276 Journal of Equine Veterinary Science June 2003

Foot Science

The “ideal” front hoof conformation of 50- to 55-de-gree toe and equal heel angle is a rare occurrence.Reports on the findings of Ovnicek, Redden,Jackson, and Pollitt should lead us to question the

significance and validity of the ideal hoof conformation andinquire as to the parameters necessary to minimize the op-portunity for insult to the foot and lower leg. This is the far-rier’s primary responsibility day in and day out; however, itbecomes the veterinarian’s duty to sort through the lamehorse to determine contributing factors and determine aplan of action to halt and, it is hoped, reverse pathologicprocesses already in place. To do this successfully and re-peatedly requires recognizing “normal” and “abnormal”physically, radiographically, and possibly sonographically,or with other imaging modalities. Are all “hurts” injuries,and do the radiographic findings actually signify a sourceof pain? Is the pain a component of inflammation, or areother mechanisms at work? In the biomechanical literatureI poured through for this presentation I failed to find anystudy relating the outside of the hoof to the bones and jointswithin. Dr Page’s article related toe length to the coffinbone and coffin joint structures, but no other relationshipswere made. However, I believe we can take the findings ofa number of studies, combine them with clinical observa-tions and a bit of horse sense, and draw some conclusionsregarding what may or may not be occurring in the foot.

As has been stated before, the relationship between theveterinarian and farrier must be healthy to provide for thehealth of the patient. Radiographs are and will continue tobe a critical component of the examination of the foot, andwhile equipment improvements continue to refine the qual-ity of images, it is the information gleaned from these im-ages that we must use to direct our therapies. Common rec-ommendations are to “shorten the toe,” “raise the heels,”“add support or a pad,” and put on an eggbar shoe. Little re-gard is given to specifics, and although it may be difficultto take an idea from a radiograph and apply it to a foot, this

Reprinted with permission from the 16th Annual Bluegrass LaminitisSymposium 2003.doi: 1053/jevs.2003.77

Long Toe, Low Heel, Short Toe, No FootBruce Lyle, DVM

approach certainly can increase the likelihood for successand provide a starting point for future alterations.

For this approach to work, the veterinarian must con-sider the limitations faced by the farrier, and both profes-sionals must keep in mind the structures within the hoofcapsule (which, when all is said and done, will, it is hoped,still be inside the hoof capsule). One of the most commonand most useful views of the foot is the weight-bearing lat-eral-medial projection. From this view, the relationship ofthe hoof wall to the coffin bone can be assessed, the rela-tionship of the coffin bone to the pastern bones can be as-sessed, etc. One parameter seldom mentioned yet vital tothe horse (and farrier) is the sole shadow beneath P3. Thisvital piece of information can yield multiple clues as to thefunction of the foot and what can be done to improve it.

The first thing that must be done is to establish a nor-mal. Being that the radiographic measured distance fromthe dorsal hoof wall to the parietal surface of P3 is in theneighborhood of 15 to 18 mm, this would seem to be a min-imum pad and protection necessary for the bottom of thefoot if it is appropriate to protect and unite the dorsum ofthe foot. It should be mentioned that this is live sole, not ex-foliating sole, and being a minimum, should be present atthe beginning of the shoeing cycle. This is measured verti-cally and perpendicular to the solar surface of P3.

Using the dorsal wall comparison again, our solewould consist of 6 to 8 mm of solar corium/vascular zone,a 2- to 4-mm interfacing of the rete pegs with the cornifiedsole, and then 6 to 8 mm of cornified sole. Hence, a horsewith a 4-inch toe but only 8-mm sole depth may have a longtoe but certainly has no foot. Since learning to pay attentionto this detail, I consistently see lame horses with less than10-mm sole depth, some with as little as 4 inches. Soledepth becomes vital in assessing the foot’s needs and thetype of trimming and shoeing that can be applied in a ther-apeutic fashion. Wall length (toe length) without accompa-nying sole depth obviously predisposes the wall to separa-tions, chips, cracks, and avulsions. The wall, whenprimarily weight bearing, acts as a lever against the laminaeand corium. Solae compression then occurs as the coffinbone is pulled palmarly during loading, working against thefriction created between the wall or web of the shoe and the

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ground. Whereas most lower limb maneuvers occur pas-sively, once pain enters the equation, contraction of thedeep flexor and, to some extent, the superficial flexor be-gins a vicious cycle of adding injury to insult. After insultoccurs, the breakover must be reduced to a point that neu-tralizes the pull of the deep flexor tendon. Thus toe lengthas viewed physically and radiographically should beviewed not only with respect to the tip of P3 but also rela-tive to the coffin joint and in consideration of the tension inthe flexor tendons (not easily measurable). Without ade-quate assessment of the foot, stride, and lower limb confor-mation, what appears to be a long toe may or may not be,whereas what appears to be a short toe may be long or maybe a component of a deep, healthy hoof mass.

So what about the heel? Heel length and angulation isdetermined by use, tendon forces, and rasps. Radiographsare invaluable in determining what to do with the heel inseveral respects. Protection to the impact zone can be mea-sured in much the same way as previously described. Withor without bony changes, this alone may be informative asto the cause of pain in a horse whose use is hard on its heelarea. The heel impact area should be assessed relative to thecoffin bone as well as the coffin joint. An elongated verti-cal heel (as in a club foot) often is advantageous, whereasan elongated sloping heel may be far enough anterior tocreate a fulcrum that results in palmar rotation of P3 at im-pact, placing undue stress on the impar ligament and navic-ular structures, especially in the fatigued or under-conditioned limb. This phenomenon is commonly observedin the “underrotated” laminitis case following a deep flexortenotomy. Splayed heels and underrun heels are a commonsequel to the founder horse that undergoes deep flexor teno-

tomy and provides a true education into the significance ofthe deep flexor tendon muscle in the horse’s gait and the ef-fect it has as a cause of and result of foot and upper limbpathology. The heel should be of sufficient length relativeto its angle to prevent ventral rotation of the coffin bonewhen the toe is loaded in particular gaits and maneuvers,but not so long as to create a fulcrum effect that “slaps” thetoe to the ground when inertial forces are dictating lowerlimb movements at speed.

Although few specifics as to toe and heel length arepresented within these notes, it is somewhat by design. Theintent is to encourage the farrier to realize that the horn withwhich he or she has to work is largely a function of thebones within and the forces above, as well as the environ-ment. Few horses meet the criteria for normal, and often alook to the inside can be beneficial to all involved to seewhat is externally available to manipulate without disturb-ing the internal structures. It is hoped that the veterinarianwill realize the importance of the quality of radiographicimages he or she produces and be able to help formulate aplan of attack based on the pathology or biomechanics atplay relative to the internal structures of the foot. Althoughfarriery is not an absolute science yet, regards for the ef-fects of pain, training, breed, and conformation will beginto incorporate a tremendous amount of scientific thoughtinto the art of raising, restoring, and maintaining soundnessin horses.

SUGGESTED READINGBack W, Clayton H. Equine locomotion. Philadelphia: W. B.Saunders; 2001.Page B, et al. Breakover of the hoof and its effect on structures andforces within the foot. JEVS 2002;22:258-64.