Figure 1. The relationship between the
flexor tendons and bones in the forelimbs
of the horse. CL = check ligament.
© Yehuda Avisar, DVM
published in ANVIL Magazine, September 1997
INTRODUCTION
Contracted tendons in the foal can be congenital or acquired disease that most commonly involves the forelegs in one or both limbs. Causes of tendon contraction include intrauterine malposition, limited exercise, hard ground, nutritional imbalances, overfeeding and genetic predisposition. Pain and lack of use of a limb caused by lameness may lead to deep digital flexor tendon (DDFT) contracture. Most cases of flexural deformities (contraction) are acquired between the ages of six weeks and six months.
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Figure 1. The relationship between the flexor tendons and bones in the forelimbs of the horse. CL = check ligament. |
The deep digital flexor tendon (DDFT) is attached to the solar aspect of the coffin bone and its muscle flexes the limb during movement. When an injured limb is in disuse, the flexor muscle flexes the coffin joint, predisposing it to the development of club foot. The superficial digital flexor tendon (SDFT) is attached to the first and second phalangeal bones; when the muscle contracts, it results in knuckling of the fetlock (Figure 1). DDFT contraction is more common in sucklings, while SDFT contraction is seen more often in weanlings and yearlings.
Recognition of the flexural problems in young foals depends on regular inspection of the foal placed on level ground. Early treatment can give excellent results by farriery alone and can be sufficient in most mild to moderate cases. This article is focusing on the treatment of DDFT contraction in young foals.
DEVELOPMENT OF DDFT CONTRACTION
Contraction of the deep digital flexor tendon is more common in young foals from birth to three months. It is not uncommon to see the condition in the newborn foal, but most cases will resolve spontaneously as the foal exercises, stretching its muscles. Foals with mild tendon contraction stand with the foot held slightly in a straight position; the pull of the DDFT raises the heels a few millimeters off the ground, and more weight is placed on the toe. The affected hoof starts to shrink from lack of normal contact with the ground. As the case advances, hoof angle increases by 5 to 10 degrees; the heels grow and the toe wears, the white line separates from the hoof wall and bruises develop at the sole. At this stage, a pain/contraction cycle has begun, and the painful toe forces the foal to place less weight on the affected limb while discomfort caused by the stretch of the tendon results in a short, stiff gait.
 Figure 2. Excessive pressure on the toe resulted in separation at the white line and discoloration at the toe region of the sole; trimming the foot revealed a sole abcess. |
Excessive pressure on the toe can lead to complications such as dished toe or seedy toe, or the tip of the coffin bone can undergo pathological changes. The tension on the flexor tendon can cause tendinitis and coffin bone rotation. Prolonged joint flexion is followed by permanent stiffness of the joint capsule (envelope) which severely reduces joint movement.
Figure 3. Flow chart shows the development of club foot in a foal. The abnormal position of the toe can start a cycle that complicates flexural deformity. |
CLASSIFICATION OF DDFT CONTRACTION
Contracted DDFT is classified into two grades, according to Stashak (1987): In Grade 1, the angle formed by the toe and ground is less than 900 and in Grade 11, it is above 900 (Figure 4). The degree of contraction indicates how severe the case is and helps in decision making, regardless of the method of treatment and the prognosis.
Another way to assess the case is to lift the opposite limb off the ground and observe the distance the heels dropped by the extra weight. Cases in which the heels don't drop are obviously more severe and may have lost flexibility at the joint capsule.
 Figure 4. Grade II DDFT flexural contraction, the angle formed by the toe and the ground is slightly over 90 degrees. |
SURGICAL METHODS
There are several surgical methods that are being used for the treatment of DDFT contraction. One of them involves cutting the flexor tendon. This surgery is reserved for severe contraction and, following the surgery, these animals remain useless. Another surgical method is called a desmotomy, meaning cutting a ligament. Its principle is to relieve tension from the DDFT by cutting the check ligament of that tendon (Figure 1). The check ligament functions as a brake that takes some of the tension from the flexor tendon. Cutting the check ligament increases the functional length of the muscle/tendon unit so the heels can drop. Research shows that a desmotomy for Grade I cases gives the foal a good chance to perform in its intended use. Surgery results for Grade II cases are less successful. Farriery and surgery for Grade I cases are practical ways to produce rapid results. When the problem is repeated in certain bloodlines, a genetic origin has to be suspected.
