The most common orthopedic injury in the dog is the rupture of the cranial cruciate ligament. The cranial cruciate ligament is a ligament found in the stifle (the equivalent joint to a human’s knee), and is one of the ligaments that attach the tibia bone to the femur bone. It is the most important stabilizing structure of the stifle. For this reason, when the cranial cruciate ligament is torn, it will result in severe instability and degenerative joint disease.
A major contributing factor to a cranial cruciate ligament injury in the dog is a characteristic of the dog’s anatomy, called the tibial plateau angle. The tibial plateau is the upper (top, proximal) surface of the tibia, and this is where the femur rests on the tibia. This tibial plateau is sloped in dogs, sometimes up 40 degrees. This results in a force that causes the femur to constantly want to slide down the slope of the tibial plateau. The cranial cruciate ligament is the ligament that resists this force. This means that the cranial cruciate ligament always has a loading force on it when the dog is weight-bearing, placing constant stress on the ligament. This is in contrast to a human’s knee, in which the tibial plateau is very flat, and the constant straining force is not present when weight-bearing. For a better understanding of this concept, please view this short video.
When there is a tear in the cranial cruciate ligament, it will cause lameness (limping). We can also see the dog holding the affected leg off the ground, swelling in the stifle joint, and eventually thickening of the joint. This thickening occurs because once there is instability present in the stifle, osteoarthritis occurs, which causes the femur and tibia bone to remodel, causing boney enlargement. Furthermore, there is a thickening of the joint capsule and surrounding soft tissue.
A cranial cruciate tear is diagnosed in two ways. The first is by physical orthopedic exam, in which two maneuvers/tests are performed. These maneuvers are called Tibial Thrust and Cranial Drawer. When these tests are positive, it indicates that the cranial cruciate ligament is torn. Furthermore, radiographs (X-rays) are taken to evaluate the stifle. On radiographs, the veterinarian looks for a particular pattern of osteoarthritis, effusion (swelling) within the stifle joint, and also evaluates the tibial plateau angle.
There are several methods that have been developed or proposed to treat cranial cruciate ligament rupture. The chance that a torn cranial cruciate ligament tear will heal without surgical treatment is extremely low. This is due to the fact that the tibial plateau is sloped in dogs, and the constant shearing force this creates leaves no chance for the ligament to heal.
The most common method of treating cranial cruciate ligament rupture is a surgical repair called the Tibial Plateau Levelling Osteotomy (TPLO). This procedure consists of cutting the proximal portion of the tibia bone (the tibial plateau) away from the tibia and adjusting its position and then placing a bone plate to hold the bone fragment in place so it can heal in this new alignment. This procedure changes the tibial plateau angle to a target of 5 degrees, essentially removing the need for a cranial cruciate ligament.
In smaller dogs, such as those less than 10 kg, it can be appropriate to treat with a different surgical procedure called the Lateral Suture. This is a procedure that places a very strong suture across the outside of the stifle joint in a similar configuration to the cranial cruciate ligament. This essentially will perform the purpose cranial cruciate ligament and stabilize the stifle joint. In this procedure, the tibial plateau angle is not changed.
Whichever surgery is used as a treatment, it is also important that a stifle arthrotomy is performed. This is a surgical exploration of the joint to evaluate the cranial cruciate ligament and the meniscus. The meniscus is shock-absorbing cartilage within the stifle joint. The meniscus is often torn/injured in dogs that have a cranial cruciate rupture. If the meniscus is damaged, and it is not debrided to remove the damaged material, the dog will often remain sore after surgery.
As an adjunct to surgical treatment, several medical treatments are instituted such as non-steroidal anti-inflammatories, pain-relieving medications, and joint supplements/nutraceuticals that help to treat osteoarthritis and acupuncture for pain relief. This can be especially important when surgery is not an option. There is also some potential to have a custom stifle brace created to help stabilize the stifle joint, but it is important to remember that a brace is not a substitute for surgery when surgery is an option.
After surgical treatment, the prognosis for the dog to be comfortable on the affected leg is good.