Jury Still Out on Angular Limb Surgery

Crooked legs may look cute on awkward newborn foals, but they are liabilities in the auction ring, where yearlings with the best conformation often attract the highest prices.

That's why procedures to correct angular limb deformities rank among the most common surgeries performed in young Thoroughbreds. The operations can transform sale candidates into more attractive physical specimens, and improve their chances for remaining sound after they begin training and racing.

But, while techniques such as transphyseal bridging and periosteal elevation are widely accepted in the equine community, their use is not free of controversy. Some veterinarians argue the procedures are not as successful as some people think. Others maintain the surgeries are performed more frequently than is necessary.

Recent research conducted by Colorado State University (CSU) scientists indicates a slight deviation from normal can be a good thing and doesn't always need to be corrected. In addition, studies in Florida and Canada raised questions about the effectiveness of periosteal elevation.

"There is a certain level of screwing with nature that we shouldn't be doing," said Dr. Wayne McIlwraith, the director of the Orthopaedic Research Center at CSU's College of Veterinary Medicine.

The CSU research project involved Thoroughbreds owned by French art dealer Daniel Wildenstein. McIlwraith examined and photographed the horses as weanlings, yearlings, 2-year-olds, and 3-year-olds. Dr. Tina Anderson, who was working on her doctorate, documented conformation changes in the horses at various ages using McIlwraith's photos and computer-based measurements. The scientists also collected information about the horses' racing performance and their soundness.

"We found that some degree of carpal valgus protects a horse from knee injuries," McIlwraith said. "In other words, if you have a really badly knock-kneed horse, that's a problem. But if he's got only a little bit of carpal angle -- less than eight degrees -- that's good. When we looked at the correlation coefficient between carpal angle and clinical problems, we found the straighter the leg, the more problems they had.

"So," McIlwraith concluded, "some people's obsession at the sales with having a dead straight knee is a little bit counterproductive to racing soundness."

The studies on periosteal elevation were conducted at Peterson and Smith Equine Hospital in Ocala, Fla., and the University of Saskatchewan.

Periosteal elevation (also known as periosteal stripping) has been around since about 1980. Swiss veterinarian Joerg Auer developed the technique while he was at Texas A&M University. The procedure is performed on the slower-growing side of the joint near the growth plate. Two incisions, in the shape of an inverted T, are made in the periosteum, the connective tissue that sheaths and protects bones. The edges of the tissue then are peeled back from the bone in two flaps that are left to heal on their own.

Many veterinarians believe periosteal elevation releases the tension on the shorter, slower growing side of the joint, allowing it to develop more rapidly and catch up with the longer, faster growing side.

Dr. Donnie Slone of Peterson and Smith does not agree.

"I think you can probably boil down what I believe to two statements that I consider to be facts," he said. "One is that most angular limb deformities that foals are born with will correct on their own. The second is that I am now convinced that periosteal stripping does not do anything to alter growth of bone at the growth plate."

Slone and his fellow researchers conducted a study similar to Auer's periosteal stripping research on normally conformed foals first reported in 1982. In Auer's project, periosteal stripping was performed on one leg in each foal on the medial side of the distal radius. Auer concluded the procedure caused the foals to become knock-kneed by day 30 following surgery. Finding no asymmetric growth at the distal (lower) end of the radius, he theorized the discrepant growth occurred at the proximal (upper) end of the bone.

The Florida study looked at eight mixed-breed foals with a median age of 33 days. They had carpal angles between zero and eight degrees before undergoing periosteal elevation in one limb.

"Nothing happened," said Slone, who reported the results at last year's American Association of Equine Practitioners' convention in Texas. "The foals didn't become knock-kneed. No statistically significant difference between medial and lateral growth rates at either the proximal or distal end of the radius could be detected between the treated and the control limbs."

In the Peterson and Smith practice, restricted exercise corrects almost all of the congenital angular limb deformities, according to Slone. Transphyseal bridging corrects the 10-20 cases each year that do not respond to restricted exercise.

"We don't usually do anything drastic to their feet, but trimming is important," Slone said. "Almost any foal that is knock-kneed will turn out at their feet. They need to have the outside of their feet trimmed shorter and their toes rounded. But mostly, you just have to be patient, unless you are dealing with fetlock angular limb deformities."

Added Slone: "Periosteal stripping is something that just needs to go away. We haven't recommended it in this practice for at least 10 years. We believe the procedure gets credit for correcting those angular limb deformities that would correct without intervention."

Continued . . .