What is a cranial cruciate ligament rupture?

The cranial cruciate ligament helps attach the femur (thigh bone) to the tibia (shin bone) within the stifle joint (knee). It corresponds to the anterior cruciate ligament in humans. The ligament is one of several structures that stabilize this hinge joint while allowing only limited flexion and extension in a single plane. In the dog, this ligament prevents the tibia from sliding cranially (toward the head) every time weight is placed on the leg. Therefore, this ligament always carries stress when the dog bears weight on the leg.

The stifle joint is designed as a very strong and durable structure. As a result, the ligaments and other supportive structures have very little blood supply. Blood vessels would create weak points, predisposing the structures to injury. This also makes it very difficult for some of the structures in the joint to heal.

Rupture or tear of the cranial cruciate ligament represents one of the most common orthopedic diseases of dogs. There appear to be several processes that lead to ligament rupture. They include: trauma, conformational problems, genetic predisposition, congenital predisposition, and likely immune mediated disease. Approximately 70% of dogs that rupture one cranial cruciate ligament will rupture the other cranial cruciate ligament at some time.

The ligament ruptures can be complete or partial when the problem first arises. Partial tears invariably progress to complete tears. Because the ligament has no blood supply, even partial tears will not heal.

Common scenarios for dogs with a cranial cruciate ligament ruptures follow similar patterns. Usually the dog is running, playing or roughhousing and becomes suddenly lame. Often, the owner does not witness a specific injury. The lameness may be non-weight bearing or minimally weight bearing. If the dog does not present to a veterinarian at this time, often the lameness almost resolves over the next 1 to 3 weeks. About 6 months later, most of these dogs will become increasingly lame again, especially after rest.

When the ligament ruptures acutely, pain and acute inflammation arise quite rapidly. Over the next few weeks, the inflammation resolves and the pain subsides. Thus, the acutely lame dog appears to recover relatively quickly. However, the joint has not healed. The joint is not stable and the joint fluid shows inflammatory changes. With the now unstable joint, the body attempts to stabilize the joint by creating new bone. This process is referred to as degenerative joint disease (DJD) or arthritis. Thus, the lameness returns.

Additionally, either at the time of initial rupture or later and secondary to joint instability, meniscal cartilage injuries are common. These usually greatly increase the degree of lameness.

Once the cranial cruciate ligament is ruptured, the joint will never again be normal. The ligament will not heal by itself. Therefore, surgery is required to stabilize the joint, normalize function as best as possible, and decrease the rate of degenerative joint disease. Patients that do not have surgery generally do poorly.

At this time, there are 3 surgical techniques commonly performed. I do not have space to go into the procedure details, but will list them. The oldest procedure is referred to as an extracapsular stabilization. The 2 newer procedures are called the TPLO (tibial plateau leveling osteotomy) and the TTA (tibial tuberosity advancement). All appear to have generally good outcomes, but some patients are better candidates for a specific procedure.

Many veterinarians do not have the equipment and expertise to do orthopedic surgeries. Therefore, many of us refer patients to board certified veterinary surgeons. Living near a major metropolitan area with a veterinary school, we have several very good choices to consider.

A patient with a cranial cruciate ligament rupture identified before DJD has significantly developed generally has a much better long-term outcome than a patient with DJD. However, even dogs with chronic DJD changes in the stifle benefit from surgery. Stabilizing the joint decreases the pain and slows further progression of the DJD.

Ancillary treatments that are often needed include joint supplements, pain control, weight reduction and physical therapy. Many studies show that by maintaining muscle strength and flexibility postoperatively, patients have a much more rapid return to function and comfort.

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