How delightful to watch a newborn foal totter unsteadily on four sticklike legs and soft, slippered feet. That joyful feeling at the first few precious steps can rapidly turn to concern, though, if you dwell too long on their conformation. What will become of this bowlegged, crooked neonate?!

“Foals normally have some joint laxity (looseness) at birth, giving the impression of poor conformation,” says Taralyn McCarrel, DVM, an assistant professor of large animal surgery at the University of Florida’s College of Veterinary Medicine, in Gainesville. “In most cases this joint laxity improves quickly and is therefore no longer a concern moving forward.”

Unless you notice a severe defect of the foal’s limbs at birth (such as a premature foal with collapsed knee or hock joints because the small cuboidal bones had not yet calcified), don’t make any verdicts about their alignment in the first few days of life. What matters is whether that foal’s legs begin to straighten out quickly or if they have a conformational abnormality, such as an angular limb deformity (ALD), that needs to be addressed.

If, as the foal reaches one to two weeks of age, his crooked limb persists, then you and your veterinarian must take swift action to correct the deformity.

“Luckily, most foals with angular limb deformities can usually be managed conservatively, reserving surgery for only those with severe deformities or foals that are not responding to conservative therapy quickly enough,” says Craig Lesser, DVM, CF, a shareholder at Rood & Riddle Equine Hospital in Lexington, Kentucky.

We’ll review why angular limb deformities occur and how veterinarians characterize them, then get up-to-date information on the best ways to manage affected foals.

ALD Definitions and Development

The term “conformational defect” refers to any abnormality in the shape or appearance of the horse’s musculoskeletal system. Angular limb deformities are one type of conformational defect. They occur when the foal’s limb deviates abnormally in a side-to-side direction, as viewed facing the front or back of the foal. If the leg angles inward toward the middle of the body, it is called a varus deformity. When the limb deviates laterally—to the outside of the foal away from the midline—it is called a valgus deformity. One way to remember the distinction between the two ALDs is by associating the words valgus and laterally because of all the Ls they contain.

These deformities develop when asymmetric growth occurs across growth plates, which are regions near, but not at, the ends of long bones where bone growth occurs (i.e., bone does not grow from the ends). If you’ve ever seen a radiograph (X ray) of a foal’s limb, these growth plates might look like an extra joint extending along the entire width of the bone near the actual joint.

Pinpointing ALDs

Classifying ALDs involves identifying the affected joint and the direction of limb deviation. The most commonly affected joints include:

• The fetlocks (often referred to as ankles), due to asymmetric growth across the growth plate in the lower (distal) aspect of the cannon bone, right above the fetlock joint;
• The knee (carpus), due to asymmetric growth at the distal end of the radial growth plate located just above the knee joint; and
• The tarsus (hock), as a result of abnormal growth across the plate in the distal tibia, located directly above the hock joint.

“A fetlock varus of the forelimbs is the most commonly encountered ALD in foals,” says Lesser. “The next most common ALDs are the fetlock varus of the hind limbs and carpal valgus and varus.”

Tarsal ALDs occur even less commonly, and a fetlock valgus occurs only rarely.

When evaluating a foal’s conformation, the veterinarian should distinguish ALDs from other abnormalities. Flexural deformities, occurring in a front-to-back direction, might include an over- or back-at-the-knee conformation or a club foot. Rotational deformities might give the foal a toed-in or toed-out appearance.

Also realize that foals can have more than one ALD—such as the “windswept foal.” In this case, the foal has a varus on one limb and a valgus on the opposite limb. With both limbs deviating in the same direction, it appears as if the wind is sweeping the legs right out from underneath him.

Alternatively, a foal can have an ALD at more than one joint in the same limb (e.g., a carpal and fetlock varus). Angular and rotational deformities can also occur simultaneously.

Evaluating Live Foals

While identifying and describing the affected limb might seem straightforward, remember that foals are rambunctious moving targets.

Ideally, face the foal and have him stand as squarely as possible. Youngsters only stand for very short periods, so reposition the foal as needed, and evaluate each limb independently. This will allow the foal to stand in a relaxed, natural position for a shorter period rather than a potentially awkward, restrained one as you try to evaluate all four limbs at once. Examine the foal by standing directly behind him, as well. Finally, stand shoulder to shoulder with the foal, and look down the limb toward the ground. Also assess the foal’s conformation at the walk.

In a picture-perfect foal, a virtual line drawn along the middle of the long bone above the affected joint will match a line drawn down the middle of the long bone below the joint. In this case the normal angle is 180 degrees (i.e., a straight line). When the line down the middle of the long bone below the joint does not line up, veterinarians note its degree of deviation from 180.

Lesser uses a 4-point scale to grade and track ALDs in foals, with each grade corresponding to a 3° lateral or medial (away and toward the midline, respectively) deviation. In other words:

• Grade 1 is a 1-3° deviation from normal;
• Grade 2 is up to 6°;
• Grade 3 is up to 9°; and
• Grade 4 is over 9°.

“While we attempt to manage the majority of ALDs conservatively, when the ALD is getting into double digits we need to start seriously considering surgical correction, as the abnormal loads can risk permanent joint damage in the long term,” says McCarrel.

Veterinarians can take radiographs of the affected joint and measure the angles, but this step is not always practical or necessary.

“I see up to 150 foals a day at certain times of the year, and approximately 90% of those foals have ALDs,” says Lesser. “It simply isn’t possible to radiograph all of them.”

Further, for radiographs to be useful, the limb must be absolutely perpendicular (i.e., lined up) to the X ray plate or the ALD will appear more or less severe on the image than in reality. And, just as it is for a visual exam, lining up a foal with an X ray plate is no easy feat.

Therefore, practitioners typically reserve radiographs for severe cases or those that are not improving with conservative therapy.

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