Overview:A normal dog's knee joint works like a hinge, keeping the animal's leg stable as it bends. When the knee has a ruptured cruciate ligament, the "hinge" becomes loose and no longer functions as effectively. This looseness prevents the knee from maintaining stability of motion. As a result, the dog suffers pain, inflammation, and eventually develops arthritis. This is a very common orthopedic disease in dogs.
When a knee injury occurs suddenly -- as it usually does among humans who suffer from injuries to the cruciate ligament due to a skiing, football, or other sports-related accident -- the ligament will tear rapidly. But usually with dogs, the tearing is partial and occurs gradually, resulting in low-level lameness that may improve initially over time. However, progressive injuries can be quite damaging; because of the trauma to the ligament, the knee joint becomes inflamed, leading to arthritis, which only grows worse with continued weight bearing.
In more severe chronic cases, the "shock absorbers" of the knee -- quarter-moon shaped sections of cartilage called the medial and lateral menisci -- tear or become crushed because of exposure to abnormal stress that occurs when the knee is loose. Animals with this condition often are severely lame and may not be able to put any weight on the affected leg.
Both surgical and non-surgical methods for treatment are available. Generally, dogs have a good chance of recovering normal, or almost normal, movement after surgery, but the arthritis that has occurred already will not be reversible. Additionally, dogs that have ruptured the cruciate ligament on one side are more likely to tear the ligament in the other knee.
Obesity is a major risk factor for this injury and certain breeds of dogs are more likely than others to rupture their ligaments.
Ligaments are very strong tissues, but once they are damaged, they tend to heal slowly and incompletely. In people, cruciate ligament tears are often the result of rapidly occurring trauma, such as injuries resulting from skiing, football, soccer, and other sports accidents. Although this type of injury can also occur in dogs -- jumping up to catch a Frisbee, for example, can cause rapid trauma -- ruptured cranial cruciate ligament injury in the canine usually occurs progressively, over a period of time. There is often a partial tearing, which may show up as a low-level lameness and appears to improve in days to weeks. This partial tearing sets up inflammation within the knee joint, and the weakened ligament is further damaged with continued weight bearing. Eventually, this leads to complete rupture.
Due to a possible genetic component, some breeds, such as the rottweiller and cocker spaniel, are very prone to this disease. They may have some underlying genetic, conformational, or inflammatory disorder that predisposes the ligament to rupture; their susceptibility to the injury is a topic of research at many veterinary institutions. Obese animals are also at increased risk for this disease. However, dogs of all sizes and breeds can develop ruptured cranial cruciate ligaments.
Dogs with a ruptured cranial cruciate ligament in one knee have a 20 to 40 percent chance of injuring the other side, making a full recovery less likely.
If the dog's meniscal cartilage -- the knee's "shock absorbers" -- has been torn, the veterinarian may feel a "meniscal click." Thirty to 50 percent of dogs that have knee joints with chronically ruptured cruciate ligaments will experience damage to their cartilage, resulting in arthritis. X-rays can help confirm the diagnosis and give an indication of how much arthritis already is present. This information may be important for determining prognosis. X-rays can also rule out diseases such as rheumatoid arthritis and fractures that may display similar symptoms.
Occasionally, the veterinarian will obtain and analyze a sample of joint fluid in an attempt to rule out other types of arthritic diseases. However, this procedure usually will not be performed unless there is suspicion that an underlying disease is causing the ruptured cruciate ligament.
In general, animals stabilized with any surgical technique will require three to six months of rehabilitation. After that time, depending on how arthritic the joint was before surgery, they should return to fairly normal activity levels, although they are unlikely to regain 100 percent of their pre-injury function. These dogs may be sore after heavy exercise and occasionally may require pain medication. Athletic animals will have some decrease in function and will be unlikely to return to competition. Hunting dogs may not be able to hunt as frequently or for extended periods of time as they did prior to injury. The TPLO- surgery is purported to be able to return animals to performance levels; however, definitive objective studies have not been published to date.
Transmission or Cause:
Dogs that are obese are much more likely to develop this disease than dogs that are of normal weight. In addition, certain breeds are more prone to developing the disease, especially the rottweiller and cocker spaniel.
Most veterinarians will recommend surgery for treatment of a ruptured cranial cruciate ligament. The many surgical procedures that are available for treatment can be organized into three basic categories: intracapsular stabilization, extracapsular stabilization, and a patented procedure called the Tibial Plateau Leveling Osteotomy® (TPLO).
Intracapsular ligament replacement involves either transplanting tissue from other parts of the dog's body, such as the patellar ligament or fascia lata, into the knee joint. Other options for ligament replacement include a synthetic graft made from materials such as Gore-Tex® or ligament from a tissue bank. The goal of intracapsular ligament replacement is to position the replacement ligament in an anatomically correct configuration.
Extracapsular stabilization stabilizes the knee joint, using materials such as fascia lata, which is a strong fibrous sheet of tissue surrounding the muscles in the outside of the leg, monofilament nylon or other suture material, or stainless steel wire. Fibular head transposition is an extracapsular technique that allows another ligament in the knee joint, the lateral collateral ligament, to replace the function of the cranial cruciate ligament. These techniques are not performed inside the joint; rather, they function to counteract the instability in the joint by acting in a manner similar to an intact cranial cruciate ligament.
Tibial Plateau Leveling Osteotomy® (TPLO) is a technique that utilizes a different approach to treating cranial cruciate ligament injury. Rather than trying to oppose the forces acting on the cranial cruciate ligament in the normal knee joint, a TPLO® eliminates these forces -- and thus the need for a cranial cruciate ligament -- by changing the anatomy of the knee joint. This procedure requires that a bone cut be made in the tibia, which is then stabilized with a specialized bone plate. Only veterinarians that have been trained and licensed by the developer of the technique are permitted to perform this surgery. In general, dogs weighing less than 40 pounds are too small for this procedure.
There are advantages and disadvantages to each of these techniques. The results of these procedures are generally very good; however, some surgeries are more promising than others for complete return to function. There also can be substantial differences in cost and recovery time. A veterinarian can detail these surgical options and further explain the various procedures. Although cruciate ligament surgery can be very demanding, many veterinarians have a great deal of experience and success with these procedures.
Rehabilitation regimens vary, but most veterinarians recommend range-of-motion exercises, gradual return of activity, swimming, weight reduction, and pain medication.