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The cranial cruciate ligament stabilizes the knee by attaching the femur and tibia. If the ligament ruptures, the shin “gives out” in a forward direction and inwardly rotates. The ligament can rupture all of a sudden or gradually depending on the use of the leg.
Large breed dogs such as Rottweilers and Labrador Retrievers rupture acutely at <3 years of age, but the average for all dogs is 5 years and only 20% are acute. The dog will limp all of a sudden after an activity such as catching a frisbee and not bear weight on the affected leg. A gradual rupture may appear during a routine activity such as stepping off a curb. A gradual rupture occurs due to aging (>5 years) or poor conformation such as straight knees or bow legs. Diseases of the immune system and infection also weaken the ligament. A partial tear may cause limping over a long period of time. The muscles of the hind leg shrink when dogs use the legless. When the ligament ruptures, you can feel the laxity in the knee called “Cranial Drawer”. Sometimes a click can be heard because of a torn cartilage shock absorber called the meniscus. The meniscus is torn >50% of the time when the ligament is no longer stabilizing the knee.
Radiographs show arthritic changes in the bone if the tear occurred over a period of time. Surgery is the treatment of choice to stabilize the knee, slow the arthritic process, and allow earlier use of the leg. Several surgical procedures are available but the general success rate is 85% and recovery is 2-4 months. Regardless of the surgery performed, arthritis will occur but stabilizing the knee will result in less arthritis and less pain. With or without surgery, weight loss helps improve limping caused by arthritis. Glucosamine and chondroitin sulfate help keep remaining cartilage healthy. Only use pain medication such as Deramaxx or Rimadyl prescribed by a veterinarian. After surgery, while the pet is recovering, dogs will favor the leg and 30% will tear the ligament in the other knee within 2 years.