Research May Provide New Insights About Cruciate Ligament Ruptures

Norma Dikeman remembers well the painful yelp that came from her 2-year-old Rottweiler when he slipped on ice while running. She feared the worst when "Opie" came in limping.

"I was just sure he had torn the cruciate ligament," recalls Dikeman of Westfield, N.Y. "I was relieved to learn Opie had only broken his toe. That sounds bad, but a broken toe is less painful for a dog and easier to manage than a CCL (cranial cruciate ligament) tear. I live in fear of CCL ruptures."

Fear of dogs rupturing their cranial cruciate ligaments is a justified concern for breeders of Rottweilers and other large breeds. Among the large breeds susceptible to CCL tears, which can occur at virtually any age, are Rott­weilers, Labrador Retrievers, Newfoundlands, Mastiffs, Great Pyre­nees, and Greater Swiss Mountain Dogs.

CCL tears are the most common orthopedic injury seen by veterinarians, accounting for more than 1 million surgeries annually. An Iowa State University College of Veterinary Medi­cine survey of 501 board-certified veterinary surgeons and 4,000 veterinarians reported that dog owners spent $1.32 billion in 2003 on veterinary and surgical management of CCL injuries.

"That survey was done six years ago," says Vicki L. Wilke, D.V.M., Ph.D., DACVS, professor of surgery at the University of Minnesota College of Veterinary Medicine and an author of the report. "Owners probably spend even more money today on CCL tears."

A Rottweiler breeder who breeds under the Nordike prefix, Dikeman has had three Rotties suffer from ruptured cranial cruciate ligaments. Two dogs had CCL tears that led to an acute onset of lameness, and a third dog's CCL tear occurred gradually. In all three cases, Dikeman paid for expensive surgeries for treatment of the CCL rupture and nursed her dogs through the six-to-14 week post-surgical recovery.

A dog's CCL is similar to the anterior cruciate ligament (ACL) in humans. Located in a dog's stifle (knee joint), the CCL plays a key role in controlling motion between the joint surfaces of the femur (thighbone) and the tibia (shinbone), and allowing a dog to bear weight on his leg. When the CCL tears, the stifle joint is destabilized and the dog becomes lame. In the majority of dogs, arthritis of the stifle develops before the CCL ruptures.

In some cases, dogs can tear their CCL because of a traumatic injury that involves twisting or wrenching the stifle. However, in the majority of affected dogs, the ligament slowly stretches and tears over time, after arthritis of the stifle has developed. When this happens a dog may have a low-grade limp. When a complete tear eventually occurs, affected dogs develop severe lameness and are often no longer able to put weight on the leg. Unfortunately, there is no known way of preventing CCL injuries because the specific underlying cause is not known. Controlling body weight may help to minimize risk.

Research under way at veterinary schools at the University of Wisconsin in Madison and the University of Minnesota is helping to provide new insights about CCL ruptures. One study examines the effect of inflammatory arthritis on degeneration of the stifle joint and looks at drug therapy as a possible treatment option. The other study uses gene mapping to potentially identify the gene mutation that causes the condition.

Effects of Inflammatory Arthritis "Our research has shown that the majority of cruciate ruptures in dogs are not associated with accidental injuries," says Peter Muir, BVSC, Ph.D., DACVS, associate professor at the University of Wisconsin-Madison. "We believe that CCL ruptures are secondary to development of stifle arthritis. In the majority of dogs, the rupture is a pathological consequence of joint disease, not traumatic injury."

The arthritis that precedes cruciate rupture is an inflammatory arthritis or rheumatic disease rather than the "wear-and-tear" arthritis or osteo­arthritis found in older dogs, Muir says. Affected stifle joints contain a mixture of inflammatory cells that include T lymphocytes, which are associated with immune-mediated rheumatic arthritis. Over time, the inflammation appears to cause weakening of the ligament, which then ruptures during normal daily activity.

Muir is the editor of "The Canine Cranial Cruciate Ligament," a textbook that will be published next year by Wiley-Blackwell. He is pleased there is growing interest in the mechanisms that lead to development of CCL tears, as advances in knowledge about CCL ruptures potentially will lead to improved treatment of affected dogs.

"There is increasing recognition by veterinarians that dogs with stifle arthritis and a stable joint present with a low-grade lameness," says Muir. "We are seeing growing numbers of referrals at our veterinary medical teaching hospital, where treatment is sought for dogs with mild-to-moderate lameness that have stifle arthritis and a stable joint."

Funding from the AKC Canine Health Foundation helps to support Muir's research. Currently, he and his colleagues are working to identify causes of stifle joint arthritis in affected dogs. Some research indicates a genetic pre­disposition. Bacterial material within the stifle joint may also be an important trigger for development of joint inflammation and eventual CCL rupture.

His work aims to advance treatment options using medical therapy to help reduce inflammation and degradation in the stifle joint, and thus block the rupture of the cruciate ligament. "If so, you can potentially prevent a dog from needing surgery," he says.

Drug therapy options for reducing joint inflammation as a medical treatment for dogs with arthritis are limited. "Corticosterioids for this condition are not a good choice because steroids can promote weakening of ligaments and tendons," Muir says.

In related research, Muir has found leflunomide, a potent anti-inflammatory drug, is a safe and effective treatment for dogs with idiopathic immune-mediated polyarthritis (IMPA). This work will be published in an upcoming issue of the Journal of the American Veterinary Medical Association.