TREATMENT PRINCIPLES
The principles of corrective trimming and shoeing of DDFT contracture in foals include:
Some of the contracted cases will require gradual trimming (lowering the heels) as the only treatment. Others may require toe reconstruction with acrylics or the application of special shoes. Surgery may be combined with each of these treatment methods.
Application of acrylics to reconstruct the toe or the use of glue-on shoes will provide a protection to the toe and will help stop the pain/contraction cycle. Leverage created by this treatment and exercise will stretch the flexor muscle. Continuous tension on a muscle leads to a response called inverse myotatic reflex, meaning a lengthening response. This is a protective response from the excessive tension. In moderate cases of
DDFT contraction, this response can be observed in a few days by noticing the dropping of the heels to the ground. Excessive trimming can increase strain on the DDFT and subject the coffin bone to concussive forces.
 Figure 5. The foot of a foal following trimming. The straw is used as a pointer to illustrate the space created between the toe and the ground. |
TRIMMING
Trimming the contracted foal can begin as soon as a change in the shape and angle of the hoof is noted. Trimming is repeated each time the heels contact the ground, 2-3 millimeters each time, until an angle of 50 to 55 degrees is established. Cracks and splits at the toe can be difficult to observe. The toe has to be inspected carefully and the white line and sole are trimmed to expose thrush and debris accumulation. The hoof is trimmed to explore discoloration and abscess formation until healthy tissue is reached. It is important to check and diagnose any painful conditions in the toe and treat it. If sensitive tissue is exposed, the foot can be treated with pine tar bandaged for several days. During the treatment period, the foal should be kept on a wooden or rubber floor to prevent further damage to the toe caused by gravel or coarse ground. Placement of foals with contracted tendons on sand can worsen the condition because the toes rotate into the ground. Excessive pressure on the toe can be decreased by cutting a curved section at the toe (Figure 5). Exercise is an important component of the treatment, but has to be controlled to avoid excessive tension on the tendon that could initiate the pain/contraction cycle.
Figure 6. Toe reconstruction of a club foot. The dark area represents the acrylic. No sole pressure should be created by the acrylic material. |
ACRYLICS
Acrylics are used to reconstruct the toe and protect it while providing normal hoof function. Acrylics can be applied to mild cases as the only treatment or be combined with a desmotomy in Grade I cases. To increase adhesiveness, the acrylic is applied over the toe area up to 2/3 distance from the coronet. It is important to avoid contact of acrylic with the sole, as this can lead to bruising and lameness (Figure 6). It is best to apply the acrylic material when the foal is being restrained on the ground or under general anesthesia, before being moved to the surgery room. Teamwork is important; an assistant applies the acrylic material to the hoof as the farrier reconstructs the toe. During the curing process, the acrylics can produce excessive heat that can lead to thermal injury of the foot. Some brands produce less heat than others and should be used on foals. The temperature of the material is checked during the procedure by placing a hand over the hoof and the hoof is cooled with water if excessive heat is produced. Cooling the acrylic will not affect the results of the work to any significant extent.
 Figure 7. Glue-on shoe on a unilateral case. (Mustad) |
Figure 7b. A combination of a glue-on shoe and aluminum plate with toe extension. |
SHOEING
Several types of shoes can be used for orthopedic treatment in foals. The glue-on shoes are safe because no horseshoe nails are required for their application. Acrylics can be used to reconstruct the toe before the application of a shoe. There are two types of glue-on shoes that can be applied to foals: a plastic shoe with tabs (Mustad) or the Dallmer Foalshoe. The advantage of shoes with tabs is that they are made to fit the hoof, but their construction requires a hot-air welder that can be set to 270 degrees celsius and knowledge is necessary about plastic welding.
 Figure 7c. Bottom view of iron plate connected to a glue-on shoe with rivets. |
 Figure 7d. Application of hoof packing (Forshner's Hoof Packing) to debrided sole before gluing a shoe. |
Horseshoes can be applied to foals that are three to four months old with the smallest size horseshoe nail. The foal has to be observed for any signs of lameness caused by the nails and the suspected nail has to be removed. The shoes are reset every two weeks and the heels are lowered until normal angle is established. It is important to keep the shoe in place until the next reset. The owner can be instructed to glue loose tabs or place adhesive tape around them.
In moderate to severe cases, toe extension is used to increase tension on the DDFT by creating leverage and delaying breakover. The length of the toe extension at the center is set between 34 to I 1/2 centimeters, according to the severity of the case. Mild cases don't require toe extension, but the shoe is made to fit the normal contour of the hoof. Shoeing the opposite limb in unilateral cases is not mandatory (Figure 7).
References
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