Guarding Against Ruptured Ligaments in Dogs

Tracy Libby

Did you know that your dog need not be a canine athlete to experience a torn knee ligament? It's true. As owners and their dogs become more active—agility, dock diving, herding, and so forth—the odds of a torn ligament may increase. But your four-legged couch potato is also at risk because the primary cause of torn cranial cruciate ligaments (CrCL) is slow degeneration that has been taking place within the ligament - rather than the result of trauma.

Torn knee ligaments are one of the more common orthopedic injuries in dogs, and the major cause of arthritis of the knee joint. An Iowa State University College of Veterinary Medicine survey of 501 board-certified veterinary surgeons and 4,000 veterinarians reported that U.S. dog owners spent an estimated $1.32 billion in 2003 on veterinary and surgical management of CrCL injuries. That report is 10 years old and experts say it's highly likely owners are spending even more money today.

How It Work

A dog’s stifle (knee) joint is fairly complicated, but, in the simplest of terms, it consists of the femur (the long thigh bone), the tibia (one of the lower leg bones), and the patella (the kneecap). The knee joint, unlike the hip and elbow joints, has no interlocking bones. Instead, it relies on an assortment of soft tissue structures to hold everything in place while allowing the knee to bend the way it should and keeping it from bending in ways it should not.

Two cruciate ligaments running in opposite directions criss-cross inside the knee: the cranial cruciate (anterior cruciate) and the caudal cruciate (posterior cruciate). The function of each is to stabilize the knee and prevent excess movement in their respective directions. The cranial cruciate ligament tends to rupture most often, thereby allowing the tibia to move excessively in the forward direction. This causes joint instability, as well as irritation and inflammation of the joint capsule and soft tissues surrounding the joint.

To further complicate matters, a ruptured CrCL, which is the equivalent of a torn anterior cruciate ligament (ACL) in humans, predisposes a dog’s knee to other painful injuries including damaged cartilage—specifically the medial meniscus that is sandwiched between the femur and tibia and reduces the pressure of bone against bone. Without proper treatment, the process of degeneration continues to snowball until the knee joint develops permanent osteoarthritis.

Why It Happens

Although all breeds are at risk, some larger breeds, such as Rottweilers, German Shepherd Dogs, and Labrador Retrievers, appear to be predisposed to an inherent ligament degeneration—meaning the ligaments surrounding the knee deteriorate and weaken over time, thereby predisposing the joint to injury under normal activity or minimal trauma.

A dog's individual knee conformation may also be a contributing factor. And there is direct trauma, with one of the more common causes occurring at a point when the stifle is turning while in full extension. For instance, when a dog is running full speed ahead and suddenly turns, skids on a slippery surface, or steps in a hole while running.

Symptoms You're Likely to Notice

Symptoms of CrCL injury can occur suddenly or gradually depending on the extent of the injury and often depending on the dog. The hallmark symptom is stiffness or limping in the dog’s hind leg, particularly after exercise or prolonged periods of rest. Such limping may become progressively worse over time.

A complicating factor is that the pain often subsides after a few days if the cartilage was not damaged. Some dogs also learn to compensate for the pain by shifting additional weight from their hind end to their front end. To most people, the dog may look reasonably well, but, in actuality, he’s not. The injured knee’s load is shifted to other ligaments, scar tissue forms in the joint capsule, and, while the dog may not show physical symptoms of injury, the process of degenerative joint disease is in motion.

Diagnosis and Treatment

Diagnosis of a ruptured ligament involves a physical examination, observation of joint movement, and manipulation of the joint. Magnetic resonance images (MRI) are an option in making a diagnosis, but, in many instances, veterinarians rely on a thorough orthopedic examination. The primary diagnostic test is the anterior drawer motion test, which is a physical manipulation of the stifle joint to assess the tibia's forward movement in relation to the femur. Radiographs are frequently recommended to document the knee’s condition.

Treatment options vary depending on the extent of the tear and can include "conservative management" such as chiropractic adjustments, acupuncture, massage, nutrition, a custom leg brace, swimming, anti-inflammatory medications, medicinal herbs, weight loss for overweight dogs, and restricted activity—no running or jumping—for six to eight weeks. This is often a daunting challenge for owners of high-drive, high-energy dogs.

For ruptured ligaments, surgery—to stabilize the joint—is often the best option, with studies indicating that without surgery "large dogs will have permanent instability in the knee and develop progressive arthritis."

Will My Dog Recover?

Studies indicate post-surgical prognosis is good, with approximately 70 to 80 percent of dogs returning to normal or near normal function. For owners opting for a non-surgical, conservative approach, the outcome, which is often good, depends on the dog's age, size, weight, the nature of the injury, activity level, physical therapy, and, most importantly, owner compliance with treatment.

If you suspect your dog has a knee injury—seek veterinary assistance right away. The sooner a CrCL injury is diagnosed, the sooner a treatment plan can begin; thereby putting your four-legged companion on the fast track to recovery. 

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