The anterior cruciate ligament (ACL) is one of several ligaments that support the stifle (knee) joint in the dog and cat. When the ligament ruptures there is instability in the joint, which causes inflammation and pain. This also causes extra stress to be placed on the meniscal cartilage in the joint and often it will tear after the ligament has ruptured. When this occurs the joint becomes even more painful.
Usually the ACL will tear secondary to trauma. All it takes is a quick twist or turn while running or playing. It frequently happens during the winter months from slipping on the snow or ice. But it can happen just as easily in the house or yard regardless of the time of year. The dog or cat will become acutely lame after it happens. Sometimes the owner will even hear their pet cry out in pain.
Some animals will improve without surgery, but in most cases without surgery the knee joint remains unstable. This instability leads to the accelerated development of arthritis and ultimately a very painful joint. It is generally recommended that animals with ruptured cruciate ligaments have surgery to reconstruct the torn ligament, remove any damaged cartilage, and stabilize the joint. Surgery will give the patient the best chance for a healthy, functional knee joint.
Patients that have surgery soon after injury have the best chance for a successful recovery.