The foaling season is getting into full swing again and every breeder has high hopes for a healthy foal with correct conformation and stance of the legs. Most births are indeed problem-free, but some foals will be born with leg deformities which are however, easy to cure when prompt action is taken.
We differentiate between innate or congenital leg deformities and those that are caused by developmental factors, the so-called acquired leg deformities.
Temporary laxity of flexor tendons in a young foal.
Innate or congenital leg deformities have their origin in premature birth caused by illness of the mare, certain positions of the foal in the womb, flaccidity and/or genetic predisposition.
Acquired leg deformities develop at a later stage due to unbalanced nutrition, excessive growth or trauma and/or inflammation of the growth plates.
The key to success in foals with deviations in leg conformation is early treatment. Young foals have a very active leg skeleton because they are still in their rapid growth phase. The advantage of an active leg skeleton is that many leg deformities can be completely or partially corrected. The final result obviously depends on the degree of leg deviation, the location, the cause and whether or not this cause can be treated effectively.
There are many deviations that can be treated successfully until the age of approximately six months, which is in fact rather a short time frame.
Treatment of leg deviations often involves a mix of many things, for instance measured movement and tackling the underlying cause in combination with conservative or, if necessary, surgical treatment.
Crucial in conservative treatment is adjusting the stance of the foot by way of trimming the hoof and/or the use of personalised irons/shoes. The farrier can either make his own shoe but there are also commercial hoof shoes on the market for all sorts of leg deviations. If however, conservative treatment is insufficiently successful then surgical treatment will be unavoidable.
Weak foals vulnerable to various infections run a greater risk of leg deformities (cow-shaped at the height of the fore knee).
Seen from the front the stance of the forelegs of a foal or horse must form a straight line through the forearm, knee, fetlock joint, pastern and hoof. Seen from behind the hind legs must form a straight line through the upper leg, hock, fetlock joint, pastern and hoof. If however, this line is affected by an angle then we distinguish between two types of angular limb deviations, one is called a Valgus deformation and the other a Varus deformation.
In the case of Valgus deformation, (cow-shaped), there is an outward deviation in the lower part of the limb from the point where the straight line breaks.
In the opposite case, when there is an inward deviation in the lower part of the limb, we speak of Varus deformation, (sickle-shaped or bow-legged). Valgus- or Varus deformation most often occurs at the height of the fore knee, pastern region and is far less frequent at the height of the hock.
To gain an insight into the causes of such leg deviations it is important to understand how growth in bone length develops.
Increase in bone length develops from the ‘growth plate’. At the height of this growth plate cartilage transforms into bone after multiplication of cells. In most cases of angular deformation we see uneven growth in the growth plate as a result of trauma, or possibly infection.
Additional, less frequent causes can be when the angle develops from adjacent joints and/or bone. This sometimes happens when the soft tissues, including ligaments, are still too weak. Other possible causes for angular deformation can be deformation in bone predisposition or insufficient calcification of joints due to prematurity.
Conservative treatment of angular deformations consists of shortening of the outer hoof wall in the case of cow-shaped legs (Valgus Deformation) and in case of sickle-shaped limbs shortening of the inner hoof wall. Often repetitive treatment is needed and frequent rasping of one side might be limited. There are specific hoof shoes available on the commercial market which are slightly lower on one side to help achieve the desired correction. By adjusting the stance of the foot it is possible to effect a corrective influence on the still active growth plate.
However, when the uneven stance can be insufficiently corrected by way of trimming then surgical treatment remains the only option. Surgical intervention offers two possibilities to manipulate this asymmetrical growth plate, one being stimulation of one side of the growth plate by way of ‘stripping’. The treatment of stripping involves incision and elevation of the periosteum at the height of the growth plate. In case of Valgus Deformation (cow-shaped) treatment must be performed on the outside of the growth plate and in the case of Varus Deformation (sickle-shaped) on the inside.
