Cruciate Ligament Rupture

There are actually two cruciate ligaments. The anterior and posterior cruciate ligaments provide stability to the knee. The anterior cruciate ligament (ACL) is the generally tears more often than the posterior cruciate ligament. The knee joint is one of the weakest in the dog’s body and can often suffer tears when a dog is exercising with vigor or making a changing directions at a fast pace. Just as athletes can suffer knee injuries, so can dogs.

What Causes My Dog to Injure His Cruciate Ligament?¹:
The knee joint is relatively unstable because ligaments hold it together. Two bones, the femur (thigh bone) and the tibia (shin bone) are joined by several ligaments. Sudden, excessive twisting or shearing forces on the knee may tear the cruciate ligament.

When the ligament is torn, the knee joint becomes unstable and the dog cannot bear weight on that limb without considerable pain. You can suspect the ligament is torn if your dog limps, shifting most of his weight to one leg and if he consistently sits irregularly, holding one or both of his legs out to the side. Many dogs also tear a cartilage in the knee called the meniscus when the ligament tears.

There is some evidence that indicates certain dogs are genetically predisposed to the injury. These breeds include:

The supporting evidence for this was obtained primarily through assessment of family lines and general knowledge on the injury. Other factors that may affect the development of this injury include:

How Do I know if My Dog has a Torn Cruciate Ligament?:
Diagnosing a torn cruciate ligament needs to be done by your veterinarian. Your veterinarian will first observe the way your dog walks. If he walks with a limp, as described in the previous section, then the veterinarian will proceed to manipulate the knee to detect instability.

The instability being looked for is called a drawer sign because the tibia and femur will slide over each other like a drawer in injured dogs. Sometimes the dog will need to be anesthetized to allow the veterinarian to do these manipulations, as they can be painful or cause discomfort. Radiography can also be used to confirm the diagnosis.

Lastly, the veterinarian would likely perform an arthroscopy. This procedure is an initial surgery to look inside the dog’s joint and both confirm the diagnosis and examine the severity of the damage. This also can be used to determine which corrective procedure would best benefit the dog.

Can A Torn Cruciate Ligament Be Treated?
There are three competing methods for repairing torn cruciate ligaments: The first technique is to replace the ligament with synthetic material. This graft can also be made of material from another part of the body or from a deceased donor. First, the veterinary technician anesthetizes the dog and prepares the knee for sterile surgery. The veterinary surgeon opens the knee joint to remove the pieces of the torn ligament. The surgeon also inspects the cartilaginous meniscus for damage. If the damage is significant the meniscus is removed. The joint capsule is closed and a stabilization procedure is done to eliminate the drawer motion. This technique works well but the most commonly used technique for a replacement is the Tibial Plateau Leveling Osteomoty (TPLO).

The TPLO is a bit more common than the replacement technique but is arguably the more effective method and some surgeons find it easier to perform. The surgery stabilizes the stifle joint by cutting the tibia and rotating it. This moves the slope of the bone such that the femur is prevented from sliding down the tibial plateau. This leads to a fast recovery time and most dogs are expected to recover fully without complications or medication.² This being said, it has been noted by researchers that dogs that undergo TPLO are still prone to Pivot Shift or rotational instability that can lead to arthritis as the dog ages. The third option, recently developed, aims at resolving this issue.

A third popular procedure is the Tibial Tuberosity Advancement (TTA). TTA is the newest procedure applied to dogs and works to counteract the problem by altering a particular tendon. The surgery changes the angle that the Patellar Tendon pulls on the tibia by rotating the large quadriceps muscle.

There are many different techniques that may be used to stabilize the knee. Each surgeon has his or her own preferred method. If surgery is not performed as soon as possible after the ligament is torn then arthritic changes will occur that cannot be corrected, even with surgery.

What Happens if a Cruciate Ligament Injury Goes Untreated?
If the dog weighs less than twenty pounds it may not have to have surgery to be able to walk again; however, it is likely that there will be some permanent damage. Dogs over twenty pounds will most likely develop severe arthritic changes that will cause pain for the rest of its life. In severe cases, arthritis can be fatal. Therefore, surgery is highly recommended for larger dogs. The expedience of treatment is also a large factor when treating your pet. Your veterinarian can advise you as to the best treatment for your pet.