09/07/2022
Really good information. I try to explain some of this to a lot of people, but not sure I always get it across so well. Worth the read.
Shoeing problem hooves without radiographs.
Radiographs are a luxury most farriers do not have access to in their daily work. Depending on the client's situation and location, any discussion about seeking veterinary assistance may often be impractical and futile. The latest data presented at AAEP was that only 1% (down from 6% a decade ago) of veterinary school graduates are reportedly going into equine medicine, with only 30 accredited vet schools in the US, and graduating class sizes plus or minus 100, you can do the math. Rural areas are desperately underserved and farriers working in these areas are routinely required to provide the only professional care and treatment many of these horses will ever get or see.
Laminitis and founder are especially prevalent conditions in the horse population and to a far greater extent among what is broadly termed the "backyard horse" population. These horses may often be over fed and under worked, there are a greater number of aged horses in this population, and many of these novice owners are unknowingly purchasing horses that are metabolic or show signs and symptoms of past or potential problems that more experienced horsemen would immediately recognize and steer clear of.
When horses were viewed in a more utilitarian manner, many, maybe most were euthanized once they had foundered and their usefulness was deemed spent. Few treatment options were available anyways and the general knowledge of the condition was poor. Now, horses are increasingly viewed as pets, or if not viewed as "pets", then at least they are largely viewed with a greater empathy than was the case decades ago. Now foundered horses are kept alive and owners are increasingly desperate for help and answers.
This means encountering foundered horses (especially chronic cases) now can be a daily routine for farriers who service these "back yard" accounts. But, in having to work on these cases alone, how can the farrier know the orientation of the coffin bone within the hoof capsule without a radiograph? Many would say, the farrier cannot, because no one has x-ray vision. Okay. So, let's momentarily ignore what "many" say, and look at what we can use externally to derive some pertinent information when we must employ knowledge in lieu of technology.
To preface much of this I would take a moment to credit the work of Redden, Savoldi, Duckett, and Aalders as being instrumental in contributing to my personal approach and understanding. Those familiar with their work should recognize where each shines in the midst of the ramblings that follow,
The frog plane, or more specifically maybe the plane of the frog corium will mirror the palmar angle of the coffin bone. If you place a barium marker at the frog skin juncture at the center of the caudal most aspect of the frog and another barium marker just forward of the true apex of the trimmed frog, the angle formed between these two markers will reflect the palmar angle of the coffin bone and can be demonstrated radiographically. Once you are familiar with these two points you see the frog plane readily and easily and this observation becomes extremely useful or even critical.
Sole depth. A dropped or pr*****ed sole that is bulging or distorted via compression from coffin bone rotation is easily recognized and may also be accompanied by a dip in the hairline at the toe, and a dish in the dorsal hoof wall. The depth of the dorsal wall dish (when present) in the undressed hoof can mirror the degree of solar displacement (sag) and compression, though the tip of the coffin bone may demineralize in long standing cases leaving in its absence what appears to be greater sole depth.
The depth of the tip of the frog relative to the immediate surrounding sole is one of the best indications of sole depth. A deep frog tip infers depth of sole while a flat sole with a frog set proudly upon it can indicate a lack of sole especially if vertical depth of the entire hoof is lacking. Assessing the overall vertical depth of the hoof relative to the size of the horse and hoof is a pretty straight forward experience-based comparison. The farrier should have a pretty clear visualization of the size and depth of the coffin bone relative to the hoof surrounding it and see clearly when that depth is proportionally lacking. We see and handle enough hooves to pick up on a lack of vertical depth immediately. Palpation of the sole with thumb pressure and/or hoof testers can support a visual assessment.
Regarding depth, venograms have taught us that the more sole depth a horse has the longer and straighter the solar papillae, some papillae have been measured 10mm below the coffin bone, and this correlates with anecdotal evidence in the field when farriers encounter hooves that cannot responsibly be trimmed as short as one may first think. Radiographs cannot differentiate between sensitive and insensitive sole and cannot be relied upon for this reason to determine exactly how much hoof can actually be safely removed. The farrier has to learn to recognize when to stop removing sole. When in doubt err on the side of being conservative, no horse ever went lame from having a little excess sole.
The sole plane will generally reflect the ventral plane of the coffin bone which can tell us whether we have a medial or lateral list in the bone. We know that the coffin bone will often be driven down or pitched medially on hooves that are more upright on the medial wall and this is even more likely the case when the coronary band is "ledging" medially as many founder cases do that are said to be sinking medially. "The medial side of the hoof does not grow as fast as the lateral side of the hoof simply because horses have 4 legs. The medial side is under greater compression being closer to center mass. If you want to find a hoof that grows symmetrically you must find a horse with only one leg that comes directly out of the center of it's girth"~Redden.
