Ask Dr. Dolamore
September 20, 2010
Sudden onset rear limb lameness is often caused by a torn ligament in the knee. The torn “anterior cruciate” ligament or ACL is the most common knee injury of the dog. When the anterior cruciate ligament ruptures (is torn), the joint becomes unstable. Often the dog or cat can barely put weight on the affected leg. The anterior cruciate ligament is commonly torn when the dog twists on his hind leg. The twisting motion puts too much tension on the ligament and it tears. The tear can be partial or complete. Causes include slippery surfaces, making a sudden turn while running, or being hit by a car. Being overweight will put too much stress on the knee and overweight dogs tend to have more occurrences of ruptured cruciate ligaments. .In some dogs, the ACL may slowly degenerate and becomes weaker until it ruptures, even without any sudden injury. Certain breeds appear to be at increased risk of ACL degeneration and include the Newfoundland, Labrador Retriever, Rottweiler, Bichon Frise, St. Bernard, and others. Many dogs with a degenerating ACL will have the condition in both knees. In small breed dogs, a luxating patella (knee cap) may predispose them to a ruptured anterior cruciate ligament.
Diagnosis of the ruptured cruciate ligament made by your veterinarian by feeling the knee and finding abnormal knee motion called a “drawer sign.” It is not possible for a normal knee to show this sign. It is not unusual for animals to be tense or frightened at the vet’s office. Tense muscles can temporarily stabilize the knee preventing demonstration of the drawer sign during examination. Often sedation is needed to get a good evaluation of the knee. This is especially true with larger dogs. Eliciting a drawer sign can be difficult if the ligament is only partially ruptured..
Initial treatment may include strict rest,(i.e. keep pet in a large cage, take out to the bathroom on a leash and back in the cage), icing the knee, anti inflammatory medication, and pain medication. Surgery may be needed, but the only way to know if your pet really needs surgery is to restrict activity and see if the he can re-stabilize the joint. Activity restriction may be needed for 8 to 12 weeks or longer followed by very slow return to activity. A bandage or knee stabilizing device may be needed as well.