The cranial cruciate ligament (CCL), which in people is called the anterior cruciate ligament (ACL), is part of the knee or stifle joint in the rear legs of dogs. It stabilizes that joint and, when partially torn or completely ruptured, leaves only muscles and surrounding soft tissue to hold the two lower leg bones and the upper thigh bone in place (these bones are the tibia, fibula and femur, respectively). The CCL can be damaged due to sudden trauma or chronic repetitive injury. Damage to the cranial cruciate ligament is one of the most common causes of acute hind limb pain and lameness in domestic dogs. If left untreated, CCL injuries can cause permanent degenerative changes in the stifle joint. It’s important for owners to recognize the causes and symptoms of CCL injuries, so that they can get appropriate treatment for their dogs and relieve the extreme pain that accompanies this condition.