Angular Limb Deformities and Associated Problems in Young and Developing Foals

Whether for racing, performance, or pleasure, we would all love to have foals born with perfect legs, however angular limb deformities and associated problems are very common in the newborn and developing foal.

There are three common types of limb conditions found in the young foal; angular limb deformity or deviation of the limb, flexor and extensor abnormalities, and ruptured extensor tendon. These abnormalities are often found in one or more limbs, but in most instances these abnormalities do not affect a foal’s ability to stand or walk.

Factors that may contribute to these conditions include: abnormal intrauterine positioning, hormonal Imbalances, nutritional Imbalances, unfavorable conformation, incomplete ossification, immaturity of musculoskeletal tissues, flexor tendon laxity, flexor tendon contracture, and young rapidly growing foals.

ANGULAR LIMB DEFORMITIES

Angular limb deformity (ALD) refers to an outward (valgus) or inward (varus) deviation of a limb. The point of deviation for most limb deformities is associated with a joint. The carpus (knee) is, by far, the most common joint affected. The fetlock (ankle) and tarsus (hock) can also be affected. More than one leg is often involved.

The cause of angular limb deformities is quite complex. In general, it can be associated with unequal (asymmetric) growth of the limb long bones, such as the radius or cannon bone. One side of the long bone grows faster than the opposite side. This occurs in the growth plate near the joint, resulting in deviation of the limb. This asymmetric growth may develop as a result of abnormal weight-bearing on the limb such as with;

Excessive body development in relation to bone/joint development,

A lameness,

Inflammation of the growth plate (physitis),

Or injury to the growth plate.

Many angular limb deformities can be diagnosed from the clinical appearance of the limbs. However, radiographs are sometimes required to be taken of the affected leg or legs. This will help the veterinarian to determine more specifically the exact location of the deviation.

Treatment

The type of treatment indicated for ALD depends on several factors including the

Age of the foal,

The joint involved,

And the location and severity (degrees) of the deviation.

There is a narrow time window for correction of an ALD – this lies only while the growth plate is open and there is potential for bone growth. For example, for a fetlock ALD the window of opportunity for correction closes after only 3-4 months of age and all intervention must be performed well before this time. It is therefore very important that a foal with ALD be assessed and treated as soon as possible in order to improve the chances of a successful outcome.

Confinement and Diet Modification

Regardless of the severity and location of the ALD, confinement is important. Excessive exercise will only aggravate and make the problem worse. In many cases, stall rest alone can assist with correcting the ALD. Diet modification of creep fed or older foals is also important.

Along with stall confinement and diet modification, corrective hoof trimming is also important. Your veterinarian or farrier will be able to assist with hoof care.

Surgery

Severe forms of ALD require surgery. The goal of surgical intervention is to alter growth at the growth plate of the long bone involved, such as the radius. The surgical procedures used are periosteal stripping or transphyseal bridging.

Periosteal stripping involves lifting the covering of the bone (periosteum) just above the growth plate on the “short” side of the long bone. This surgical procedure is used to enhance the growth on the side of the long bone that is slower, to encourage it to “catch-up” with the other side. This procedure is performed on cases of ALD of mild-moderate severity. It does not result in overcorrection.

Transphyseal bridging involves placing a screw in the long bone above and below the growth plate on the “long” side of the bone and placing a piece of stainless steel wire between them, or placing a screw directly across the growth plate on the faster side. The purpose of these implants is to slow or stop the growth at the growth plate on that side of the bone which is longer, so that the other side can catch-up. It is very important that the foal be closely monitored as the implants must be removed as soon as correction has occurred, otherwise overcorrection may occur. This type of procedure is usual performed on more severe cases, or on older foals where there is only limited growth left at that particular growth plate.

Limb Casts or Splints

Limb casts or splints may be used if the ALD is due to weak ligaments and bones associated with the affected joint. This type of ALD mainly affects the carpus (knee) and tarsus (hock). It is observed more frequently in premature foals in which the bones of the carpus or tarsus are not completely mineralized at the time of birth.

A cast or splint is applied to the limb to help support the limb and maintain it in a straight position until the ligaments and bones mature enough to hold the weight of the foal. Usually only 10 to 14 days is required.

Prognosis

In general, foals with ALD have a good outcome for future performance if the condition is not severe, if joint damage has not occurred, and if they are treated appropriately and in a timely fashion. While there are many high performing adult athletes with angular limb deformities, abnormal loading can increase the risk of injury, time out of training and need for costly treatments or interventions.

FLEXOR AND EXTENSOR ABNORMALITIES

The most common flexural weaknesses are carpal overextension ("back at the knees") and weak pasterns/fetlocks. Both of these conditions improve in the first few weeks of life.

When the supporting soft tissues strengthen, many moderately affected foals with carpal overextension will gradually improve to normal. In severe cases, the foal should be confined until the conformation improves.

Weak pasterns/fetlocks are a very common finding. Most foals improve in a few days and require very little special attention. In mild cases, simply trimming the heels slightly will rid the foot of the rocking motion and keep the foot on the ground. In cases where the foal is “down on its bumpers”, rocking back on its pasterns to the fetlock with the toe tipping up, special shoes, glued or taped on, with a heel extension can be used for support. A small, light bandage with extra padding behind the heel bulbs can serve as adequate protection until the foal strengthens or until shoes can be applied. Without protection, heel bulb and pastern abrasions are common in these foals. Heavy bandages however must be avoided as they make the laxity worse. Foals should be confined to a stall until the shoes are applied.

The most common flexural deformities involve the carpus, fetlock, or coffin joints. Oxytetracycline is often used to relax mild flexor tendon contractures in neonates. In more severe cases, splinting or casting is required to induce relaxation of the flexor muscles and relieve contraction.

If a foal with a fetlock flexural deformity cannot walk without the fetlock flexing forward, a splint is applied. The foal is not turned out until the splinting is no longer needed. Most fetlock contractures take 2 - 3 days to correct. Few foals take longer than 3 days of steady splint pressure and enforced relaxation on the flexor muscles to obtain normal limb position.

Flexural deformity of the carpus (over at the knees) is very common but has a large variation in severity. Most milder cases improve with normal exercise. In more severe cases however, excessive exercise can actually worsen the problem by inducing a vicious cycle of contraction-pain-contracture. Intermittent brief turn-out exercise or hand-walking exercise with the mare may be used. In cases where the foal has difficulty standing, the legs are bandaged from the elbow to the foot or a splint or cast is used.

RUPTURED EXTENSOR TENDON

A ruptured extensor tendon generally appears as a swelling on the front of the knee of a young foal. The filling is soft and fluid filled, but usually not inflamed or sore. One or both legs may be affected. Surgical intervention is unnecessary, generally restricted exercise or box rest is advised. If the foal is stumbling as a result of the rupture, bandaging and splinting may be required initially to help the foal move the foot forward.

The majority of foals will recover well with no further treatment.

As with all foal conditions, early detection is vital for the most successful outcome. Ensuring that a foal’s conformation and development is monitoredover the early stages on its life, is a great way to give it the best start possible. If you have any concerns about your newborns conformation, contact your local veterinarian.