Though IMPA is a different condition from stifle arthritis in dogs, the fact that leflunomide is a successful treatment shows that "newer drug treatments could potentially help reduce joint inflammation in canine arthritis and thus be applied to stifle arthritis," Muir says. "A lot of drugs may be suitable, but more work needs to be done to figure that out. It's going to take a substantial amount of funding and time to fully evaluate new drug therapies for this condition."

At the University of Minnesota, Wilke and a team of researchers are conducting gene mapping research to identify the mutation that causes CCL ruptures. The research has been ongoing for nine years. DNA collected from a large group of Newfoundlands and a smaller set of Labrador Retrievers showed in a genome-wide association study a possible link to four chromosomes. Validation of the chromosomes was performed last summer, narrowing the focus to chromosome 3.

Follow-up DNA research is planned with a variety of breeds including Rottweiler, Greater Swiss Mountain Dog, Bernese Mountain Dog, Great Pyrenees, and Mastiff. The collaborative work involves researchers at the University of Liverpool in England.

"My goal is to find a mutation that is highly correlated with the trait," Wilke explains. "We probably won't find a single gene trait that is the answer, but if we can find a genetic mutation highly associated with the trait, we can develop a test that breeders can use to base breeding decisions. We're getting close. I hope within a year or two to have some answers.

"The idea is to be able to predict the likelihood of a dog rupturing his CCL. Breeders, obviously, do not want to pass this trait on to future generations. Also, keep in mind, if a dog does have the trait for developing a CCL rupture, this doesn't mean he'll definitely have the disease. Owners can work to modify environmental factors, such as nutrition and exercise, to decrease the risk of a particular dog developing a CCL tear."

Surgical Options Preventing a full-blown CCL rupture after a dog shows signs, such as limping, is possible, but steps should be taken cautiously. Penelope White of Englewood, Colo., declined surgery for her 14-month-old Rottie, "Tassie," four years ago after two orthopedic specialists diagnosed a probable tear of the cruciate ligament in the left leg.

Instead, White opted for rehabilitation, which involved walking the dog four times a day and only taking her outside on leash for the first three weeks. Next, Tassie spent two days a week trotting on an underwater treadmill at a specialized veterinary orthopedic facility, which was later reduced to one visit a week. White bought a canine bicycle customized with two wheels in front and one in back to help Tassie build stability and strength in the injured stifle joint. She also guided the dog through hip-strengthening and balance exercises.

"Fortunately, Tassie has had no recurrence of lameness and is fully recovered," says White, who continues the exercise but still worries her dog may suffer a CCL tear.

Veterinarians recommend owners bring in dogs for an examination if they notice mild limping or signs of pain. Early treatment may help to reduce the risk that a CCL rupture will develop. A veterinarian can evaluate the way a dog walks and palpate his legs, feeling the stifle carefully for any slipping.

Cruciate tears do not show up on radiographs, but the arthritis that typically precedes development of a cruciate rupture can be identified using X-rays. To help determine whether a partial cruciate tear may be present, a veterinarian may also opt to view the ligament using surgery or arthro­scopy, a procedure in which a small camera is attached to a rigid endoscope.

During an initial examination, a veterinarian bases treatment and recovery on a dog's fitness level, extent of the injury, level of pain, and functioning of the joint. Surgery is usually the recommended treatment of choice and may range from $1,000 to $5,000. Surgical techniques used to repair CCL tears include: Extracapsular Repair: The conventional surgical treatment, this procedure involves anchoring and tying a strong surgical suture around the stifle joint to restore normal position and stability of the femur on the tibia. The procedure provides support and acts as an internal brace to the joint.

Tibial Plateau Leveling Osteotomy (TPLO): This procedure levels the slope of the tibial plateau so the cruciate ligament isn't necessary to keep the femur from sliding down the plateau of the tibia during walking and running. Surgery involves cutting and rotating the top of the tibia, then screwing a bone plate into place so the bone will heal in its new position.

Tibial Tuberosity Advancement (TTA): Similar to TPLO surgery, TTA stabilizes the stifle joint by changing the geometry and physics of the stifle and enabling it to work without a cruciate ligament. TTA surgery may be less invasive and quicker than TPLO surgery, but its long-term benefits have not been assessed.

The good news is that surgery for CCL ruptures frequently improves use of the affected leg. However, the bad news is that none of the procedures currently used are curative, and progression of stifle arthritis develops over time after surgery. Surgical recovery takes from six to 14 weeks, during which time a dog must be quiet and controlled. Post-surgical physical therapy and rehabilitation are key in a dog's ability to regain full function of the stifle joint.

Unfortunately, once a dog has had a cruciate injury in one stifle, it's common to have the same problem in the other stifle. In addition, a CCL tear can lead to injury of a meniscus. The stifle has two menisci or cartilage cushions that sit inside the joint and serve as shock absorbers when a dog walks. If the meniscus tears, it can be very painful to the dog and must be treated surgically. When the meniscus is torn, the stifle may make a characteristic popping sound when the dog is walking.

Since there is no proven treatment that will prevent development of a CCL rupture, veterinarians speculate on prevention. Excess weight, for example, is believed to put a dog at increased risk. In the meantime, owners are encouraged to watch their dogs closely for limping or reluctance to bear weight on their leg. The sooner that stifle joint disease is discovered, the better.

As Norma Dikeman says, "CCL ruptures are an often talked-about subject in Rottweiler circles. It happens often, and when it does it is expensive and involves a long recuperation."