Cranial Cruciate Ligament Rupture

Anatomy
The femur (large bone of the thigh) and the tibia and fibula (two smaller bones in the shin) meet to form the stifle joint. Articular cartilage attaches to and covers the ends of bones, protecting and cushioning them. Ligaments, tendons, and muscles hold the bones in place, stabilize the joint, and enable movement. A joint capsule, filled with nourishing and lubricating synovial fluid, surrounds the entire joint.

Four major ligaments (dense bands of fiber) support and stabilize the stifle joint by connecting the femur to the tibia and the joint capsule to the bones. The medial and lateral collateral ligaments are located outside the joint and the caudal and cranial cruciate ligaments are located inside the joint.

The cranial cruciate ligament (CCL) attaches to the femur, runs across the stifle joint, and attaches to the tibia. The CCL holds the tibia in place and prevents internal rotation and hyperextension.

The meniscus (fibrocartilage located between the femur and tibia) absorbs impact and provides a gliding surface between the femur and tibial plateau. The patella (kneecap) protects the tendon of insertion of the cranial thigh muscles.

Incidence and Prevalence
Cranial cruciate ligament (CCL) rupture occurs in both dogs and cats. CCL rupture occurs more frequently in dogs than in cats.

CCL is one of the most common orthopedic injuries in dogs and is the most common cause of degenerative joint disease in the stifle joint. Female dogs (especially spayed), overweight, and poorly conditioned dogs have a higher incidence. CCL rupture occurs in dogs of all sizes, but is most prevalent in large and giant breeds including:

• Bernese mountain dog
• Bullmastiff
• Chow
• German shepherd
• Golden retriever
• Labrador retriever
• Rottweiler
• Saint Bernard

Chronic onset (degeneration and rupture usually from aging) occurs in 80% of cases and occurs in dogs 5 to 7 years old. Acute onset (tear caused by injury) is most common in dogs under 4 years old. Young dogs of large breeds are more susceptible to rupture than young dogs of small breeds.

Causes

Acute rupture of the cranial cruciate ligament (CCL) is caused by sudden, severe twisting of the ligament. The injury usually occurs when the animal steps in a hole while running or turns with its paw remaining planted. The twisting motion causes the ligament to hyperextend or rotate excessively and partially or completely rupture. The meniscus is often damaged as well.

Chronic rupture occurs after the ligament has degenerated with age. The fibers weaken and partially tear, the joint becomes unstable, and degenerative joint disease develops. A partially torn CCL eventually tears completely.

Risk Factors
Risk factors include the following:

The goal of treatment is to alleviate pain and increase use and mobility. Factors to consider when planning treatment include the following:

• Ability of owner to comply with aftercare requirements
• Age, size, and health of dog
• Availability of surgeon
• Cost
• Intended use of dog

Conservative treatment is less expensive and requires less rigorous owner compliance than surgery. It may be appropriate for older dogs and those with other serious health problems. Surgery is performed only on healthy animals, and it requires an experienced surgeon and owner compliance for proper healing.

Conservative
Conservative treatment (weight control, rest, medication) is often combined with surgery, but it can be used alone for dogs that weigh less than 25 pounds and for cats. Lameness may continue until surgical repair. Degenerative joint disease often progresses regardless of treatment.

Losing weight reduces stress on the joint. The recommended diet has a low fat, protein, and calcium content and is given at specific times of the day.

Rest and confinement for 4 to 8 weeks alleviates inflammation. Short walks on a leash are permitted.

Drugs
Nonsteroidal anti-inflammatory drugs (NSAIDs) reduce inflammation. They cannot be used in animals with hemostatic disorders (reduced ability to form blood clots).

Buffered aspirin is used for long-term conservative treatment. Side effects may include gastric complications such as ulceration, vomiting, diarrhea, loss of appetite, and bloody stools. Giving aspirin with food can reduce or prevent side effects.

Carprofen (Rimadyl®) is an anti-inflammatory painkiller used to treat joint pain. Side effects can include nausea, diarrhea, constipation, and loss of appetite, and if they occur, the veterinarian should be notified. Tests to monitor liver function may be necessary because long-term use may cause idiosyncratic liver problems. Rimadyl is not given concurrently with other NSAIDs or with corticosteriods because the risk for side effects increases.

