Anterior Cruciate Ligament Rupture

One of the most common joint surgeries performed by veterinarians is the repair of an anterior cruciate ligament rupture. The anterior cruciate ligament is located in the stifle or knee joint. As shown in the illustration, this ligament is one of a pair of cruciate ligaments that cross over each other as they go from one side of the joint to the other.  They help stabilize the knee and keep the bones from sliding back and forth.

Humans, cats and dogs have the same basic anatomical structure and function in their knee joints. The main difference is that in humans, the knees support all of the body weight, while the weight load is distributed between the front and back legs of dogs and cats. Anatomically, the knee joint differs from the other large joints in the limbs, being held together mainly by a number of ligaments. The knee joint is a hinged joint that is meant to move primarily in a front to back direction, while the other large joints of the legs are capable of a wider range of motion.  If the knee joint is twisted to the side, the ligaments will stretch.

Typically, an anterior cruciate ligament rupture occurs as a result of a sudden, severe twisting movement to the knee. Frequently, this happens to dogs that are running on uneven ground or are roughhousing with other dogs (especially if they are playing "doggy-tag"). With humans, the injury (which goes by the slightly different name of cranial cruciate ligament rupture) is common in athletes such as hockey and football players. With cats, injuries to the cruciate ligament are often associated with a fall.

When the bones in the knee joint are twisted in different directions, the ligaments are forced to stretch. If the twisting motion is abrupt or severe, the ligaments can snap. Once the ligaments rupture, the bones are no longer held in proper alignment, and the joint becomes unstable. In most cases, the injury is extremely painful. Usually, the animal is not able to bear weight on the affected leg. In some cases the tear is only partial, but with continued weight bearing, the weakened ligament will eventually rupture.

In humans, it is reported that the risk of injuring the knee joint is as much as 15 times greater in individuals that are obese. Although no specific statistics are available for animals, veterinarians agree that cruciate ligament ruptures occur much more frequently in overweight animals.  In obese animals, cruciate ligament injuries are not always associated with obvious or severe trauma. In these cases, it is speculated that the ligaments degenerate, developing small tears that cause intermittent lameness. With continued use of the joint, the ligaments continue to weaken and degenerate, ultimately leading to a complete rupture. Surgical treatment is almost always required to stabilize the joint once the ligament has ruptured. 

In addition to increasing the likelihood of injury to the knee joint, obesity also increases the length of the recovery time following surgery, and increases the risk of injury to the other knee during the recovery period. Lowering your pet's risk of injury to his or her knee joint is just one more reason why you should strive to keep your pet at its optimal body weight. If your pet is overweight, we can give you advice and formulate a diet plan to help achieve this goal.