Many clients are quite confused when the farrier and veterinarian start to discuss foot/hoof balance. I hope to clarify some of the principles. It is beyond the scope of this article to discuss all that is involved in hoof balance and its achievement, yet a discussion of the key principles will help in understanding the basics and appreciating the repercussions of improper balance (unbalanced). The subject of foot balance and how we effect and achieve it, is one that includes both science and art. Since our horses are not free roaming and wild we are forced to modify their feet both by removing excess growth and protecting them from excessive wear and deterioration. Our ability to trim and shoe these athletes without placing additional stress on their feet and limbs has a lot to do with balance.
Balance is three-dimensional and may be defined and viewed from either of two perspectives, a geometric basis, including only the hoof capsule standing in place, this is known as static balance. The other approach is that of dynamic balance and this refers to the foot landing and placement when in motion, a foot that is in dynamic balance is one that will land flat when moving on a flat surface. To achieve dynamic balance, the trimming and shoeing must take into account conformation and pathology of the foot and limb. If the horse in question has no conformational abnormalities, or deviations from that of textbook geometry, and there is no pathology or gait abnormality to accommodate, then geometric or static balance will usually achieve dynamic balance. The big problem is that many of our horses do not resemble the textbook examples of perfect conformation. This creates a challenge for our farriers and for the veterinary farrier team.
Dorsal-palmar/plantar (front to back) (DP) balance refers to the overall hoof angle and the alignment of the hoof angle with the pastern bone angle when the cannon bone is perpendicular to the ground surface. When evaluating this angle from the side not only should the dorsal (front) hoof wall be in alignment with the pastern but the hind or heel portion of the hoof should also follow this alignment. Some of the most recent studies of bone structure / hoof angles have found that the old assumption of a forefoot angle ranging from 45-50 and hind-foot of 50-55 were to sloped. It is now concluded that the range of appropriate angles are 53-58 for the front feet and 50-60 for the hind feet. Of course each horse has an angle that is appropriate for their particular conformation and these are just guidelines. If the toe of the foot is to long for the horse the axis of the pastern angle is broken backwards and there is additional stress placed upon the deep digital flexor tendon as well as the navicular ligaments and potentially the navicular bursa. If the hoof is upright and the axis broken forward significantly enough there is additional strain on other areas of the foot and limb. Since historically foot angles have been kept a bit broken back and many horses have suffered from deep digital flexor tendon strain and navicular syndrome and since the horses tend to grow toe faster than heel, the tendency now is to place the hoof more upright and in many cases just a bit broken forward. This trend has helped many horses since the additional few degrees of foot angle (over the ideal) seem to be better tolerated than the opposite. Although, if this is taken to the extreme several problems can develop such as coffin joint arthritis, pedal osteitis, extensor process injury, superficial digital flexor tendon and suspensory ligament strain. So by increasing the angle when applying new shoes the horse spends more of it's shoeing interval, which is commonly 6-8 weeks, at a close to proper angle without undue stress on the navicular region of the foot. The added benefit in maintaining the steeper hoof is that it shortens the overall length of the foot and may decrease break over time, which is also believed to decrease stress and strain on the soft tissues and joints of the distal limb. Although this DP balance sounds fairly straight forward it is not always as easy to achieve as one might think since in some horses the achievement of the angle may be difficult due to hoof deformity, weight bearing and the position of the limb underneath the body. In some of these cases it takes a good eye as well as skill with the nippers and rasp to adjust to the proper angle.
The topic of medial-lateral (inside to outside) (ML) balance can be one of even more confusion and difficulty than that of DP balance. When balancing the foot we refer to either static balance or dynamic balance. Static or geometric balance is the balance of the foot as it sits on the ground on a level surface. Dynamic balance on the other hand refers to the balance of the foot when the foot is in motion. For this balance to be true the hoof must land symmetrically when being placed on a level surface after the limb flight; in other words when landing during motion. In the ideal horse static or geometric ML balance will produce dynamic ML balance. Achieving dynamic ML balance can be difficult if the horse does not have straight limbs or the horse suffers from pathology (some disease process or disruption of normal) that alters the gait. Should you own a horse that does not have straight limbs and there is some type of pathology that also alters the gait your veterinarian and farrier may have the ultimate challenge in attempting to achieve dynamic balance and minimize trauma to the horses locomotive apparatus. These horses when evaluated on the ground at rest may appear to be out of balance and most are out of static balance. The adjustments away from static or geometric balance will be in an attempt to have the hoof land flat when placed on the ground as the horse is in motion. The goal is that the whole limb is landing in as flat a manner as possible with the least amount of stress or strain. Based upon this statement one can imagine that it is best not to try to reposition the limb, on an adult horse, through manipulation of the balance when trimming or shoeing, as this can lead to severe stress of both the bony column and soft tissue structures. There are many methods used to attempt to achieve ML balance and none will work on every horse or in every situation and the more severe the limb deformity and pathology is the more patience it may take to achieve. Problems associated with poor ML balance include distorted hooves, chronic heel soreness, sheared heels, hoof wall cracks, thrush, side bones, navicular syndrome, ringbone, and chronic fetlock joint inflammation.
Many horses do not have perfectly straight limbs and the choice of experienced and well-qualified veterinarians and farriers can have a major effect on the current as well as future soundness of your horse. The farrier is responsible for achieving balance, but as you can see from the above discussion, their job can at times be hampered by a lack of information including, lameness evaluation, pathology, radiographic and ultrasound findings as well as ongoing or future veterinary medical therapy. Although routine in certain circles, it can seem like an expensive proposition for some clients, but most horses would benefit from the combination of a veterinarian and farrier that worked as a team to maintain the optimum health of both the foot as well as the rest of the limb.