Cranial Cruciate Ligament Rupture

A ligament consists of tough, fibrous tissue connecting 2 bones. The knee joint is particularly susceptible to damage from strained or torn ligaments. In the knee, rupture of the cranial cruciate ligament allows the femur (thigh bone) to slide back and forth over the tibia (shin bone) as the knee has lost its stability. Over-extension of the knee joint may tear this ligament allowing two bones to slide back and forth causing pain, lameness, and instability.

The ruptured ligament first causes pain, then abnormal wear and tear leads to arthritis. This sequence of events occurs most frequently in overweight, middle-aged to old dogs. Overweight dogs are most susceptible due to the excess pressure created on the joints. Depending on the severity of the rupture, treatment usually consists of surgical repair of the torn ligament.

Surgical corrections may vary, but surgical techniques usually involve the following: tightening of the joint capsule, reconstruction of the ligament, making and inserting an artificial ligament, and reconstruction of the entire bone of the tibia. All surgical cases usually involve entering the joint and cleaning out ligament remnants as well as damaged cartilage and joint surface.

The knee is a fairly complicated joint. It consists of the femur above, the tibia below, the kneecap (or patella) in front, and the bean-like fabellae behind. Pieces of cartilage called the medial and lateral menisci fit between the femur and tibia like cushions and there is an assortment of ligaments holding everything together, allowing the knee to bend correctly.

There are two cruciate ligaments that cross inside the knee joint: the anterior (cranial cruciate) and the posterior (caudal cruciate). The anterior cruciate prevents the tibia from slipping forward out from under the femur.

The ruptured cruciate ligament is the most common knee injury of dogs. Chances are that any dog that suddenly has rear leg lameness has a ruptured anterior cruciate ligament. The history usually involves a rear leg suddenly so sore that the dog can hardly bear weight on it. If left alone, it will appear to improve over the course of weeks but the knee will be notably swollen and arthritis will set in quickly.

The key to the diagnosis of the ruptured cruciate ligament is the demonstration of an abnormal knee motion called a drawer sign. It is not possible for a normal knee to show this sign. The veterinarian stabilizes the position of the femur with one hand and manipulates the tibia with the other hand. If the tibia moves forward (like a drawer being opened), the cruciate ligament is ruptured.

Other signs of an ACL injury include joint effusion (fluid accumulation in the joint), fibrosis, muscle atrophy, decreased range of motion, popping (crepitus) or meniscal clicking of the knee on range of motion and osteoarthritis (degenerative joint disease).

Since arthritis can occur relatively quickly after a cruciate ligament rupture, radiographs to assess arthritis are often recommended. Another reason for x-rays is that occasionally when the cruciate ligament tears, a piece of bone where the ligament attaches to the tibia breaks off as well. This will require surgical repair. X-rays can also be used to rule out concurrent disease conditions such as cancer.

There are several clinical profiles seen with ruptured cruciate ligaments. One is a young athletic dog playing roughly who injures the knee while playing. This is usually a very sudden lameness in a young large breed dog.

A recent study identified the following breeds as being particularly at risk for this phenomenon: Neapolitan mastiff, Newfoundland, Akita, St. Bernard, Rottweiler, Chesapeake Bay retriever, and American Staffordshire terrier.

Alternately, an older large dog, especially if overweight, can have weakened ligaments and slowly stretch or partially tear them. The partial rupture may be detected or the problem may not become apparent until the ligament breaks completely. In this type of patient, stepping down off the bed or a small jump can be all it takes to break the ligament. The lameness may be acute but have features of more chronic joint disease or the lameness may simply be a more gradual/chronic problem.

Without an intact cruciate ligament, the knee is unstable. Wear between the bones and meniscal cartilage becomes abnormal and the joint begins to develop degenerative changes. Bone spurs called osteophytes develop and chronic pain and loss of joint motion result. This process can be arrested by surgery but cannot be reversed.

Depending on the severity of the rupture, treatment may consist of rest and medication or surgical repair of the torn ligament. Your veterinarian will advise you concerning the treatment necessary for your pet.

If surgery is recommended, it may consist of the following:

1. Removal of the damaged cartilage.

2. Replacement of the torn ligament.

3. Tightening of the joint to help prevent abnormal movement.

Even after surgery, recovery may take several weeks depending upon the individual. Due to the injury, some arthritis is inevitable. Therefore, the joint will rarely be perfect, but should be noticeably better.

Rupture of the anterior cruciate ligament most frequently occurs in overweight dogs. Because of this, the problem could occur in the other leg at a later time. Weight reduction is highly recommended.

1. Exercise: Restrict your pet's activity for several weeks. Do not let your pet run unrestrained. On- leash walking is the only activity permitted outside the home. Prevent jumping whenever possible. Begin increasing exercise gradually.

2. Diet: Ordinarily no special diet is required for healing. If your pet is overweight, weight reduction can speed recovery and possibly prevent further injury. The doctor will discuss weight control with you if necessary.

3. Care of the splint/bandage: Certain surgical corrections require use of a splint or bandage for 1-3 days after surgery. If your pet has a splint or bandage, extra care is needed to protect it. Do not let the apparatus become wet. In damp weather, place a plastic bag over it when you walk your pet. Do not allow unrestrained exercise.

4. Physical Rehabilitation: Supervised rehabilitation of the knee should start within 48 hours of the surgery and should include a regimen of passive range of motion, balance exercises, and walks on a leash. Underwater treadmill exercise (hydrotherapy) or swimming are also excellent non-weight bearing activities. All therapies should first be cleared through your veterinary surgeon, prior to their implementation.

5. Prognosis: Long term prognosis for animals with repaired ACL is good, with clinical reports of improvement in 85-90% of the cases. Unfortunately, degenerative joint disease or osteoarthritis may progress regardless of treatment. Long term outcome includes a decrease in activity over time, an adverse response to cold weather, and stiffness after inactivity related to progressive degenerative joint disease. Weight loss and an exercise regime of daily moderate activity can help to ameliorate these clinical signs.


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