CSU uses distraction osteogenesis technique to help lengthen dog's leg


Fort Collins, Colo. — To save a dog's leg, a veterinary orthopedic surgeon tried something radical. With the owner's approval, he severed the tibia and used a novel device to facilitate bone growth thereby lengthening and straightening a dog's leg.

"In fact, Ross H. Palmer, DVM, MS, Dipl. ACVS, who is associate professor of orthopedic surgery at Colorado State University's veterinary teaching hospital, pursued a technique first tested more than 20 years ago. In the 1980s and early 1990s human and veterinary orthopedic surgeons began to work with a technique called distraction osteogenesis (or callus distraction) in which an osteotomy was first allowed to start healing, then was gradually distracted each day to gain limb length or bridge large bone defect."

Photo gallery: Novel veterinary surgical technique helps lengthen dog's leg

He details how a team at Texas A&M reported the early applications of this technique in 1992 (Veterinary Surgery 21:480-487, 1992). According to Palmer, instrumentation was "crude"—as in, part orthopedic equipment and part hardware store purchases, but "the clinical validity of the technique was established."

Such cases often present challenges for pet owners. If handled improperly, Palmer says there can be "devastating outcomes that require amputation. Thus, there is a need for a very close working relationship between the surgeon and the pet owner, and there is the need for a 'user-friendly' device."

In the latest case, which involved a Great Dane puppy named Cooper, the situation not only required straightening, but the relatively shortened tibia of the dog also required lengthening. According to Dr. Palmer, the dog had a rear leg that did not develop properly following a leg break shortly after it was born. Compared to its oversized body, the previously broken leg dangled short.

"The only practical way to (address this) was to use the concept of distraction osteogenesis. Ideally, we would hope to correct the tibial length discrepancy and then continue the distraction at a rate that would keep pace with the ongoing growth of his contralateral tibia," he says.

As part of the procedure, Palmer inserted a metal jack that was screwed to each end of the bone. And every day the pet owner lengthened the jack by about 2 millimeters.

Everything had to be handled with precision. "Go too fast and the muscle and nerves cannot adapt ... go too slow and the bony gap heals prematurely," he adds.

Over several months, Cooper's leg slowly grew. Now, the leg is just an inch shorter than it should be. Overall, the dog's tibia grew 76 mm, about 3 inches. Thirty-six mm were added as a result of the corrective surgery and 40 mm were added because of the pet owner's daily adjustments.

Since the 1980s, the technique Palmer used on the Great Dane has been modified and honed, especially regarding variables that influence "lag time" between execution of the osteotomy and starting the distraction process, the distraction rate and distraction rhythm (how fast and how frequently distraction should be performed) in the dog.

Additionally, enhanced instruments are now available, including the circular external skeletal fixation (CESF, Imex Veterinary, Longview, TX) systems. In Cooper's case, the surgical team used a human device, because of the size of his tibia.

Palmer says that he loved the device for use in the dog because of its ease of use for the surgeon and pet owner. It was applied to the bone, and the team then performed a corrective osteotomy and used the device to straighten the limb. With the device locked down, the pet owner was instructed on how to perform the daily distractions.

"I am excited about the possibility to develop devices for use in smaller dogs and look at how it affects the array of deformities that we can correct," he says. Post-op care

What is most significant about cases like this, Palmer explains, is the complexity of postoperative management. Pet owners must plan on weekly rechecks, radiographs, etc.

"It is, in my estimation, the rare pet owner and pet who are really up for such a challenge," he says. "Perhaps an arrangement of extended medical boarding would be a consideration for that special combination of pet owner and patient who do not have access to such services locally."

Also critical to the success of the surgery was the collaborative efforts of his colleagues, Palmer adds, including Bob Radasch in Dallas and Dr. Massimo Petazzoni in Milan, Italy.

"The device itself belongs to Massimo, and he was kind enough to loan it to me for use in Cooper. Massimo has really pushed the envelope in the field of distraction osteogenesis, and it has been a professional stimulus to get the opportunity to collaborate with him on Cooper and other patients," he says.

Although this case was a great success, Palmer says it's critical that pet owners are made aware that their investments don't always pay off. "A pet owner needs to know that the return on their investment of time, heart and money won't necessarily turn out this way every time," he says.

Down the road, Palmer suggests that veterinarians stay tuned for new gateways in human instrumentation adaptation that may lead to veterinary instrumentation development.

"This will fuel how we can manage complex deformities of upper limbs (femur, humerus, etc) and should decrease the pet-owner burden," he says.