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May 1, 2009

Should Angular Limb Deformities In Foals Cause Concern?

Learning how to identify and effectively monitor angular limb deformities in foals may help save you money while creating a stronger athlete.

More often than not, a foal has some degree of angular limb deformity at birth. But will the issue resolve itself naturally, or does it require assistance? Evaluating the degree of severity of the deformity within the first few weeks of the foal’s life helps an owner develop a plan for treating the afflicted limb.
   
Angular limb deformities take two forms—those that are congenital and those that are acquired. Acquired deformities occur sometime after the foal is born and can be the result of an injury or inflammation of the growth plate or just the natural conformation the foal will develop. Congenital deformities are present at birth and may be the result of how the foal is positioned in the uterus. These deformities are then further categorized as either valgus (the limb below the joint described deviates laterally, or to the outside of, the axis of limb) or varus (the limb below the joint described deviates medially, or to the inside, of the axis of the limb).
   
Due to a foal’s cramped placement within the mare’s uterus, it is not unusual for a newborn to exhibit a varus or valgus deformity, and some of these foals will naturally correct without human assistance. An example of one such deformity is carpal valgus (knock kneed), which, if not severe, can straighten without medical intervention. However, some deformities, such as fetlock varus (bow legged), require immediate medical attention.

Evaluating The Foal


“Most foals are not born straight,” said Alan Ruggles, DVM, ACVS, who, since starting his work in veterinary medicine more than 20 years ago, has treated thousands of foals with angular limb deformities at Rood And Riddle Equine Hospital in Lexington, Ky. “Limb deformities result from a combination of muscular and ligament weaknesses, so it is necessary to be cautious in labeling a foal within the first two weeks of life because most limbs change dramatically once they become weight-bearing.”
   
Brooke Royster, owner of Chance Farm in Gordonsville, Va., has been breeding Thoroughbreds for three decades and has seen hundreds of foals born.
   
“When I see a foal born with certain more minor deformities like slightly knock kneed, I tend not to worry too much because I know that if the deformity is not too severe that it is apt to correct in time,” he said. “But if I don’t see improvement in the first month or so then I might consider a more aggressive approach.”

Foals that did not have a long enough gestation period are at a higher risk of acquiring a deformity within a few weeks or months after birth, even if they are born conformationally correct. They may not have had adequate time for bone development and are therefore unprepared to put weight on their limbs. “These types of foals should be monitored closely for any changes in the angle of their limbs,” recommended Ruggles.
   
“For any foal, be it angularly deformed or not, I would recommend having a veterinarian do a conformation exam around 3 weeks of age. That way foals born with deformities can be reevaluated with radiographs if necessary, and those foals who appear conformationally correct can be monitored for any future changes,” Ruggles advised.
   
He said the key is to evaluate the whole foal—its age, family history and maturity. “There are things that can be done to improve foot conformation that encourage normal growth of the limbs,” he said. “The body at this age is like plastic—you can mold it either badly or properly—and by dressing or trimming the feet, you can promote normal healthy growth of muscle, bone and ligament.”
   
The most common ways of treating angular limb deformities include corrective shoeing, splinting, exercise restriction and surgery.

Exercise Restriction And Splinting


Conservative therapy, such as controlled exercise or hand walking, is sometimes all an angularly deformed foal needs to self-correct, assuming the deformity is mild.
   
If a deformity to the fetlock does not improve with exercise restriction within the first two to three weeks after birth, then a veterinarian should be consulted.
   
Deformities to the carpus and tarsus have a little more leeway. Foals with mild deformities are typically allowed to reach 2 to 3 months of age before starting treatment since those growth plates don’t close until the foal reaches about 20 months of age. That being said, regardless of the severity of the deformity, it is crucial that it is corrected well in advance of growth plate closure and early enough to prevent secondary damage to other bones and joints.
   
“With a faster growing foal that starts to exhibit some problems I first cut back their feed and then, if I don’t see results, I consider limiting the amount of daily exercise. However, I am usually reluctant to cut back on exercise because I feel that it is a key ingredient to raising a good and healthy horse,” said Royster.
   
“At the same time, I believe that foals, and really weanlings in particular, that grow rapidly and are overfed have a higher tendency to acquire angular limb deformities,” he added. “If cutting back on exercise and feed don’t bring satisfactory results, then these horses may require more aggressive treatments.”
   
Splinting is another non-surgical approach that can be beneficial to flexural deformities. “I don’t recommend splinting for angular deformities because pressure rubs can result, which, if severe, may leave scars. The only reason I would place a splint on a angular deformity is if there is laxity in the ligament and I needed to give it stability while it tightened on its own, but that is a rare case,” explained Ruggles.
   