Nutraceuticals
Nutraceuticals, also called dietary supplements, are oral agents that provide health benefits but are not regulated as drugs. Chondroprotective agents, made from extracts of components necessary for cartilage development, are used to promote the development of new cartilage and strengthen existing cartilage. Two chondroprotective agents used to treat arthritis in humans (chondroitin sulfate and glucosamine) are being used to prevent further joint degeneration caused by CCL rupture. Chondroitin sulfate blocks enzymes that break down cartilage, and glucosamine builds cartilage and may also decrease inflammation.

The supplements are promising and are available in tablet or capsule under these names: SynoviCre®, Glycoflex®, and Arthramine® (all contain glucosamine); Adequan® (contains chondroitin and glucosamine), and Cosequin® (contains chondroitin, glucosamine, and manganese). Glucosamine can be injected directly into the joint or into a vein and works more quickly than the oral form.

An uncommon side effect is gastrointestinal upset; taking the supplements with food can help. If upset continues or if there is no improvement within 6 months, other treatment methods are required. Taking the supplements with aspirin may cause problems in forming blood clots.

Surgery
Surgery is the preferred treatment in dogs over 25 pounds. It may not completely restore function, but does provide good results if performed within a few weeks of the injury. Surgery will slow, but not stop, degenerative joint disease.

Multiple surgical procedures are available, all with comparable results. The surgeon's expertise and the size and type of the dog determine the surgical technique used to replace the function of the torn ligament.

In all procedures, the joint first is opened and the remnants of the CCL are removed. The meniscus is assessed and if damaged, it is removed. The joint is flushed and closed, and the surgeon stabilizes it. Scar tissue forms, providing additional joint stability.

Extracapsular imbrication technique
A heavy suture (i.e., thick stitches or staples) is placed across the joint, beginning at the outside aspect of the femur and circling the tibial crest.

Fibular head transfer
The fibular head is pulled forward, and pin and wire keep it in its new position. The lateral collateral ligament, which attaches to the fibula, is also pulled forward, taking over the function of the CCL. A suture may be used to hold it in place. This surgery is best for dogs that weight over 35 pounds and is often used with the extracapsular imbrication technique.

Tibial plateau leveling
In the stifle joint, the femur rests at a set angle against the tibial plateau. A ruptured CCL allows the femur to slide caudally off the tibia. Surgically changing the angle prevents the femur from sliding off of the tibia. Many dogs can move the limb within a week and recovery time is usually short. This complex surgery reportedly has good results in dogs that weigh more than 35 pounds. As the procedure involves cutting and bone plating the tibia, potential complications are more severe than for other surgical procedures.

Complications
Complications from surgery include adverse reactions to anesthesia (nausea, vomiting, fatigue, and in rare cases, death) and infection. Antibiotics are given after surgery to prevent infection.

Fluid may build up at the site of the incision (seroma) and must be drained (aspirated).

Sometimes animals have a reaction to the material used to suture the incision or a bump forms over the pin. Sutures or pins may have to be removed.

After surgery, the animal should rest until the joint is fully healed to avoid re-injury. The joint may be unstable or the surgical repair may fail and another surgery may be required.

Up to 40% of animals have a ruptured CCL in the other hind leg within 18 months after surgery. Up to 15% require additional surgery to repair damage to meniscus.

After care
The owner must examine the incision for signs of infection—redness, swelling, heat, and pain—for two weeks after the surgery. The stifle joint is rarely bandaged.

Pain medication may be necessary. A cold pack applied several times a day for brief periods helps to decrease swelling and control pain.

The animal must be confined and activity strictly limited for several weeks after surgery. The diet should be modified to prevent weight gain. The animal is initially allowed outside only to eliminate. Subsequent exercise may be gradually increased after a 6-week follow-up. Normal activity usually resumes within 2-3 months after surgery.

If the CCL in the other stifle joint is ruptured, surgery is postponed until the repaired joint recovers fully.

Prognosis
Prognosis is good to excellent with full function restored in over one-half of the cases. The presence of degenerative joint disease negatively affects the long-term prognosis.