A newborn foal, teetering on spidery legs, has a knock-kneed, awkward charm that can melt the hardest of hearts. But it's not so charming if, after a couple of weeks, his legs still look as if they're bending in all the wrong places. Some crookedness of the limbs is to be expected in most newborns, but generally it resolves of its own accord within a week or two. When it doesn't, you might have a foal with an angular limb deformity.

A number of factors can contribute to the birth of a crooked foal, including genetics (inheriting faulty conformation from sire and/or dam), fractures leading to growth deviations, and hormonal imbalances the mare might experience while pregnant. The foal's abnormal position in the uterus also has been implicated in some cases, as have unbalanced nutritional programs that fail to provide the fetus with the nutrients it needs for optimal bone and cartilage growth.


Premature and twin foals are more predisposed to crooked limbs, as are foals born to mares with placentitis, or those whose dams have been exposed to certain toxins while in foal. Sometimes, too, even when everything looks fine at first, incomplete ossification of the knees and hocks in a foal can lead to uneven loading of those joints. Then, when foals engage in the type of exuberant, rough play foals are known for, they run the risk of traumatizing the vulnerable growth plates with each buck or leap. Continued nutritional imbalances in the foal's diet, too little or too much exercise, and injuries also can play a role.

When the skeletal system grows normally, cartilage on the ends of the bones (at the growth plates, or physes) gradually is replaced by true bone through a process called ossification. Young foals are constantly changing--that is, their joints are in a constant state of remodeling while they grow, with each settling into its final, adult shape at a different rate. Generally speaking, the joints closest to the ground (such as the fetlocks) complete their growth first, and those farther up the limb take a little longer.

Angular limb deformities are considered one form of developmental orthopedic disease, or DOD, a multifactorial syndrome that includes any sort of abnormal bone growth in a young horse. What often happens is that one side of a joint grows more slowly than the other, resulting in an asymmetry or imbalance. Fortunately, if you catch such an asymmetry early, there are several ways in which your veterinarian can influence the growth rate and help your foal to develop straighter limbs.

Correct conformation is important, of course, because a horse whose limbs are malaligned will be more prone to injury from uneven load distribution across the joint. Horse owners in virtually every discipline and every breed look for correct, clean limbs--which hopefully equates with soundness as well as performance.

Assessing Angularity

When a very young foal looks crooked, it's important not to push the panic button immediately, says Rick Conrad, DVM, whose Millbrook Equine Clinic in Millbrook, Ontario, Canada, counts among its clients a wide array of racehorses, sport horses, and draft breeds.

"I have seen some foals who look really bad at one week (of age) and have had remarkable turnarounds by 30 days or so. A lot of early crookedness will resolve spontaneously if you give it a chance," he says. "If a breeder is worried, I often suggest they wait until the mare is bred back at the 30-day point, then we'll reevaluate the foal."

Free exercise in those first 30 days of life is one important ingredient in helping crookedness resolve itself.

The most common angular deformity, by most researchers' reckoning, is carpus valgus, commonly called "knock-kneed." But knees also can be "varus," which makes the foal look bow-legged. Hocks and fetlocks can be affected in similar ways, and there are an infinite number of possible complications, including rotational deformities and other signs of DOD such as contracted tendons, club foot, and tendon laxity. Some angular limb problems, unfortunately, have little chance of being corrected (such as bench knees, back at the knee, and toeing out), but others, especially the relatively straightforward (if you'll pardon the term) valgus and varus defects, often respond well to some careful management.

For example, a foal whose angles are only slightly "off" from normal (defined by some orthopedic veterinarians as less than six degrees of variation) frequently will respond to some judicious trimming from an educated farrier, who might rasp the foot so as to help it to land flatter and more squarely, thus gently encouraging the joints above to align correctly. Because foals' hooves are thin-soled and relatively soft, this must be done carefully to avoid making him foot-sore.

Therapeutic glue-on shoes have been used with some success to help encourage crooked limbs back into a more functional line. Restricted exercise, physical therapy, and even fiberglass tube casts are other conservative management approaches.

However, there are some situations which call for a more aggressive approach. If, after three to four weeks, your foal still has significant valgus or varus deformities in his knees, hocks, and/or fetlocks, your veterinarian might recommend further diagnostic procedures such as radiographs to determine the extent of the deviation. Then he or she might suggest one of two common surgeries to help resolve the problem: periosteal transection (also called periosteal stripping), or transphyseal bridging.