When using a splint approach, it is imperative that the skin be adequately padded and the bandages checked and changed daily.

Corrective Shoeing

Farriers, through regular trimming and shoeing, can help support and keep the foot directly beneath the bone column to help correct a deformity.

“It is essential to closely monitor growing foals and correct angular deformities in a timely manner to optimize on their future athletic potential,” said Scott Morrison, DVM, a veterinarian and farrier who practices at Rood And Riddle. He is lenient for the first month of a newborn’s life because the foot is manipulative and weak at such a young age.
   
In most cases, the higher up on the limb the deformity, the less chance of fixing with corrective shoeing. Fetlock deformities are the most responsive to foot manipulations, but it is imperative to start work early because the growth plate closes around 4 months of age. If Morrison feels he can’t improve a fetlock deformity within 30 days, then he recommends surgery be performed before the growth plate closes.
   
“Valgus deformities of the fetlock usually improve with time and usually don’t require treatment unless severe. Fetlock varus on the other hand generally doesn’t improve with time and requires aggressive trimming, shoeing or extensions to correct,” explained Morrison, who added that extreme care should be taken with trimming and putting extensions on young foals. “Sheared heels and excessive flaring can be easily created in the immature foot. I recommend shoes in cases that require a lot of correction as they can provide this without focal tearing on one region of the hoof wall.”
   
Carpal valgus deformities can also be helped through the use of medial extensions, but care must be taken not to create a fetlock deformity as an attempt to correct the carpus. So, timing is essential.
   
“I usually focus on keeping the fetlock directly beneath the cannon bone until the distal metacarpal/tarsal physis has closed (around 4 months old) and then focus on correcting the carpus/tarsus,” Morrison said.
   
“Especially with newborns, a lot of severe deformities can be fixed with splinting or surgery but also with manipulation of the foot. It’s best to do things that are least invasive first, but there can be secondary complications that can arise from overdoing foot manipulation, so it is best if a veterinarian and farrier work together to monitor and keep a finger on the situation,” added Morrison.
   
The juvenile growth period is a crucial time for stress adaptation of the internal foot structures and development of a strong, robust foot able to accommodate various conditions later in life. “For this reason I think it’s imperative that anytime we use the foot to correct a deformity higher up on the limb we realize the negative impact it may have on the foot. Using a shoe for example may correct a limb deformity, however it drastically changes normal foot loading,” Morrison continued.

Surgical Options


If corrective shoeing doesn’t dramatically improve the deformity, then surgery is usually the next step.
   
Transphyseal bridging is a surgical procedure that aims to slow the growth of the convex surface of the limb by bridging the physis with a mechanical device such as screws, wires, staples, or bone plates to allow the other side of the limb (the concave surface) to catch up. In all cases, a second surgery must be performed to remove the hardware.
   
“In my experience, transphyseal bridging is most effective for congenital deformities and bowed cannon bones,” said Ruggles. “It can also be used in the carpus, but I try not to perform this surgery until the yearling year because growth goes on longer in the carpus than the fetlock. In any case, good management is required because if left in too long, the screws can actually cause the limb to over-correct.”
   
“If given the option, I would always prefer a less invasive approach,” commented Royster. “When using screws and wires, there is usually scarring involved. Surgeries can be extremely useful in correcting angular limb deformities, but I know from experience that blemishes left on the skin from more aggressive approaches to treatment can be counterproductive at a sale.”
   
Another, albeit more controversial surgical approach, is periosteal stripping, which is performed by cutting the bone covering or periosteum and elevating the concave surface of the limb proximal to the affected growth plate in order to encourage growth.
   
The exact science behind why periosteal stripping works is not completely understood. One belief is that periosteal stripping increases the blood supply to the affected growth plate. Another theory is that the thickened periosteum acts as a bowstring and when cut relieves the tension, allowing growth to resume.
   
Periosteal stripping can be performed at any time and is beneficial up to the time that the growth plate on the affected limb closes.
   
“People should think about the fact that we have the abilities to make big changes, but we also have the ability to make changes that aren’t so good. Before starting to address any angular limb deformity, it is best for horse owners to have the attitude that they will monitor their foals and implement a plan,” said Ruggles. “Even bad deformities can be helped quite a bit, so don’t give up. Mother nature can correct a lot, but don’t rely on her to correct everything! Have a backup plan of intervention rather than waiting until it’s too late and saying, ‘Oh, I should have done something sooner.’ ”

 
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