BACK TO BASICS: LAMENESS AND PODIATRY


Fig. 5. A, Lateral view shows the proportions (red arrow) on either side of the middle of the foot (black line). 5, Solar view shows the proportions of the foot on either side of the widest part of the foot. Yellow dot denotes the COR.


Fig. 6. A, Note the broken back hoof pastern axis. The yellow arrow is the end of the ground surface of the hoof wall at the heels. Note the proportions on either side of the middle of the foot and the thickening of the coronet at the heels with the “knob”- shaped appearance. B, Shows a marked decrease in the structural mass of the digital cushion.


access foot conformation from the lateral side as well as the ground surface of the foot by using theCORas the intersection between the proportions (Figs. 5A and 5B).


5. Long-Toe, Low-Heel Foot Conformation


A low-heel conformation can readily occur with or without excessive toe length. This type of foot con- figuration is so common in equine practice, espe- cially in Thoroughbred horses, that it is thought to be normal.15 A long-toe/low or underrun heel con- formation (LT-LH) is defined as the angle of the heels being considerably less than the angle of the dorsal hoof wall. When this difference in angles is considerable, it is characterized by a broken back HPA where the angle of the dorsal hoof wall is lower than the angle of the dorsal pastern. It is often the result of leaving the heels to migrate dorsally when trimming, which allows them to grow forward and lose their angle. When evaluating the foot from the lateral aspect, there will be disproportionate dis- tances on either side of the middle of the foot to the toe and to the heel. There may or may not be a flare in the dorsal hoof wall. The coronet will reveal an acute angle from the toe to the heel and the coronet at the heels will thicken and begin to form a “knob”- shaped appearance. The angulation of the horn tu- bules will decrease from toe to heel and may often be parallel with the ground at the heel (Fig. 6). The ground surface of the foot will again show a dispro- portionate distance from the widest part of the foot to the perimeter of the toe and to the base of the frog. The heels of the hoof capsule will have migrated dorsally while the soft tissue structures are located palmar to the end of the heels, and, in many cases, the frog is situated distal to the bearing border of the hoof wall. Interestingly, when observed in motion on a firm flat surface, a horse with LT-LH confor- mation may have a markedly heel-first landing due to the lack of ground surface in the palmar foot, the horse may land flat, or the horse may land toe first if they are experiencing discomfort in the palmar foot.


356 2018  Vol. 64  AAEP PROCEEDINGS A low hoof angle results in dorsiflexion of the DIP


joint, which concentrates weight bearing on the pal- mar section of the foot and increases strain on the DDFT. This excess load, in turn, may cause in- creased stresses on the navicular apparatus and the soft tissue structures associated with the palmar foot and the joints proximally16 (Figs. 7A and 7B). If low or underrun heels are allowed to progress,


this condition can be readily observed both visually and radiographically; the point at which the angle that the hoof capsule or the distal phalanx forms with the ground is lower palmarly/plantarly than it is dorsally. A negative angle of the solar border of the distal phalanx, as noted radiographically, means that the soft tissue structures (frog, digital cushion) are underdeveloped or have decreased in mass, usu- ally due to damage, or they have prolapsed palmarly which allows the distal phalanx to descend distally (Fig. 8). Biomechanically, it changes the angle of insertion of the DDFT on the distal phalanx, in- creases the peak force on the navicular bone bursa, and moves the GRF dorsally toward the toe (Fig. 9).4,5


Farriery


The treatment of low or underrun heels is difficult, and often the conformation of the heels can only be maintained rather than improved. Farriery seeks to reduce the length of the dorsal wall and redistrib- ute the weight on the ground surface of the foot. The traditional farriery for low or underrun heels is to use an egg bar shoe to support the heels, often accompanied by some form of heel elevation to raise the angle of the heels and correct the broken back HPA. However, it is questionable whether “support” can be applied to compromised structures (heels) that no longer have the ability to accept weight, and the egg bar shoe may do little more that apply leverage to the palmar foot. The ability to improve the soft tissue structures in


the palmar foot and to produce new hoof wall growth at the heels may be limited. In the author’s experience,


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