Anterior/Cranial Cruciate Ligament Rupture

Cruciate ligament rupture is a common orthopedic condition found in the dog. The canine knee is a hinge joint composed of the femur (end of the thigh bone) and the tibia (top of the shin bone). The cruciate ligament is the main stabilizing force within the canine knee keeping it functioning as a hinge. When the cruciate ligament becomes damaged, the knee no long functions as a hinge. Instead the knee starts to move forward-to-backward like a drawer opening and closing. This drawer motion overloads the soft tissue and ligaments surrounding the knee resulting in swelling and pain. The initial overload results in symptoms similar to a severe sprain. The tissues may be hot to the touch, soft and painful when pressed. As time passes and the knee remains unstable, the tissues become hard and thick as the body tries to stabilize the knee. The result is a firm swelling on the inside of the knee commonly known as a medial buttress. Inside of the joint, the instability causes inflammation and increased fluid production. The fluid and chemicals from the inflammation cause the cartilage in the joint to become soft and degenerative leading to arthritis. 
Sudden rupture of the cruciate ligament us usually characterized by severe non-weight bearing or toe-touching lameness. With time and restricted activity, the lameness will improve or resolve only to relapse with increased activity or stiffness after long periods of rest. Gradual rupture of the cruciate ligament is characterized by sitting to the side, slow to rise, reluctance to jump or use the stairs, hold the paw out when standing to eat, stiffness after rest and limping after activity. As the rupture progresses, the symptoms become more severe and consistent. Chronic rupture and instability result in body imbalance as the weight is shifted to the contralateral support limb and front limbs, the back hunches in the lumbar region, the muscles of the thigh begin to atrophy and the the gait changes to a waddle. The instability can cause the medial meniscus to become damaged resulting in severe pain, non-weight bearing lameness, little or no response to pain medication and no improvement with rest. 

Diagnosis of a ruptured cruciate ligament

The diagnosis of a ruptured cruciate ligament is made through observing abnormal movement of the joint through palpation and diagnostic radiography. With palpation, the veterinarian can elicit a 'drawer sign'. It is called that because the movement of the femur in relation to the tibia is similar to pulling and pushing in the drawer of a cabinet. Many dogs with a ruptured cruciate ligament will have swelling on the inside aspect of the knee, and this is called a medial buttress. Radiographs are commonly performed to better assess the amount of arthritis that may be present.

Treatment of a ruptured cruciate ligament

Surgery is indicated with a complete ACL tear, especially in large dogs. There are several methods of repairing the knee joint, those of which should be discussed with your veterinarian and the surgeon.

Lateral Suture Stabilization (LSS)

 The lateral suture technique involves placing a polypropylene line around the outside of the knee joint to stabilize it from moving front to back.

Tibial plateau leveling osteotomy (TPLO)

In this procedure, a portion of the tibia is cut, moved, and reattached to a different portion of the tibia using plates and screws. By changing the conformation of the tibia, the joint is stabilized. This is a technically difficult surgery but it has shown to produce excellent results, often with less arthritis.


If the dog's exercise is restricted as instructed, and overweight dogs return to normal body weight, the prognosis is good. Depending on the amount of injury to the knee and length of time between the injury and correction of the problem, degenerative joint disease may occur as the pet ages.