What and where are the cruciate ligaments?

There are two bands of bibrous tissue called the cruciate ligaments in each knee joint. They join the femur and bibia (bones above and below the knee) together so that the knee works as a hinged joint.

They are called cruciate ligaments because they "cross over" inside the knee joint. One ligament connects from inside to outside the knee joint and the other outside to inside, crossing each other in the middle.

Humans have the same anatomical structure of the knee. Cruciate ligament rupture is a common knee injury of athletes called "ACL".

How does the injury occur?

The knee joint is a hinged joint and only moves in one plane, backwards and forwards. Traumatic cruciate damage is caused by a twisting injury to the joint. This is most often seen in dogs and athletes when running and suddenly changing direction so that the majority of the weight is taken on this single joint. This injury usually affects the anterior (front) ligament. The joint is then unstable and causes extreme pain, often resulting in lameness.

Many pets will "toe touch" and place only a small amount of weight on the injured leg.

During the examination, the veterinarian will try to demonstrate a particular movement, called a drawer sign. This indicates laxity in the knee joint. Many dogs will require mild sedation or pain medications to perform this test. Other diagnostic tests such as radiographs (x-rays) may also be necessary.

Other tests such as arthroscopy may be needed to rule out other damage to the joint.

What does surgery involve?

There are various techniques available to replace the action of the cruciate ligament. These surgeries most often involve the placement of artificial ligaments along the outside of the knee joint. There is a newer surgical technique available called tibial plateau leveling osteotomy (TPLO) that is especially beneficial for larger, more athletic dogs. Your veterinarian will discuss with you the best treatment option for your dog.