Encouraging Straightness

As surgeries go, periosteal stripping is a major success story. Not only is the procedure very uncomplicated, in the grand scheme of equine surgeries, but its success rate is nothing short of remarkable.

"That's one of the biggest keys for owners," says Conrad, who performs dozens of these procedures every year. "It's a very successful surgery, as a rule. I have seen many crooked foals go on and win at the track after this procedure. It's very gratifying."

Periosteal stripping is a minimally invasive surgery, involving a small skin incision and some stitches. It also has a relatively uncomplicated post-operative routine, including the regular minimal bandaging and exercise restrictions. Unlike its alternative, transphyseal bridging, it's virtually impossible with periosteal stripping to "overcorrect" the joint (change the pattern of growth so much that the joint ends up bulging the other direction). As a result, this surgery, developed about 1980 by Swiss veterinarian Jürg Auer, has become an extremely popular technique.

Time, however, is of the essence when you're trying to correct a crooked foal. For best results, valgus or varus knees or hocks should be operated on before three months of age, and crooked ankles need to be addressed even sooner than that--at six to eight weeks of age. The reason is that the surgery must be performed while the joint in question still is growing rapidly; leave it too late, and the growth plates will have closed, effectively closing the window of opportunity for change.

"The success rate depends on the rapid growth of the bones," says Donald R. Trout, DVM, PhD, Dipl. ACVS, associate professor of large animal surgery at the University of Guelph's Ontario Veterinary College, in Guelph, Ontario.

Knock-kneed is the most common reason for performing periosteal stripping, according to Conrad, and about 50% of the time, both front legs are operated on simultaneously. (The degree of angular deformity might vary from limb to limb.) The foal is placed under general anesthesia, and an incision is made in the skin over the bone on the side which is growing more slowly. Once the skin and subcutaneous layers are penetrated, the surgeon can expose the periosteum, a fibro-elastic tissue that covers and protects the bone. Two incisions are made in the periosteum, in an inverted T shape, with the surgeon taking care not to disturb the actual growth plate.

According to Trout, it's best to make the incisions at least one centimeter from the growth plate, although when you're dealing with the delicate joints of a young foal, "the spacing sometimes gets tight in there!"

Once the periosteum has been cut, the edges of the tissue are carefully peeled back from the bone in two flaps which are left to heal on their own. A series of small stitches are used to close the skin.

The foal then is bandaged and allowed to recover from the anesthetic. His post-operative care is fairly uncomplicated, requiring only monitoring of the incision to make sure no infection sets in, regular changing of the bandages, and restricted exercise (very limited turn-out in a small enclosure, or being kept in a large box stall the foal shares with his dam).

Why peel back the periosteum? Most veterinarians feel that this procedure releases the tension on the slower-growing side of the joint, allowing it freer rein for rapid growth that will enable it to catch up with the longer, faster-growing side. The periosteum is a resilient tissue, generally healing naturally within about three weeks, by which time the two sides of the bone usually have evened out.

Conrad says the procedure is effective in most cases, "and the worst complication is usually a little thickening or scar tissue, which is just cosmetic."

If the results aren't satisfactory, however, stripping can be repeated at the same site in about six weeks, with minimal risk. However, the older the foal gets, the less rapidly his bones are growing, and the less dramatic the response to surgery. Conrad observes that in his practice, he repeats the procedure on fewer than 5% of cases, and the most he has ever done is three strippings on a foal (a Quarter Horse which later raced successfully).

Periosteal stripping is the treatment of choice for most serious angular limb deformities in the knees, fetlocks, or hocks, but it's not the only approach available. Occasionally, circumstances demand another approach--transypheal bridging. This surgical procedure, which pre-dates periosteal stripping by a couple of decades, is a more invasive and complicated technique, but if a foal is too old to make stripping a good prospect, if he has failed to respond adequately to stripping, or if his problems are severe, it could be the best answer. Sometimes, if the case warrants, a surgeon might combine the two techniques for the best chance of a successful outcome.

Bridging The Gap

In transphyseal bridging, the principle is not to speed the growth of the concave side of the joint, but to restrict the growth on the convex side so that the opposite side can catch up. This is accomplished by making an incision over the longer side of the knee, ankle, or hock joint, and inserting into the adjacent bones an implant that restricts growth on that side of the bone. (As with periosteal stripping, it's very important not to invade the growth plate itself, says Trout.)

