This case involves a sevenyear-old Thoroughbred gelding with a year-long history of chronic lameness. The horse had been turned out for the past six months and displayed the typical long-toe/underrun heel conformation in both forefeet, with the left forefoot being more severe (Figure 1).
As a result of the foot conformation, the horse displayed a broken-back pastern axis. Toe length was exceptionally long at 4 1/4 inches, with a concavity (dish) in the dorsal hoof wall.
Both forefeet had full thickness cracks in the dorsal hoof wall. The crack in the left hoof wall was movable— opening in the non-weight bearing position and closing when the limb bore weight.
Examination of the ground surface of the foot showed a widened sole wall junction (white line) and a flat sole. Hoof testers applied to the sole caused pain and testers applied to the horny sole detected movement, indicating a decreased sole depth. The hoof wall was thin in the heel and had started to roll under. Limited farriery had been used during the previous year to correct the foot conformation.
Lateral radiographs were taken to evaluate the distorted hoof capsule and its relationship to the third phalanx (P3). Radiographs can also be used for guidance when trimming and placing the shoe, allowing a distorted hoof capsule to be realigned relative to the bone.
The foot was placed on a wooden block with a wire embedded in the surface. A second wire was attached to the length of the dorsal hoof wall. A marker (thumbtack) was placed behind the apex of the frog and he end of the hoof wall (Figure 2). Markers allow taking measurements from a radiograph and applying those measurements to the foot (Figure 3).
The heels were trimmed, starting at the widest part of the foot and working in a palmar direction (toward the heels), until flat solid hoof wall was reached. A marker was placed at the end of the trimmed heel and a second radiograph was taken (Figure 4).
Note increased ground surface in the heel. The ground surface in front of the widest part of the foot was left untouched. The toe of the hoof wall was shortened (backed up) from the dorsal hoof wall, guided by the direction of growth at the coronary band and lower portion of the concavity (dish) (Figure 5).
When the dorsal hoof wall was shortened, the hoof wall crack didn’t extend to the ground surface. The point of breakover can now be established for placement of the shoe.
Using the radiograph, a vertical line was dropped from the center of rotation, defined as a vertical line drawn from the center of the distal end of the second phalanx (P2) through the joint to the ground (1) (Figure 6). Using the marker in the frog to measure from, this point could be located on the foot.
Again using the radiograph, the point of breakover was measured from the center of rotation which, in turn, was measured on the foot. That same distance was then measured from the point of rotation to a point in the heel area. The heel of the shoe should extend to this point. Wide web shoes with quarter clips and a rolled toe were used on both forefeet (Figure 7).
After correct placement of the shoe, the horse was hand-walked for two days and then started back in light work. It showed no signs of lameness and no movement was detected in the crack after shoeing. Shoes were reset on the horse 30 days later and solid growth was observed at the coronet (Figure 8).
Long toe/underrun heel occurs when the heel angle is five or more degrees less than the toe angle. This foot conformation is generally accompanied by a broken-back hoof pastern axis.
An underrun heel will usually have its genesis in a long toe. Excessive toe length causes heels to draw forward and inward. As the heel grows forward and lower, the pastern also moves forward, developing this abnormal pattern axis.
Excessive toe length creates a lever arm that exerts a bending force on the horn tubules in this area, resulting in a concavity (dish) in the dorsal hoof wall. Increased toe length also weakens the white line, stretches the laminae and flattens the sole.
The bending of horn tubules in the toe area can cause a full thickness crack. Crack movement at the coronary band causes pinching, resulting in pain (Figure 9). In this case, the crack didn’t extend to the ground surface.
Quarter clips are of little value in stabilizing such cracks. In this case, they were used to keep the shoe in place and put less stress on the nails.
The hoof crack stopped moving after the excessive toe was removed and the breakover point was moved back.
A radiograph takes the guesswork out of trimming and fitting shoes by providing an accurate guide for reshaping the hoof capsule around the third phalanx (P3). A line drawn from the center of rotation, perpendicular to the ground, should bisect the bearing surface of the foot (1).
The center of rotation provides a basis for modifying each individual foot. A radiograph helps assess the overall shape of the hoof capsule and the position of the third phalanx (P3).
1. Colles CM, Interpreting Radiographs 1: The Foot, Equine Vet J 1983; 15, Vol. 4; p. 297-303. Dr. Stephen O’Grady is a veterinarian and farrier who operates the Northern Virginia Equine Practice in The Plains, Va; Derek Poupard is a Certified farrier who operates Equine Services Overseas in The Plains, Va.