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This is a very common disease of the new born foal. It can be presented by valgus deformity, where the limb deviates to the outside, outward rotation (splay foot) (picture1) or a varus deformity where the limb deviates to the inside (pigeon toes). In most cases, these deformities are just postural. However with time the bone adapts to the abnormal loading of the limb which results in a permanent rotational deformity. Many foals are born with a mild carpal valgus and toe-out, this is considered normal and as the foals growths and the chest widens, the limbs straighten progressively.
This condition can be congenital or developmental and have numerous causes. An acquired angular deformity is defined as worsening or failure of correction of normal mild valgus. Foals are like molding plastic and the conformation changes slowly with growth. The conformation is influenced by many factors including genetics, nutrition, amount of exercise, weight bearing and veterinary intervention. At the time of planning the management of the deformation, the foal should be evaluated with the remaining growth in mind and not just with the present status. Early recognition and regular re-evaluations are essential to correct the deformity because the greatest impact on conformation is made during the period rapid growth.
Most of the growth around the knee (carpus) or hock (tarsus) area is within the first 6 months of age and from the fetlocks areas is within the first months of age. Radiographs alone cannot be used to determine the end of the bone growth because the physis looks radiographically “open” after clinically growth has finished. Normally a foal corrects a deviation of 5 to 7 degree of normal by 4 months of age and should be almost straight by 8 to 10 months of age.
The foal should stand square and evaluated from the front and behind. The foal should be walked away and towards the examiner paying particular attention to the breakover for each foot.
Long and narrow cassettes should be used to measure the angle of the deformity. The small bones of carpus or tarsus can be assessed for malformation or injury.
Is the major cause of congenital angular deformities and usually improves in the first 4 weeks of life without intervention as the tissues strengthen (photo 2). For example a foal with windswept limbs (tarsus valgus in one limb and varus in the other limb). The only treatment that is necessary is rest for these foals. Some foals can suffer from severe deformities, eg: fetlock, that they are unable to bear weight on the sole of their feet (photo3).
These foals are treated immediately with shoe extensions and rest (photo4).
Rest in a stall or in a small paddock is mandatory because otherwise can lead to sesamoid fractures and other injuries. Splints are used only if are only absolutely necessary because they can damage the soft tissues and also cause limb laxity (photo5).
Deformities related to trauma
Developmental causes of angular deformities are likely secondary to excessive or asymmetrical weight bearing.
If the foal has incomplete ossification of the cuboidal bones, the overload of that limb can cause the crushing of these bones with a secondary angular limb deformity. The most commonly affected bones are the carpal bones resulting in carpus valgus. Here, radiography is a very important diagnostic tool to assess the carpus or tarsus. Incomplete ossification can be shown in x-rays as wedge shaped, overlap opposing bones or are fractured. This condition can be managed in a hospital with a strict stall rest and monitoring. Otherwise, sleeve casts can be placed for 10 to 14 days and then reevaluate the bones with radiographs.
Limited small paddock turn out.
Monitoring the feet
Shoe extensions/ trimming
The foals with severe deformity and the ones that do not improve despite restriction of exercise and corrective farriery will need surgical intervention.
The goal of surgery is to accelerate or decrease the growth in a particular side of the bone in order to correct the deformity. The surgical technique depends on the age of the horse, the degree of angular limb deformity, anatomical site, and whether the deformity is varus or valgus.
Periosteal stripping (hemicircunferential periosteal transaction and elevation) is a surgical technique that is used to accelerate the growth on the concave side of the limb, external side of the limb for the valgus and in the internal side of the limb for the varus deformity. This procedure can be done on outpatient basis where the mare and foal are admitted to the hospital and they can be discharged after the recovery from surgery the same day. It can also be performed in the field with a short acting anesthesia. After surgery the foal is kept in a stall rest or small paddock until the deformity has been corrected. This surgery has better results if it’s done in the first 2 months of life but not earlier than 2 to 4 weeks of age. If further correction is needed it can be repeated and no over correction is reported. Recently this surgery has been questioned since many foals with mild deformities would improve without surgery and also an experimental study was conducted which concluded that there is no difference in results with or without periosteal stripping. However there are many arguments against this study and the surgery is still used widely with good results.