Depending on the surgeon's preference, the implant can be a metal staple (the original method, dating back to the 1960s), a plate similar to those used to repair fractures, a surgical pin bent in a U shape, or two screws with surgical wire "figure-eighted" between them. Screws and wire are the most popular choice now, according to Trout, because surgeons are likely to have the equipment already available if they do fracture repairs, and because they allow some flexibility of fit. Staples, he notes, have a tendency to work loose prematurely, although some surgeons still prefer them, feeling that the eventual cosmetic results are better.

Regardless of what sort of implant is used, transphyseal bridging is usually very effective at restricting the runaway growth of one side of the joint. The downside is that without careful monitoring, the joint can "over-correct" as the foal continues to grow, causing, for example, a knock-kneed foal to become bow-legged!

To prevent this, the implant must be removed, at the appropriate time, in a second surgery. Periodic radiographs can help the surgeon and owner assess the angles of the joint more accurately and let them decide when it's time for the foal to go back under the knife. This second surgery is the major disadvantage to transphyseal bridging.

A foal which has undergone transphyseal bridging must be bandaged carefully post-operatively so as not to put pressure on the implant sites. Trout observes that foal skin is "rather thin, so there's more potential for trauma or scarring than there would be with an adult horse."

A knock-kneed foal which has had surgery on both front legs might present a special bandaging challenge after transphyseal bridging, because the implants will be situated on the insides of the legs, where they could rub against each other. Restricted exercise is part of the equation, "both to protect the incisions, and also because the crooked joints have a limited ability to take the impact of a foal's rough play," says Trout. "A bouncing, rambunctious foal could traumatize the growth plates, or even risk fracture."

A Fish Fairytale

One racing superstar recently in the spotlight could be considered the "poster child" for the effectiveness of transphyseal bridging; his name is Real Quiet, and he won the Kentucky Derby in 1998. Nicknamed "The Fish" as an awkward yearling because he was so narrow in the chest he appeared almost two-dimensional, Real Quiet also had a pronounced case of knock-knees, with the right leg more severely affected than the left. As a yearling, he underwent transphyseal bridging on both of his knees, with screws and wires that were removed after three months. The result, two years later, was a Derby victory and a place in the history books.

Although Real Quiet underwent surgery in April of his yearling year, most veterinarians agree that the best time to do transphyseal bridging on the knee joint is at nine to 12 months of age at most. Ankles should be addressed by four to six weeks of age for best results. However, it's continued rapid growth of the joint that's the important factor, and growth spurts can be very individual.

"Sometimes the results can be fairly dramatic," says Trout. "Sometimes, usually with an older foal, they're more subtle. I always point out to clients that that doesn't mean other approaches, such as therapeutic farriery, won't help as well."

Periosteal stripping and transphyseal bridging have become popular options for owners looking to sell expensive, well-bred Standardbred and Thoroughbred babies destined for the yearling sales. A crooked yearling, regardless of his pedigree, tends to attract few bidders at the sales--and rightly so, since his racing future is by no means a sure thing. With a fairly inexpensive surgery (often costing less than $300-$500), a $3,000 yearling might become a $30,000 one and stand a better chance of remaining sound because his joints are loading evenly with each step, instead of rolling in or out.

Of course, these surgeries do not alter the genetics of the horse, which might have predisposed him to crooked limbs. That's something to keep in mind if you purchase a horse which has undergone stripping or transphyseal bridging (neither of which currently is required to be disclosed in a sale catalogue) as breeding stock.

On the whole, the success rates and relative simplicity of periosteal elevation and transphyseal bridging make them welcome options for any breeder hoping to improve the future athletic prospects of a crooked foal. After all, they've taken at least one overlooked, $17,000 yearling all the way from disaster to Derby winner--for Real Quiet, it was quite a journey.

About the Author

Karen Briggs

Karen Briggs is the author of six books, including the recently updated Understanding Equine Nutrition as well as Understanding The Pony, both published by Eclipse Press. She's written a few thousand articles on subjects ranging from guttural pouch infections to how to compost your manure. She is also a Canadian certified riding coach, an equine nutritionist, and works in media relations for the harness racing industry. She lives with her band of off-the-track Thoroughbreds on a farm near Guelph, Ontario, and dabbles in eventing.

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