Hoof Angle

Stephen E. O’Grady, DVM, MRCVS

Hoof angles have always been considered an integral part of hoof balance. The angle of the hoof is the angle formed at the junction of the dorsal hoof wall and the ground surface of the foot. A hoof gauge is used to determine this measurement.

Until recently, the veterinary and farrier literature recommended that the normal hoof angle be 45-to-50 degrees for the forefeet and 50-to-55 degrees for the hind feet. These angles have been proven erroneous, as they do not take into consideration the conformation of the horse’s individual limbs. Ideal hoof angulation occurs when a line drawn down the dorsal surface of the hoof wall and a line drawn along the surface of the heel are in alignment or parallel to a line drawn through the three phalanges (P1, P2, P3; Figure 1). This type of foot conformation allows normal physiology within the foot to take place, it maintains hoof health and prevents lameness. Unfortunately, we are not always able to attain this ideal type of foot conformation.

 

The foot is trimmed appropriately and the hoof angle is correct for the individual horse when the dorsal hoof wall and the dorsal surface of the pastern region are parallel. This is known as the hoof pastern axis (Figure 2). In order to confirm this hoof-pastern axis visually, the horse must stand squarely on all four feet with the cannon bones positioned vertically on a hard, level surface. The terms low hoof angle and high hoof angle can be used simply to describe a non-parallel relationship between the dorsal hoof wall and the dorsal pastern region. The correct hoof-pastern alignment may be hard to achieve when the toe of the foot is either too long or too short and the heels are either too high or too low. Therefore, trimming the foot plays a key role in achieving and maintaining a normal hoof-pastern axis. A brief discussion of what constitutes an abnormal hoof-pastern axis and its detrimental implications may help demonstrate the importance of correcting any abnormalities that exist.

 

Low hoof angles, where the angle of the dorsal hoof wall is lower than the angle of the dorsal pastern, create a broken-back hoof pastern axis (Figure 3). This type of foot configuration is commonly caused by the long-toe/underrun-heel. If the toe is allowed to grow excessively long, the heels grow forward and hence, lower. This causes the pastern to move forward, creating a broken-back pastern axis. A low hoof angle causes coffin joint extension (constant strain on that joint), increased strain on the deep digital flexor tendon and promotes toe-first landing which causes friction in the navicular bursa and delays the speed of breakover. There is experimental evidence that a low hoof angle will compromise circulation in the heel area of the foot. Obviously, these detrimental effects are proportional to the severity of the low hoof angle. It was believed for many years (especially by racetrack trainers) that lowering the heel would increase the length of stride. This has been proven to be a fallacy.

A severe broken-back pastern axis is a concern to both veterinarians and farriers. For veterinarians, this abnormal hoof conformation is know to contribute to navicular syndrome, chronic heel pain (bruising), coffin joint inflammation, quarter and heel cracks and interference problems. The farrier is confronted with the essential task of preventing, correcting and/or maintaining this type of foot conformation.

 

On the other hand, high hoof angles, where the angle of the dorsal hoof wall is higher than the angle of the dorsal pastern, create a broken-forward pastern axis (Figure 4). An extremely high hoof angle is often classified as a “club foot.” Some horses with extremely upright pasterns may be falsely identified as having a club foot. A high hoof angle causes coffin joint flexion, increases strain on the suspensory ligaments, promotes heel-first landing and increases pressure in the heel. Some injuries associated with a high hoof angle are coffin joint inflammation due to abnormal loading of this joint, pedal osteitis and suspensory desmitis due to the increased strain on the suspensory ligament. Hoof trimming or preparation is the most important aspect of horseshoeing. An objective of proper hoof trimming is to reduce unnecessary forces exerted on the toe, heels or joints within or above the foot. This can be accomplished by making the dorsal surface of the foot parallel with the dorsal surface of the pastern region. Adjusting the hoof angle so that the dorsal surface of the hoof parallels the dorsal surface of the pastern region will decrease the effects of high or low hoof angles along with the abnormal physiology they create.

 

In many cases of abnormal hoof-pastern axes, radiographs are helpful to provide guidance when trimming the foot. The first step in correcting a broken-back pastern axis with excessive toe length, is to rasp the dorsal hoof wall (“backing up” the toe) in an attempt to align it with the pastern. Often, if the misalignment is mild or in the early stages, this adjustment will correct the hoof-pastern axis, but an underrun heel will remain which decreases the ground surface of the foot (Figure 5). This can be corrected easily by extending the heels of the shoe to the appropriate distance beyond the heel of the foot (Figure 6).

If the hoof-pastern axis is not corrected by backing up the toe and extending the shoe, then some form of heel elevation is necessary (Figure 7). To correct a broken-forward hoof-pastern axis, the area from the point of the frog to the heel is lowered in a tapered fashion when trimming the foot. If excess heel is removed in order to normalize the hoof-pastern axis, this may place excessive tension on the deep digital flexor tendon. If this occurs, a small heel wedge can be placed between the shoe and the foot to decrease the tension.

 

Knowledge and awareness by owners and farriers of the importance of a proper hoof-pastern axis allows an abnormal foot to be corrected through trimming. Better yet, it can prevent abnormal hoof alignment from occurring in the first place.