Getting a Leg Up on Cruciate Ligament Rupture

As soon as she saw her one-year-old Golden Retriever, Morgan, limping, Nina Zitzer knew what was wrong.

"My dad and I had Morgan at the local dog park with her sister Carley," recalls Zitzer, who is a veterinary student and research assistant at the University of Wisconsin. "Morgan was chasing Carley through the tall grass and when they came back toward us, Morgan was lame on her left hind limb."

Morgan had ruptured the cruciate ligament in her left hind leg. Cruciate ligament rupture, or CLR, is quite common, particularly among large purebred dogs such as Golden Retrievers, Labrador Retrievers, Rottweilers, and Newfoundlands. "It’s the most common problem I see in my clinic," says Dr. Peter Muir, a veterinary orthopedist who teaches and practices at the University of Wisconsin in Madison. "Twenty-five percent of the cases I see each week are CLR cases."

CLR results when one or both of the ligaments that connect the femur (thigh bone) to the tibia (shin bone) tear apart. Normally these ligaments work like a hinge so that the two bones don’t slide over each other whenever the dog moves. When one or both of the ligaments rupture, the hinge function is lost, the bones slide across each other, and the dog becomes lame.

The standard treatment for CCL is for a veterinary orthopedist to perform a tibial plateau leveling osteotomy, or TPLO. This surgical procedure surgery involves cutting into and then rotating the tibia so that it can no longer slide across the femur. Surgical plates are used to keep the two bones in position.

Although the TPLO procedure usually succeeds, the surgery can be very expensive. Individual procedures run several thousands of dollars. Moreover, Dr. Muir notes that a recent study shows that U.S. dog owners spend much as $2 billion annually to treat their dogs for CLR. "Clearly, this condition imposes a large economic burden on the American public," Dr. Muir says.

In addition to the expense of TPLO surgery, a dog may need several months to fully recover from the procedure. Physical activity is severely limited during the beginning of the recovery process, followed by physical therapy later on. Still another down side to the surgery is that it addresses only the end result of a process that usually results from pathology or disease, not a true injury or trauma. Thus, a dog treated with a TPLO on one leg remains just as vulnerable to rupturing the ligaments in the other leg as he was before the surgery.

Those factors troubled Dr. Muir, who began studying CLR 10 years ago. "I thought that if we could identify a dog in the early stage of the disease, we could provide treatment that would combat the disease and be much less traumatic and risky than surgery," he explains. "But it’s not clear what the causative factors are, so the early treatment options are unclear, too."

That said, Dr. Muir and his team at Wisconsin—which includes Zitzer—have made significant progress in solving the mystery of what causes CLR. Thanks to support from the AKC Canine Health Foundation, Dr. Muir has been able to test his hypothesis that bacteria cause the deterioration that leads to CLR. Now he’s focusing on whether that invasion occurs in the ligament itself, the lining of the knee joint or both.

Dr. Muir’s work has included a contribution from Morgan, Zitzer’s Golden Retriever. Before she underwent a TPLO procedure for the CLR in her left hind leg, Morgan’s joint fluid was tested—and the test showed the presence of bacterial material. "So she was placed on a six-week regimen of an antibiotic after the surgery," explains Zitzer. "It [had been] indicated to us by the clinicians that she had a good possibility of rupturing her right cruciate ligament within the year, so the fact that she has not ruptured the contralateral side since her surgery [five years ago] is a success, in our opinion … Morgan’s contribution to Dr. Muir’s research was that her joint fluid supported the hypothesis that bacteria are present" in the knee joints involved in CLR.

Such discoveries lead Dr. Muir to believe he’s on the right track—but he points out there’s still a long way to go. For one thing, he’s trying to determine whether the bacterial invasion occurs in the ligament itself, the lining of the knee joint, or in both places. In any case, "in challenging conditions like this one, it’s difficult to determine exactly what the disease mechanism is," Dr. Muir explains. "In dogs, it takes a substantial amount of work to definitively determine that."

Making that determination could mean a lot not only to dogs like Morgan, who could avoid facing pain, surgery and confinement, but also their owners, who would be spared distress of seeing their dogs in discomfort, not to mention paying several thousand dollars for the TPLO procedure. Meanwhile, Morgan has recovered from her bout with CLR. Nearly five years after her TPLO, Zitzer reports that "Morgan is a healthy and happy dog … She loves playing with her sister and the other dogs in the neighborhood."

As of August, 2010, the AKC Canine Health Foundation has funded more than $400,000 to research that seeks to determine causes and treatments for cruciate ligament rupture.