Anterior cruciate ligament (ACL) injury is the most common orthopedic injury we see at Westgate Pet Clinic. Although rarely seen in cats, ACL injuries are often seen in dogs. The typical presenting signs are of a dog that has been active, often doing a combination of running and jumping that suddenly becomes lame on one of the rear legs. Often, the dog will immediately not bear weight on the injured leg.
Like people, dogs have 2 cruciate ligaments in each knee. They are fibrous bands of tissue that attach to the femur and tibia and act to stabilize the knee front to back. The anterior cruciate ligament can tear if twisting of the knee occurs while bearing weight on that leg. Most often this occurs with vigorous exercise but it can also occur from trauma, such as being hit by a car, or through a fall. Obesity can increase the likelihood of sustaining a torn ACL.
Once the anterior cruciate ligament is torn, instability in the knee in the form of forward sliding of the tibia with respect to the femur causes inflammation and pain. Without treatment, permanent damage can occur to the joint.
Anterior cruciate ligament injuries are typically diagnosed through a combination of the dog's history, examination showing excessive forward-backward movement between the femur and tibia (cranial drawer sign), and radiographs (x-rays).
Surgical stabilization is the treatment of choice. There are multiple surgical techniques used to improve the performance of the knee joint once the anterior cruciate ligament has been torn. Extracapsular repair is typically reserved for smaller dogs. With this procedure a synthetic band is secured outside the knee joint and mimics the orientation of the anterior cruciate ligament. The two most common surgical techniques done on larger dogs with ACL tears are tibial plateau leveling osteotomy (TPLO) and tibial tuberosity advancement (TTA). Both of these procedures use metal implants to alter the knee joint to prevent sliding of the femur and tibia.
Recovery following surgery, usually takes 8 - 12 weeks. During that time exercise is initially restricted, then slowly built back up to allow the knee to heal. Physical therapy helps to speed the recovery process.
Early intervention is critical in preventing arthritis and permanent joint changes. Approximately 50% of dogs that tear one anterior cruciate ligament, will tear their other ACL within a year. If you are concerned that your dog may have injured its anterior cruciate ligament, contact your veterinarian.