When people "blow out" a knee, chances are they’ve suffered a cruciate ligament rupture. Dogs can experience the same injury. They have two cruciate ligaments in each knee (or stifle joint)—a caudal ligament and a cranial ligament, which is most commonly injured.
Cranial cruciate ligament (CCL) rupture is a common cause of rear leg lameness in dogs. In people, a ruptured cruciate ligament usually results from a sports-related knee injury. Dogs, on the other hand, often suffer from chronic degeneration of the ligament, which finally gives way under mild strain from running, jumping, or climbing stairs.
Risk factors and detection
Factors that predispose dogs to ligament degeneration and CCL rupture include:
Age. As dogs age, their ligaments and tendons weaken.
Abnormal conformation of the knee. Dogs with bowed legs, knock knees, or knee caps that pop in and out (patellar luxation) experience abnormal wear and tear on their knees.
Obesity. Extra weight strains all joints, making them prone to ligament breakdown and arthritis.
Breed. In 1- to 2-year-old dogs, more CCL ruptures occur in Rottweilers and Labrador retrievers.
When a cranial cruciate ligament ruptures, most dogs will hold up the affected rear limb and stop bearing weight on it. Often, the inside of the knee swells, and dogs with partial tears may limp intermittently on the injured leg.
CCL ruptures are painful. If not treated, the knee joint instability and damage to the knee’s inner structures can cause arthritis and chronic lameness. With time, scar tissue builds up to help stabilize the joint, but it won’t relieve the arthritis.
To diagnose a CCL rupture, your veterinarian will look for the "cranial drawer sign." He or she will try to move the tibia (shinbone) forward on the femur (thighbone), like sliding a drawer out. In a normal knee, the CCL restricts this movement. The movement can be dramatic if the joint is loose after a recent complete rupture, or it can be subtle if the rupture is long-standing or partial. To perform an accurate test, the veterinarian may sedate your dog. He or she also may use X-rays to rule out other causes of lameness and to assess the degree of arthritis present.
Prevention and treatment
CCL ruptures and the degenerative changes that affect the ligaments are difficult to prevent. In fact, up to 40 percent of dogs with CCL rupture of one back leg will tear the other ligament within one or two years. You can reduce the risk of injury in your dog by avoiding such risk factors as obesity and correcting patellar luxation.
If your dog suffers from a CCL rupture, your veterinarian will try to re-establish the knee’s stability so the joint functions normally and arthritis doesn’t progress. Small dogs or dogs with partial tears may only need rest and anti-inflammatory drugs. However, most dogs need surgery.
Surgical treatment for CCL ruptures falls into three categories: extracapsular (outside the joint), intracapsular (inside the joint), and tibial plateau leveling osteotomy (TPLO). Extracapsular repairs stabilize the joint with wires, sutures, or other ligaments placed outside the joint. Intracapsular repairs replace the torn CCL with an artificial ligament. TPLO corrects knee malformations that predispose the joint to rupture. Your dog’s age, weight, and activity level determine which technique your veterinarian will use. Or your veterinarian may refer your dog to an orthopedic surgery specialist for repair. Despite surgical treatment, many dogs won’t return to full athletic function and may suffer from arthritis.