I have observed the heel angle is usually a pretty closely related to the tendon surface angle of the navicular bone (but not always), and the size of the navicular bone may be larger in hooves that demonstrate less DF suspension force (but not always).
Growth rings. A horse with a positive palmar angle of more than 5-10 degrees will have diverging growth rings. We also know growth rings occur at approximately 30 day intervals, these illustrate compression where they converge. While not a perfect representation, the angle created between these growth rings can strongly hint towards the palmar angle of the coffin bone.
We know that a forward set pastern within the coffin joint evident in the profile or silhouette of the pastern and dorsal hoof wall is indicative of a high deep flexor tendon suspension force and a setback pastern viewed from the same lateral perspective is an indication of a low of deep flexor suspension force.
We can outwardly locate the center of articulation of the coffin joint which is 2/3rds forward along the hairline when the hoof is viewed from the side and then dropping an imaginary plumb line down from that point, we can easily see the ratio of support (or lack of support) forward and behind that point.
We can derive additional information from the commissures on either side of the frog in regard to arch, caudal depth, and ML compression. While the caudal displacement of a compressed digital cushion is made evident by the heel bulbs protruding "out the back door" of the hoof well beyond the heel.
The high trajectory of the hairline and usual bull nosing of the dorsal wall are textbook signs of a negative palmar angle and we can also predict the shape and contour of a NPA coffin bone being more domed and beak like while the club foot coffin bone is the exact opposite with a dorsal bow or dish. We can suspect or expect remodeling on the front end of the coffin bone in a high hoof and remodeling on the back end of the coffin bone (the palmar processes) in a low hoof correlating with the severity of the abnormal PA and the age of the horse.
The presence of a stretched white line and it's measurable width indicates the severity of longstanding laminar damage creating an angle from the junction with healthier proximal hoof wall growth offering another contextual indication of the coffin bone's orientation relative to the dorsal wall. In most cases with a dorsal dish, following a line from the proximal wall growth down is a close representation of where the toe should have been (relative to the coffin bone) if not for pathologic phalangeal or capsular displacement.
In a healthy hoof that has not yet foundered we could (if for some strange reason existed in which we needed to) even estimate rather closely the bone angle by subtracting the palmar angle (estimated by the frog plane) from the hoof angle, (if the dorsal wall hasn't recently been over rasped).
External hoof mapping can also methodically tell us where the coffin bone is relative to the capsule. I don't personally map hooves as I am accustomed to utilizing other reference points but the methods utilized by those who do map hooves contribute more data points to help train one's eye.
"1 inch forward of the widest part of the hoof is the true apex of the frog. 3/8th of an inch back from the true apex of the frog is "Duckett's dot", this is the center of weight bearing on the hoof. 1 inch back from the true apex of the frog is "Duckett's bridge", this is the mechanical center of the hoof. 1and 3/4 inch forward of Duckett's bridge is the distal edge of the coffin bone. Theoretical breakover occurs 1/4 inch forward of the distal edge of the coffin bone. From this breakover point to the buttress we would like to see a 50/50 ratio of support."~ (not really sure who said that, but it may have likely been Mark Caldwell)
There is a wealth of information that can be garnered from the hoof, far more than can be listed or explained in a one evening essay. Radiographs should be confirming your observations as a farrier and should not be a grand revelation. The spatial position of the coffin bone and all of the measurable parameters should already be very similarly drawn in your mind's eye.
All that said, opportunities to work with radiographs should always be welcomed and the owner should be encouraged to pursue them if at all possible and practical. We should always embrace any opportunity to increase the available information we can accrue mentally on any given hoof and any given case. The more you work with radiographs the more you can fine tune your observations and the more accurate your future assessments will be, (so long as you are observant). It is important to note that we have no way of outwardly estimating things such as the degree of coffin bone loss or the extent of remodeling that may be present with any certainty without radiographs.
Radiographs are an excellent tool to illustrate to an owner the severity of a hoof problem and the owner often gains a greater appreciation and understanding of what you are contending with. Radiographs are also an excellent baseline tool of reference to quantify progress or regression. Cultivating a working relationship with an equine veterinarian can be a mutually beneficial endeavor. The reality however persists that as farriers we must very often navigate through the majority of cases independently and logically while employing every tool at our disposal which may only be our personal experience and knowledge of the hoof.
(photo credit: RF Redden Understanding Laminitis- demonstrating a rasp being used to illustrate the frog plane)