In addition to ‘stripping’ there is the option of so-called ‘stapling’, which is a technique to slow down the growth of the growth plate. Stapling inhibits the growth by the application of a screw across the growth plate (Transphyseal Bridging). In extreme cases of angular deformation both techniques can be combined. Corrections must be carried out as soon as possible because the growth plates are more active in younger foals. Angular deviation in the pastern region must be corrected before the age of three months because these growth plates quickly complete their active growth phase. Deviations at the height of the fore knee can be treated up to the age of six months. On the condition that such deviations are corrected in a very early stage, the prognosis for a good outcome is good.
After birth many foals can be so weak in the legs that the toes of the foot develop a bit of an upward stance. In the more severe cases these foals may even walk on the back of the pastern or fetlock joint.
The cause for these deviations is often too much laxity in the still weak flexor tendons and in most cases the condition will spontaneously disappear with limited exercise. Because the flexor tendons/- muscles grow stronger and bone length increases at a faster rate than the length of flexor tendons, spontaneous recovery takes place.
In extreme conditions tailor-made shoeing with a few extensions can support the foot to stop the toes from turning upwards. It is crucially important not to bandage these foals because that would exacerbate the laxity.
We speak of retraction and contraction of flexor tendons when the foal is unable to fully stretch the limb. This condition can be inborn but also develop at a later stage after birth. Innate contractions can be caused by insufficient room or otherwise wrong positioning in the womb. Additionally, causes of acquired deformity can also be traced back to the use of a specific posture during grazing.
Valgus in Shetland foal caused by insufficient room in the womb.
In case of a grazing- foot (or clubby foot) retraction of the deep flexor tendon, which fastens deep in the foot, occurs and causes mild tipping of the coffin bone. Because there is a strong connection between coffin bone and hoof wall the front edge of the hoof wall can become so steep that at some point the heels no longer make full contact with the ground.
When the condition is very mild it is important to preserve the toe area and shorten the heels a tiny bit. If however, there is no more support in the heel area, then shortening of the heels will have little effect. In order to curb retraction of the deep flexor tendon it is key to lengthen the toes with the help of a glued-on shoe or a toe extension. This toe extension will force the foal to step through further and this way prevents contraction of the deep flexor tendon. Foals subjected to this treatment will need pain killers in order to alleviate the pain.
Cases of retraction with virtually no more contact of the heels with the ground will insufficiently benefit from the use of corrective shoeing. Then surgical treatment is required along with the use of corrective shoeing. Surgical treatment will involve severing of a ligament, the distal check ligament, which runs from the cannon bone just below the fore knee and fuses together with the deep flexor tendon. Severing this ligament improves the flexibility of the deep flexor tendon and serves to correct the anomalous stance.
Young foals may develop retraction of the deep flexor tendon because of their posture during grazing
In addition to the more common retraction of the deep flexor tendon, foals can also develop retraction of the superficial flexor tendon, which produces very steep pasterns and forward-tilting of the fetlock. This particular form of deviation hugely increases the risk of stumbling and tripping up. Trying to counterbalance retraction of the superficial flexor tendon can be achieved by the application of a toe extension in combination with lifting of the heels. Unfortunately however, these cases have a less favourable prognosis than cases of retraction of the deep flexor tendon, where full recovery is usually possible.
Deviating leg conformation in foals is quite common and can be the source of considerable disappointment for breeders. Rapid and correct treatment will result in a complete recovery of a large majority of these deformities without any limitations for a potential career in sports.
The key to success always lies in speedy and effective treatment at a young age.
Tim Samoy graduated as a veterinarian in 2006 and his main specialist areas of expertise are orthopaedics and sports guidance of horses at all levels. After graduation he forthwith started working at the University of Gent and in 2008 he made the switch to a private equestrian clinic. Since March 2016 he has owned his own orthopaedic clinic. Next to his day-to-day work he is often assigned to various international events in the capacity of official FEI veterinarian.