Growth retardation is other surgical technique used to correct angular limb deformities, and is called transphyseal bridging either by placing 2 screws and wires or a single screw. The surgery is performed on the convex side of the deformity to decrease the growth rate on that side of the physis. The decision to do the procedure is based on the severity of the deformity and the age of the horse. This technique needs special equipment. Implants have to be placed therefore is a procedure that must to be performed under strict aseptic conditions in a hospital. Postoperatively the foal is kept in stall rest and close monitoring with periodic follow-up radiographs. This is essential to avoid over correction of the condition.
For those foals that the deformity persists after physeal closure, a corrective ostectomy or osteotomy can be performed. These techniques are very complex and are considered as salvage procedures.
Flexural limb deformity in foals
Flexural limb deformity is the inability to extend a limb fully or can be manifested as hyperextension deformities (photo 3). This condition can be congenital or acquired and can be occurred in utero or at any time after birth. The anatomical structures than can restrict the extension of the limb can be flexor tendons, suspensory apparatus, joint capsule, surrounding fascia, skin and bone (photo 6).
Congenital flexural deformity
The deformity occurs in utero and the cause is often unknown. The most common areas that are involved are the carpus, tarsus and fetlocks alone or in combination. Usually both limbs are involved and a combination of deformities can be seen also deformities in other parts of the body can be expressed such as spinal deformities, rye nose (photo rye nose) and cleft palate. In utero deformities can cause distocia at the time of birth, resulting in loss of the foal and possible loss of the reproductive capacity of the mare. Therapeutic intervention for these severe deformities should be discouraged and humane euthanasia should be performed.
Mild flexural deformities of carpus or fetlocks where the foal can move around they usually correct on their own. Medical therapy include physiotherapy by manual manipulation of the limbs, swimming, bandaging, splinting or casting, some commercial braces and boots are also available (photo 7) and the administration of the antibiotic oxytetracycline is helpful. The foal usually responds quickly to the cast application but very close monitoring should be instituted because severe wounds and abrasions and also necrosis of the limb can be caused by the incorrect placement of a cast, splint or a bandage. A foal with casted legs should have intensive care to be assisted to nurse and monitor for complications that can occur in other body systems.
Prognosis is good for those foals that respond favorably in the first 2 weeks of life.
Acquired flexural deformities
These deformities develop after birth until the second year of life. Usually joints of the digit (distal interphalangeal joint, fetlock joints and knee joints (carpus) are involved. This pathology usually occurs between the first month and 18 months of age.
Common causes for acquired flexural deformities of the fetlocks and carpus are believed to include a genetic propensity for rapid growth, over nutrition and pain. Any cause of pain in one limb reduces the weight bearing and may result in contraction of the musculotendinous unit.
There are genetic reasons for the development of this condition of the digit joints (clubfeet) (photo8). Other factors involved are diet and exercise. Clubfoot also can be associated to pain in other region of the limb therefore is very important a complete lameness exam in order to discard a lesion elsewhere in the limb. Clinical signs of a clubfoot are a prominent bulge at the coronary band, increase in length of the heel relative to the toe, and failure of the heel to touch the ground after trimming. As the hoof growths it develops a boxy shape and a dish shape at the level of the toe.
The treatment for foals with clubfoot are pain management, lower the heels, exercise and dietary restriction. In order to avoid excessive wear of the toe area a supplement with a hoof composite can be placed and also it can act as a lever arm. Glue on shoes can be used as well but careful monitoring is necessary since they can induce boxy shape hoof because the restriction of hoof expansion. Another treatment option is to inject the antibiotic oxytetracycline which has shown to relax the musculotendinous unit but it can cause exacerbation of back-at-the-knee conformation.
If no improvement is seen within 1 to 2 months of conservative treatment, surgery will be necessary. Surgery described for this condition is to cut (desmotomy) the accessory ligament of the deep digital flexor tendon, this is a tendon that runs from the back side of the cannon bone and attaches to the deep digital flexor tendon. In more severe cases of contraction, it might be necessary to cut (tenotomy) the deep digital flexor tendon, although the desmotomy of the accessory ligament in conjuction farriery, oxytetracycline and phenylbutazone (bute) has been helpful. These severe cases also are accompanied with other soft tissue contractions such as the joint capsules which impairs the athletic future.
When contraction is localized at the level of the knee (carpus), if the condition is recognized early it can be managed conservatively correcting nutrition by reducing the energy intake and slowly growth, exercise restriction and bute. If the foal still nursing, the milk intake can be controlled or the baby can be weaned. The contraction can take weeks or months to be corrected and splints, bandages and or oxytetracycline can be used. In order to correct the disease permanently is mandatory to find and address the underlying cause.