LAMENESS


Fig. 4. A line drawn through the angle of the coronet of a horse with low heel “bull nose” conformation forms a trajectory to the elbow of the forelimb. A horse with good foot conformation will form a trajectory to a point just above the carpus.


block sound with posterior digital nerve blocks be- cause this hind foot conformation may lead to pain in the hocks, proximal suspensory ligament and glu- teal and lumbar region.4–6,8


The Low Heel “Bull Nose” Foot Conformation


This abnormal conformation of the hind feet is easy to recognize. When looking at the limb from the side, the digit will show a broken back hoof pastern axis. The slope of the coronary band from the toe to the heel will have an acute angle of 40–45°, and the coronet will bend distally at the heel to become al- most vertical. The bulbs of the heels will be pro- lapsed plantar to the heels of the hoof capsule and will form a “knob”-shaped appearance that can be seen lying against the shoe. The hair on the coro- net at the heels may project horizontally rather than lying flat against the hoof due to excessive load on the associated hoof wall. There will be a disparity


in the growth rings below the coronet from the toe to the heel, with the growth rings wide apart at the toe and then tightly packed at the heel. The dorsal hoof wall will assume a “bull nose” appearance (Fig. 5A). Looking at the foot from behind, the frog will be large and bulbous from the constant stimulation with the ground, a ledge will form in the frog from bearing weight, and it will be situated well below the hoof wall with the bulk of the frog now located be- tween the two branches of the shoe (Fig. 5B). The solar surface of the foot will show an inclined plane of the entire frog from the base to the apex in a dorsal cranial direction toward the coronet. This inclined plane or angle will match the angle of the solar border of the distal phalanx in the hoof cap- sule. The toe area on the solar surface of the foot will show a deep or exaggerated concavity between the apex of the frog and the inner branch of the shoe instead of a steep, yet smooth transition of the sole from the frog to the sole wall junction. There will usually be a palpable “trough” located just dorsal to the apex of the frog (Fig. 5C). Upon removing the shoe, the end of the heel of the hoof capsule is lo- cated well forward from the base of the frog and the horn tubules will be parallel with the ground. The hoof wall at the heel will be thin, the bars may be damaged or missing, and the angle of the sole will be absent. Lightly paring the area adjacent to the hoof wall at the end of the heel with a hoof knife will often show moderate to severe hemorrhage from the pressure of the damaged hoof capsule against the shoe. When the foot is placed on the ground, total weight bearing will be placed on the frog, which is located distal to the ground surface of the hoof capsule, and many horses will be reluctant to stand on it when the opposing limb is lifted off the ground. As noted previously, hoof testers placed on either side of the heel at the angle of the sole will often elicit a painful response and the struc- tures will deform (Figs. 6A, 6B).


Radiographs


A lateral radiograph of the hind foot will show a broken back hoof pastern axis, with the middle pha- lanx (P2) being displaced plantar and distal relative


Fig. 5. A, Lateral view of a moderate low heel “bull nose” conformation of a hind foot. Note the disparity in growth rings and the acute angle of the coronet. B, Plantar view shows the prolapsed frog as well as the incline of the frog. C, Solar view shows the incline of the frog in a dorsal cranial direction (black lines), and the marked concavity of the sole (red arrow).


422 2018  Vol. 64  AAEP PROCEEDINGS


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