Radiology of the equine hoof is used to confirm various disease processes such as laminitis, third phalanx fractures, osteoarthritis (ring bone), navicular disease and extensive hoof wall separations. It has evolved to where it quite beneficial for the farrier to use radiographs for guidance when trimming the equine foot. We can immediately see the additional information that can be gained from a radiograph taken of a distorted hoof capsule. One can see the orientation of P3 within the hoof capsule, the hoof/pastern axis, how much and where the foot should be trimmed for better alignment and where the shoe should be placed under the limb for the best mechanical advantage. The extent of a hoof wall separation associated with White Line Disease can also be observed. The two radiographic views useful to the farrier are the lateral view (from the side) and the dorsal/palmar view (from the front).

Method

When using radiographs for guidance in trimming the foot it is important that the image generated by the x-ray machine is the same as the foot i.e. no magnification. In this way, measurements taken from the x-ray can be transferred to the foot. This is controlled by what is known as the focal-film distance (FFD) and it is easy to check. Place two nails in the face of the wooden radiograph block and then measure the distance between the nails. Now take a radiograph and if the distance measured between the nails is the same on the radiograph film as it is on the block, there is no magnification.

The shoes should always be removed and the feet thoroughly cleaned. The horse should be stood on a flat, level surface. To appreciate bone position, the radiographs should be taken with the horse bearing weight and both feet placed on wooden blocks of equal height. The cannon bone should be perpendicular to the ground. This can be accomplished by placing a level on the dorsal surface of the cannon bone. A small carpenter's line level can be placed on top of the x-ray machine to ensure that it is level with the ground. The wooden block should have a wire imbedded in the surface and another wire should be placed on the dorsal hoof wall. The wire on the dorsal hoof wall is held in place with play-doh. These wires will outline the hoof capsule (Fig 1). Radiopaque markers such as a thumbtack can be placed near the apex of the frog and the end of the heel. After taking the radiographs, the spot in the apex of the frog where the thumbtack was placed should be marked by creating a small channel in the frog with the hook of the hoof knife. Likewise, a small channel can be placed in the outer hoof wall next to where the tack was placed at the end of the heel. These marks will act as landmarks for transferring measurements obtained from the radiographs to the foot.

Interpretation
 

The lateral radiograph will show the position of P3 within the hoof capsule. The ideal situation is to have the center of rotation in the middle of the foot (Fig 2). A perpendicular line dropped from the center of rotation should correspond to the widest part of the foot. The distance from this line to the heels and the distance from this line to the toe should be approximately equal or a ratio of 60% toe / 40% heel. The lateral view with the markers in place will show the length of toe present and the alignment of the dorsal surface of P3 with the dorsal hoof wall. In the laminitic horse, rotation or distal displacement of the third phalanx can be accessed along with whether a flexure deformity is present involving the distal interphalangeal joint. One of the most important aspects of using radiographs is to accurately determine the sole depth and what steps can be taken to improve it if necessary. Inadequate sole depth will usually be accompanied by excessive toe length.

The x-ray will show whether the hoof pastern axis is parallel. If the axis is broken forward (club foot) or if the axis is broken back (long toe underrun heel), the radiograph will reveal the degree of deformity and the best way to trim the foot to improve it.

Using the opaque markers, measurements can be drawn on the radiographs and transferred to the foot. These measurements can be used to realign the third phalanx within the hoof capsule in the case of the laminitic horse Using the groove placed in the frog when the x-rays were taken, the distance to the center of rotation or to the point of optimum breakover can be determined. Using the channel placed at the heel, one can determine how much additional heel support should be provided, how far to extend the shoe or how long to make a bar shoe.

The dorsal/palmar view can be used to evaluate medial/lateral orientation (Fig 3). Caution should be used here as a change in the medial/ lateral orientation is often coupled with the conformation of the limb. What is important when viewing the dorsal/palmar radiograph is if there is narrowing on one side of any of the joint spaces within the foot or above. This can often be corrected through trimming. A veterinarian can point out this finding.

In summary, using radiographic guidance when trimming feet can be an asset to the farrier. It will also enhance communication between veterinarians and farriers. This added communication can only benefit both professions and most of all--the horse.