin bone down and back. The DDFT is a suspension component and is in tension anytime the foot is weight bearing. It has massive influence on what happens inside the foot. Think about palpating tendons on the back of the cannon bone. When the horse is standing, they are taut. Only when the foot is non-weight-bearing are they loose. When the horse is in motion, just before picking the foot up off the ground, the DDFT is at maximum tension – this is how the foot moves. For optimal equilibrium, the opposing suspension components are the laminae and inner horn wall. They will undergo stretch and tension from the action of the DDFT, maximally at the toe, and when healthy have total recall when the foot is non-weight-bearing. When the laminae or inner hoof wall is unhealthy, the system breaks down and the DDFT action can overcome the other components.
Why do toe cracks happen in neglected feet? Because maybe the diet is also neglected and the horn quality is poor. Or maybe the toe is excessively long, has not been worn or trimmed and the breakover (the measurement in millimeters from the apex of the coffin bone to where the foot or shoe leaves the ground) is also excessively long. Breakovers longer than about 25 mm require more tension in the DDFT for it to do its job…hence chronic excessive pull of the coffin bone away from horn wall. Or the foot has been subjected to excessive moisture which is causing disruption of healthy horn. Or the foot has white line disease from an external cause. Even if the problem starts because of any of the above – the action of the DDFT is perpetuating the problem.
Why do toe cracks happen due to internal causes? Because the mechanics are not in equilibrium and the action of the DDFT is overcoming toe wall strength. Either the DDFT has excessive chronic tension in it due to club foot syndrome (very common) or the foot has white line disease (when a unilateral problem, WLD is almost always in a club foot due to the excessive inner horn stretch). Or the inner horn wall is unhealthy (see above). The DDFT pull is still there. It is all related.
Therefore… We cannot separate the mechanics of the foot from the problem… Toe cracks close when loaded due to the pulling action of the DDFT, regardless of how they originated.
Quarter cracks are different – there is excessive load on the quarter tubules, almost invariably because. of unhealthy support and suspension components in the back half of the foot. The DDFT likely does not have enough suspension, the digital cushion, frog and buttresses do not have enough supportive health, so the load is transferred to the quarters. This is what we call crushed heels – and in some feet even the mildest level of crushed heels will lead to a quarter crack. The tubules begin to emerge at a lower and lower angle, they fray at the ground surface, and eventually the wall cracks. Quarter cracks open when loaded, as the components of the back half of the foot push the two sides of the crack apart. This is why toe cracks and quarter cracks are treated differently – the mechanics are different.
Toe crack treatment goal is to stop the pinching of the two sides. We do this primarily by decreasing tension in the DDFT. If we need to add a toe crack repair – it is best to use a specific technique that stabilizes the crack in the open and non-pinched position using a band seared, screwed and maybe also glued over the screws, into the foot. Quarter crack treatment goal is to keep the crack closed. We do this also using mechanics to unload the crack, but we have optimal success when we lace the crack closed being extremely careful to not ever close any crack that has any infection present.
*KEY POINT: All of these characteristics that result in horn cracks can be identified in the feet long before toe or quarter cracks ever happen.*
I hope I have provided a sensible, brief intro into what you all will read in the following resources. I will attach an article on the general mechanics of the foot and also articles on toe cracks and quarter cracks. Since this is an educational post, we can allow questions for a couple of days. Please read ALL of the material thoroughly before asking any questions and please tag me if you make a comment or ask a question.
HEALTHY EQUINE FOOT
• Hoof angle at toe between 50-58 degrees, heel angle frequently 15-20 degrees less
• Relatively linear wall
• Medial (inside) wall may be slightly more upright than lateral (outside), with exceptions for toed-in or toed-out feet
• Strong, durable, intact hoof wall with a hard, natural glistening appearance
• All horn tubules are tight along entire ground surface, whether barefoot or shod
• End tubules can be easily visualized with a fresh trim and should not be frayed
• Terminal laminae are tightly grouped at the ground surface, especially at the toe where they are most vulnerable
• Heel tubules should be relatively straight even though they emerge at a lower angle than the toe. This angle decreases during loading and the heel tubules are distorted to some degree at the ground surface with or without a shoe, but healthy heel should have total recall and maintain its height
• Growth rings should be even from the toe to around the heels, inside and out (medial and lateral)
• Mass of digital cushion and frog should range between 2-3” in light breeds and 3-4” in heavier breeds
• Sole has a natural cup (not man made) and is approximately 20mm in depth.
• Sole has a tough, calloused ground surface
• Strong, durable frog has texture and resilience of a rubber tire, smooth borders and tough appearance that seldom requires trimming
***THE OUTSIDE HEALTH OF THE FOOT IS DETERMINED BY ITS INSIDE HEALTH!***
Taken from Dr. Ric Redden’s Advanced Equine Podiatry Course Notes, October 2015
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