by William Moyer, DVM, & James Schumacher, DVM
reprinted in ANVIL Magazine December 1996, with permission from the Equine
Medical Review, vol. 6, no. 2, April 1996. Published for Bayer Corporation,
Agricultural Division, Animal Health by Veterinary Learning Systems
(see ANVIL Magazine, March, 1996, beginning on page 28 for paper by Balch and associates)
In this article, Balch and associates define frequently encountered forms of abnormalities of horses' feet and describe how these abnormalities contribute to problems with athletic performance. The elements of hoof balance discussed in this article - toe length, hoof angle, and mediolateral hoof balance - relate to one another. Performance problems that result from hoof imbalance can be obvious or quite subtle, and hoof imbalance, even in an extreme presentation, may not cause any apparent problems.
TOE LENGTH
Toe length (the distance between the weight-bearing surface at the
center of the toe to the proximal edge of the toe wall) is easily measured
and is perhaps the most frequently and easily modified element of hoof balance.
The most extreme toe length is artificially created in gaited show horses;
the feet of these horses are usually allowed to attain a length greater than
that normally encountered with other light breeds, and then thick pads are
added between the hoof and shoe. The other group of horses that are often
encouraged to have excessively long hooves are the show draft horses.
The opposite extreme of toe length is a very short toe length (i.e., overall hoof length), which occurs as a result of inherited factors and/or excessive trimming or wear. Excessive wear (i.e., broken hoof walls) often occurs in horses with poor quality hoof walls that are turned out on abrasive surfaces.
An excessively long toe (i.e., excessive length relative to body size and limb length) may create distortion (dishing of the toe) and separation of the toe wall and increases the length of the lever arm over which the hoof rotates. It is, perhaps, this single mechanical feature (i.e., increased lever arm length) that can lead to injury of the suspensory apparatus (digital flexor tendons, suspensory ligament and proximal sesamoid bones, and associated supporting ligaments).
Excessive trimming and/or wearing of the toe, quarters, and heel places the sole and its underlying corium at risk of excessive trauma, which leads to bruising and pain. Preventing problems associated with too much or too little hoof wall length requires establishing a balance between a length that allows sufficient subsolar protection and one that causes tension on the suspensory apparatus. The authors suggest that toe length should be related to body weight, but caution that circumstances and exceptions to this relationship definitely exist.
ANGLE
Hoof angle is simply the angle of the toe (i.e., the angle formed
by the dorsal and bearing surfaces of the hoof). The authors point out that
the often quoted "proper" angles for both front and hind feet are probably
erroneous and that a more appropriate silhouette (or angle) is attained when
the dorsal surface of the hoof wall parallels the dorsal surface of the pastern
when the limb is fully bearing weight. Information gathered using instrumented
shoes on horses moving on a treadmill at various gaits determined that the
forces are lowest at the toe, medial heel, and lateral heel when the dorsal
surfaces of the hoof and pastern regions are parallel.
The authors also indicate that manipulating hoof angles to correct or adjust gait patterns does not necessarily achieve a return to the ideal gait pattern and can influence the tension on the supporting tissues of the lower limb. For example, decreasing the hoof angle by lowering the heel or raising the toe increases tension on the deep digital flexor tendon, increases the time of foot breakover, and influences the position of the joints of the lower limb at full weight bearing. Thus, changing hoof angles can induce certain injuries or alleviate various maladies.
BALANCE
Improper mediolateral hoof balance has been classically associated
with problems (e.g., sheared heels, distorted hoof walls, chronic heel soreness,
hoof cracks) that result from exertion of disproportionate forces on the
medial or lateral aspects of the foot. The authors point out that although
improper mediolateral hoof balance may be responsible for these problems,
providing supportive evidence has been difficult. Further complicating the
understanding of the effects of improper mediolateral balance is attained
in one of two ways: either by trimming the foot so that the ground surface
is perpendicular to the long axis of the limb or by trimming the foot so
that the medial and lateral aspects of the foot land simultaneously. Each
of these two methods of achieving mediolateral balance may produce a foot
with a different shape if limb flight or conformation deviates from the norm.
The question of which method of trimming truly achieves mediolateral balance
remains.
VETERINARIAN/FARRIER RELATIONSHIP
The authors conclude that trimming and shoeing influence a horse's ability
to work, the potential for lameness, and the animal's efficiency of motion.
Veterinarians and farriers should maintain good working relations; the experience
and innovations of farriers are important elements in treating some types
of lameness.
Source: Hoof balance and lameness: Improper toe length, hoof angle, and mediolateral balance, O. Balch, D. Butler, K. White, and S. Metcalf, Compendium on Continuing Education for the Practicing Veterinarian, Vol. 17, No. 12, 1995, pp. 1275-1283.
COMMENTARY
This review article presents the best published description of the basic
elements of hoof balance. A multitude of factors influence the way in which
a foot ultimately accepts the energy of impact. The elements of balance defined
in this article are the ones most frequently discussed, manipulated, and
abused. During the last several years, a great deal of information has been
published about how abnormal balance initiates foot and limb disorders. (1-12)
There is, however, no question that a great deal remains to be understood
about the relationship between hoof balance and lameness. It appears that
each individual limb should have an ideal toe and hoof length, hoof angle,
and mediolateral balance. That is, the horse should have a foot/shoe
configuration that best matches its size, its conformation and limb motion,
and, to some degree, the sport for which it is intended and the ground
conditions.
The single most frequently encountered abnormal foot configuration is the combination of the underrun (low) heel and long toe. This conformation provides little protection to the submural and subsolar tissues of the heel and quarter region. Lameness associated with this poor design originates from pain caused by damaged (crushed) coria and may be subtle (possibly only experienced at speed, on turns, landing on hard surfaces, etc.) or quite severe. Common features of horses with this foot conformation include significant and often chronic subsolar heel bruising and abnormally high tension on the joint supporting tissues of the lower limb. (13)
Correction of this configuration requires patience, a skilled farrier, and understanding of the problem by the owners/trainers. Success is difficult to achieve simply because these requirements cannot always be met and because some of these horses are born with poorly conformed feet, which are difficult to permanently alter. In my opinion, the simplest attempt at correction is the application of an egg-bar shoe with a squared toe; the most complicated attempt is composite hoof wall reconstruction. (14) Toe length can be decreased by squaring the toe of the hoof and the shoe.
Another complicating feature of this poor configuration is the fact that most affected horses, in my experience, also have thin quarter walls, which makes nailing on shoes an art form. Composite hoof wall reconstruction and/or glue-on shoes can be helpful, but this treatment does not always provide a long-term solution. The problem of relative absence of foot may be solved only as long as the artificial hoof wall is in place.
Other factors that play heavily into the creation of weak and poorly balanced feet are the environmental and managerial factors to which a horse is subjected. Several situations, alone or in combination, may create substantial problems in hoof quality:
Several of these factors may coexist, especially in the warmer months.
Overall hoof balance and health and how they ultimately affect the equine athlete is a complex, and at times perplexing, problem. The shape and strength of the foot is influenced by a multitude of factors, and truly successful therapeutic outcomes require an appreciation of all these factors rather than simply expecting so-called "corrective" shoeing to solve the problem. This review article succinctly and clearly describes those elements of hoof balance that should be considered.
REFERENCES
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