Articles
Foal foot care II
A foundation for future athletic performance
In the first article we looked at the importance and aims for trimming your foal's foot. In this article we look at flexural deformities. In the final article we will then look at angular limb deformities.
Despite the recent advances in breeding, nutrition and farm management, flexure deformities continue to be seen at an alarmingly high rate. Flexure deformities have been traditionally referred to as “contracted tendons.” Since tendons lack the real ability to contract, the primary defect is a shortening of the musculotendinous unit rather than a shortening of just the tendon, making the descriptive term “flexure deformity” the best to use.
This shortening of the musculotendinous unit produces a structure of insufficient length for normal limb alignment and results in variable clinical signs ranging from an upright pastern angle to club feet.
Flexure deformities can be divided into congenital (apparent at or close to the time of birth) or acquired (developing during the growth period).
ANATOMY
The deep digital flexor tendon (shown in green) lies
directly on the caudal (back) aspect of the radius
(forearm). It consists of three muscle
bellies (the humoral head, radial head
and ulnar head) that form a common
tendon just above the knee. This
tendon, along with the superficial digital
flexor tendon then passes through the
carpal canal, continues down the
palmar (back) aspect of the limb, and
bisects the tendon of the superficial
digital flexor tendon below the fetlock to
insert on the palmer surface of the
third phalanx (pedal bone).
A strong tendinous band, known as the inferior check ligament (red), originates from the deep palmar knee ligament and joins the deep flexor tendon at the middle of the canon. It is obvious from the anatomy that any prolonged shortening of the musculotendinous unit will affect the DIP (distal interphalangeal) or ‘coffin’ joint, pulling it into a flexed position. Changes in the hoof capsule can then follow rapidly.
You should also note that cutting the inferior check ligament will result in a lengthening of the musculotendinous unit. Congenital flexure deformities can affect one or more legs. They are thought to result from mal-positioning of the foetus when in the uterus, nutritional management of the mare during pregnancy, exposure to influenza virus (not in New Zealand) or possibly a genetic link.
The foal will walk on his toe, unable to place the heel on the ground.
With a fetlock deformity the foal may be able to stand but knuckle over. Generally the superficial and deep flexor tendons are shortened in these cases.
Congenital flexure deformity of the carpus (knee) is also common.
Treatment of foals will vary with the severity of the deformity. Some improve spontaneously. Administration of oxytetracycline under the supervision of a veterinarian is frequently beneficial in the first one or two days. Intervals of brief exercise (1 to 2 hours) in a small paddock are recommended and physical therapy, which involves manually straightening the limb for 15 minutes three-to-four times daily, can also help.
In severe cases, splints can be applied to the back of the limb. The basic principle here is forced extension of the limb and to have during weight bearing the tensional forces acting on the flexor tendons, this then in turn induces relaxation of these tendons. The most effective material here in my opinion is PVC tubing. All splints require careful placement, padding, constant evaluation and changing to prevent skin necrosis and pressure sores.
Casts can be used similarly but also require close monitoring and careful application and are usually reserved for the really severe cases.
The application of a toe extension can be considered and may be useful in some cases. The toe extension can be made simply with Equi-Thane® hoof extension material and applied as soon as three days old.
The final alternative is surgery where the inferior check ligament is cut, but this is not usually necessary.
ACQUIRED FLEXURE DEFORMITIES
Acquired flexure deformities develop between two months and up to two years of age. The cause of this deformity is usually related to pain, although genetics, nutrition (excessive carbohydrates (energy) and unbalanced minerals) and exercise are thought to play roles.
Any discomfort in the foot or lower limb will initiate the flexure
withdrawal reflex which
causes the flexor muscles
above the tendon to
contract, leading to altered
positions of the distal joint.
Since, in this case, the
flexure deformity is
secondary to discomfort,
the source of any
lameness that
accompanies a flexure
deformity should be
investigated with physical evaluation, local anaesthesia
and radiographs if necessary.
A genetic component must also be considered for acquired flexure deformities, as, year after year, some mares will consistently produce foals that develop flexure deformities in the same limb. With any flexure deformity, an attempt should always be made to determine the cause and correct it immediately.
Clinically there are two distinct signs. Flexure deformity of the ‘coffin’ joint or so-called deep digital flexor contracture results in a ‘club foot’. The foot develops a boxy shape and the heels fail to contact the ground, even after trimming. A prominent coronary band may or may not be present at this stage.
Treatments for this includes exercise restriction, diet restriction and anti-inflammatory drugs. Frequent trimming to lower the heels and Equilox® can be applied to the dorsal hoof wall to form a toe extension. The Equiloximpregnated fiberglass is continued over the solar surface to protect that area from further bruising. The toe extension will serve as a leverarm for the toe. Weaning the foal may also help and if no improvement occurs after one to two months with conservative treatment then surgery is indicated whereby the inferior check ligament is cut.
The second sign is flexure deformity of the fetlock joint. Again the same treatment and management options are available in these cases, however foals with severe deformity in this region rarely respond to conservative or surgical treatment. Treatment for a flexural deformity of the carpus (knee) is generally however favourable, although your vet needs to make sure that there is no associated rupture of the extensor tendons across the front of the knee which can sometimes be mistaken in these cases.
WEAKNESS OF FLEXOR TENDONS IN FOALS
I will mention this topic in this section, as it is a common condition in newborn foals affecting mostly the hind limbs but occasionally all four. It usually spontaneously corrects itself and so can therefore almost be considered a physiological problem rather than a true disease.
The affected foals walk on the
back of the foot, essentially
rocking back on the bulbs of
the heel. In foals that do not
correct themselves within the
first few days corrective
trimming to lower the heels
and forced exercise (1 to 2
hours daily to induce muscle tone) can be instigated. The
use of bandages splints or casts will only exacerbate the
tendon weakness and is to be discouraged. Special shoes
with heel extensions are then necessary in these more
severe cases.
SUMMARY: If a farm is experiencing contracture or laxity problems, then an evaluation of the farm environment and the nutritional programme should be made.
Toxins, unusual plants, chemicals and possible pasture, hay or water contaminants should be investigated. Nutritionally, broodmares should be receiving a balanced diet with neither excessive protein nor calories. Vitamins and minerals should also be available in a balanced formulation that avoids excesses. This is commonly ignored in the extensive New Zealand grazing situation. Remember, preparation of your future athlete should start when the mare is first diagnosed as being in foal!
It is in well-managed farms where possible genetic factors may actually come into play more noticeably. Certainly past foalings and the development and outcome of those foals should factor heavily into future breeding decisions. New research may help identify more causes for laxity and contracture in foals, but that information is still on the horizon. Rapid identification of foals with problems and aggressive treatment is still the best method of straightening out these crooked foals.